外文翻译--ALSiC颗粒金属基复合材料的加工 英文版

Journal of Materials Processing Technology 83 (1998) 151158Machining of Al:SiC particulate metal-matrix compositesPart I: Tool performanceM. El-Gallaba, M. Skladb,*aPratt and Whitney Canada, Mississauga, Ontario, L5T 1J3, CanadabDepartment of Mechanical Engineering, McMaster Uni6ersity, Hamilton, Ontario, L8S 4L7, CanadaReceived 20 March 1997AbstractDespite the superior mechanical and thermal properties of particulate metal-matrix composites, their poor machinability hasbeen the main deterrent to their substitution for metal parts. The hard abrasive reinforcement phase causes rapid tool wear duringmachining and, consequently, high machining costs. A series of dry high-speed turning tests were performed to select the optimumtool material, tool geometry and cutting parameters for the turning of 20%SiC:Al metal-matrix composites. The results indicatethat polycrystalline diamond tools (PCD) provide satisfactory tool life compared to alumina and coated-carbide tools, where thelatter tools suffered from excessive edge chipping and crater wear during the machining of the metal-matrix composite understudy. Furthermore, the cost of PCD tools could be justified by using dry cutting at feed rates as high as 0.45 mm rev 1, cuttingspeeds of 894 m min 1and a depth of cut of 1.5 mm. With these cutting parameters, the relatively small built-up edge formedon the tool protects it from further wear by abrasion and micro-cutting. Polycrystalline tools with zero rake angle and large toolnose radii are recommended for the roughing operations. 1998 Elsevier Science S.A. All rights reserved.Keywords: Metal-matrix composites； Tool wear1. IntroductionMetal-matrix composites (MMCs) form one group ofthe new engineered materials that have received consid-erable research since the trials by Toyota in the early1980s 1. The most popular reinforcements are siliconcarbide and alumina. Aluminium, titanium and magne-sium alloys are commonly used as the matrix phase.The density of most MMCs is approximately one thirdthat of steel, resulting in high specific strength andstiffness 2. Due to these potentially attractive proper-ties coupled with the inability to operate at high tem-peratures, MMCs compete with super-alloys, ceramics,plastics and re-designed steel parts in several aerospaceand automotive applications. The latter materials, how-ever, may not have much further capacity for theinevitable future increases in service loads 3.Particulate metal-matrix composites (PMMCs) are ofparticular interest, since they exhibit higher ductilityand lower anisotropy than fiber reinforced MMCs 2.Moreover, PMMCs offer superior wear resistance 3.While many engineering components made fromPMMCs are produced by the near net shape formingand casting processes, they frequently require machin-ing to achieve the desired dimensions and surface finish.The machining of PMMCs presents a significant chal-lenge, since a number of reinforcement materials aresignificantly harder than the commonly used high-speedsteel (HSS) and carbide tools 4. The reinforcementphase causes rapid abrasive tool wear and therefore thewidespread usage of PMMCs is significantly impededby their poor machinability and high machining costs.2. Literature reviewFrom the available literature on PMMCs, it is clear* Corresponding author. Fax: 1 905 5727944； e-mail: mech-macmcmaster.ca0924-0136:98:$19.00 1998 Elsevier Science S.A. All rights reserved.PII S0924-0136(98)00054-5M. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158152Table 1Typical physical properties of Duralcan F3S.20S 20PropertyDensity (g cm 3) 2.77Thermal conductivity (cal cm 1s 1K 1) at 22C 0.47Specific heat (cal g 1K)0.218100C0.239200C0.259300CAverage coefficient of thermal expansion17.550100C50300C 21.121.450500CUltimate strength (MPa) 262Yield strength (MPa) 21.41.9Elongation (%)98.6Elastic modulus (GPa)6791.5Rockwell hardness (B)Table 2Tool geometryTool GeometryPCD (tipped-80rhomboid) Rake angle, a: 5, 0, 5Clearance angle: 7Approach angle: 5Tool nose radius (mm), r: 0.8, 1.6TiN coated carbide Rake angle, a:0(triangular)Clearance angle: 7Approach angle: 5Tool nose radius (mm), r: 1.6Rake angle, a:0Al2O3:TiC ceramic(triangular)Clearance angle: 7Approach angle: 5Tool nose radius (mm), r: 1.6crystalline diamond (PCD) tools are the only tool mate-rial that is capable of providing a useful tool life duringthe machining of SiC:Al PMMCs. PCD is harder thanAl2O3and SiC and does not have a chemical tendencyto react with the workpiece material. Tomac et al. 5compared