me 482 - manufacturing systems sheetmetal bending sheetmetal bending

ME 482 - Manufacturing SystemsME 482 - Manufacturing Systems

Sheetmetal

Bending

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

• Machines are called presses

• Plastic deformation

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


Bending automation

Robots used to tend the press brake

Bending automation

Robots used to tend the press brake


Bending typesBending 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

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


Bending modelBending 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

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 angleA = bend angle


Bending model - springbackBending model - springback

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Elastic Recovery

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

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


Bending model – bend allowanceBending 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 A (R + Kbat)/ 360

where if R/t < 2, Kba = 0.33

R/t 2, Kba = 0.50

and Kba is a stretching factor.

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 A (R + Kbat)/ 360

where if R/t < 2, Kba = 0.33

R/t 2, Kba = 0.50

and Kba is a stretching factor.


Bending model – force rangesBending model – force ranges

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

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


Sheet metal bending video clipSheet metal bending video clip


Sheet metal bendingSheet metal bending

What have we learned?What have we learned?

me 482 - manufacturing systems sheetmetal bending sheetmetal bending

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