Sheetmetal

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Sheetmetal Bending
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• Bending process
• Points
• Sheet thickness (t) in range 1/64 t
  1/4
• If t gt 1/4 then stock called plate
• Usually cold-worked, but warm worked if brittle
  material or thicker stock
• Tooling is punch and die
• Products are called stampings
• Machines are called presses
• Plastic deformation

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Bending automationRobots used to tend the press
brake
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Bending types

• V-bending
• Large range of angles
• Dies expensive
• Low production operations
• Edge bending
• Cantilever bending
• Pressure pad to hold part from slipping
• For angles 90
• More expensive

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Bending model
Bending force estimated from bending force
equation for simply supported beam F Kbf TS w
t2/D where TS tensile strength w plate
width t plate thickness D die opening
dimension or cantilever length Kbf bending
factor, where for V-bending Kbf
1.33 Edge bending Kbf 0.33
A bend angle
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Bending model - springback

• Springback is a measure of elastic recovery after
  plastic load released
• SB (A Ab)/ Ab
• To compensate
• Overbending increase punch angle and decrease
  punch radius
• Bottoming plastically deform with additional
  punch pressure

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Bending model bend allowance
If R/t is small (R is punch radius), the sheet
metal will stretch some, changing length of stock
required to complete final shape. In effect, the
neutral axis displaces from the center of the
stock. The bend allowance (BA) accounts for this
from the equation BA 2 p A (R Kbat)/
360 where if R/t lt 2, Kba 0.33 R/t ³ 2,
Kba 0.50 and Kba is a stretching factor.
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Bending model force ranges
Examples in text show that punch forces are in
the thousands of pounds rather than hundreds of
thousands!
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Sheet metal bending video clip
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Sheet metal bending
What have we learned?