Sheetmetal Bending ME 482 Manufacturing Systems Bending process

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 = Kbf TS w t 2/D where TS = tensile strength A = bend angle w = plate width t = plate thickness D = die opening dimension or cantilever length Kbf = bending factor, where for V-bending Kbf = 1. 33 ME 482 - Manufacturing Systems Edge bending Kbf = 0. 33

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 ME 482 - Manufacturing Systems s 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 + Kbat)/ 360 where if R/t < 2, Kba = 0. 33 R/t ³ 2, Kba = 0. 50 and Kba 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