ANALYSIS OF GRAIN STRUCTURE IN FORGING A study and analysis carried out at Engineering Shops and Foundry (ES&F) Vishakhapatnam Steel Plant
Mini Project Work
Under estimated guidance of
SRI S. MANDAL AGM (ES&F) Vishakhapatnam Steel Plant
DEPARTMENT OF PRODUCTION ENGINEERING NATIONAL INSTITUTE OF TECHNOLOGY, AGARTALA 1
DECLARATION
We hereby declare that the Project Work entitled the “Analysis of grain structure in forging”, (A study and analysis carried out at Forging shop/ES&F, Vishakhapatnam Steel Plant) is an original work done by us and not submitted earlier for the award of our degree and diploma or any other universities similar to this.
Group member PRASENJIT BISWAS
10UPE018
SRIJIT BISWAS
10UPE027
DIPANJAN DAS
10UPE006
PLACE: - VISAKHAPATNAM STEEL PLANT DATE –
2
CERTIFICATE
This is to certify that “PRASENJIT BISWAS, SRIJIT BISWAS, DIPANJAN DAS” has satisfactorily completed the project work entitled ““ANALYSIS OF GRAIN STRUCTURE IN FORGING”” (A study and analysis carried out at Forging shop / ES&F, Vishakhapatnam steel Plant).In partial fulfillment of the requirement for the degree of Bachelor of Technology in Production Engg. during the academic year 20102014.
MR. SUBRATA. MANDAL AGM, (ES&F) (Project Guide)
PLACE: VISAKHAPATNAM STEEL PLANT DATE :
3
BIO-DATA OF GUIDE
NAME
: S. MANDAL
Designation
: Asst. General Manager (Mech) Engineering Shop & Foundry, Vishakhapatnam Steel Plant Vishakhapatnam
Qualification: 1. B.E (Hoers) M.E, Utkal University 2. M.B.A (Finance), IGNOU 3. DCA, Academy of computer education 4. M.Tech (M.E Design) BITS, MESRA 5. Gold Medal Award in HIMER International Conference 6. Member in institute of Engg, India 7. Project Grade:
51 UG project work 03 PG project work
Address
: 219-C, sector 3, Ukkunagaram, Vishakhapatnam-533032 Andhra Pradesh.
4
ACKNOWLEDGEMENT We hereby express our profound sense of gratitude to our guide Mr.Subrata Mandal, [AGM (Mechanical) of Engineering shops and Foundry (ES&F), Visakhapatnam Steel Plant, Visakhapatnam], for providing the necessary information and taking great pain to help us complete this project. He has been kind enough to guide us throughout this project by shedding light on our weaknesses and has enhanced our strengths. We also want to thank Mr.Sanjib Kr. Das [(DGM (Mechanical) RMHP (works)] for lending us his help to the complete this project. He has been very much kind and provided us his self-less support in our long run. We also want to thank Visakhapatnam Steel Plant Authority for which we have been able to do our training out here in VSP. We also want to thank Mr. Anirban Bhattacharjee (Training and Placement officer, National Institute of Technology, Agartala) for whom we have been able to come here in Visakhapatnam Steel Plant and explored as much as we can. We also want to thank all the guides of VSP for lending their support towards us for which we were able to learn to our best. We also want to thank all our friends and seniors who helped us to come this way throughout.
5
CONTENTS Topic
Page no
Synopsis
1
Introduction to the project work
3
Visakhapatnam steel Plant-Overview
4
Introduction to metal manufacturing
16
processes and advantage and disadvantage of various metal manufacturing processes Introduction to Forging
25
Fording equipments and furnaces
30
Importance of forging temperature
37
Recrystallization and Grain growth -an
40
introduction Mechanical metallurgy in forging
43
Analysis of Grain structure in forging
46
Data analysis
47
Conclusion
48
Bibliography
49
6
SYNOPSIS The project deals with the analysis of grain structure in forging process. This project lays emphasis on the importance of changing the grain structure and its importance to improve the mechanical properties of the material used in forging purpose. Forging can produce a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics. Some metals may be forged cold, but iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forging, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening. Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high-temperature furnace (sometimes referred to as the forge) is required to heat ingots or billets. Owing to the massiveness of large forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations use metal-forming dies, which must be precisely machined and carefully heat-treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved. So grain structure takes a major role in forging. Or other words in forging all the advantage we got due to proper grain formation. So we have to give a wide importance on grain study. So it is a very importance to know about grain formation. This is a well-known phenomena that the forging process deform the material in desired shape and improve the mechanical properties of a material, so by applying a suitable temperatures and by impact or gradually increasing force with the help of hammer and die to the material to increase its strength and reduce the ductility. The reason for pursuing this project is the study of grain structure of the material has wide application in industries and has been used from early stages of manufacturing; also it is a work of precise engineering because of its controlled range of heating and applied force conditions. The planning to undertake this project is to get in-depth knowledge of grain structure in forging process and its requirement for industrial purpose, also we see the different types of forging processes and so as to understand the changes in grain structure in a proper forging process, simultaneously consideration of the material composition of the material also plays an important role in selection of forging temperature. Though forging is not a new area, it has not been put into effective use in the fact that most of the researchers look at the process in general so the main idea behind the project is to analyze the existing grain structure, so as to understand the micro structural level of change that takes place due to forging process. 7
After the analyzing the different forging processes, we can understand which properties and to what extend those properties are imparting in the material. Further we can understand the grain structure that is been given in forging process and co relate it with the iron carbon equilibrium diagram. At the final stage we conclude that to which extent temperature enhance the grain structures of a material and how it is changing at the required properties of forging processes. This is the main thing because of which we are doing this project so that we can know what would happen when the grain size or grain structure rearrange itself.
8
INTRODUCTION TO THE PROJECT WORK The project entitled “THE ANALYSIS OF GRAIN STRUCTURE IN FORGING”. Which explores information about grain structure, grain boundary and grain formation in forging. Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press. Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. Grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has, crystals randomly oriented. Forgings are consistent from piece to piece, without any of the porosity, voids, inclusions and other defects. Thus, finishing operations such as machining do not expose voids, because there aren't any. Also coating operations such as plating or painting are straightforward due to a good surface, which needs very little preparation. A Forged metal can result in the following: Increase length, decrease cross-section, called drawing out the metal. Decrease length, increase cross-section, called upsetting the metal. Change length, change cross-section, by squeezing in closed impression dies. This results in favorable grain flow for strong parts. The grain structure refers to the arrangement of the grains in a metal, with the grain having a particular crystal structure. A very important feature of a metal is the average size of the grain. The size of the grain determines the properties of the metal. For example, smaller grain size increases tensile strength and tends to increase ductility. A larger grain size is preferred for improved high-temperature creep properties. Creep is the permanent deformation that increases with time under constant load or stress. Creep becomes progressively easier with increasing temperature. It also builds up a link between iron-carbon equilibrium diagrams which enable the analysis of grain structure. This gives an influence on heating process of the material on forging furnace. Grain structures are analyzed by seeing the grain formation of forged material during forging. This project is widely help us to know that in which type of grain formation the material will be more useful and its property will be better.
