OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 4 (Fig. 7–8). With copy-piercing EDM at I = 8A, Ton = 100 μs, U = 100 V, the presence of chaotic cracks up to 1–3 μm wide was found (Fig. 8). Cracks on the TE surface arise due to rapid heating of the surface (with the increase of the current value and pulse on time the temperature in the processing zone increases) and rapid cooling by dielectric liquid. Hollows on the surface of the electrode after copy-piercing EDM are associated with the accumulation of sludge from the products of destruction of the electrode material and detail electrode (DE). With the increase of current and pulse activation time the intensification of the fracture process occurs. Material melt zones appear with increasing energy of single pulses (with an increase in current). The EDM process is accompanied by high temperatures at the breakdown spot. Rapid heating and subsequent cooling cycles cause thermal stresses on the TE surface. These stresses contribute to the formation of cracks on the TE surface. The presence of microcracks and other surface defects leads to macro-defects of the surface layer and to a decrease in the operational properties of the TE. The topology of the machined surface of additively grown TE, shown in Fig. 7a at magnification ×500, shows that to exclude surface defects of TE it is required to use the minimum mode of copy-piercing EDM at current of I = 4 A, voltage of U = 100 V. Conclusions Tool electrodes were produced by selective laser melting from MS1 maraging steel powder. It is found that tool electrode sample No.4 contains a minimum number of pores and cracks. It was produced using a single point exposure time of 20 μs; operating current of 1,400 mA; distance between points of 20 μm; average laser power of 35 W; filling step of 0.05 μm; thickness of a single layer of 30 μm; scanning speed of 1 m/s. A regression dependence between modes of copy-piercing EDM and wear of tool electrode when machining TE from maraging steel is obtained. In the minimum mode with a current of I = 4 A and a voltage of U = 50 V the wear of the electrode is minimal and amounts to γ = 0.0063875 g. The maximum wear of the electrode-tool amounts to γ = 0.13938 g with a current of I = 8 A and a voltage of U = 50 V. A regression dependence between modes of copy-piercing EDM and the surface roughness quality parameter of the additively grown TE made of MS1 maraging steel is obtained. It is shown that at constant pulse on time Ton = 75 μs the smallest roughness of TE Ra = 2.83 μm is obtained at a current of I = 4 A and a voltage of U = 100 V, and the maximum roughness of the TE Ra = 4.1568 μm is obtained at I = 8 A and U = 100 V. It is established that on the surface of additively grown TE from MS1 maraging steel there are chaotically located surface defects (microcracks, hollows, broken sections and remelting zones), reducing the strength characteristics of ET. To exclude surface defects and to form a homogeneous surface it is necessary to use finishing modes with the value of current I = 4 A, voltage U = 100 V and pulse turn-on time Ton = 75 μs. It is established that with increasing values of current up to 8 A in the interelectrode gap there is an increase in temperature and the value of pulse discharge, which leads to structural defects. References 1. Rajurkar K.P., Sundaram M.M., Malshe A.P. Review of electrochemical and electrodischarge machining. Procedia CIRP, 2013, vol. 6 (2), pp. 13–26. DOI: 10.1016/j.procir.2013.03.002. 2. Dimla D.E., Hopkinson N., Rothe H. Investigation of complex rapid EDM electrodes for rapid tooling applications. The International Journal of Advanced Manufacturing Technology, 2004, vol. 23 (3), pp. 249–255. DOI: 10.1007/s00170-003-1709-8. 3. Ho K.H., Newman S.T. State of the art electrical discharge machining (EDM) // International Journal of Machine Tools and Manufacture. 2003. Vol. 43 (13), рр. 1287–1300. DOI: 10.1016/S0890-6955(03)00162-7. 4. Ayesta I., Flaño O., Izquierdo B., Sanchez J.A., Plaza S. Experimental study on debris evacuation during slot EDMing. Procedia CIRP, 2016, Vol. 42, pp. 6–11. DOI: 10.1016/j.procir.2016.02.174. 5. Uhlmann E., Polte J., Bolz R., Yabroudi S., Streckenbach J., BergmannA. Application of additive manufactured tungsten carbide-cobalt electrodes with interior flushing channels in S-EDM. Procedia CIRP, 2020, vol. 95, pp. 460– 465. DOI: 10.1016/j.procir.2020.03.136. 6. Uhlmann E., Bergmann A., Bolz R., Gridin W. Application of additive manufactured tungsten carbide tool electrodes in EDM. Procedia CIRP, 2018, vol. 68, pp. 86–90. DOI: 10.1016/j.procir.2017.12.027.
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