TPT September 2011

A rticle

Forming tubes and strategies to minimise waste By Phillip Aspinall, general manager, AddisonMckee

• Component(s) length - the developed length along the centreline of the component, including material needed for subsequent end-forming operations and, if there are multiple components being bent in one tube, material required for parting. • Collet stock – the extra material needed to sufficiently grip the tube in order to rotate and position for bending.

GLOBAL leader in the design, manufacture and supply of the world’s finest tube bending and endforming technologies, AddisonMckee of Lancashire, UK is also gaining a global reputation for forming unique strategies to deal with the bane of the tube former’s life: ‘off-fall’ or, more prosaically, unusable material or waste. In a world in which budgets grow ever tighter while global steel prices continue to soar, the issue of waste is increasingly being seen as one of the industry’s most pressing problems and, alongside accelerating manufacturing times, negating waste has become one of AddisonMckee’s principal preoccupations in the design and manufacture of its world-leading tube bending solutions. So, while the most obvious bugbear for anyone involved in the tube bending process will be perishables, such as wiper dies, mandrels and lubricants, a peek into the scrap bin sitting beside the tube trim machine in any tube forming facility will quickly establish where the biggest problem lies, namely in bending ‘off-fall’. Of course it is impossible to eliminate ‘off fall’ altogether. However, there are ways and means to minimise the amount of ‘off fall’ incurred in bending and make significant cost savings in the process. And AddisonMckee is at the very forefront of developing cost-saving strategies to minimise material waste. Making theoretical tube calculations There are three main components that must be considered when calculating the length of material needed to produce a bent part (see Figure 1). These components are: • Clamping stock – the extra material needed to sufficiently grip and bend the first bend of the component.

Examining sample figures, based upon tube centreline data of XYZ, YBC

60.3 diameter x 1.75mm wall, 409SS

X

Y

Z CLR Y

B C

150.70 67.60 -7.45 130.40 44.50 0.00 63.50 94.10 0.00 0.00 63.50

23.97 19.61 48.45

13.78 50.79

-98.62

15.50 0.00 0.00

0.00

Determining clamping stock When determining clamping stock, several factors must first be considered: • Will the bender have boost capabilities? • Does the product require a square end? • Cosmetic details (grip type – saw tooth, carbide spray) • Will the extra clamping stock be removed with a saw or stab-cut type operation? Where a bender is equipped with boost and it is intended to use the minimum grip length of 1D, the end of the tube will be out of square. A good rule of thumb, therefore, is the first straight must be at least 1.5D before the end of the tube is not pulled out of square by the bending process. If boost is not used, the first straight should be at least 2D. Looking at the sample data, we see that the first straight is 23.97mm. This is a 0.40D straight (23.97/60.3). Assuming the bender used does not have boost capabilities, we will need to add enough extra stock to increase the first straight to 2D. Clamping stock formula: • OD = Tube outside diameter • SLx = Straight length (where x is the first straight)

Figure 1

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S eptember 2011

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