9
VISHAKAPATANAM STEEL PLANT OVERVIEW
Steel is one of the most important components that can strengthen the economic backbone of any country. The high versatility of steel allows a vast range of products to use steel as their raw material. Visakhapatnam Steel is one of the leading steel companies of India. Their mission is to increase the production of liquid steel to 16 million ton by upgrading and expanding the infrastructure of the Plant technologically. It also aims at producing international steel quality. The infrastructure of Visakhapatnam Steel Plant is very well developed with many modern and upgraded equipments and manufacturing units like Continuous Casting Rolling Mills, Plant Blast Furnace, Coke Ovens & Coal Chemical, Steel Melt Shop and Plant Sinter. The major raw materials used in Visakhapatnam Steel Plant are coal, iron ore, flux etc. Visakhapatnam Steel Plant's product mix consists of Rounds, Reinforcing bars, Squares, Flats, Equal angles, Unequal angles, T-bars, Channels, Saleable billets providing a great variety in the composition as per customer requirements. The Plant is designed to produce three million tons of liquid steel per annum to be converted to 2.656 million tons per annum of saleable steel. In addition, Visakhapatnam steel Plant will produce annually about 5.56 lakh tons of pig iron and various by-products and benzol products for sale. Salient Features of the Plant: The production facilities in the Visakhapatnam steel Plant are most modern amongst the steel industry in the country. The know-how and the technology have been acquired from different parts of the world from the reputed and established sources. Some of the novelties of the Visakhapatnam steel Plant are: 7meter height coke ovens of VSP are the tallest so far built in the country. Base mix yard for sinter Plant introduced for the first time in the country helps in excellent blending of the feed material to the sinter machine and production of consistent good quality sinter. 3200 cubic meters two blast furnaces with bell less top charging equipment and 100% cast house slag granulation. 100% continuous casting of liquid steel into blooms result in less and better quality of blooms. The VSP have three sophisticated and large rolling mills with the latest features of automation and optimization. The operations of blast furnace, steel melting shop and rolling mills have been entirely computerized to ensure consistent quality and efficient performance. 10
The major production departments of Visakhapatnam steel Plant are the raw materials handling system, coke ovens, sinter Plant, blast furnace, and steel melting shop and rolling mills. Extensive facilities have been provided for repair maintenance as well as manufacturing of spare parts. There is a Central machine shop, Structural shop, forge shop, foundry, wood working shop and loco repair shop. Visakhapatnam steel Plant has got its own Air separation Plant for production of oxygen and acetylene Plant for production of acetylene gas. A captive power Plant has also been provided for power generation with 4 Units, each of 60MW generation capacity. The steel Plant has many technological features, which are unique amongst the steel Plants in the country. The company is a pioneer in introducing many new technologies in the country. The production of TMT rebar‟s by temp core process is a shining example in this respect. The IT applications at RINL have been developed and implemented keeping the overall organizational business objectives in view. IT infrastructure has been upgraded recently with IBM-RS 6000 servers and ORACLE-91 as the data base server and data communication with back bone fiber-optic network. In the area of marketing VPN based wide area network has been implemented to provide vital information to regional marketing offices as well as customers. The Plant also produces Pig Iron, Granulated Slag and Coal Chemicals. The rolled products find extensive usage in the Construction, Infrastructure, Railways, Power, Defence, Transport and Ship Building sectors. Coir‟s and Rods are used mainly for reinforced concrete work for housing, construction of dams, buildings factories, manufacture of agricultural implements, fabrication of Light engineering components. The Wire rods are used in Wire Drawing industry for electrodes Transmission lines etc. The structural‟s find application in engineering, house building, agricultural implements machinery, transmission towers, etc. The Raw Material Handling Plant (RMHP) receives the basic raw materials required for the steel making process from various sources through railway wagons and by road. The Raw Material Handling Plant is divided into two sections Coal Handling Plant (CHP) and Ore Handling Plant (OHP). VSP consists of coke oven and coal manufacturing department. From the storage yard, the coking coal is sent to foreign material removing section to remove foreign matter .Iron traps for ferromagnetic articles and cylindrical screens are provided for this. The prepared coal charge in the coal tower is drawn by a charging car on the top of the batteries and charged into the ovens as per sequence. Thus the by-product of the coke oven is properly utilized .Moreover in the coke dry cooling Plant there are three such drying setups having a capacity of 50-52 TPH. After this the coke sorting Plant comes into picture where the coke is discharged into deducting units by conveyer. Next the Plant also consists of the coke sorting Plant along with the gas condensation section in which the coke oven gas is cooled in goosenecks and in gas collecting mains in the batteries by means of spraying ammonia liquor. Deducting units are provided with equalizing bunkers and belt feeders to compensate for irregularity of coke discharge from dry cooling Plant. The main by
11
product in the process of coke making is crude coke oven gas and this has lot of valuable chemicals. Coal Chemical Plant recovers Ammonia (NH3), Tar and Benzol from Co-Gas. Moreover the Plant consists of sections in which the various by-products such as ammonium sulphate and benzol are separated and extracted in order for further use or sale in order to get profit .These includes the gas condensation section ,final gas cooling and naphthalene section ,benzol recovery ,gas bleeder and tar distillation Plant. Then the recovered Benzol is refined and then rectified .Then it consists of the sintering Plant in which the iron ore agglomerated into a porous mass by incipient fusion caused by combustion within the mass of the ore particles. Calcining Plant produces lime and calcined dolomite, which are used for refining of hot metal to steel in the converter. There are four hot blast stoves for each furnace with a total heating surface of 224,000 m2.The dome can be heated to a temperature of 1450∞C maximum while the waste flue temperature is up to 400∞C. The stoves are capable of giving a blast temperature up to1300∞C. Stoves are heated by a mixture of blast furnace gas and coke oven gas having a calorific value of 1,100 Kcal/Ncum. Pressure of mixed gas before burners is 600mm W.C.
The major raw materials and their sources are: Raw Material Iron Ore Lumps & Fines BF Lime Stone SMS Lime Stone BF Dolomite SMS Dolomite Manganese Ore Boiler Coal Imported Boiler Coal Imported Coking Coal Medium Coking Coal (MCC) Imported LAM Coke Quartzite Lump & Fines Sand
Bailadila, Chattisgarh Jaggayyapeta, AP Dubai Madharam, AP Madharam, AP Chipurupalli, AP Talcher, Orissa Indonesia Australia / US Kathara / Swang / Rajarappa / Kedla China Local Sarepalli, AP
12
Major Units
Department
Annual Capacity(„000T) Units (3.0 MT Stage)
Coke Ovens
2,701
4 Batteries of 67 Ovens & 7 Mtrs. Height
Sinter Plant
5,256
2 Sinter Machines of 312 Sq. Mtr. grate area each
Blast Furnace
3,400
2 Furnaces of 3200 Cu. Mtr. volume each
Steel Shop
Melt 3000
3 LD Converters each of 133 Cu. Mtr. Volume and Six 4 strand bloom casters
LMMM
710
2 Strand finishing Mill
WRM
850
MMSM
850
4 Strand high speed continuous mill with no twist finishing blocks 6 STAND FINISHING MILL
Main Products of VSP Steel Products
By-Products
Blooms
Nut Coke
Granulated Slag
Billets Channels, Angles
Coke Dust Coal Tar
Lime Fines Ammonium Sulphate
Beams Squares Flats Rounds Re-bars Wire Rods
Anthracene Oil HP Naphthalene Benzene Toluene Zylene Wash Oil
13
THE MAJOR DEPARTMENTS OF VSP STEEL PLANT ARE: Raw Material Handling Plant VSP annually requires quality raw materials viz. Iron Ore, fluxes (Lime stone, Dolomite), coking and non-coking coals etc. to the tune of 12-13 Million Tons for producing 3 Million Tons of Liquid Steel. To handle such a large volume of incoming raw materials received from different sources and to ensure timely supply of consistent quality of feed materials to different VSP consumers, Raw Material Handling Plant serves a vital function. This unit is provided with elaborate unloading, blending, stacking & reclaiming facilities viz. Wagon Tipplers, Ground & Track Hoppers, Stock yards Crushing Plants, Vibrating screens, Single / twin boom stackers, wheel on boom and Blender reclaimers, Stacker – cum – Reclaimer (SCR). In VSP peripheral unloading has been adopted for the first time in the country. Coking coals are received through conveyors directly from M/s Gangavaram Port Limited to Coal Stock Yard. Coke ovens & Coal Chemical Plant (CO&CCP) Blast Furnaces, the mother units of any Steel Plant require huge quantities of strong, hard and porous solid fuel in the form of hard metallurgical coke for supplying necessary heat for carrying out the reduction and refining reactions besides acting as a reducing agent. At VSP there are Four Coke Oven Batteries, 7 Meter tall and having 67 Ovens each. Each oven is having a volume of 41.6 cu. Meter & can hold upto 31.6 Tons of dry coal charge. There are 4 Coke Dry Cooling Plants (CDCP) each having 4 cooling chambers. Nitrogen gas is used as the Cooling medium. The heat recovery from nitrogen is done by generating steam and expanding in two back pressure turbines to produce 7.5 MW each The Coal chemicals such as Benzole (& its products), Tar (& its products), Ammonium Sulphate etc. are extracted in Coal Chemical Plant from C.O. Gas. After recovering the Coal chemicals the gas is used as a byproduct fuel by mixing it with gases such as BF Gas, LD Gas etc. A mechanical, Biological & chemical treatment Plant takes care of the effluents. Sinter Plant Sinter is a hard & porous ferrous material obtained by agglomeration of Iron Ore fines, Coke breeze, Lime Stone fines, Metallurgical wastes viz. Flue dust, mill scale, LD slag etc. Sinter is a better feed material to Blast Furnace in comparison to Iron Ore lumps and its usage in Blast furnaces help in increasing productivity, decreasing the coke rate & improving the quality of Hot Metal produced. Hot Sinter discharged from Sintering machine is crushed to +5 mm - 50 mm size and cooled before dispatching to Blast Furnaces. Parameters of Sintering Machines are:
Total area : 312 Sq. Meter Effective Sintering area : 276 Sq. Meter Sinter bed height : 500 mm Sinter Machine Capacity : 400 T P H each 14
The dust laden air from the machines are cleaned in scrubbers & electrostatic precipitators to reduce the dust content to 100 mg/ m3 level before allowing to escape into the atmosphere and thus helping in maintaining a clean & dust free environment. Blast Furnaces VSP has two 3200 cu. Meter Blast Furnaces (largest in India) equipped with Paulworth Bell less top equipment with conveyor charging. Rightly named as "Godavari" & "Krishna" after the two rivers of AP, the furnaces will help VSP in bringing prosperity to the state of Andhra Pradesh. Provision exists for granulation of 100% liquid slag at blast furnace cast house and utilization of blast furnace gas top pressure (1.5-2.0 atmospheric pressure) to generate 12 MW of power in each furnace by employing gas expansion turbines. The two furnaces with their novel circular cast house and four tap holes each are rated to produce 9720 tons of Hot Metal daily or 3.4 Million Tons of low sulphur Hot Metal annually. Record Performance of Blast Furnace department: TECHNO-ECONOMICS: Productivity Power Fuel rate Heat cons. Nut coke uses
2.23 t/m3/day 51.31 kwh/thm 509 kg/thm 450 Mcal/thm 56 kg/thm
Feb 06 Feb 06 Jan 04 Apr 05 Mar 04
6820 Tons
23.03.06
PRODUCTION Day Peaks Blast Furnace - 1 Blast Furnace - 2
6805
Tons
21.03.06
Shop
13325 Tons
10.02.06
PCM Pouring
6723
31.03.93
Tons
15
Monthly Peaks Hot metal
374419
Tons
Mar ‟06
PCM Pouring
107463
Tons
Mar ‟93
Pig Iron Despatch
110387
Tons
Mar ‟94
G. Slag Despatch
150942
Tons
May ‟02
Steel Melt Shop VSP produces steel employing three numbers of top blown Oxygen Convertors called LD Convertors or Basic Oxygen Furnaces / Convertors. Each convertor is of 133 cu. Meter volumes, rated to produce 3 Million Tons of Liquid Steel annually. Besides Hot Metal, Steel Scrap, Fluxes such as calcined lime or Dolomite form part of the charge to the Convertors. Different grades of steel of Superior quality can be made by this process by controlling the Oxygen blow or addition of various ferro alloys or special additives such as FeSi, FeMn, SiMn, Coke Breeze, Aluminum etc. in required quantities while liquid steel is being tapped from the convertor into a steel ladle. Convertor / LD Gas produced as by product is used as a secondary fuel. Characteristics of VSP Convertors:
Capacity Volume Convertor Sp. Volume Tap to Tap Time
: 150 Tones per heat blow : 133 Cu. Meter : 0.886 Meter Cube per ton : 45 mts - 60 mts
Liquid Steel produced in LD Convertors is solidified in the form of blooms in continuous Bloom Casters. However, to homogenize the steel and to raise its temperature, if needed, steel is first routed through, Argon rinsing station, IRUT (Injection Refining & Up temperature) / ladle Furnaces. Continuous casting Department VSP has six-4 strand continuous casting machines capable of producing 2.82 million Tons / year Blooms of size 250 x 250 mm and 250 x 320 mm. Entire quantity of molten steel produced (100%) is continuously cast in radial bloom casters which help in energy conservation as well as production of superior quality products. Facilities at continuous casting machines include a lift and Turn table for ladles, Copper mould, oscillating system tundish, Primary & Secondary Cooling arrangement to cool the steel bloom. Gas cutting machines are used for cutting the blooms in required lengths (Av. 6Meters long).
