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Sheet Metal Forming
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2. CO
Identify and select proper manufacturing process for a specific component.
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3. SHEET METAL WORKING Cutting Operations Bending Operations Drawing
Other Sheet Metal Forming Operations
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4. Sheet Metalworking Defined
Cutting and forming operations performed on relatively thin sheets of metal
Thickness of sheet metal = 0.4 mm (1/64in) to 6mm (1/4 in)
Thickness of plate stock > 6 mm
Operations usually performed as cold working
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5. Sheet and Plate Metal Products
Sheet and plate metal parts for consumer and industrial products such as
Automobiles and trucks
Airplanes
Railway cars and locomotives
Farm and construction equipment
Small and large appliances
Office furniture
Computers and office equipment
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6. Advantages of Sheet Metal Parts
High strength
Good dimensional accuracy
Good surface finish
Relatively low cost
Economical mass production for large quantities
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7. Sheet Metalworking Terminology
Punch‑and‑die - tooling to perform cutting, bending, and drawing
Stamping press - machine tool that performs most sheet metal operations
Stampings - sheet metal products made by press machine
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8. Basic Types of Sheet Metal Processes
Cutting
Shearing to separate large sheets
Blanking to cut part perimeters out of sheet metal
Punching/ Piercing to make holes in sheet metal
Bending
Straining sheet around a straight axis
Drawing
Forming of sheet into convex or concave shapes
Blanking and piercing/punching are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap
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9. Shearing, Blanking, and Punching
Three principal operations in press working that cut sheet metal:
Shearing
Blanking
Punching
Piercing
In blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap.
Punching is like when Mike Tyson hits you. Piercing is when he bites you on the ear. A slug (the material punched out) is produced in punching operations but not in piercing work
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10. Sheet Metal Cutting - Shearing
Shearing of sheet metal between two cutting edges: (1) just before the punch contacts work;
(2) punch begins to push into work, causing plastic deformation;
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11. Sheet Metal Cutting - Shearing
Shearing of sheet metal between two cutting edges: (3) punch compresses and penetrates into work causing a smooth cut surface;
(4) fracture is initiated at the opposing cutting edges which separates the sheet.
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12. Shearing
Sheet metal cutting operation along a straight line between two cutting edges
Typically used to cut large sheets
Shearing operation: (a) side view of the shearing operation; (b) front view of power shears equipped with inclined upper cutting blade.
Engagement of entire blade into cutting need higher forces. Therefore, inclined blade is used to reduce force and to improve cut- edge.
Engagement of entire blade into cutting need higher forces. Therefore, inclined blade is used to reduce force.
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13. Shearing
Shearing is a process for cutting sheet metal to size out of a larger stock such as roll stock.
Shears are used as the preliminary step in preparing stock for stamping processes, or smaller blanks for CNC presses
The shearing process produces a shear edge burr, which can be minimized to less than 10% of the material thickness.
The burr is a function of clearance between the punch and the die, and the sharpness of the punch and the die.
Burr: Metals particles produced during shearing operation
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14. Blanking and Punching
Blanking - sheet metal cutting to separate piece (called a blank) from surrounding stock
Punching - similar to blanking except cut piece is scrap, called a slug
(a) Blanking and (b) punching.
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15. Slug is cut and bur is minimum
Punching and Piercing ….
……..
Piercing tool
Punching tool
Bur
3. … This is not to say the punched material will not have a burr, but the pierced holes will have a significantly more pronounced bur
Punching
Piercing
Slug is cut and bur is minimum
No slug is cut, only bur
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16. Punching
Punching is a metal fabricating process that removes a scrap slug from the metal workpiece each time a punch enters the punching die. This process leaves a hole in the metal workpiece
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17. Punching is an operation of cutting holes into a sheet blank
Punching: operation
1. Punch, made of hardened steel, is forced through a work-piece.
2. The punch cuts the metal and separates it in the form of scrap
3. The hole size depends on the punch size
Characteristics:
Ability to produce economical holes in both strip and sheet metal during medium or high production processes.
The ability to produce holes of varying shapes - quickly
Punching is an operation of cutting holes into a sheet blank
The illustration that follows shows a few common punch and die configurations and the workpieces that would be formed by this combination. Multiple punches can be used together to produce a complete part with just one stroke of the press
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18. TiN coated tool steel punches
Punch Tools
TiN coated tool steel punches
To reduce punch wear
To increase punch life
To increase dimensional accuracy of holes
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19. Other shearing processes
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Close tolerances and low v

20. Angular Clearance Purpose: allows slug or blank to drop through die
Typical values: 0.25 to 1.5 on each side
If u give angle to the full depth of the die, the die size will increase whenever u sharp the die for adjusting the angle
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23. Types of Sheet Metal Bending
V‑bending - performed with a V‑shaped die
Edge bending - performed with a wiping die
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24. V-Bending For low production Performed on a brake press
V-dies are simple and inexpensive
2. A press brake, also known as a brake press or just brake
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25. Edge Bending For high production Pressure pad required
Dies are more complicated and costly
If u move the die in (1) towards right what is gonna happen -> Shearing will occur instead of bending
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26. Stretching during Bending
If bend radius is small relative to stock thickness, metal tends to stretch during bending
Important to estimate amount of stretching, so that final part length can be obtained as specified dimension
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27. Drawing
Sheet metal forming to make cup‑shaped, box‑shaped, or other complex‑curved, hollow‑shaped parts
Sheet metal blank is positioned over die cavity and then punch pushes metal into opening
Products: beverage cans, ammunition shells, automobile body panels
Also known as deep drawing (to distinguish it from wire and bar drawing)
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28. Drawing Difference between wire drawing & deep drawing?
(a) Drawing of cup‑shaped part: (1) before punch contacts work, (2) near end of stroke; (b) work-part: (1) starting blank, (2) drawn part.
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29. Mechanics of Drawing Fh: Holding force F: Punch force
Straightening the bent sheet, stretching
Bending at die and punch radius
Fh: Holding force
F: Punch force
Wall thickness variation: yes
Wall thinning maximum at bottom corner of cup (max: 25%)
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