The mechanical working of the metal during the spinning process provides natural metallurgical benefits, with a refined and strengthened grain structure. The heavy pressures required to produce plastic flow of the metal during spinning cause an orientation of grain parallel to the principle axis, in much the same manner as a forging. Cold working of the metal also increases tensile properties appreciably. According to one test, mild steel with a yield strength of 33,000 psi was improved to 60,000 psi. Integrity of metal is another important advantage. Unlike a casting, a spun part that requires further machining will not be scrapped by a hidden blowhole or inclusion. This same integrity assures a higher degree of reliability on parts that have a structural function. Certain shapes lend themselves more readily to spinning than casting. In particular, those cast shells or forms that have a re-entrant configuration in which a detail tends to come back toward the center making it difficult to remove a core. A spun shell could be made in halves and welded to form a single unit without complex, expensive tooling. A quality weld, possibly further refined by planishing and inspected by Magnaflux, X-ray or another NDT technique, can provide strength and uniformity comparable to the base metal.

With the current stress on conservation of materials, and with constantly rising material and labor costs, spun metal parts offer significant savings. Cast and forged items are usually made in thicker cross section to provide stock for a special contour and to prevent warping, then they are machined down to achieve the desired thickness and contour. The spinning process permits the contour to be formed with little or no added machining, avoiding the need to pay once for the extra metal and then pay again to convert the extra metal into chips.

To prevent warping, a cast part may have to be thicker as the diameter increases. For example, a 20 inch diameter part might be 1/4 inch thick, whereas a 100 inch diameter casting of the same type might have to be 1 inch thick just to hold its shape. The nature of the spinning process avoids this problem, with the result being lower cost and less weight for a spun part - in addition to the usual benefits of grain structure refinements and integrity of metal. Because spinning requires less complicated tooling, which can often be produced on the same equipment used to make the final parts, lead times are usually shorter than for castings or forgings.

History of Metal Spinning
Advantages of Metal Spinning
Spinning/Deep Drawing
Design Suggestions

The text in this primer is printed with permission of the PMA.

metal spinning: spun metal parts

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