Me6402 Mt2 Notes Rejinpaul

www.rejinpaul.com MANUFACTURING TECHNOLOGY – II (ME 6402)

UNIT – 1 THEORY OF METAL CUTTING

Prepared by S. Senthil Kumar AP/Mech SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com SVCET

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THEORY OF METAL MACHINING 1. Overview of Machining Technology 2. Theory of Chip Formation in Metal Machining 3. Force Relationships Equation

and

the

Merchant

4. Power and Energy Relationships in Machining 5. Cutting Temperature 6. Cutting tool 7. Tool wear and tool life 8. Cutting fluids 9. machinability SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Material Removal Processes A family of shaping operations, the common feature of which is removal of material from a starting work part so the remaining part has the 





desired geometry Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling Abrasive processes – material removal by hard, abrasive particles, e.g., grinding Nontraditional processes - various energy forms other than sharp cutting tool to remove material SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Machining Cutting action involves shear deformation of work material to form a chip 

As chip is removed, new surface is exposed

(a)negative A cross-sectional view of the with machining process, (b) tool with rake angle; compare positive rake angle in (a). SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Why Machining is Important 

Variety of work materials can be machined 





Most frequently used to cut metals

Variety of part shapes and special geometric features possible, such as: 

Screw threads



Accurate round holes



Very straight edges and surfaces

Good dimensional accuracy and surface finish

SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Disadvantages with Machining 

Wasteful of material 



Chips generated in machining are wasted material, at least in the unit operation

Time consuming 

A machining operation generally takes more time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming


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Machining in Manufacturing Sequence 

Generally performed after other manufacturing processes, such as casting, forging, and bar drawing 



Other processes create the general shape of the starting work part Machining provides the final shape, dimensions, finish, and special geometric details that other processes cannot create


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Machining Operations 



Most important machining operations: 

Turning



Drilling



Milling

Other machining operations: 

Shaping and planning



Broaching



Sawing


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Turning Single point cutting tool removes material from a rotating work piece to form a cylindrical shape

Three most common machining processes: (a) turning, SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Drilling Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges

(b) drilling,


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Milling Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface 

Two forms: peripheral milling and face milling

(c) peripheral milling, and (d) face milling. SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Cutting Tool Classification 1. Single-Point Tools  



One dominant cutting edge Point is usually rounded to form a nose radius Turning uses single point tools

2. Multiple Cutting Edge Tools 

More than one cutting edge



Motion relative to work achieved by rotating



Drilling and milling use rotating multiple cutting edge tools SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Cutting Tools

(a) A single-point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with multiple cutting edges.


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Cutting Conditions in Machining 

Three dimensions of a machining process: 

Cutting speed v – primary motion



Feed f – secondary motion





Depth of cut d – penetration of tool below original work surface

For certain operations, material removal rate can be computed as

RMR = v f d where v = cutting speed; f = feed; d = depth of cut SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Cutting Conditions for Turning

Speed, feed, and depth of cut in turning.


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Roughing vs. Finishing In production, several roughing cuts are usually taken on the part, followed by one or two finishing cuts 

Roughing - removes large amounts of material from starting workpart Creates shape close to desired geometry, but leaves some material for finish cutting High feeds and depths, low speeds 





Finishing - completes part geometry Final dimensions, tolerances, and finish Low feeds and depths, high cutting speeds  


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Machine Tools A



power driven machine that performs machining operation, including grinding Functions in machining: 

Holds work part



Positions tool relative to work





a

Provides power at speed, feed, and depth that have been set

The term is also applied to machines that perform metal forming operations SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Orthogonal Cutting Model Simplified 2-D model of machining that describes the mechanics of machining fairly accurately

Orthogonal cutting: (a) as a three-dimensional process.


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Chip Thickness Ratio r 

where



to tc

r = chip thickness ratio; to = thickness of the chip prior to chip formation; tc = chip thickness after separation

Chip thickness after cut always greater than before, so chip ratio always less than 1.0


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Determining Shear Plane Angle 

Based on the geometric parameters of the orthogonal model, the shear plane angle  can be determined as: tan 



r cos  1  r sin

where r = chip ratio  = rake angle


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Shear Strain in Chip Formation

Shear strain during chip formation: (a) chip formation depicted as a series parallel slidingstrain, relative to (c) each other, (b) one of the plates of isolated to plates show shear and shear strain triangle used to derive strain equation. SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Shear Strain Shear strain in machining can be computed from the following equation, based on the preceding parallel plate model:  = tan( - ) + cot 

where  = shear strain,  = shear plane angle, and  = rake angle of cutting tool


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Chip Formation

More realistic viewAlso of chip formation, showing shear than shear plane. shown is the secondary shearzone zonerather resulting from tool-chip friction. SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Four Basic Types of Chip in Machining 1. Discontinuous chip 2. Continuous chip 3. Continuous chip with Built-up Edge (BUE) 4. Serrated chip


