Page 45 - MetalForming August 2012

The Science of Forming
Fig. 3—Minimum corner radius for 200,000 Psi yield strength martensitic steel created by bending and roll forming. WorldAutoSteel - AHSS Application Guidelines 4.1
deformation. When a flat blank contacts a curved punch sur- face, the blank curvature instantaneously grows from Rc = 0 to Rc of the punch. This highly localized sharp bend creates tensile stress in the outer bend surface, adding extra stress and additional stretching at the bend. Once bent, the shape of the sheetmetal is locked and subjected to punch con- formity and friction.
Hydroforming can completely change the material’s defor- mation. At the start of forming (Fig. 2), the entire blank within the die opening begins to uniformly stretch without gradients. The blank continues to stretch until the die cavi- ty is completely filled. If the cavity is too deep, the excess stretch exceeds the FLD and a thickness neck/failure occurs.
Hydroforming is not restricted to water. Laboratories have formed domes of numerous shapes with a lubricated rubber disk of the correct durometer and volume to fill the cavity. Placed on a flat-bottom punch, the rubber disk is com- pressed by the die to change shape like a fluid. Other defor- mation modes simulating hydroforming include explosive forming and electromagnetic pulse waves. Need to form one 20-ft.-dia. hemisphere? Try using explosive forming with a female die made from concrete.
The instantaneous bending of the sheetmetal upon punch contact described above also occurs in traditional bending operations. In contrast, the rollforming process allows the gradual shaping of the bend with unrestricted edge motion as the workpiece material moves through a series of roll sta- tions. Fig. 3 shows the improvement in minimum corner radius for 200,000-PSI yield strength martensitic steel formed by rollforming, compared to traditional bending. Under- standing the mechanics of forming often allows production of more difficult stampings with less forming severity. MF
On August 21-22, Stuart Keeler and Peter Ulintz will pres- ent a comprehensive High Strength Steel seminar at the Hol- iday Inn Detroit Metro Airport. Complete information can be found on www.pma.org.
22nd
Roll Formed
Bent
www.metalformingmagazine.com
MetalForming/August 2012 43

Sheet metal, Tube, Section Handling Forming Finished products, Parts, Assemblies Separation Flexible sheet metal working Machine elements Tube/Section working Composites Joining, Welding Surface treatment Tools, Dies Safety at work Controlling, Regulating, Measuring, Inspection Data capture / processing Quality control
Factory and warehouse equipment Environment protection, Recycling Research and development CAD/CAM systems

For a Sustainable Future

© Mack Brooks Exhibitions 2012