Mechanical Technology August 2015

⎪ Local manufacturing and beneficiation ⎪

Tube bender eliminates waste for exercise machines A Unison tube bender with a unique swing-away wiper die that facilitates waste-free bending of short and complex tubular shapes has been chosen by Cybex International, the manufacturer of physical exercise equipment.

U nison has won an order for a custom-designed tube bend- ing machine and special tool- ing from Cybex International, a manufacturer of physical exercise equipment. Incorporating a unique servo- driven wiper die mount, the machine has been specifically designed to enable Cybex to reduce waste material costs by eliminating the need to cut shorter tubular parts to length after bending. Cybex produces a diverse array of physical exercise machines at two large state-of-the-art manufacturing facilities in Medway, Massachusetts and Owatonna, Minnesota. Its unique machines are de- veloped with the help of exercise science principles to be biomechanically correct and generate optimum results with mini- mum stress on the body. Nearly all Cybex exercise equipment is based on high quality tubular steel framework, most of which is produced at the Owatonna plant. The framework is a highly visible part of the brand image and

therefore needs to combine an aesthetic look and feel with structural strength. To achieve this, Cybex constructs frames from three different sizes of robust 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. Cybex currently uses hydraulic tube benders to handle the bulk of its produc- tion needs, together with a single all- electric CNC machine for more complex parts that require multiple bends with different radii. The tube parts range in length from two to 10 ft and involve a diversity of bends – from shallow curves to tight bends with a centre-line radius as small as 4.8 inches. Most parts require bend accuracies of ±1.0˚ or better, to help achieve end-to-end positional toler- ances as tight as 0.03 inches. After bending, the parts are welded,

Cybex will use the Unison tube-bending machine to produce high quality tubular steel framework for a diverse array of physical exercise equipment. cleaned, shot blasted and powder coated. To ensure that the final product is un- blemished, every stage of this process is subject to stringent quality control. Parts with complex bend shapes are produced in small batch sizes – typically of between 12 and 30 – on the compa- ny’s existing CNC bending machine. Like most rotary drawtube benders, this is fitted with a stationary wiper die to help control material flow and prevent tube collapse during tight radius bending. The permanent presence of the 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 overly long tubes and then cut them to length after bending. This has several drawbacks: it is time-consuming – it is much more difficult to cut a formed part than a straight tube – and demands additional processing and quality control stages. It also creates material scrap, which is ex- pensive and at odds with the company’s commitment to environmentally respon- sible manufacturing practices. The custom-bending machine that Unison has designed will bend these complex and short tube shapes without generating cut-off waste. Instead of a stationary wiper die, Unison’s machine uses a unique swing-away tool mount, which – like all motorised axes on the machine – is driven by a software- controlled servomotor. Moving the wiper die away from the pressure die towards 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-inch (100 mm) all-electric CNC tube bender from Unison’s Breeze range. It has also

Unison is supplying Cybex with a custom tube bending machine that will be based on a 4-inch multi-radius Breeze model, with multi-stack tooling, laser spring-back correction and a unique swing-away wiper die.

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Mechanical Technology — August 2015