Book Name: Sheetmetal User's Guide - Note this is taken off the web from Pro/Engineer

# Bend Allowance

Bend allowance is a method to calculate the length of flat sheet metal required to make a bend of a specific radius and angle. Bend tables are used for the accurate calculation of this length. Bend tables are used to calculate the bend allowance. When Pro/ENGINEER looks for a value and does not find it in the bend table data, it uses the formula equation.

If you want to use the formula equation only to calculate developed length, but you do not like the formula which is used by Pro/ENGINEER (see Y-factor) then you must create a bend table. The data in the table will be:

## Y-factor

If you do not assign a bend table to the part, Pro/ENGINEER uses the following equation to determine developed length:

L-Developed length.

Y-factor-A part constant defined by the location of the neutral bend line (see the following illustration). The default Y-factor is 0.5.

T-Material thickness.

-Bend angle (in degrees).

#### Developed Length of Material and Y-factor

The default Y-factor value is 0.5. Use the following configuration file option to modify the default system value:

initial_bend_y_factor <value>

If you specify a value other than 0.5 and re-load the configuration file, all new sheet metal parts created in the current session use the new value.

Use the Enter Val menu found under the Bend Allow menu to do the following:

#### How To Modify the Y-factor

Note:

For stretched bends (see the following illustration) is negative, which makes the Y-factor negative too.

## Pro/SHEETMETAL Bend Tables

Bend tables are used to accurately calculate the length of flat material (developed length) required to make a bend of a specific radius and angle.

Bend tables can be read in at any time. Note, however, that once a part is associated with a bend table, its geometry depends on the table data. The bend table information is not stored with the part.

Every time the part is regenerated, it looks up the associated table for appropriate length values. If you modify a bend table, all parts associated with it are updated upon regeneration.

Pro/SHEETMETAL provides the following three bend tables for your use:

Table Name

Material

Y-Factor

K-Factor
TABLE1
Soft Brass and Copper
0.55

0.35

TABLE2
• Hard Brass and Copper
• Soft Steel
• Aluminum

• 0.64

0.41

TABLE3
• Hard Copper
• Bronze
• Cold Rolled Steel
• Spring Steel

• 0.71

0.45

The bend tables provided with Pro/SHEETMETAL are used with permission from Machinery's Handbook, 23rd Edition.

Note:

Bend Tables are applicable only for constant-radius bends. Bends with a varying radius (such as a cone have their developed length calculated using the Y-factor.

Bend tables are normalized for 90° bends. For other than 90° bends, Pro/ENGINEER takes those values and multiplies them by /90, where is the specific bend angle, in degrees.

(The Y-factor value for each table is shown above).

Note:

Since Pro/SHEETMETAL table data in the provided tables is the developed length, no CONVERSION statement is used.

## Types of Bend Tables

You can make a particular Wall or Bend feature reference a different bend table from the bend table or Y-factor associated with the overall part. At the time of creating a Wall or Bend feature, you have two options:

After feature creation, use Redefine Attributes to change its bend table from the Part Table to a Feature Table or vice versa. Note that you cannot change directly from one feature table to another-you have to change to the part table as an intermediate step.

## Creating Bend Tables with Pro/TABLE

You can create your own bend tables to support additional material types or if you have an established bend table standard that uses a different method for calculating the developed length.

pro_sheet_met_dir directory_<pathname>

and give the path to the directory in which they are stored. When you specify a bend table by name, the system looks for it in the current directory and the above directory.

You do not have to insert a bend allowance value (A) in every cell in a bend allowance table. If you leave a particular cell blank, the system calculates a value for the exact combination of R (inside bend radius) and T (material thickness) that it represents by using the formula.

The illustration Developed Length of Material and Y-factorshows variables associated with a bend. The illustration Pro/TABLE Bend Table is an example of a bend table. It shows the layout and data that needs to be provided to Pro/ENGINEER for it to correctly unbend a sheet metal part.

The following table, Bend Table Format shows the Pro/TABLE format. Enter the appropriate data in the columns.

#### Bend Table Format

Column 1

Column 2

Column 3

Column 4

etc.
FORMULA

equation

...

ENDFORMULA

!

CONVERSION

equation

...

START MATERIALS

MATERIAL

...

END MATERIALS

!

TABLE

thickness
bend allow
bend allow
bend allow
...

thickness
...

...

...

...

