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
ME 482 - Manufacturing Systems