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Discontinuous Chip 

Brittle work materials



Low cutting speeds





Large feed and depth of cut High tool-chip friction

Four types of chip formation in metal cutting: (a) discontinuous


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Continuous Chip 

Ductile work materials



High cutting speeds



Small depths

feeds

and



Sharp cutting edge



Low tool-chip friction

(b) continuous


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Continuous with BUE  





Ductile materials Low to medium cutting speeds Tool and chip friction causes portions of chip to adhere to rake face BUE forms, then breaks off, cyclically

(c) continuous with built-up edge SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Serrated Chip 





Semi continuous – saw tooth appearance Cyclical chip forms with alternating high shear strain then low shear strain Associated with difficult-to-machine metals at high cutting (d) serrated.

speeds SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Forces Acting on Chip 

Friction force F and Normal force to friction N



Shear force Fs and Normal force to shear Fn

Forces in metal cutting: (a) forces acting on the chip in orthogonal cutting


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Resultant Forces 

Vector addition of F and N = resultant R



Vector addition of Fs and Fn = resultant R'



Forces acting on the chip must be in balance:   

R' must be equal in magnitude to R R’ must be opposite in direction to R R’ must be collinear with R


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Coefficient of Friction Coefficient of friction between tool and chip: 

F N

Friction angle related to coefficient of friction as follows:

  tan 


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Shear Stress Shear stress acting along the shear plane: S



Fs A s

where As = area of the shear plane

As 

t ow sin 

Shear stress = shear strength of work material during cutting


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Cutting Force and Thrust Force  

F, N, Fs, and Fn cannot be directly measured Forces acting on the tool that can be measured: Cutting force Fc and Thrust force Ft 

Forces in metal cutting: (b) forces acting on the tool that can be measured


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Forces in Metal Cutting 



Equations can be derived to relate the forces that cannot be measured to the forces that can be measured:

F = Fc sin + Ft cos N = Fc cos - Ft sin Fs = Fc cos - Ft sin Fn = Fc sin + Ft cos Based on these calculated force, shear stress and coefficient of friction can be determined


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The Merchant Equation 

Of all the possible angles at which shear deformation can occur, the work material will select a shear plane angle  that minimizes energy, given by   45 

 

 2



 2

Derived by Eugene Merchant Based on orthogonal cutting, but validity extends to 3-D machining


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What the Merchant Equation Tells Us  



45 

 2



 2

To increase shear plane angle  

Increase the rake angle Reduce the friction angle (or coefficient of friction)


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Effect of Higher Shear Plane Angle 

Higher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperature

Effect of shear plane angle  : (a) higher  with a resulting lower shear plane area; (b) smaller  with a corresponding larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Power and Energy Relationships  

A machining operation requires power The power to perform machining can be computed from:

Pc = F c v where Pc = cutting power; Fc = cutting force; and v = cutting speed


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Power and Energy Relationships 

In U.S. customary units, power is traditional expressed as horsepower (dividing ft-lb/min by 33,000) HPc



Fcv 33 000 ,

where HPc = cutting horsepower, hp


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Power and Energy Relationships 

Gross power to operate the machine tool Pg or HPg is given by

Pg  Pc E

or

HPg  HPc E

where E = mechanical efficiency of machine tool 

Typical E for machine tools



90%


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Unit Power in Machining 



Useful to convert power into power per unit volume rate of metal cut Called unit power, Pu or unit horsepower, HPu PU =

Pc RMR

or

HPu =

HPc RMR

where RMR = material removal rate


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Specific Energy in Machining Unit power is also known as the specific energy U U =P = u

Pc RMR

=

Fc v vt ow

Units for specific energy are typically N-m/mm3 or J/mm3 (in-lb/in3)


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Cutting Temperature 





Approximately 98% of the energy in machining is converted into heat This can cause temperatures to be very high at the tool chip interface The remaining energy (about 2%) is retained as elastic energy in the chip


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Cutting Temperatures are Important High cutting temperatures 1. Reduce tool life 2. Produce hot chips that pose safety hazards to the machine operator 3. Can cause inaccuracies in part dimensions due to thermal expansion of work material


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Analytical method derived by Nathan Cook from dimensional analysis using experimental data for various work materials

 vt o  T    C  K  0.4U

0.333

where T = temperature rise at tool-chip interface; U = specific energy; v = cutting speed; to = chip thickness before cut; C = volumetric specific heat of work material; K = thermal diffusivity of work material SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Experimental methods can be used to measure temperatures in machining Most frequently used technique is the tool-chip thermocouple Using this method, Ken Trigger determined the speed-temperature relationship to be of the form: 



T = K vm where T = measured tool-chip temperature, and v = cutting speed

interface


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Thermal Aspects 



Energy dissipated at the cutting edge is converted into heat Three regions where heat is generated are 1. Shear zone 

