Page 45 - MetalForming February 2022 Special Automotive Issue

machined hole results in the best hole expansion—as much as three times that of a hole punched with 10-percent clear- ance. This results from the lack of a work-hardened shear- affected zone around the hole circumference. Other approaches that result in minimal edge work hardening, such as laser or waterjet cutting, also fall into this category. However, this information is difficult to put into practice, since punching holes remain the standard approach used in high-volume operations.
Historically, 10-percent punch-to-die clearance has been the rule of thumb used throughout the world. For mild and HSLA steels, this produces sufficient results since these grades have decent edge stretchability. With AHSS grades, however, the influence of punching clearance deserves greater attention.
Researchers have determined that thicker steels require greater clearance, with some recommending an extra 1-per- cent clearance for each additional 0.5 mm in thickness. Other sources suggest that optimized performance occurs at 15- to 18-percent clearance, depending on the strength, thickness and microstructure. For example, Fig. 3 highlights the effect of cutting clearance on a CP steel with 1200-MPa tensile strength and reinforces that the historical rule-of- thumb guidance of 10-percent clearance does not apply for all grades. Increasing the clearance to 15 percent leads to a significant improvement in hole expansion. And while the
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HER resulting from a 20-percent clearance was substantially better than that from a 10-percent clearance, it was not as good as from a 15-percent clearance. Importantly, these dif- ferences do not appear when testing only to the requirements of ISO 16630, which specifies the use of 12-percent clearance.
Prediction Difficulties
Again, most forming-simulation software does a great job predicting locations at risk for necking failure, as researchers understand the mechanism for necking failure and the software incorporates the mathematical expressions of these mecha- nisms. However, substantially more challenges exist when predicting edge-cracking failures. Among them: mathematically defining the interplay between the damage from shearing on the microstructural components, which varies by type and distribution in each grade, and sometimes from each supplier. Isolating the effects from other variables, such as punch-tool sharpness, shearing angle and tool coating, only enhances the difficulty in defining the mathematical relationships.
Even in the face of these challenges, advanced models have begun to incorporate the necessary tools to capture these many variables, ultimately leading toward improve- ments in simulation accuracy of all failure modes.
Note: The images included here are based on content pre- sented at www.AHSSinsights.org; visit that site for information and forming/joining best practices related to AHSS. MF
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Metal Matters
Stamping & Lubrication Technology Conference Rescheduled for March
Due to the ongoing COVID-19 pandemic, PMA and MetalForming magazine resched- uled the Metal Stamping and Lubrication Technology Conference from January to March 29-30, 2022. Held at the Hyatt Regency in Cincinnati, OH, the event offers the opportunity to network with peers and learn from industry-leading profes- sionals, while attending breakout educa- tional sessions on the topics most relevant today. Discounted registration rates have been extended until March 20. Visit www.pma.org/stamping-conference for more information.
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Upcoming Calendar of Events
February 13-16, Live and Virtual Event, Forming Our Future Leadership Conference, Key Largo, FL
February 25, Webinar, One Voice in Washington: Public Policy and COVID-19 Update
March 9-10, Live Event, Die Mainte- nance Seminar, Cleveland, OH
March 22-23, Live Event, Sales & Marketing Roundtable, Cleveland, OH
March 29-30, Live Event, Metal Stamp- ing & Lubrication Technology Conference, Cincinnati, OH
Please visit www.pma.org/calendar for the most up-to-date information.
PMA has expanded its partnership with ITR Economics to provide PMA mem- ber companies with additional economic intelligence to drive practical and profitable business decisions. Members have access to monthly advisory reports and economic articles; enhanced quarterly forecast reports featuring additional industry sec- tors; huge savings on the ITR Alliance Tool, an on-demand portal allowing com- panies to upload their data and compare it to more than 100 industry key indicators; and more. Visit www.pma.org/member- ship/economics.asp for details.
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MetalForming/February 2022 43
PMA Welcomes Its Newest Members
• Ajacs Die Sales Corp., Grand Rapids, MI • Cedar Lake Engineering Inc., Maple Lake, MN
• Crawford Manufacturing Co., Baltic, OH • ERICO / nVent, Solon, OH
• Precision Resource, Cambridge, ON; Arteaga, MX; Mount Sterling, KY; Troy, MI • QAD, Inc., Santa Barbara, CA
• StartProto, Inc., Atlanta, GA
• Victory Tool, Inc., Anoka, MN
Join PMA and experience the power of membership! Contact Diana Novak at 216/901-8800 ext. 104 or dnovak@pma.org with questions.