16
Rolling Mills Blooms produced in SMS-CCD are shaped into products such as Billets, rounds, squares, angles (equal & unequal), Channels, I-PE Beams, HE Beams, Wire rods and reinforcements bars by rolling them in three sophisticated high capacity, high speed, fully automated rolling mills, namely Light & Medium Merchant Mills (LMMM), Wire Rod Mill (WRM) and Medium Merchant and Structural Mill (MMSM).
Light & Medium Merchant Mill (LMMM)
LMMM comprises two units, namely Billet Mill and Bar Mill. The Billet Mill is facilitated with 2 Walking Beam Furnaces and it is a continuous seven stand mill. In the Billet Mill 250 x 320 mm size blooms are rolled into Billets of 125 x 125 mm size. Billets are supplied from this mill to Bar Mill of LMMM, Wire Rod Mill and for sale. Bar Mill is facilitated with temp-core heat treatment technology, automated bundling facilities and high degree of automation. Bar Mill is a 2 strand continuous mill having a capacity of 7,10,000 tons per annum and produces rounds and rebars of various sizes from 16 mm to 36 mm.
Wire Rod Mill (WRM)
Wire Rod Mill is fully automated & sophisticated mill. The billets are rolled in 4 strands, high speed continuous mill having a Annual Capacity of 8, 50,000 Tons of Wire Rod Coils. The mill produces rounds in 5.5 - 14 mm range and rebars in 8, 10 & 12 mm sizes. The mill is equipped with standard and Retarded Stelmor controlled cooling lines for producing high quality Wire rods in Low, Medium & High carbon grade meeting the stringent National & International standards viz. BIS, DIN, JIS, BS etc. and having high ductility, uniform grain size, excellent surface finish.
Medium Merchant & Structural Mill (MMSM)
This mill is a high capacity continuous mill. The feed material to the mill is 250 x 250 mm size blooms, which is heated to rolling temperatures of 1200 °C in two walking beam furnaces. The mill is designed to produce 8,50,000 tons per annum of various products such as rounds, squares, flats, angles (equal & unequal), T bars, channels, IPE beams I HE beams (Universal beams)
17
OVERVIEW OF PLANT
18
ENGINEERING SHOPS & FOUNDRY Engineering Shops & Foundry (ES&F) is a set up to meet the requirements of Ferrous & Non Ferrous Spares of different departments. The ES&F is divided into 5 Sections. Central Machine Shop (CMS) Steel Structural Shop(SSS) Forge Shop (FS) Foundry (Fdy) Utility Equipment Repair Shop (UERS)
CENTRAL MACHINE SHOP (CMS): Inputs: Iron & steel castings from Foundry shop, Forgings from Forge Shop, Rolled Sections, Repair & Rectification parts, Non Ferrous Castings. Facility available for value addition: The machining section has over 100 major machines including heavy & light Lathes, Milling, Boring, & Planning, Slotting, Shaping, Grinding& other machines. Lathe Machine - 1.5Mt Lathe, 3.0Mt Heavy Lathe, Vertical Turret Lathe, Relieving Lathe. Milling Machine - Horizontal milling Machine, Vertical Milling Machine, Plano Milling Machine. Boring Machine - Horizontal Boring Machine, Vertical Boring Machine. Drilling Machine - Column Drilling Machine, Radial Drilling Machine. The assembly section undertakes medium repair and general over hauling of mechanical equipment. The heat treatment section is provided with annealing, normalizing, tempering furnaces, carburizing furnaces Outputs: Shafts, pinions gears, crane wheels, rollers, machining of various assembly jobs.
STEEL STRUCTURAL SHOP (SSS) Inputs: Various sizes of plates, Angles, Channels, Beams, Flats, Rounds for fabrication of jobs Facility available for value addition:
19
There are two CNC Profile Gas Cutting Machines used for profile cutting, a straightening cum Bending machine used for bending sheets up to a maximum thickness of 25mm, a hydraulic guillotine shearing machine, Combination shearing machine used for cutting metal sheets by shearing, a 200 ton vertical press etc. Outputs: All type of fabrication jobs, repair of slag pots of SMS, mfg and repair of tundishes for SMS, mfg of Scrap Boxes for SMS , hot metal Ladle for SMS, 500 Launder for SMS, body for FMD, repair of Buckets for LMMM,WRM
FORGE SHOP (FS) Forging is the hot working of metals performed by means of hammer blown or under the pressure of press. Various kinds of machine parts of different shapes & sizes are made by forging operation. Inputs: Ingots from foundry, blooms from SMS, round rods from mills Facility available for value addition: The shop is designed for production of forging for shafts, coupling flanges etc and also of forged shapes such as crusher hammer heads, special bolts, nuts etc. There is facility for repair of and testing chains is existing. The annual production from the shop is about 2400 tones. In heavy forging section open die forgings of long shafts, gear blanks, coupling etc is made with the help of 2 ton & 3 ton bridge type pneumatic hammers. Each hammer will be provided twin chamber heating surface are provided. A 2 ton drop stamp hammer with a heating furnace trimming press etc is provided for stamping. For cutting them to size a cold saw, a billet shear and gas cutting facilities are provided. For stress relieving a bogie type annealing furnace is provided. Output: Finished forgings Main productsPlain shafts up to 300 mm dia & 3000 mm length Stepped shafts (300dia max, dia 70 min up to 4000 mm length) Gear blanks Crane wheels (800 dia max, dia 300 min) V bends & U bends Tap hole drill rods etc.
20
FOUNDRY (FDY) Inputs: Pig Iron, M.S. Scrap, Ferro Alloys, Sodium Silicate, Silica Sand, CO2 gas, Moulding additives etc Facility available for value addition: The wood work shop manufactures patterns for Foundries. The principal equipment for pattern making are Saws, Disc Grinding, Wood working Lathes, adequate facilities are provided for saw grinding, painting, Timber And Pattern Storage etc. The foundry shop has different bays for moulding and casting. Raw material is kept at one end and this is used for preparation of mould and casting. The foundry shop also has a arc furnace and two induction furnaces for melting the raw materials. The arc furnace has a capacity of 8-10 tons while the induction furnace has a capacity of 5-30 tons. Outputs: The main Products are Steel, Cast Iron & Non Ferrous Castings, Emergency Containers, and Bull gear for SMS, Hot metal runners, Ladle paw for Blast Furnace. Coke roll liners, Non Ferrous casting like bushes (below 20 kg) etc
UTILITY EQUIPMENT REPAIR SHOP (UERS) Inputs: Sheets, Plates, Channels, Angles, Beams, Billets, Rounds from Forge Shop for manufacturing Shafts, Steel & Iron casting Facility available for value addition: Repair of Steam exhausters for SMS ,supply of Cones & Ducts of various sizes, Manufacturing of impellers to various departments, build up & machining of various components, reclamation jobs like valve repairs, Conveyor Idlers, PCM Rollers etc.