the performance of chemical vapor deposi-tion (CVD) inserts to that of TiN, Ti(CN) and Al2O3coated tools. CVD tools offered better overall perfor-mance than that of the other tools. Lane et al. 18studied the performance of different CVD tools withthin and thick films. According to their observations,CVD tools with thin films failed catastrophically duringthe end milling of 20%SiC:Al PMMC. This tool failurewas attributed to coating spalling and consequent dam-age to the relatively soft carbide substrate. Further-more, PCD tools with a grain size of 25 mm betterwithstand abrasion wear by micro-cutting than toolswith a grain size of 10 mm 8,14. Further increases inPCD grain size do not benefit the tool life, but rathercause significant deterioration in the surface finish. Thisthat the morphology, distribution and volume fractionof the reinforcement phase, as well as the matrix prop-erties, are all factors that affect the overall cuttingprocess 2,4, but as yet relatively few works related tothe optimization of the productivity process have beenpulished. For example, Monaghan 2 studied the wearmechanism of carbide tools during the machining of25% SiC:Al PMMC at speeds below 20 m min 1.Tomac et al. 5 developed a tool life relationship forcarbide tools during the machining of SiC:Al PMMCsat speeds lower than 100 m min 1. However, theauthors of Ref. 5 recommended further research onthe built-up edge phenomenon that is observed in alltools during the machining of SiC:Al PMMCs. OReillyet al. 6 ranked various tool materials with respect totool wear, however, their cutting parameters did notexceed 125 m min 1and 1.0 mm depth of cut, whichwas achieved using cubic boron nitride tools. Similartest results were reported by Brun et al. 7 who relatedthe tool wear rate, mainly due to abrasion, to the toolhardness. Winert 8 attributed the wear of the carbidetools to abrading Al2O3particles that form on thesurface and rub the tool in the direction of the chipflow. However, pulled SiC particles could also lead tothe same effect, SiC particles also being harder than theWC. Tomac et al. 5 suggested that coatings with lesshardness than that of Al2O3and SiC offer little to noadvantage during the machining of SiC:Al PMMCs,Brun et al. 7 suggested using lower cutting speeds toreduce the cutting temperature, which accelerate diffu-sion and adhesion wear and thermally weaken the tool.Since aluminium tends to seize on the tool face andsince grain boundaries are the sites of seizure, theauthors recommended using cemented carbide toolswith a large grain size.Several researchers 725 have indicated that poly-Fig. 1. SEM figure showing wear on Al2O3tool (6 488 m min 1,f 0.2 mm rev 1, doc 0.5 mm, r 1.6 mm, a 0).M. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158 153Table 3Effect of tool material on cutting forces and temperatures (r 1.6mm； a 0)Measured cut-Tool material Measured cuttingtemperature (C)ting force (N)PCD (6 894 m min 1； 97.00 440f 0.45 mm rev 1；doc 2.5 mm)98.10PCD (6 670 m min 1； 410f 0.25 mm rev 1；doc 1.5 mm)520Al2O3(6 248 m min 1； 183.85f 0.2 mm rev 1；doc 0.5 mm)143.52 500TiN (6 248 m min 1；f 0.2 mm rev 1；doc 0.5 mm)Fig. 3. Effect of depth of cut on the cutting forces (PCD tool: r 1.6mm, a 0； square points: 6 894 m min 1, doc 1.5 mm； roundpoints: 6 894 m min 1, doc 2.5 mm).of cut that are as aggressive as possible during theroughing operations. Finally, with regard to the coolantapplication, researchers at Duralcan USA 1123, rec-ommend investigating the possibility of dry-rough ma-chining in order to take advantage of the protectivebuilt-up edge phenomenon.In summary, the literature review carried out showedthat the effect of more aggressive cutting parameters(speed, feed and depth of cut) still needs further re-search in order to improve the economics of the cuttingprocess. Also, several important parameters have beenoverlooked by previous researchers, among which arethe tool geometry and coolant application.3. Test material and cutting tools3.1. Workpiece materialThe machining investigations were carried out usingDuralcan F3S.20S Al:SiC metal-matrix composite. TheSiC particles had an average diameter of 12 mm. Table1 shows some of the physical and mechanical propertiesof A356-20%SiC PMMC. Prior to carrying out thecutting experiments, the test material was fully heat-treated to the T71 condition. The test material was inthe form of bars of 177.8 mm diameter and 305 mmlength.3.2. Cutting toolsVarious tool materials (coated carbide, Al2O3:TiCand PCD) and geometries were employed in