The cutting machines using plasma are at present the most efficient means of preparatory cutting. These machines were developed and are manufactured by the following enterprises of the branch: VNIIAvtogenmash, the "Kislorodmash" Scientific-Produ

Cutting by plasma is based on through-melting along the contour of the part being produced by the plasmotron with a high-energy concentration arc. Therefore, with steel thicknesses of 40-60 mm, which is the predominant thickness for thick sheet steels, cutting by plasma can take place at higher rates than by gas oxygen cutting. The cutting speed for 5-30-mm-thick steel is 3-10 times higher than that of gas cutting. Cutting of 1 m by plasma is 50% cheaper. In contrast to gas oxygen cutting, plasma cutting can be used for cutting carbon steels, as well as aluminum, copper, and other alloy steels and bimetals. This is most important for chemical and petroleum engineering, which is one of the main users of these metals. Cutting of nonferrous metals by plasma is practical within the entire accessible range of thicknesses (at present up to 100-160 mm). With regard to the organization-economic aspect, manual plasma cutting of low-alloy steels is less efficient than gas-plasma cutting, since the electrical equipment required is more complex and costly than that for gas, but cutting by hand at speeds in excess of 1 m/min is difficult. At the same time, high-speed plasma cutting markedly reduces the thermal flux from the edge of the material being cut into its mass. The result is a reduction of structural changes in the zone of the metal near the cut edges. A considerable reduction is al~o observed in the thermal deformation of thin metal, especially in the case of large sheets. The surface roughness of the plasma cuts and the reduction in the dynamic strength of the part surface are better than with oxygen cutting. However, the advantages of speed and quality of plasma cutting can only be fully utilized with mechanically performed cutting processes. The institutes and enterprises of the autogen machinery industry develop and manufacture a variety of machines and accessories for plasma and gas cutting of sheet metals. These machines must be economical in operation and ensure by the accuracy and quality of the blanks being cut that they meet the requirements of their subsequent use. All-Union State Standard (GOST) 14792--80 specifies the accuracy and quality of machine cutting by four indicators: roughness of the cut surface; size of the structural change zone in the metal at the edges; accuracy of the cut edge shape (non-perpendicularity); the dimensional accuracy of the cut blanks. The three first-mentioned indicators characterize the surface quality of the cut and the adjoining metal which results, generally, from the ratio between the cutting activity of the arc and the cutting speed which depends primarily on the parameters of the plasma cutting elements of the machine. The dimensional accuracy of the blanks being cut depends on the design (scheme) of the machine, its control system, and the qualitative level of the cutting process.