SHEET METAL DESIGN
Contents 1 2 3 4
Introduction Metals used in Sheet Metal Working Gauges Sheet Metal Forming Processes 4.1 Piercing 4.2 Blanking 4.3 Fine Blanking 4.4 Punching 4.5 Trimming 4.6 Nibbling 4.7 Notching 4.8 Drawing 4.9 Spinning 4.10 4.10 Bend Bendin ing g 4.11 4.11 Em Embo boss ssin ing g 4.12 4.12 Coin Coinin ing g 5 Comparison to other forming processe esses s 6 Die Manufacturing 7 Pro Progr gres essi sive ve die with ith scr scrap stri strip p and stam stampi pin ng 8 Die operations and types 9 Design calculations 10 For Bl Blanking an and Pi Piercing 11 Draw Die Designing 12 Bending Design 13 Punching Design 14 Die Co Construction 15 Workshop Practice 16 Safe Safetty Gu Guide ide for for Sh Shee eett Met Metal al Wor Worker kers
Introduction 1.
Shee Sh eett meta metall is is simp simply ly met metal al for forme med d into into thin thin and and flat flat pie piece ces. s. It It is is one one of
the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. 2.
Thic Thickn knes esses ses can can var vary y signi signifi fica cant ntly ly,, alth althou ough gh ext extre reme mely ly thi thin n thic thickn knes esse ses s
are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate. 3.
Shee Sh eett meta metall is is avai availa labl ble e as flat flat pie piece ces s or as a coil coiled ed str strip ip.. The The coil coils s are are
formed by running a continuous sheet of metal through a roll slitter.
4.
The thickness of the sheet metal is called its gauge. The gauge of sheet
metal ranges from 30 gauge to about 8 gauge. The higher the gauge, the thinner the metal is. 5.
Ther There e are are man many y dif diffe fere rent nt met metal als s that that can can be be mad made e into into she sheet et met metal al,, such such
as: Aluminium, brass, copper, steel, tin, nickel and titanium. Sheet metal has applications in car bodies, airplane wings, medical tables, roofs for building and many other things. 6. Sheet Sheet metal metal worki working ng involv involves es manufa manufactu cturin ring g articl articles es from from sheet sheet metal metal or thin thin shee sheets ts,, whic which h may may be of blac black k iron iron,, galv galvan aniz ized ed iron iron,, copp copper er or stainless steel. 7. The The arti articl cles es made made of shee sheett meta metals ls are are ligh lighte terr in weig weight ht,, and and are are less less expens expensive ive.. With With proper properly ly design designed ed shapes shapes and struct structur ures, es, sheet sheet metal metal arti articl cles es are are repl replac acin ing g cast castin ings gs and and forg forgin ings gs in seve severa rall engi engine neer erin ing g applications. 8. Besid Besides es the the arti articl cles es such such as funn funnel els, s, hopp hopper ers, s, cans cans,, pipe pipes, s, elbo elbows ws and and boxes, sheet metal products are used for the purpose of covering machines and other structures in the form of safety guards or facade of attractive shapes. 9. Since sheet sheet metal working working involve involves s forming shapes shapes from from flat metal sheets, sheets, the ‘development and drawing of shape of the article in actual size’ on the sheet metal is the most important and prime operation of the work. The
knowledge of geometry, mensuration and properties of metals is therefore most essential. Nearly all patterns of articles come from the development of the surfaces of few geometrical models like cylinder, prism, cone and pyramid. A properly drawn pattern on the sheet metal saves time and money because because if the pattern pattern (or development development of surface of the article) is wrong, then the blank cut from the sheet would just result into wastage of material, time and labour besides delay in production. 10. The sheet metal metal working working also involves involves knowledge knowledge of various various operation operations s of joining metals like mechanical jointing or soldering and brazing brazing etc.
Metals used in Sheet Metal Working 1. A larg large e vari variet ety y of metal metals s in the form form of sheets sheets and plates plates used in shee sheett meta metall work workin ing g incl includ ude e blac black k iron iron,, galv galvan aniz ized ed iron iron,, copp copper er,, br bras ass, s, tin, tin, aluminum, lead and zinc. 2. The metal metal sheets sheets are are design designate ated d either in terms terms of gauge gauge numbers numbers (such as Imp Imperi erial al or Legal Legal Standa Standard rd Wire Wire gauge) gauge) or thickn thickness ess in millim millimetr etres es (along with width and length) given in standard metal reference tables. 3. The thickne thickness ss of sheets sheets vary vary invers inversely ely as their their gauge number number,, higher higher the gauge gauge num number ber,, smalle smallerr the thickn thickness ess and and vice-v vice-vers ersa. a. For exampl example, e, for gauge no. 20, thickness is 0.914 mm, for gauge number 10, the equivalent sheet thickness is 3.251 mm, for gauge no. 3, it is 6.401 mm, etc.
4. Cold rolled sheets (annealed) are usually available in thickness 0.8 mm to 3.25 mm, width 1000 mm and length 2000 mm.
5. Black Iron Sheet or uncoated sheet is the cheapest material used for sheet meta metall work work.. Sinc Since e thes these e shee sheets ts carr carry y no pr prot otec ectio tion n coat coatin ings gs on thei theirr surfaces, these are likely to corrode quickly. These are, therefore, used for marking those articles, which are later enameled or painted before use. Arti Articl cles es like like pans pans,, tank tanks, s, cabi cabine nett work works, s, almi almira rahs hs and and furn furnit itur ure’ e’s s are are commonly made from black iron sheets.
6. Galvanized Iron Sheets or G.I. sheets are soft iron sheets carrying zinc coating on their surface to resist corrosion and to add to the aesthetic of the the shee sheet. t. Zinc Zinc coat coatin ing g in vary varyin ing g thic thickn knes ess s is give given n acco accord rdin ing g to the the
severity of corrosive atmosphere to which the sheet metal product is likely to be subjected. Special care is, however, required in welding or brazing these sheets to avoid excessive damaging of the coating. G.I. sheets are used for making articles such as trunks, storage tanks for food grains, buckets and other containers for water storage, pans, roofing sheets etc.
