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Truth for radial forming.

At the Owatonna plant of Truth, an SPX division, a minor change in product design resulted in major production problems. One of Truth's many zinc diecast window opening and closing devices became a manufacturing and assembly headache after the change.

The assembly consists of a one-piece base and tube neck zinc casting. In the assembly operation, an operator loads a worm gear, shaft, and bearing; then a spin-roller forming tool swages the top end of the diecast neck. The spin-forming operation captivates the bearing and holds the completed assembly together.

However, a minor change in the zinc diecast piece made it virtually impossible to successfully perform an inward swage on that same area. Engineers at Truth were puzzled because the configuration and dimensions of the area to be cold formed had not been changed.

They discovered that in the diecasting process, an added detail in the cast piece caused an alteration in the flow of the zinc material. This resulted in micro-sized air pockets and a more porous material. The rotating action of the spin rollers and the resulting forces caused the zinc material to fracture, resulting in a weaker joint.

Truth manufacturing engineer Tom Raetz told Dan Baumann, president of Bracker Corp, about the problem, which was caused by failure to properly swage the top edge of the neck. Some sample parts were sent to Bracker, manufacturers of radial forming machines. Bracker engineers in Pittsburgh, working in conjunction with Truth engineers, developed some special form tools that were able to produce parts that met all assembly specifications. These specifications included a very important pull-out test, plus friction-free rotation action in the worm gear cranking mechanism.

The newly designed pieces were not adversely affected when subjected to the patented Bracker radial forming process. A comparison of pull-out test results indicated that the unique radial tool motion actually compacted the material and prevented propagation of cracks along grain boundaries, resulting in improved tensile strength.

Structural benefits

Radial forming offers a simple, low-cost method of forming, assembling, and fastening a wide range of metallic and nonmetallic materials. The special kneading motion of radial forming produces joints, flares, rivet heads, and a wide range of other shapes by spreading the material from the center outward. A patented cycloidal movement guides the forming tool through an eleven-point rosette pattern to achieve a uniform spread of the material.

Tooling lasts longer because nonrotating forming tools operate with low pressure and produce no torque and minimal friction between the peening tool and the material. Minimal to nonexistent sideloads allow the radial forming system to operate with simple, low-cost support fixtures and eliminate the need to clamp-fixture parts. The peen firmly and quietly produces the desired shape with consistent accuracy from part to part. To prevent galling, the operator occasionally applies some grease to the area where the tool makes contact.

Tooling up at Truth

Since the successful implementation of the first RN-280 Bracker riveter in 1981, Truth has acquired 11 additional modular units. For their manual just-in-time work cells, Truth is using about 20 RN-280 benchtop Radial riveters.

Most machines are half-inch size, single spindle units, with a few quarter-inch machines. On each of these machines, the riveting forces are generated via compressed air, with forces that usually are only from 15% to 25% of what a vertical press would require. This light touch approach in the radial cold-forming of metals, diecast materials (zinc and aluminum), and thermoplastics makes it possible to use simple fixturing and to incorporate modular units into nonsynchronous palletized assembly systems.

According to Truth manufacturing engineers Tom Raetz and Jim Seaser, the initially purchased machine is still operating without a hitch after having performed for 15 to 20 shifts per week since 1981. Ken Best, manufacturing engineering manager, said that only once was a toolholder broken, and that was because of a wreck on the index system. Damage was only incurred on the toolholders, and no other parts needed to be replaced. Recently, Truth acquired one- and two-position peening heads, mounted upside down and incorporated into a fully automated assembly system. The multihead forms two different diameter heads that are situated on two different elevations. Typical machine cycle time is 0.8 to 1.7 sec, depending on the application and spindle strokes.

For more information, contact Bracker Corp, P 0 Box 441, Carnegie, PA 15106 or circle 502.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:zinc die-castings manufacture
Publication:Tooling & Production
Date:Feb 1, 1991
Previous Article:Modules build cells.
Next Article:Cold-drawn parts for super magnets.

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