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Coatings Enhance the Diemaker's Craftsmanship

By: Brad Kuvin

Thursday, July 01, 2010
 
Surface-treatment facilities represent the back lines in the battle against die wear. Worn dies go there for healing, and new dies go for boot camp before they head out to the front lines to take on the challenges of the press shop. As those challenges continue to mount —in the form of tightening tolerances on dimensions and surface finish, the stamping of advanced high-strength steels and deep drawing of aluminum alloys (to name a few)—die coaters are stepping up to the plate to do their part

Coatings-hub seal parts
Richter customer K.S. of West Virginia boasts of a significant increase in die life using the Richter Titankote C2-SL process when deep drawing bushings and forming surface-critical hub-seal parts. Shown here: a bushing 80-mm dia. by 82 mm tall, and a hub seal 6 mm tall by 80-mm dia.

 Integrating a Dry-Film Lube into the Coating

“We can help metalformers with their up-front die engineering to make sure they evaluate all of the coating options available to them, and optimize their selection based on the specifics of an application,” says Matthew Thompson, sales manager at Richter Precision Inc., a surface-coating supplier headquartered in East Petersburg, PA. “Sophisticated metalformers and tool and die shops do a good job of tracking the life of their tools and work with us early in the design phase to specify surface treatments into their designs. That’s the best to avoid problems down the road.”

Richter Precision, which also operates facilities in Clinton Township, MI, and Florence, KY, offers PVD, CVD and TD coatings. It’s recently developed a couple of new coating processes designed to address specific needs of the metalforming industry

Coating- Richer Titankote C2-SL PVD coating
Alternating 4.2-nanometer layers of AlTiN (dark layer) and CrN make up the Richter Titankote C2-SL PVD coating. Wear resistance is optimized since the layers prevent the propagation of micro-fractures, the company says.

“The film forms a mechanical-chemical bond that holds up well in high-stress applications,” says Thompson, “such as severe draws and other applications where galling can become an issue. About half of our customers now specify the additional dry-film application. We’re seeing tool life increase by at least 30 to 50 percent, and in some cases die life between maintenance cycles increases by five or six times.”

The Synergy of Two Crystalline Structures

For hard-working dies where dimensional tolerances also prove particularly challenging, effectively prohibiting the use of high-temperature TD coatings, Richter has developed a new, low-temperature PVD process called Titankote C2-SL (Super Lattice). The process deposits complementary, alternating nano-layers of AlTiN and CrN. The resulting film consists of more than 1000 highly oxidation-resistant layers and a coating hardness in excess of 3500 Vickers.

“We developed the C2-SL process early in 2009,” says Thompson, “for those applications where the toughness of a TD coating is required but where a low-temperature coating process is needed.”

Automotive-industry supplier K.S. of West Virginia Co. (KSWV), Ravens-wood, WV, is a believer in the C2-SL process, having approached Richter early in 2009 for help with a deep-draw dies used to stamp bushings.

Says KSWV quality manager Jeff Easter: “The draw dies generate a lot of heat forming the mild-steel (1.8 mm) bushings. The press runs at 18 to 22 strokes/min. and parts exit the die at around 120 F. Our TiCN PVD coatings were failing after 25,000 parts. We tried different coatings, fine-tuned the die radii and adjusted the clearances, and still struggled, finally turning to Richter for the Titankote C2-SL coating.

“Since September 2009, the Titankote C2-SL-coated die has run more than 150,000 parts,” Easter continues, “and we’re approaching 200,000 parts. And, in addition to the huge increase in run time, surface finish of the parts also has improved dramatically. Based on that success, we’ve used the coating for many other dies and generally experience triple the life compared to other TiCN coatings, at about one-third the cost.

“Surface finish on these rings is critical,” says Kerns, “to ensure the durability of the seals. And it’s difficult to avoid scratches when drawing 430 stainless. While a TD coating might be ideal for its durability, we tried the lower-temperature C2-SL process to help maintain the tight tolerances (0.01 mm) on the punch dimension that governs the ID of the seal ring. The C2-SL-coated punches have run more than 250,000 parts and continues to meet our surface-roughness tolerances Ra 0.8 micrometer) and minimum scratch-depth requirements (6 to 8 micrometers).”

Expert Symptom Diagnosis Leads the Optimum Treatment Plan

Coatings double door aperture die
Our Teikuro tour took us by this huge double-door aperture die in the midst of polishing to prepare it for chrome plating. A team of trained die finishers were using a variety of air tools and custom inhouse—developed and manufactured polishing wheels on the die, which had last been chrome plated in 200
We consider ourselves die experts first and foremost,” says John Emerich, plant manager at the Springfield, OH plant of die-coating company Teikuro Corp. “We can look at a die—worn either from tryout or from production runs—evaluate its wear conditions and identify specific issues we need to address during surface preparation, before applying the coating.”
Teikuro, a Japanese hard-coating company established in the United States in 1987 to support NUMMI operations in California, specializes in chrome plating of large OEM automotive dies. In 2000 the firm added a thermo-reactive diffusion (TRD) coating to its resume to round out its offerings to the stamping industry. It’s most proud of the expertise its employees have in die prep—grinding and polishing—to optimize the life of its coatings.

