sheet metal

1. Sheet Metal
Working
S D Lembhe

2. Sheet Metal
• Sheet metal is metal formed by an industrial process into thin, flat pieces. It is
one of the fundamental forms used in metalworking and it can be cut and bent
into a variety of shapes. Countless everyday objects are fabricated from sheet
metal.
• In most of the world, sheet metal thickness is consistently specified in
millimeters. In the US, the thickness of sheet metal is commonly specified by a
traditional, non-linear measure known as its gauge.
• The larger the gauge number, the thinner the metal. Commonly used steel sheet
metal ranges from 30 gauge to about 7 gauge.
• Sheet metal is used in automobile and truck (lorry) bodies, airplane fuselages and
wings, medical tables, roofs for buildings (architecture) and many other
applications. Sheet metal of iron and other materials with high
magnetic permeability, also known as laminated steel cores, has applications
in transformers and electric machines.
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3. Standard Sheet Metal Gauges
Standard sheet metal gauges
Gauge
US standard
for sheet and plate
iron and steel
decimal inch (mm)
Steel
inch (mm)
Galvanized steel
inch (mm)
Stainless steel
inch (mm)
Aluminium
inch (mm)
Zinc
inch (mm)
14 0.0781 (1.98) 0.0747 (1.90) 0.0785 (1.99) 0.0781 (1.98) 0.0641 (1.63) 0.036 (0.91)
15 0.0703 (1.79) 0.0673 (1.71) 0.0710 (1.80) 0.07 (1.8) 0.057 (1.4) 0.040 (1.0)
16 0.0625 (1.59) 0.0598 (1.52) 0.0635 (1.61) 0.0625 (1.59) 0.0508 (1.29) 0.045 (1.1)
17 0.0563 (1.43) 0.0538 (1.37) 0.0575 (1.46) 0.056 (1.4) 0.045 (1.1) 0.050 (1.3)
18 0.0500 (1.27) 0.0478 (1.21) 0.0516 (1.31) 0.0500 (1.27) 0.0403 (1.02) 0.055 (1.4)
19 0.0438 (1.11) 0.0418 (1.06) 0.0456 (1.16) 0.044 (1.1) 0.036 (0.91) 0.060 (1.5)
20 0.0375 (0.95) 0.0359 (0.91) 0.0396 (1.01) 0.0375 (0.95) 0.0320 (0.81) 0.070 (1.8)
21 0.0344 (0.87) 0.0329 (0.84) 0.0366 (0.93) 0.034 (0.86) 0.028 (0.71) 0.080 (2.0)
22 0.0313 (0.80) 0.0299 (0.76) 0.0336 (0.85) 0.031 (0.79) 0.025 (0.64) 0.090 (2.3)
23 0.0281 (0.71) 0.0269 (0.68) 0.0306 (0.78) 0.028 (0.71) 0.023 (0.58) 0.100 (2.5)
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4. Sheet Metal Working
Operations
• Cutting Operations
• Blanking
• Punching/ Piercing
• Notching
• Perforating
• Trimming
• Shaving
• Slitting
• Nibbling
• Forming Operations
• Bending
• Deep Drawing
• Lancing
• Bending
• Drawing
• Coining
• Embossing
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5. Blanking & Punching Video
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6. Sheet Metal Working Operations
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7. Sheet Metal Working Operations
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8. Classification of presses.
• Types of presses for sheet metal working can be classified by one or
a combination of characteristics,
• source of power,
• number of slides,
• type of frame and construction,
• type of drive, and
• intended applications.
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9. Classification on the basis of source of power.
• Manual Presses. These are either hand or foot operated through levers,
screws or gears. A common press of this type is the arbor press used for
assembly operations.
• Mechanical presses. These presses utilize flywheel energy which is
transferred to the work piece by gears, cranks, eccentrics, or levers.
• Hydraulic Presses. These presses provide working force through the
application of fluid pressure on a piston by means of pumps, valves,
intensifiers, and accumulators. These presses have better performance and
reliability than mechanical presses.
• Pneumatic Presses. These presses utilize air cylinders to exert the required
force. These are generally smaller in size and capacity than hydraulic or
mechanical presses, and therefore find use for light duty operations only.
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10. Mechanical versus Hydraulic Presses
Characteristic Mechanical Presses Hydraulic Presses
Force Depends upon slide position.
Dose not depend upon slide position.
Relatively constant.
Stroke length Short strokes Long strokes, even as much as 3 m.
Slide speed High. Highest at mid-stroke. Can be variable
Slow. Rapid advance and retraction.
Variable speeds uniform throughout
stroke.
Capacity About 50 MN (maximum) About 500 MN, or even more.
Control Full stroke generally required before reversal.
Adjustable, slide reversal possible from any
position.
Application
Operations requiring maximum pressure near
bottom of stroke. Cutting operations(blanking,
shearing, piercing, Forming and drawing to
depths of about 100 mm.
Operations requiring steady pressure
through-out stoke. Deep drawing. Drawing
irregular shaped parts. Straightening.
Operations requiring variable forces and
/or strokes.
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11. Classification on the basis of number of slides.
• Single Action Presses. A single action press has one reciprocation slide that
carries the tool for the metal forming operation. The press has a fixed bed. It is
the most widely used press for operations like blanking, coining, embossing, and
drawing.
• Double Action Presses. A double action press has two slides moving in the same
direction against a fixed bed. It is more suitable for drawing operations, especially
deep drawing, than single action press. For this reason, its two slides are
generally referred to as outer blank holder slide and the inner draw slide. The
blank holder slide is a hollow rectangle, while the inner slide is a solid rectangle
that reciprocates within the blank holder. The blank holder slide has a shorter
stroke and dwells at the bottom end of its stroke, before the punch mounted on
the inner slide touches the workpiece. In this way, practically the complete
capacity of the press is available for drawing operation.
• Triple Action Presses. A triple action press has three moving slides. Two slides
(the blank holder and the inner slide) move in the same direction as in a double –
action press and the third or lower slide moves upward through the fixed bed in a
