LASER ASSISTED MACHINING OF ALUMINIUM COMPOSITE REINFORCED BY SIC PARTICLE Paper 1906

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1 LASER ASSISTED MACHINING OF ALUMINIUM COMPOSITE REINFORCED BY SIC PARTICLE Paper 196 M. Kawalec 1, D. Przestacki 1, K. Bartkowiak 1-3, M. Jankowiak 1 1 Poznan Univ. of Technology, Institute of Mechanical Technology, 3 Piotrowo St, Poznan, 6-965, POLAND 2 Fraunhofer USA, Center for Coatings and Laser Applications, 4625 Port St., Plymouth, MI 4817, USA 3 Fraunhofer Institute Material and Beam Technology IWS, Winterbergstr. 28, 1277 Dresden, Germany Abstract Metal matrix composites (MMCs) have many industry applications in different sectors, e.g.: automobile and aerospace. However, due to hard ceramic reinforcing components in MMCs, difficulties can arise when machining via conventional manufacturing processes. Heavy tool wear is especially problematic. The Laser Assisted Machining (LAM) method could potentially improve the processing of these materials. In laser assisted cutting, the workpiece area is heated directly by a laser beam before the cutting edge. The work reported here centres on improving Al/SiC composites machinability by laser assisted machining when compared with conventional turning process. Influence of laser during laser assisted turning on cutting force, tool wear and machined surfaces roughness was investigated. This research was carry out for polycrystalline diamond inserts (PCD) and sintered carbide inserts with coated and uncoated. The results obtained with the laser assisted machining were compared with results obtain in conventional turning. Introduction The ongoing demand for more economical, efficient and reliable products, especially in automotive and aeronautical industries, requires the use of lightweight materials with excellent mechanical properties. Among the many advanced engineering materials, SiC reinforced aluminum-based composites are one of the most important lightweight metals. Mechanical and physical properties of light metal matrix composites such as high specific strength, stiffness and wear resistance indicate that these materials are becoming increasingly attractive for engineering applications. Aluminum reinforced with SiC particles is one of the combinations of MMC s, which has more significance in the areas of aerospace and automotive engineering components and other diverse industries. However, the abrasive ICALEO 28 Congress Proceedings reinforcement particles used in these materials make them difficult to machine using conventional methods. Several researchers have carried out experiments on machining of MMC s as well. The main concerns when machining MMC is the extremely high tool wear due to the abrasive action of the ceramic particles [2], [3], [7], [8], [1] and [11]. Therefore, materials of very high resistance to abrasive wear are often recommended. The cemented carbide tools are preferred for rough machining and PCD tools for finish machining operations. The cost of PCD tools increases the cost of production so it is necessary to find an alternative method to machine MMCs. As a consequence, hybrids machining processes, e.g. Laser Assisted Machining (LAM), are become more popular to machine difficult machining materials. The laser irradiation heats the workpiece area directly before the cutting edge. This makes the material softer and easer in plastic deformation. It was found that LAM is an efficient way of improving the machinability of aluminum matrix composites, without resulting in the significant negative influences on the properties of bulk materials [12]. These authors have also studied the effect of YAG continuous solid laser heat assisted machining during turning Al 2 3 p/al composite. They noticed that LAM can effectively reduce tool wear and increase tool life. The machined surface quality was improved in LAM in comparison with conventional cutting. In our previous LAM investigation of AlSi9Mg, reinforced with 2 vol. % SiC, CO 2 laser was involved in the process. The laser power range was P = 2.34 kw [6]. Those experiments proved that LAM is an effective method of SiCp/Al composite machining, especially in low range value up to 1kW of laser power. The LAM of MMC has been studied to demonstrate tool life and show improvement of the machined surface quality as well. Currently our study is an extension of previous work by examining the tool wear and machined surface roughness during turning the Al/SiC composite. This paper also reports up to date LAM of Al/SiC composite results using CO 2 laser. Page 895 of 99