7. Copper Sheets find application in making radiators of automobile engines, heating appliances, equipment for chemical plants etc. These sheets are costlier than aforesaid black iron sheets and G.I. sheets but these have better resistance to corrosion. These can be easily worked upon, being highly ductile and soft. Brass Sheets are used for making variety of articles through cold working processes like pressing, drawing and spinning. These are often used for making kitchenware’s and utensils. 8. Tin Sheet eets are the tin coated iron sheets and hence have silvery appearance appearance.. These offer good resistance against rusting rusting and atmospher atmospheric ic corrosion. Articles made from tin sheets find application in food industry for making containers for edible oils and ghee, cans, and dairy equipment etc.
Gauge The sheet metal gauge (sometimes spelled "gage") indicates indicates the standard thickness of sheet metal for a specific material. As the gauge number increases, the material thickness decreases. Sheet metal thickness gauges for steel are based on a weight of 41.82 pounds per square foot per inch of thickness. This is known as the Manufacturers' Standard Gage for Sheet Steel. For other materials, such as aluminium and brass, the thicknesses will be different. Thus, a 10 gauge steel sheet which has a thickness of 0.1345 inches will weigh 41.82*0.1345 = 5.625 pounds per square foot. Examples: 16 ga CRS is 2.5 pounds per square foot. For 18 ga CRS the weight is 2.0 pounds per square foot and for 20 ga CRS the weight is 1.5 pounds per square foot.
SHEET METAL FORMING
Standard sheet metal gauges Gaug Steel
Galvanized
Stainless
Aluminum
Zinc
e 3
0.2391
steel -
steel -
-
0.006
4
(6.0731) 0.2242
-
-
-
0.008
5
(5.6947) 0.2092
-
-
-
0.010
6
(5.3137) 0.1943
-
-
-
0.012
7
(4.9352) 0.1793
-
0.1875
0.1443
0.014
8
(4.5542) 0.1644
0.1681
0.1719
0.1285
0.016
9
(4.1758) 0.1495
0.1532
0.1563
0.1144
0.018
10
(3.7973) 0.1345
0.1382
0.1406
0.1019
0.020
11
(3.4163) 0.1196
0.1233
0.1250
0.0907
0.024
12
(3.0378) 0.1046
0.1084
0.1094
0.0808
0.028
13
(2.6568) 0.0897
0.0934
0.094
0.072
0.032
14
(2.2784) 0.0747
0.0785
0.0781
0.0641
0.036
15
(1.8974) 0.0673
0.0710
0.07
0.057
0.040
16
(1.7094) 0.0598
0.0635
0.0625
0.0508
0.045
17
(1.5189) 0.0538
0.0575
0.056
0.045
0.050
18
(1.3665) 0.0478
0.0516
0.0500
0.0403
0.055
19
(1.2141) 0.0418
0.0456
0.044
0.036
0.060
20
(1.0617) 0.0359
0.0396
0.0375
0.0320
0.070
21
(0.9119) 0.0329
0.0366
0.034
0.028
0.080
22
(0.8357) 0.0299
0.0336
0.031
0.025
0.090
23
(0.7595) 0.0269
0.0306
0.028
0.023
0.100
24
(0.6833) 0.0239
0.0276
0.025
0.02
0.125
25
(0.6071) 0.0209
0.0247
0.022
0.018
-
26
(0.5309) 0.0179
0.0217
0.019
0.017
-
27
(0.4547) 0.0164
0.0202
0.017
0.014
-
28
(0.4166) 0.0149
0.0187
0.016
0.0126
-
29
(0.3785) 0.0135
0.0172
0.014
0.0113
-
30
(0.3429) 0.0120
0.0157
0.013
0.0100
-
31
(0.3048) 0.0105
0.0142
0.011
0.0089
-
32
(0.3200) 0.0097
-
-
-
-
33
(0.2464) 0.0090
-
-
-
-
34
(0.2286) 0.0082
-
-
-
-
35
(0.2083) 0.0075
-
-
-
-
36
(0.1905) 0.0067
-
-
-
-
37
(0.1702) 0.0064
-
-
-
-
38
(0.1626) 0.0060
-
-
-
-
(0.1524)
PROCESSES PIERCING
1.
Pier Pierci cing ng is is a she shear arin ing g proc proces ess s wher where e a pun punch ch and and d die ie are are used used to to crea create te
a hole in sheet metal or a plate.
2.
The process and machinery are usually usually the same as that used in
blanking, except that the piece being punched out is scrap in the piercing process. 3.
Ther There e are are man many y spec specia iali lize zed d type types s of pier pierci cing ng:: lanc lancin ing, g, per perfo fora rati ting ng,,
notching, nibbling, shaving, cutoff, and dinking. 4.
The The amo amoun untt of of cle clear aran ance ce betw betwee een n a pu punc nch h and and die die for for pier pierci cing ng is
governed by the thickness and strength of the work-piece material being pierced. 5.
The The punc punchh-di die e clea cleara ranc nce e dete determ rmin ines es the the loa load d or pr press essur ure e expe experi rien ence ced d at
the cutting edge of the tool, commonly known as point pressure. 6.
Exce Ex cessi ssive ve poi point nt pre pressu ssure re can can lead lead to acc accel eler erat ated ed wea wearr and and ulti ultima mate tely ly
failure. 7.
Burr Burr heig height ht is is typi typical cally ly use used d as as an inde index x to to measu measure re tool tool wea wear, r, beca because use it
is easy to measure during production
BLANKING 1.
A blan blanki king ng die die pro produ duce ces s a fla flatt pie piece ce of of mate materi rial al by by cu cutt ttin ing g the the des desir ired ed
shape in one operation. 2.
The finis inish h par part is is ref refer errred to as a blan blank. k.
3.
Gene Genera rall lly y a bla blank nkin ing g die die may may onl only y cu cutt the the out outsid side e cont contou ourr of of a par part, t, ofte often n
used for parts with no internal features.