the study.Oblique turning tests were carried out and differentcutting parameters were employed for each tool mate-rial. However, for the purpose of comparing tool wear,all cutting tests were carried out at a fixed volume ofmetal removed (300 mm3). Table 2 summarizes the tooldata.is because PCD grains with size 25 mm are easilypulled out of the cutting edge.Regarding the effect of the cutting parameters on thetool life, Lane et al. 1115,1719 attributed the in-crease in the wear of PCD tools (by abrasion) toincrease in kinetic energy gained by abrading SiC parti-cles. On the other hand, Brun et al. 7 attributed theincrease in tool wear in the thermal degradation of thetool material. Tool wear was found to be inverselyproportional to the feed rate 9. Tomac et al. 5attributed the increase in tool life at higher feed rates tothe thermal softening of the composite. The authorssuggest that the workpiece material becomes softer andthe SiC particles become pressed into the workpiece,causing less abrasion on the tool itself. However, Finnet al. 24 and Morin et al. 25 attributed the reductionin tool wear with greater feed rates to the reducedcontact between the cutting edge and the abrasive SiCparticles. Despite the controversy in explaining themechanism behind the tool wear at different feed rates,all researchers recommend using feed rates and depthsFig. 2. Effect of cutting speed on the cutting forces (PCD tool: r 1.6mm, a 0； square points: 6 670 m min 1, doc 1.5 mm； roundpoints: 6 894 m min 1, doc 1.5 mm).M. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158154Dry turning tests were carried out on a 10 HPStandard Modern NC lathe. The cutting force compo-nents (Fx, Fy, Fz) and tool wear were measured contin-uously for each combination of cutting parameters. Thetool forces were measured using a Kistler 3-componentdynamometer and the cutting conditions were selectedcarefully for each tool material. In some of the cuttingtests, the tool temperature was measured using K-typethermocouples that were glued onto the tool rake face,1 mm away from the cutting edge. The reliability of themeasurement techniques was checked constantly byrepeating the experiments and the results of each set ofexperiments were accepted if they exhibited a varianceof less than 5%. At the end of each cutting test, the toolwear was examined using a scanning electron micro-scope and the X-ray dispersion technique. The toolFig. 5. (a) Built-up edge on PCD tools (6 670 m min 1, f 0.45mm rev 1； doc 2.5 mm, r 1.6 mm)； (b) as for Fig. 5(a), but for6 894 m min 1.Fig. 4. (a) Built-up edge on PCD tools (6 670 m min 1, f 0.25mm rev 1, doc 2.5 mm, r 1.6 mm, a 0)； (b) X-ray dispersionof built-up edge shown in Fig. 4(a).flank wear (VB) was measured using a toolmakersmicroscope.4. Results and discussion4.1. Effect of tool materialA series of preliminary tests was conducted to assesthe effect of tool material on the tool wear, cuttingforces and cutting temperature during the rough turn-ing of 20%SiC:Al PMMC. Fig. 1 shows that Al2O3:TiCtools suffered excessive wear in the form of edge chip-ping. Al2O3particles are pulled out by the abradingworkpiece particles, which have a greater Vickers hard-ness number (VHN) than the Al2O3particles (VHN forAl2O3TiC 2500 kgfmm 2； VHN for SiC 3000 kgfmm 2). Crater wear was also observed, which is due tothe widening of grooves that were caused by abrasion.Due to severe edge chipping, the cutting forces for theM. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158 155Al2O3:TiC tool were much higher than those experi-enced by TiN coated tools (Table 3). The TiN coatingprovided some protection against the abrasive effects ofthe SiC particles. The superior performance of poly-crystalline diamond tools, compared to both Al2O3:TiCand TiN coated carbide tools, is attributed to their highabrasion resistance and high thermal conductivity,which led to lower cutting temperatures, as shown inTable 3. Therefore, all machinability studies carried outthereafter were concerned with the optimization of thecutting process using PCD tools.4.2. Effect of cutting parametersFigs. 