OPTIMIZATION OF INJECTION MOULDING PROCESS PARAMETER FOR REDUCING SHRINKAGE OF HIGH DENSITY (HDPE) MATERIAL

1HARSHAL P.KALE, 2UMESH V. HAMBIRE

1Student of Government College Aurangabad, Maharashtra, India 2Assistant Professor of Government Engineering College Aurangabad, Maharashtra, India E-mail: [email protected], [email protected]

Abstract - Injection is an important processing operation in the . In this process, polymer is injected into a mold cavity, and solidifies to the shape of the mold. Optimizing the parameters of the injection molding process is critical to enhance productivity. For process optimization, parameters must operate at optimum levels for acceptable performance. Taguchi method is one of the methods of optimization, in which orthogonal array is generated based on experimental design. Optimization of injection molding process parameters will be carried out using high density polyethylene (HDPE) as the molding material Injection moulding has been a challenging process for many plastic components manufacturers and researchers to produce products meeting the requirements at very economical cost. Since there is global competition in injection moulding industry, so using trial and error approach to determine process parameters for injection moulding is no longer hold good enough. Since plastic is widely used polymer due to its high production rate, low cost and capability to produce intricate parts with high precision. It is much difficult to set optimal process parameter levels which may cause defects in articles, such as shrinkage, warpage, line defects. Determining optimal process parameter setting critically influences productivity, quality and cost of production in plastic injection moulding (PIM) industry. In this optimal injection moulding condition for minimum shrinkage were determined by the DOE technique of Taguchi methods. The various observation has been taken for material namely HDPE. The determination of optimal process parameters were based on S/N ratios.

Index Terms - Injection Moulding, DOE, Taguchi Optimization, Design Expert.

I. INTRODUCTION complex geometries. The quality of the injection mouldings depends on the material characteristics, Optimizing process parameter problems is routinely the mould design and the process conditions. Defects performed in the industry. Final in the dimensional stability of the parts result in optimal process parameter setting is recognized as shrinkage. Severe shinkage lead to deflection of one of the most important steps in injection molding warpage in moulded parts as well as negatively for improving the quality of molded products. influence the dimensional stability and accuracy of Previously, engineers used trial-and-error processes the parts. Many factors including materials selection, which depend on the engineers’ experience and part and mould design, as well as injection moulding intuition to determine initial process parameter process parameters can affect shrinkage behavior in settings. Subsequently, numerous engineers applied an injection moulded part. The study carried by Taguchi’s parameter design method to determine the Chang and Faison [1] reported that more shrinkage optimal process parameter settings. However, the occurs across the flow direction than along the flow trial-and-error process is costly and time consuming, direction. Chang and Faison studied the shrinkage thus it is not suitable for complex manufacturing behavior and optimization of PS, HDPE and ABS processes (Lam et al., 2004). Hsu (2004b) argued that parts by using the Taguchi and ANOVA methods. when using a trial-and-error process, it is impossible They stated that the mold and melt temperatures to verify the actual optimal process parameter along with the holding pressure and the holding time settings. Moreover, Taguchi’s parameter design were the most significant factors affecting the method can only find the best specified process shrinkage behavior of the three materials studied. One parameter level combination which includes the of the main goals in injection moulding is the discrete setting values of process parameters. improvement of quality of moulded parts besides the Application of the conventional Taguchi parameter reduction of cycle time, and lower production cost. design method is unsuitable when one of the process For instant, poor cooling system will give rise to non parameter variables is continuous, and it cannot help uniform mould surface temperature and irrational engineers obtain optimal process parameter setting gate results. Furthermore, when engineers deal with a multi-response process parameter design problem. II. EXPERIMENTAL STUDIES Taguchi parameter design method runs into difficulties (Hsu, 2004a).Injection moulding 2.1 Materials represents one of the most important processes in the HDPE is the natural color polymer with Good process of manufactured plastic parts with ability, very good mechanical properties. HDPE is

