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Tough Tubes

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A high strength steel forming mill from Yoder. Note the progressive forming stations. Image: Formtek Group.

Ever wonder about the legs on a folding chair? How about the exhaust pipe on your car? Tubing is everywhere, but most of us don’t give it a second thought. The technology used to make this important product is quite amazing, however, requiring equipment longer than a football field and more expensive than a mansion on Vancouver Island.

Someone who knows all about tube rolling is Brian Kopack, senior sales engineer at Formtek Inc., Warrensville Heights, OH. The Formtek Group represents a number of metal forming equipment manufacturers, including Cooper Weymouth, Tishken, Hill Engineering, Dahlstrom, Rowe Machinery and the Yoder brand of tube and pipe mills.

Roll forming is a broad topic. It’s used to manufacture everything from bicycle rims and auto bumpers, rain gutters to aircraft fuselage. In fact, almost any shape—angles, channels, S, T, U, V, W and Z-shapes—can be roll formed, and done so quickly and accurately. Tube manufacturing is a small part of the roll forming process (see sidebar page 83).

Kopack explains that tube mills are just another type of roll forming machine, but one with a critical difference: these monstrous systems weld the rolled form shut partway through the manufacturing process, then trim and smooth the weld bead to create a strong, precise and mechanically stable product.

Almost any aluminum, steel or stainless steel, is a candidate for tube making, but as Kopack points out, high strength steel is being called for with increasing frequency. Automakers in particular have their eye on weight reduction, and this means maintaining or in some cases increasing the structural integrity of their products, and doing so with less material.

“The term high strength is relative,” Kopack says. “The generic, low carbon steel tubing that’s been around since the 50s is typically 40,000 to 50,000 psi yield strength material. By comparison, we have ultra high strength, low
alloy (HSLA) steels today that offer yield strengths of 150,000 to 180,000 psi. Those materials form much differently than do commodity grade materials, and may require additional forming passes, different tooling and even modifications to the machine configuration.”

As material becomes stronger, manufacturers can reduce tubing wall thickness with no loss of product strength. This provides for a lighter weight product, and allows manufacturers to cut costs. For example, the ratio of tubing diameter to wall thickness runs between 10:1 up to 50:1 in the “plain Jane” materials mentioned in the chair leg and exhaust pipe examples cited earlier, whereas high performance tubing like that used in a modern automobile could easily be 80:1 or higher.

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