2 and 3 show that as the cutting speed and:orthe depth of cut increase, the cutting forces decrease.This could be attributed to thermal softening of theworkpiece material. Another possible reason is due tothe changes introduced into the tool geometry upon theformation of built-up edge. Fig. 4(b) shows the X-raydispersion of the built-up material shown in Fig. 4(a).Fig. 7. (a) SEM image illustrating the wear on the PCD tool rake faceafter dissolving the BUE with NaOH (6 670 m min 1, f 0.15 mmrev 1, doc 1.5 mm, r 1.6 mm, a 0)； (b) higher magnification ofrake face of the tool shown in Fig. 7(a).Fig. 6. (a) Built-up edge on PCD tools (6 670 m min 1, f 0.35mm rev 1, doc 1.5 mm, r 1.6 mm, a 0)； (b) as for Fig. 6(a),but for doc 2.5 mm.Built-up edge was observed in all tools under all cuttingconditions. This is because particulate SiC:Al MMCshave all of the characteristics of materials that formFig. 8. Effect of cutting speed on the tool flank wear (PCD tool:r 1.6 mm, a 0； square points: 6 670 m min 1, doc 1.5 mm；round points: 6 894 m min 1, doc 1.5 mm).M. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158156Fig. 9. Effect of depth of cut on the tool flank wear (PCD tool:r 1.6 mm, a 0, 6 894 m min 1； square points: doc 1.5 mm；round points: doc 2.5 mm).illustrate this point, in the case of a greater depth of cuta larger surface area of the tool flank face is exposed toabrasion.Increasing the feed rate had a beneficial effect. Asshown in Figs. 8 and 9, as the feed rate increases, thetool wear decreases. In the case of higher feed rates, fora fixed volume of metal removal, the tool surfaces willhave less contact with the abrasive PMMC. AnotherFig. 10. (a) Effect of PCD tool rake angle on tool flank wear (6 894m min 1, doc 2.5 mm, r 1.6 mm； square points: 0； round points: 5； star points, 5)； (b) effect of PCD tool rake angle on thecutting forces (6 894 m min 1, doc 2.5 mm, r 1.6 mm； squarepoints: 0； round points: 5； star points, 5)； (c) SEM imageillustrating the PCD tool wear by pitting (6 670 m min 1, doc 1.5mm, f 0.25 mm rev 1, r 1.6 mm, a 5).BUE (i.e. strain-hardened two-phase material underhigh temperature and pressure).At high cutting speeds (6 894 m min 1(Fig. 5(b),a smaller BUE is formed, compared to the BUE formedat 6 670 m min 1(Fig. 5(a)； the height of the BUEwas measured perpendicular to the rake face) In con-trast, by increasing the depth of cut from 1.5 to 2.4mm, a large BUE is formed (Fig. 6(a,b), which couldbreak off the tool causing tool chipping and consequentadverse effects on the workpiece surface roughness anddimensional accuracy.Topographies of the tool indicate that the main wearmechanism of PCD is abrasion (manifested as groovesparallel to the chip flow direction). These grooves couldbe attributed to three factors. The first is that Al2O3isformed at the tool edge, which is hard enough toproduce grooving wear in the PCD. The second expla-nation for the PCD grooving is aluminium seizure andthe pull-out process of the PCD grain, as shown in Fig.7(a,b). The third possible reason behind PCD groovingis that SiC particles abrade the tools. Thus, PCD toolswith PCD grains larger than the grain size of the SiCparticles could better withstand the abrasion and mi-cro-cutting by the SiC particles. However, one shouldnote that as the size of the PCD grains increases, thefracture properties of the PCD tool deteriorates, due toan increased number of flaws in the material.The grooves that were formed on the tool face werefilled with the workpiece material. This adhering layersomewhat protected the tools rake face against furtherabrasion. Nonetheless, the tool flank face continued tobe subjected to abrasion. Hence, flank wear (Vb) wastaken as the tool life criterion with Vb1im 0.18 mm.Fig. 8 shows that as the cutting speed increases, theflank wear increases. This could be attributed to theincrease in the kinetic energy of the abrading particles,as previously hypothesized by Lane 17.Increasing the depth of cut leads to an increase in theflank wear (Fig. 9). This is attributed to enhancedabrasion by micro-cutting at the tool flank face. ToM. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158 157Fig. 11. (a) SEM image illustrating the PCD tool wear by chipping(6 894 m min 1, doc 1.5 mm, f 0.35 mm rev 1, r 0.8 mm,a 0)； (b) effect of tool nose radius on the tool flank wear (6 894min, doc 2.5 mm, a 0； tool FW: square points, r 1.6 mm；round pitch points, r 0.8 mm).wear in the case of negative rake angle, is the greatercutting forces encountered with such a rake angle (Fig.10(b). Moreover, the chips produced became caughtbetween the tool and the workpiece, causing damage tothe tool surface. Tools with positive rake angle showedirregular flank wear and excessive pitting in the cuttingedge zone, as shown in Fig. 10(c).The tool nose radius plays a key role in determiningthe wear mode of the tool. As the tool nose radius wasdecreased from 1.6 to 0.8 mm, the tool was found tosuffer from excessive chipping and crater wear, asshown in Fig. 11(a). This tool chipping leads to anincrease in cutting forces and flank wear, as shown inFig. 