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Custom-made tube bender handles challenging shapes, eliminates scrap

Bending process relies on swing-away wiper die

Cybex designs have an abundance of bent tubing. To manufacture its products efficiently, it invested in a bending machine that helps the company eliminate scrap on short bent lengths.

It has been almost four decades since Jim Fixx wrote The Complete Book of Running, which many credit with starting a fitness revolution in the U.S., and it’s still going strong. According to data gathered by Fitness USA, a nonprofit organization, the number of people who finished a running event more than doubled from 2005 to 2013. Fitness is more than running, of course. In 2014 people in the U.S. spent $63.5 billion on sporting equipment, an increase of 32 percent over the previous decade. The International Health, Racquet & Sportsclub Association reports that 54.1 million people in the U.S. belonged to a health club in 2014, up from 41.3 million a decade earlier.

This is good news for sports equipment manufacturers such as Cybex International. The company produces a diverse array of physical exercise machines at its state-of-the-art manufacturing facilities in Medway, Mass. and Owatonna, Minn. Its machine designs comply with exercise science principles and are intended to be biomechanically correct and generate optimal results with minimum stress on the body.

Having a large and growing market doesn’t mean that Cybex can take it easy. Just like the many Americans who strive to better themselves by working out or running, Cybex tries to improve its manufacturing processes.

Short Lengths, Odd Shapes

Nearly every Cybex exercise machine is based on a tubular steel framework, most of which is produced at the Owatonna plant. The frame is a highly visible part of the brand image and therefore needs to combine an aesthetic look along with structural strength. To achieve this, Cybex constructs frames from three sizes of 11-gauge steel tubing, using a variety of proprietary tube profiles, including flat-sided oval and compressed octagonal shapes. Producing smooth, wrinkle-free bends in these types of tubular profile is technically challenging and demands considerable expertise.

The tubular components range in length from 2 to 10 ft. and involve various bends, from shallow curves to tight bends with a centerline radius as small as 4.8 in. Most parts require bend accuracies of ± 1 degree or tighter to help achieve end-to-end positional tolerances as tight as 0.03 in. After bending, the parts are welded, cleaned, shotblasted, and powder-coated. To ensure that the final product is unblemished, the company subjects every stage of this process to stringent quality control checks.

That’s all very straightforward, but a persistent problem concerning short-length tubular components was an ongoing headache for the company.

Shortening Bent Lengths

The company’s conventional CNC bending machine, like most rotary draw tube benders, is fitted with a stationary wiper die to help control material flow and prevent tube collapse during tight-radius bending. The presence of this permanent die imposes a limit on the minimum length of tube that can be bent. This means that to produce short parts, Cybex has to use longer lengths of tube than necessary and cut them to length after bending. This has several drawbacks: It is time-consuming to cut a formed part rather than a straight part; it demands additional processing and quality control stages; and it creates scrap, which is expensive and at odds with the company’s commitment to environmentally responsible manufacturing practices.

A custom machine was designed by Unison to bend these complex and short tube shapes without generating waste. Instead of a stationary wiper die, this machine uses a swing-away tool mount that, like all motorized axes on the machine, is driven by a software-controlled servomotor. Moving the wiper die away from the pressure die near the end of the bend cycle allows the tube feed mechanism to be driven closer to the rotary bending head, facilitating fully automated production of short parts.

The new machine is based on a 4-in. all-electric CNC tube bender from Unison’s Breeze series. It has been configured with multiradius bending capability and stacked tooling to allow complex parts to be produced in a single, uninterrupted machine cycle. The precision of the new machine also is aided by a laser-based system that automatically measures and adjusts bend angles to compensate for tube springback after bending.

The all-electric design provides overlapping benefits such as fast and repeatable, software-controlled setups; improved bend accuracy; and decreased power consumption.

About the Author
FMA Communications Inc.

Eric Lundin

2135 Point Blvd

Elgin, IL 60123

815-227-8262

Eric Lundin worked on The Tube & Pipe Journal from 2000 to 2022.