80 - 85% of heat is generated

2. Chip - tool interface region 15 – 20 % oh heat is generated 

3. Tool – work interface region 1 – 3 % of heat is generated 


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Cutting Tool Materials 

Selection of cutting tool depends on 

Volume of production



Tool design



Type of machining process







Physical and chemical properties of work material Rigidity and condition of machine

Properties / Characteristics of cutting tool 

Hot hardness



Wear resistance



Toughness



Low friction



SSK, AP/MECH, SVCET Cost tool Getof useful study materials from www.rejinpaul.com

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Cutting Tool Materials 

Classification of tool materials 

Carbon tool steel



High Speed steel



Cemented carbides



Ceramics



Diamonds



Cubic boron nitride


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Tool Wear 

Classification 

Flank wear



Crater wear



Nose wear


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Tool Life 



Ways of expressing tool life 

Volume of metal removed per grind



Number of work pieces machined per grind



Time unit

Factors affecting tool life 

Cutting speed



Feed and depth of cut



Tool geometry



Tool material



Cutting fluid



Work material



Rigidity of work, tool and machine SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Tool Life v Tool Wear


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Cutting Fluids 



Used to carry away the heat produced during machining Functions of cutting fluids 

Cools the tool and work piece



Lubricates the cutting tool



Reduces co-efficient of friction between tool and work piece



Improves surface finish



Causes the chip to break up into small pieces



Washes away the chips from the tool



Prevents corrosion of work and machine SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Cutting Fluids 

Properties of cutting fluids 

Should possess good lubricating properties



Should have high heat absorbing capacity



Should have high specific heat



Should be odorless



Should be non-corrosive



Should have low viscosity



Should be harmless



Should not stain



Should be economical



Should be transparent SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Cutting Fluids 



Types of cutting fluids 

Water based cutting fluids



Straight or heat oil based cutting fluids 1.

Mineral oils

2.

Straight fatty oils

3.

Mixed oils

4.

Sulphurised oils

5.

Chlorinated oils

Methods of applying cutting fluids   

Drop by drop under gravity Flood under gravity Form of liquid jet SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Machinability 



Defined as the ease with which a material can be satisfactorily machined Also defined as 

Life of tool before tool failure



Quality of machined surface





Power consumption per unit volume of material removed

Variables affecting machinability 

Work variables



Tool variables



Machine variables



Cutting conditions SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Machinability 

Evaluation of machinability 

Tool life per grind



Rate of metal removal per grind tool grind



Surface finish



Magnitude of cutting forces and power consumption



Dimensional stability of the finished work



Heat generated during cutting



Ease of chip disposal



Chip hardness



Shape and size of chips SSK, AP/MECH, SVCET Get useful study materials from www.rejinpaul.com

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Machinability 



=

Advantages 

Good surface finish can be produced



Higher cutting speed can be used



Less power consumption



MRR is high



Less tool wear

Machinability Index

C.S. of metal investigated or 20 mins tool life C.S. of standard steel for 20 mins tool life


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MANUFACTURING TECHNOLOGY – II UNIT III SHAPER, MILLING AND GEAR CUTTING MACHINES Prepared by S. Senthil Kumar AP / Mech SVCET Get useful study materials from www.rejinpaul.com

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MANUFACTURING TECHNOLOGY – II 

Reciprocating Machine Tools: Shaper, Planer, Slotter



Milling: Types, Milling Cutters, Operations



Hole Making: Drilling, Quill

Mechanism

,

Reaming,

Boring, Tapping 

Sawing Machine: Hack Saw, Band Saw, Circular Saw



Broaching Machines: Broach Construction, Push, Pull, Surface and Continuous Broaching Machines Get useful study materials from www.rejinpaul.com

SHAPER 

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SHAPER is a reciprocating type of machine tool with single point cutting tool used to produce flat surface.



The flat surface may be horizontal, vertical or inclined.

Parts of Shaper: 1. Table 2. Tool Head 3. Ram 

The tool head is fitted on the front end of the ram while the job is rigidly fixed on the table.

 

The tool is mounted on the tool post or head. The ram reciprocates along with the tool to remove the metal in the forward stroke called cutting stroke.

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www.rejinpaul.com Classification of Shaper

1. According to the type of driving mechanism i.

Crank drive type

ii. Whit worth driving mechanism type iii. Hydraulic drive type 2. According to the position of ram i. Horizontal shaper ii. Vertical shaper iii. Travelling head shaper 3. According to the table design i.

Standard or plain shaper

ii. Universal shaper 4. According to the type of cutting stroke i. Push out type ii. Draw out type Get useful study materials from www.rejinpaul.com

www.rejinpaul.com Principle Parts of Shaper


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The specification of a typical shaper are listed below. 

