Page 26 - MetalForming June 2010

Tooling Technology
Stuart Keeler (Keeler Technologies LLC) is best known worldwide for his discovery of forming limit diagrams, development of circle grid analysis and implementation of other press shop analysis tools. Stuart’s sheetmetal forming experience includes 24 years at National Steel Corporation and
12 years at The Budd Company Technical Center, enabling him to bring a very diverse background to this column and the many seminars he teaches for PMA. His most recent project is technical editor of the AHSS Application Guidelines—Version 4.1, which now is available for downloading free from www.worldautosteel.org. Keeler Technologies LLC
P.O. Box 283
Grosse Ile, MI 48138
Fax: 734/671-2271
E-mail: keeltech@comcast.net
Last month’s column focused on GIGO. Historically, GIGO meant Garbage In Garbage Out. Today, widespread application of computers has morphed GIGO into Garbage In Gospel Out. The lack of good data or the insertion of wrong data into virtu- al metalforming codes causes even the best codes to produce wrong answers. When the computer indicates the virtual forming process is well designed with an appropriate safety margin and then the physical part drastically fails, all virtual metalforming codes receive a bad name.
However, the code is not at fault because it designed the forming opera- tion to make a virtual part with the data the operator entered into the code. If the physical press shop uses material with properties, lubricant or other parameters different from the virtual press shop, why would one expect a successful outcome?
STUART KEELER
has some form of sheared edge. Exam- ples include cut blanks, trimmed stamp- ings, punched holes, cutouts, lances and notches. Look at your sheared edge. Nice and clean, no rollover, few very minor burrs, 40-percent burnish/60- percent break, very little shear damage. Why does that sheared edge tear at low strain levels when subjected to tension?
While one assumes that a normal- looking sheared edge has suffered little damage, data has proven differently. A classic test was performed by Bob Hilsen of Inland Steel (See graph). The tradi- tional 10-percent shear clearance pro- duced a hole expansion of 80 percent. Cleaning off any burrs and squaring the edge increased available hole expan- sion to about 140 percent. When a milled hole was tested, a hole expansion of 280 percent was achieved. If one assumes very little cold worked damage to the sheared edge, then any edge
THE SCIENCE OF FORMING Lack of Good Data Leads to Disaster
Unfortunately, most press shops do not have the capa- bility to utilize the tremendous benefits of virtual press shops. Therefore, most press shops do not have to worry about GIGO. Wrong thinking. Many routine proce- dures in a normal physical press shop are vulnerable to lack of good data or misunderstanding of basic sheetmetal processes. Wrong thinking leads to bad parts out.
Almost every sheetmetal stamping
Damage done by various hole-punching operations tested by the traditional hole expansion test. (Research by R.R. Hilson of Inland Steel and presented at Microalloying 75 in Washington, D.C.)
300
200
100
A = Milled
B = 10% Clearance burr removed
C = 10% Clearance D = 40% Clearance
30 Ksi YS
0
AB C D
Stuart Keeler’s next seminar is “Higher Strength Steels—Solving the Problems” scheduled for June 23 in Grand Rapids, MI. Check www.pma.com for this and other seminars.
24 METALFORMING / JUNE 2010
www.metalformingmagazine.com
Hole Expansion, %