Surface Quality of AlSiCp Composites

Applied Mechanics and Materials Vol. 42 (2011) pp 363-366 Online available since 2010/Nov/11 at © (2011) Trans Tech Publications, Switzerland doi:10.4028//AMM.42.363Study on Surface Quality of Al/SiCp Composites with Ultrasonic Vibration High Speed Milling Daohui Xianga, Xintao Zhi, Guangxi Yue, Guofu Gao and Bo ZhaoSchool of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo 454000, China dhxiang@ Key words: Ultrasonic Milling, Al/SiCp composites, Surface Quality, Surface Microstructure, MMCsAbstract. Al/SiCp composites with excellent physical and mechanical properties are applied widely in the aerospace, automotive, national defense, electronics and other fields. High content and high hardness SiC particles lead to poor machinability and that further application is restricted. Surface microstructure and surface formation mechanism of Al/SiCp composites were studied under condition of ultrasonic vibration milling and conventional milling. The experimental results show that machined surface had the same defects, but SiC particles were mainly direct sheared in ultrasonic milling different from the conventional milling, the roughness (Ra) of the surface generated in the ultrasonic vibration milling was smaller. At last, the formation mechanism of surface topography in the ultrasonic milling was analyzed. The research indicated that ultrasonic milling could obtain better surface quality than conventional milling and with high efficient. Introduction Al/SiCp composites are widely applied in the aerospace, national defense and other fields, and are being researched and developed at above domain [1-3]. Due to SiC particles existence, Al/SiCp composites chip formation is similar to the crack propagation and fracture process of brittle materials, machined surface existing cracks and flaws [4, 5]. As the ultrasonic vibration cutting can reduce cutting force and cutting temperature, which has been researched in drilling and turning [6], it will be a useful trial to apply ultrasonic vibration to the machining of Al/SiCp composites. According to correlative literature, no research has yet been carried out on Al/SiCp composites with ultrasonic milling; in addition, SiC particles content of volume was lower than 40% in the previous researches. When SiC particles content of volume is higher than 40%, tool wear is very serious, so that it is difficult to cut with the current conventional methods. At present, with the development of material, the higher SiC content of volume in MMCs materials is needed especially in aerospace fields. Milling is the only method of achieving efficient machining of cast Al/SiCp composites with variation shapes and larger machining allowance, particularly in many cavity machining. So roughness and surface quality of high volume Al/SiCp composites in ultrasonic milling were researched and analyzed in this paper. Experimental Equipment and Methods PCD milling cutter has been widely applied on high efficiency, precision machining of the non-ferrous materials [7]. Hence, PCD cylindrical end milling cutter with diameter 6 mm and 3 blades is used. The type of machining center is DMU80U with the spindle speed of 20~20000 r/min. The size and content of SiC particles contained in the Al/SiCp composites are 30μm and 65% respectively. Hardness of SiC particles is HV 11.9~12.6 GPa. Ultrasonic vibration produced by self-made vertical vibration device is acted on the tool and its direction is longitudinal in ultrasonic vibration milling. And amplitude and frequency of ultrasonic vibration are 15μm and 35kHz respectively(as shown in Fig.1). Machined surface is observed with the scanning electron microscopy S-520-type SEM. Roughness of machined surface is measured with JJI-B-type three-parameter surface roughness measuring instrument. The experiment is carried out betweenAll rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, . (ID: 112.122.130.188-29/03/12,13:52:36)364History of Mechanical Technology and Mechanical Designconventional milling and ultrasonic milling at the same situation where only milling speed changes from 113 m/min to 337 m/min, and invariable feed engagement, milling depth, milling width is 0.02mm/z, 0.2mm, 6mm respectively.1.8 1.6 1.4ultrasonic milling conventional millingRoughness Ra [µm]1.2 1.0 0.8 0.6 0.4 0.2 0.0 100 150 200 250 300 350Milling speed [m/mm]Fig. 1The schematic for ultrasonic milling apparatusFig. 2The effect of the milling speed on surface roughnessExperimental Results and Analysis Surface Roughness in Ultrasonic Vibration Milling and Conventional Milling. Milling speed is changed from 113 m/min to 337 m/min, but feed and depth of milling are respectively remained 0.02 mm/z and 0.2 mm during conventional milling and ultrasonic milling. Surface roughness (Ra) of Al/SiCp composites is shown in Fig. 2. As can be seen from Fig.2, surface roughness gradually increases as the milling speed (lower than 290m/min) increase in both ultrasonic vibration and conventional milling. As the cutting speed increases, cracks can easily cross high strength SiC particles and expand, thus results in more fragmentation of SiC particles in the non-directional slip of matrix. But, surface roughness value under the condition of ultrasonic vibration milling is smaller than those of conventional milling. This is because that the homogeneous vibration tool indirectly contacts with the workpiece, and the workpiece cooling conditions in the cutting area could achieve improvement. Thus the material surface is uniformly removed, with surface carved out of uniform depth. So the surface roughness is small in ultrasonic vibration milling. Effect of SiC Particles on the Machined Surface in the Ultrasonic Milling. Analysis on surface microstructure is carried out in the ultrasonic milling. All the images are obtained by the SEM at the condition where milling speed, feed, depth and width of milling are respectively remained 262 m/min, 0.2 mm/z, 0.6 mm and 6mm. Fig. 3 shows the damaged surface caused by SiC particles in the ultrasonic milling with PCD milling cutter. Fig. 3(a) shows the images of the