21
Introduction to Metal Manufacturing Process Manufacturing is the production of goods for use or sale using labor and machines, tools, chemical and biological processing, or formulation. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale. Such finished goods may be used for manufacturing other, more complex products, such as aircraft, household appliances or automobiles, or sold to wholesalers, who in turn sell them to retailers, who then sell them to end users – the "consumers". Manufacturing takes turns under all types of economic systems. In a free market economy, manufacturing is usually directed toward the mass production of products for sale to consumers at a profit. In a collectivist economy, manufacturing is more frequently directed by the state to supply a centrally planned economy. In mixed market economies, manufacturing occurs under some degree of government regulation. Modern manufacturing includes all intermediate processes required for the production and integration of a product's components. Some industries, such as semiconductor and steel manufacturers use the term fabrication instead. The manufacturing sector is closely connected with engineering and industrial design. Examples of major manufacturers in North America include General Motors Corporation, General Electric, and Pfizer. Examples in Europe include Volkswagen Group, Siemens, and Michelin. Examples in Asia include Toyota, Samsung, and Bridgestone. History and development In its earliest form, manufacturing was usually carried out by a single skilled artisan with assistants. Training was by apprenticeship. In much of the pre-industrial world the guild system protected the privileges and trade secrets of urban artisans. Before the Industrial Revolution, most manufacturing occurred in rural areas, where household-based manufacturing served as a supplemental subsistence strategy to agriculture (and continues to do so in places). Entrepreneurs organized a number of manufacturing households into a single enterprise through the putting-out system. Toll manufacturing is an arrangement whereby a first firm with specialized equipment processes. Types of Manufacturing Processes: Manufacturing processes are the steps through which raw materials are transformed into a product. The manufacturing processes can be broadly classified into various categories... The selection of a particular process from a wide range of choices for a given application requires a hierarchical classification of the processes. Depicts how the shaping family can be expanded in different classes such as casting, deformation, moulding, composite and powder processing, and prototyping. Next moulding is a class can be enlarged into a number of member processes such as compression, rotational, transfer, injection moulding, etc. Lastly, each member process can be identified with a number of 22
attributes, which would facilitate the selection of a member process for a given material dimension, level of requisite tolerances and so on. A brief description of the seven broad categories of the manufacturing processes:
Casting Moulding Forging Forming Rolling Drawing Sintering Machining CASTING:
Most of the manufactured parts start its journey with casting process. In a typical casting process, metal is first heated in a furnace until it melts and then the molten metal is poured into a mold so that the liquid metal takes the shape of the mold cavity, which is the final shape of the part. Once the liquid metal in the mold cavity solidifies, the mold is broken or opened to take the final part out of the mold cavity, liquefying of metallic material by properly heating it in a suitable furnace. • pouring of hot molten metal into a previously made colder mould cavity, • Extraction of the solidified cast from the mould cavity The various types of castings are as follows –
Centrifugal casting Continuous casting Die casting Evaporative-pattern casting Full-mold casting Lost-foam casting Investment casting (lost wax casting) Low pressure Permanent mold casting Plastic mold Resin casting Sand casting Shell molding Slush or slurry Spray forming
23
Advantages
It is economical with very little wastage. Even the extra metal produced during each casting can be re-melted and reused. It can produce parts with complex geometrical features such as internal cavities, hollow sections with fair dimensional accuracy. Casting can be used to make very small to extremely large and complex parts It is possible to cast metallic materials with very low to reasonably high melting temperatures. Further, the mechanical properties of a cast are usually isotropic. Disadvantages
Accurate shape and size are not found Not suitable for large skill production Poor Surface finish
MOULDING Moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern. A mould is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. A mold is the counterpart to a cast. The manufacturer who makes the molds is called the moldmaker. A release agent is typically used to make removal of the hardened/set substance from themold easier. The various types of mouldings are as follows –
Blow molding Compaction plus sintering Compression molding Expandable bead molding Extrusion molding Foam molding Injection molding Laminating Reaction injection molding Matched mold Matrix molding Plastic moulding Pressure plug assist molding Rotational molding Transfer molding Thermoforming
24
Advantages of Molding
High Production rates Design flexibility Repeatability within tolerances Can process a wide range of materials Relatively low labor Little to no finishing of parts Minimum scrap losses
Disadvantages of Molding
High initial equipment investment High startup and running costs possible Part must be designed for effective molding Accurate cost prediction for molding job is difficult
FORGING: Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: "cold", "warm", or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons. Forged parts usually require further processing to achieve a finished part. A Forged metal can result in the following:
Increase length, decrease cross-section, called drawing out the metal. Decrease length, increase cross-section, called upsetting the metal. Change length, change cross-section, by squeezing in closed impression dies. This results in favorable grain flow for strong parts.
The various types of forgings are as follows:
Press forging Drop forging Machine forging Roll forging open die forging Closed die forging
Advantage and disadvantage:
Forging can produce a piece that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.
25
Some metals may be forged cold, but iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forging, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable. Alloys that are amenable to precipitation hardening, such as most aluminium alloys and titanium, can be hot forged, followed by hardening. Production forging involves significant capital expenditure for machinery, tooling, facilities and personnel. In the case of hot forging, a high-temperature furnace (sometimes referred to as the forge) is required to heat ingots or billets. Owing to the massiveness of large forging hammers and presses and the parts they can produce, as well as the dangers inherent in working with hot metal, a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer.
Most forging operations use metal-forming dies, which must be precisely machined and carefully heat-treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved. FORMING Forming or metal forming, is the metalworking process of fashioning metal parts and objects through mechanical deformation; the workpiece is reshaped without adding or removing material, and its mass remains unchanged. Forming operates on the materials science principle of plastic deformation, where the physical shape of a material is permanently deformed. Metal forming tends to have more uniform characteristics across its subprocesses than its contemporary processes, cutting and joining. On the industrial scale, forming is characterized by:
Very high required loads and stresses, between 50 and 2500 N/mm2 (7-360 ksi) Large, heavy, and expensive machinery in order to accommodate such high stresses and loads Production runs with many parts, to maximize the economy of production and compensate for the expense of the machine tools Forming processes tend to be typified by differences in effective stresses. These categories and descriptions are highly simplified, since the stresses operating at a local level in any given process are very complex and may involve many varieties of stresses operating simultaneously, or it may involve stresses which change over the course of the operation
26
Compressive forming Tensile forming‟ Combined tensile and compressive forming Bending Shearing Extrusion Pressing Stamping Bending Shearing
Advantage:
Product performance is improved over other manufacturing processes as the forming process rearranges the grain structure to follow the part configuration. This favorable characteristic eliminates the potential for porosity fatigues, increases over-all strength performance (shear strength, etc.) and reduces risk of other types of material integrity.
Production costs are reduced by the high speed manufacturing process. Speeds range from 50 pieces per minute to 400 pieces per minute on the cold heading process.
Surface finish is improved versus machined surfaces. ROLLING
Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact with each other without sliding. Rolling is achieved by a rotational speed at the line or point of contact which is equal to the translational speed. When no sliding takes place the rolling motion is referred to as 'pure rolling'. In practice, due to small deformations at the contact area, some sliding does occur. Nevertheless, rolling resistance is much lower than sliding friction, and thus, rolling objects, typically require much less energy to be moved than sliding ones. As a result, such objects will more easily move, if they experience a force with a component along the surface, for instance gravity on a tilted surface; wind; pushing; pulling; an engine. Unlike most axially symmetrical objects, the rolling motion of a cone is such that while rolling on a flat surface, its center of gravity performs a circular motion, rather than a linear one. Rolling objects are not necessarily axially-symmetrical. Two well known non-axially-symmetrical rollers are the Reuleaux triangle and the Meissner bodies. Objects with corners, such as dice, roll by successive rotations about the edge or corner which is in contact with the surface.
27
The various types of forgings are as follows –
Cold rolling Hot rolling Sheet metal Shape Shape Ring Transverse Cryorolling Orbital Cross-rolling Thread DRAWING
Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis. For wire, bar, and tube drawing the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually done at room temperature, thus classified a cold working process, however it may be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces. The various types of forgings are as follows :
Sheet metal Deep drawing Bar drawing Tube drawing Wire drawing Plastic drawing SINTERING
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature below the melting point. The atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece. Because the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points such as tungsten and molybdenum. Sintering is traditionally used for manufacturing ceramic objects but finds applications in almost all fields of industry. The study of sintering and of powder-related processes is known as powder metallurgy. A simple, intuitive example of sintering can be observed when ice cubes in a glass of water adhere to each other.
28
The various types of forgings are as follows –
General sintering Ceramic sintering Plastics sintering Liquid phase sintering Electric current assisted sintering Spark plasma sintering Pressure less sintering
Advantages 1. Very high level of purity and uniformity in starting materials. 2. Stabilizations of the details of respective operations, by control of grain size during the input stages. 3. Absence of binding contact between segregated powder particles or “inclusions‟‟ (called sintering) as often occurs in melting process. 4. No deformation needed to produce directional elongation of grains. MACHINING Machining is any of various processes in which a piece of raw material is cut into a desirable‟s final shape and size by a controlled material-removal process. The many processes that have this common theme, controlled material removal, are today collectively known as subtractive manufacturing, in distinction from processes of controlled material addition, which are known as additive manufacturing. The precise meaning of the term "machining" has evolved over the past two centuries as technology has advanced. During the Machine Age, it referred to (what we today might call) the "traditional" machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planning, reaming, and tapping. In these "traditional" or "conventional" machining processes, machine tools, such as lathes, milling machines, drill presses, or others, are used with a sharp cutting tool to remove material to achieve a desired geometry. Since the advent of new technologies such as electrical discharge machining, electrochemical machining, electron beam machining, photochemical machining, and ultrasonic machining, the retronym "conventional machining" can be used to differentiate those classic technologies from the newer ones. In current usage, the term "machining" without qualification usually implies the traditional machining processes. Machining is a part of the manufacture of many metal products, but it can also be used on materials such as wood, plastic, ceramic, and composites. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Machining can be a business, a hobby, or both. Much of modern day machining is carried out by computer numerical control (CNC), in which computers are used to control the movement and operation of the mills, lathes, and other cutting machines.
