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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Journal of Materials Processing Technology, Volume 209, Issue 8, 21 April 2009, Pages 4207–4216
For the development and introduction of new coated cutting tools (i.e. new combinations of cutting materials and hard coatings), it is necessary to carry out a number of studies with the purpose of optimizing the coatings composition and processing procedures, and also to test new tools under working conditions. The aim of this paper is to establish a common model for environmentally oriented quality management in the use and development of coated ceramic cutting tools with new coating systems. The paper also presents an investigation of the results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from (Al2O3 + TiC) tool ceramics. Tests were carried out on ceramic inserts, uncoated and PVD or CVD-coated, with gradient, mono-, multi- (nano) layers and multicomponent hard wear resistant coatings composed of TiN, Ti(C, N), (Ti, Al)N, (Ti, AlSi)N and Al2O3 layers.
The use of coated cutting tools in the machining of various materials now represents state-of-the-art technology. Developments in coating equipment and processes now enable us to produce a wide range of different hard nitride-, carbide- and oxide films and to deposit them on various tool substrates as monolayer, multilayer, or composite coatings. Soković (1997a) clearly revealed that irrespective of whether or not cutting tool materials (HSS, cemented carbides, cermets or ceramics) are coated, the primary concern is to control and optimise properties such as coating adhesion, coating structure, coating thickness, resistance to high temperatures, etc. Therefore, it was taken into consideration that Koenig et al. (1992) had even earlier defined the “complex composite” as seen in the coated cutting tool. The present studies are of importance from two viewpoints: on the one hand, it is considered that the substrate material is important for the production of a highly effective cutting tool, and on the other hand, Navinšek et al. (1991) reported that the maximum performance of hard coatings on different substrates is dependent upon the precision of interface characteristics. For the characterisation of these parameters, modern analytical techniques are used.
نتیجه گیری انگلیسی
One of the prerequisites in successful production is the use of quality cutting tools with definite mechanical and technological properties. Therefore, for the development and introduction of a new kind of cutting tool (substrate material or coating), it is necessary to carry out a number of studies with the purpose of optimizing the substrate and coating composition, coating processing procedures, and the resulting workpiece material machinability. In this paper the authors emphasize the importance of the improvement of ceramic tool performance for finish machining by application of PVD or CVD coatings. Results are taken from the experimental application of the common model of a quality management system based on “closed loop quality circuits” in the development and introduction of coated ceramic tools in the practice; the strategy of the machinability in finish machining has been determined, where the dimensional accuracy, surface roughness and tool life are the major aspects of interest. The cutting tool surface and surface coatings characterisation, as well as quality assurance, are very important parts of effective cutting tools development. A great variety of powerful testing methods exist to characterise surface coatings and to ensure that the quality is adequate. Accordingly, of great importance is the presented model of an environmentally oriented quality management approach in the field of development and introduction of coated ceramic cutting tools deposited with new coating systems. New cutting tool coatings and innovative processes allow us to achieve optimal environmental conservation (with dry or near dry cutting) in conjunction with suitable technologies that provide high process stability, reliability, and acceptable economic results. All investigated PVD and CVD coatings deposited on the (Al2O3 + TiC) ceramic substrate are characterized by a structure without pores and discontinuities and by a tight adherence to themselves and of the entire multilayer coating to the substrate. The TiAlN (PVD) coating displays the best adhesion (the highest critical load value Lc = 76–80 N). The microhardness of coated systems, (Al2O3 + TiC) ceramic substrate and different deposited coatings, grows significantly after deposition. The maximum microhardness of HV0.07 = 4030 MPa was observed in case of the (TiN + multi TiAlSiN + TiN) coating system deposited onto the ceramic substrate. The value of the roughness parameter Ra grows after deposition of the coatings, especially in the case of the CAE PVD process, which should be connected to the process character and to the structure of the deposited coatings (i.e. the initial roughness of uncoated inserts was 0.06–0.07 μm and was further increased to 0.21–0.37 μm for CAE PVD-coated tools). The maximum value of Ra = 0.37 μm was obtained for the coating system (TiN + TiAlSiN + TiN), sample B. In all investigated cases, deposition of the PVD and CVD coatings on the CM ceramic tool substrate results in a significant increase of tool life (a CTE-index(0.2) from 1.29 to 1.83 was obtained) and also in the lowering of the value of surface roughness of the machined workpiece (Ra is below 2.5 μm—class N8), and therefore ultimately in the improvement of machined workpiece quality, especially in the final machining process sequence. Depositing hard PVD or CVD coatings onto the investigated CM ceramic tool inserts makes it possible to achieve: - improvement of tool life, - better quality of the machined surfaces, - reduction of machining costs and - elimination of cutting fluids used in machining. Therefore, it was determined that deposition of different coatings on the ceramic tool substrate is justified and that composite tool materials developed in this way offer potentially valuable applications and technological significance within the industry.