Manufacturing of Coated Production Tooling
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 : 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.
Hang Gao, Zhuji Jin and Yannian Rui
V.P. Smolentsev et al., "Manufacturing of Coated Production Tooling", Advanced Materials Research, Vols. 24-25, pp. 13-16, 2007