2 Experiments The machinability investigations defined by the wedges wear, determined by VB c parameter and the machined surface roughness, determined by Ra parameter, cutting force Fc and structure of machined surface was carried out during LAM and conventional straight turning of the metal matrix composites. The laser assisted turning workstation is illustrated in Figure 1. The workpiece material consisted of a AlSi9Mg aluminum alloy matrix (composition: 9.2% silicon,.6% magnesium,.1% iron) to which 2% of silicon carbide with a particle size of between 8 to 15 µm had been added. The investigated material was produced by molten metal mixing and direct chill casting by DURALCAN Inc. Original cast was melt and cast again by gravity casting method in Division of Foundry at the Poznan University of Technology. Structures of these alloys have been shown in Figure 2. The workpieces (cylindrical shape of 1 mm length and 5 mm in diameter) were coating by absorptive substation each time to reduce laser beam reflectivity. Fig.1 View of workstation. 1-workpiece material, 2- cutting tool, 3- low-temperature pyrometer (measurement temperature in cutting zone), 4- high-temperature pyrometer (measurement temperature in heating zone by laser beam), 5-laser head The workstation is consisted from CO 2 molecular 26W power laser (TLF 26t, TRUMPF) and universal lathe (TUM 25D1). Surface temperatures were measured by two RAYTEK pyrometers (model: MA2SC and S5XLT). Temperature was measured in the heating area, by ICALEO 28 Congress Proceedings laser beam and also in the machining zone at the same time (Fig.1). Distance angle between heated area by laser beam and machining zone was 3 degree. Emission was set in the software to a value of =.3 based upon preliminary calibration tests. Fig.2 Microscope image of the Al/SiCp material microstructure. The SiC particles (have darker colour on the pictures) are distributed through the matrix The tool wear and the machined surface roughness were measured for each trial of the experiment. The machined surface roughness of the turned surface was measured by portable surface measuring system (Hommel T5). The measuring head was traced over the machined surface in the direction of feed motion. The arithmetic mean deviation Ra (µm) with cut-of length was.8 mm (measuring length was 4.8 mm) was applied as criterion for evaluating the surface finish. The machined surface finish was characterized by the average arithmetic roughness, which was determined by averaging the arithmetic roughness values for the surface roughness profiles at 6 equally angular spaced radial sections on a turned surface. Another more precise roughness measuring machine (Hommel T8) was used to determine geometrical surface structure and power spectral density (PSD) of the machined surface roughness. This surfscan apparatus is a high accuracy measuring system with a resolution of 6 nm over the entire measuring range of 6 mm. Tool wear was measured on the primary flank face by the optical microscope. Conventional and laser assisted turning tests were carried out using different wedges. The characteristic of applied edges are shown in Table 1. During turning experiments, machining forces were measured by force gauge extensometer own construction as well. The research were carried out with constant cutting parameters: a p =,1mm, f =,4mm/rev and v c = 1m/min. Variable parameter was laser power P = 1 W. Page 896 of 99

