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September 16, 1998

7 Min Read
Spray-On Tooling Hopes to Slash Mold Load Times

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The spray-formed tin mold above (right) was applied over an HDPE pattern (left).

So, where do you conjure up your brilliant ideas? In the shower? In the car? At your desk? Kevin McHugh had his epiphany in the kitchen. "I was doing the dishes, staring out the window at my kids playing in the sandbox in the backyard," he says. Specifically, McHugh was looking at the toy molds his kids were using to shape the sand. "I thought, 'Boy, what would happen if we could make those molds by spray forming?'"

McHugh is an advisory scientist in the Metals and Ceramics Dept. at the Idaho National Engineering and Environmental Laboratory (INEEL) in Idaho Falls, ID. INEEL is a U.S. Dept. of Energy lab operated for the government by Lockheed Martin Idaho Technologies Co. and specializes in nuclear technology development, systems engineering, and environmental technologies. Another thing INEEL does is develop new technologies for transfer to commercial industry, and that's where McHugh was headed with his new idea.

Back in the lab, McHugh started experimenting with his idea and came up with this simple concept: Melt metal to its molten state and then pass it through a special nozzle where it's mixed with a gas. This molten metal/gas mixture is then sprayed on a surface to create a relatively uniform layer of hardened metal. "You can visualize what we do as a souped-up paint sprayer," he says.

McHugh started experimenting. Early trials with the specially made nozzle proved kirksite- and tin-based compounds could be sprayed onto an inflated balloon without popping it. But so what? "At first it was, 'Gee, look what we did,'" he says. McHugh first targeted the continuous casting and rolling industries for possible applications before realizing the potential it held for toolmakers. "We knew it was a huge market, but we didn't know just how big or how much work was in it," he says.

McHugh then successfully sprayed a tin-based metal on an SLA model. He was headed in the right direction, but needed someone who knew the industry to help lead the way. That's when he hired Gary Nelson. "We call him 'Litmus,'" McHugh says. Nelson, a former toolmaker at a local molding shop, made the research more practical and provided the details the project needed to take the concept to market.

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Early tests of spray-on metal applied to a balloon showed the rapid solidification and net-shape forming capabilities of the process.

How it Works
Today, the project is in the first of three stages intended to make spray-on tooling a practical, low-cost, high-speed alternative to traditional tooling. It's called Rapid Solidification Process (RSP) tooling, and it's designed to help make high-quality tools faster. "As you know," says McHugh, "tooling is expensive mainly because it's labor intensive." The advantage of spray-on tooling, he says, is the inherent ability of the spray to replicate surface shape and detail, which eliminates the need to machine-grind and polish a block of steel. As a bonus, McHugh estimates that the spray-on process represents a savings of five- to tenfold in time and money to produce a tool.

In the current stage of the RSP project, McHugh is spraying H-13 and P-20 tool steel on ceramic patterns. The steel is melted via induction heat in a crucible and then pressure-fed to the nozzle. At the nozzle, a high-temperature inert gas (nitrogen) is introduced into the molten mix, which is then sprayed onto the ceramic surface. The droplets of steel--about 10 to 20 µm in diameter--have a relatively large surface area and actually lose much of their heat between the nozzle and the tool. After they hit the tool, the droplets solidify quickly.

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A tool steel cavity (left) was built in 4 minutes using the Rapid Solidification Process tooling method by depositing spray onto a ceramic pattern (right).

On a ceramic surface, the steel hardens to a finish of about 30 to 40 microinches--acceptable for most applications, but not suitable for applications that require a higher polish, such as lens molding. The deposit builds up quickly to the desired thickness at a rate of about 500 lb/hour. After the ceramic is broken out, this bulk is then finished to a block that can be inserted into a mold base. Rough edges can be squared off with a grinder, or a wire EDM can be used for H-13 and harder steels. McHugh does report he's done some test-spraying on glass and achieved a 3-microinch finish, fine enough to replicate a fingerprint on the surface of the glass.

Where to From Here?
The technology, he says, is heading in the direction of developing a nozzle that can spray a larger surface area. Although the application concept is similar to spray painting, unlike that process, spray-on tooling must be applied to the entire surface uniformly and simultaneously. That is, to get a microstructure with finish, you can't spray the metal back and forth across the tool. The aspect ratio of the tool can also hinder the process; some depths and channels are just too deep for the spray to reach. But, says McHugh, when properly applied, the material properties of the spray-on tooling are similar to those of commercially forged tool steel.

Phase 1 of the spray-on project, concluding right now, is the demonstration phase. Crucible melt capacity is 20 lb, spray pattern coverage is an area 3 by 3 inches, and bench-scale samples are used to prove the process. Phase 2, starting soon, will produce a 75-lb-capacity crucible with 6-by-6-inch coverage. "The main goal is to increase the spray pattern, increase the coverage," McHugh says. Phase 3, scheduled to start in early 1999, intends to produce a full-scale turnkey system with a 500-lb-capacity crucible and 12-by-12-inch coverage, large enough for many applications.

To help fund this endeavor, INEEL created a consortium of companies that contributes to the RSP project and helps give it direction. The list of contributors so far includes some heavy hitters: Baxter Healthcare, Chrysler, Diemakers, Ford, Johnson Controls, Lockheed Martin Aeronautical, Hach Plastics, Northwest Mettech, Proctor & Gamble, LaserFare, and United Technologies Automotive. The consortium itself is organized and maintained by the National Center for Manufacturing Sciences (NCMS) in Ann Arbor, MI.

Phase 1 of the project cost each contributor about $5000. McHugh says Phase 2 will be $30,000 per company, unless more join the consortium. To that end, INEEL is still soliciting companies to join--toolmakers, molders, OEMs, equipment vendors--that want to help build and sell the system. The more members the consortium has, the smaller the financial burden each company must bear. To date, McHugh estimates he's spent just more than $1 million and expects the project will cost about $3 million when all is said and done.

More importantly, when all is said and done, McHugh and the consortium members hope to have a new tool for toolmaking. "I want to see it out and being used by U.S. industries to make tooling quicker and cheaper," McHugh says. When it comes time to take the process to market, Lockheed Martin holds most of the patents. The Dept. of Energy, because the project was partially funded by its metals initiative program, holds a minority of patents, but Lockheed doesn't expect that relationship will prevent the company from commercializing the process.

During Phase 1, because the consortium contribution was relatively small, there was no transfer of intellectual property rights. However, in phase 2, given the larger contribution, some property rights will probably transfer to the consortium members. Lockheed says it's developing those contracts right now. Consortium members will also have first rights to license the technology. To inquire about joining the consortium, call INEEL's Technology Transfer Office at (208) 526-7631.

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