Evolution of Die Wear and Sheared Edge Parameters in Trimming of DP980 Steel

• Research Team at Oakland University
Saeid Nasheralahkami
Weitian Zhou
Scott Dawson
Daniel Kowalsky
Elizabeth Lekarczyk
Nan Wang
Sergey Golovashchenko

• Research  Team at  Ford

Lloyd Mason
Constantin Chiriac
Darryl Young
Raj Sohmshetty

• Research Team at US Steel

Brandon Hance
Ming Shi

• Research Team at AK Steel

Matt Folkner
Kavesary Raghavan
Yu-Wei Wang

• Research Team at PNNL

Guang Cheng
Kyoo Sil Choi
Xiaohua Hu
Xin Sun

• Sponsors: Ford, DOE VTO, FCA, NSF

• Introduction
• Traditional Trends in Trimming and Punching
• Mechanism of Fracture in Trimming of DP980
• Sheared Edge Stretchability for DP980 vs. DP600
• Die Wear Trend for Trimming of DP980
• Effect of Die Wear on Sheared Edge Stretchability
• Conclusions

Effect of Cutting Clearance on DP500 Edge

Mechanism of Fracture in Trimming

Equipment Utilized During Experimentation

Mechanism of Fracture in Shearing of DP980

Evolution of Burrs on Trimmed Edge - DP980

• The die wear test was conducted with 10% clearance
• After 35,000 cuts, the tool had some “wear”
• Experiments with various clearances were performed on new tool and 35k/10% tool

Typically, more wear is observed from the upper cutting tool due to excessive abrasion on the sheared edge of the blank during shearing and return motions.

Multiple publications on punch wear for punching round holes.

Excellent correlation of local burrs on the trimmed sample with the local chippings sites on the lower trimming tool

• Hole Expansion
Test (ISO 16630)

• Tensile Test of
Samples with One
Sheared Edge

• Side-Bending Test

No Visible Sources of Fracture
Cracks Forming in the Central Area
Cracks are Visible in Multiple Locations
Throughout the Thickness

No Visible Sources of Fracture
Cracks Forming in the Central Area
Cracks are Visible Throughout the Thickness
Including Burr Side and Burnish Side

No Visible Sources of Fracture

Hairline Cracks Seen in Burr Zone
Macro Cracks Propagating from the Burr Zone

The Burr affected zone (broken burr and burr formation) is 30%mof the gauge length.

If the localized necking coincides with the burr affected zone, the sample fails similarly to the high clearance samples (>20%), which have the entire length affected by the burr.

• DP980 shows lower tendency to form burrs in trimming due to breaking them off at the end of the trimming process;

• Chipping of the lower die prevails as a die wear mechanism for D2 inserts in trimming of DP980; and

• Avoiding burr formation helps to maintain sheared edge stretchability of DP980 throughout the life of the tool.

• Among reviewed methods to measure sheared edge stretchability, in-plane side bending of the strip with the sheared edge seems to have high potential for industrial applications.

1. Chintamani, J. and Sriram, S., "Sheared Edge Characterization of Steel Products used for Closure Panel Applications," SAE Technical Paper 2006-01-1589, 2006, doi:10.4271/2006-01-1589.

2. Konieczny, A. and Henderson, T., "On Formability Limitations in Stamping Involving Sheared Edge Stretching," SAE Technical Paper 2007-01-0340, 2007, doi:10.4271/2007-01-0340.

3. Coryell, J.J. “Edge Fracture in Mixed Microstructure Steels,” GDIS 2016

4. Zhou, D., Du, C., Hsiung, G., and Schmid, K. “Lessons Learned from Ultra High-Strength Steel Blanking,” GDIS 2015.

5. Golovashchenko, S.F. and Ilinich A.M., Analysis of trimming processes for stamped body panels, GDIS 2008.

6. Le, Q.B., deVries, J.A., Golovashchenko, S.F., and Bonnen, J.J.F., “Analysis of sheared edge formability of aluminum,“ Journal of Materials Processing Technology 214 (2014) 876– 891.

7. Nasheralahkami, S., Golovashchenko, S.F., Malek,C., Rugh, E., Kowalsky, D. and Zhou, W., “Sheared Edge Stretchability of Steels Suitable for Automotive Applications,” SAE Paper 2017-01-1708.

8. Nasheralahkami, S., Golovashchenko, S.F., Dawson, S.A., Sohmshetty, R. “Analysis of Tool Wear for Trimming of DP980 Sheet Metal Blanks,” 2017 SAE International doi:10.4271/2017-01-0302.

9. Nasheralahkami, S., Golovashchenko, S., Pan, K., Brown, L. et al., "Characterization of Trimmed Edge of Advanced High Strength Steel," SAE Paper .