Page 92 - MetalForming October 2017

The Science of Forming
By Stuart Keeler
Gaining More Data During Forming
Assume you are taking a long car trip. You fill up the gas tank, check the oil level, top off the washer fluid and antifreeze, etc. Your calcula- tions say you have enough fluids, and you are set to go. However, your car is different—it has no gauges to provide information on how the car is functioning during the trip. Would you take such a trip?
The same problem can occur during metalforming.
You are given the yield strength, tensile strength,
total elongation and thickness of the material. You
cut the sheet into blanks, feed directly from a coil or
create other shapes to place into the press, add lubri-
cant, set press speed and force, etc., and create the
part. Do you know what is happening during the
forming process? Cars have gauges to obtain ongoing
process information. Press shops offer the same
opportunity. Here are some possible problem sce-
narios and the process information for solving them. Fig. 1—Differences between production steel and reference steel (A)
Problem: Parts exit the press varying in shape relative reveal steel problems. to the print. Is the damage caused by the material or by the
forming process? This can be solved by forming five pieces of
production steel and then forming five parts from a reference
Time
B
Production Steel
Reference Steel
A
Production Steel
Time
Reference Steel
02468
Time – Hours
steel (Fig. 1). If the production steel has a high variability of forming severity, and the reference steel has a stable forming severity, the problem is with the production steel. If both the production steel and reference steel have similar patterns and degree of forming severity, the problem is the forming process.
Problem: The stamping has differing severity levels throughout the day (Fig. 2). The variation is the temperature of the parts; if part temperature consistently climbs at the same rate, a control system can be added. However, the production has a shutdown for lunch at 4 hours into the shift, and mid-shift reliefs at 2 and 6 hours. The timing and duration of shutdowns can change depending on mainte- nance, discussions, stocking blanks, etc.
Problem: After one week during summer, the high severity variation of the parts drops to a low number (Fig. 3). After two weeks the high severity returns. A study of the problem
Stuart Keeler (Keeler Technologies LLC) is known worldwide for his discovery of forming limit diagrams, development of circle-grid analysis and implementa- tion of other press-shop analysis tools. Keeler’s metal- forming experience includes 24 years at National Steel Corporation and 12 years at The Budd Compa- ny Technical Center, enabling him to bring a very diverse background to this column and to the semi- nars he teaches for PMA.
Keeler Technologies LLC
P.O. Box 283 | Grosse Ile, MI 48138 keeltech@comcast.net
Fig. 2—Changes in production shutdown time for breaks can change product status.
01234
Time – Weeks
90 MetalForming/October 2017
www.metalformingmagazine.com
Fig. 3—Changes of production operators can bring major changes in product severity.
Severity
Severity
Forming Severity Forming Severity
Forming Severity Forming Severity