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Wang X.,Shandong University | Wang X.,Qingdao Hisense Mould Co. | Zhao G.,Shandong University | Wang G.,Shandong University
Materials and Design | Year: 2013

Rapid heat cycle molding (RHCM) is a recently developed innovative injection molding technology to enhance the surface quality of the plastic parts without extending the molding cycle. Most of the common defects that occur in the plastic parts produced by conventional injection molding (CIM), such as flow mark, silver mark, jetting mark, weld mark, exposed fibers, short shot, etc., can be well solved by RHCM. However, RHCM is not a nostrum for all the defects in injection molding. Sink mark and warpage are two major defects occurring in RHCM. The purpose of this study is to investigate and further solve the sink mark and warpage of the molded parts in RHCM. To solve the problem of sink mark, a new " bench form" structure for the screw stud on the product coupling with a lifter structure for the injection mold was proposed. The external gas assisted packing was also proposed to reduce the sink mark in RHCM. To solve the problem of warpage, design of experiments via Taguchi methods were performed to systematically investigate the effect of processing parameters including melt temperature, injection time, packing pressure, packing time and also cooling time on the warpage. Injection molding simulations based on Moldflow were conducted to acquire the warpages of the plastic parts produced under different processing conditions. A signal to noise analysis was conducted to analyze the effect of the factors, and the optimal processing parameters were also found out. ANOVA was also conducted to quantitatively analyze the percentage contributions of the processing parameters on the warpage. The verification results show that part warpage can be reduced effectively based on the optimal design results. © 2012 Elsevier Ltd. Source


Li S.,Shandong University | Zhao G.,Shandong University | Wang G.,Shandong University | Guan Y.,Shandong University | And 2 more authors.
Journal of Cellular Plastics | Year: 2014

A complex medical instrument exterior shell was chosen as a studying object to investigate the influence of relative low (<10 MPa) gas counter pressure process on microcellular injection molding process. The gas counter pressure microcellular injection mould and related experiments were designed. The relative low gas counter pressure under which the melt can foam was mainly considered to improve the surface quality of molded parts without significantly prolonging production cycle. The effects of the gas counter pressure parameters on the surface quality, cell morphology, and cell density of microcellular parts were studied. A critical melt flow front pressure to effectively eliminate surface swirl marks of microcellular injection molded part was proposed. The mechanism of the influence of gas counter pressure process on foaming behavior of melt in filling process was analyzed. The reasonable gas counter pressure parameters to improve surface quality of products without significantly increasing molding cycle were obtained. By using the obtained reasonable gas counter pressure parameters, a sound microcellular injection molded product was injected finally. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav. Source


Wang G.,Shandong University | Zhao G.,Shandong University | Wang X.,Shandong University | Wang X.,Qingdao Hisense Mould Co.
International Journal of Advanced Manufacturing Technology | Year: 2013

The influences of the cavity surface temperature just before filling on part surface appearance and texture in rapid heat cycle moulding are investigated. It is observed that the cavity surface temperature just before filling has a very significant influence on part surface appearance. As the cavity surface temperature increases, aesthetic quality of the moulded part can be greatly improved by reducing surface roughness, increasing surface gloss and reducing weld mark. There is a critical cavity surface temperature just before filling for each plastic material. As the cavity surface temperature reaches the critical value, the part surface appearance will reach the optimal level with lowest roughness, highest gloss and without any weld mark. The critical cavity surface temperature on surface gloss and roughness is close to the Vicat softening point of the plastic material. The critical cavity surface temperature on weld mark is 10-20 C higher than that on surface roughness and gloss. The mechanisms for generating the rough surface of the part moulded with a low cavity surface temperature and improving part surface appearance by increasing cavity surface temperature are disclosed. © 2013 Springer-Verlag London. Source


Dong G.,Shandong University | Zhao G.,Shandong University | Guan Y.,Shandong University | Li S.,Shandong University | And 2 more authors.
Journal of Cellular Plastics | Year: 2016

The microcellular injection-molded part usually consists of a foamed core region and two unfoamed skin layers on the cross section. This paper investigated the formation process, formation mechanism and structural characteristics of the unfoamed skin layers in microcellular injection-molded part. It is found that the unfoamed skin layers are formed in two processes namely "during filling" process and "after filling" process. The shear flow and the fountain flow behaviors of the melt in the filling stage are the main controlling factors on the formation of the unfoamed skin layer in "during filling" process, and the cooling solidification of the melt in cooling stage is the fundamental reason for the formation of the unfoamed skin layer in "after filling" process. Further studies found that the unfoamed skin layer in microcellular injection-molded part has two distinct regions, the outer region is a thin frozen layer which contains deformed and broken cells, and the inner region is a relatively thick solid-like layer which has no visible cells in. The unfoamed skin layer has a minimum thickness in the gate location. The whole thickness of the unfoamed skin layer is decreased with the increase of injection speed and mold temperature, but is slightly affected by melt temperature. © SAGE Publications. Source


Wang G.,Shandong University | Zhao G.,Shandong University | Wang X.,Shandong University | Wang X.,Qingdao Hisense Mould Co.
International Journal of Heat and Mass Transfer | Year: 2014

A new rapid mold heating and cooling method is developed in this study. For rapid mold heating, cartridge heaters are assembled in the holes of the mold. Between the heaters and the corresponding mounting holes, there are annular gaps which are full of water. During mold heating, the heat generated by the heaters passes through the water gaps firstly and then transfers into mold base to raise cavity surface temperature. For rapid mold cooling, pressured cooling water is passed though the annular gaps. Firstly, a cell model was established to evaluate the effectiveness of the new rapid mold heating and cooling method. Thermal response analysis based on numerical simulations was conducted to investigate the influences of the gap size, the power density of the heaters and also the layout of heaters on thermal responses of the cavity surface. Further, the injection mold of a large LCD TV frame was designed and manufactured based on the developed rapid mold heating and cooling method. Both numerical simulations and experiments were performed to evaluate the thermal response efficiency of the cavity surface. The results show that the cavity surface temperature can be changed in a large temperature range within relatively short time. The simulation results are consistent well with the experimental results, which verifies the effectiveness of the established analysis method. Finally, production testing was conducted to produce the LCD TV panel. The results show that the weld marks on the outer surface can be eliminated completely and the outer surface gloss of the part can reach higher than 90 GU with a molding cycle of about 60 s. The consumption of energy and water can be greatly reduced by comparing with other conventional rapid mold heating and cooling methods. © 2014 Elsevier Ltd. All rights reserved. Source

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