Bend tables for sheet metal materials

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:

  • Windows XP: ...\Program Files
  • Vista: Users\Public\Public Documents

Bend tables are saved as an ASCII text file (*.txt).

NoteA bend table for a particular part need only have rows for the angles used within the part. If a part only uses a single bend radius, a bend table only requires a single column. If a part only has 90 degree bends of a single bend radius, there is no benefit in using a bend table versus adjusting the uniformly applied KFactor value. A useful bend table for a particular shop floor machine has a full-range of angles and bend radii. Each cell in such a table requires measured sample pieces to ensure the highest accuracy.

 

Procedures

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.

NoteA column for a specific bend radius must contain values for each specified angle row. Each cell within the table must contain 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.

  1. On the ribbon, click Manage tabStyles and Standards panel Styles Editor.
  2. 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.
  3. Click on the Default rule to serve as the template for the rule you create.
  4. Click New along the top of the right-hand portion of the Style and Standard Editor dialog box.
  5. The New Style Name dialog box appears. Name the new sheet metal unfold rule you are about to create. Enter a descriptive name to replace the supplied Copy of Default in the Name field and click OK.
  6. The New Style Name dialog box is closed and a new sheet metal unfold rule is listed. The new rule is an exact copy of the Default rule. Make edits as described in the following steps before your new unfold rule definition is completed and saved.
  7. Set the method to: Bend Table.
  8. Set the linear units for the bend table.
  9. Using Excel, open the bend table that you want to use.
  10. In Excel, select the range of cells containing the bend angle column and the row of bend radii and all cells for the selected angles and radii. Using CTRL+X, cut these cells to the clipboard.
  11. Within the Autodesk Inventor Style and Standard Editor dialog box, click to add a thickness value and edit the thickness as required.
  12. A table consisting of rows and two columns appears to the right. Position your cursor in the empty cell located in the upper left, right-click and select Paste Table from the context menu. The cells in the integrated editor populate with the data that was cut from Excel.
  13. Click within any cell to edit that cell.
  14. When you have completed making edits to your bend table, click Save (located at the top of the dialog box) to save your edits.
  15. Click Done (located near the lower right corner of the dialog box) when you have completed making edits to your styles and rules.
NoteRows and columns can be added by right-clicking in any cell and selecting Insert Row or Insert Column as required.

Set up an externally stored bend table file using Excel

Using the sample bend table, you specify units of measure, and tolerances.

  1. Browse to the sample bend table spreadsheets in the \Autodesk\Inventor [version]\Design Data\Bend Tables folder (which can be found under \Documents and Settings\All Users\Application Data) and double-click one of the .xls files to open.
  2. Enter units of measure. Scroll to the line that starts with /U and enter units of measure. The default is cm.
  3. Enter tolerances. Scroll to the lines that starts with /T and enter the following:
    • On line /T1, enter the +/- tolerance for sheet thickness.
    • On line /T2, enter the equal minimum and maximum bending radius.
    • On line /T3, enter the tolerance for equal minimum and maximum opening angle.
    NoteTolerances 2 and 3 are used only under special conditions, as noted in the table.
  4. Select FileSave 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.

  1. Enter sheet thickness. Scroll to the line that starts with /S and enter thickness.
  2. Enter bend radii. Scroll to the line that starts with /R and enter radii.
  3. Edit the value of specific bend deductions, as necessary.
    NoteThe bend deduction values provided in the sample spreadsheets are all determined by a conditional equation. To be of value, a bend table should be populated with empirical values determined by measuring sample pieces produced on a specific piece of equipment.
  4. Highlight the table, then press Ctrl+C to copy. Scroll down to an empty area of the spreadsheet and then press Ctrl+V to paste.
  5. Rename the table and reset the material thickness, as needed.
  6. Continue to copy and paste the table, renaming it and setting a new material thickness, as needed.
  7. Select FileSave As, select .txt file type, and then click OK.
NoteIt is important to save the spreadsheet in a text (*.txt) file format. The analyzer uses the text format to calculate bends.

Sample bend table

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:

  1. On the ribbon, click Manage tabStyles and Standards panel Styles Editor.
  2. Click Import located on the lower left side of the dialog box.
  3. From the Import Style Definition dialog box browse to the folder where your bend table text file is located.
  4. Set the Files of type field to: Bend Table Definition (*.txt)
  5. Select the file containing the bend table that you want to import.
  6. Click Open.
  7. Enter a more meaningful name in the field on the New Style Name dialog box.
  8. Click OK.

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.

 

References

Sheet metal bend table

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.

NoteAll columns in the bend table must contain values. For decimal values, use the dot character (".") as a separator, not a comma.
Access:
 

Browse to the Autodesk\Inventor [version]\Design Data\Bend Tables folder. Double-click a bend table.

Units of measure

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.

Tolerances

The flat pattern analyzer uses three tolerances to determine if a parameter in the part model is valid.

  • T1 represents the default sheet metal thickness specified in the Sheet Metal Styles dialog box.
  • T2 determines if a bend radius parameter that is outside the range of bend radii values is valid. If the parameter falls between two bend radii, then the analyzer interpolates to determine the correct value.
  • T3 determines if a bend angle parameter that is outside the range of bend angle values is valid. If the parameter falls between two bend angles, then the analyzer interpolates to determine the correct value.
NoteIf tolerances are not specified in the bend table file, the default values are:
  • /T1 = 0.0001 (thickness)
  • /T2 = 0.01 (radius)
  • /T3 = 0.01 (angle)

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.

Sheet thickness

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.

Bending radii

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.

Opening angle

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.

Sample bend table

 

Sheet metal bend table example

NoteResize the window as needed to see the entire table.

;

; 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