Maximum length of stroke



Maximum crosswise movement of the table

 

Maximum vertical adjustment of the table Type of driving mechanism



Power of the motor



Speed and feed available



Type of shaper (Plain or Universal)



Floor space required

 

Total weight of the shaper Ratio of cutting stroke time to return stroke time. Get useful study materials from www.rejinpaul.com

Hydraulic Drive www.rejinpaul.com


Crank and Slotted Link and QRwww.rejinpaul.com Mechanism


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Whit worth Mechanism


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Stroke length arrangement


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Position arrangement


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Feed Mechanism – Hand feed


Feed Mechanism – Automatic Table feed

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Work Holding devices – Clamping in a vise

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Work Holding devices – Clamping on the table

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Work Holding devices – Clamping on a V Block

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Work Holding devices – Clamping on angle plate

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Shaper Tools


Shaper Operations – Machining Horizontal Surfaces

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Shaper Operations – Machining Vertical Surfaces

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Shaper Operations – Machining Angular Surfaces

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Shaper Operations – Machining Slots , grooves and Keyways

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Shaper Operations – Machining Irregular Surfaces

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PLANER

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

PLANER is a very large reciprocating machine tool.



The work is mounted on the table by any one of the work holding devices.



Two vertical columns with vertical guide ways are provided on both sides of the bed and connected by a cross-rail to mount the tool heads and also connected by a cross beam at the top.



These tool heads are used to hold the tools.



The tool cuts the workpiece when the table reciprocates.



The cross feed is given by moving the tool head along the cross-rail.



Vertical feed is given by moving down the tool.



The tool slide can be tilted or swivelled at any required angle using a swivel head for machining inclined surfaces. Get useful study materials from www.rejinpaul.com

www.rejinpaul.com Classification of Planer

The various types of planer are as follows. 1. 2. 3. 4. 5.

Double housing planer Open side planer Pit planer Edge planer Divided table planer

Specification of Planer 

The distance between two columns



Stroke length of the planer



Radial distance between the top of the table and the bottom most position of the cross rail



Maximum length of the table



Power of the motor



Range of the speeds and feed available



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Open Side Planerwww.rejinpaul.com


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Pit Planer


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Edge Planer


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Divided Head Planer


Quick return mechanism – Open and Cross belt drive www.rejinpaul.com


Quick return mechanism – Electric drive

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Feed mechanism


Work Holding devices www.rejinpaul.com – Angle plate , Screw stops, Planer Jacks


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Work Holding devices - Fixtures


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Planer Tools


Planer Operations –www.rejinpaul.com Horizontal , angle, Vertical , CURVED Surfaces


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Difference Between Shaper and Planer


SLOTTER

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

SLOTTER is a reciprocating type machine tool.



In this machine, the ram reciprocates vertically.



The tool held in the ram cuts during downward stroke only.

Parts of Slotter 1. 2. 3. 4. 5. 6.

Base Column Saddle Rotary table Ram Tool head

Slotter Operations    

Machining flat surface Machining grooves, slots, keyways Machining cylindrical surface Machining irregular surface Get useful study materials from www.rejinpaul.com

www.rejinpaul.com Principle Parts of Slotter


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Drives 1. Whit worth mechanism 2. Variable speed reversible electric motor drive 3. Hydraulic Drive


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Feed mechanism


Work Holding Devices – Slotting fixtures www.rejinpaul.com


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Slotter Tools


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Slotter Operations


MILLING 

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MILLING is the process of removing metal by feeding the workpiece against a rotating multipoint cutter.



The metal is removed in the form of small chips.

Principle of Operation In Up Milling Process, the workpiece is fed opposite to the cutter's tangential velocity. Each tooth of the cutter starts the cut with zero depth of cut. In Down Milling Process, the workpiece is fed in the same direction as that of the cutter's tangential velocity. the cutter enters the top of the workpiece and removes the chip that gets progressively thinner as the cutter tooth rotates. Get useful study materials from www.rejinpaul.com

MILLING

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Specification of Milling Machine 



The table length and width Maximum longitudinal cross and vertical travel of the table Number of spindle speeds and feeds Power of driving motor Floor space and net weight

 

Spindle nose taper size Type of milling machine

  

Classification of Milling Machine 1. Column and Knee Type i. Plain Milling Machine ii. Vertical Milling Machine iii. Universal Milling Machine iv. Ram-type Milling Machine

4. Plano-Type Milling Machine 5. Special Purpose Milling Machine i. Rotary Table Milling Machine ii. Drum Milling Machine iii. Profile Milling Machine

v. Omniversal Milling Machine 2. Bed-Type Milling Machine i. Simplex Milling Machine ii. Duplex Milling Machine Get useful study materials from www.rejinpaul.com iii. Triplex Milling Machine

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Column and Knee Type -Horizontal Milling


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Milling Machines


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Column and Knee Type - Universal Milling Machine


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Column and Knee Type Omniversal Milling Machine


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Bed Type- Fixed Plain Milling machine


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Plano type Milling Machine


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Drum type Milling Machine


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Rotary and Profile Milling Machines


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Work Holding Devices


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Tool Holding Devices


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Milling Attachments


Milling Cutters – Slab Milling Cutter

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Milling Cutters – Side Milling Cutter

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Milling Cutters


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Milling Cutters


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Milling Cutters


Milling Cutterswww.rejinpaul.com


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Nomenclature of Plain Milling Cutter


Milling operations – Peripheral and Face milling operations

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Milling operations


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Milling operations


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Milling operations


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Milling operations


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Milling operations


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Gang Milling


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Indexing mechanisms


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Index Plates with sector arms


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Indexing mechanisms


DRILLING 

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DRILLING is the process of producing hole ion the work piece by using a rotating cutter called drill.