direction opposite to that of the other two slides. This action allows reverse –
drawing, forming or bending operations against the inner slide while both upper
actions are dwelling.
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12. Classification on the basis of frame
and construction.
• Arch – Frame Presses. These presses have their frame in
the shape of an arch. These are not common.
• Gap Frame Presses. These presses have a C-shaped frame.
These are most versatile and common in use, as they
provide un – obstructed access to the dies from three
sides and their backs are usually open for the ejection of
stampings and / or scrap.
• Straight Side Presses. These presses are stronger since the
heavy loads can be taken in a vertical direction by the
massive side frame and there is little tendency for the
punch and die alignment to be affected by the strain. The
capacity of these presses is usually greater than 10 MN
• Horn Presses. These presses generally have a heavy shaft
projecting from the machine frame instead of the usual
bed. This press is used mainly on cylindrical parts
involving punching, riveting, embossing, and flanging
edges.
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13. Press Selection
Proper selection of a press is necessary for
successful and economical operation. Press is a
costly machine, and the return on investment
depends upon how well it performs the job. There
is no press that can provide maximum
productively and economy for all application so,
when a press is required to be used for several
widely varying jobs, compromise is generally made
between economy and productivity.
• Size.
• Bed and slide areas of the press.
• Shut height of press
• Throat Depth
• Force and Energy
• Press Speed.
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14. Simple blanking Die & Progressive Die
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15. Compound Die & Combination Die
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16. Dieset
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17. Deep Drawing
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18. Deep Drawing Video
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19. Metal Spinning Video
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20. Design of Simple
Blanking Die
Scrap Strip Layout
Design of Die Block
Design of Stripper
Design of Punch
Design of Punch Holder
Force Calculations
Press Selection
Centre of Pressure
Selection of Die Set
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21. Scrap Strip Layout
• Factors to be considered for the scrap strip layout
• Economy of material
• Direction of material grain
• Strip or coiled stock
• Direction of burr
• Press used
• Die cost
• Types of layout
• Single row single pass
• Single row double pass
• Double row double pass
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22. Scrap Strip Layout
a= t+0.015h
W= Width = calculate at actual
No of components
N=(1000-b)/s
MUF=(N*Area of blank)/(1000*W)
Material Thickness, mm b, mm
upto 0.8 mm 0.8
0.8 to 3.2 mm t
Over 3.2 mm 3.2
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23. Design of Die Block
• Types of Die Block
• Solid
• Sectional
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24. Design of Die Block
• Thickness of die block
• A=1.5 to 2.0 times the thickness of die block
• Land= 3 mm for stock thickness up to 3mm
• = t, for stock thickness above 3mm
• Angular clearance between ¼ to 20
• Fasteners and dowel pin
Perimeter, mm Die block thickness, mm
Upto 75 mm 20 mm
75 to 250 mm 25 mm
Above 250 mm 30 mm
Surface area of
die block
Dowel pins Socket Head Cap screws
No of Size No of Size
Up to 25 cm2 02 10 mm 02 M10
Above 25 cm2 02 12 mm 04 M12
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25. Types of strippers
• Fixed Stripper • Spring Loaded Stripper
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26. Design of Stripper
• Design of fixed stripper
• Overall Size of the stripper
• Thickness of the stripper
• Dimensions of stripper opening
• Dimensions of the strip feeding
channel
• Width of the channel
• Depth of the channel
• Provision of finger stop
• Check for buckling of punch and
Provide support if necessary
• Clamping of strippers
• Design of spring loaded stripper
• Stripping force calculations
• Design of springs for the stripping
force
• Design of guide for the strip.
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27. Types of Punches
Peened Head Punch
Square Head Punch
Peened Head Punch Headless Punch
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28. Design of Punch and Punch Holder
• Design of Punch
• Cross section of the Punch
• Apply Clearances
• Length of Punch
• Punch Mounting
• Design of Punch Holder
• Overall Dimensions of punch
holder
• Length width and Thickness
• Mounting of the Punch holder on
Upper shoe
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29. Press Selection
• Force calculations
Force = perimeter*thickness* shear stress
• Methods of Reducing Cutting Force
• Staggering of Punches
• Application of shear on Punches
• Selection of press
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30. Center of pressure
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31. Design of
Progressive Die
Scrap Strip Layout
Design of Die Block
Design of Stripper
Design of Punch
Design of Punch Holder
Force Calculations
Press Selection
Centre of Pressure
Selection of Die Set
Plan the sequence of operation
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32. Deep Drawn Components
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33. Deep Drawing Dies
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34. Design of Deep
Drawing Die
Calculation of Blank Size
Determine No of Draws
Design of Punches
Design of Dies
Force Calculations for each draw
Size of shell after each draw
Press Selection
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35. Calculations of Blank Size
• Area Method
• Volume Method
• Using old component
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36. BVDUCOEPune

