Autodesk Inventor allows flat patterns to be generated by unfolding sheet metal features using: a uniformly applied linear KFactor, a bend table or a custom unfolding equation. Because a bend table can take into account specific (nonlinear) equipment behavior, the piece parts produced from models using bend tables are closer in tolerance to the folded model.
A bend table is a table of bend deductions arranged in rows and columns. Each row specifies a bend angle while each column specifies a bend radius. When unfolding, Autodesk Inventor interpolates between adjacent values in the table if a bend radius or angle does not correspond to a specific entry.
A bend table file can contain multiple bend tables as long as the tables are for different materials or thicknesses. Typically, a bend table file contains a bend table for each sheet thickness that is used. Since aluminum deforms differently than steel, a separate bend table file should be created for each material type.
Autodesk Inventor provides an integrated editor for creating and editing bend tables. You can also edit bend tables with a text editor or spreadsheet. The integrated editor supports using either text files or spreadsheets: text files can be imported while ranges of cells can be pasted in as required. Sample bend table text files and spreadsheets are included in the ...\Autodesk\Inventor [version]\Design Data\Bend Tables directory which can be found under:
Bend tables are saved as an ASCII text file (*.txt).
Create bend tables for sheet metal materials
When you select Bend Table as the unfolding method in the Sheet Metal Styles dialog box, the flat pattern analyzer uses a bend table to create the flat pattern. A bend table contains bend deductions for the specified material thickness at specific bend radii and bend angles. If a specific bend angle or bend radius is not in the table, the flat pattern analyzer interpolates between adjacent cells to determine a value.
Autodesk Inventor provides sample Imperial and metric bend tables as spreadsheet files. The bend deduction values in the sample bend table spreadsheets are based on formula however the true value of a bend table is the ability to provide measured results from your machinery and tooling which may not be uniform across all angles and radii. The supplied samples can be used as a starting point for the creation of tables which reflect your particular requirements.
Include an Excel bend table using the integrated editor
While the integrated editor can be used to create a bend table within an unfold rule definition most often you use all or part of an existing spreadsheet.

.
In the Style and Standard Editor dialog box, click the expand/collapse “+” to the left of the Sheet Metal Unfold Rule entry to display the list of existing unfold rules.Set up an externally stored bend table file using Excel
Using the sample bend table, you specify units of measure, and tolerances.
Save As, give the spreadsheet a new name, and click OK.Edit an externally stored bend table using Excel
Use a bend table file that was set up with your units of measure and tolerances to create a bend table for each material thickness.
To begin, browse to the bend table *.xls file and double-click to open.
Save As, select .txt file type, and then click OK.Import bend tables previously saved as *.txt
Releases of Autodesk Inventor before R2010 required bend tables to edit and saved as ASCII text files (*.txt). These files can be imported and saved as an unfold rule by following these steps:

.The bend table that was previously saved as text is imported to the new named style. You can make any additional edits using the integrated bend table editor.
Specifies the length correction value for a specified material thickness at specific radii and bend angles for the flat pattern analyzer. Autodesk Inventor provides a sample bend table in a spreadsheet. You can customize the sample spreadsheet by copying and editing tables.
You can have multiple bend tables for different materials or material thicknesses in one file.
| Access: | |
|---|---|
| Browse to the Autodesk\Inventor [version]\Design Data\Bend Tables folder. Double-click a bend table. | |
Centimeters are the default units of measure for a bend table file. To use different units, enter one of the following unit types: m, cm, mm, micron, inch, ft, or yd.
The flat pattern analyzer uses three tolerances to determine if a parameter in the part model is valid.
Tolerances are used at the minimum and maximum values only. For example, if a bend table file has the tolerances listed previously and a maximum bend radius value of .05, the analyzer finds a correction value for bend radii up to .06.
Specifies thickness in decimal units. If the thickness parameter in the Sheet Metal Styles box is different from this value, the analyzer uses T1 tolerance to determine if the parameter is valid.
Specifies the bend radius. If the bend radius parameter from the part falls between two bend radii, the analyzer interpolates the correct value.
If the bend radius falls outside the range of values, the analyzer applies the T2 tolerance to determine if the parameter is valid.
Sets the opening angle. If the bend angle parameter from the part falls between two bend radii, the analyzer interpolates the correct value.
If the parameter falls outside the range of values, the analyzer applies the T3 tolerance to determine if the parameter is valid.
Sheet metal bend table example
;
; Use an ASCII file editor to customize the values to your specific conditions. All bend radius columns must contain values.
;
;-----------------------------------------------------------------------
;
; Notations used in tables:
;
; ';' = remark character
;
; '*' = start of a new table
;
; '/' = special character
; U = units of tolerance; thickness; bend radius; and correction values
; m; cm; mm; micron; in; ft; or yd
; S = sheet thickness
; R = bending radii
; A = opening angle
; T1 = Tolerance (+/-) for sheet thickness S (valid for the whole file)
; T2 = tolerance for equal min and max bending radius R
; The T2 tolerance is used at the minimum and maximum
; bending radii R in the tables. For model bend radii that fall
; between two values existing in the table, the resultant
; correction value X is determined by linear interpolation
; using the appropriate x values in the table.
; T3 = tolerance for equal min and max opening angle A
; The T3 tolerance is used at the minimum and maximum
; opening angles A in the tables. For model opening angles
; that fall between two values existing in the table, the
; resulting correction value X is determined by linear
; interpolation using the appropriate X values in the table.
;
;-----------------------------------------------------------------------
;
; The correction value X is applied as follows:
;
; L = A + B - x
;
; (L = unfolded length in flat pattern)
; (A = length of side A (outside measurement of bending zone))
; (B = length of side B (outside measurement of bending zone))
;
;-----------------------------------------------------------------------
;
; Angle A expressed in degrees.
;
;-----------------------------------------------------------------------
;
;
;UNITS for tolerance; thickness; bend radius and correction values
/Ucm
;
;TOLERANCES valid for the whole file
;
/T10.000100
/T20.010000
/T30.010000
;
*** TABLE 1
;
;sheet thickness
/S0.050000
;
| ; | bending radii |
|
|
|
|
| /R |
| 0.500000 | 1.000000 | 1.500000 | 2.000000 |
| ; | opening angle | -------------------- correction value x ------------------- | |||
| /A | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 |
| /A | 5.000000 | 0.029508 | 0.026252 | 0.024359 | 0.023024 |
| /A | 10.000000 | 0.059349 | 0.053004 | 0.049384 | 0.046881 |
| /A | 15.000000 | 0.089863 | 0.080765 | 0.075755 | 0.072419 |
| /A | 20.000000 | 0.121398 | 0.110057 | 0.104168 | 0.100510 |
| /A | 25.000000 | 0.154319 | 0.141429 | 0.135353 | 0.132067 |
| /A | 30.000000 | 0.189014 | 0.175462 | 0.170086 | 0.168059 |
| /A | 35.000000 | 0.225899 | 0.212779 | 0.209200 | 0.209526 |
| /A | 40.000000 | 0.265428 | 0.254063 | 0.253600 | 0.257602 |
| /A | 45.000000 | 0.308101 | 0.300062 | 0.304289 | 0.313537 |
| /A | 50.000000 | 0.354475 | 0.351613 | 0.362380 | 0.378726 |
| /A | 55.000000 | 0.405180 | 0.409660 | 0.429132 | 0.454742 |
| /A | 60.000000 | 0.460932 | 0.475279 | 0.505980 | 0.543377 |