Surface smoothing straightens out the sheets and removes any tension within the material. This is an essential step of the process: if neglected, tensions and irregularities present in the material can disrupt the machining and result in significant time loss.

Many machining processes (e.g. laser cutting) apply extremely high temperatures to the sheet along the cutting line. This can cause stress along the edges of the part and may result in distortion. Internal tensions may also be present within the material and can be released by processes such as punching.