The Fabricator - Sample Issue

bending force requirements (see Figure 2).

•Lubrication of the material is often recommended. As the material flows over the die shoulder radii during bending, lubrication helps to reduce drag, thus reducing the amount of bending force required. It also helps to reduce tooling wear and material surface damage. Lubricants specifically designed for HSS are available.

• Preheating the material often is recommended to reduce the bending force required and to reduce cracking.

CFIGURE 1 Die shoulder radii should be hardened and very smooth to help to reduce drag during forming.

• Always bend the material to the largest radius possible. This will help to reduce material fatigue and the subsequent cracking that may occur on the outside of the bend radius.

• Grind out all surface scratches and all other surface defects, as they may cause cracks.

•Some HSSs require that all bends be created in a single stroke. These materials must not be allowed to spring back during the stroke. It is very important for you to verify whether this is the case with the material you will be forming if your press brake has automatic springback compensation. Also, the yield strength of the material has a tremendous influence on the amount of springback that occurs during bending. The higher the yield strength is, the greater the amount of springback will be. Be sure to check the yield strength of the material with your steel supplier.

•Die shoulder radii should be hardened and very smooth. This will help to reduce drag during forming,

which, in turn, will help to reduce the amount of force required to bend the material (see Figure 1).

• Dies that use hardened rollers on the shoulders significantly reduce

Simply put, HSS requires high-quality tooling that can withstand the great force generated when bending it.

For example, the tip radius on the punch and the shoulder radii on the dies must be hardened and remain intact. The deeper the hardening zone is, the better, because any breach of the hardened area will lead to a rapid deterioration of the working surfaces, which will decrease accuracy and increase tooling costs.

Wear on the die shoulder radii also increases drag on the material as it flows over the shoulder radii. This significantly increases the amount of force required to bend the material.

Angles Allow Overbends. Make sure the tooling you plan to use has an

included angle on both the punch and the die that will provide adequate capacity to overbend the material as necessary to compensate for springback (see lead image). Because HSSs often have high yield strengths, the amount of springback that occurs probably will be greater than the springback that occurs when you bend softer materials such as mild steel and aluminum. If so, your current tooling may not be able to compensate for it.

Heavy Tooling Affects Setup. Setup time is one of the greatest contributors to the cost of bending thick materials in general. This is caused, in part, because handling the large, heavy tooling is difficult. The punches normally have large tip radii and often are composed of a combination of a punch holder and a large-radius insert. The dies normally have large openings and weigh well in excess of 100 pounds, requiring two or more operators and possibly a forklift to load and unload them.

The use of short, modular tooling segments that match properly when installed will make tooling changes faster and safer and, during most setups, will eliminate the need for additional personnel and/or forklifts.