29
Advantages
The machining processes can produce a wide variety of dimensions with fine form accuracy. Almost all kind of engineering materials and plastics can be machined, The machining processes can be easily automated to achieve an excellent productivity, The role of the process parameters and their control to obtain a desired part with good Dimensional accuracy is well established in most of the machining processes.
30
Introduction to Forging: Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: "cold", "warm", or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons. Forged parts usually require further processing to achieve a finished part. Processes: There are many different kinds of forging processes available; however they can be grouped into three main classes:
Drawn out: length increases, cross-section decreases Upset: length decreases, cross-section increases Squeezed in closed compression dies: produces multidirectional flow
Drop forging: Drop forging is a forging process where a hammer is raised and then "dropped" onto the work-piece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and closed-die drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the workpiece, while the latter does. Open-die drop forging Open-die drop forging (with two dies) of an ingot to be further processed into a wheel. Open-die forging is also known as smith forging. In open-die forging, a hammer strikes and deforms the work-piece, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the surfaces that are in contact with the work-piece) do not enclose the work-piece, allowing it to flow except where contacted by the dies. Therefore the operator, or a robot, needs to orient and position the work-piece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For example, a die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool. Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. In some cases, open-die forging may be employed to rough-shape ingots to prepare them for subsequent operations. Open-die forging may also orient the grain to increase strength in the required direction. Impression-die drop forging Impression-die forging is also called closed-die forging. In impression-die forging, the metal is placed in a die resembling a mold, which is attached to the anvil. Usually, the hammer die is shaped as well. The hammer is then dropped on the workpiece, causing the metal to flow and fill the die cavities. The hammer is generally in contact with the workpiece on the scale of milliseconds. Depending on the size and complexity of the part, the hammer may be dropped multiple times in quick succession. 31
Excess metal is squeezed out of the die cavities, forming what are referred to as flash. The flash cools more rapidly than the rest of the material; this cool metal is stronger than the metal in the die, so it helps prevent more flash from forming. This also forces the metal to completely fill the die cavity. After forging, the flash is removed. In commercial impression-die forging, the workpiece is usually moved through a series of cavities in a die to get from an ingot to the final form. The first impression is used to distribute the metal into the rough shape in accordance to the needs of later cavities; this impression is called an edging, fullering, or bending impression. The following cavities are called blocking cavities, in which the piece is working into a shape that more closely resembles the final product. These stages usually impart the workpiece with generous bends and large fillets. The final shape is forged in a final or finisher impression cavity. If there is only a short run of parts to be done, then it may be more economical for the die to lack a final impression cavity and instead machine the final features. Impression-die forging has been improved in recent years through increased automation which includes induction heating, mechanical feeding, positioning and manipulation, and the direct heat treatment of parts after forging. One variation of impression-die forging is called fleshless forging, or true closeddie forging. In this type of forging, the die cavities are completely closed, which keeps the workpiece from forming flash. The major advantage to this process is that less metal is lost to flash. Flash can account for 20 to 45% of the starting material. The disadvantages of this process include additional cost due to a more complex die design and the need for better lubrication and workpiece placement. There are other variations of part formation that integrate impression-die forging. One method incorporates casting a forging perform from liquid metal. The casting is removed after it has solidified, but while still hot. It is then finished in a single cavity die. The flash is trimmed, and then the part is quenching hardened. Another variation follows the same process as outlined above, except perform is produced by the spraying deposition of metal droplets into shaped collectors (similar to the Osprey process). Closed-die forging has a high initial cost due to the creation of dies and required design work to make working die cavities. However, it has low recurring costs for each part, thus forgings become more economical with more volume. This is one of the major reasons closed-die forgings are often used in the automotive and tool industry. Another reason forgings are common in these industrial sectors is that forgings generally have about a 20 percent higher strength-to-weight ratio compared to cast or machined parts of the same material. Press forging Press forging works by slowly applying a continuous pressure or force, which differs from the near-instantaneous impact of drop-hammer forging. The amount of time the dies are in contact with the workpiece is measured in seconds (as compared to the milliseconds of drop-hammer forges). The press forging operation can be done either cold or hot.
32
The main advantage of press forging, as compared to drop-hammer forging, is its ability to deform the complete workpiece. Drop-hammer forging usually only deforms the surfaces of the workpiece in contact with the hammer and anvil; the interior of the workpiece will stay relatively undeformed. Another advantage to the process includes the knowledge of the new part's strain rate. We specifically know what kind of strain can be put on the part, because the compression rate of the press forging operation is controlled. There are a few disadvantages to this process, most stemming from the workpiece being in contact with the dies for such an extended period of time. The operation is a time-consuming process due to the amount and length of steps. The workpiece will cool faster because the dies are in contact with workpiece; the dies facilitate drastically more heat transfer than the surrounding atmosphere. As the workpiece cools it becomes stronger and less ductile, which may induce cracking if deformation continues. Therefore heated dies are usually used to reduce heat loss, promote surface flow, and enable the production of finer details and closer tolerances. The workpiece may also need to be reheated. When done in high productivity, press forging is more economical than hammer forging. The operation also creates closer tolerances. In hammer forging a lot of the work is absorbed by the machinery, when in press forging, the greater percentage of work is used in the work piece. Another advantage is that the operation can be used to create any size part because there is no limit to the size of the press forging machine. New press forging techniques have been able to create a higher degree of mechanical and orientation integrity. By the constraint of oxidation to the outer layers of the part, reduced levels of microcracking occur in the finished part. Press forging can be used to perform all types of forging, including open-die and impression-die forging. Impression-die press forging usually requires less draft than drop forging and has better dimensional accuracy. Also, press forgings can often be done in one closing of the dies, allowing for easy automation. Upset forging: Upset forging increases the diameter of the workpiece by compressing its length. Based on number of pieces produced, this is the most widely used forging process. A few examples of common parts produced using the upset forging process are engine valves, couplings, bolts, screws, and other fasteners. Upset forging is usually done in special high-speed machines called crank presses, but upsetting can also be done in a vertical crank press or a hydraulic press. The machines are usually set up to work in the horizontal plane, to facilitate the quick exchange of workpieces from one station to the next. The initial workpiece is usually wire or rod, but some machines can accept bars up to 25 cm (9.8 in) in diameter and a capacity of over 1000 tons. The standard upsetting machine employs split dies that contain multiple cavities. The dies open enough to allow the workpiece to move from one cavity to the next; the dies then close and the heading tool, or ram, then moves longitudinally against the bar, upsetting it into the cavity. If all of the cavities are utilized on every cycle, then a finished part will be produced with every cycle, which makes this process advantageous for mass production.
33
These rules must be followed when designing parts to be upset forged:
The length of unsupported metal that can be upset in one blow without injurious buckling should be limited to three times the diameter of the bar. Lengths of stock greater than three times the diameter may be upset successfully, provided that the diameter of the upset is not more than 1.5 times the diameter of the stock.
In an upset requiring stock length greater than three times the diameter of the stock, and where the diameter of the cavity is not more than 1.5 times the diameter of the stock, the length of unsupported metal beyond the face of the die must not exceed the diameter of the bar. Automatic hot forging The automatic hot forging process involves feeding mill-length steel bars (typically 7 m (23 ft) long) into one end of the machine at room temperature and hot forged products emerge from the other end. This all occurs rapidly; small parts can be made at a rate of 180 parts per minute (ppm) and larger can be made at a rate of 90 ppm. The parts can be solid or hollow, round or symmetrical, up to 6 kg (13 lb), and up to 18 cm (7.1 in) in diameter. The main advantages to this process are its high output rate and ability to accept low-cost materials. Little labor is required to operate the machinery. There is no flash produced so material savings are between 20 and 30% over conventional forging. The final product is a consistent 1,050 °C (1,920 °F) so air cooling will result in a part that is still easily machinable (the advantage being the lack of annealing required after forging). Tolerances are usually ±0.3 mm (0.012 in), surfaces are clean, and draft angles are 0.5 to 1°. Tool life is nearly double that of conventional forging because contact times are on the order of 0.06 second. The downside is that this process is only feasible on smaller symmetric parts and cost; the initial investment can be over $10 million, so large quantities are required to justify this process. The process starts by heating the bar to 1,200 to 1,300 °C (2,192 to 2,372 °F) in less than 60 seconds using high-power induction coils. It is then descaled with rollers, sheared into blanks, and transferred through several successive forming stages, during which it is upset, preformed, final forged, and pierced (if necessary). This process can also be coupled with high-speed cold-forming operations. Generally, the cold forming operation will do the finishing stage so that the advantages of cold-working can be obtained, while maintaining the high speed of automatic hot forging. Examples of parts made by this process are: wheel hub unit bearings, transmission gears, tapered roller bearing races, stainless steel coupling flanges, and neck rings for LP gas cylinders. Manual transmission gears are an example of automatic hot forging used in conjunction with cold working. Roll forging Roll forging is a process where round or flat bar stock is reduced in thickness and increased in length. Roll forging is performed using two cylindrical or semi-cylindrical rolls, each containing one or more shaped grooves. A heated bar is inserted into the rolls 34
and when it hits a stop the rolls rotate and the bar is progressively shaped as it is rolled through the machine. The piece is then transferred to the next set of grooves or turned around and reinserted into the same grooves. This continues until the desired shape and size is achieved. The advantage of this process is there is no flash and it imparts a favorable grain structure into the work-piece. Examples of products produced using this method include axles, tapered levers and leaf springs. Net-shape and near-net-shape forging This process is also known as precision forging. It was developed to minimize cost and waste associated with post-forging operations. Therefore, the final product from a precision forging needs little or no final machining. Cost savings are gained from the use of less material, and thus less scrap, the overall decrease in energy used, and the reduction or elimination of machining. Precision forging also requires less of a draft, 1° to 0°. The downside of this process is its cost; therefore it is only implemented if significant cost reduction can be achieved. Induction forging Unlike the above processes, induction forging is based on the type of heating style used. Many of the above processes can be used in conjunction with this heating method.