Comment lines can appear anywhere in a bend table. Each comment line in the table must start with an exclamation point (!).

Note:

Enter the words FORMULA, END FORMULA, CONVERSION, END CONVERSION, START MATERIALS, END MATERIALS and TABLE exactly as shown.

The following illustration shows a Pro/TABLE bend table.

#### Pro/TABLE Bend Table

See Pro/TABLE Editor, in the Pro/ENGINEER Fundamentals manual for more information on using Pro/TABLE.

An explanation of the data for Pro/TABLE follows.

## Formula Equation

Formula is an equation used to calculate the developed length for any radius or thickness values that fall outside the range of the table data. The variables that you can use in the table are:

Follow these rules when you enter the formula equation in a bend table:

For more information on the operators permitted in the equations and conditional statements, see Operators and Functions in the Fundamentals manual.

## Conversion Equation

The conversion equation tells the system how table data (A) is related to the developed length (L). If no conversion equation is defined, the system assumes that table data equals required length, that is L = A. In a case where the table data represents, for example, the bend deduction value (see Example of Determining a Conversion Equation for an example) such an equation might look like:

L = 2*(T + R) - A

Note:

L must never be negative.

The equation above would appear in a table as shown in the illustration Example of Determining a Conversion Equation.

The variables you can use in a conversion equation are:

Follow these rules when you enter the conversion equation in a bend table:

#### Determining a Conversion Equation

Determine and apply the bend table values in the following manner:

The conversion equation shown on the right is based on the graphic on the left.

## Material Data

Enter a list of the materials for which a particular bend table is intended.

Note that material tables contain a parameter Bend Table. If you enter a bend table in a material table and then assign the material to the part, by choosing Assign from the Mater_Mgmt menu, the system checks that the bend table lists the material. If it does not, the system goes ahead and assigns the specified bend table to the part, but it issues a warning message Part Table Bend Error: The part material does not appear in the bend-table material list.

## Table Data

The table data are the bend allowances (A) for specific bend radii and material thickness. The table data and the conversion equation are used together, so make sure that the two together give you the correct results.

Note that the values in the bend tables are independent of the model units. They do not change if you change the model units. For example, you originally create a sheet metal part with the model units set to inches. The sheet metal thickness is 0.25 and the bend radius is 0.5. The system looks up the bend table to find the developed length at the ordinates (0.25, 0.5). If you change the model units to centimeters and keep the model the same size, the thickness of the sheet metal becomes 0.625 and the bend radius 1.270. The system looks up the table to find the developed length at the ordinates (0.625, 1.270).

#### Example of Bend Table Data

Use the Bend Tab menu to do the following:

#### How to Access Pro/TABLE

Use Pro/TABLE to create or edit your own bend table.

[protab]

...or...

#### How To Edit a Bend Table

Within a session, you can only edit bend tables created with the current part or applied to the current part.

#### How To Remove a Bend Table from a Part

The system automatically assigns the previous Y-factor to the part and completely regenerates it so as to update the geometry.

# Bend Order Tables

You can create bend order tables and display them in sheet metal drawings to document the order and dimensions of bend features. Bend order tables can be updated by reviewing the bend sequence. When a bend order table is stored, the file name is <modelname>.bot. (See Drawings for placing a bend order table in a drawing.)

Note:

You cannot create or edit a bend order table on a completely unfolded model.

Use the Bend Order menu found under the Smt Setup menu to do the following:

Use the Show/Edit menu to do the following:

## Displaying a Bend Order Table

To write the bend order table to a file and display it on the screen, choose Info from the Bend Order menu. In the bend order table, a bend's direction is considered to be in when it is less than 180° (i.e. acute or obtuse) on the green side. It is considered to be out when it is greater than 180° (i.e. oblique) on the green side. A typical bend order table is shown below.

This bend order table is based on the completed part below.

The bend sequences for the part are shown below.

# Fixed Geometry

When you are unbending or bending back the part, the system always needs to know which surface or edge is to remain fixed. If you select a surface or edge through the Fixed Geom menu, that geometry is used as the default from then on. If you create an Unbend or Bend Back feature after that, the Feature Window immediately shows that the fixed geometry is defined and you are not asked to select the edge or surface that is to remain fixed.

#### How To Access the Default Fixed Geometry

When you are creating any kind of feature that contains a bend, the system needs to know the bend radius. Often times, you want to use a default value that might be a function of the material, the material thickness and so on.