Page 47 - MetalForming August 2017

Fig. 3—Graph shows the forming limits of the corner and nose radii.
Fig. 4—Difference in final stretch capability of two corner ends from the same bumper.
stretch that crossed the forming limit. The following morning, the team reported its conclusions to the plant manager. When he learned about the problem with the driver’s-side bumper, he asked for verification. The team took the manager out to the die and made another hit, reproducing the results shown in Fig. 4. They then rotated the die in the press and stamped another bumper. The same weak end indicated a die problem, not a press problem. MF
The Science of Forming
80
60
40
20
0
300 400
Maximum allowable stretch
500 600
Actual peak strain of nose radius
Corner radius
No neck Necked
(MPa)
40 50 60 70 80 90 Yield Strength (ksi)
Driver
Passenger
Part Location
Forming limit
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MetalForming/August 2017 45
Percent Stretch
Stretch