The machine on which the drilling is carried out is called drilling machines.



The drilling machine sometimes called drill press as the machine exerts vertical pressure to originate a hole.

Specification of Drilling Machine         

Maximum size of the drill in mm that the machine can operate. Table size of maximum dimensions of a job can mount on a table in square metre. Maximum spindle travel in mm. Number of spindle speeds and range of spindle speeds in RPM. Number of automatic spindle feeds or feed range available in mm/rev. Morse taper number of the drill spindle nose. Power input of the machine HP. Floor space required in m2. Net weight of the machine in Tonne. Get useful study materials from www.rejinpaul.com

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Hole Making


www.rejinpaul.com Classification of Drilling Machine

1. Portable Drilling Machine 2. Sensitive Drilling Machine i. Bench Type ii. Floor Type 3. Upright Drilling Machine i. Round Column Type or Pillar Type ii. Box Column Type or Square Section Type 4. Radial Drilling Machine i. Plain Type ii. Semi-Universal Type iii. Universal Type 5. Gang Drilling Machine 6. Multiple Spindle Drilling Machine 7. Automatic Drilling Machine 8. Deep Hole Drilling Machine


www.rejinpaul.com Portable Drilling Machine


www.rejinpaul.com Bench Type Sensitive Drilling Machine


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Automatic Feed Mechanism


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Drilling operations


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Twist Drill nomenclature


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Twist Drill nomenclature


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Mounting the Drill tool


Mounting the Drill tool – By directly fitting into the spindle

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Mounting the Drill tool - By using a sleeve


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Mounting the Drill tool - By using a socket


Mounting the Drill tool – By using chucks www.rejinpaul.com


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Reaming Tool


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Various reamers


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Tapping Tool


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Boring


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Horizontal Boring Machine


Floor Type Horizontalwww.rejinpaul.com Boring Machine


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Table type Horizontal Boring Machine


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Planer type Horizontal Boring Machine


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Multi spindle Horizontal Boring Machine


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Vertical & Turret Boring Machine


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Jig Boring Machine


Sawing – Selection of Blade for Sawing machine

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Broaching


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Horizontal type Internal Broaching machine


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Horizontal type surface Broaching machine


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Push down type Vertical Broaching machine


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Pull down type and Up type Vertical Broaching machine


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Horizontal type continuous Broaching machine


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Rotary type continuous Broaching machine


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Broach tool nomenclature


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Push type Broach


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Pull type Broach


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Progressive type Broach


Broaching operations – Spline Broaching

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Broaching operations – Keyway Broaching www.rejinpaul.com


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Manufacturing Technology II (ME 6402) Unit 5 – CNC Machining

09-Feb-15

SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com

1

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NC Machine Tools Mechanical actions of a machine tool or other equipment are controlled by a program containing coded alphanumeric data Alphanumeric data represents the relative position between a work head and a work part

When the current job is completed, a new program can be entered for the next job

09-Feb-15


2

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Constructional Details Basic Components of NC system 1. Program of Instructions

2. Machine Control Unit

3. Processing Equipment

09-Feb-15

•

Part programming in machining

•

Controls the processes

•

Performs the processes


3

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Types of CNC Based on Motion type Based on Control Loops Based on Power Supply Based on Positioning System

09-Feb-15

• •

• •

• • •

• •

Point to point Continuous path Open Loop Closed loop Electric Hydraulic Pneumatic Incremental obsolete


4

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Special Features in CNC High Precision Increases Production Reduces Labor intensity Improves Working Condition Enables unmanned operation

09-Feb-15


5

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Design Considerations of CNC Machine •

Productivity • • •

• •

•

Reduction of machine Time Reduction of non-productive time Machining with more than one tool simultaneously Improved reliability of machine components Proper maintenance to prevent unscheduled stoppage

Accuracy •

Improve geometrical accuracy of machine elements Lead screw Guide ways Improves kinematic accuracy of machine tools Increases static and dynamic stiffness of machine tool structure Provides accurate machine tool for measuring distance Reduces thermal deformation of tool while machining • •

• • • •

09-Feb-15


6

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Machine response • •

•

Safe and easy control • •

• • •

•

Shield should be provided on the rotating and moving part Protects the operator from chips, abrasive ducts and coolants by using screens and shield Better clamping mechanism to withstand tool force Provides emergency stop buttons Provides over load production switches, buttons, etc.,

