Bend Table in BricsCAD Mechanical Sheet Metal Explained

Quick answer: Bend tables are a more reliable way to express material deformation properties than the K-factor, confirming the mention on this hub’s K-factor page. Physically bend a flat sheet of a given material, measure its length before and after, repeat across different bend angles, radii, and thicknesses, and save those measurements to compute correct unfolded lengths for every part made of that material. In practice, measuring just a 90 degree angle usually suffices, BricsCAD interpolates the rest reliably, though you can add as many angles as you want.

File Format and Structure

Bend tables save as .CSV files, editable in any ASCII text editor like Notepad, though building the table in a spreadsheet (Excel or LibreOffice) and exporting to CSV is more reliable and easier.

Structure rules:

• The first cell must read BricsCAD.
• Version: currently only version 1 is supported.
• AngleType: currently only internal bend angles are supported.
• LengthType: defines what the cell values mean; currently only BendDeductionTangent is supported, bend deduction (BD) measured as the difference between the sum of two flange lengths (to the tangent point on the 3D model) and that same fragment’s length once unfolded, confirming exactly the same Bend Deduction formula covered on this hub’s K-factor page.
• Multiple tables can exist within one header; each table’s primary key is Thickness, with an optional secondary key, DieWidth. Thickness/DieWidth pairs must be unique; without a DieWidth key, only one Thickness value is allowed per table, though multiple separate thickness tables can still exist. When unfolding, the part’s own Thickness and DieWidth must exist in the table, if not found, BricsCAD falls back to the default K-factor policy instead.

How Lookups and Interpolation Work

Once BricsCAD finds a matching table in the CSV, it uses it to unfold the part (T = Thickness, R = Internal Bend Radius, A = Bend Angle):

• T = 1, R = 2, A = 45: both R and A exist directly in the table for that thickness, giving BD = 0.466.
• T = 1, R = 2.5, A = 45: A is found, but R = 2.5 isn’t, so BD interpolates between the R = 2 and R = 3 entries.
• T = 1, R = 2.5, A = 75: neither value is found, so BD calculates from four surrounding cells: (R=2, A=60), (R=3, A=60), (R=2, A=90), and (R=3, A=90).

This interpolation uses a dedicated algorithm rather than simple linear interpolation between adjacent BD values, since that produces results that don’t match real bending behaviour. Not every combination of T, R, and A yields a sensible BD, some would place the neutral surface outside the sheet metal part, or imply a K-factor (derivable from BD) outside the valid [0, 1] range, in which case BricsCAD falls back to the BD implied by the default K-factor instead.

Multiple Tools with DieWidth

If you produce parts with different tools, describe them all in one bend table using the DieWidth parameter. A sample bend table ships in [BricsCAD Installation folder]\Samples\Mechanical\bend_tables (write access to that folder may be restricted, copy the file elsewhere if you need to edit it).

Setting the Bend Table

1. Select the root node in the Mechanical Browser.
2. Select the Bend table field.
3. Click Browse.
4. Select the .CSV file.
5. Double-click it, or click Open.

Updating a Previously Set Bend Table

1. Select the root node in the Mechanical Browser.
2. Select the Bend table field.
3. Click Reload file.

Assigning DieWidth to Specific Bends

If the bend table isn’t assigned to the document, or lacks a DieWidth secondary key, DieWidth can’t be assigned to any bend. To make it available:

1. Prepare the CSV’s DieWidth secondary keys and thickness to match the current part (for a 1 mm thick part with a bend radius of 1, for example, you might vary bend deduction across three sub-tables: no tool specified, DieWidth 20, and DieWidth 30).
2. Assign the bend table to the sheet metal part.
3. New fields appear in the Mechanical Browser; the global setting lets you choose a default DieWidth suitable for the part’s thickness, applied to every bend by default (verify this on an individual bend’s properties by clicking it).
4. Optionally select a specific tool for a given bend by expanding its dropdown.
5. With that selection, unfolding that specific bend uses the matching sub-table (its DieWidth-specific value); every other bend without an explicit DieWidth set falls back to the no-die-width default from the table.

After assigning DieWidth values and saving, they persist with the bends. But the next time you reopen the drawing, you need to click Reload file again before you can assign DieWidth to any additional bend, after that reload, the table’s values become available again. Bend tables can also be varied per solid using a local Sheet Metal Context, confirming the local context concept covered on this hub’s Mechanical Browser for Sheet Metal page.

Frequently Asked Questions

What happens if a part’s exact Thickness and DieWidth combination isn’t found in the assigned bend table? BricsCAD falls back to the default K-factor policy for that unfolding instead.

Do I need to measure every possible bend angle to build a usable bend table? No, measuring just 90 degrees is usually enough, BricsCAD reliably interpolates other angles from it.

Why would I need to reload a bend table after reopening a drawing? To assign DieWidth to any additional bend, you need to click Reload file first, previously assigned DieWidth values on existing bends persist without this, but new assignments require the reload.

Can I use a different bend table for different solids within the same model? Yes, by defining a local Sheet Metal Context for each solid individually.