37. BVDUCOEPune
Straining sheet metal around a straight axis to take a
permanent bend
Bending of sheet metal
Sheet Metal Bending

38. BVDUCOEPune
Metal below the neutral axis is compressed, while metal above the neutral axis
is stretched
Metal on neutral axis neither stretched nor compressed
Sheet Metal Bending
•The material is stressed beyond the yield strength but below
the ultimate tensile strength.
•The surface area of the material does not change much.,
why??
•Bending usually refers to deformation about one axis

39. BVDUCOEPune
Types of Sheet Metal Bending
• V-bending - performed with a V-shaped die
• Edge bending - performed with a wiping die

40. BVDUCOEPune
• For low production
• Performed on a brake press
• V-dies are simple and inexpensive
V-Bending

41. BVDUCOEPune
• For high production
• Pressure pad required
• Dies are more complicated and costly
Edge Bending

42. BVDUCOEPune
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

43. BVDUCOEPune
Bend Allowance Formula
where Ab = bend allowance;  = bend angle; R= bend radius; t =
stock thickness; and Kba is factor to estimate stretching
• If R < 2t, Kba = 0.33
• If R  2t, Kba = 0.50
)
t
K
R
(
A b a
b +
3 6 0
2
=
α
π

44. BVDUCOEPune
Springback
Increase in included angle of bent part relative to included angle of
forming tool after tool is removed
• Reason for spring-back:
• When bending pressure is removed, elastic energy remains in bent part,
causing it to recover partially toward its original shape

45. BVDUCOEPune
Springback in bending is seen as a decrease in bend angle and an increase in bend radius: (1) during bending,
the work is forced to take radius Rb and included angle b' of the bending tool, (2) after punch is
removed, the work springs back to radius R and angle ‘.
Spring back (SB)
 
SB= (α’-α’b)/α’b

46. BVDUCOEPune
Bending Force
Maximum bending force estimated as follows:
where F = bending force; TS = tensile strength of sheet metal; w = part width in
direction of bend axis; and t = stock thickness. For V- bending, Kbf = 1.33; for
edge bending, Kbf = 0.33; D is opening width of a V-die or wiping die
D
TSwt
K
F bf
2
