Groove Bending Unfolded: Calculating the Unfolded Length

Calculation of the difference between the unfolded length of grooved bending and non-grooved bending.

Calculation of the difference between the unfolded length of grooved bending and non-grooved bending

Grooved bending

For grooved bending, the total length is calculated as:


Non-grooved bending

For non-grooved bending, the total length is calculated as:


Note: “t” represents the material thickness and “k” is the coefficient.

The value of “k” is dependent on the material thickness, usually ranging between 0.2 and 0.25. The value of “k” increases as the material thickness increases.

For this particular case, “k” is selected as 0.2.

1. Square tube grooving

As shown in the figure, a 20 × 20mm square tube with a plate thickness of 1mm needs to be grooved and bent.

Square tube grooving
Square tube grooving

The thickness “a” of the remaining material in the groove is determined by the size of the right-angle arc after bending, as well as the material thickness “t”.

Typically, when the material thickness is less than or equal to 1mm, “a” equals 0.4mm. For materials thicker than 1mm, “a” is equal to “t/2”.

The unfolded length of the example shown is:

L=2×(L1+L2)=2x((Edge length-1xa-0.2)+(Edge length-2xa))=2x((20-1×0.4-0.2)+(20-2×0.4))=77.2mm

Note: For one end of “L1” that is grooved off, 0.2mm is deducted regardless of the material thickness.

2. Z-shape grooving

The bending unfolding length is calculated using the following combination of grooved and ungrooved Z-shapes.

Z-shape grooving

For a 2mm plate, the remaining material thickness of the groove is taken as t/2 = 1mm. If the customer requires a smaller direct arc, a value less than 1mm should be chosen.

Therefore, the unfolding length is:


For a 2 mm-thick plate without groove bending, the factor k is chosen to be 0.25. Therefore, the unfolded length is:


3. Multi-bend grooving

The following calculation presents an example of a workpiece with multiple bends, both grooved and ungrooved.

Multi-bend grooving

Assuming that the customer requires a small rounding of the right angle, for a 3 mm-thick plate, the remaining material thickness is chosen to be 0.5 mm.

Unfolded length:


For a 3 mm-thick plate, the coefficient k is chosen to be 0.25. Therefore, the unfolding length is:


4. Reverse bending after grooving

The method of calculating the unfolding is presented below, using an example of reverse bending after grooving.

Reverse bending after grooving

To calculate the length of unfolding for the reverse bend after grooving shown in the figure, use the following steps:


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Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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