DETERMINATION OF TECHNOLOGICAL FACTOR EFFECT UPON INTENSIFICATION OF PNEUMATIC IMPACT EXTRUSION AND ACCURACY OF EXTRUDED PARTS

Abstract

This work is devoted to experimental studies to determine the influence of technological factors on the process of intensification of pneumatic shock punching by drawing and accuracy of stamped products. The process of pneumatic shock extraction, as well as other impulse methods of extraction (explosive, electrohydraulic and magneto-pulse) is complicated by the high speed of deformation and, accordingly, by the occurrence of considerable inertial forces that counteract the movement of the flange of the extracted part. In the case of pneumatic shock reduction of the deformation rate can be achieved by adjusting the relative weight of the striker or by applying a two-stroke stretching. It is experimentally confirmed that the greatest influence on the limit values of the stamping ability in pneumatic impact stamping have the properties of the workpiece material, its surface properties, the scheme of the deformation process, the rate of deformation, the geometry of the matrix or punch, the value of contact friction and intensification techniques. Experiments have shown that the following factors have the greatest influence on the ultimate degree of drawing and the quality of the products: the condition of the surface and the physical and mechanical properties of the workpiece material; the radius of curvature of the working edge of the matrix; the relative thickness of the workpiece; workpiece loading rate (parameter α); the frictional properties of the matrix material and the workpiece; quality of greasing; technological scheme of operation. For two-stroke stretching, the stretching limit is increased by 8-10%. Also, when using two-stroke load, as shown by experiments, the amount of thinning in dangerous sections of the finished product is reduced. The reduction of radial deformation in the centre of the samples reaches 20-25%. The accuracy of pneumatic shock punching by a liquid is very high, since the deviation of the measured diameters does not exceed 0.1 mm. The surface quality of the pneumatic impacted products is determined only by the surface quality of the starting material. The pneumatic shock method of punching using a two-stage folded dash allows to increase the degree of drawing, accuracy and quality by means of a two-stroke loading, that is, to intensify the process of deep drawing of sheet products. The intensification is due to the successive double shock load for one cycle of the PUSH installation – the first blow is a formative, and the subsequent blow of the second stage is a calibration.