Page 45 - MetalForming June 2011

Press Solutions
Consider two identical stamping presses operating at the same average slide velocity—20 ft./min., for example. We’ll also assume one of the upper dies (A) has twice the mass (1000 lb.) of the other (B, 500 lb.), or A = 2B.
We can calculate the kinetic energy (KE) for each of the upper press slide tools:
KEB =1⁄2x500x202 =100,000
KEA =1⁄2x1000x202 =200,000
Kinetic energy increases linearly with mass; thus, when
mass doubles so does kinetic energy. Now let’s assume the upper die weights are identical—500 lb.—and both presses are identical, except that press B has a slide velocity at mate- rial impact twice that of press A. The upper-die kinetic ener- gy comparison:
KEB =1⁄2x500x202 =100,000
KEA =1⁄2x500x402 =400,000
Here, kinetic energy increases proportionally with the
square of its speed. When press speed doubles, kinetic ener- gy quadruples. Some of the kinetic energy from the press will be transferred and expended in the form of mechanical energy to deform the sheet into a stamping—a desirable result. However, some of the energy will be transformed
Don’t get caught behind the 8 ball
Have you been wanting extra copies of an article published in MetalForming for your own promotional efforts—trade shows, meetings, mailings, etc?
Reprints are cost effective and will produce a high- quality piece of literature for your particular needs.
We do all the work, and you’ll have your reprints in three weeks—all at a surprisingly low cost!
Call Sue Cubranich at 216-901-8800/scubranich@pma.org for full details.
into less-desirable energy states such as heat, dynamic deflections and vibration associated with impact force trans- ferred into the press frame. Stampers must understand and control the increased kinetic energy and impact vibrations associated with higher-speed stamping operations in order to prevent damage to the tooling and the press.
Depending on the magnitude of inertia forces and the rigidity of the machine design, the pitman will elongate, effectively reducing shut height. This shut-height reduction introduces additional stresses, including impacting the large end of the pitman on the crank journal and introducing additional frame deflections.
Material fracture during punching and cutting also can create higher snapthrough forces, and transfer additional kinetic impact energy into the frame structure in the form of vibrations. As press speeds increase, there is less time to dissipate these vibrations and they eventually can reach critical levels. This is where a stamper begins to experience nuisance problems such as nuts and bolts loosening, and catastrophic problems such as crankshaft and tie-rod breakage.
Clearly, increasing stamping efficiency involves far more than simply turning up the speed. MF
www.metalformingmagazine.com
MetalForming/June 2011 43
Tooling by Design