Ch4- SheetMetal

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Sheetmetal

Bending

ME 482 - Manufacturing Systems

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

ME 482 - Manufacturing Systems

Bending automation

Robots used to tend the press brake

ME 482 - Manufacturing Systems

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

ME 482 - Manufacturing Systems

Bending model

Bending force estimated from bending force equation for simply supported beam:

F = K bf

TS w t 2 /D where

TS = tensile strength w = plate width t = plate thickness

D = die opening dimension or cantilever length

K bf

= bending factor, where for

V-bending K bf

ME 482 - Manufacturing Systems

= 1.33

A = bend angle

Edge bending K bf

= 0.33

Bending model - springback

Springback is a measure of elastic recovery after plastic load s released

SB = (A’ – A b

’)/ A b

To compensate:

Overbending – increase punch angle and decrease punch radius

Bottoming – plastically deform with additional punch pressure

ME 482 - Manufacturing Systems

Elastic

Recovery e

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 + K ba t)/ 360 where if R/t < 2, K ba

= 0.33

R/t

2, K ba

= 0.50

and K ba is a stretching factor.

ME 482 - Manufacturing Systems

Bending model – force ranges

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

ME 482 - Manufacturing Systems

Sheet metal bending video clip

ME 482 - Manufacturing Systems

Sheet metal bending

What have we learned?

ME 482 - Manufacturing Systems

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