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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.