Improving the efficiency of metal-bonded diamond abrasive end tools by improving manufacturing technology

OBRABOTKAMETALLOV MATERIAL SCIENCE Том 20 № 3 2018 EQUIPMEN . INSTRUM TS Vol. 3 No. 2 2021 Fig. 1. Scheme of capacitor welding of a steel shank to the working part: 1 – lower copper electrode; 2 – working dia- mond-bearing part; 3 – steel insert in the form of a screw pin with a contact ledge; 4 – dielec- tric coupling; 5 – cylindrical body (shank); 6 – collet grip of the welding gun; 7 – wel­ ding gun ing the hot additional pressing process, a cold-pressed briquette is made 0.5...1.0 mm less in diameter than the diameter of the dia- mond head finished working part. Welding of the grinding head body made of quenched steel to the working diamond-bearing part of the tool by the method of condenser butt welding includes the following operations. The surfaces to be welded are pre-cleaned and degreased. Turn on the welding machine. Insert the quenched shank (5) as shown in Fig. 1 into the welding gun collet (6). The diamond head working part (2) is installed into the coupling (4) from below, with a steel insert (3) and with a contact protrusion upwards. The coupling with the diamond head inserted working part are thrust against the copper plate-electrode (1). The electrode surface shape is determined by the head working part shape. A welding gun (7) with a fixed shank is inserted into the coupling so that the shank end touches the working head contact protrusion, then press on the gun handle until the spring stops compressing. In the last turn, the discharge button on the welding gun is pressed. For the manufacture of experimental samples of diamond grinding heads of the AW type by the method described above, for example, with a diameter of 12 mm and a height of 12 mm (GOST 17122), cylindrical cases (shanks) with a diameter of 6 mm and a length of 68 mm from different grades of quenched carbon steels 35, 45, 60 and U8 were used. The shanks made of steel, 35 and 45 were quenched to the maximum hardness in water, and those made of steel 60 and U8 were quenched in oil. The working diamond part of all heads was made on a metal bond M2-01 with a 100 % concentration of AC32 160/125 dia- mond powder (GOST 9206-80) according to the above-described manufacturing technology. As an intermediate case (3), located in the center of the diamond working part, ready-made copper-plated screw studs M6 with a contact end of the PT type (GOST R 55738-2013 (ISO 13918: 2008) and 8 mm in length were used. Such steel studs of 4.8 strength class (GOST ISO 898-1-2014) have a tensile strength of at least 400 MPa and conventional yield strength of at least 320 MPa. The chemical composition is similar to that of St.3 or St.4 steels. Condenser welding of cases made of quenched carbon steel with a diameter of 6 mm to the end of the working diamond part intermediate case was carried out on a welding machine for condenser welding of STC-2500 model in the sequence described above. The charging voltage for condensers recommended by the manufacturer for welding steel studs with a diameter of 6 mm to a steel case is 100...120 V. The samples of diamond heads under study, shown in Fig. 2, were connected to a quenched steel case according to the above technology at a condenser charging voltage of 110 V. Subsequently, for stress relief in the welded joint, the diamond grinding heads under study, connected to the shank using the condenser welding method, were tempered at a temperature of 240 ± 10 ° С for 1.5 h. The joint quality was assessed visually by the presence of discontinuities in the joint, as well as by examining the microstructure and measuring microhardness of the weld and the heat-affected zones. The welded joint microhardness was measured using a HMV-G21ST semi-automatic microhardness tester (Shi- madzu, Japan) under load of 50 g. The joint efficiency of the case with the working diamond-bearing part of the grinding head samples was determined by the tensile test method on a breaking machine 1958U10 with a maximum load of 100 kN.