35
Forging equipment & furnaces: Equipment: 1. FORGING HAMMER OR DROP HAMMER a. b. c. d. e. f.
Board hammer Power hammer Impact hammer Industrial forged steel hammer Swing type hammer Fixed type hammers
a. Board Hammer or forging hammer The upper die and ram are raised by friction rolls gripping the board After realizing the board , the ram falls under gravity to produce the blow energy The hammer can strike between 60 to 150 blows per minute depending on size and capacity. The board hammer is an energy restricted machine. The blow energy supplied equal to the potential energy due to the weight and the height of the fall. Potential energy = mgh Where m= mass g =acceleration of gravity h= height of drop The energy will be delivered to the metal work piece to produce plastic deformation. It provides rapid impact blows to the surface of the metal. The dies are divided in two halves. The lower die is fixed to anvil and the upper die moves up and down. The energy (from the gravity drop) is absorbed into the metal, in which the maximum impact is on the metal surface. Dies are expensive being accurately machined from special alloys (susceptible to thermal shock). Drop forging is good for mass production for complex shape. b. Power hammer Power hammer provides greater capacity, in which the ram is accelerated on the down stroke by steam or air pressure in addition to gravity. Steam or air pressure is also used to raise the ram on the upstroke. The total energy supplied to the blow in a power drop hammer is given by W = 1/2 mv2 + pAH = (mg=pA)H Where m=mass v=velocity of ram at start of deformation g=acceleration of gravity p=air or steam pressure acting on ram cylinder on down stroke 36
A= area of ram cylinder H=height of the ram drop c. Impact hammer These hammers are manufactured using advanced techniques and quality raw materials in compliance with the international quality standards of hammers manufacturing. Moreover, manufactured product undergoes strict quality inspection procedure, additionally available at cost effective rates. These hammers are extensively used in the steel mining and mineral processing industry, sugar industry, cement industry, etc. Features:
Sturdy construction Easy to handle Durable
d. Industrial forged steel hammer These hammers are available in a wide variety of shapes and sizes. For the fabrication of these products our professionals make use of optimum quality basic material and most modern technology. Forged steel hammers are highly durable and easy to handle. We offer the product to our clients at a reasonable rate. Features:
Available in different sizes Durability Dynamically balanced
e. Swing type of hammer These hammers are manufactured from mild steel plates, cast steel and forged steel. The complete product range is manufactured using high quality raw material and special hard facing alloys with high precision under expert supervision. These hammers find application in many industries like mining & mineral processing industry, sugar industry, cement & steel industry. Features:
Long lasting usage Optimum performance Excellent workmanship
37
f. Fixed type hammers For the manufacturing process of these products rich quality alloys and raw material are procured from the reliable and trusted vendors of the industry. This product range is being tested by our experienced controllers to avoid flaws. In order to meet the specific requirements of our esteemed clients Features:
Robust construction Long life Corrosion resistant
2. FORGING PRESSES A forging press, often just called a press, is used for press forging. There are two main types: a. Mechanical presses Mechanical presses function by using cams, cranks and/or toggles to produce a preset (a predetermined force at a certain location in the stroke) and reproducible stroke. Due to the nature of this type of system, different forces are available at different stroke positions. Mechanical presses are faster than their hydraulic counterparts (up to 50 strokes per minute). Their capacities range from 3 to 160 MN (300 to 18,000 short tons-forces). b. Hydraulic presses. Hydraulic presses use fluid pressure and a piston to generate force. The advantages of a hydraulic press over a mechanical press are its flexibility and greater capacity. The disadvantages include a slower, larger, and costlier machine to operate. The roll forging, upsetting, and automatic hot forging processes all use specialized machinery.
Forging furnace: CHAMBER FURNACE: Working principle: Chamber Furnace is offered for a range of heat-treatment applications including stress reliving, normalizing, hardening and tempering. Effective insulation reduces heat loss into the work environment and aids in faster heat-up. Heating source: Chamber furnaces utilize electrical heating elements. 38
Control: Chamber furnaces are designed to provide consistent results through uniform heating, accurate temperature control and control of furnace atmosphere. Each furnace is fitted with standard and special accessories including vertical doors fans, cooling ventures, racks, baskets, loading devices, quench systems, various controlled atmospheres, special thermocouples, temperature controllers/recorders and alarms. Temperature range is 5000 C to 16000C PIT FURNACE A furnace made in pit for melting metal for taking casting process is called a pit furnace. Working principle The pit furnace consists of a cylindrical steel shell, closed at the bottom with a gate and covered with a removable lid. The shell is lined with refractory bricks from inside .Sometimes the furnace is completely made in brick work instead of a steel shall .The draft of the air through the furnace may be a natural draft for low melting temperature metals but a force draft with the help of a blower to accelerate the melting process in case of higher melting temperature metals and alloys. To prepare the furnace for melting, a deep bed pf coke is kindled and allowed to burn until a state of good combustion is attained .Some of the coke is removed to make place for the crucible .The crucible is then lowered into furnace .The coke is replaced and additional coke is put to surround the crucible on all sides. Metal is then charged in the crucible and the furnace lid is replaced to give natural draft .When the metal melts and reaches the desired temperature .The crucible is removed from the furnace with special long handle tongs. De -gas and de-oxidize the metal when necessary. Control
Digital, microprocessor based, thermocouple actuated, indicating temperature controller Modulating burner on gas furnaces Motor control push buttons and on-off heat switch LED pilot light
Electric Furnace Adjustable, thermocouple actuated, manual reset excess temperature interlock Separate heating element control contactors Door interlock switch turns off power to heating elements when door is opened; restores power when door is closed Gas Furnace Adjustable, thermocouple actuated, manual reset excess temperature interlock Electronic flame safeguard protection 39
Combustion air blower with air flow safety switch Purge timer High and low gas pressure switches Two pilot safety shutoff valves with leak test stations Two main safety shutoff valves with leak test stations* Valve position indicator on main safety shutoff valves Over 400,000 BTU/HR safety shutoff valve interlocked with purge timer
MUFFLE FURNACE/TUBULAR FURNACE Working principle: In an Automatic Oil Muffle Furnace (circa 1910), Petroleum is contained in tank A, and is kept under pressure by pumping at intervals with the wooden handle, so that when the valve B is opened, the oil is vaporized by passing through a heating coil at the furnace entrance, and when ignited burns fiercely as a gas flame. This passes into the furnace through the two holes, C, C, and plays under and up around the muffle D, standing on a fireclay slab. The doorway is closed by two fireclay blocks at E Pit furnace are designed for applications such as ashing most types of organic and inorganic samples, ceramics firing and decorating, wax burn-out, copper enameling, mold heating, crucible melting of non-ferrous metals, assaying, and for determination of volatile and suspended solids. This furnace is insulated with thermal efficient material for cost and energy efficient operation. The outer case of is made of double walled thick PCRC sheet and duly painted with attractive stove enamel. Gap between the walls is insulated with special grade ceramic wool with high grade international standard heating elements arranged at the side of the furnace to give even temperature. + / -10°F temperature uniformity may be achieved with this heating element. For convenient access and viewing, furnace controls are mounted on front panel. Muffle furnace models are available in various sizes and also manufacture customized designs as per customer requirements. Control: These muffle furnace models are durable from top to bottom, energy efficient and perfectly work in tough conditions. Coming with ergonomic design, these muffle furnace by Industrial Furnace and Controls are easy to install and operate. Just set your desired process temperature and the digital controller will heat and control your furnace automatically. Digital single set point temperature 950°C to 1800°C Ceramic wool insulation permits faster heat up, reducing energy consumption Door safety switch stops power to heating elements when door is opened. Equipped with thermocouple break protection, that helps preventing thermocouple failure runway condition. 40
IFC-1600BL BOTTOM LOADING FURNACE: Working principle: The single zone, high temperature, bottom loading furnace is capable of operating at temperatures up to 1650oC in air. The furnace utilizes 1800oC molydisilicide heating elements positioned on three sides of the internal chamber. The furnace utilizes an energy efficient insulation package consisting of graded ceramic-fiber, high temperature insulation. It is an ideal tool for materials annealing and sintering. Sample Size: 200x200x 200mm (8"x8"x8") BOGIE HEARTH FURNACE: RT3 series high-temperature bogie-hearth furnace is an exclusive patents and together with the most advanced high-temperature. International bogie electric furnace technology, it has become the major product exported to the international market and joining in international competition in India. The course of Car-Plant resistance furnace comes to mass production on the production line, reaching the largest India production. Working principle: The shell is welded by steel plate and steel form, the furnace lining material using ultra-light 0.6g/cm3 energy-saving insulating refractory brick building, dissecting highpurity aluminum blanket to insulate, expansion of home insulation powder filling, furnace mouth using quality furnace bull bricks, car surface quality-pressure high alumina bricks. Between bogie furnace and furnace body using Labyrinth refractory, but also by using the latest technology automatically sealed agencies to reduce heat loss and improve temperature uniformity. Furnace bottom even with the light rail vehicle are for the integration, and users do not need to install foundation, using it only by putting it in the formed ground. Heating elements materials are the general international OCr27Al7Mo2 resistance wire, exclusively produced Bending Upwards of 200 0C swap silk dormant silk brick, the maximum use temperature of 1440 0C. Taiwan Cr-Mn car equipped with nitrogen or 12 0 C heat-resistant steel floor bearing silicon carbide furnace workpiece. Furnace Door movements through rolling round in the upper and lower guide rail rolling realized, ensuring that the closure Furnace Door at the Furnace Door furnace anastomosis between the seal, ensuring that the opening will not be in the process of friction injuring masonry. Furnace Door and the Taiwan-car campaign is conducted by motor through worm reducer and the chain of transmission, and equipped with electricity magnetic brakes to make an appropriate adjustment. To improve temperature uniformity, High Temperature Bogie-hearth Resistance Furnace used bogie-type multi-zone heating and Furnace Door and after the wall layout heating components, high-power High Temperature Bogie-hearth Resistance Furnace multiple automatic temperature control counters were carried out on the multizone automatic temperature control heating and Furnace Door Bogie Operation.