Three benefits to die blanking are:
1.
Accuracy : A properly sharpened die, with the correct amount of
clearance between the punch and die, will produce a part that holds close dimensional tolerances in relationship to the parts edges.
2.
Appearance: Since the part is blanked in one operation, the finish edges
of the part produces a uniform appearance as opposed to varying degrees of burnishing from multiple die cutting operations.
3.
Flatness: Due to the even compression of the blanking process, the end
result is a flat part that may retain a specific level of flatness for additional manufacturing operations.
FINE BLANKING
1.
Fine blanking is a fully automated precision metalworking process.
2.
It is a form of precision metal stamping in which extremely tight
tolerances can be held, and usually additional machining steps can be avoided post-production.
3.
Materials that can be fine blanked include carbon steels, alloy and
stainless steels , as well as soft non ferrous alloys like aluminum, brass or copper.
Typical fine blanking press cross section
Fine blanking presses are similar to other metal stamping presses, but they have a few critical additional parts. A typical compound fine blanking press includes a hardened die punch (male), the hardened blanking die (female), and a guide plate of similar shape/size to the blanking die. The guide plate is the
first applied to the material, impinging the material with a sharp protrusion or stinger around the perimeter of the die opening. Next a counter pressure is
applied opposite the punch, and finally the die punch forces the material through the die opening. Since the guide plate holds the material so tightly, and since the counter pressure is applied, the material is cut in a manner more like extrusion than typical punching. Mechanical properties of the cut c ut benefit similarly with a hardened layer at the cut edge from the cold working of the part. Because the material is so tightly held and controlled in this setup, part flatness remains very true, distortion is nearly eliminated, and edge burr is minimal. Clearances between the die and punch are generally around 1% of the cut material thickness, which typically varies between .5-13mm. Currently parts as thick as 19mm can be cut using fine blanking. Tolerances between ±.0003"-.002" are possible based on material thickness & tensile strength, and part layout. With standard compound fine blanking processes, multiple parts can often be completed in a single operation. Parts can be pierced, pierced, partially pierced, pierced, offset (up to 75•), embossed, embossed, or coined, coined, often in a single operation. Some combinations may require progressive fine blanking operations, in which multiple operations are performed at the same pressing station however.
Advantages •
excellent dimensional control, accuracy, and repeatability through a
production run. •
excellent part flatness is retained.
•
straight, superior finished edges to other metal stamping processes.
•
smaller holes possible relative to thickness of material[6].
•
little need to machine details.
•
multiple features can be added simultaneously in 1 operation [7].
•
more economical for large production runs than traditional operations
when additional machining cost and time are factored in (between 1000-20000 parts minimum, depending on secondary machining operations).
Disadvantages
•
slightly higher tooling cost when compared to traditional punching
operations. •
slightly slower than traditional punching operations.
Broaching Broaching is the process of removing material through the use of multiple cutting teeth, with each tooth cutting behind the other. A broaching die is often used to remove material from parts that are too thick for shaving. s having.
Bulging A bulging die expands the closed end of tube through the use of two types of bulging dies. Similar to the way a chefs hat bulges out at the top from the cylindrical band around the chefs head. Bulging fluid dies: Uses water or oil as a vehicle to expand the part. Bulging rubber dies: Uses a rubber pad or block under pressure to move the wall of a workpiece.
PUNCHING 1.
Punching in metal fabrication is the process of using a machine to press a
shape through a sheet of metal and into a die to create the desired shape in the metal. 2.
This is most commonly done by use of a turret , a computer numerical
controlled machine that houses tools and their corresponding dies in a revolving indexed turret. These machines use hydraulic, hydraulic, pneumatic, pneumatic, or electrical power to press the shape with enough force to shear the metal. 3.
The The shap shape e is is for forme med d by by pre pressi ssing ng the the mat mater eria iall aga again inst st a die die with with a hug huge e
force. The shear forces generated between the material and die separate the material into the desired shape. 4.
The The desi desire red d shap shape e is not not obta obtain ined ed,, howe howeve ver, r, as as burr burred ed edg edges es and and rou rough gh
surfaces are formed. These edges and surfaces must be further processed until the desired shape is achieved. 5.
The The pun punch ch forc force e req requi uire red d to to pun punch ch a pie piece ce of shee sheett met metal al can can be be
estimated from the following equation:
F = 0.7tL(UTS)[citation needed ]
Where t is the sheet metal thickness, L is the total length sheared (perimeter of shape), and UTS is the ultimate tensile strength of the material. 6.
Die Die and and pun punch ch sha shape pes s affe affect ct the the punc punchi hing ng pr proc oces ess. s. The The pu punc nch h for force ce
increases during the process as the entire thickness of the material is sheared at once.
7.
A beveled punch helps in the shearing of thicker materials. Beveling
reduces the force at the beginning of the stroke. However, beveling a punch will disort the punched shape because of lateral forces that develop. 8.
Comp Compou ound nd dies dies allo allow w mul multi tipl ple e shap shapin ing g to to occ occur ur.. Usin Using g com compo poun und d die dies s
will generally slow down the process and are typically more expensive than other dies. 9.
Prog Progre ressi ssive ve dies dies may may be used used in in hig high h pro produ duct ctio ion n ope opera rati tion ons. s. Dif Diffe fere rent nt
punching operations and dies are used at different stages of the operation on the same machine. 10.
Other Other pro process cesses es such such as stampi stamping, ng, blan blankin king, g, perfo perforat rating ing,, partin parting, g,
drawing, notching, lancing and bending operations are all related to punching.
11. A punch press is a type of machine of machine press used for forming and cutting material.
12. The punch press can be small and manually manually operated and hold one simple Die set, or be very large, CNC operated, and hold a much larger and complex die set.
13. A Die set consists of a set of (male (male)) punches and (female (female)) dies which, when pressed together, may form a hole in a workpiece or may deform the workpiece in some desired manner. 14.
