TPT November 2008

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127 November 2008 ›
Without boost (collet will release the tube during the last bend):
When bending without boost, the pressure die length is not a
consideration. As seen in figure 6, the pressure die can be ‘backed’
out of the way while the tube is positioned for the last bend. As
the tube is positioned, the wiper die becomes the only point of
interference. Once the tube is in position and clamped, the collet is
retracted and the pressure die is advanced.
• WL = Wiper die length
• CD = Collet depth
• SLx = Straight length (where x is the last straight)
• CF = Clearance factor (5mm)
• ALy = Length along the arc (where y is the last bend)
• LL = Limiter length (distance from tangent at which the collet
housing will encounter interference)
Arc length formula:
ALy = (Π * CLR / 180 * degree of last bend)
Limiter length formula:
LL = WL (Pressure die length is not considered)
Collet stock formula:
LL + CF + CD – SLx – ALy
Using the sample data:
• LL = 100mm
• CD = 30.15mm
• SLx = 48.45mm
• ALy = (Π * CLR / 180 * 50.79) = 56.29
Collet Stock = LL + CF + CD – SLx– ALy
Collet Stock = 100 + 5 + 30.15 – 48.45 – 56.29
Collet stock without boost = 30.41mm
Note: If the calculated Collet Stock is a negative number and the last
straight is less than 2D, then only add enough material to make the
last straight 2D. If the calculated collet stock is a negative number
and the last straight is greater or equal to 2D, then no additional
collet stock material is required.
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Theoretical tube length
The theoretical tube length is the sum of the three main components:
clamping stock, component(s) stock, and collet stock:
Theoretical tube length formula:
Clamping stock + Component(s) stock + Collet stock
From the sample data:
Theoretical tube length (with boost) = 96.63 + 509.27 + 106.41
Theoretical tube length (with boost) = 712.31mm
Theoretical tube length (without boost) = 96.63 + 509.27 + 30.41
Theoretical tube length (with boost) = 636.31mm
Conclusion
As process consultants, AddisonMckee is often asked to advise
clients on the amount of material required to bend a component or
series of components. To aid in a smooth ramp-up to production,
AddisonMckee typically calculates the numbers in accordance
with a ‘play-safe’ policy. It is vital that a client is not left with twenty
bundles of tubes that are an inch too short.
However, it is often the case that the initial tube length is accepted
and never re-evaluated. In these circumstances, the opportunities
for efficiency improvements are tangible and easily achievable. For
this reason, it is essential that material length and potential wastage
is properly observed and evaluated. This approach holds the key
to efficiency improvements and possibly the success or failure of a
business.
 Figure 6
Before Bend After Bend