The termal deformation reducing in sheet metal at manufacturing parts by CNC cutting machines

In various industries for the manufacturing of parts (workpieces) from sheet metal the CNC machines for thermal cutting (laser/plasma/gas cutting) are used. During process of thermal cutting, various deformations of the metal can occur, that cause the distortion of the geometric forms and sizes of the cut parts. These distortions are caused both by the uneven distribution of temperature in the sheet, and by certain geometric characteristics of the cutting process. Geometric characteristics are determined by the set sequence (order) of cutting of figured parts, as well as by selecting the piercing points of sheet material, i.e. the places of inserting the tool into the material. Previously, the authors formulated heuristic geometric rules, that allow reducing the value of geometric deformations of parts produced by the CNC cutting machines. To comply with these rules, users of Computer-Aided Design (CAM) systems that are used to generate NC programs, have to use interactive design methods. One of these rules (so-called "Part Hardness Rule") refers to the selecting the location of points for inserting (piercing) a CNC machine tool into the material. The paper describes a model based on the use of the heat conduction equation, which makes it possible to calculate the temperature of the sheet material at each moment of cutting process. The computational experiments showed that the points, which according to the "Part Hardness Rule" can't be used for piercing, have a higher material temperature than the points that satisfy this rule. In the paper the results of the computational experiments are given. Another rule (socalled "Sheet Hardness Rule"), which also reduces the deformation of the material during thermal cutting, refers to the order of parts cutting from the sheet. A heuristic algorithm that automatically generates the order of cutting parts that satisfy the rules of "Part Hardness" and of "Sheet Hardness" is developed. Developed software allows us to abandon the interactive methods of the NC programs generation for the thermal cutting of figured parts on CNC machines.