Christof Lehner General Manager Laser Technology Center Trumpf Inc. Plymouth MI
www.us.trumpf.com
ADVANCED MANUFACTURING NOW The Laser – An Essential Tool for Lightweighting
T
he 2025 EPA fuel economy standards have made lightweighting and the reduction of greenhouse gas emissions a necessary pursuit for automotive manufacturers. In fl ange reduction, joining of aluminum or
dissimilar materials, joint preparation and welding of hot-formed components, plastic welding, and high- speed cutting of boron steel, lasers are more than a modern and perfect tool for the job; they are enablers for future innovations that will be critical in achiev- ing the EPA standards. Why? Lasers can focus energy to very small spots without costly environments, such as vacuum cham- bers. The process is contact-free and only requires accessibility from one side of the work zone. These qualities provide benefi cial metallurgical properties, tremendous process fl exibility, and are cost effective. The latest developments in the fi eld of laser diodes further enhance the effectiveness and effi ciency of lasers while making them an even more attractive tool for lightweighting designs. The ability to focus energy precisely and to very small spots is being exploited today, for example, in welding high-strength steel. The resulting heat-affected zones (HAZs) are small compared to the larger and strength-compromising HAZs associated with con- ventional welding. In fact, the HAZs of laser welding have little to no negative infl uence on the overall stiffness of the part. Laser welding also opens the door to new design methods, including size reduction or complete elimination of fl anges. When combined with the use of high-strength steel, this can lead to signifi cant weight savings. In addition to high-strength steels, aluminum is used increasingly to further reduce weight. The very precise energy input of lasers enables high quality welds, solving some of the problems that plague conventional techniques, such as MIG weld- ing. Compared to MIG welding, laser welding is faster, with less heat input, a smaller HAZ and much lower distortion. It can also be welded autogenously. However, these advancements are not enough to meet the future EPA standards. To further reduce
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weight while also increasing safety and comfort, it is necessary to combine several materials and optimally use them within a car’s body structure. This leads to the joining of dissimilar materials. Some of the most interesting material combinations are aluminum-steel and plastic-steel. Using powder as deposit material, a process
known as laser metal deposition (LMD) is a promis- ing approach for joining aluminum to steel. For this, it is essential to keep the brittle intermetallic compounds in the weld zone to less than a 10-µm layer. The focusability and low heat input that are unique to laser processing are the key to success. Initial research shows that with a copper-based al- loy as the powder material, relevant joint geom- etries can be “welded” with good strength. Further investigations will include corrosion resistance of these joints, as well as a study of the infl uence of part tolerances. A less obvious application of a laser is join- ing plastics to steel. Recently, special lasers with nanosecond pulse durations have been developed for cleaning and structuring surfaces. The cleaning function is increasingly used to prepare the surface for weld seams, for example, when welding gears in powertrain or to ablate AlSi layers of tailor-welded blanks prior to welding. A new approach empowers these nanosecond lasers to join plastic and steel. The fi rst step is to structure the steel surface with thou- sands of Velcro-like fi ngers. Next, the plastic part is pressed on the structured surface and simultaneously heated. The plastic part melts into the structured fu- sion zone and creates a tenacious mechanical bond after re-solidifying. Fuel economy mandates of the near future
have made automotive lightweighting a necessity, and lasers are sure to play a signifi cant role in that endeavor. Innovations in laser technology, combined with their ever-increasing affordability and advance- ments in laser processing, will set the stage in a wide variety of application areas to address the weight reduction challenge head-on.
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