Appearance •

•

Magnitude of load Range of travel

Good appearance and attractiveness to the workers to interest on machines

Cost •

09-Feb-15

Low cost for manufacturing and operation SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com

7

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Operating characteristics • •

•

Component characteristics • •

•

Reliability Maintainability

Frictional characteristics and amount of backlash Inertia and stiffness

Simplicity in Design •

09-Feb-15

Uses simplified standard and sub-parts


8

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Structural members of CNC Slide Ways Linear Bearings Ball Screw Spindle Drives Feed Drives

09-Feb-15


9

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Slide Ways •

Designed to provide a free motion in one direction • •

Laterally Longitudinally

•

Also called as linear motion bearing slide

•

Powered by either manual operation or inertial operation

09-Feb-15


10

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Types of Slide Ways

Hydrostatic slide ways

Antifriction slide ways

• •

• •

•

Wear resistant slide ways

•

•

09-Feb-15

Oil lubricated slide ways Air bearing slide ways

Ball type slide ways Roller type slide ways Induction hardened slide ways Flame hardened slide ways Surface coatedslideways


11

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Hydrostatic Slide ways •

Liquid friction condition of the interface of mating surface are achieved by supplying under pressure

•

Sliding bodies must not be inclined to each other

•

Used in high expensive machine

•

Example • •

09-Feb-15

Grinding machine - programmed controllable copying machine


12

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Oil Lubricated Slide Ways •

•

Friction is minimized by forcing oil under pressure between mating surfaces

Pressure is automatically varied according to the load on surface

09-Feb-15


13

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Air Lubricated Slide Ways •

•

•

Pressurized air is used instead of oil Used for positioning the slide when no machining is carried out

Disadvantages • •

09-Feb-15

Misalignments may happen due to lifting of slides Uneven distribution of load on work table


14

www.rejinpaul.com Anti friction slide ways

•

•

•

Conventional machines have the property of stick-slip due to high sliding friction at low velocity To avoidinthis sliding, contact is avoidedsliding by making contact point or line by converting frictionthe to rolling friction Types • •

09-Feb-15

Ball bearing guide ways Roller bearing guide ways


15

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Ball bearing slide ways •

•

•

The bed forms the guide way for the ball to recirculate Hardened inserts are fitted into the table which is located on the ball track with a single flat structure in contact with the balls

The ball rolls between four rods, two fixed to the table and two fixed to the bed

09-Feb-15


16

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Roller bearing Slide ways •

•

•

•

Instead of ball, which avoids direct contact of the surface, roller is used Increases the load carrying capacity Hardened steel inserts are used as rollers to minimize the friction Suitable for using in boring and milling machines

09-Feb-15


17

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Wear Resistant Slide Ways •

Non metallic parts or plastic inserts are used

•

Inserts stick to the underside of the moving element

•

Inserts are made up of 2 materials • •

•

09-Feb-15

First material reduces coefficient of friction Other increases strength, load bearing capacity and self lubricating capacity

Poly Tetra Fluro Ethene (PTFE), Ferobestos – CA, turcite B are some of the materials used to make positive contact


18

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Linear Bearings Types Roller Element bearing Ball bearing slides Roller Slides Plain Bearing Dovetail Slides Compound Slides Rack Slides

09-Feb-15


19

www.rejinpaul.com Roller element bearing •

Composed of a sleeve-like outer ring and several rows of balls retained by cages.

•

The cages were srcinally machined from solid metal and

•

were quickly replaced by stampings. Features smooth motion, low friction, high rigidity and long

life. •

They are economical, and easy to maintain and replace

•

Can run only on hardened steel or stainless steel shafting.

•

•

More rigid than plain bearings. Do not handle contamination well and require seals. SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com Requires lubrication.

09-Feb-15 •

20

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Ball Bearing Slides •

•

•

Ball bearing slides offer smooth precision motion along a single-axis linear design

self-lubrication properties that increase reliability applications include • • • • •

delicate instrumentation, robotic assembly, cabinetry, high-end appliances clean room environments manufacturing industry furniture electronics construction industries • • • •

•

powered by either a drive mechanism, inertia or by hand

09-Feb-15


21

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Ball Bearing Slides •

•

For example , a widely used ball bearing slide in the furniture industry is a ball bearing drawer slide Constructed from materials such as –

aluminum,

–

hardened cold rolled steel

–

•

galvanized steel

Ball bearing slides consist of two linear rows of ball bearings contained by four rods and located on differing sides of the base, which supports the carriage for smooth linear movement along the ball bearings

A lower load capa city for their size compared to other linear slides because the balls are less resistant to wear and abrasions. 09-Feb-15 SSK, AP / MECH, SVCET 22 •


Roller Slides •

•

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Also known as crossed roller slides non-motorized linear slides that provide low-friction linear movement for equipment powered by inertia or by hand.

•

Provide heavier load capabilities and better movement control.

