Effects of process parameters on surface gloss in Rapid Heat Cycle. Molding process

Transcription

1 Advanced Materials Research Online: ISSN: , Vol. 497, pp doi: / Trans Tech Publications, Switzerland Effects of process parameters on surface gloss in Rapid Heat Cycle Molding process Li Jiquan 1,2,a,Chen Chuan 1,b, Jiang Shaofei 1,c,, Chai Guozhong 1,d, Lian Zhibiao 3 1 Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Zhejiang University of Technology, Ministry of Education, Hangzhou, China, State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan, China, North City Industrial Area, Jingsi(1) Road, Huangyan, Taizhou, China, a lijq@zjut.edu.cn, b chench008@163.com, c jsf75@zjut.edu.cn, d chaigz@zjut.edu.cn Keywords: process parameters; surface gloss; Rapid Heat Cycle Molding Abstract: Rapid Heat Cycle Molding is a novel injection molding, which may improve product surface quality effectively. In this paper, one-factor experimental design and Taguchi method were used and the influence of different process parameters (mold heating temperature, melt temperature, injection rate, injection pressure, and packing pressure) on surface gloss of injection product was studied. The results showed that temperature is the significant factor to the surface gloss. Mold heating temperature is principal factor in mold process parameters, while the melt temperature is the secondary factor and injection pressure is the least. The surface gloss increases with increasing mold heating temperature, melt temperature, injection rate through whole processing, while it increases to top then decreases with increasing injecting and packing pressure. 1. Introduction Rapid Heat Cycle Molding(RHCM) is a promising injection molding which may improve products surface quality obviously. The advantages of Rapid Heat Cycle Molding compared with Conventional Molding lie in eliminating the weld line and surface fiberglass revealed, improving the gloss and surface hardness, canceling the secondary processing, shortening the forming cycle and reducing the cost of production [1-5]. RHCM is used in the fields of TV panels, computer LCD monitors, air condition cases, cell phone cases and other products which need high requirement of surface quality. The researches of RHCM are mainly focused on the mold heating methods, while investigations for surface quality are rarely to be reported [6, 7]. In this study, surface gloss was selected as the main index of surface quality and injection molding experiments were taken to investigate the effects of different process parameters in RHCM on surface gloss. 2. Experiment equipment and experiment method 2.1 Experiment equipment The injection machine used in this experiment is MA3800 with clamping force of 3800KN and maximal injection pressure of 210MP, made by Ningbo Haitian plastic machinery group co., LTD. The mold heating equipment is electric heating controller with type MTS32-Ⅱ. The material used in this experiment is HDPE (T60-800). And surface gloss is measured by gloss meter WGG-60. 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-13/05/16,02:18:07)

2 Advanced Materials Research Vol Experiment method In this study, one-factor experimental design is used to research on influence of process parameters on the product surface gloss first. Then Taguchi method is employed to find the influential effect of the parameters. pressure, injection rate, melt temperature, mold heating temperature and packing pressure are regarded as recommendable factors. 3. Experiment results and discussion In the experiment, each parameter is changed while other parameters remained unchanged to observe the trends of the product surface gloss, after ensuring there is no flash or short filling of the product. Experiments are listed in Table 1 and the experimental sample is shown in Fig.1. Fig.1. Experimental sample of RHCM No. Table.1 The experiments of one-factor experiment Mold heating temperature ( C) 1 25(no heating) 2 70 Melt temperature ( C) pressure rate(%) Packing pressure

3 Surface gloss/gs 134 Ultra-Precision Machining Technologies, CJUMP2011 As is shown in Fig.2, surface gloss is improved with increasing mold heating temperature significantly. Surface gloss of conventional injection molding is about 64Gs, while gloss of RHCM is above 80Gs. When the light beam exposure on the product surface, the direction of reflection will be scatted. The bad ability of the light reflection results in low gloss looked. The smoother surface is, the better the gloss will be [8]. While increasing mold temperature during filling and packing stage of Rapid Heat Cycle Molding, temperature gradient between the center of melt and wall, especially when the mold temperature is raised over plastic heat distortion temperature, the liquidity of polymer melt is improved, the production of frozen layer is avoided, heat loss of melt in the cavity is reduced, leading the melt filling effect to be better and the surface to be smoother. Later, in the late packing stage the rapid cooling turns the melt into curing rapidly, with no time to shrink to ensure the quality of product. So the surface quality is improved and the surface gloss is increased finally. Surface gloss is increased slightly with increasing melt temperature. High mold temperature makes good liquidity of polymer melt and viscosity of the melt is reduced with increasing the melt temperature. So the melt contact with mold, the liquidity will be higher and surface will be smoother, leading surface gloss to be better. It is also found that the increasing rate of gloss with melt temperature keeps almost the same, while increasing rate of gloss with mold heating temperature decreases when the mold heating temperature gets higher. The influence of injection pressure, injection rate and packing pressure on surface gloss is less than the formers. The fluctuation value of injection pressure, injection rate and packing pressure is 0.6Gs, 2.86Gs and 1.29Gs, while the mold heating temperature and melt temperature s is 33.79Gs and 3.54Gs. pressure shows pressure of screw top on melt, which overcome the flow resistance. For good liquidity of polymer melt needs smaller flow resistance to overcome, the influence of injection pressure is little. Increasing injection rate can improve the melt liquidity and melt flow rate is increased. Increasing packing pressure can compact the melt, they both improve the surface gloss finally. While the result of injection pressure and packing pressure both increases first and then decreases Mold heatig temperature/ Melt temperature/ pressure/mpa rate/% Packing pressure/mpa Fig.2 Change trend of surface gloss with the main process parameters Ensuring that there is no flash or short filling, the Taguchi method is used to find the influential effect of the parameters. The experiments are shown in table.2.

4 Advanced Materials Research Vol Table.2 The levels value of parameters Rank Mold heating temperature ( C) Melt temperature ( C) pressure rate(%) Packing pressure By range analysis of the Taguchi method experiment results, it s found that the most significant factor is mold heating temperature; the second significant effect is melt temperature and injection pressure is the least. The significant factor decreases in the order mold heating temperature>melt temperature>packing pressure>injection rate>injection pressure. The results are showed in Tab.3. Tab.3 Results of range analysis Rank difference Mold heating temperature( C) Melt temperature( C) pressure rate (%) Packing pressure K K K K R order Conclusions molding experiments have been performed in the study. From the results, some useful conclusions can be stated as follows: (1) Temperature is the significant factor to the surface gloss. Mold heating temperature is principal factor in mold process parameters, while the melt temperature is the secondary factor and injection pressure is the least. (2) The surface gloss increases with increasing mold heating temperature, melt temperature, injection rate through whole processing, while it increases to top then decreases with increasing injecting and packing pressure. 5. Acknowledgment The Project was Supported by State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology(No P04), the Public Industrial Technology Projects of Zhejiang Province (No.2010C31050), the State Funds for Key laboratory of E & M(Zhejiang University of Technology) Ministry of Education & Zhejiang Province(No.2010EM004), National Nature Science Foundation of China( ).

5 136 Ultra-Precision Machining Technologies, CJUMP2011 References [1] Chen Shiachung, Jong Wenren, Chang Jenan. Dynamic mold surface temperature control using induction heating and its effects on the surface appearance of weld line. Journal of Applied Polymer Science, 101 (2006) [2] Zhang Peng,Cheng Yongqi,Song Caifu. Rapid heat cycle molding for high glossy product and its key technology. Engineering Plastics Application, 37(2009) [3] DongGang Yao, Byung Kim. Development of Rapid Heating and Cooling Systems for Molding Applications. Polymer Engineering And Science,42 (2002). [4] Wang Guilong, Zhao Guoqun, Li huiping, Guan Yanjin. Study of variotherm injection molding technology and analysis on its application. Modern Chemical Industry,29 (2009) [5] Wang Guilong, Zhao Guoqun, Li huiping, Guan Yanjin. Research and application of rapid heating cycle molding technology. Journal of Plasticity Engineering, 16 (2009) [6] Liu Donglei. Research on Rapid Heat Cycle Molding technology. Nanchang University, [7] Zhong Jiasheng. Variable Mold Temperature Method and Study the Surface Quality of Product. National Central University, [8] Liu Donglei, Xin Yong. Process Mechanism in Microstructure of High-gloss Surface Parts Molded by RHCM Technology. China Plastics, 22(2008):71-74.

6 Ultra-Precision Machining Technologies, CJUMP / Effects of Process Parameters on Surface Gloss in Rapid Heat Cycle Molding Process /