The sheet metal and plate that gets delivered to a metal fabricating company looks flat enough. But looks can be deceiving, and that is especially true with metal. What might seem flat at first is likely to lose its flatness during fabricating.
This makes sense when you consider what happens to the raw material before it’s delivered to the shop. Sheets and plates come from the mills in coils. In metal service centers, these coils are uncoiled, straightened, and finally cut to length. Although the sheets appear to be flat, they still have stress inside. (The stress is evident in the material’s grain.)
When these materials are cut using a thermal power source, such as a laser or plasma cutting machine, the stress is released, and the results are obvious. Parts become uneven. This goes for both thin and thick metal parts.
This also goes for both ferrous and nonferrous parts. The use of the assist gas during cutting actually plays a large part in this process. For example, when oxygen is used for cutting carbon steel, the oxygen reacts with the metal in an exothermic reaction. That introduces a great amount of heat to the cutting zone, which allows the cutting process to occur rapidly. (The byproduct of this chemical reaction is an oxidized edge, which needs to be cleaned to allow for paint adhesion.) The additional heat, however, also releases more stress in the metal. Cutting with nitrogen, an inert gas, reduces the heat input when compared to oxygen, but even with the gentler process, stresses are still being released.
This can become particularly troublesome for the fab shop with new laser cutting technology because some parts may tilt on the slats after being laser-cut and become an obstacle for the cutting head, especially when cutting speeds reach 30 m/min. or more and acceleration of more than 2 m/s² has become the standard. A very expensive piece of fabricating technology runs the risk of being wrecked by an uneven part on the cutting bed.
Any blanking process is able to release stress first introduced during coiling. That stress probably is most evident in the metal’s springback after the cutting or punching is done. (Punching works the material to the point that additional stress is released in material. This can be seen on the newly perforated parts, for instance.)
Combating the Material Stresses
What are metal fabricators to do to combat the stresses introduced during coiling and released after the parts have been cut or punched? This is where a part leveling machine can help. It can deliver flat parts for applications in which it is absolutely necessary for downstream fabricating processes to receive leveled parts to help ensure higher productivity and fewer rejects during bending and welding.
A part leveling machine delivers flatness through a series of rollers that apply pressure to the sheet metal or plate part. The rollers work the material as it makes its way through the machine. The intensity of the pressure applied to the material reduces and eventually eliminates the stresses that are introduced at the metal service center.
Read more: The importance of part leveling in metal fabrication