11(b). Tools with small nose radii are thus recom-mended for finishing operations where light cuttingparameters are used. Small nose radii are also expectedto yield better geometrical accuracy.5. ConclusionThe results of the machinability studies carried outon 20%SiC:Al particulate metal-matrix composites in-dicated the following.(1) The main tool wear mechanism is abrasion andmicro-cutting of tool material grains, manifested asgrooves on the tool face parallel to the chip flowdirection. All of the tools tested also suffered fromflank wear due to abrasion. There was no evidence ofchemical wear (e.g. by diffusion).(2) PCD tools sustained the least tool wear com-pared to TiN coated carbide tools and Al2O3:TiC tools.This is undoubtedly due to PCDs superior hardnessand wear resistance, as well as low coefficient of fric-tion, together with high thermal conductivity. This ledto lower cutting temperatures when PCD tools wereemployed. On the other hand, the TiN coated carbidetools and Al2O3:TiC tools suffered from excessivecrater wear and edge chipping.(3) The grooves formed on the rake face of PCDtools were filled with smeared workpiece material. Thisform of built-up edge is beneficial, since it protects thetool rake from further abrasion.(4) The cutting parameters play a key role in deter-mining the amount of tool flank wear, as well as thesize of the built-up edge. Tool wear is minimized byincreasing the feed rate, which leads to a reduction incontact between the tool and the abrading SiCp. Al-though increasing the cutting speed is expected to accel-erate the flank abrasion wear dramatically, the resultsindicated that the increase in wear is minimal. Highercutting speeds were associated with the increase in thecutting temperatures, which led to the formation of aprotective sticking thin layer of workpiece material onthe tool. This form of protective built-up edge wasprevented from growing in size by the increase speed ofadvantage gained by increasing the feed rate is thechange in chip form. At low feed rates, the chipsformed were continuous, also being difficult and haz-ardous to handle. At high feed rates and high depths ofcut ( f0.35, doc2.0 mm), the chips formed werediscontinuous. Despite the fact that in all experimentswith PCD tools high feed rates resulted in lower toolwear, a conclusive decision about the optimum cuttingparameters should take into consideration the effect ofthe cutting parameters on the surface integrity andsub-surface damage produced in the workpiece. Com-prehensive analysis of the surface integrity and chipmorphology will be presented in the Part II of thisresearch study.4.3. Effect of tool geometryThe tool rake angle had a profound effect on thewear of PCD tools. Three different rake angles wereexamined. As can be seen from Fig. 10(a), tools with 0rake angle out-performed positive and negative rakeangle tools. A possible reason for the increased flankM. El-Gallab, M. Sklad : Journal of Materials Processing Technology 83 (1998) 151158158rubbing. Within the tested range of cutting parameters,the speed of 894 m min 1, f 0.45 mm rev 1anddepth of cut 1.5 mm resulted in the smallest toolwear. These cutting parameters enhance the productiv-ity rates upon using PCD tools.(5) PCD tools with nose radii 16 mm and rakeangle 0 also led to lower flank wear.AcknowledgementsThe authors would like to thank R. Bruski, fromDuralcan, USA and D. Dyer from GE Superabrasives,for supplying the test material and cutting tools and fortheir helpful comments throughout the research project.The experiments were conducted in the machining labo-ratories of the Intelligent Machines and ManufacturingResearch Center at McMaster University.References1 P. Rohatgi, Advances in cast MMCs, Adv. Mater. Process. 2(1990) 3844.2 J.M. Monaghan, The use of quick-stop test to study the chipformation of an SiC:Al metal matrix composite and its matrixalloy, Process. Adv. Mater. 4 (1994) 170179.3 B. Boardman, Metal Matrix CompositesAn Opportunity forthe Off-Highway Industry, SAE International, OH, USA, 1990.4 S. Ramrattan, F. Sitkins, M. Nallakatala, Optimization of thecasting and machining processes for a metal-matrix composite,Proc. Canadian Soc. Mech. Eng. Symp., McMaster University,1996, pp. 624629.5 N. Tomac, K. Tonnessen, Machinability of particulate alu-minum matrix composites, CIRP Ann. 41 (1992) 5558.6 J. Monaghan, P. OReilly, Machinability of aluminum