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New choices in precision parts: cold-drawn profile shapes in larger sizes.

New choices in precision parts: Cold-drawn profile shapes in larger sizes This article describes the benefits of cold drawing, briefly describes the manufacturing process, and presents some examples of larger parts now being made by Rathbone cold draw.

Cold-drawn parts can improve product performance and lower material and production costs compared to conventional manufacturing methods. Until recently, cold drawing has been limited to a size range from 3/32" to 1 1/2". When larger profile parts were produced by cold drawing, close tolerances demanded by users of precision parts generally were not available.

Now, however, our ability to cold draw precision-tolerance parts has been improved by investment in new and larger tooling and production machinery. This allows production of larger precision profile parts while maintaining tight tolerances. Also, proprietary techniques and new equipment handle 50-percent more drawable cross-sectional area.

Dies are made in-house with wire-EDM equipment, which provides quicker turnaround and lower-cost production. Computerized diemaking makes it possible to hold [+ or -]0.002" consistently throughout the size range, even with relatively intricate shapes.

Benefits of cold drawing

The cold-draw process provides important advantages that generally are unobtainable with other production methods such as machining, extrusion, or powder metallurgy. Among them are improved mechanical properties. As shown by analysis of microstructure, cold drawing actually compresses the metal, making it more homogeneous. Increased tensile and yield strengths also are achieved without subsequent heat treatment. Many times, a smaller cross section can be used without loss of wearing quality or strength.

Unlike a hot-extruded rod that varies in density--some areas being hard and others soft--a cold-drawn shape possesses uniformity of hardness throughout the bar or coil. Because of this uniform hardening, gears, pinion rods, and other parts made from cold-drawn materials run smoother and last longer. The hardness and smooth surfaces produced by cold drawing help to ensure longer part life at peak performance and lower replacement costs. In addition, cold drawing eliminates both the ruptured surface that occurs in machining and the irregularity caused by cutter chatter. The smooth, polished surface of the carbide draw die imparts a smooth burnished surface finish to the product.

The metal displaced in the drawing operation goes to increase the length of the bar, unlike cutting or machining methods where scrap is lost. Cold drawing produces a far greater number of usable parts per pound of metal than can be obtained by machining or cutting, resulting in significant cost savings.


Cold-drawn profile shapes are precise enough for use in computers, watches, cameras, eyeglasses, staplers, telephones, typewriters, and other business machines. They are found in locks, valves, motors, capacitors, bearings, household appliances, chain saws, electric razors, and firearms.

Even large equipment such as cranes and hoists, industrial and marine turbines, jet aircraft, helicopters, agricultural equipment, and sluice gates rely on precision shapes, pinions, and gears that started as cold-drawn bars.

The photographs show representative parts between 1 1/2" and 2" that have been produced by cold drawing. Shapes may be pinion and gear profiles, or they may be special sections whose contours have any required shape.

The manufacturing process

Cold drawing consists of production of special engineered formations or profile shapes in metal bars by a combination of precision cold rolling and cold drawing. Starting with a customer blueprint, draw tools (dies) are designed and programmed to be made on computer-controlled wire-EDM equipment using a CAD/CAM system. A sample of the shape is produced and approved by the customer before production begins.

Initially, the basic contour is established by cold rolling a bar or coil. The shape is then refined and reduced to extremely close tolerances by cold drawing. Some shapes require multiple rolling and drawing operations. Each is usually preceded by annealing and followed by inspection. The finished product is shipped as coils or in 10-ft to 12-ft bar lengths, whichever is more convenient for the customer. The customer slices the final part from the bar, and in many cases the part is ready for assembly with no further finishing operations. If preferred, Rathbone can meet customer requirements for burr-free parts on automatic cutoff equipment holding length tolerances as close as [+ or -].002".

Process limitations

Cold draw has some limitations. For instance, it can make only solid shapes. If a hole is required in the finished part, it must be drilled afterwards. Sharp corners are not a problem in cold drawing, but deep, narrow grooves can be. A groove shouldn't be any deeper than half its width unless a generous radius is allowed at the bottom.

PHOTO : A bronze gear for a heavy-duty hoist used in the petro-chemical industry. The process

PHOTO : maintains the 2" OD to tolerances as close as [+ or -]0.001".

PHOTO : An alloy steel firearm component. Overall dimensions are 1.750" x 0.940". Tolerances of

PHOTO : better than [+ or -]0.002" are routinely held.

PHOTO : A 2" x 1" alloy steel section used in industrial pumps. Tight tolerances and smooth

PHOTO : surface finish are critical in this application. Frank Carter, PE President Rathbone Precision Metals Inc Palmer, MA 01069
COPYRIGHT 1989 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Author:Carter, Frank
Publication:Tooling & Production
Date:Aug 1, 1989
Previous Article:Press system mixes automatic and manual operations.
Next Article:Machine-tool thermal compensation.

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