direct sheared SiC particles. This phenomenon is expected in the machining of Al/SiCp composites. Sharp cutting nose accumulating a great deal of energy in the ultrasonic vibration conditions could directly shear silicon carbide particles, easily. Fig. 3(b) shows the SEM images of surface microstructure pressed into by SiC particles. When the cutting edge encounters the upper of SiC particles in the later period, SiC particles were pressed into the soft matrix by flank. Fig. 3(c) shows that SiC particles are pulled-out of matrix. Shear stress is greater than bonding strength between the SiC particles and the matrix, when the cutting edge encounters the bottom of SiC particles, SiC particles are pulled out from the soft matrix. Fig. 3(d) shows the defected surface of matrix scratched by SiC particles. The reasons are as follows. The size or shape of SiC particles is not the same and their distribution is discontinuous. Along with the tool wear in the later period of ultrasonic milling, fractured SiC particles could not effectively be cut, then accumulate on the rack face, then scratch the machined surface.Applied Mechanics and Materials Vol. 42365(a) SEM of sheared SiC particles(b) SEM of SiC particles pressed into the matrix(c) SEM of SiC particles pulled out (d) SEM of SiC particles scratch the surface Fig. 3 SEM of machined surface of Al/SiCp composites under the conditions of ultrasonic millingAnalysis of Surface Micro-morphology in Ultrasonic Vibration Milling. Machined surface micro morphology of the Al/SiCp composites under condition of ultrasonic vibration milling and conventional milling are showed in Fig. 4. From Fig. 4(a), we can see that majority SiC particles are directly sheared by the tool, few are pulled out of matrix, voids in surface are little, cracks and scratches in surface are not obvious at the junction of SiC particles and matrix. Fig. 4(b) shows there are many of voids and crack. From above, good surface quality was obtained by using ultrasonic vibration milling. The reason is that high hardness and high strength SiC particles are directly sheared by the PCD tool, not putted off the soft matrix under condition of ultrasonic vibration milling.(a) ultrasonic milling (b) conventional milling Fig. 4 Al/SiCp composites micro-morphology in milling Analysis of Experimental Results. Under the conventional milling conditions, existence of high hardness SiC particles results that the harmful vibration aggravate, tool sharpness gets down, tool flank wear increases, and cutting force and cutting heat of continuous milling increase. Hence, surface quality is poor in conventional milling. For the additional ultrasonic vibration existence, under the same conditions, ultrasonic milling can obtain better surface quality than conventional milling. The reasons are as follows. First, the contact of tool and chip is a discontinuous separation process, which has advantage of the cooling between chip and tool. Second, PCD tool nose gathered a great deal of energy in ultrasonic vibration, which can easily shear high hardness SiC particles directly. Third, milling cutter attached axial vibration has advantage of reducing torque in the milling and enhancing the rigidity of milling366History of Mechanical Technology and Mechanical Designcutter, can achieve a smooth cutting of Al/SiCp composites, and effectively avoid that the pulled-out SiC particles scratch the machined surface and other defects. In addition, additional axial vibration is equal to the rolling on the surface by the tool flank, which can greatly increase surface smoothness. Conclusions Through the study of Al/SiCp composites micro-morphology in ultrasonic vibration milling and conventional milling, SiC particles affect on the surface in ultrasonic vibration milling is identical to conventional milling. There are four types of SiC particles directly sheared, SiC particles pulled-out, SiC particles pressed into the matrix and matrix scratched. However, most SiC particles are directly sheared in ultrasonic vibration milling. From experiment it is found that when the cutting speed is below 290 m/min, the surface roughness values in the ultrasonic vibration milling are smaller than conventional milling. Therefore, ultrasonic vibration milling can get a better surface quality in practical work and improve machining efficiency. Milling cutter attached axial vibration has advantage of reducing torque in the milling and enhancing the rigidity of milling cutter, can get better surface quality. Hence, axial ultrasonic vibration technology can expand the range of machining components in the practical production, with the capable of machining large, thin-walled parts. Acknowledgement This topic of research is supported by National Natural Science Foundation of China (No. 50975080), Foundation of He’nan Educational Committee (No. 2010A460008), Research Fund for the Doctoral Program of Henan Polytechnic University (No. B2009-71) and Key Laboratory of Mechanical Engineering of Henan Province. Reference [1] Cole GS and Sherman AM: Materials Characterization, Vol. 35 (1995), pp.3-9. [2] Davim JP and Baptista AM: Journal of Materials Processing Technology, Vol. 103 (2000), pp. 417-423. [3] Lin JT, Bhattacharyya D and Ferguson GW: Composites Science and Technology, Vol. 58 (1998), pp.285-291. [4] A.B. Sadat and M.Y. Reddy: Experimental Mechanics, Vol. 33 (1993), pp. 343–348. [5] A. Abdel Hamid, A.S. Wifi and M. El-Gallab: Journal of Materials Processing Technology, Vol. 56 (1996), pp. 643-654. [6] Z.X.Tie and B.Zhao: Manufacturing Technology & Machine Tool, Vol. 4 (2003), pp. 36-38 (In Chinese) [7] El-Gallab.M and Sklad. M: Journal of Materials Processing Technology, Vol. 83 (1998), pp. 151-158History of Mechanical Technology and Mechanical Design 10.4028//AMM.42Study on Surface Quality of Al/SiCp Composites with Ultrasonic Vibration High Speed Milling 10.4028//AMM.42.363 DOI References [1] Cole GS and Sherman AM: Materials Characterization, Vol. 35 (1995), pp.3-9. doi:10.1016/1044-5803(95)00063-1 [4] A.B. Sadat and M.Y. Reddy: Experimental Mechanics, Vol. 33 (1993), pp. 343–348. doi:10.1007/BF02322151。