A Case Study on Machining the Cell Phone Shell

This paper presents a fast and effective methodology for the optimal process conditions of an injection-molded thermoplastic part with a thin shell feature based on the orthogonal array with the grey relational analysis and fuzzy logic. The proposed optimal procedure in solving the optimal multi responses problem applies the grey relational co-efficient for each machining response and converts a grey fuzzy reasoning grade to evaluate the multiple machining responses. One real case study in the injection molding process of Poly carbonate Styrene (PC/ABS) cell phone shell has been performed to substantiate the proposed optimal procedure in order to indicate its feasibility and effectiveness. Through the grey fuzzy logic analysis, the principle injection molding parameters, namely the opening mold cavity time, mold temperature, melt temperature, filling time, filling pressure, packing time, packing pressure and cooling time, are optimized with considerations of multiple machining responses including the strength of welding line, shrinkage and difference of forming distributive temperature. The results of confirmation test with the optimal levels of process parameters have obviously shown that the above machining responses in the injection molding process can be improved effectively together through this procedure. In addition, the analysis of variance (ANOVA) is utilized to find the effect of machining parameters on the multiple machining responses problem of the injection molding process.

The objection of design concept for an injection molded thermoplastic part with a thin shell feature in the computer, communication and consumer electronic (3C) products have more space for the tightly packed components inside the housing. Therefore the wall thickness of the housing parts will reduce to 1 mm or less in thickness from the original of 2 or 3 mm in thickness. As a result, the selection of appropriate process parameters for the injection molding operation is becoming more difficult increasingly and important as the wall thickness of these thermoplastic products becomes thinner. It is an unstable cyclical work in the process of injection molding, which includes filling, packing, cooling, opening the mode cavity, injecting and closing the mode cavity. During production of these thermoplastic products, many factors easily cause the defects of an injection molded thermoplastic part with a thin shell feature, such as warp-page, shrinkage, sink marks, residual stress, and so on. Due to the complexity of injection molding, numerous mathematical models have been proposed and extensively developed by a growing numbers of papers for the analysis of different stages of the injection molding process. Huang and Tai had applied the Taguchi optimization method to deduce the optimum sets of effective factors in the injection molding process in order to produce plastic parts with minimum warpage. Ozcelik and Erzurumlu also had presented the optimal process parameters for minimization of wrapage of thin shell plastic parts using integrated response surface method and genetic algorithm. Liao et al, had investigated the optimal process conditions of shrinkage and warpage of thin wall parts with the consideration of interaction effects between process parameters. Therefore, selection of appropriate process parameters for an injection-molded part with a thin shell feature in the status of considerations of multiple machining responses including strength, shrinkage and warpage is enormously difficult and complicated, and relies heavily on huge experimental operation, more details.

The optimization of the multiple machining responses in the meantime is much more complicated than optimization of a single machining response. The grey relational analysis theory initialized by Deng makes use of grey relational generating and calculates the grey relational co-efficient to handle the uncertain systematic problem under the status of only partial known information. The grey relational co-efficient can express the relationship between the desired and actual experimental results and the grey relational grade is simultaneously computed correspondent to each machining response. The single grey relational grade can provide an optimal constitute of process parameters in which manufacturing simultaneously requests multiple machining responses. The optimal level of process parameters were confirmed through the level with the highest grey relational grade. The theory of fuzzy logic which was originated by Zadeh is an effective mathematical module of resolving problems which contain the uncertain huge information. The fuzzy logic analysis including the max min fuzzy inference and centroid de-fuzzification method adopts the fuzziness of human concepts to deal with multiple responses.

Therefore the fuzzy logic can also be applied to establish the optimal set of control parameters with considerations of multiple machining responses. The main objective of the present study is to apply the grey relational analysis and fuzzy logic to establish the optimal set of control machining parameters with considerations of multiple machining responses including strength, shrinkage and warpage during the plastic injection molding process of an injection molded thermoplastic part with a thin shell feature, complete report read here. One real case study in the injection molding process of Polycarbonate Styrene (PC/ABS) cell phone shell has been performed to substantiate the proposed optimum procedure in order to indicate its feasibility and effectiveness. The market scope of smart cell phone has been especially overtaken the other electronic consumer products. The shell of cell phone is not only durable, enduring fall and well looking, but also convenient and with many variable style. It is great challenge to the manufacturers of cell phone. Especially, for original equipment manufacturers (OEM), it is critically important to acquire the optimal process parameters effectively and adjusting factors for decreasing trail and error time and consuming cost in which the size, thickness and construction of this product were restrained and not modified again. The experimental results for the optimal setting through the grey fuzzy logic will confirm the above machining responses in the injection molding process of PC/ABS cell phone shell and reveal that it can be improved effectively together through this approach.

In this study, a fast and effective methodology using the grey relational analysis and fuzzy logic analysis is introduced for the optimal process conditions of an injection molded thermoplastic part with a thin shell feature.

Sources: 1. Unlocked Phones 2. GSM Unlocked Phones 3. Unlocked GSM Phones


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