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Fineblanking gains in precision shops.

Fineblanking is a process that was developed in Europe to make miniature gears and other components for Swiss watches, right?

Well, yes and no. The process was in fact developed in Switzerland in the late 1950s, and for years was applied almost exclusively in making parts for mechanical office equipment, says Joe K Fischlin, vice president, Feintool Equipment Corp, White Plains, NY.

And, he adds, you wouldn't be alone if you thought fineblanking was useful only for small parts. "In the '70s, I used to make presentations to potential automotive customers in the United States, and they'd say, 'This is wonderful, but this is jewelry. We don't need jewelry.'"

Fineblanking is a carefully engineered stamping and forming process that results in near-net shape parts with edge and hole finish comparable to that achieved in grinding. And with high-tonnage presses available from Feintool and other equipment suppliers, the process is being used more and more for relatively large parts as well as for stock thicknesses greater than 1/2".

"Our parts range from 0.060" to 0.070" thick up to 5/8", but the majority are between 3/16" and 3/8"," says Mr Fischlin. "That thickness range is where fineblanking really can eliminate a lot of other operations. To get a fairly nice, clean part in stock 0.020" or 0.030" thick is relatively easy with conventional stamping; you probably don't need fineblanking. But once you go into the heavier materials, that's where fineblanking really pays off."

That payoff comes not only in the form of ready-to-use, near-net shape parts with typical tolerances of |+ or -~0.001", but also in capabilities that are beyond conventional stamping and blanking. Fineblanking can produce holes with diameters as small as 60% of stock thickness, and webs--the metal between features such as holes--also can be as little as 50% to 60% of thickness. The process can even produce blind holes and semi-pierce projections in a single hit.

The added capabilities are a result of modifications in both the press and the tooling used. Mr Fischlin says fineblanking requires triple-action presses with independently adjustable hold-down, blanking, and counter forces. Tooling is designed to hold the work material firmly around the part contour, and a counterpunch below the work material maintains flatness and provides the needed counter force.

"When you fineblank a part, you get completely straight edges and a finish almost the same as you'd get from grinding," says Mr Fischlin. "In conventional blanking or stamping, you get die break and generally a more rough-looking part."

"Die break" is the result of plastic strain--permanent deformation--of the metal as the part is stretched in the die during conventional stamping. As the die closes, both plastic and elastic strain exceed the tensile strength of the metal, and the part breaks away from the metal stock. Much of the deformation resulting from the elastic strain is recovered in the form of springback, but the part is left with a rough edge, and the gross distortion of the part inherent in the process pretty much precludes close-tolerance features.

But precision has its price. Both presses and tooling for fineblanking are more highly engineered--and thus more expensive--than conventional machines and dies. Mr Fischlin says consider the potential benefits when weighing whether fineblanking is worth the extra up-front cost for your application, because bottom-line costs for usable fineblanked parts may be lower than other processes.

"Disregarding the results, the fineblanking tool will be about double the cost of a conventional tool. But I'd venture to say that if you want to approach the shape and finish of a fineblanked component with conventional stamping, the only way you can do it is with very complicated progressive conventional tools. So if you're talking about a four- or six-station progressive die compared to a compound die for fineblanking, the fineblanking tool is probably about half the price," he says.

Production of automotive components currently accounts for about 70% of fineblanking applications, according to Mr Fischlin. Parts produced include automatic transmission components, brake components, exhaust and catalytic converter flanges, exhaust manifolds, and components for "virtually every automotive door lock in the world," he says.

Feintool's equipment line includes mechanical and hydraulic CNC presses with tonnage ratings to 1500 metric tons. The company's CNC hydraulic machines start at 280 metric tons and offer automatic programming of press stroke height, stroke speed, pressure, stock in and out feeds, part blow-off or mechanical sweep removal, and coil unwinding/straightening. The control also features a tool safety device that prevents cycling if parts or slugs from the previous stroke are not completely cleared, as well as on-board tooling parameter data storage for up to 200 part programs. In addition to presses, the company supplies tooling and does contract fineblanking from facilities in White Plains and Cincinnati, OH.

So what about the US automotive engineers who pooh-poohed the need for fineblanked part quality during Mr Fischlin's presentations in the 1970s? "Along about the mid-1980s, those same people started calling us and saying, 'Remember when you came in here? We're ready,'" he says.
COPYRIGHT 1993 Nelson Publishing
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Manufacturing Update
Publication:Tooling & Production
Date:Sep 1, 1993
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