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Shear spinning for the pressroom.

Shear spinning for the pressroom

Multiple-pass spinning is not new. It began with pottery and then came to metalworking some 150 years ago. Most of it is done on machine tools that look like CNC lathes--from a distance.

Close-up, you see that the workpiece is a flat sheet, usually round, and that the tool is a roller. The tool can operate manually or under CNC control. The final product can be a small bowl, a tire rim, a dish antenna.

There is a similar process called flow forming or shear spinning, and it's relatively new. It does the job in just one pass, and thus it's easy to automate. Working in conjunction with stamping presses, it boosts pressroom efficiency.

Shear spinning uses a free-turning roller pressing against a rotating workpiece. In a vertical machine, positive cam action forces the roller downward, pushing the stock against a mandrel to shape the work and reduce stock thickness.

Multiple-spindle flow-forming adds versatility and speed to the technique. BFL Associates, Hillsboro, NH, offers such a machine, called the Spinamatic. The firm also provides tooling, which includes robot-like automated loading and unloading systems. The machine processes 500 to 2000 pcs/hr, combining operations such as beading and flanging in the forming cycle.

Because it thins the stock, shear spinning produces a part with the same diameter as the blank, thus saving material. (Conventional metal spinning usually doesn't thin the stock, so must begin with an oversized workpiece.) Toolchange time is about 2 hr in the Spinamatic, and skill is required only for setup.

BFL's Burton F Lewis believes that shear spinning should be more widely accepted. It's often more economical than other methods. Spun parts usually don't require trimming or other metal-removal operations, not even deburring. Simple parts can go from flat, round blanks to spinning, then final polishing.

In a typical cell, a press blanks out the round workpiece, followed by shear spinning, then perhaps another press operation to punch out holes. Robots and conveyors handle the transport duties between the machines, directed by a programmable logic controller (PLC) in the Spinamatic. The PLC also controls four separate spindles in the machine, which can be individually programmed.

Shear spinning creates a smooth, contoured shape in a single continuous motion that would be almost impossible in conventional presses without expensive multiple-operation tools. Tool cost for the Spinamatic can be as low as $1000, and rarely exceeds $5000. Tooling for similar parts on a press could cost ten times this amount.

In many cases, justification for purchase of a shear-spinning machine relies simply on materials savings. Burt Lewis notes one customer who uses stainless-steel blanks weighing 8 oz to 12 oz. A typical 25% reduction in material usage saves 2 oz to 3 oz per piece, amounting to 200,000 lb to 300,000 lb saved per year. If stainless steel costs $1.50/lb, annual material savings come to $300,000 to $450,000.

Often, the press stamps out preforms, which are not limited to strictly round shapes, but may be square, hexagonal, or irregular--as long as the part is reasonably balanced when gripped and rotated for forming. The use of such preforms, where only the center portion requires shear spinning, makes it possible to produce many parts from much less material--and with lower tool cost--than if done on presses alone.

Finally, compact press units can mount right in the Spinamatic. Parts then go directly from a spin station into the press unit, handled by the built-in unloader. This makes neat work of secondary operations such as piercing, stamping, and notching. For information, circle 374.

PHOTO : Aluminum, steel, and brass parts are 3" to 10" dia in this group.
COPYRIGHT 1992 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Jan 1, 1992
Words:614
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