TPT September 2011

A rticle Clamping Stock = (OD * 2) – SL x (without boost) Clamping Stock = (OD * 1.5) - SL x (with boost) Using the sample data: Clamping Stock = (60.3 * 2) – 23.97 (without boost) Clamping Stock = 96.63mm (extra stock added to existing first straight) Money-saving strategy 1 In this example, 120.6mm of total grip stock is a safe starting condition. Once the tube is developed, we will want to shorten the actual grip length by 5mm and re-run the trial. If there is no slippage, shortening by another 5mm can be implemented prior to re-run. This process can then be repeated until slippage occurs, at which point 5mm to 10mm should be added back to the tube. Shortening the tube for bending trials When shortening the tube for bending trials, the tube need not be physically cut in order to shorten it relative to the first straight. Instead, you can simply ‘tell’ the bender that the tube is longer than it really is and the bender will adjust the tube back, effectively shorting the first straight. Once the final length is determined and the tube is physically cut to length, it is then necessary to ‘tell’ the bender the actual length. Minimum requirements for trimming There are also minimum requirements for trimming. If you plan to saw, you will need to allow a minimum of 3mm + the saw blade width. On the other hand, a stab-cut process will need about 15mm + the blade width. Determining component(s) length To determine the length of stock required for the components, you will need to calculate the distance along the centreline path. In addition to the centreline length, any additional material for subsequent end-forming operations will need to be added. In the case of multiple components, this includes material required for splitting or parting operations. • SL x = Straight length (x is the straight number) • ALy = Length along the arc (y is the bend number) • NC = Number of components in tube • CW = Cut width • EF = Material length required for subsequent end-forming Arc Length Formula: AL y = (Π * CLR / 180 * DEGREE OF BEND) Component Length Formula: [(SL 1 + AL 1 + SL 2 + AL 2 + SL 3 … + EF) * NC] + [CW * (NC-1)] Using the sample data: (Assuming 3mm for end-forming and 4.75mm cut width) [(23.97 + 15.27 + 19.61 + 56.29 + 48.45 + 3) * 3] + [4.75 * (3-1)] = 509.27mm Component Length = 509.27mm Determining collet stock length In order to determine collet stock length, several tooling components must be evaluated: pressure die, wiper die and collet.

Determining pressure die length Pressure die calculations are straightforward and are based on the deepest bend. The pressure die is typically set to travel at 1:1 ratio with the perimeter of the bend die. The calculation can be simplified as follows: Pressure die length formula: Π * CLR / 180 * DEEPEST BEND If this were the pressure die’s final length, it would leave a deep impression at the end of the bend. Therefore, it is necessary to add an additional amount to ‘support’ the tube at the end of the bend. This is typically 2D. Pressure die support adder formula: 2 * TUBE DIAMETER Using the sample data: Pressure die length = (Π * CLR / 180 * DEEPEST BEND) + (2 * TUBE DIAMETER) Pressure die length = (3.14 * 63.5 / 180 * 50.79) + (2 * 60.3) = 176.89

Pressure die length =176mm Money-saving strategy 2

If the tube in the collet is gripped through the last bend, the end of the pressure die will normally be the first point of interference the collet housing encounters (see Figure 2). This is especially true if the ‘deepest bend’ is not the last bend. If the pressure die is shortened, then the tube length may likewise be shortened. As stated above, 2D support is normal but in some cases can be reduced to 1.5D.

Figure 2 Determining wiper die length

Because many tooling manufacturers are producing wipers in high volumes, they have standardised lengths. Typically, insertable tips lengths are: • 100mm for tube diameters < 76mm • 127mm for 76 tube diameter • 1.5D for tubes larger than 76mm • Minimum length for specials should be 1.5D Using the sample data:

Wiper Die Length =100mm Money-saving strategy 3

If a wiper is used that is greater than 2D in length, then the wiper die may be the first point of interference (see Figure 3). As with the pressure die, this is a safe number but may not be necessary to produce an acceptable bend.

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S eptember 2011

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