Page 43 - MetalForming August 2011

the best coating method for a new proj- ect, as the company has had good suc- cess using a physical-vapor-deposi- tion (PVD) process (FortiPhy, from Phygen Coatings, Inc., Minneapolis, MN). The goal this time: Protect large tooling details in production of deep- drawn parts for tractor-trailer air-regu- latory units, which comprise a portion of the new work arising from emission regulations.
“These deep-drawn stainless-steel parts are very large, with draws from 8 to 10 in.,” explains Michael Stull, Pentaflex tooling manager.
The firm employs two hydraulic presses, 2300- and 1600-ton models, to draw the parts, mostly via hand trans- fer. Tooling details used to produce these large parts are very large, some stretching to 36 in. long. Coating such large parts occurs at a recently installed PVD chamber at Phygen, a chamber that tripled its previous capacity.
“This means that we can deliver the same coating quality with practi- cally no size limitation for draw rings, draw pads and form dies,” says Phygen president David Bell. “Also, tooling that before would have to be made and coat- ed in smaller segments now can be made in larger pieces, eliminating tooling lines in parts and the risk of tool distortion or size change that might occur using high- er-temperature coating processes.”
Ideal Tool Protection
The selection of Phygen for the deep-draw details resulted from a pre- vious tool-coating quest.
“About seven years ago we started looking for coatings for tooling used to stamp large brake drums from 1025 and 1026 high-strength low-alloy steel,” recalls Stull. “We experienced excessive galling that only allowed us to produce 900 parts before having to repolish and clean the details. We tried all types of coatings without any improvement.”
Searching for an answer, Pentaflex shipped precision die sleeves—large details with tolerances maintained at ±0.0005 in.—to Phygen. The tool coater
applied its FortiPhy process—which creates a thin and dense nanocrys- talline coating structure that adheres to virtually any tool-steel substrate—to the rings. The coating process creates highly energetic nanoparticles, report- edly resulting in a higher level of adhe- sion—three times higher—than is pos- sible with conventional coating processes. The coating also boasts a low coefficient of friction, less than 0.1 in typical lubricated conditions.
A previously tested coating, which only brought an uninterrupted tool life of 900 hits, would fail owing to an adhe- sion process that would pull out carbon from the tools, according to Stull. The FortiPhy coating, on the other hand, uses a process that doesn’t deplete the tools’ carbon grains.
In addition, the coating process offered another feature that caught Stull’s attention. While chemical-vapor- deposition and thermal-diffusion coat- ings typically are applied at tempera- tures exceeding 1800 F, FortiPhy requires significantly lower temperatures. This
lessens the chance of distortion that can play havoc with tolerances, and minimizes tool-hardness concerns.
“After employing the FortiPhy process, we went from polishing details after 900 hits to surpassing 40,000 hits before required mainte- nance,” says Stull. “In the past seven years we’ve coated a number of tools with this process, mostly of DC53 material and some D2. For the large drums, we use A2 due to the high iron- ing pressures during forming—requir- ing a minor amount of expansion
within the tools to prevent them from fracturing. The coating process and heattreating does lower the Rockwell hardness a bit, but doesn’t distort the tools. We send them out at Rc 60-62, and after coating they come back at Rc 58-59, well within their working range.”
Coating a Surer Bet Close to Home
With a toolroom roster of 11 employees across two shifts, focusing mostly on tool maintenance and
repair with a bit of build, Pentaflex appreciates tooling that lasts over the long haul. Finding coatings that keep tools producing help the company service its growing tractor-trailer cus- tomer base. A few years back, Pentaflex made business decisions that revealed how critical the correct coating can be to maintaining top-notch production.
“At one time we had details pro- duced overseas to reduce costs,” recalls Stull. “Those suppliers could only rec- ommend thermoreactive-diffusion coatings for these details. But these coatings failed to hold up given the type of work we perform and the types of tool steels we use. So we purchased the details coating-free and shipped them to Phygen for the correct coating. Now we source all of our tooling domestically, and combining that with ideal coating performance, we produce parts that meet our customers’ needs.”
MF
Article provided by Phygen Coatings, Inc.: 888/749-4361; www.phygen.com.
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MetalForming/August 2011 41
Tooling Technology
These brake drums, of 3⁄8-in.-thick 1025 HSLA steel, are produced in a 2300-ton press with- out galling or ID/OD imperfections allowed. Coated tooling details have run in the press for more than 3.5 yr. without replacement.