If you want to produce perfect metal parts and assemblies with tight tolerances from sheet metal or heavy plate, you have to be able to rely on the material. This cannot be taken for granted: many parts or sheets contain residual stresses and unevenness and these interfere with efficient further processing.
Residual stresses in sheet metal can arise in different ways: by using thermal cutting processes like laser, flame and plasma cutting, introduces a high amount of heat into the material at the cutting beam. The resulting temperature gradient in the material causes stresses and hardening along the edges. As a result, the metal parts are warped after cutting. During punching, the sheet metal part is deformed by the punching process and existing internal stresses in the material are released.
How to Flatten and Remove Residual Stresses from Sheet Metal and Heavy Plate?
There is only one way to safely eliminate residual stresses: leveling. In a roller leveling machine, the material goes through several successive alternating bends. As a general rule, the more alternating bends, the better the leveling result. Afterwards you can be sure that your sheet metal parts or heavy plate will retain the desired shape and that your downstream processes will be improved dramatically. Welding times and results will be a day and night difference when working with not leveled materials.
As a general rule of thumb, all metals with an elongation at break of at least five percent and a pronounced yield strength are suitable for leveling. If these values are not known, the suitability for leveling can be determined by leveling tests. The rule of thumb is: if it can be bent, it can be leveled. The situation is different for hardened materials: if the material has an elongation at break after the hardening process, it can be assumed that it can be leveled to a certain extent. However, high forces in conjunction with small roller diameters are required to deform such materials. If the material has no elongation at break, there is a risk of cracking or even breakage. In such cases, only leveling tests can show whether leveling is possible and what results can be expected.
What Solutions are there to Level my Sheet Metal and Heavy Plate?
In addition to roller levelers, there are other straightening methods. Straightening with a hammer and flame, for example, is very time-consuming and requires a lot of experience. Some sheet metal workers use simple plate rolls to eliminate flatness deformations. Although this solution brings visible improvements, residual stresses in the material are hardly reduced. The use of manual straightening presses is similarly complex to that of plate rolls. These manual straightening presses are often used for heavy plate and parts with thicknesses over 2.36" (60 mm). With this process, a processing time of up to 20 minutes per part is not uncommon.
In a precision leveler, also known as a roller leveler, rollers bend the sheet metal or heavy plate alternately upwards and downwards until it is straight and stress-free. There are mechanically or servo-hydraulically operated roller levelers. Mechanical roller levelers quickly achieve the desired result for parts with lower flatness requirements. For tighter requirements, the sheet metal parts often have to be leveled several times. Servo-hydraulic roller levelers are designed for tighter flatness requirements. The straightening rollers are optimally supported and have a small gaps between them. The integrated straightening gap control keeps the straightening gap constant during the entire leveling process, even with changing part cross-sections. Even difficult flame-cut parts can be level and stress-free within a few minutes.