•

Serving industries such as • • •

manufacturing, photonics, medical and telecommunications,

•

roller slides are versatile

•

Applications include •

09-Feb-15

• •

clean rooms, vacuum environments, SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com material handling and automation machinery.

23

www.rejinpaul.com Roller Slides - Construction •

•

•

Consisting of a stationary linear base and a moving carriage, roller slides work similarly to ball bearing slides, except that the bearings housed within the carriage are cylinder-shaped instead of ball shaped. The rollers crisscross each other at a 90 ° angle and move between the four semi-flat and parallel rods that surround the rollers. The rollers are between "V" grooved bearing races, one being on the top carriage and the other on the base.

Typically, carriages are constructed from aluminum and the rods and rollers are constructed from steel, while the end caps are 09-Feb-15 SSK,steel. AP / MECH,materials SVCET Get useful study from www.rejinpaul.com 24 constructed from stainless

•

Roller Slides •

•

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Although roller slides are not self-cl eaning, they are suitable for environments with low levels of airborne contaminants such as dirt and dust. Roller slides offers line contact versus point conta ct as with ball bearings, creating a broader contact surface due to the consistency of contact between the carriage and the base and resulting in less erosion.

09-Feb-15


25

Plain Bearings •

•

•

•

•

Plain bearings can run on hardened steel or stainless steel shafting (raceways), or can be run on soft steel or aluminum. The specific type of polymer/fluoro-polymer will determine what hardness is allowed. Less rigid than rolling-element bearings. Handles contamination seals/scrapers.

well

and

often

do

not

need

Generally handles a wider temperature range than rollingelement bearings

09-Feb-15 •

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Plain bearin s do not re uire oil or lubrication

26

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Dovetail Slides •

•

•

•

Typically constructed from cast iron, but can also be constructed from hard-coat aluminum or stainless steel Carriage has a v-shaped, or dovetail-shaped protruding channel which locks into the linear base's correspondingly shaped groove. Once the dovetail carriage is fitted into its base's channel , the carriage is locked into the channel's linear axis and allows free linear movement.

When a platform is attached to the carriage of a dovetail slide, a dovetail table is created, offering extended load carrying capabilities.

09-Feb-15


27

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Dovetail Slides •

•

Greater force is required to move the saddle than other linear slides, which results in slower acceleration rates Advantageous when it comes to • • • •

load capacity, affordability and durability. Capable of long travel more resistant to shock than other bearings mostly immune to chemical, dust and dirt contamination

•

Used in the manufacturing and laboratory science industries

•

Not ideal for high-precision applications.

09-Feb-15


28

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Compound Slides •

•

•

Slides can be constructed with two sections or multiple sections A slide with two sections can only extend approximately 3/4 of the total compressed slide length.

A compound slide typically has three sections • • •

•

fixed, floating intermediate member and the section attached to the equipment.

A compound slide can extend at least as far as the compressed slide length and typically a bit more.

09-Feb-15


29

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Rack Slides •

•

•

•

•

These can be friction bearing, ball bearing, or roller bearing. They are size d to fit into racks with moun ting flanges on the ends to mate to the mounting holes in racks. In some cases, one mounting flange is formed into the rack slide with an adapter bracket attached to the other end to accommodate different depths of the rack. The outer fixe d member is attached to the rack and the inner moving member is generally screwed to the side of the mounted equipment.

Rack slides are mounted typically equipment compoundand or generally 3-part slides allowing full extension of the include provision for sliding the inner member completely free to allow removal of the equipment from the rack. 09-Feb-15 SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com 30

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Ball Screw •

•

•

•

•

A ball screw is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw.

As well as being able to apply or withstand high thrust loads, they can do so with minimum internal friction. They are made to close tolerances and are therefore suitable for use in situations in which high precision is necessary. The ball assembly acts as the nut while the threaded shaft is the screw.

09-Feb-15


31

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Ball Screw •

•

Another form of linear actuator based on a rotating rod is the thread less ball screw.

Three

(or

more)

rolling-ring

bearings

are

arranged

symmetrically a housing surrounding a smooth (thread-less) actuator rod or in shaft. •

The bearings are set at an angle to the rod, and this angle determines the direction and rate of linear motion per revolution of the rod.

09-Feb-15


32

Part Programming

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•

Sequence of instructions

•

Task of preparing a program sheet from a drawing sheet

•

The machining data is as follows •

• •

09-Feb-15

Machining sequence classification of process, tool start up point, cutting depth, tool path Cutting conditions, spindle speed, feed rate, coolant Selection of cutting tools


33

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Steps involved in Part programming •

Determine the start up procedure

•

Select the tool and determine the tool offset

•

Set up the zero position for the work piece

•

Select the speed and rotation of the spindle

•

Set up the tool motions according to the profile required

•

•

Return the cutting tool to the reference point after completion of work End the programGet byuseful stopping the spindle and control SSK, AP / MECH,materials SVCET study from www.rejinpaul.com

09-Feb-15

34

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Types of part programming •

Manual Part Programming

•

Computer Aided Part Programming

09-Feb-15


35

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Manual Part Programming •

•

•

The programmer prepares the program manuscript in a standard format Manuscripts are typed in flexo writer, which is used to type program instructions

Once the program is typed, the punched tape is prepared on the flexo writer Complex shaped components require tedious calculations

•

•

This type of programming is carried out for simple machining parts produced on point-to-point machine tool.