41
Control The control system of International and temperature use the most advanced process technology curve in microcomputer automatic temperature control, ruling out manual error. According to the user needs heat treatment technology power curve automatically changes the size, outputting reasonable energy-saving power, making ideal curve achieves practical application of high-precision implementation in the heat treatment process. Under the heat treatment process needs, arbitrary set each heating rate (that is, heating degree), each holding temperature (that is the need to start insulation), and each holding time (that is, how long the need for the temperature insulation is).The process can be set Ba Duan curve. Temperature is controlled in precision of ±1℃. Uses: It is super-energy-efficient cycle operation furnace, mainly used for highchromium; high manganese steel castings, ductile iron, Roller, Ball, Crusher hammerhead, wear-resistant liner quenching, annealing, timeliness and various mechanical parts used heat treatment HIGH TEMPERATURE/PLC FURNACE: Working principle
Mainly used in ceramic or Refractory industries. High temperature furnaces with maximum operating temperatures of 1400°C, 1500°C , 1600°C & 1700°C. Chamber capacities of 3, 8, 15 & 35 liters. Powerful silicon carbide / MoSi2 elements located on both sides of the chamber ensure good thermal uniformity. Silicon carbide elements can withstand the stress of everyday operation and provide good longevity. Hardwearing refractory brick in chamber entrance and hearth provide good resistance to abrasion. Elsewhere, lightweight ceramic fiber insulation is used to ensure good energy efficiency and rapid heating. Vertical counter-balanced door keeps hot door insulation away from operator. Positive break door safety switch isolates chamber from power supply, when the door is opened. Double skinned construction allows convection air flow to cool the outer case, to conform to EN61010 safety standard. Choice of PID controller or programmers. Applications in general industry include sintering alumina, smelt trials and checking Al2O3 content in alumina. Applications in the ceramics industry include disintegration, testing and analysis of cement samples, refractory porosity tests, long term high temperature tests and firing & sintering of ceramic samples. Applications in the semi-conductor industry include annealing silicon, silicon carbide & nitride samples and solid state synthesis.
42
Forging Temperature All of the forging processes can be performed at various temperatures; however they are generally classified by whether the metal temperature is above or below the recrystallization temperature. If the temperature is above the material's recrystallization temperature it is deemed hot forging; if the temperature is below the material's recrystallization temperature but above 30% of the recrystallization temperature (on an absolute scale) it is deemed warm forging; if below 30% of the recrystallization temperature (usually room temperature) then it is deemed cold forging. The main advantage of hot forging is that as the metal is deformed work hardening effects are negated by the recrystallization process. Cold forging typically results in work hardening of the piece. Temperature Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain hardening, which ultimately keeps the yield strength and hardness low and ductility high. This contrasts with cold working. The lower limit of the hot working temperature is determined by its recrystallization temperature. As a guideline, the lower limit of the hot working temperature of a material is 0.6 times its melting temperature (on an absolute temperature scale). The upper limit for hot working is determined by various factors, such as: excessive oxidation, grain growth, or an undesirable phase transformation. In practice materials are usually heated to the upper limit first to keep forming forces as low as possible and to maximize the amount of time available to hot work the workpiece. The most important aspect of any hot working process is controlling the temperature of the workpiece. 90% of the energy imparted into the workpiece is converted into heat. Therefore, if the deformation process is quick enough the temperature of the workpiece should rise, however, this do1es not usually happen in practice. Most of the heat is lost through the surface of the workpiece into the cooler tooling. This causes temperature gradients in the workpiece, usually due to non-uniform cross-sections where the thinner sections are cooler than the thicker sections. Ultimately, this can lead to cracking in the cooler, less ductile surfaces. One way to minimize the problem is to heat the tooling. The hotter the tooling the less heat lost to it, but as the tooling temperature rises, the tool life decreases. Therefore the tooling temperature must be compromised; commonly, hot working tooling is heated to 500–850 °F (325–450 °C).
43
Lower limit hot working temperature for various metals Metal
Temperature
Tin
Room temperature
Steel
2,000 °F (1,090 °C)
Tungsten
4,000 °F (2,200 °C)
Advantages & disadvantages The advantages are:
Decrease in yield strength, therefore it is easier to work and uses less energy or force.
Increase in ductility.
Elevated temperatures increase diffusion which can remove or reduce chemical inhomogeneities.
Pores may reduce in size or close completely during deformation.
In steel, the weak, ductile, face-centered-cubic austenite microstructure is deformed instead of the strong body-centered-cubic ferrite microstructure found at lower temperatures.
Usually the initial workpiece that is hot worked was originally cast. The microstructure of cast items does not optimize the engineering properties, from a microstructure standpoint. Hot working improves the engineering properties of the workpiece because it replaces the microstructure with one that has fine spherical shaped grains. These grains increase the strength, ductility, and toughness of the material. The engineering properties can also be improved by reorienting the inclusions (impurities). In the cast state the inclusions are randomly oriented, which, when intersecting the surface, can be a propagation point for cracks. When the material is hot worked the inclusions tend to flow with the contour of the surface, creating stringers. As a whole the strings create a flow structure, where the properties are anisotropic (different based on direction). With the stringers oriented parallel to the surface it strengthens the workpiece, especially with respect to fracturing. The stringers act as "crack-arrestors" because the crack will want to propagate through the stringer and not along it.
44
The disadvantages are:
Undesirable reactions between the metal and the surrounding atmosphere (scaling or rapid oxidation of the workpiece).
Less precise tolerances due to thermal contraction and warping from uneven cooling.
Grain structure may vary throughout the metal for various reasons.
Requires a heating unit of some kind such as a gas or diesel furnace or an induction heater, which can be very expensive.
45
Introduction to Recrystalisation and Grain Growth: Recrystallization: Recrystallization is a process by which deformed grains are replaced by a new set of undeformed grains that nucleate and grow until the original grains have been entirely consumed. Recrystallization is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. Thus, the process may be introduced as a deliberate step in metals processing or may be an undesirable byproduct of another processing step. The most important industrial uses are the softening of metals previously hardened by cold work, which have lost their ductility, and the control of the grain structure in the final product. Definition: It can be defined as the temperature at which destroyed grains of a crystal structure are replaced by the new strain free grains. A precise definition of recrystallization is difficult to state as the process is strongly related to several other processes, most notably recovery and grain growth. In some cases it is difficult to precisely define the point at which one process begins and another ends. Doherty et al. (1997) defined recrystallization as: "... the formation of a new grain structure in a deformed material by the formation and migration of high angle grain boundaries driven by the stored energy of deformation. High angle boundaries are those with greater than a 10-15° misorientation" Thus the process can be differentiated from recovery (where high angle grain boundaries do not migrate) and grain growth (where the driving force is only due to the reduction in boundary area). Recrystallization may occur during or after deformation (during cooling or a subsequent heat treatment, for example). The former is termed dynamic while the latter is termed static. In addition, recrystallization may occur in a discontinuous manner, where distinct new grains form and grow, or a continuous manner, where the microstructure gradually evolves into a recrystallised microstructure. The different mechanisms by which recrystallization and recovery occur are complex and in many cases remain controversial. The following description is primarily applicable to static continuous recrystallization, which is the most classical variety and probably the most understood. Additional mechanisms include (geometric) dynamic recrystallization and strain induced boundary migration.
46
Laws of recrystallization: There are several, largely empirical laws of recrystallization:
Thermally activated. The rate of the microscopic mechanisms controlling the nucleation and growth of recrystallized grains depend on the annealing temperature. Arrhenius-type equations indicate an exponential relationship. Critical temperature. Following from the previous rule it is found that recrystallization requires a minimum temperature for the necessary atomic mechanisms to occur. This recrystallization temperature decreases with annealing time. Critical deformation. The prior deformation applied to the material must be adequate to provide nuclei and sufficient stored energy to drive their growth. Deformation affects the critical temperature. Increasing the magnitude of prior deformation, or reducing the deformation temperature, will increase the stored energy and the number of potential nuclei. As a result the recrystallization temperature will decrease with increasing deformation. Initial grain size affects the critical temperature. Grain boundaries are good sites for nuclei to form. Since an increase in grain size results in fewer boundaries this results in a decrease in the nucleation rate and hence an increase in the recrystallization temperature Deformation affects the final grain size. Increasing the deformation, or reducing the deformation temperature, increases the rate of nucleation faster than it increases the rate of growth. As a result the final grain size is reduced by increased deformation.