3 Table 1 Characteristic of applied edges Type of edge material Symbol of insert Coating Insert 1 Sintered carbide inserts with fine-grain substrate 2 Sintered carbide inserts 3 Sintered carbide inserts 4 Polycrystalline diamond PCD material KC551 (PVD) TiAlN coated H1S cemented uncoated H1S cemented uncoated KD1 cemented uncoated SNMG1248 SNMA1248 TNMA1248 TPGN1134F In this research the worn out cutting tools were examined under an optical microscope. It was observed that flank wear was associated with uniform abrasion wear track (Fig.4). It correlates well with the previous work [4], [9] and [13]. This wear land on the flank surface appeared due to severe abrasion between the cutting tool and the reinforced ceramic particles that were significantly harder in case of sintered carbide inserts than the cutting tool material. The hard particles SiC grind the flank face of the cutting tools on similar way of a grinding wheel during machining of materials. Results and discussion In Figure 3 the effect of the different laser power on the temperatures in cutting area are shown. It was noticed that the temperature ( ) in cutting area increases with laser power. [ C] AlSi9Mg + 2% SiC d=5 mm, l=1 mm, f l =.4mm/rev, =.3, a p =.1mm, v c =1m/min, d l =2mm P=W P=3W P=6W P=8W P=1W t [s] Fig.3 Comparison of measured temperatures in cutting area with different power of laser beam Many of the investigations contain some element of tool wear analysis with the majority finding that tool wear depends on process temperature. Bames [1] found that increasing of aluminum/sic metal matrix composites machining temperature resulted in decreasing tool life. They claim that the increase of workpiece temperature reduces the Built-Up Edge (BUE), which protects the tool rake face from wear. These conclusions can explain the lower tool wear for laser power P = 6W (Fig.5), which respond temperature about 36 o C (Fig.3) and increased tool wear with increased power of laser (Fig.5). ICALEO 28 Congress Proceedings Fig.4 View of abrasive wedge wear H1S insert KC551 insert In Figure 5 wear of difference material inserts investigated during conventional and laser assisted turning process for selected power of laser beam is presented. These results indicated that as a consequence of heating the wedge wear was decreased significantly for two uncoated inserts made of H1S material. VBc [mm],9,8,7,6,5,4,3,2,1 TNMG 1248 H1S SNMA 1248 H1S d=5 mm, l=1 mm, f=.4mm/obr, a p =.1mm, v c=1m/min, SNMG 1248 KC551 KD P [W] Fig.5 Influence of laser power on wedge wear parameter VBc with different tool materials, when turning aluminum composites For those inserts the lowest wear was noticed for 6W of laser power. This value gave about 35% lower wedge wear in comparison with conventional turning. However, it is equally important to note that when comparing all results, for all examined values Page 897 of 99

4 of laser power LAM the wedge wear for uncoated sintered carbide inserts was smaller compared to conventional turning when machining Al/SiC metal matrix composite. Whereas for residual two inserts (KC551, KD1) wear is comparable for conventional and laser hot turning. This result is itself very important. It indicates that although SiC particle as well the hardness of the matrix materials are known to dominate the wear characteristic of these materials, the tool geometry and material of coating can also considerable effect on the value of wear rates observed during cutting. The machined surface roughness is one of the most important quality indices of machined surface MMCs. Figure 7 shows the influence of power machining on machined surface roughness characteristic, i.e. Ra parameter during turning of Al/SiC metal matrix composite m 18.8 µm Fc [N] d=5 mm, v c=1m/min, P=6W, f=.4mm/rev, a p =.1mm, Conventional cutting SNMA 1248 H1S KD1 LAM t [s] Fig.6 Cutting forces distributions during conventional and laser assisted turning During turning aluminum matrix composites noticed decrease of cutting force for sintered carbide inserts during LAM in comparison with conventional turning (Fig.6). It s important to mention that in both cases cutting force increase during turning process. Intensive wedge wear was cause for this effect. In case of PCD insert cutting forces value was comparable for conventional and laser hot turning (Fig.6) because wedges wear in both cases had the comparable values (Fig.5). Ra[µm] 1,1 1,5 1,95,9,85,8,75,7,65,6,55,5,45,4,35,3,25,2,15,1,5 AlSi9Mg + 2% SiC -range d=5 mm, l=1 mm, f=.4mm/rev, a p =.1mm, v c=1m/min, - conventional cutting - LAM - SNMG 1248 KC551 - SNMA 1248 H1S - TNMG 1248 H1S - KD P[W] Fig.7 Comparison of machined surface roughness between conventional