Views:261 Author:zhangyun Publish Time: 2019-03-05 Origin:Site
The use of high strength steel has become so popular in the automotive industry mainly because of their very high strength to weight ratio. However, formability in these materials have become a great challenge, this is because the yield strength is very high in these materials which implies that the springback is very high. This same process make roll forming parts a challenge. However, the efficiency of roll forming machine makes it an ideal process for the production of certain parts when compared to hot stamping. If you aim to roll form high-strength steels, it is crucial to understand how to adjust your equipment so as to get the most appropriate results. It is also crucial for you to consider the steel you are purchasing as well as how the material will affect the process.
With the aid of mild steel, if you bend a part through 45 degrees, it will stay at 45 degrees or spring back perhaps 1 or 2 degrees. However, in steel with high strength, you will have very high springback. This implies that a 45-degree bend can have an overbend which is up to 50 or 60 degrees.
It was also noted by most manufacturers that the distortion occurs at the end of roll formed parts and this is well pronounced on high-strength steel roll formed parts for this same reason.The leading and tailing ends of parts will react differently than the middle of the material. “This is usually more pronounced with high-strength steels, so it is necessary to ‘kill’ the memory of the material by overbending and under-bending it. The strength of the material implies that you need more power, more tonnage and usually the material and tooling costs are generally higher because of the added passes which is involved.
Machine-wise, most companies like to put larger-diameter spacers in backup rolls to keep the column strength steady throughout the shafts with the higher-strength steel. In the roll tooling itself, majority use the shortest possible roll space to minimize spindle deflection. Depending on the size of your spindle, you can get a lot of deflection. If you have a 24-in. roll space and you are running a 10-in.-wide coil through the machine, you may want to choke up the outboard stands to minimize the roll space width so that you avoid spindle flex.”
If the horizontal distance between passes is large, it is recommended to use side rolls to add extra support. As the part exits one pass, it opens up and then go back into the next roll. If the customer has enough side roll stands, the part keeps a better uniform shape by using them. This likewise minimize some of the end flare which are seen on parts but might not be removed completely.
It was also noted that when high-strength material is run and because of the amount of forming being done, the tooling will wear faster in the working areas. It is also recommended to add carbide rolls to the high-wear areas doing the forming so as to increase the tooling life.
Roll forming machine can wear twice as fast when they are used for high-strength steels but with the addition of carbide, they can last up to 50 times longer than conventional, hardened tool steel rolls. However, the use of tight hems in designs for high-strength steels should be discouraged. Hems should be avoided if the material will not allow the amount of elasticity or elongation needed to form the hems.