Papers by Author: V.P. Smolentsev

Abstract: The worn surface is usually coated with a layer, which thickness exceeds magnitude of wear. In order to provide required clearances (or tightness) in the assembling of parts, uniform clearances (this suggests the presence of the perfect mating should be provided. In the paper, the effects on the layer were discussed and forecasting the clearance sizes or (when the limit values are specified) determining the assembly life. In the process of repairing, the worn surface is usually coated with the layer, which thickness exceeds magnitude of wear. After the surface is coated it is machined by one of the available methods. During recent years, new so-called “cold” methods of coating have appeared, some of them (particularly galvanomechanical machining) enables to obtain required dimensions and quality metrics of surface layer without complete machining. The final goal of repair is to provide required clearances (or tightness) in the assembling of parts. It is required to provide uniform clearances (this suggests the presence of the perfect mating surfaces before assembly). Depending on accuracy grade, variations in the clearance dimensions may be within the limits from some microns to decile of millimeter. This depends on mating surface accuracies and is independent of the fact whether these surfaces were repaired or not. If the parts were machined separately, thickness of the layer shall be determined subject to the actual size of mating part areas, size and dimensional tolerances of clearance. When developing the process of parts repair, the following shall be considered: - wear degree of contact mating locations; - requirements for quality of surface layer in part assemblies; - permissible errors of mating surfaces; - allowance (or tightness) between mating parts and its variation limits in the assembly. The wear in mating locations is determined by supervision of part defects before repair. The limiting wear of products shall not exceed capability of galvanomechanical method. It is required for qualitative surface coating to limit the thickness to 0,5-0,6 mm. Depending on wear degree, two methods of repair can be used: -smoothing of macrosurface with a galvanomechanical coating, for example with chromium and thereafter application of qualitative surface layer. Such process shall be applied in the case when degree of surface unevenness does not exceed 50%. If wear degree is out of the stated limits, preliminary machining is required. This machining is necessary to reduce surface unevenness up to 50%. After this procedure, effective thickness of coating shall be applied. The acceptable surface unevennesses with different degrees of wear are shown on Fig.1 At the first stage of coating the stock shall be evened. After this, the surface roughness does not exceed the roughness coefficient specified for a new part, but other quality indexes of the surface (residual stress character, wear-resistance) are not in conformance with the requirements for the repaired parts. Therefore, after evening, another “slower” method of galvanomechanical repair with specified contact pressure and mechanical effect conditions is applied. As a result of this method, the following indexes are available. See Table 1.

Abstract: It is difficult to select the materials combining in modern industry, this paper analyzed the drawbacks of different materials (the stainless, the copper alloys, aluminum and its alloys) on selecting materials for tooling and selection of coatings that help to eliminate drawbacks, analyzed the micro-arc oxidation (MAO) and its application of different materials. It is ascertained that aluminum alloys may be practical to use for electrodes for electroerosive machining only in exceptional cases when the wear of the tool is not determinative. Selection of materials combining required physical and mechanical properties may be a difficult task in tooling designing and manufacturing in modern industry. This problem is especially evident when current-conducting elements of tooling used for electrophysical and electrochemical processing methods are manufactured. The main distinctive feature of these methods is maintenance of values under the influence of electrical current and corrosive medium and during electrochemical reactions. The article addresses comparative analysis of properties of different materials used for tooling manufacture, advantages and drawbacks of these materials and selection of coatings that help to eliminate drawbacks. When selecting materials for tooling, the alloy in use shall have the following properties [4]: high electrical conductivity, high corrosion resistance, high resistance to local fracture, high adhesion to dielectric coatings, sufficient mechanical strength, high machinability and low cost. The following materials are considered to meet operating requirements to the fullest extend [4.5]: stainless steels and copper alloys that have high machinability, electrical conductivity, weldability and mechanical strength; titanium- and chromium-base alloys that have high mechanical strength, corrosion resistance and resistance to local fracture and enables to make oxide insulating layer protecting surface from anodic dissolution. However, these materials have a number of drawbacks, the most important of which is high cost that impedes their usage especially in serial production. Furthermore, stainless steels and titaniumand chromium-base alloys have the following drawbacks that affect product cost: - complexity of machinability that results in high labor-intensiveness of manufacturing process of tooling; - heavy losses in electric voltage provided that these materials are used as current-carrying elements that makes current supply calculation difficult and requires application of more powerful sources; - cracking and fracture of oxide surface coating even when mechanical effect is insignificant that results in loss of isolating and protective properties [1,2]. Furthermore, oxide coating application process cannot be controlled completely and as a result, coating uniformity in thickness, composition and properties cannot be achieved. Application of coatings to the areas with varied sections and to the surfaces with projections and sharp edges is a difficult problem. Layers applied to these surfaces have little adhesion to parent material and their thickness is limited due to high stress concentration and etching. The revealed drawbacks require development and usage of surface layer improvement process to receive required physical and mechanical properties of composite material.