The punc punches hes and and dies dies are are remo removab vable le with with the the punch punch being being temp tempor orari arily ly
attached to the end of a ram during the punching process. The ram moves up and down in a vertically linear motion.
15. Commonly machines are large metal framed equipment having two types of machine frames. A ‘C’ type frame or a 'portal' type frame.
16. The ‘C’ type commonly has the hydraulic hydraulic ram at the top foremost foremost part to enable the punching process to be carried out, whereas the portal frame is much akin to a complete circle with the ram being centred within the frame to stop frame deflection or distortion. 17.
All punc punch h press press mach machine ines s have have a table table or or bed bed with with bru brushe shes s or rolle rollers rs
mounted in the tables to allow the sheet metal workpiece to traverse with low friction. Brushes are commonly used in production environments where minimal scratching to the workpiece is required, such as brushed aluminium or high polished materials. 18.
The main main bed bed of of most most mach machine ines s is call called ed the the 'Y' 'Y' Axis Axis with with the the 'X' Axis Axis
being at right angles to that and allowed to traverse under CNC control. Dependent on the size of the machine, the beds and the sheet metal workpiece weight, then the motors required to move these axis tables can vary in size and power. Older styles of machines used DC motors to move, however with advances in technology, today's machine mostly use AC brush less motors for drives. 19.
The proc process ess of of opera operatio tion n begins begins with with the the CNC CNC cont control roller ler comm command anding ing the the
drives to move a particular axis to a desired position.
20. Once in position, the control initiates the punching sequence and pushes the ram to Bottom Dead Centre and returns it to Top Dead Centre. The Origins of BDC and TDC go back to older machines where this was a pitman type press with a Pneumatic or Hydraulic operated clutch system.
21. On today's machines BDC/TDC does not actually exist but is commonly used as a term to derive the top and bottom of a stroke of the ram. The Punch enters the Sheet metal, and pushes it through the die, obtaining the required shape of the punch and die set. This will form a slug of metal that is collected underneath the die and ejected to a scrap container. The whole punching process on modern machines is extremely fast compared to older pitman style machines and thus gives rise to increased production volumes.
22.
The sequen sequence ce take takes s appro approxim ximate ately ly 0.5 0.5 mill millii secon seconds ds to to comp complet lete e
( variant from machine to machine and manufacturer)and signals to the control the next movement command allowed after the ram has reached the top of its stroke. 23.
As a meta metall formi forming ng proc process, ess, the pun punch ch pres press s is used used for the highest highest
volume production. Cycle times are often measured in sheet yield as a percentage of waste to parts required ratios per sheet processed. 24.
As most most progr programm amming ing is is done done by skil skilled led CAD/ CAD/CAM CAM operat operators ors part parts s within within
the sheet workpiece are commonly nested. Machine setters are mostly used to set up tooling and programming but thereafter once the machine is running an operator of low skill can oversee its continued operation. Often one operator will monitor several punch presses simultaneously making this one of the lowest cost metal manufacturing processes. 25.
Punch Punch presse presses s are usuall usually y refer referred red to by by their their tonn tonnage age.. In a produc productio tion n
environment a 20 ton press is mostly the prevalent machine used today. The tonnage needed to cut and form the material is well known so sizing tooling for a specific job is a fairly straightforward task. 26.
Most Most punch punch presses presses toda today y are are hydrau hydraulic licall ally y power powered, ed, how howeve everr there there
remains a legacy of older machines which are mechanically driven rams, meaning the power to the ram is provided by a heavy, constantly-rotating flywheel. The flywheel drives the ram using a Pitman arm. In the 19th century, the flywheels were powered by leather drive belts attached to line shafting, which in turn ran to a steam plant. In the modern workplace, the flywheel is powered by a large electric motor. 27.
Mechan Mechanica icall punch punch pres presses ses fall fall into into two two dist distinc inctt types types,, depend depending ing on the the
type of clutch or braking system with which they are equipped. Generally older presses are "full revolution" presses that require a full revolution of the flywheel for them to come to a stop. This is because the braking mechanism depends on a set of raised keys or "dogs" to fall into matching slots to stop the flywheel. A full revolution clutch can only bring the flywheel to a stop at the same location- top dead center. Newer N ewer presses are often "part revolution" presses equipped with braking systems identical to the brakes on commercial trucks. When air is applied, a band-type brake expands and allows the flywheel
to revolve. When the stopping mechanism is applied the air is bled, causing caus ing the clutch or braking system to close, stopping the flywheel in any part of its rotation. 28.
Hydrau Hyd raulic lic punc punch h presse presses, s, which which powe powerr the the ram ram with with a hydr hydraul aulic ic cylin cylinder der
rather than a flywheel, and are either valve controlled or valve and feedback controlled. Valve controlled machines usually allow a one stroke operation allowing the ram to stroke up and down when commanded. 29.
Contr Controll olled ed feedb feedback ack systems systems allow allow the the ram ram to to be propor proportio tional nally ly
controlled to within fixed points as commanded. This allows greater control over the stroke of the ram, and increases punching rates as the ram no longer has to complete the traditional full stroke up and down but can operate within a very short window of stroke. s troke.
Trimming & Shaving: 1.
Trimming dies cut away excess or unwanted unwanted irregular features from from a
part, they are usually the last Shaving Shaving::
2.
The shaving operation removes removes a small amount of material from the
edges of the part to improve the edges finish or part accuracy operation performed. 3.
The The shav shavin ing g proc proces ess s is a fini finish sh ope opera rati tion on wher where e a sma small ll amo amoun untt of of meta metall
is sheared away from an already blanked part. Its main purpose is to obtain better dimensional accuracy, but secondary purposes include squaring the edge and smoothing the edge. 4.
Blan Blanke ked d par parts ts can can be shav shaved ed to an accu accura racy cy of up to 0.02 0.025 5 mm mm (0. (0.00 001 1 in) in)
Nibbling: Nibbling: The nibbling process cuts a contour by producing producing a series of overlapping slits or notches.