and laser assisted turning of aluminium matrix composite 1.11 mm f f=,4 =,4mm/rev PSD µm ,12.1.8,6.6.4,149mm (,368µm).21m m (.339µm ).149m m.239m m (.368µm ) (.256µm ) 3.91 mm 4.7 mm mm Zoom factor: x4 Smoothing: 3,646mm.55m m (.28µm ).646m m (,257µm) (.257µm ),2,4,6,8,95 mm Fig.8 Machined MMC geometrical structure ( and power spectrum density of the roughness profile ( after conventional turning process within uncoated sintered carbide H1S inserts. Parameters: v c = 1m/min, a p =,1mm, f =,4mm/rev and obtained VB c =,72 mm 9.9 m.25.15, µm 1.23 mm f =,4mm/rev PSD,117mm.1 45m m,225mm.255 m m (.3 55µ m ).44µ m ).11 7m m.213m m µm 2 µ m 2 (,512µm) (.51 ) (.498µ(,44µm) m ),2.2,538mm (,393µm).538 m m (.393 µm ).47 7m m (.27 6µm ).62 8m m (.36 µm ) 4.7 mm 4.7 mm mm,2,4,6,8,95 mm Fig.9 Machined MMC geometrical structure ( and power spectrum density of the roughness profile ( after laser assisted turning within uncoated sintered carbide H1S inserts. Parameters: v c = 1m/min, a p =,1mm, f =,4mm/rev, P = 6W and obtained VB c =,57 mm ICALEO 28 Congress Proceedings Page 898 of 99

5 The significant differences in machined surface roughness have been observed for laser assisted turning and conventional turning by sintered carbide inserts (Fig.7, 8a and 8. However, for conventional turning, it is seen that average machined surface roughness value increased in comparison with LAM. It can be explained if the cutting zone was not heated by laser beam; the SiC reinforcement was pushed through the soft matrix or pulled out of matrix during cutting. Cracks and pits were formed on the machined surface (Fig.8 and this caused poor surface finished. Surface roughness produced by LAM is much lower, for all value of laser power, than that by conventional turning (Fig.7). The test results show the significant differences (about 31% for SNMA1248 H1S, 37% for SNMG1248 KC551 and about 45% for TNMA1248 H1S) in machined surface roughness for laser assisted turning with 6W of laser power in comparison with conventional turning m 17.6 µm f =,4mm/rev PSD,127mm µm 2 (.3 47µ m ) (.24 3µ m ).6 2m m.1 53 m (.22(,347µm) 2µm ) (.2 45 ),2,1 (.1 81µ m ).298 m m (.215 µm ) 3.85 mm 4.7 mm,2,4,6,8,95 mm Figure1. Machined MMC geometrical structure ( and power spectrum density of the roughness profile ( after conventional turning process within polycrystalline diamond (PCD) inserts. Parameters: v c = 1m/min, a p =,1mm, f =,4mm/rev and obtained VB c =,7 mm Other research [11] pointed out that the creation process of machined surface for aluminum reinforced alloys depends on the cutting temperature. Another reason for the random character of the machined surface creation could be the built-up edge appearance during turning process. In case of PCD inserts the wedge wear had the same value during conventional and laser assisted turning so also machined surface roughness had compared values ICALEO 28 Congress Proceedings (Fig.7, 9a and 9 nevertheless larger than obtained after sintered carbide by reason of difference in corner radius m 17.3 µm f =,4mm/rev PSD,114mm,259mm µm 2 (,227µm),12,6.2 3m m (.3 6 7µ m ) m m.2 5 9m m (,272µm) ) (.2 2 7µ m ),477mm (,31µm).4 3 m m (.1 8 7µ m ).4 7 7m m (.3 1 µm ) 3.85 mm,643mm 4.7 mm.5 5 2m m.72 5 m m (.1 9 5µ m ) (.18 4 µm ) m m (,259µm) ),2,4,6,8,95 mm Figure11. Machined MMC geometrical structure ( and power spectrum density of the roughness profile ( after laser assisted turning within polycrystalline diamond (PCD) inserts. Parameters: v c = 1m/min, a p =,1mm, f =,4mm/rev, P = 6W and obtained VB c =,7 mm The analysis of power spectrum density (PSD) roughness profile proved that all machined geometrical structure had random character with significant disturbances of the cutting edge kinematics representation. On PSD diagrams can not observe dominate length profile come from using feed rate (f =,4mm/rev) in case of conventional and laser assisted turning (Fig.8b, 9b, 1b and 11. Conclusions The results of turning studies on SiC particlereinforced aluminium alloy composites using three different inserts were presented. The effect of laser assisted machining on wedge wear, cutting force and machined surface roughness was measured. The work reported here confirms that it is beneficial to make an integration of laser technology in turning process. The following conclusions have been drawn: The primary wear mechanism on the wedge wear was abrasion wear of the tool flank during laser assisted and conventional turning, Laser Assisted Machining (LAM) can effectively reduce tool wear and improves the surface quality in comparison with conventional turning in case of sintered carbide inserts, Page 899 of 99

