INCREASING THE WEAR RESISTANCE OF THE WORKING BODIES OF TILLAGE MACHINES BY ELECTRICAL DISCHARGE MACHINING

Abstract

In this work, the effective technological parameters of electrical discharge machining for increasing the wear resistance of steels operating under abrasive wear conditions were determined. It has been established that the optimal technological parameters of electrical discharge machining are as follows: current 350–450 A, voltage 45 V, temperature of the working environment 30–40 ℃. According to the results of the studies, it was found that the most significant effect on the wear resistance of the treated surface is the current strength, since it affects the quality of the surface layer melting and the depth of processing. Another significant factor is the temperature of the dielectric cooling medium: with an increase in the temperature of the cooling medium, the surface cooling rate cannot meet the conditions (200 ℃/s) for the formation of martensitic structures, and with a decrease in temperature, internal stresses occur in the hardened surface, which lead to the formation of microcracks. As a result of electrical discharge machining, the microhardness of the treated layer increases for X12 steel within 12–12,8 GPa, for 65Г steel within 10,5–11,2 GPa, and for 45 steel within 7,3–8,2 GPa. The hardness increase is due to the formation of a fine-needle martensite structure and alloying of the surface layer with Mn, Si, Ni and Cr. It has been established that the use of electrical discharge machining increases the wear resistance of 65Г steel when operating on soils with different mechanical composition, abrasive properties, and various external factors by an average of 60–80%. The use of electrical discharge machining to strengthen the working bodies of disc tillage tools made of 65Г steel allows to increase wear resistance in comparison with: serial ones – by 1,76 times, with the working surface strengthened by T-590 electrode – by 1,1 times, with the working bodies of Bellota (made of 28MnB5 steel) – by 1,16 times. In addition, during the operation of the working bodies hardened by electrical discharge machining, the effect of self-sharpening was observed, which in turn contributed to a decrease in traction resistance by 4–16% compared to the serial ones.