This allows for for complex shapes to be formed in sheet metal up to 6 mm (0.25 in) thick using simple tools. The process is often often used on parts that do not not have quantities that can justify a dedicated blanking die. The edge smoothness is is determined by the shape of the cutting die and the amount the cuts overlap; naturally the more the cuts overlap the cleaner the edge.
Notching The notching process removes material material from the edge of the workpiece. workpiece. A notching machine is shown in the below fig.
The machine shown above will create 90 90 degree notches in sheet metal. This makes it possible to create profiles that can then be bent into three dimensional shapes (like boxes). Lay the work on the table. The guides can be used to help orient the part as desired. Pulling on the actuating lever will cut a notch in the work.
Drawing: 1.
The The draw drawin ing g oper operat atio ion n is very very simil similar ar to to the the for formi ming ng ope opera rati tion on exc excep eptt
that the drawing operation undergoes severe plastic deformation and the material of the part extends around the sides.
2.
A met metal al cu cup p wit with h a deta detail iled ed feat featur ure e at at the the bott bottom om is an an exa examp mple le of the the
difference between formed and drawn. The bottom of the cup was formed while the sides were drawn.
Spinning 1.
Spinning is used to make axis-symmetric parts by applying a work piece
to a rotating mandrel with the help of rollers or rigid tools. 2.
Spin Sp inni ning ng is is used used to make make roc rocke kett moto motorr casi casing ngs, s, miss missil ile e nos nose e cone cones, s, and and
satellite dishes, for example.
3.
Metal spinning, or spin forming, is a metal working process by which a
disc or tube of metal of metal is rotated at high speed and formed into an axially symmetric part using tools.
4.
Metal spinning is often performed by hand to produce decorative items,
or using machine tools, such as CNC lathe, lathe, when tight tolerances are required. Metal may be formed into a die to shape the outside diameter or onto a mandrel to size the inner diameter.
5.
Metal spinning ranges from an artisan's specialty to the most
advantageous way to form round metal parts for commercial applications. Artisans use the process to produce architectural detail, specialty lighting, decorative household goods and urns urns.. Commercial applications include rocket nose cones, cones, cookware cookware,, gas cylinders, cylinders, brass instrument bells, and public waste receptacles.
6.
Virtually any ductile metal may be formed, from aluminum or stainless
steel, to high-strength, high-temperature alloys. The diameter and depth of formed parts are limited only by the size of the equipment available. Metal spinning by hand 1.
Metal Spinning is a process by which circles of metal of metal are shaped over
mandrels (also called forms) while mounted on a spinning lathe by the application of levered force with various tools. 2.
It is perf perfor orme med d rot rotat atin ing g at at hig high h spee speeds ds on a man manua uall spi spinn nnin ing g lat lathe he..
3.
The The flat flat met metal al disc disc is spu spun n agai agains nstt the the man mandr drel el and and a serie series s of sweep sweepin ing g
motions then evenly transforms the disc around the mandrel into the desired shape. It takes a very skilled workman to correctly shape and finish a hand spun piece. Safety considerations
When spinning metal by hand, care must be taken to not touch the spinning metal with one's hands until the metal edge has been "turned over" (rolled to a rounded edge so that the bare edge of the metal stock is protected). This is mentioned specifically because wood turners are accustomed to touching the spinning wood in the lathes (once it reaches relative smoothness) to monitor their progress. This practice is very dangerous in metal spinning. Lexan/Clear plastic lathe shields and guards are recommended.
Metal spinning tools The basic hand metal spinning tool is called a Spoon Spoon , though many other tools tools (be they commercially produced, ad hoc, hoc, or improvised) improvised) can be used to effect varied results. Spinning tools can be made of hardened steel for using with aluminium or solid brass for spinning stainless steel/mild steel.
Mandrels
The mandrel/chuck can be made made from wood, steel alloys, or synthetic materials. The choice of material is dictated by the hardness of the material to be spun and by how many times the tool is expected to be used.
Cut-off tools
Cutting of the metal is done by hand held cutters, often foot long hollow bars with tool steel shaped/sharpened files attached. This is dangerous and should only be done by skilled tradesmen. In CNC applications, traditional carbide or tool steel cut-off tools are used.[1]
Rotating tools
Some metal spinning tools are allowed to spin on bearings during the forming process. This reduces friction and heating of the tool, extending tool life and
improving surface finish. Rotating tools may also be coated with thin film of ceramic to prolong tool life. Rotating tools are commonly used during CNC metal spinning operations. Commercially, rollers mounted on the end of levers are generally used to form the material down to the mandrel in both hand spinning and CNC metal spinning. Rollers vary in diameter and thickness depending the intended use. The wider the roller the smoother smoother the surface of the spinning; the thinner thinner rollers can be used to form smaller radii.[1]
Lathes
Woodworking lathes are often used, although a wilson lathe is the most common manual spinning lathe for spinning s pinning metal by hand. The mandrel having been formed from wood on the lathe or steel chuck machined on a CNC lathe previous to mounting on the metal stock. stock. All stock sizing is done prior to the spinning.
BENDING Bending is a common technique to process sheet metal. metal. It is usually done by hand on a box and pan brake, brake , or industrially on a brake press or machine brake.. Typical products that are made like this are boxes such as electrical brake enclosures,, rectangular ductwork enclosures ductwork,, and some firearm parts such as the receiver of the AKM AK-47 variant.
Press Brake Usually Bending has to overcome both tensile stresses as well as compressive stresses. When Bending is done, the residual stresses make it re bend or spring back towards its original position, so we have to overbend the sheet metal keeping in mind the residual stresses.
The bending
operation is the act of
bending blanks at a predetermined angle. An example would be an "L" bracket which is a straight piece of metal bent at a 90° angle. The main difference between a forming operation and a bending operation is the bending operation creates a straight line bend (such as a corner in a box) as where a form operation may create a curved bend (such as the bottom of a drinks can).
EMBOSSING 1.
Embossing is the process of creating a three-dimensional image or
design in paper and other ductile materials. 2.