09-Feb-15


36

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Computer Aided Part Programming •

•

The programmer communicates with this system through the system language, which is based on words Programming languages are • • • • • • •

09-Feb-15

APT (Automatically programmed Tools) ADAPT AUTOSPOT COMPAT-II 2CL ROMANCE SPLIT


37

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Computer Aided Part Programming •

The programmer has to do the following things • • •

09-Feb-15

Define the work part geometry Define the repetition work Specify the operation sequence


38

Machining Center • • •

Most important types of CNC machine tools ATC is used here Following operations are carried out – – – – –

• • • •

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Milling Drilling Reaming Boring Tapping

I ndexable tool magazine carries 16 to 100 tools

Machining centre has 2 or more tables named as pallets An automatic pallet centre is used and time will be reduced Classification – – –

09-Feb-15

Horizontal spindle machining centre Vertical spindle machining centre universal machining centre SSK, AP / MECH,materials SVCET Get useful study from www.rejinpaul.com

39

Machining Center •

Horizontal machining centre –

Single spindle machines

–

Automatic Tool Changer (ATC)

–

–

Bed type machine Axis •

–

•

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•

X = Table or Column Y = Spindle Head

•

Z = Saddle or column or head stock or spindle

Rotary indexing table

Vertical machining centre –

Single or multi spindle

–

ATC or Turret head

–

Axis

09-Feb-15

•

X = Table or Column

•

Y = Saddle or Colum or Ram

•

Z = Head Stock


40

Machining Center •

Universal machining centre –

Has single spindle

–

Spindle is capable of fitting horizontal to vertical

–

It has five axis of machine

–

Flexibility is more than other two type of machines

–

–

•

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Tool breakage detection is possible Automatics loading and unloading of work piece are possible

Turning centers –

–

09-Feb-15

Horizontal machines •

Chucking machines

•

Shaft machines

•

Universal machines

Vertical machines


41

www.rejinpaul.com Preparatory function – G Codes •

G 00 – rapid motion

•

G 01 – linear motion

•

G 02 – circular motion (clockwise)

•

G 03 – circular motion (anticlockwise)

•

G 20 – inches programming

•

G 21 – metric programming (mm)

•

G 28 – reference point

•

G 33 – thread cutting operation (constant lead screw)

•

G 37 – calling of sub-route

•

G 40 – cutter nose radius compensation (cancel)

•

•

G 41 – cutter compensation (in left) G 42 – cutter composition (in right)

09-Feb-15


42

www.rejinpaul.com Preparatory function – G Codes •

G 63 – tapping operation

•

G 70 – finishing cycle lathe

•

G 71 – rough cutting cycle lathe

•

G 78,79 – milling cycle

•

G 83 – drilling cycle G 90 – absolute dimensioning

•

G 91 – incremental dimensioning

•

G 92 – position preset

•

G 94 – feed rate in mm/min

•

G 95 – feed rate in mm/rev

•

•

•

G 98 – absolute datum G 99 – floating datum

09-Feb-15


43

Miscellaneous functions –www.rejinpaul.com M Codes •

M 00 – program stop

•

M 02 – end of program

•

M 03 – spindle start (clockwise)

•

M 04 – spindle start (anticlockwise)

•

M 05 – spindle stop

•

M 06 – tool change

•

M 07 – coolant ON (flood cooling)

•

M 08 – coolant ON (mist cooling)

•

M 09 – coolant OFF

•

M 10 – clamping

•

•

M 11 – unclamping M 30 – end of tape

09-Feb-15


44

Micromachiningwww.rejinpaul.com •

•

•

•

A technique for the fabrication of 3D structures on the micrometer scale Refers to super finishing, a metal working process for producing very fine surface finishes Types of micromachining process are –

Bulk micromachining

–

Surface micromachining

Mainly applied in MEMS –

Examples include •

Airbag sensor

•

Medical devices

•

Micro dies

•

09-Feb-15

molds


45

Micromachiningwww.rejinpaul.com •

Part to be machined should be made ready by doing the following preliminary processes 1.

Photolithography process

2.

Ethching

3.

1.

Wet etching

2.

Dry etching

LIGA (Lithographic, Galvanoforming, Abforming) 1.

Resist development

2.

X-ray radiation and masking

3.

Electroforming

4.

Resist removal

5.

Plastic molding

4.

Laser ablation process

5.

Mechanical microforming

09-Feb-15


46

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Bulk and surface micromachining

09-Feb-15


47

Me6402 Mt2 Notes Rejinpaul

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