TPT November 2008

Efficiency improvements: strategy 1 In this example, 120.6mm of total grip stock is a safe starting condition. Once the tube is developed, it will be necessary 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, it is possible to 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. Determining component(s) length To determine the length of stock required for the components, the distance along the centerline path will need to be calculated. In addition to the centerline 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. Minimum requirements for trimming There are also minimum requirements for trimming. If there is a plan to saw, a minimum of 3mm + the saw blade width will be required. On the other hand, a stab-cut process will need about 15mm + the blade width. • SLx = 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 : ALy = ( Π * CLR / 180 * degree of bend) Component length formula : [(SL1 + AL1 + SL2 + AL2 + SL3… + 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 Efficiency improvements: 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.

Interference point

 Figure 2

Determining wiper die length Because many tooling manufacturers are producing wipers in high volumes, they have standardized lengths. Typically, insertable tip 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

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N ovember 2008

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