Special Tools Bending High Strength Steel

Special Tools Bending High Strength Steel

With high-strength steels like SSAB made Hardox, Weldox steel, tensile strength over 1000 Mpa, we’ve got to deal with machine deflection, and then we also have to deal with the concentrated load on the machine. With a press brake, your ram is kind of a linear beam. You’re concentrating a load basically on a line. Normally, a typical machine can handle somewhere around a hundred tons per meter. If you have a 3 mmachine, you could put a hundred tons on 3m Max. Everything would be fine. What happens if it takes 1500 tons to bend 3m sheet? It will bring big trouble for press braek main structure and tools.

Most of the press brakes in the world were designed to bend somewhere under that 800Mpa material. Now, we get into the high strength materials. Often we need larger load bearing surfaces or elements; the part of the machine that touches the tooling has to be bigger, stronger, wider, harder. The machine itself doesn’t yield, although it deflects.

The tooling need to be special designed more than press brake itself

You have to increase the load bearing surface.

When you look from the end of a press brake, you might see the thickness of a ram in a larger machine being over 150mm thick. It starts tapering down from there, because the tip of the punch, where we’re bending, we want to concentrate it on a small spot.

When you get into the higher strength materials,  it’s made a little bit flatter. The beams themselves, the upper beam and the lower beam, don’t change very much if at all for bending high strength material, but how the tooling is adapted into the machine is significantly different.

On a typical press brake, the load bearing surface on the top of the punch is maybe around 30mm front to back. Then the punch goes into a punch holder. That punch holder may be 60mm front to back. Then the ram itself might be 150mm front to back.

When you get into high strength materials, the upper portion of the punch, the load bearing portion, is normally larger. Then the punch holder itself, the load bearing surface where it touches the ram, is also made larger.

If you call up any of the press brake tool suppliers and you ask for a typical punch, it will have typical load bearing surfaces. Once you get above that typical press brakes tool, it’s a little bit in the hands of the machine designer, because how the beam is made, and how the punch holder is made for these higher strength applications, comes from the machine designer — how they design the punch holder, and then how they design the punch.

Where the tool fits into the tool holder, it would be larger and wider. It’s normally a custom tool. Once you get into SSAB high tensile strength sheet, the tool is a little bit customized, because all the press brake manufacturers have different size beams. They have different size punch holders. In some cases, the punch holder is machined right into the ram that is not a separate removable element. Instead of having a pyramid that’s stacked up, you have a pyramid that just cut right into the ram.

The press brake upper tool holder now is larger, the upper tool is larger, and so the load bearing surface is larger. Now, the press brake operators are dealing with bigger, heavier elements. Often at the same time, these tools and tool holders are made larger. They’re also made with roller bearings to make it a little bit easier to slide the new tools and the tools out when you’re changing the tools.

If you’re bending a part with a small nose on the parts of tight radius, you’re concentrating all the force into small spot and the material would tend to crack. When we put a large radius on the punch, when we start bending, now we’re wrapping the material around the larger diameter, the radius that distributes the force a little bit more evenly across the material. It also makes the punch heavier.

The same phenomenon we have on the punch, we also have on the die or the bed. If the material gets harder, normally the lower die becomes larger and heavier as well. The die adaptor or the bed adaptor becomes larger with the high strength material.

Some manufactures machine this into the bed, and some make them bolt-on. Even when they’re bolt on, they’re normally not intended to be replaceable or removable. It’s just a way of manufacturing them, which varies by manufacturer. It is a little bit scary for customers trying to spec such a piece of equipment, because if it’s not spec’d right, it’s very expensive or difficult to change later in the field.

Use the correct bending toosl for SSAB High Tensile Strength Sheet Bending

When you’re bending strong material, there are a couple of ways to deal with getting the bend right. The classic system is the operator makes the bend. He checks his angle all the way down. When he find that there’s a variation in the angle, the angle is opened a little bit, he takes a piece of banding, crate banding

That’s a very common method in the high strength industry. What happens when you bend the steel plate, especially with the high strength materials, there are a lot of scales that come off.

The next step-up, the next improvement in the process is some type of an adjustable crowning table that changes the radius of the bed. These do the job very well.

Press brake bending Tools are usually made to order. Probably 95 % of the press brakes in the world are under 400Tons. Most people bending harder steel are in a different way. Then you see machine tonnages between 500 and 1000 tons. Few people have those capabilities. The machines are expensive. The required  tooling is expensive as well. You really don’t see much of the tooling wearing out or being damaged.

A little bit of less expensive alternative in some applications is to take two smaller machines, set them with tandem running mode. Instead of having 1000 ton 12m huge press brake, you’d have two 500 ton 6m cnc press brake, cnc controlled synchronized bending Max 12m sheet metal, especially designed for bending poles&longer channel. This is not necessarily dedicated for high strength material,When you’re bending mild steel, your springback is about 2-3 degrees. Your springback variation is about 0.2 to 0.3 degrees, which is almost immeasurable. In the high strength material, 15-20 degrees is a typical range.

AHYW China Yawei factory can design and manufacture different tonnage large cnc press brakes with special designed bending tooling which suitable all your sheet metal bending applications, email us for further discussion. AHYW Yawei china made sheet metal cutting&bending machine factory&suppliers.