**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：

L=20-0.4+20-2X0.4+20-0.4=58.4

**Non-grooved bending**

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

L=(20-1xt+k)+(20-2xt+2xk)+(20-1xt+1xk)=(20-1+0.2)+(20-2+2×0.2)+(20-1+0.2)=56.8mm

Note: t is the material thickness and k is the coefficient.

The size of k is related to the material thickness, generally between 0.2 and 0.25. The thicker the material, the larger the k value.

In this case, k is chosen as 0.2.

Table of Contents

**1. Square tube grooving**

**1. Square tube grooving**

As shown in the figure, now to use the groove and bend a 20 × 20mm square tube, the thickness of the plate is 1mm.

The remaining material thickness a of the groove is related to the size of the customer’s right-angle arc after bending, and also to the size of the material thickness t.

Generally speaking, when the material thickness is less than or equal to 1mm, a=0.4mm; when the material thickness is greater than 1mm, a=t/2.

The unfolded length of the illustrated example 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: One end of L1 is grooved off, regardless of the thickness of the material, are deducted 0.2mm

**2. Z-shape grooving**

**2. Z-shape grooving**

The following combination of a Z-shaped grooved and ungrooved is used to calculate the bending unfolding length.

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

So the unfolding length.

L=15-1+20-2×1+15-1=46mm

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

L=(15-2+0.25)+(20-2×2+2×0.25)+(15-2+0.25)=43mm

**3. Multi-bend grooving**

**3. Multi-bend grooving**

The following calculation is presented with an example of a multi-bend workpiece grooved and ungrooved.

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

Unfolded length:

L=(40-0.5)+(30-2×0.5)+(30-2×0.5)+(10-0.5)=107mm；

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

L=(40-3+0.25)+(30-6+2×0.25)+(30-6+2×0.25)+(10-3+0.25)=93.5mm

**4. Reverse bending after grooving**

**4. Reverse bending after grooving**

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

For the reverse bend after grooving as shown in the figure, the length of the unfolding is calculated as

L=(20-2+0.2)+(30-2×2+2×0.2)+(20-2+0.2)=62.8mm