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Sheetmetal Bending - PowerPoint PPT Presentation


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Sheetmetal Bending. Bending process Points: Sheet thickness (t) in range 1/64” £ t £ 1/4” If t > 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

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Presentation Transcript
slide1

Sheetmetal

Bending

slide2

Bending process

  • Points:
      • Sheet thickness (t) in range 1/64” £ t £ 1/4”
      • If t > 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
slide4

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
slide5

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

slide6

s

Elastic Recovery

e

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
slide7

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 < 2, Kba = 0.33

R/t ³ 2, Kba = 0.50

and Kba is a stretching factor.

slide8

Bending model – force ranges

Examples in text show that punch forces are in the thousands of pounds rather than hundreds of thousands!

slide10

Sheet metal bending

What have we learned?