TPT November 2008

ovember

2008

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Efficiency improvements: 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.

Determining collet depth

When determining collet depth stock, several factors must be

considered:

• Rotational torque from tube

• 0.5D minimum

• Bender manufacturer’s standards

Again, the idea is to reduce the amount of tube needed to

sufficiently hold the tube during the bending process. For the

sample calculations, we will use the 0.5D minimum.

Collet depth formula

Tube OD * 0.5

Using the sample data

Collet depth = 60.3 * 0.5 = 30.15

Collet depth = 30.15mm

Collet stock length

Once all the tooling lengths are determined, it is possible to

calculate the additional material need for the collet end. At this point

it is necessary to decide whether or not boost will be used.

With boost

(collet will hold tube during the entire bending cycle):

• PLt = Pressure die length (where t is the total length)

• PLr = Pressure die length (where r is the remaining length from

tangent after the last bend is made) (see figure 4)

• 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 = (

* CLR / 180 * degree of last bend)

Pressure die length remaining formula

PLr = PLt - ALy

Limiter length formula

LL = WL or PLr (whichever is greater)

Collet stock length formula

LL + CF + CD – SLx

Using the sample data

• WL =100mm

• PLt = 176mm

• SLx = 48.45mm

• CD = 30.15mm

• ALy = (

* CLR / 180 * 50.79) = 56.29

• PLr = 176 – 56.29 = 119.71

• LL = 119.71 (PLr is greater than WL)

Collet Stock = LL + CF + CD – SLx

Collet Stock = 119.71 + 5 + 30.15 – 48.45

Collet stock with boost = 106.41mm

Note: If the calculated collet stock is a negative number then no

additional collet stock material is required.

Efficiency improvements: strategy 4

For part configurations, where the deepest bend is not the last

bend, the pressure die is typically extended past the wiper as the

bend cycle completes (see figure 4). When this situation occurs, a

‘split pressure die’ should be considered. The two halves will act as

one die until the last bend.

Before the last bend is position, the rear

pressure is lifted out of the way, allowing the

collet housing to approach further towards

tangent (see figure 5).



Figure 3



Figure 4



Figure 5

Interference point