Page 24 - MetalForming August 2012
P. 24
Die Engineering at Chrysler
Die Structure Analysis
Topology Topography Failure
Part Correlation
stamping production. Trimming ele- ments are of furnace-hardened D2 tool steel, with a standard breakage of 10 percent plus sheetmetal thickness. No additional coating was applied, and we found that with good preventive main- tenance, we can satisfy high-volume
requirements (more than 400,000 parts/yr.).
Flanging operations, in most cases, produce the greatest local tool wear of all operations. Thus, we’ve mandat- ed use of D2 inserts with nitride with the additional PVD coating applica-
Fig. 5—To process and design draw dies for AHSS parts, Chrysler engineers sought to account for abnormal die deflection and increased tool wear, and develop geometry to better control springback. New and unique die struc- tures feature increased rib thickness in working areas; use of separate details made from D2 steel; and special heeling to combat thrust. Shown here is the use of finite-element topology and topogra- phy developed to study key load paths in the die structure.
tion for all working areas. Since the high working forces are local in the flange areas, these structures were only locally increased; the remainder of the die structure in nonworking areas remain similar to the die standards used for mild-steel panels.
Pierce-Die Design
Over the past several programs, Chrysler’s pierce-die standards have evolved through a combination of pro- duction experience and applied research, through consortium project participation. Among the results:
• Conical-tip punches optimize longevity for Type D standard parts. Compared to traditional flat-profile punches, performance increased by as much as 40 percent (measuring quali- ty by burr height).
• For all high-strength and AHSS steel parts thicker than 1.2 mm and with yield strength exceeding 250 MPa yield strength, a 10- to 15-percent clear- ance per side provides optimum results.
• Traditional M2 punches with A2 buttons—uncoated—are used. PVD- CrN coatings have been applied in pro- duction, with little benefit.
• To optimize piercing performance with high-strength steels, conical-tip punches, larger punch clearances and more stringent maintenance intervals (approximately every 100,000 hits) get the call.
• Lower value for maximum pierce angles allowed than for mild-steel parts.
Punches and buttons following these guidelines show little wear after 100,000 cycles, even for parts running DP980 material at 1.6 mm. MF
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22 MetalForming/August 2012
www.metalformingmagazine.com
