Research on ultra precision Mirror Machining Technology for. Aluminum Alloy Mobile Phone Shell. Zhu Lili 5, e

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1 Advanced Materials Research Online: ISSN: , Vol. 797, pp doi: / Trans Tech Publications, Switzerland Research on ultra precision Mirror Machining Technology for Aluminum Alloy Mobile Phone Shell Guan Jialiang 1, a, Zhang Xiaohui 2, b, Ma Xinqiang 3, c, Wang Zhiwei 4, d, Zhu Lili 5, e 1,2,3,4,5 College of Mechanical Engineering and Applied Electronics Technology,Beijing University of Technology,Beijing ,CHN a guanjl@bjut.edu.cn, b zhang-xiaohui-ok@163.com, c maxin-qiang@163.com, d wangzhiwei @126.com, e zhulili0216@163.com Keywords: aluminum alloy; Surface quality; polishing parameters; surface roughness Abstract: In this paper, the ultra-precision mirror polishing technology was adopted for mirror processing experimental study of Aluminum Alloy mobile phone shell. The experiments show that: polishing pressure, Grinding disc speed, the texture and hardness of polishing pad and abrasive particle size are the main factors to affect the surface quality. Through to optimize these parameters matching combination, can effectively improve the surface quality and reduce the surface roughness and obtain surface roughness is Ra0.026µm. Introduction Aluminum alloy is a kind of nonferrous metal structure material widely used in industry, it have been extensively applied in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industries. With the rapid development of science technology and industrial economy, the demand for Aluminum Alloy is increasing, and the research of Aluminum Alloy in the field of ultra-precision mirror processing more and more deeply. Meanwhile, it promotes all kinds of processing technology continuously developing such as turning, milling, grinding, polishing and so on, at the same time, the development of various technology expand the application field of Aluminum Alloy. This paper based on mechanical polishing technology,achieving ultra-precision mirror processing effect for Aluminum Alloy mobile phone shell. 1. The basic principle of polishing Mechanical polishing is under the conditions of certain pressure and speed, pouring the polishing liquid between workpiece and polishing disk, relying on the fine grinding machine grain to removal the workpiece surface, to meet the requirement of the workpiece surface ultra-precision mirror machining. This experiment adopts precision and ultra-precision mirror machining to polish aluminum alloy mobile phone shell. Polishing principle as shown in Figure.1, at the begin of machining, the workpiece in the form of grinding removal, abrasive is in the form of sliding and rolling on the surface to removal the material; At the same time, under the action of proper pressure, abrasive will be broken, the number of blunt abrasive increased, the cutting effect gradually weakened, at the same time, the abrasive disk is in the form of friction to removal the workpiece surface, so the surface smoothness increased. On the basis of this, the polishing additive in the liquid formats film All 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 Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-11/05/16,19:56:17)

2 386 Advances in Abrasive Technology XVI layer on the workpiece surface, with the further increase of workpiece surface roughness, grain size is further reduced and homogenization, abrasive and adhesive film combined, so the polishing film is smoothness, flexibility and uniformity, with the new surface and attached film alternating generation and removal, the surface machining quality is getting better, so as to achieve the lower surface roughness. Figure.1 Polishing process schematic diagram 2. Polishing conditions and parameters This experiment adopts precision and ultra-precision mirror machining to polish aluminum alloy mobile phone shell. Aluminum alloy mobile phone shell chemical composition and mechanical properties are shown in Table.1, process parameters are shown in Table.2 and experimental conditions are shown in Table.3. Table.1 Chemical composition and mechanical properties materials Chemical composition (Mass fraction / %) mechanical properties aluminum alloy Cu Si Fe Mn Mg ó b /MPa elongation rate 10(%) ~ ~ ~ Ni Zn Pb Sn 0.05 Ti HB 70 1 Polishing process parameters Table.2 Polishing process parameters polishing pressure(n/cm 2 ) 0.2~0.6 Polishing-disc speed(r/min) 60~150 Polishing eccentricity(mm) 30~40 Table.3 Experimental conditions Laboratory equipment Polishing conditions Machine tools Measuring instrument Polishing pad polishing liquid Frequency control of motor speed optical biaxial polishing machine Beijing times surface roughness measuring instrument TR300 Image acquisition microscope + Panasonic WV-CP460 Leather, velvet, cotton, thin blankets and silk polishing liquidⅠ:diamond (GranularityW1)1:2 kerosene + small amount of animal and vegetable oils polishing liquidⅡ:diamond (GranularityW0.5)1:1 kerosene + grease and vegetable oil

3 Advanced Materials Research Vol The experimental results and analysis Under these conditions, Combined with the chemical composition and mechanical properties of aluminum alloy were analyzed. Using control variables method, By change of pressure size, polishing liquid abrasive size, coarseness of the polishing pad, polishing liquid Species and other parameters for mechanical polishing experiments of aluminum mobile phone covers,and optimize the combination,and to obtain a surface roughness Ra0.026µm the machined surface The effect of polishing and roughness measurement results as shown in Figure.2 and Figure.3, respectively. Figure.2 Polishing effect Figure.3 Roughness measurement results 4. Influence of polishing parameters on machined surface roughness 4.1Influence of polishing pressure on machined surface roughness Keeping other factors constant, changing the size of the polishing pressure, have a significant impact on the machined surface. Within a certain range, the polishing pressure is higher, the greater the efficiency of the processing of the artifacts, but the roughness also becomes larger and larger as the polishing pressure. When pressure is greater than 0.6N/cm 2, abrasive broken serious polishing liquid is extrusion, and splashing around, leading to inadequate polishing liquid between the artifacts and the grinding base plate, polishing uneven, and easy processing surface pitting or pits, the surface quality is not high of the artifact. When the pressure is less than 0.2 N/cm 2, the abrasive particles are not easily damaged and it is difficult to generate scratches in the machining surface, and the removal of the material of surface to be processed is very slow, leading to polishing inefficient. Thus, under the conditions of the other factors constant, the control polishing pressure between 0.2 N/cm 2 and 0.6 N/cm 2 allows filling polishing liquid between the polishing base plate and the artifacts, and the abrasive particles are crushed thinned to expose a new surface and sharp, favorable chip rolling treatment of the machined surface, thereby forming a good machined surface. 4.2Influence of polishing pad on machined surface roughness The polishing pad is the important part in the mechanical polishing process, the polishing pad must have a good corrosion resistance, hydrophilicity and mechanical properties. The hardness and surface roughness of the polishing pad has a direct impact on the accuracy of the machined surface and the removal rate. When the surface roughness of the polishing pad (cotton, fine felt) is high, the gap between the polishing pad and the machined surface is large, and the contact area is small, so that the adequacy of the polishing liquid can be stored between the polishing pad and the artifacts, and the machined surface can be sufficiently in contact with the polishing liquid. Increase the force on single abrasive,

4 388 Advances in Abrasive Technology XVI high removal efficiency, and help to improve processing efficiency. While the rough surface, the residual substances stay in the polishing pad inside can not be discharged which are removed from the surface to be processed and producing scratches in the machined surface. When the roughness of the polishing pad (leather) is extremely low, the polishing liquid filling is not enough, the processing efficiency is lowered. But it can promptly remove residual material resulting from processing, not prone to scratches. The experiments using silk as a polishing pad, get the better the quality of the surface and roughness Ra up to 0.026µm. 4.3Influence of polishing fluids on machined surface roughness As can be seen from Figure.4, the polishing efficiency of polishing liquid Ⅱis lower than that of polishing fluid I, but it can reach the lower surface roughness. This is mainly duing to the different sizes of abrasive grains of the two types of polishing fluid, under certain conditions of other polishing parameters, the smaller abrasive particle size is, the smaller unit area of the force of the individual abrasive grains is, and the removal amount of the surface of the artifacts material also reduce, and the efficiency of processing also reduce ; However, as research the conduct of the polishing, the polishing fluid II may form more and finer abrasive grains, the process involve more abrasive, and it can get a higher quality of surface and lower roughness. Figure.4 The comparation polishing effect of liquidⅠwith polishing liquid II 4.4The morphology analysis of workpiece surface As can be seen from Figure.5, Figure.6, under the mechanical polishing processing, it is the morphology SEM images of the artifacts of surface of aluminum cell phone case.the Lines of the surface of the artifacts is neat and clear after processing, the surface of the artifacts is no chunks of scratches and pits. However, from the following two figures, it can be seen that the scratches of surface of the artifacts of the particle size of W1 of diamond polishing fluid after machining is much more than that of W0.5 multi. The main reason is that when the artifacts is polishing, the smaller the size of abrasive particles are used, the more and the more finer abrasive grains will be formed during processing, so that the abrasive grains per unit area in contact with the surface of the artifacts is much more,and the scratches left after polishing is much weaker. So, the surface quality of W0.5 particle size of the abrasive after machining is better.

5 Advanced Materials Research Vol Figure.5 (left), Figure.6 (right) The morphology SEM images of the surface of the artifacts after processing of polishing liquid I and polishing liquid II 5. Conclusion In the processing of aluminum phone casing by mechanical polishing technology, its polishing effect and processing efficiency were analyzed to the following conclusions: (1)The polishing technology can be adopted for ultra-precision mirror processing effect of aluminum phone casing to obtain clearly texture and good surface quality. (2)In the processing of the mechanical polishing, the different of the polishing pressure and the polishing pad has a significant impact on the roughness of the machining surface, and the polishing pressure was controlled within the range of N/cm 2, and silk is selected as a polishing pad, when machining aluminum alloy phone casing, it can obtain a surface roughness Ra 0.026µm of the Machined surface. (3) The difference of polishing liquid has a significant impact to machining accuracy of the material, in the experiment, it is the use of the polishing solution I (W1 grit diamond 1:2 times kerosene + small amount of animal oils and vegetable oils) and polishing fluid Ⅱ (W0.5 granularity diamond 1:1 times kerosene + grease and vegetable oil) to do polishing experiments in aluminum alloy cell phone case, and the roughness Ra of the surface of the machined surface were 0.034um and 0.026um. That reduce of abrasive particle s size can improve the quality of the artifacts surface. References [1] Guan Jialiang, Yu Xinai, Yang Zhaoxu Young the H62 brass precision mirror polishing process experimental study [J]. Diamond & Abrasives Engineering, 2006, 155 (5):97-98 [2] Guan Jialiang, Lu Hongwei, Chen Zhide, Wang Wenchang. Hardness experimental study of the effect of ELID grinding and machining surface treatment of cold rolled steel carburizing [J]. Diamond Abrasives engineering, (4):46-49 [3] Guan Jialiang, Yuan Zhejun, Zhang Feihu. Development of the new ELID precision mirror grinding fluid. Diamond & Abrasives Engineering [J], 2000(116):40~41 [4] Rong Lierun. Introduction to Ultra-precision Grinding Polishing Method [J]. Aviation Precision Manufacturing Technology, 2005, 41(2):4~7

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