Proceedings of 69th IRF International Conference, 19th March, 2017, Pune, India, ISBN: 978-93-86291-639 27 Optimization of Injection Moulding Process Parameter for Reducing Shrinkage of High Density Polyethylene (HDPE) Material designed to make injection molded product like III. TAGUCHI METHOD industry handling, pallets and luggage shells Taguchi’s philosophy is an efficient tool for design of Table 1: The General property of HDPE material high quality manufacturing system, which has been developed based on orthogonal array experiments, which provide much reduced variance for experiment with optimum setting of process control parameters[8].The signal to noise ratio is a simple quality indicator that researchers and designers can use to evaluate the effects of changing a particular design parameter on performance of the products.[9,10] Taguchi methods [11] use a special design orthogonal array to study the entire factor with only a small number of experiments[12].It introduces an integrated approach that is simple and efficient to find the designs for quality, performance and computational cost[14]. In product or process design of Taguchi method, there are three steps: i) System design: selection of system for given objective function. ii) Parameter design: selection of optimum levels of parameter iii) Tolerance design: determination of tolerance

around each parameter level [15]. Table 2: The effective factor and levels Taguchi method uses the signal-to-noise (S/N) ratio instead of average. The S/N ratio reflects both the average and the variation of the quality characteristics[6].As discussed by Oktem el at.[16] the S/N ratio is a measure of performance aimed at developing products and processes insensitive to noise factors. The standard S/N ratio used is as follows: Nominal is best (NB), lower the better (LB) and higher the better (HB) [4]. In this study lower value of shrinkage behavior is expected. Thus S/N ratio characteristics the lower – the- better is applied in the analysis which is given in table 4 and can be calculated by using

S/N=-log10 (1/n∑yi2) (2) 2.2. Experimental procedure The experiments were performed on injection Where yi is the value of the quality characteristics for molding De –Tech85LNC5 to produce the ith trials, n are number of repetitions. The plastic disc of 3mm thickness and 100mm diameter. response table of the S/N ratio is given in table 3, and The discs were produce by HDPE of grade 080M60 the best set of combination parameter can be material. The experiment was conducted with four determined by selecting the level with highest value controllable, three level processing parameters: melt for each factor. As a result, the optimal process temperature, injection pressure, packing pressure, parameter combination for. The difference value packing time, therefore the L27 orthogonal array was given in table 5 denotes which factor is the most selected for this study. significant for shrinkage of PP molding. Packing is the difference between the size of a mold cavity pressure was found most effective factor for PP and the size of the finished part divided by the size of followed by packing time, injection pressure and melt a mold. Usually it is expressed in percentage. Four temperature points were marked on the specimen, and measurements were made with micrometer screw Shrinkage is the difference between the size of a gauge (with an accuracy of 0.01 mm). For each mold cavity and the size of the finished part divided specimen, the average thickness was calculated as the by the size of a mold. Usually it is expressed in arithmetic mean of the three points. The relative percentage. Four points were marked on the shrinkage was determined as specimen, and measurements were made with

micrometer screw gauge (with an accuracy of 0.01 S = X100% (1)

Proceedings of 69th IRF International Conference, 19th March, 2017, Pune, India, ISBN: 978-93-86291-639 28 Optimization of Injection Moulding Process Parameter for Reducing Shrinkage of High Density Polyethylene (HDPE) Material mm). For each specimen, the average thickness was IV. ANALYSIS OF VARIANCE (ANOVA) calculated. The ANOVA test was applied to determine the Table 3: The Orthogonal Array significance of each parameter in the designed experimental study. The ANOVA results for HDPE moldings are given in Table no 4 respectively. Since the one P-value was less than 0.05, this parameter had a statistically significant effect on the shrinkage at the 95% confidence level. The ANOVA test was applied to determine the significance of each parameter in the designed experimental study. The ANOVA results for HDPE moldings are given in Tables 4 respectively. Since the one P-value less than 0.05, this parameter had a statistically significant.

Main Effects Plot for SN ratios Data Means

A B C D

-7

-8 s o i t

a -9 r

N S

f -10 o

n a e

M -11

-12

-13 1 2 3 1 2 3 1 2 3 1 2 3 Signal-to-noise: Smaller is better Figure 1: Main effect plot for SN ratio

Table 4: ANNOVA table and result analysis

CONCLUSIONS

1. Taguchi and ANOVA methods were used to investigate the effects of melt temperature, injection pressure, packing pressure, packing time and cooling time on the shrinkage of the HDPE material. 2. In Taguchi method, S/N ratios were used for determining the optimal set of process

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Proceedings of 69th IRF International Conference, 19th March, 2017, Pune, India, ISBN: 978-93-86291-639 30