Sheet metal parts are defined by their folded or functional state, but are fabricated from a flat sheet. The bends that are unfolded to form the flat pattern deform the material within the bending zone. The amount of deformation depends on some variables. Transforming the folded model to the flattened state requires accounting for this deformation using one of three methods:

a linear approximation using a defined KFactor
measured values captured in a bend table for specific materials, bend angle values and tooling
custom equations that provide uniform deformation within specified angular bounding conditions

Use custom equations to specify exactly how you want to account for the flattening of the bend zones within your folded sheet metal part models. These custom equations are defined within a named unfold rule that is defined using the Style and Standard Editor dialog box.

The equation types for solving the flattened deformation are further described in the following sections.

Bend Compensation Type

The bend compensation equation allows you to determine the total developed length using the equation:

where:

	is the total developed length.
	is the length from the first detail face to the virtual sharp.
	is the length from the second detail face to the virtual sharp.
	is the result of the bend allowance calculation.

Inventor calculates a bending allowance using the following equations. For angular cases:

the equation used is:

where:

	is the bend angle.
	is the bend allowance length.
	is the bend plate inner radius.
	is the sheet thickness.
	is the result of the bend allowance calculation.

Expanding the original equation to include the bend allowance calculation results in:

For angular cases:

the following equation used is:

Expanding the original equation to include the bend allowance calculation results in:

Once the bend allowance has been determined the KFactor can be derived using:

Bend Deduction Type

The bend deduction equation allows you to determine the total developed length using the equation:

where:

	is the total developed length.
	is the length from the first detail face to the virtual sharp.
	is the length from the second detail face to the virtual sharp.
	is the result of the bend allowance calculation.

The bend deduction equation provides a calculation method which can be thought of as the direct opposite of the bend compensation method.

For bend deductions, Inventor calculates a bending allowance using the following equations. For angular cases:

the equation used is:

where:

	is the bend angle.
	is the bend allowance length.
	is the bend plate inner radius.
	is the sheet thickness.
	is the result of the bend allowance calculation.

For angular cases:

The equation used is:

Bend Allowance Type

The bend allowance equation allows you to determine the total developed length using the equation:

where:

	is the total developed length.
	is the length of the first bend plate.
	is the length of the second bend plate.
	is the result of the bend allowance calculation.

A defined equation is supplied to solve for the bend allowance directly. The KFactor can be derived from the following equation:

KFactor Type

Determining the total developed length using the KFactor method uses the equation:

where:

	is the total developed length.
	is the length of the first bend plate.
	is the length of the second bend plate.
	is the result of the bend allowance calculation.

The bend allowance is calculated using the following equation:

Procedures

Edit custom unfold equations

While editing a named unfold rule, four types of custom equations can be defined using the Equation Editor. The variable defining the left side of the equation is determined by the equation type selected on the Style and Standard Editor dialog box.

On the Style and Standard Editor dialog box, double-click in the Custom Equation cell located to the left of the bounding condition for which you want to define a custom equation. The Equation Edit dialog box is displayed.
Using a combination of keystrokes (parentheses, mathematical operators, numeric constants, trigonometric functions) and the character insertion keys on the Equation Edit dialog box, enter the equation which defines the variable shown outside of the equation entry field.
When the equation is complete, click OK to accept the equation and close the dialog box. Optionally, click Cancel to close the dialog box without defining an equation.

NoteCharacter insertion keys on the Equation Edit dialog box provide single-click insert ability for: angle, radius, thickness, and Pi.

Edit custom unfold equation bounding conditions

Custom unfold equations are defined for ranges of angles, radii, or thicknesses. These ranges are defined by specifying bounding conditions using the Bounding Edit dialog box.

On the Style and Standard Editor dialog box, double-click in the Bounding Condition cell located to the right of the custom equation for which you want to define a bounding condition. The Bounding Edit dialog box is displayed.
Select the equality operators and range type using the drop-down selections in the upper row of the Bounding Edit dialog box.
Enter values that define the bounding condition limits in the fields on either side of the range definition shown in the center of the lower row on the Bounding Edit dialog box.
When the equation is complete, click OK to accept the equation and close the dialog box. Optionally, click Cancel to close the dialog box without defining an equation.

References

Sheet metal custom unfold equation edit dialog box

Allows edit of a custom unfold equation associated with a sheet metal unfold rule.

Access:
	When the Unfold Method selected on the Style and Standard dialog box is Custom Equation, double-click a Custom Equation cell on the dialog box.

	Inserts the measured angle variable into a custom unfold equation.
	Inserts the measured inner radius variable into a custom unfold equation.
	Inserts the measured thickness variable into a custom unfold equation.
	Inserts the mathematical value of Pi into a custom unfold equation.
Variable =	Defines the variable type for which the custom equation solves. The variable type is defined by the Equation Type selected on the Style and Standard Editor dialog box before opening the Equation Editor dialog box. To change the variable type click Cancel and select the correct Equation Type on the Style and Standard Editor dialog box.
Equation Entry Field	Edit field accepts keyboard entry of parentheses, mathematical operators, trigonometric functions, and character command button clicks to define a custom unfold equation.
Help	Open this page.
OK	Accept the custom equation and close the dialog box.
Cancel	Discard any edits to the custom equation and close the dialog box.

Sheet metal custom unfold equation bounding conditions edit dialog box

Allows edit of the bounding condition associated with a specific custom unfold equation.

Access:
	When the Unfold Method selected on the Style and Standard dialog box is Custom Equation, double-click a Bounding Condition cell on the dialog box.

Top Row

	Lower Equality Operator	Drop-down selection that includes the equality operators: less than, less than or equal, equal.
	Range Type	Drop-down selection that includes range variables to define: angle, thickness, radius.
	Upper Equality Operator	Drop-down selection that includes the equality operators: less than, less than or equal, equal.

Bottom Row

	Lower Limit	Value entry field to define the lower bounding limit.
	Range Equality	Indicates range type and equalities. Edit using drop-down selections in top row.
	Upper Limit	Value entry field to define the upper bounding limit.

Help	Open this page.
OK	Accept the bounding condition and close the dialog box.
Cancel	Discard any edits to the bounding condition and close the dialog box.

Comments

Comments2

billybTue Sep 25, 2012 4:38 pmIn the second to the last sentence before the Bend Compensation Type section, there are two links listed. Both go to the same topic. Is that an error? Should the links go to different locations or should there be just one link?
Thanks,
billyb
patrick.millerThu Sep 27, 2012 5:12 amHey billyb,

I noticed that not only do they go to the same page, but the link back to this page. The links point to the two procedures on this page. The wiki does not have the functionality to expand topics so the links just open this page again. I've removed the links from the wiki and from the source content for future releases.

Patrick Miller
Autodesk

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