“It’s the elbow grease and the time we take to hand-work the die steels that optimizes coating performance in the stamping press,” says Mike Hamell, Teikuro vice president of sales and marketing. “We use proprietary techniques and specially engineered finishing tools developed here and in Japan to allow stampers to (often) get hundreds of thousands of hits before requiring the dies to be replated.

“We can turn around a chrome job in 24 to 48 hr.,” continues Hamell, “getting our customers’ presses back up and running during a planned weekend shutdown. A lot of times stampers can’t wait for the typical three to five days needed for a TRD coating.”

A Quick Plating Saves the Day

Case in point: Teikuro customer Elsa LLC, an Elwood, IN stamper of automotive parts including fuel tanks, exhaust pipes, mufflers and cross members. While most of Teikuro’s coating work for Elsa is TRD coating of prog-die form stations, in one recent case, expedited chrome plating saved the day.“In early production runs stamping a catalytic converter shell from a particularly tough stainless steel (18Cr-Cb, more oxidation- and creep-resistant than Type 409),” says Elsa production engineer Earl Land, “we quickly discovered that we needed to redesign a couple of the form dies and draw beads. Rather than delay production for a TRD coating, we sent the tools to Teikuro for a quick chrome application, and in just two days we got the die back in the press. That allowed us to run off a sufficient inventory of parts so we then could send the form dies back to Teikuro to strip off the chrome and apply the more durable TRD coating.”

 Coating Stamped class-A part
When Teikuro takes in a die for replating, it also evaluates a sample panel that the die recently produced. “We need to see the stamped part together with the die to get the complete story,” says John Emerich, Teikuro’s plant manager. Here a Teikuro technician takes a diamond file to a stamped class-A part to get a better look at a low spot appearing on the surface

Stripping chrome from worn dies is a carefully crafted process at Teikuro, as well. “What’s common in the industry is reverse plating,” says Emerich, who manages the plant’s chrome-plating operations. “This reverse-etching process, we feel, can harm the substrate die steel, particularly when a tool receives several chrome applications during its lifetime. Instead, we strip with a solution that works slowly, over an hour or two in a dip tank. The chrome washes a and the acid is mild enough to not attack the substrate.”

Heavy Metal (Chrome)

Substrate condition is key to optimum coating performance, and for the most challenging applications Teikuro takes its chrome plating up a notch with a process it refers to as heavy metal chrome. Protective of its proprietary process, Hamell describes the heavy metal process as “not applying more chrome, but rather it’s how we do the surface preparation to allow the coated tooling to better handle tougher draws and particularly thick materials. The process gains favor primarily for structural automotive parts,” he says. “We want the 100,000th hit to look like the first—ultimately, that’s the job of the coating, to enhance the workmanship of the diemaker.”

“Our success is based entirely on the skill level of our employees,” Emerich adds. “The majority of the operators in our die-finishing department have completed seven levels of competency testing over a 7- to 9-yr. period. Each level comprises 800 hr. of documented on-the-job training in grinding, finishing and welding skills.

“Once we strip the old chrome off of a tool, these highly skilled operators can gain valuable insight into how and why the tool has worn,” continues Emerich. “The customer doesn’t get to see that. For example, if a tool gets dinged and damaged and the customer applies heat to repair the tool, that can affect the underlying quality of the tool steel and ultimately the performance of the coating. Our operators will grind down any affected areas and reweld as a countermeasure before recoating.”

Zeroing in on Die-Steel and Repair-Weld Metallurgy

However, before attempting to repair a die surface or weld, it’s essential that the shop determines the exact composition of the base material and of any repair welds that the stamper has made, says Teikuro’s TRD superintendent John Murphy.

“Often, the tool-steel composition is not exactly what the customer believes it is,” says Murphy. “Using a proprietary process, we can determine the exact steel composition and then tailor the TRD process to optimize the performance of the coating.”

The Teikuro TRD building houses several coating lines that cool coated die components slowly from 1750 to 1850 F down to room temperature, minimizing shock and distortion.

“We can tell the customer exactly how thick the coating will be, every time,” Murphy continues, adding that the firm’s internal standard for optimum coating thickness for metal-stamping tooling generally falls between 7 and 10 microns.

Adds Teikuro TRD customer Pat Welsh, owner of small die-repair shop City Tool & Machine, Hartford City, IN: “We’ve recently been using the TRD coating on DC53 tool steel (from International Mold Steel) on draw rings, as an upgrade over D2, and the steel combined with the coating definitely provides a significant upgrade in run time between die maintenance.

Asked to quantify that improvement in die life, Welsh summarizes his thoughts succinctly:

“When I don’t hear from my customers for very long periods of time, I know we’re (City Tool & Machine and Teikuro) doing our job.” MF

 

See also: Richter Precision Inc., Teikuro Corp.

Related Enterprise Zones: Materials/Coatings, Tool & Die

 


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