Original-equipment manufacturers of automotive dies from all over Europe are using laser heat treating to deliver higher-quality dies faster and cheaper than U.S. OEMs.
Laser heat treating (LHT) has become largely mainstreamed in Europe. But, surprisingly, it is barely practiced in the U.S. even though most analysts believe its ultimate adoption by U.S. OEMs is inevitable.
The most likely reasons U.S. automotive-die OEMs have not adopted LHT are:
- It’s new! U.S. OEMs don’t fully understand it yet.
- It’s not well documented. Cost, quality and schedule improvements from LHT have not yet arrived on the desks of U.S. decision makers.
- It’s scarce. There aren’t many reliable U.S. LHT job shops yet.
But, like British rock and roll in 1964, LHT is about to hit U.S. shores. This article provides both a technology discussion of LHT and also a case study of LHT’s cost and schedule savings for automotive dies (Fig. 1).
Laser Heat-Treating Technology
Laser heat treating (aka laser hardening) is a process in which a laser (with a typical spot size from 0.5 inch x 0.5 inch to 2 inch x 2 inch) illuminates the surface of a metal part to deliver very high-energy flux precisely in both time and geometry. This brings both the metal’s surface and its heat-affected zone (HAZ) up to the desired transition temperature very rapidly.
The laser heat source is then turned off nearly instantaneously, and the metal’s thermal mass rapidly quenches the heated area by conduction, along with the normal cooling from radiation and convection. The result is that the treated areas of the part cool below the transition temperature very quickly, retaining the desired hardness.
The fine details of the laser beam’s operation can be tuned to exercise precise control over all aspects of the hardening process, delivering energy with extreme precision in time and space. The extremely high flux results in very large temperature gradients between the illuminated spot and the unilluminated metal immediately adjacent to it. The result is that the footprint of the HAZ is a close match to that of the laser spot itself. The rapid quenching prevents distortion of the HAZ boundary (Fig. 2).
Importantly, LHT also allows treatment via line-of-sight for areas that are difficult to reach by other means, depending on geometry. This alone represents a major improvement over current processes.
Benefits of Laser Heat Treating
Compared to conventional heat-treatment techniques (e.g., induction, furnace and flame), LHT has several benefits.
- Consistent hardness depth: The precise delivery of extremely high-energy flux to the metal itself, along with multi-parameter, millisecond-speed feedback control of the laser spot, allows LHT to produce an HAZ with exacting specifications, including consistent hardness depth.
- Minimal to zero distortion: Due to the high-energy flux, LHT automatically delivers the smallest-possible total energy to the die under treatment for any given HAZ size. This intrinsic feature of LHT results in minimal to zero distortion in most large sizes of automotive dies (Fig. 3).
- Precise application of beam energy to work spot: Unlike processes that use either flames or induction coils (even when close to the work area), the laser spot delivers heat to the intended area extremely precisely with minimal to zero heating of adjoining areas.
- No hard milling required on large automotive dies: Because of LHT’s low-to-zero dimensional distortion, post-treatment material removal is limited to tiny amounts by polishing and abrasion. No hard milling is required.
Downsides for LHT
There really are no downsides to LHT when compared to traditional heat-treating processes, as long as the materials are laser heat treatable. LHT basically always results in cost and schedule savings in the fabrication and maintenance of automotive dies (Fig. 4), primarily from the complete elimination of post-hardening dimensional-restoration processes (hard milling).
Laser Heat-Treatable Materials
Any steel with 0.2% carbon content or higher is treatable by LHT. LHT dies are generally as hard as, or harder than, conventionally treated dies.
To illustrate the potential for LHT, consider the following actual case study from one of the very few U.S. domestic OEM die suppliers.
This study concerns new part manufacture of automotive-trim stamping dies. A mid-sized OEM typically produces 40 such dies in a year. For this process, both cost in hours while the product was being worked on and also the calendar days for each step were measured.
The results are shown pictorially and in summary form in Fig. 5 and Table 2.
- LHT reduced the yearly manufacturing cost for this product line from $436,000 to $312,000 at a billing rate of $50/hour and from $697,000 to $499,200 at a billing rate of $80/hour for a 28.4% savings.
- Delivery time dropped from 16 to 13 days, a net improvement of 18.75%.
- Total energy reduction was significant, although not computed here. This may result in additional savings if carbon credits become monetized.
Laser heat treatment is a process whose time has clearly come. It has been tested and proven throughout Europe, so no serious risks to its adoption remain for U.S. shops.
It faces no real barriers to adoption aside from those common to any emerging technology, including lack of familiarity and measured adoption rate. The savings measured by cost, schedule, quality and energy reduction are significant and well-supported.