Metal Forming Success Story
PVD Coating Greatly
Increases Stamping Tool Life
LuK USA, LLC, Wooster, OH, is a manufacturer of flywheels, continuously variable transmissions, auto-shift gearboxes, pressure plates, and torque converters for automotive and light trucks. Stamping tough steel such as stainless and spring steel is common, but it often causes problems. LuK stamps steel in thickness ranging from 0.5mm to 7mm. One problem the company has experienced says Paul Gray, section leader, is 4mm thick steel becomes distorted when the outer bodies of torque converters are drawn. There’s so much force on the drawn steel that it’s polished or smeared from the die, which is a clear indication of extreme pressure, adds Gray.
 For deep draws and stamping operations with extreme pressure, Gray says coating the tools is the way to go. “In the past, our only choice for forming steels was to use CVD coating,” says Gray. Now, with the newer coatings, we have an option to use a PVD coating, such as FortiPhy from Phygen, a comparatively cold coating process (950°F).” With this process, there’s no reason to worry about die movement, such as die or punch parts growing from the process and later having to re-cut them.
“FortiPhy works well when the metal is being squeezed in the die, such as a shallow draw with thick metal or a deep draw with thick or thin metal. We’ve found that it even outperforms chemical vapor deposition (CVD) coatings in certain applications,” says Gray.
On one ring that LuK started production on in January 2005, the company had to coat the die just to get it through the prototype stage because the operation was so difficult. Gray says TiN PVD was put on the tooling, but even with this, the die had to be hand worked to bring it back into specification every 500 pieces. Another PVD coating was tried but it failed after 1,200 pieces. Finally LuK tried the FortiPhy PVD CrN coating, which yielded 38,000 pieces.
LuK doesn’t use coatings on low runs of about 5,000 pieces, even if the tooling would benefit from a coating, says Gray. Instead, LuK might keep polishing the tooling just to make it work. But a coating is used if a die does high-volume work, 50,000 pieces or more. “In high-pressure squeezing areas, we really need the coatings and PVD coatings are about the best for punching or blanking operations, as well as for trim dies,” says Gray.
The key to FortiPhy’s exceptional toughness, low coefficient of friction, and corrosion resistance is its uniform, nanocrystalline structure. Phygen’s patented plasma acceleration process improves upon traditional PVD methods to produce the most uniform coating deposition layer possible, with exceptionally high adhesion.
Having solved the uniformity problems inherent in the PVD process of the past, Phygen can apply thinner coatings that outperform thicker, less-uniform coatings. In addition, Phygen FortiPhy coatings are applied at much lower temperatures. Low-temperature processing and thinner coatings help keep critical tool dimensions within tolerance, without the costly rework of other processes..
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