What Is Sheet Metal Setback?

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What Is Sheet Metal Setback?

Before understanding the sheet metal setback, we need to know the definition of the mold line and bend line.

The bend line refers to the straight line on the bend plates on both sides.

It is a straight line at the intersection of the bend area and the flange edge.

The mold line refers to the straight line at the intersection of the outer surfaces of two bent flanges.

The mold line is divided into the outside mold line and the inside mold line.

In this case, the setback refers to the distance from any bend line to the mold line.

It can also be said to be the difference between the mold line length and the flange length.

In a 90° bend, the setback value is equal to the bend radius plus the thickness of the sheet metal.

When we know the setback size, we can determine the bending tangent position of the workpiece.

The setback is a very important part of workpiece design.

If the workpiece needs to be bent several times, the setback shall be subtracted for each bend.

We know that the bend allowance and bend deduction depend on the change in the value of the K factor.

However, the setback will not change due to the change in the K factor.

Setback Calculation and Formula

The setback is divided into the inside setback and outside setback. The factors affecting setback are bend angle and radius.

The inside setback is the distance from the tangent point of the inside radius to the vertex of the inside mold line.

If the bend angle and radius change, the bend line moves down and the vertex moves as well.

The value of the outside setback is the distance from the tangent point of the radius to the outside bend vertex of the flange.

The bend allowance can be obtained by knowing the values of outside setback and bend deduction.

The value of the bend deduction plus the bend allowance is equal to two times of outside setback.

BA(Bend Allowance)=2OSSB-BD(Bend Deduction)

The outside setback can be calculated by the following formula

Outside Setback(OSSB)=Tan(A/2) × (T+R)

Where:

T is the sheet thickness, A is the bend angle, and R is the inside bend radius

When the bend angle is 90 °, the setback value is equal to the bend radius plus the sheet thickness.

When the bend angle is less than 90 °, the complementary angle is usually used.

When the bend angle is greater than 90 °, the included angle or complementary angle is usually used.

Conclusion

This blog introduces the definition of the setback in sheet metal bending, the calculation method, and some related terms.

The setback is an important part of the workpiece design, which is closely related to the K factor, bend allowance, bend deduction, and other parameters.

However, if the bend angle is close to 180 °, the values of the inside setback and outside setback need not be considered.

Because the setback value is close to infinity, the bend is also very close to the plane.

ADH is committed to the design and production of sheet metal machines, such as press brakes, laser cutting machines, etc.

If you need to know the product information, you can contact our business personnel.

FAQs

What Is the Sheet Metal Bend Radius?

The bend radius refers to the distance from the bend axis to the inner surface of the sheet. Generally, it refers to the inner radius.

The value of the outside radius is equal to the sum of the inner radius and the sheet metal thickness.

The smaller the radius, the greater the tension and compression of the material.

The characteristics of the metal material, such as tensile strength, ductility, thickness, and the opening size of the die, will determine the size of the radius.

Generally speaking, the larger the die opening size is, the larger the radius is.

Bend Allowance Chart

Bend Deduction Chart

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