Thermal diffusion extends stamping die life, reduces press downtime
November 8, 2005
"Okay Industries, New Britain, Conn., serves diverse market segments including medical, automotive, electronics, defense, and specialty industrial. The stamper produces a roller finger follower for automotive applications. There are 14 stations on the die. The TD process is used on three of them," DeVecchis said. "It has given us better product quality, less scrap, faster throughput, longer die life, and reduced die dressing."
|Applying a thermal diffusion coating to stamping tooling has doubled tool life. Production runs now exceed 100,000 cycles, according to the company.|
In the 35 years Okay Industries, New Britain, Conn., has been in the stamping business, it has grown to 160 employees, including 11 tool designers/engineers and 25 toolmakers. The stamper uses all 100 of its 10-ton to 800-ton presses in its 100,000-square-foot facility.
Okay serves diverse market segments, including medical, automotive, electronics, defense, and specialty industrial.
The precision stamper likes to take on the tough jobs—the ones other companies don't want. However, those tough jobs came with a price tag in the form of high die maintenance costs caused by high wear or galling, excessive press downtime, and overuse of lubricants.
The stamper produces a roller finger follower for automotive applications. The part is made of 0.098-inch-thick 1008 cold-rolled steel.
The traditional method of manufacturing the roller finger follower was to cast it and then run it through secondary operations such as boring, grinding, and lapping. The part performed satisfactorily, but the high cost needed to be reduced, especially since engines were being designed with more valves.
So the automotive industry had it remanufactured as a stamped and formed (flanged) part to reduce cost.
However, this design had several disadvantages. The component was heavier and less stiff than the cast version, which had an adverse impact on fuel economy and emissions. In addition, flanges were thicker than the cast version. Finally, the stamped component required a clip assembly in the socket area for final assembly into the engine, which also increased costs.
Okay partnered with its customer to understand the critical requirements of the application and developed (and joint-patented) a method for manufacturing a lower-cost stamped roller finger follower that was lighter, narrower, and stronger: stamping and forward extruding it into the same configuration as a cast part. The part could be net-shape stamped, heat-treated, and shipped to the customer without adding additional components or secondary operations.
|Thermal diffusion is a hot process that combines carbon from the tool surface with vanadium to grow a vanadium/ultradense carbide layer that is bonded to the substrate metallurgically.|
There were many challenges to developing this version of a stamped roller finger follower, however. One was creating valve stem guide side walls long enough so the parts would not tip over during assembly. The stamper addressed this challenge by forward-extruding material into a die cavity that produced net-shape valve guide side walls to keep the valve stem aligned during assembly.
While this process worked, the forces involved fractured the tooling components after only a few parts were produced. "In this die, we have stations that blank, pierce, and form the part," said Jim DeVecchis, design engineer. "In the forming stations we are pushing the metal around in a small radius and the material wants to slide. As a result, we experience extreme heat and galling in these areas. This condition will distort the part and wear down the tool at an unacceptable rate," he said.
To achieve an acceptable tool life, the stamper engineered a tooling concept that prestressed the tool components by heating retainers and supercooling die components. When assembled together, the retainers and die inserts return to ambient temperature, causing the retainers to shrink and the die inserts to expand. This robust design increased the rupture strength for tooling components to 50,000 cycles.
In an effort to extend tool life even more, the stamper applied a thermal diffusion process coating from TD Center, Columbus, Ind., to the tool components.
Thermal diffusion is a hot process (1,800 degrees F) that combines carbon from the tool surface with vanadium to grow a vanadium/ultradense carbide layer—0.0002 to 0.0003 in. thick with a hardness of 3,500 to 3,800 Vickers hardness, well above 90 Rockwell C—that is bonded to the substrate metallurgically.
This method creates a bond stronger than deposited coatings, according to TD Center. The coating is durable, will not chip or peel off the substrate, and provides good abrasive wear protection.
Applying the thermal diffusion process to the tooling has doubled tool life and, subsequently, production runs, which now exceed 100,000 cycles, DeVecchis said.
"There are 14 stations on the die. The TD process is used on three of them," DeVecchis said. "It has given us better product quality, less scrap, faster throughput, longer die life, and reduced die dressing."
"We have changed over our lubrication to a nontoxic oil and coolant," DeVecchis said. He added, "Because of the TD process, we can use a water-based coolant for many of our dies. Otherwise, more expensive coolant or oils would have to be used. In areas of the die where the part normally would run hot, the coolant significantly reduces the heat. Now with the TD process and our new water-based coolant, we have a part coming off that you can pick up."
The company has applied the thermal diffusion coating process to other stamped components as well. Almost all of Okay's new dies now have a thermal diffusion coating specified for them, DeVecchis said. "They are used primarily for areas of high wear or galling and to reduce lube costs, especially for drawn parts."
Okay Industries Inc., 200 Ellis St., New Britain, CT 06051, 860-225-8707, fax 860-225-7047, www.okayind.com
TD Center, 2020 15th St., Columbus, IN 47201, 877-832-3687, fax 812-378-1591, www.tdcoating.com