MEASURING OF DIMENSIONAL ACCURACY OF PLASTIC PRODUCT MANUFACTURED BY INJECTION MOLDING

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1 THE INTERNATIONAL CONFERENCE OF THE CARPATHIAN EURO-REGION SPECIALISTS IN INDUSTRIAL SYSTEMS 7 th EDITION MEASURING OF DIMENSIONAL ACCURACY OF PLASTIC PRODUCT MANUFACTURED BY INJECTION MOLDING Jozef Dobránsky, Janka Mihalčová, Technical University of Košice, Faculty of Manufacturing Technologies with a seat in Prešov, Štúrova 31, Prešov, Slovakia Abstract: Paper deals with measuring of dimensional accuracy of plastic product manufactured by injection molding. Based on planned experiment measurements were made and after that was evaluated dependencies of individual technological parameters to quality parameter of plastic product. Based on these graphs some results were made which are needed to make production process perfectly. Key words: dimensional accuracy, plastic, technological parameters, quality parameters. 1.INTRODUCTION The basic concept of injection molding is the ability of a thermoplastic material to be softened by heating, formed under pressure, and hardened by cooling. It would be difficult to imagine our modern world without plastics. Today they are an integral part of everyone s lifestyle with application varying from commonplace domestic articles to sophisticated scientific and medical instruments. Injection molding is a major processing technique for converting thermoplastic materials. Task of planed experiments is filling up model of real situations of injection molding technological processes by specific numbers. At the practice don t affect these technological parameters always only by additive style, but together at the cross interaction. Analyzed of this model enabled factor experiments, by those are attempts realized for all level combinations of appraisal factors. 2. THEORY OF PLANNED EXPERIMENTS From theoretical analyze is obvious that technological process of injection molding is a complex process to which come into technological parameters actuated in their relative interaction by different levels on quality parameters of finished product. Evaluation of technological parameters and evaluation to their properties is complex process which is consisting of each other consequential steps. Every of them affected quantum parameters which has effect to result and by classic type of evaluation could by induce doubts at final results. Task of every research work is decrease time and financial expensiveness on acceptable level what needed solid preparation of experiments. By experimental work is possible to proceed with classical style when is by constant conditions changed level always only one value (factor) and from experiment result is obvious that examination value affected changes and eventually what style.

2 A result of experiments is not often uniform and in this case is needed to repeat measurement and for evaluation of result (response) use some statistics characteristic as mean or median. We can predict that some observed values are incidental character and in this case is needed to use mathematical statistic mechanism. Disadvantages as especially time seriousness and financial loading by classical experimental solution markedly reduced using of planned experiments. Its advantage consists in minimal costs on one experiment, ortogonality and from this consequent simplified calculation. Based on planned experiments is possible to evaluate also interaction effect of individual factors. 3. DESIGNED PLANNED EXPERIMENT Based on analyze of all technological parameters was selected three technological parameters: injection pressure p 4 injection speed v 4 switch point V 4 (a point by which is injection pressure running to re-pressure). Equally based on analyze of all quality parameters was selected quality parameter hole diameter d 4B (Fig. 1) which is needed to observe by production of this product, especially in this case it was mowing machine safety cover. In this experiment it was observed products from two cavities of injection molding machine. The products from the both cavities were evaluated separately. Fig.1 Observed quality parameter By statistical evaluation of factors was used three-level planned experiment type of 3 3. By 27 attempts with 5 repetitions was evaluated effect of factors to select quality parameter. Table 1 shows encoding of factors by levels with additional actual values. table 1. Encoding of factors by levels with additional actual values. Factors Factor values N.of f. marking name dimension x 1 injection speed (v 4 ) cm 3 /s x 2 injection pressure (p 4 ) MPa 80 93, x 3 switch point (V 4 ) cm ,5 40 Table 2 shows encoded conditions of attempts. Based on these conditions was made measurements needed to evaluated this experiment. table 2. Encoded conditions of attempts. num. of num. of Encoded conditions of attempts Encoded conditions of attempts attempt x 1 x 2 x 3 attempt x 1 x 2 x

3 GRAPHS AND ITS INTERPRETATION For chosen quality parameter was made three types of graphs: Pareto chart of standardized effects Plot of marginal means and confidential limits 3D fitted surface Fig.2 Pareto chart of standardized effects

4 Result from pareto chart of standardized effects that the biggest effect to hole diameter by cavity 1 has switch point and injection speed has minimum effect. By cavity 2 switch point has considerable effect. Injection speed has no effect to hole diameter by cavity 2. Injection pressure is situated under the confidence limit by both cavities that means that this technological parameter has no effect to hole diameter value. Fig.3 Plot of marginal means and confidential limits Graphs on figure 3 expressed dependency of injection pressure and switch point at interaction with injection speed to a hole diameter value. By both cavities at the switch point 3 cm 3 are hole diameter values situated close by upper toleration limit. Increased by switch point on middle and upper level is incoming to considerable accumulation of hole diameter value.

5 Fig. 4 3D dependency of injection pressure and injection speed to hole diameter As we can see in this picture, all values of diameter are situated above the toleration limit. By the cavity 1 injection pressure and injection speed has influence to hole diameter value and by the cavity 2 only the injection pressure. Fig. 5 3D dependency of injection speed and switch point to hole diameter Figure 5 shows 3D dependency of injection speed and switch point to hole diameter. In the first case by the cavity 1 the biggest diameter is by the switch point from the middle to upper value and by the minimum and maximum value of injection speed. By the cavity 2 exercise an influence on diameter switch point. Fig. 6 3D dependency of injection pressure and switch point to hole diameter

6 By the cavity 1 exercise an influence on diameter switch point from the middle values. By the cavity 2 exercise an influence on diameter the both technological parameters in his interaction. 5. CONCLUSION By the appreciated of products separately we can see less variances between the both cavities. From the Pareto charts of standardized effects, Plot of marginal means and confidential limits and 3D fitted surfaces we give answers to needed questions. During the planned experiments it was observed three technological parameters and its influence to choose quality parameter hole diameter. All of these technological parameters in his mutual interaction influenced to hole diameter. In a further experiment it was examined influence of other technological parameters to dimensional accuracy of plastic product. 6. REFERENCES [1] DOBRÁNSKY, Jozef, TODEA Mihai: Analyze of process capacity by the observation of quality parameters by injection moulding. In: Annals of MTeM for TU Cluj- Napoca, 2007, [2] DOBRÁNSKY, Jozef HATALA, Michal: Influence of selected technological parameter to quality parameters by injection moulding. In: Annals of DAAAM for 2007 & Proceedings of the 18th international DAAAM symposium, DAAAM International, Vienna, 2007 [3] DONNELLY, R.: Statistics. New York: ALPHA [4] HARPER, Ch. - PETRIE, E.: Plastics materials and processes. New Jersey: John Wiley and sons [5] OSSWALD, T. - LI-SHENG, T. - GRAMANN, P.: Injection moulding handbook. Munchen: Carl Hanser Verlag [6] STRONG, A.: Plastics: Materials and processing. New Jersey: Prentice Hall [7] SULLIVAN, M.: Statistics. New Jersey: Prentice Hall ADDRESS FOR CORESPONDANCE SLOVAKIA Ing. Jozef DOBRÁNSKY, PhD. Technical university of Košice Faculty of manufacturing tachnologies with a seat in Prešov Department of technology systems operation Prešov SLOVAKIA dobransky.jozef@gmail.com