Page 98 - MetalForming October 2016

Tooling by Design
By Peter Ulintz
Advances in Metal-Stamping Technology
Technologies in metal stamping continue to advance and mature—as they always have done—but today this happens more rapidly than in the past and the technologies are profoundly more complex.
Hot forming is a good example. Today it is common prac- tice to form some automotive components from boron steel sheetmetal at high temperatures (approximately 900 C) in a die that simultaneously forms and quenches the stamp- ing—essentially heattreating the formed part in the die.
Hot forming is very different from a traditional deep- drawing process. No blankholder is used; instead, special clamping units are installed to hold the part material in position and to prevent the formation of wrinkles. Cooling lines often are required in close proximity to the die surface to facilitate the quenching process, which makes the use of special die steels
alloy (HSLA) steels, placing unprecedented demands on new tooling and older press lines.
A third generation of AHSS materials—currently under development—have tensile strengths equivalent to some hot-formed stampings but with enough ductility to be cold- formed at room temperature. These ultra-high-tensile- strength materials surely will push existing press lines beyond the capacity limits for which they were designed.
Steel is not the only material changing the way that metal stampers operate. In the last decade, aluminum alloys have experienced a significant increase in use for sheetmetal-part applications in automotive and other transportation industries.
Processing aluminum stampings can be challenging, espe- cially when working with new or unfamiliar alloys. New alloys are being developed for ultra-high strength hot-forming appli- cations; other existing alloys are being successfully warm- formed and a few others can be super-plastically deformed. More common alloys are being refined to provide better cold forming properties. Understanding the differences and limi- tations between the various aluminum alloys and their tempers is essential in order to provide the process engineer and die designer with the best opportunity for success.
Advances in forming lubricants, lubricant application methods and lubricant thickness-measurement technologies are becoming increasingly more important and prevalent; especially considering the arrival of third-generation AHSS materials and the elimination of chlorinated paraffin in the near future.
Modern stamping dies are subjected to an ever increasing array of stresses, temperatures, chemical attack, shock and vibrations. So, it is not surprising that metal-stamping dies are prone to all a kinds of in-process failures. Tooling chem- istry, heattreating methods and engineered surface coatings are constantly improving to meet the increasing demands placed on today’s stamping dies.
Carbide materials often are chosen for metal-stamping operations when long production runs are required. They exhibit high compressive strength, resist deflection and retain their hardness values at high temperatures, a physical property especially useful in high-speed cutting, punching and forming applications. Some processes, such as perfo- rating small-diameter holes in hard, tough materials, may only be possible with tungsten-carbide punches.
Brand new metalforming-process developments such as double-sided incremental sheetmetal forming are emerging. This novel manufacturing process utilizes two generic tools to manipulate sheetmetal in an effort to produce free-form parts without the need for dies. The process can potentially
with high heat-
transfer rates and
high strength nec-
essary. Strong ejec-
tor systems also
must be designed
and built to facil-
itate part removal.
These are only a
few of the critical
features that must
hot-forming dies. Hot forming is an amazing accomplishment considering the fact that most die engineers and tool and die makers were never trained in this technology.
“Hot forming is an amazing accomplishment considering the fact that most die engineers and tool and die makers were never trained in this technology.”
be addressed when designing and building
Advancements in steel technology have led to a new class of high-tensile-strength materials referred to as advanced high-strength steel (AHSS). With the exception of the boron- based hot-forming grades, these materials are designed to be cold-formed in traditional stamping dies and press lines at room temperature. These materials can have two to three times the tensile strength of traditional high-strength low-
Peter Ulintz has worked in the metal stamping and tool and die industry since 1978. His background includes tool and die making, tool engineering, process design, engineering management and advanced product development. As an educator and technical presenter, Peter speaks at PMA national seminars, regional roundtables, international confer- ences, and college and university programs. He also provides onsite training and consultations to the met- alforming industry.
Peter Ulintz
Technical Director, PMA pulintz@pma.org
96 MetalForming/October 2016
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