6 Turning with laser heating improve machined surface roughness in comparison with conventional turning for examined inserts with the exception of PCD insert, Result review indicated that P = 6W laser power gives minimal tool wear and lower machined surface roughness during Al/SiC composite machining, There is possible the significant decreasing of wear of some cemented carbide wedges during turning of metal-ceramics composite by using laser heating after the removed cut. References [1] Barnes S., Morgan R., Skeen A., (23) Effect of laser pre-treatment on the machining performance of aluminum/sic MMC. Journal of Engineering Materials and Technology 125, pp [2] Ding X., Liew W.Y.H., Liu X.D., (25) Evaluation of machining performance of MMC with PCBN and PCD tools. Wear 259, pp [3] Ibrahim C., Turker M., Seker U., (24) Evaluation of tool wear when machining SiC reinforced Al-214 alloy matrix composites. Materials and Design 25, pp [4] Ibrahim C., Turker M., Seker U., (24) Evaluation of tool wear when machining SiC reinforced Al-214 alloy matrix composites. Materials and Design 25, pp [5] Jankowiak M., Król G. et al., (1997) Micro and macro-roughness of aluminum alloys, particularly metal matrix composites after precise machining by polycrystalline diamond wedges, Poznan University of Technology, Institute of Mechanical Technology, Research Project Nr 7S1297, Poznan [6] Jankowiak M., Przestacki D., Nowak I., (27) Effect of CO 2 laser beam applied during machining of SiC particle reinforced aluminum matrix composites. 5th International PhD Conference on Mechanical Engineering, September 6-8, Pilsen, Czech Republic, pp [9] Sahin Y., Sur G., (24) The effect of A1 2 O 3, TiN and Ti (C,N) based CVD coatings on tool wear in machining metal matrix composites. Surface and Coatings Technology 179, pp [1] Sahin Y., (25) The effects of various multilayer ceramic coatings on the wear of carbide cutting tools when machining metal matrix composites. Surface & Coatings Technology 199, pp [11] Tomac N., Tonnesen K., (1992) Machinability of particulate aluminum matrix composites. Annals of the CIRP Vol. 41/1, pp [12] Wang Y., Yang L.J., Wang N.J., (22) An investigation of laser-assisted machining of Al 2 O 3 particle reinforced aluminum matrix composite. Journal of Materials Processing Technology, Vol. 129, pp [13] Xiaoping L., Seah W. K. H., (21) Tool wear acceleration in relation to workpiece reinforcement percentage in cutting of metal matrix composites. Wear 247, pp Meet the Author Konrad Bartkowiak is a Lecturer at the Institute of Mechanical Technology, part of the Division of Machining at the Poznan University of Technology, Poland. He initially studied automotive engineering before embarking on research in lasers. After his Masters in Poznan University of Technology, he carried out doctoral research in applications of laser heat treatments for industry. He is a Marie Curie research fellow at the Fraunhofer Institute Material and Beam Technology IWS Dresden, Germany researching direct laser deposition including spectroscopy analysis. Currently his first phase of research project is hold at the Fraunhofer USA - Center for Coatings and Laser Applications, Plymouth, Michigan. He has broad research interests in the engineering applications of lasers including laser forming, laser hardening, laser alloying and laser machining hybrid technology. [7] Kilickap E., Cakir O., Aksoy M., Inan A., (25) Study of tool wear and surface roughness in machining of homogenized SiC-p reinforced aluminum metal matrix composite. Journal of Materials Processing Technology, Vol , pp [8] Kishawy H. A., Kannan S., Balazinski M., (25) Analytical modeling of tool wear progression during turning particulate reinforced metal matrix composites. Annals of the CIRP Vol.54/1, pp ICALEO 28 Congress Proceedings Page 9 of 99