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Automotive Industry

Molten-Metal Toolmaking - Ford Motor Co. developing new tooling process - Brief Article

Automotive Industries, Sept, 2000 by Angus MacKenzie

Want to dramatically speed your die- and moldmaking operations, while lowering cost? Spray-formed tooling makes it happen, as Ford is eagerly finding out.

Ford Motor Co. is developing a new tooling process that could produce an enormous step-change in auto manufacturing. Called spray-formed tooling, it involves spraying molten metal onto low-cost ceramic forms to create stamping dies and molds for metal and plastic parts. Early production trials have shown the process can produce tooling in less than one quarter the time of conventional methods, with cost savings of up to 30 percent.

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Spray forming of metal is not anew technology. The process, which involves spraying fine droplets of molten metal into a form, has been used to produce high quality billets and blanks suitable for forging. Because the liquid metal droplets typically cool two to three times faster than in conventional casting methods, the material produced has less than one per cent porosity and a very fine microscopic structure, which enhances strength.

Dimensional Accuracy Breakthrough

The idea of using spray forming to make tooling was developed by a British company, Sprayformed Holdings, which was acquired by Ford last year. The process begins with a mold made by freeze casting a ceramic slurry around a dimensionally accurate resin, or SLA representation, of the tool. The freeze casting method ensures dimensional stability of the mold and provides a surface the molten metal droplets can adhere to.

Metal is then sprayed onto the mold to a depth of about one inch, at a rate of 1mm every five minutes. Once cooled and removed from the mold, the metal tool is fixed to an epoxy backing material which matches its expansion and load rates, and allows it to be fixed in stamping presses in the conventional manner.

The key technical breakthrough has been to perfect a means of maintaining the dimensional accuracy of the sprayed-on metal as it cools on the ceramic mold. Typically shrinkage rates of four to five per cent mean the sprayed metal would peel away from the mold as it cools, but by carefully manipulating a phenomenon called martinsite transformation -- in simple terms, a structural change that occurs in the metal as it cools, which produces an increased volume of material -- it is possible to offset this shrinkage.

The degree to which the martinsite transformation takes place is directly related to the rate at which the metal cools -- the faster the rate of cooling, the greater the degree of transformation and therefore the larger the volume increase. A portfolio of 18 patents and patent applications cover this element of the process, and Ford has established a joint research facility with Oxford University in Britain to perfect software that will allow the extremely complex robotic path planning required to make large sprayformed tools.

At its Dearborn, Michigan, research center, Ford is currently producing spray-formed tools up to two square feet -- a size dictated by the logistics of handling the 200-pound ceramic molds and the layout of the metal spraying robots. Spray-formed tooling is currently used in Ford's Valencia, Spain, plant to make Focus door latch reinforcements, and has been used to produce 1.2 million automatic transmission turbine blades.

Cycle Time Reduction

While conventional tooling for the blades would have taken five to six weeks to produce, Ford's spray-formed tooling was punching out parts just one week after the relevant CAD data had been downloaded.

A research team in Dearborn headed by former Sprayformed Holdings partner Allen Roche is currently working on an experimental 6 x 8-feet spray-formed tool for a hood inner panel, made up of 12 dovetailed modular dies. Such a large tool would normally take up a year to make, but Roche expects to have the piece ready within 120 days of design freeze.

"If we could spray the 6 x 8 feet in one piece, then a two-to-three month window looks feasible," he says.

Tooling is one of the few elements of automaking that has changed little since the days of the Model T Ford, and remains a major roadblock to shorter product development cycles. Sprayformed tooling could rewrite the manufacturing rulebook, at much lower costs.

Automotive Industry

Molten-Metal Toolmaking - Ford Motor Co. developing new tooling process - Brief Article

Automotive Industries, Sept, 2000 by Angus MacKenzie

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