1. Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 16: Sheet-Metal Forming Processes and Equipment
Presentation slide for courses, classes, lectures et al.
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2. Chapter Outline Introduction Shearing
Sheet-metal Characteristics and Formability
Formability Tests for Sheet Metals
Bending Sheets, Plates, and Tubes
Miscellaneous Bending and Related Operations
Deep Drawing
Rubber Forming and Hydroforming
Spinning
Superplastic Forming
Specialized Forming Processes
Manufacturing of Metal Honeycomb Structures
Design Considerations in Sheet-metal Forming
Equipment for Sheetmetal Forming
Economics of Sheetforming Operations
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3. Introduction Products made of sheet metals are common
Pressworking or press forming is used for general sheet-forming operations, as they are performed on presses using a set of dies
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4. Introduction
A sheet-metal part produced in presses is called a stamping
Low-carbon steel has low cost and good strength and formability characteristics
Manufacturing processes involving sheet metal are performed at room temperature
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5. Introduction
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6. Shearing
Before a sheet-metal part is made, a blank is removed from a large sheet by shearing
The edges are not smooth and perpendicular to the plane of the sheet
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7. Shearing Processing parameters in shearing are
The shape of the punch and die
The speed of punching
Lubrication
The clearance, c, between the punch and the die
When clearance increases, the zone of deformation becomes larger and the sheared edge becomes rougher
Extent of the deformation zone depends on the punch speed
Height, shape, and size of the burr affect forming operations
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8. Shearing Punch Force Maximum punch force, F, can be estimated from
Friction between the punch and the workpiece can increase punch force
T = sheet thickness L = total length sheared UTS = ultimate tensile strength of the material
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9. Shearing EXAMPLE 16.1 Calculation of Punch Force
Estimate the force required for punching a 25-mm diameter hole through a 3.2-mm thick annealed titanium- alloy Ti-6Al-4V sheet at room temperature.
Solution
UTS for this alloy is 1000 MPa, thus
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10. Shearing: Shearing Operations
Punching is where the sheared slug is scrap
Blanking is where the slug is the part to be used and the rest is scrap
Die Cutting
Shearing operation consists of:
Perforating: punching holes in a sheet
Parting: shearing sheet into pieces
Notching: removing pieces from the edges
Lancing: leaving a tab without removing any material
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11. Shearing: Shearing Operations
Fine Blanking
Very smooth and square edges can be produced by fine blanking
Fine-blanking process can control small range of clearances and dimensional tolerances
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12. Shearing: Shearing Operations
Slitting
Shearing operations are through a pair of circular blades, follow either a straight line, a circular path, or a curved path
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13. Shearing: Tailor-welded Blanks
Laser-beam butt welding involves two or more pieces of sheet metal with different shapes and thicknesses
The strips are welded to obtain a locally thicker sheet and then coiled
Resulting in:
Reduction in scrap
Elimination of the need for subsequent spot welding
Better control of dimensions
Improved productivity
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14. Shearing: Tailor-welded Blanks
EXAMPLE 16.2
Tailor-welded Sheet Metal for Automotive Applications
Production of an outer side panel of a car body is by laser butt welding and stamping
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15. Shearing: Tailor-welded Blanks
EXAMPLE 16.2
Tailor-welded Sheet Metal for Automotive Applications
Some of the examples of laser butt-welded and stamped automotive-body components.