It is typically accomplished with a combination of heat of heat and pressure on
the paper.
3.
This This is is ach achie ieve ved d by by usin using g a meta metall die die (fem (femal ale) e) usua usuall lly y mad made e of of bra brass ss and and
a counter die (male) that fit together and actually squeeze the fibers of the substrate. 4.
This pressure and a combination of heat heat actually "irons" while raising the
level of the image higher than the substrate to make it smooth. In printing this is accomplished on a letterpress. letterpress. The most common machines are the Kluge Letterpress and the Heidelberg Letterpress. Letterpress. 5.
The The term term "imp "impre ressi ssing ng"" enab enable les s one one to dist distin ingu guis ish h an imag image e lowe lowere red d into into
the surface of a material, in distinction to an image raised out of the surface of a material. 6.
The embossing process can be applied to textiles as non-wovens non-wovens to get
better finished products as sanitary napkins, diapers, tissue paper and others. 7.
In printing it is used as an accent process and can be used in conjunction
with ink called colour register embossing or with no ink called blind embossing. embossing. 8.
It also can be used with foil stamping which when embossed with foil is
known as combination stamping or combo stamping. stamping. 9.
All All of thes these e proc proces esses ses use use a die die and and coun counte terr die. die. Mos Mostt typ types es of of pap paper er and and
boards can be embossed and there are no restrictions on size. 10.
Embossi Emb ossing ng invo involve lves s a separa separate te stag stage e in the the produ producti ction on proce process, ss, afte afterr any any
varnishing and laminating. This process costs as much as printing.
Notary use: A notary public frequently uses embossing to mark legal papers, either in the form of an adhesive seal, or using a clamp-like embossing device used to certify (a signature on a document, contract, etc.) or cause to become certified through a notary public or bill. Postage stamps: Embossing has been used regularly on postage stamps.
Notable early examples include some of the earliest stamps of Italy , Natal , and Switzerland , as well as the early high values of Britain. Modern stamps still sometimes use embossing as a design element. Rubber stamp embossing / Heat embossing: Rubber stamp embossing is
another form of embossing popular in scrap booking and card making. A rubber stamp is used to apply adhesive (often a slow-drying, sticky ink called pigment ink) to paper in a desired pattern. Embossing powder is dusted onto the paper and then blown away, so that it adheres only to the stamped surface. The powder is then subjected to heat, which causes it to melt and cover the stamped area. When the heat is removed, the liquified powder fuses into a palpable smooth raised surface in the shape of the stamped pattern. Embossing powders are available in transparent, translucent, opaque, metallic, and glitter colors for a variety of artistic effects. 11.
A varia variatio tion n on heat heat embos embossin sing g stamp stamped ed imag images es is is tripl triple e embossi embossing. ng. An
area of paper is covered with pigment ink and embossing powder sprinkled all over it and heated until molten. This is repeated so that there are a minimum of 3 layers of heated powder. While this triple layer of powder is still hot, a rubber stamp can be pressed into it to leave an indented design. Embossing also refers to an image processing technique which the color at a given location of the filtered image corresponds to rate of color change at that location in the original image. Applying an embossing filter to an image often results in an image resembling a paper or metal embossing of the original image, hence the name.
COINING
1.
Coining is similar to forming with the main difference being that a coining
die may form completely different features on either face of the blank, these features being transferred from the face of the punch or die respectively. 2.
The The coin coinin ing g die die and and p pun unch ch flo flow w the the meta metall by squee squeezi zing ng the the bla blank nk wit withi hin na
confined area, instead of bending the blank. For example: an Olympic medal that was formed from a coining die may have a flat surface on the back and a raised feature on the front. If the medal was formed (or embossed), the surface on the back would be the reverse image of the front.
Compound operations 1.
Compound dies perform multiple operations on the part. The compound
operation is the act of implementing more than one operation during the press cycle. 2.
Comp Compou ound nd die die:: A typ type e of die die tha thatt has has the the die die blo block ck (ma (matr trix ix)) moun mounte ted d on on
a punch plate with perforators in the upper die with the inner punch mounted in the lower 3.
set. set. An inve invert rted ed type type of of blan blanki king ng die die tha thatt pun punch ches es upw upwar ards, ds, leav leavin ing g the the
part sitting on the lower punch (after being shed from the upper matrix on the press return stroke) instead of blanking the part through. 4.
A comp compou ound nd die die all allow ows s the the cutt cuttin ing g of int inter erna nall and and exte extern rnal al par partt feat featur ures es
on a single press stroke.
Comparison to other forming techniques 1.
Othe Otherr met metho hods ds of form formin ing g rou round nd meta metall par parts ts incl includ ude e hyd hydro rofo form rmin ing, g,
stamping and forging or casting. 2.
Hydro-forming and stamping generally have a higher fixed cost, but a
lower variable cost than metal spinning. 3.
Forging or casting have a comparable fixed cost, but generally a higher
variable cost. 4.
As mac machi hine nery ry for for com comme merc rcial ial appl applic icat atio ions ns has has imp impro rove ved, d, par parts ts are are bein being g
spun with thicker materials in excess of 1" thick steel.
5.
Conv Conven enti tion onal al spinn spinnin ing g also also waste wastes s a cons consid ider erab ably ly smal smalle lerr amo amoun untt of of
material than other methods.
Advantages These are several benefits of spinning and shear forming. forming. Several operations can be performed in one set-up. •
Work pieces may have re-entrant profiles and the profile in relation to
the center line virtually unrestricted. •
Forming parameters and part geometry can be altered quickly, at less
cost than traditional metal forming techniques. •
•
Tooling and production production costs are also comparatively low. Spin forming is easily automated and an effective production method for
prototypes as well as high production runs.
Die (manufacturing) A die is a specialized tool used in manufacturing industries to cut, shape and form a wide variety of products and components. Like molds and
templates, dies are generally customized and uniquely matched to the product they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology.
Die forming
Progressive die with scrap strip and stampings 1.
