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

OBRABOTKAMETALLOV Vol. 20 No. 3 2018 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 3 2 21 Fig. 2. Experimental samples of diamond heads with a diameter of 12 mm, made using the method of capacitor welding Results and discussion The condenser welding mode was selected visually, according to the welded joint appearance. At voltages of more than 110 V, a significant splashing of liquid metal from the weld was observed, and at lower voltages, on the contrary, insufficient melting of the welded product surfaces was observed and void formation along the welded joint edges between the main and intermediate cases occurred. As it is known [27], the condenser welding allows obtaining sufficiently firm joints between dissimilar metal materials due to the small thickness of the melted layer and the lack of dissimilar metals mixing due to the short duration of the arcing. However, when welding carbon steel products, the strongest and most reliable joints, in the case of condenser butt welding with arc ignition and reflow of the jointing surfaces, are provided when the jointing products are made of low-carbon steels [27, 32]. An increase in the carbon content in products to be weld leads to a decrease in strength properties, which is usually associated with brittle structural components appearance in the welded joint in the form of martensite and residual stresses. Moreover, as the authors’ simulation results and experimental data show [33], it is not possible to completely avoid the formation of voids in the weld area during condenser reflow welding. Indeed, as can be seen from the photo of the lon- gitudinal macrotemplet (Fig. 3), cut from the diamond grinding head under study, there are discontinuities in the area of the welded joint, reaching in our case 0.15×0.5 mm. The availability of discontinuities and residual stresses in the weld is one of the reasons for the welded joint low strength between the cylindrical case made of quenched carbon steel and intermediate case made of low carbon steel. For example, the joint efficiency between a case made of quenched steel 45 and an intermediate case made of low-carbon steel of St.3 doesn’t exceed 300 MPa, and fracture is usually brittle along the weld. Therefore, in order to remove residual stresses and increase resistance to brittle fracture, the investigated grinding heads after condenser welding of the quenched case were subjected to low tempering at a temperature of 240 ° С, for 2 h. The results of tests for the strength of the joint of the shank with the diamond-bearing part under tension of the studied samples of grinding heads are shown in the table (Table). The lowest joint efficiency in tension have diamond grinding head, made using traditional technology, as in this case, the part of the body (shank) inside the diamond layer has a smooth surface, and the joint efficiency is secured due to the cohesive forces formed between the copper-plated surface of the housing and the binder metal in the result of sintering and hot extrusion. The investigated diamond grinding heads, joined to the case made of quenched carbon steel using the method of condenser welding, have a higher tensile strength between the case and the diamond part than diamond heads joined to the case made of R6M5 steel using a standard technology as a result of sintering and hot pressing. Such a difference in joint efficiency is due to the fact that in the manufacture of