The Fabricator - Sample Issue

Bending the new breeds
of high-strength steel
New challenges, new tools, new rules
By David Bishop

Since the early 1980s, sheet metal fabricators have, for the most part, followed a pretty basic set of rules to air-bend mild steel. To determine the appropriate die opening to bend 0.5-inch- thick ( 12.7-mm) and thinner materials, you simply multiplied the material thickness times 8. To calculate the resulting inside radius, you either multiplied the width of the die opening times 16 percent, or divided it by 6. And one punch with a 0.031-in. (0.8-mm) tip radius could bend nearly anything from 20- to 12-gauge mild steel.

Bending steel plate pretty much meant following those same set of rules, except that you had to use punches with larger tip radii, and when the material thickness exceeded 0.5 in., you would multiply the material thickness times 10 to determine the correct minimal die opening.

Several new breeds of high-strength steel have arrived that bring with them a host of new opportunities. However, these new breeds also bring with them special challenges not common to bending mild steel, and with them, the need for new tools and new rules for proper bending, because the traditional rules for determining minimum bend radius, minimum punch radius, die opening, bending force, and tooling requirements do not always apply.

Construction-grade HSS is engineered to reduce the weight and increase the lifting capacity in applications such as mobile cranes, truck cranes, and trailers. Other HSSs are engineered to increase the useful life of equipment such as excavator buckets and truck beds.

Heavy-construction equipment may be made of HSSs, such as RAEX^®, that are designed to provide improved resistance to the abrasive wear caused by soil, rock, crushed aggregate, gravel, coal, and sinter. Feeders and funnels, mining equipment, pruning blades, wood processing equipment, shredder blades, and mixing blades may be constructed of this new type of HSS.

Formability Requirements and Special Considerations

So what are the high-strength steels’ unique forming requirements? If you are considering taking on a job that will require you to bend some of these materials, it is advisable to consult with the manufacturer or the technical staff at the steel service center before ordering the first piece of material and to ask the following questions:

• What is the tensile strength?

• What is the yield strength?

•What is the minimum bend radius?

•What is the recommended punch radius?

•What die opening is recommended for the material thickness I am planning to use?

• What effect does grain direction have on forming this material?

So what purposes do these new breeds • What special considerations do I of high-strength steel (HSS) serve? need to take into account?

Today’s new, stronger steels can reduce While all of these questions are part weight, increase part strength, very important, you should pay very extend part life, improve fatigue and close attention to the last one, because crash performance, and resist abrasion. many special considerations for bend-

Some HSSs, such as Domex^®, are ing these materials are not common to designed to reduce the weight of bending mild steel. If these considera-heavy vehicles, trailers, cranes, and tions are ignored, problems could containers. result: