
This section
explains the calculations related to folding/unfolding operations. 

Click SheetMetal Parameters
.
The Sheet Metal Parameters dialog box is displayed. 
The third tab concerns the bend allowance. 







The bend allowance corresponds to
the unfolded bend width.

bend < 90deg 



bend > 90deg 



 L is the total unfolded length
 A and B the dimensioning lengths as
defined on the above figure. They are similar to the DIN definition.




Physically, the neutral fiber
represents the limit between the material compressed area inside the bend
and the extended area outside the bend. Ideally, it is represented by an
arc located inside the thickness and centered on the bend axis. 

The K factor defines the neutral fiber
position:
 W = a * (R + k * T)
where:
 W is the bend allowance
 R the inner bend radius
 T the sheet metal thickness
 a the inner bend angle in
radians.
If b is the opening bend
angle in degrees:
 a = p *
(180  b) / 180



When you define the sheet metal parameters, a
literal feature defines the default K Factor and a formula is applied to
implement the DIN standard. This standard is defined for
thin steel parts. Therefore the K Factor value ranges between 0 and 0.5. 

The DIN definition for the K factor slightly
differs.
 W = a * (R + k' * T/2)
 Therefore k' = 2 * k and ranges from 0 to 1.


This formula can be deactivated or modified by
rightclicking in the K factor field and choosing an option from the
contextual menu. It can be reactivated by clicking the Apply DIN button.
Moreover, the limit values can also be modified. 

When a bend is created, its own K Factor
literal is created.
Two cases may then occur:
 If the Sheet Metal K Factor has an activated formula using the
default bend radius as input parameter, the same formula is activated on
the bend K Factor replacing the default bend radius by the local bend
radius as input.
 In all other cases, a formula "equal to the Sheet Metal K Factor" is
activated on the local bend K Factor.
This formula can also be deactivated or modified.




When the bend is
unfolded, the sheet metal deformation is thus represented by the bend
deduction V, defined by the formula:
 L = A + B + V
 (refer to the previous definitions).
Therefore the bend deduction is related to the K factor using the
following formula:
 V = a * (R + k * T)  2 * (R + T)
* tan ( min(p/2,a)
/ 2)


This formula is used by default. However, it is
possible to define bend tables on the sheet metal parameters. These tables
define samples: thickness, bend radius, open angle, and bend deduction. In
this case, the bend deduction is located in the appropriate bend table,
matching thickness, bend radius, and open angle. If no accurate open angle
is found, an interpolation will be performed. 

When updating the bend, the bend
deduction is first computed using the previously defined rules. Then the
bend allowance is deduced using the following formula:
W = V + 2 * (R + T) * tan ( min(p/2,a)
/ 2)


When the bend deduction is read in the bend
table, the K factor is not used. 
