Page 49 - MetalForming March 2013

Material received by a press shop can be accompanied by high- and low-quality valid data. Below are several examples. • Our problem steel coil came from one of five heat numbers we ran that day. This is very-poor-quality data. Heat number represents the minimum amount of data for tracing
a coil back to the mill. P
• Our problem coil came from heat number xxxxxxx1234.
This is medium-quality data. If received from an integrated steel mill, one heat of steel can include 300 to 350 tons of steel. Assuming 40,000-lb. master coils, the problem coil came from one of 15 to 18 coils. Each coil can receive different pro- cessing, resulting in different properties and other charac- teristics.
• Our problem coil was number yyyyyyy4321. This is very- high-quality data. This coil number can be tracked back through all processing stages to determine any problems or deviations from the process code.
• We threw away the coil tags. Absolutely useless data.
Another piece of available data is the mill cert that may accompany the coil. The cert represents low-quality data, pro- viding only the composition of the steel. These values can be quite constant for aluminum-killed draw-quality (AKDQ) or other low-carbon steels. The test sample is taken from the molten steel before being cast into slabs and rolled into coils. Two coils with identical certs can have different prop-
A NEW DAY IS DAWNING IN DOUBLE BLANK DETECTION
erties, and two coils with different certs can have identical properties. The processing of the steel into hot- or cold- rolled coils creates the final properties.
One piece of useful cert data can be carbon content. Val- ues of 0.04 to 0.06 percent are common with mild steel (AKDQP)a;gvealu1es 0.004 to 0.007 percent are expected for vac- uum-degassed interstitial-free ( VD-IF) steel, which has improved stretchability compared to AKDQ alloys.
All Hail the Mechanical Properties
The best-quality data are the mechanical properties of each incoming coil. Common properties recorded include yield and tensile strength, total elongation and hardness. Although this combination proves useful, a better set of properties would be yield-point elongation, yield strength, work-hardening exponent (n-value) and total elongation (calculated by a computer-controlled tensile-test machine).
In summary: Any opinion and any solution without data are simply guesses. Valid, high-quality data will help metal- formers reduce tryout time, speed problem solving and pro- duce consistent and robust stampings. MF
Stuart Keeler, Peter Ulintz and Patricia Miller will present PMA’s High Strength Steel seminar on April 9-10, 2013, in Brownsville, TX. Learn more and register to attend at www.pma.org/meetings.
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MetalForming/March 2013 47
The Science of Forming
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