Grain Growth: Grain growth is the increase in size of grains (crystallites) in a material at high temperature. This occurs when recovery and recrystallisation are complete and further reduction in the internal energy can only be achieved by reducing the total area of grain boundary. The term is commonly used in metallurgy but is also used in reference to ceramics and minerals. Importance of grain growth: Most materials exhibit the Hall–Petch effect at room-temperature and so display a higher yield stress when the grain size is reduced. At high temperatures the opposite is true since the open, disordered nature of grain boundaries means that vacancies can diffuse more rapidly down boundaries leading to more rapid Coble creep. Since boundaries are regions of high energy they make excellent sites for the nucleation of precipitates and other second-phases e.g. Mg–Si–Cu phases in some aluminium alloys or martensite platlets in steel. Depending on the second phase in question this may have positive or negative effects.
47
Rules of grain growth: Grain growth has long been studied primarily by the examination of sectioned, polished and etched samples under the optical microscope. Although such methods enabled the collection of a great deal of empirical evidence, particular with regard to factors such as temperature or composition, the lack of crystallographic information limited the development of an understanding of the fundamental physics. Nevertheless, the following became well-established features of grain growth: 1. Grain growth occurs by the movement of grain boundaries and not by coalescence (i.e. like water droplets) 2. Boundary movement is discontinuous and the direction of motion may change suddenly. 3. One grain may grow into another grain whilst being consumed from the other side 4. The rate of consumption often increases when the grain is nearly consumed 5. A curved boundary typically migrates towards its centre of curvature 6. When grain boundaries in a single phase meet at angles other than 120 degrees, the grain included by the more acute angle will be consumed so that the angles approach 120 degrees.
48
Mechanical metallurgy: Metals have a crystalline structure - this is not usually visible but can be seen on galvanized lamp posts for example. When a metal solidifies from the molten state, millions of tiny crystals start to grow. The longer the metal takes to cool the larger the crystals grow. These crystals form the grains in the solid metal. Each grain is a distinct crystal with its own orientation.
The areas between the grains are known as grain boundaries. Within each grain, the individual atoms form a crystalline lattice. Each atom will have a certain number of close neighbors with which it shares loose bonds. (The number of neighboring atoms depends upon the structure of the lattice.) When stress is applied to the metal, the atoms will start to spread apart. The atomic bonds stretch, and the attractive forces between the atoms will oppose the applied stress, like millions of tiny springs. If the metal has not yielded, the interatomic forces will pull the metal back into its original shape when the stress is removed. So it is behaving like a piece of rubber -it is elastic! When the metal is cold worked by forging, stamping or rolling its shape is permanently changed (DEFORMED) this is only possible because of defects (DISLOCATIONS) in the grain structure which move through the crystal structure. These dislocations or slips in the grain structure allow the overall change in shape of the metal. Each grain can have a very large number of dislocations (only visible under a powerful microscope). Of course if the metal is hot worked there is more energy to available for the dislocations to move. This is why the strenghth of most materials falls as the 49
temperature goes up. Strong materials are those that can slow down or stop the movement of the dislocations. This can be achieved by increasing the number of dislocations by cold work or work hardening (together known as stress hardening). Alloying where the other metal interacts with the crystal lattice blocking the movement of the dislocation takes place. (Brass is a good example of this where the small percentage of zinc makes the brass stronger than either copper or zinc). STRAIN HARDENING Cold working or work hardening generates many dislocations which pile up and entangle this will prevent the further movement of dislocations. Try this by bending a paper clip back and forth - it becomes hard to bend at the same point and will eventually break if you continue. TEMPER is the term used to describe the amount of cold working on a metal e.g. half hard, full hard, spring temper etc. Cold forging - The strip of metal is being forged by the application of force using broad hammer or. The strip is compressed and becomes much longer and thinner. The grains in the metal also become elongated. This a permanent deformation so dislocations pile up and the strength go up. The larger grain boundary in the elongated strip also helps to stop the formation of further dislocations so that it becomes harder to roll a second time. The metal also becomes more brittle and is more liable to fracture as the number of dislocations goes up. ANNEALING The metal actually becomes difficult to work as cold working continues. The only answer is annealling. This is a high temperature soak (keeping the metal at the same temperature for some time). The grains recrystallise - old grains are obliterated and new grains grow. The metal loses all the effects of cold working becoming ductile again but losing its strength. Annealling has to be carefully controlled so that the grains do not become too large.
50
HOT FORGING While cold forging is very useful for increasing the strength of matals - hot forging is widely used in manufacturing. The advantage is that the part can be formed without annealling and the grain structure will follow the form of the object being forged. So for example a spanner would have a central part where the grain structure is elongated but with few dislocations then the grain flows around following the form of the ends. The spanner will of course have to be heat treated to give the right degree of hardness and toughness at the right points. GRAIN FLOW COMPARISON
Forged Bar: Directional alignment through the forging process has been deliberately oriented in a direction requiring maximum strength. This also yields ductility and resistance to impact and fatigue. Machined Bar: Unidirectional grain flow has been cut when changing contour, exposing grain ends. This renders the material more liable to fatigue and more sensitive to stress corrosion cracking. Cast Bar: No grain flow or directional strength is achieved through the casting process.
51
Analysis of grain structure in forge material: the formation of grain structure in forged parts is elongated in the direction of the deformation The metal flow during forging provides fibrous microstructure (revealed by etching). This structure give better mechanical properties in the plane of maximum strain (perhaps) lower across the thickness. The workpiece often undergo recrystallization, therefore, provide finer grains compare to the cast dendritic structure resulting in improve mechanical properties. The rate of the microscopic mechanisms controlling the nucleation and growth of recrystallized grains depend on the annealing temperature. Arrhenius-type equations indicate an exponential relationship. Following from the previous rule it is found that recrystallization requires a minimum temperature for the necessary atomic mechanisms to occur. This recrystallization temperature decreases with annealing time. The prior deformation applied to the material must be adequate to provide nuclei and sufficient stored energy to drive their growth. Increasing the magnitude of prior deformation, or reducing the deformation temperature, will increase the stored energy and the number of potential nuclei. As a result the recrystallization temperature will decrease with increasing deformation. Grain boundaries are good sites for nuclei to form. Since an increase in grain size results in fewer boundaries this results in a decrease in the nucleation rate and hence an increase in the recrystallization temperature. Increasing the deformation, or reducing the deformation temperature, increases the rate of nucleation faster than it increases the rate of growth. As a result the final grain size is reduced by increased deformation. Driving force During plastic deformation the work performed is the integral of the stress and the plastic strain increment. Although the majority of this work is converted to heat, some fraction (~1-5%) is retained in the material as defects - particularly dislocations. The rearrangement or elimination of these dislocations will reduce the internal energy of the system and so there is a thermodynamic driving force for such processes. At moderate to high temperatures, particularly in materials with the high stacking fault energy such as Aluminium and nickel, recovery occurs readily and free dislocations will readily rearrange themselves into sub grains surrounded low-angle grain boundaries. The driving force is the difference in energy between the deformed and recrystallized state E which can be determined by the dislocation density or the sub grain size and boundary energy (Doherty, 2005):
Where ρ is the dislocation density, G is the shear modulus, b is the Burgers vector of the dislocations, γ is the sub-grain boundary energy and ds are the subgrain size.
52
Data Analysis Changing in grain structure means the micro-structural change of any material. When the grain structure change the material started to being deformed. When a material solidified from molten state millions of tiny crystals start to grow. The longer the metal takes to cool the larger the crystal grow. Then the crystals formed grains in a solid metal. Each grain is a decent crystal with its own orientation. The area between the grains are called grain boundary. From the analysis, it can be inferred that mechanical properties depends largely upon the various form of forging operations and forging temperature. In hot working process when the materials heated above recrystallization temperature the material comes in plastic stage, Metal is deform and work hardening effects are neglected by the recrystallization process. The internal stresses of grains started to release and the most notable recovery and grain growth takes place. In the process of recovery high angle grain boundary do not migrate. In the case of cold forging, the metal is not heated. Here when we hammered the metal, the grain boundaries are breaks and then the grains are goes to arrange. By this arrangement, the dislocation between them is reduced. After that, the newly arranged grains are formed various shaped metals. Thus the work hardening effect also takes place. By this process, a broad knowledge got about various forging processes and its internal changes in specified temperature for specified processes.
53
Conclusion Under engineering shops and foundry of Visakhapatnam Steel Plant, the project work on “ANALYSIS OF GRAIN STRUCTURE IN FORGING” is very fruitful for gaining knowledge in several processes, crystallite and grain growth during the deformation processes of forging. Depending upon the properties and the applications that may be required for any design purpose, a suitable form of forging should be adopted in suitable temperature. Also it is understood that how forging process changes the microstructure of any material. It is also seen that by adopting a proper hardening process cycle the properties of hardness can be achieved in forged material simultaneously we understood that tempering process follows hardening process so as to relieve the internal stress induced by hardening and to give the material its required toughness by making it more shock resistant which is required property for forged material. During the project, it is also known to us about the various departments of Visakhapatnam steel Plant, which helped us not only the completion of the project but also get a partial knowledge about this industry
54
Bibliography www.wikipedia.com www.nptel.iitm.ac.in Manufacturing Technology by P.N.Rao Gate material of brilliant tutorial www.me.iitb.ac.in www.tech.plym.ac.uk Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley Workshop technology by HAZRA CHOUDARY. www.the-warren.org
55
