【正文】 rini et al. studied diamond coated small mills for dental applications . The authors tested different coating thickness and noted that thick coatings induce high cutting forces due to increased coating surface roughness and enlarged edge rounding. Such effects may contribute to the tool failure in milling ceramic materials. The authors further indicated tools with thin coatings results in optimal cutting of polymer matrix posite . Further, Torres et al. studied diamond coated microendmills with two levels of coating thickness . The authors also indicated that the thinner coating can further reduce cutting forces which are attributed to the decrease in the frictional force and adhesion.Coating thickness effects of different coatingmaterial tools have also been studied. For single layer systems, an optimal coating thickness may exist for machining performance. For example, Tuffy et al. reported that an optimal coating thickness of TiN by PVD technology exists for specific machining conditions . Based on testing results, for a range from to 181。m TiN coating, thickness of 181。m exhibit the best turning performance. In a separate study, Malik et al. also suggested that there is an optimal thickness of TiN coating on HSS cutting tools when machining free cutting steels . However, for multilayer coating systems, no such an optimum coating thickness exists for machining performance .The objective of this study was to experimentally investigate coating thickness effects of diamond coated tools on machining performance — tool wear and cutting forces. Diamond coated tools were fabricated, by microwave plasma assisted CVD, with different coating thicknesses. The diamond coated tools were examined in morphology and edge radii by whitelight interferometry. The diamond coated tools were then evaluated by machining aluminum matrix posite in dry. In addition, deposition thermal residual stresses and critical load for coating failures that affect the performance of diamond coated tools were analytically examined.2. Experimental investigationThe substrates used for diamond coating experiments, squareshaped inserts (SPG422), were finegrain WC with 6wt.% cobalt. The edge radius and surface textures of cutting inserts prior to coating was measured by a whitelight interferometer, NT1100 from Veeco Metrology.Prior to the deposition, chemical etching treatment was conducted on inserts to remove the surface cobalt and roughen substrate surface. Moreover, all tool inserts were ultrasonically vibrated in diamond/water slurry to increase the nucleation density. For the coating process, diamond films were deposited using a highpower microwave plasmaassisted CVD process. A gas mixture of methane in hydrogen, 750–1000sccm with –% of methane/hydrogen ratio, was used as the feedstock gas. Nitrogen gas, –sccm, was inserted to obtain nanostructures by preventing columnar growth. The pressure was about 30–55Torr and the substrate temperature was about 685–830176。C. A forward power of –kW with a low deposition rate obtained a thin coating。 a greater forward power of –kW with a high deposition rate obtained thick coatings, two thicknesses by varying deposition time. The coated inserts were further inspected by the interferometer.A puter numerical control lathe, Hardinge Cobra 42, was used to perform machining experiments, outer diameter turning, to evaluate the tool wear of diamond coated tools. With the tool holder used, the diamond coated cutting inserts formed a 0176。 rake angle, 11176。 relief angle, and 75176。 lead angle. The workpieces were round bars made of A359/SiC20p posite. The machining conditions used were 4m/s cutting speed, mm/rev feed, 1mm depth of cut and no coolant was applied. The selection of machining parameters was based upon previous experiences. For each coating thickness, two tests were repeated. During machining testing, the cutting inserts were periodically inspected by optical microscopy to measure the flank wearland size. Worn tools after testing were also examined by scanning electron microscopy (SEM). In addition, cutting forces were monitored during machining using a Kistler dynamometer.5. ConclusionsIn this study, the coating thickness effects on diamond coated cutting tools were studied from different perspectives. Deposition residual stresses in the tool due to thermal mismatch were investigated by FE simulations and coating thickness effects on the interface stresses were quantified. In addition, indentation simulations of a diamond coated WC substrate with the interface modeled by the cohesive zone were applied to analyze the coating system failures. Moreover, diamond coated tools with different thicknesses were fabricated and experimentally investigated on surface morphology, edge rounding, as well as tool wear and cutting forces in machining. The major results are summarized as follows. (1) Increase of coating thickness significantly increases the interface residual stresses, though little change in bulk surface stresses. (2) For thick coatings, the critical load for coating failure decreases with increasing coating thickness. However, such a trend is opposite for thin coatings, for which radial cracking is the coating failure mode. Moreover, thicker coatings have greater delamination resistance.(3) In addition, increasing the coating thickness will increase the edge radius. However, for the coating thickness range studied, 4–29181。m, and with the large feed used, cutting forces were affected only marginally.(4) Despite of greater interface residual stresses, increasing the diamond coating thickness, for the range studied, seem to increase tool life by delay of coating delaminations.AcknowledgementsThis research is supported by National Science Foundation, Grant No.: CMMI 0728228. P. Lu provided assistance in some ?。。∫韵聝?nèi)容與本文檔無關(guān)?。。?。。。。。。。。。。以下為贈(zèng)送文檔，祝你事業(yè)有成，財(cái)