Forming dies are typically made by tool and die makers and put into
production after mounting into a press.
2.
The die is a metal block that is used for forming forming materials like sheet
metal and plastic. For the vacuum forming of plastic sheet only a single form is used, typically to form transparent plastic containers (called blister
packs) for merchandise.
3.
Vacuum forming is considered a simple molding thermoforming
process but uses the same principles as die forming.
4.
For the forming of sheet metal, such as automobile body parts, two
parts may be used, one, called the punch, performs the stretching, bending, and/or blanking operation, while another part, called the die block, securely clamps the workpiece and provides similar, stretching, bending, and/or blanking operation. 5.
The The work workpi piec ece e may may pas pass s thro throug ugh h seve severa rall stag stages es usin using g diff differ eren entt tool tools s or
operations to obtain the final form. 6.
In the the case case of of an auto automo moti tive ve com compo pone nent nt ther there e wil willl usua usuall lly y be be a she shear arin ing g
operation after the main forming is done and then additional crimping or rolling operations to ensure that all sharp edges are hidden and to add rigidity to the panel.
Die components •
Die block
•
Punch plate
•
Blank punch
•
Pierce punch
•
Stripper plate
•
Pilot
•
Dowel Pin
•
Back gage
•
Finger stop
Die operations and types Die operations are often named after the specific type of die that performs the operation. For example a bending operation is performed by a bending die. Operations are not limited to one specific die as some dies may incorporate multiple operation types.
DESIGN CALCULATIONS For Blanking and Piercing Clear Cl earanc ances es :
Clearances are one of the main factors controlling a shearing process. The clearance per side is given by C=0.0032. t . τ Where t= thickness and τ= material shear stress, MPa Clearance as percentage of stock thickness Material
Round
Other contours
Soft aluminum<1 mm
2
3
Soft aluminum>1mm
3
5
Hard aluminum
4 to 6
5 to 8
Soft copper alloys
2
3
Hard copper alloys
4
5 to 6
Low carbon steel
2
3
Hard steel
3
5
Silicon steel
3
4 to 5
Stainless steel
4 to 6
5 to 8
Angular Clearance Angular Clearance
Angular clearance or draft in a shearing operation depends on the material, thickness and shape of the stock used. Its value ranges from 0.25 to 2 deg per side.
Stripper Force:
As the punching is completed the stock tends to grip the punch as the punch moves upward which makes the use of a stripper necessary to separate the punch from the job. The force required for the same same is called stripper force
F(s) =K. L. t Where F(s) = stripping force, kN L
= perimeter of cut, mm
t
= material thickness
K
=st =stripping co constan stantt =.0103 for low carbon carbon steels with t<1.5mm t<1.5mm with cut at the edge. =.0145 for same material but for other cuts =.0207 for low carbon steels, t>1.5mm =.0241 for harder materials
Punching Force:
As the name indicates it is the force of the punch needed to cut the blank or pierce a sheet
F(p) = L . t . τ F(p)= punching force, N τ
=Sh =S hear str strength MPa
For holes with diameter d
Shear Force on the punch:
Sometimes a component is required to be sheared on a smaller capacity punching then a shear is ground ground or cut on the face of the die or that of of punch to distribute the cutting action over a period of time . This is done to relieve the shear of the punch or the die face so that it contacts the stock for some s ome time period rather than instantaneously. The relation used for calculating maximum shear stress is
F(sh)=L.t. τ (p/t1)
Where, p= penetration of punch in fractions t1=shear on punch or die, mm
Draw Die Design
Corner Radius on Punch Punch::
Customery taken as 4t to 10 t and ideally taken as equal to punch radius.
Draw Radius:
Larger radius causes the metal to be released early by the blank holder and thus lead to edge wrinkling. Too small a radius causes the thinning and tearing of the side walls of the cups, generally, Draw radius=4.t normal =6 to 8 t when the blank holder is used.
Clearences:
An allowance in the range of 7 to 20% of the blank thickness is provided, depending on the cup material and cup dimensions. Clearences in drawing in terms of blank thickness Blank thickness
First draw
Second draw
Sizing draw
Up to 0.40
1.07 to 1.09
1.08 to 1.10
1.04 to 1.05
0.41 to 1.25
1.08 to 1.10
1.09 to 1.12
1.05 to 1.06
1.30 to 3.0
1.10 to 1.12
1.12 to 1.14
1.07 to 1.09
Above 3.01
1.12 to 1.14
1.15 to 1.20
1.08 to 1.11
(mm)
Blank Size:
The calculation could be based on volume, surface surface area or by layout. Some useful relations in calculating the blank diameter for cylindrical shell for relatively thin materials are given by: D=√(d2+4dh)
when d ≥20r
D=√(d2+4dh-0.5r)
when 15r ≤d≤20r
D=√(d2+4dh-r)
when 10r≤d≤15r
D=√((d-2r)2+4d(h-r)+2πr(d-0.7r))
Where r = corner radius of the punch, punch, mm
when d<10r
h = height of the shell, mm d = outer diameter of the shell, mm D = blank diameter, mm
An additional trim allowance could be provided of 3 mm per 25mm of cup diameters.
Drawing Force:
Drawing force for cylindrical shapes can be given by the below empirical equation
P= πdts[(D/d)-C] Where P= drawing force, N t= thickness of the blank material, mm s= yield strength of the metal, MPa C= constant to cover friction and bending, its value is 0.6 to 0.7. For other shapes the above formula gives an approximation which can be used as a guide.
Blank Holding Force:
This force required depends on the wrinkling wrinkling tendency of the cup which is very difficult to determine and hence it is obtained more by trial and error. The maximum limit is generally one-third of the drawing force.
Ironing force,
In ironing the objective is to reduce the wall thickness of the cup, and hence no blank is required because the punch is fitted closely inside the cup. Neglecting
the friction and shape of the die, the ironing force can be estimated by the following equation.
F= πd1t1savloge(t0/t1) Where F = ironing force, N d1 = mean diameter of the shell after ironing t1 = thickness of shell after ironing t0= thickness of the shell before ironing sav = average of tensile strength before and after ironing.