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16. Shearing: Characteristics and Type of Shearing Dies
Clearance
Clearance control determine quality of its sheared edges which influence formability of the sheared part
Appropriate clearance depends on:
Type of material and temper
Thickness and size of the blank
Proximity to the edges of other sheared edges
When sheared edge is rough it can be subjected to a process called shaving
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17. Shearing: Characteristics and Type of Shearing Dies
Punch and Die Shape
Punch force increases rapidly during shearing
Location of sheared regions can be controlled by beveling the punch and die surfaces
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18. Shearing: Characteristics and Type of Shearing Dies
Compound Dies
Operations on the same sheet may be performed in one stroke with a compound die
Limited to simple shapes due to:
Process is slow
Complex dies is more expensive
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19. Shearing: Characteristics and Type of Shearing Dies
Progressive Dies
For high product production rates
The part shown below is the small round piece that supports the plastic tip in spray cans
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20. Shearing: Characteristics and Type of Shearing Dies
Transfer Dies
Sheet metal undergoes different operations arranged along a straight line or a circular path
Tool and Die Materials
Tool and die materials for shearing are tool steels and carbides
Lubrication is needed for reducing tool and die wear, and improving edge quality
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21. Shearing: Miscellaneous Methods of Cutting Sheet Metal
Other methods of cutting sheets
Laser-beam cutting
Water-jet cutting
Cutting with a band saw
Friction sawing
Flame cutting
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22. Sheet-metal Characteristics and Formability
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23. Sheet-metal Characteristics and Formability
Elongation
A specimen subjected to tension undergoes uniform elongation
When the load exceeds the UTS, the specimen begins to neck
Yield-point Elongation
Yield-point elongation: having both upper and lower yield points
Lüder’s bands has elongated depressions on the surface of the sheet
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24. Sheet-metal Characteristics and Formability
Yield-point Elongation
Anisotropy
Obtained during the thermo-mechanical processing
2 types: crystallographic anisotropy and mechanical fibering
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25. Sheet-metal Characteristics and Formability
Grain Size
Affects mechanical properties and surface appearance
Smaller the grain size, stronger is the metal
Dent Resistance of Sheet Metals
Dents caused by dynamic forces from moving objects that hit the sheet metal
Dynamic yield stress, instead of static yield stress, should be the significant strength parameter
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26. Formability Tests for Sheet Metals
Sheet-metal formability is the ability of the sheet metal to undergo the desired shape change without failure
Sheet metals may undergo 2 basic modes of deformation: (1) stretching and (2) drawing
Cupping Tests
In the Erichsen test, the sheet specimen is clamped and round punch is forced into the sheet until a crack appears
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27. Formability Tests for Sheet Metals
Forming-limit Diagrams
Forming-limit diagrams is to determine the formability of sheet metals
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28. Formability Tests for Sheet Metals
Forming-limit Diagrams
To develop a forming-limit diagram, the major and minor engineering strains are obtained
Major axis of the ellipse represents the major direction and magnitude of stretching
Major strain is the engineering strain and is always positive
Minor strain can be positive or negative
Curves represent the boundaries between failure and safe zones
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29. Bending Sheets , Plates, and Tubes
Bending is a common industrial forming operation
Bending imparts stiffness to the part by increasing its moment of inertia
Outer fibers are in tension, while the inner in compression
Poisson effect cause the width to be smaller in the outer region and larger in the inner region
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30. Bending Sheets, Plates, and Tubes
Approximate bend allowance is
For ideal case, k = 0.5,
Minimum Bend Radius
Engineering strain during bending is
Minimum bend radius, R, is
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31. Bending Sheets, Plates, and Tubes
Minimum Bend Radius
Increase the bendability by increase their tensile reduction of area
Bendability also depends on the edge condition of the sheet
Improve resistance to edge cracking by removing the cold-worked regions
Cold rolling results in anisotropy by preferred orientation or mechanical fibering
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32. Bending Sheets, Plates, and Tubes
Springback
Plastic deformation is followed by elastic recovery when the load is removed, called springback
Springback can be calculated by
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33. Bending Sheets, Plates, and Tubes
Compensation for Springback
Springback is compensated for by overbending the part
One method is stretch bending where the part is subjected to tension while being bent
Bending Force
Excluding friction, the maximum bending force, P, is
For a V-die, it is modified to
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34. Bending Sheets, Plates, and Tubes
Bending Force
Examples of various bending operations
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35. Miscellaneous Bending and Related Operations
Sheet metal or plate can be bent easily with simple fixtures using a press
The machine uses long dies in a mechanical / hydraulic press suitable for small production runs
Die materials range from hardwood to carbides
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36. Miscellaneous Bending and Related Operations
Bending in a Four-slide Machine
Lateral movements are synchronized with vertical die movement to form the part into desired shapes
Roll Bending
Plates are bent using a set of rolls.
Curvatures can be obtained by adjusting the distance between the three rolls
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37. Miscellaneous Bending and Related Operations
Beading
Periphery of the sheet metal is bent into the cavity of a die
The bead imparts stiffness to the part by increasing the moment of inertia of that section
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38. Miscellaneous Bending and Related Operations
Flanging
In shrink flanging, the flange is subjected to compressive hoop stresses and cause the flange periphery to wrinkle
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39. Miscellaneous Bending and Related Operations
Roll Forming
Also called contour-roll forming or cold-roll forming
Used for forming continuous lengths of sheet metal and for large production runs
Dimensional tolerances, springback, tearing and buckling of the strip have to be considered
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