Percent Reduction:
There is a limit upto which a material material can be strained. The amount of straining straining or drawability is represented by the percentage reduction which is expressed in terms of the diameter of the blank and the shell. It is convenient to use outer diameter as the cup is normally specified by outer diameter. The percentage reduction P is given by P=100[1-(d/D)] However, practically it is limited upto 40. Height to
No. of
Percent reduction
dia ratio
draws
First draw
Second draw
Third draw
Up to 0.75
1
40
0.75 to 1.50
2
40
25
1.50 to 3.00
3
40
25
15
3.00 to 4.50
4
40
25
15
Maximum reductions possible in single draw
Fourth draw
10
Materials
Percent reduction
Almunium alloys
45
Copper
45
Brass, Bronze
50
Low carbon steel
45
Stainless steel
50
Zinc
40
Air Vent:
An air vent is normally provided on the punch to reduce the possibility of formation of vaccum in the cups when it is stripped from the punch. The size of the air vent depends on the punch diameter
Punch diameter (mm)
Air vent diameter (mm)
Up to 50
4.5
50 to 100
6.0
100 to 200
7.5
Over 200
10.0
Drawing Speed :
The speed with which the punch moves moves through the blank during during drawing is termed as the drawing speed. This is very important parameter in drawing because the higher speeds are sometimes detrimental. Particularly harder and less ductile materials are likely to be excessively excess ively thinned out due to excessive drawing speeds. Material
Drawing speed (m/s)
Aluminium
0.90
Brass
1.0
Copper
0.75
Steel
0.28
Zinc
0.75
Bending: Bending refers to the operation of deforming a flat sheet around a straight axis where the neutral plane lies. The nomenclature normally used in bending is shown in fig. In a bent specimen, since neutral axis remains constant, it is the required length. Beyond the bend lines, the material is not affected. Hence to calculate the length required, it is necessary to find out the bend allowance which is the arc length of the neutral axis between the bend lines.
Bend allowance, B=α(R+Kt) Where α = bend angle, radians R = inside radius of the bend, mm K = location of the neutral axis from bottom surface = 0.33 when R< 2 t = 0.50 when R>2 t t = sheet thickness, mm
Area under tension Bend allowance
Area under compression
Bend Allowance Overview Bend allowance is a term which describes how much material is needed between two panels to accommodate a given bend. Bend allowance, while being oftentimes tricky to determine for all cases, is fairly easy to predict and calculate for many standardcircumstances. Determining bend allowance is commonly referred to as “Bend Development” or simply “Development”.
Often bend allowances are calculated for a sheet metal part and used to make costly tooling or production parts that require a lot of labor to produce. A scrap tool or production run can be very costly, much more so that a test piece. So if you are ever not sure of your developed flat length, make a test piece (laser, turret or sheared piece) to confirm your development. One of the easiest ways to make a test piece is to shear a piece to an exact length, and then form it using the exact process that will be used to create the part. After the part is formed, the part is measured and compared to the expected lengths and the bend allowance is adjusted as needed. Often times, when hard tools are produced, laser cutblanks are used to validate the forming tools and part development before the cutting tools are completed. No rule will apply to every case. While most bend developments can be predicted with ease and will develop correctly, there is no perfectly scientific method for predicting bend allowance due to the many factors like tooling conditions, actual vs. planned thickness, forming method and the given part tolerance. Many companies will develop their bend allowances based on standard formulas, standard forming practices and historical trial and error.
General Principles The Neutral Axis does not change. When developing a flat blank length, there is a length of the part that does not change. This length is called the neutral axis. Material on the the inside of the neutral axis will compress, while material on the outside will stretch. Based on the material thickness, form radius and forming methods, the ratio of compression to tension in the part will change. A part that is bent over a very sharp radius, when compared to the thickness, will stretch more on the outside, which means that the neutral axis will lie closer to the inside of the bend. A part that is gradually bent will have less outside stretch, which means that the neutral axis will lie closer to the center ce nter of the part.
Compression/Tension Ratio Depends Mostly On Geometry. K-factor – Effectively 50%T Max / .25%T Min Where the neutral axis is situated in a bend is commonly called the “K-Factor” as it is signified as “K” in the development formulas. Since the inside compression can not exceed the outside tension, the k-factor can never exceed .50 in practical use. This means that the neutral axis cannot migrate past the midpoint of the material (i.e. towards the outside). A reasonable assumption is that the k-factor cannot be less than.25.
The neutral axis migrates based on the the compression to tension relationship of the given
bend. 3. Different Bend Types & K-Factors
Wrapped Hem (.29 k factor)
Machine Bend with Set (.33 k factor)
Machine Bend With No Set (.38 k-factor)
Bend Allowance Overview V-Bend Or Brake Tool (.42 k-factor)
Rotary Benders (.43 k-factor)
Gradual Bends / Large Radii (.50 k-factor) Bend Allowance Overview
4. Related Formulas Radian Formula When a developed length is calculated in radians, the equation is extremely simplified because the radian is the actual arc length, so no additional “translation” into angles is needed as in the “standard” formula below. In fact, the “standard” formula is the radian formula plus a “built in” angle conversion from radian measure to (base 360) degrees, shown in the “Common Formula”.
Common Formula Since is more common to develop a part based on degrees instead of radians, the bend allowance formula commonly incorporates the degrees to radians conversion. Recalling that 360 Degrees = 2ðRadians, then 1 Degree = 2ðRadians / 360 To convert the radian formula formula to work with degrees, degrees, we make the substitution 2ð/360
5. Special Cases Single Hit Z-Bend When a z-bend is hit in one hit, the middle panel will stretch more than expected. This is because the middle panel is trapped between two v-forms. A typical example might be on a .312 deep zee bend with .060 material, which might elongate .010”.
Wrapped hems Wrapped hem developments should be treated with caution. While they will generally develop with a .29 k-factor, they are at minimum made with a two hit process and
