Investigating of Plastic Injecting Molding Process Optimization in Complex Shape Product Ahmad Aizuddin Bin Abd Aziz 1,a*, Shamsuddin Bin Sulaiman 2,b, Aung Lwin Moe 1,c, Kano Fukuda 1,d and Aminudin Bin Abu 1,e 1 Malaysia Japan International Institute of Technology, Universiti Teknologi Malaysia Jalan Semarak, 54100, Kuala Lumpur, Malaysia 2 University Putra Malaysia, 43400 UPM, Serdang, Selangor Darul Ehsan, Malaysia a* dynz_aziz@yahoo.com, b shamsuddin@upm.edu.my, c aunglm@ic.utm.my, d fukuda@ic.utm.my, e aminuddin@ic.utm.my Keywords: Plastics injection molding, Process optimization, Molding process parameter, Process characteristics, Mold flow Plastics Insight Abstract. Nowadays, plastic injection molding is widely used in the production of very complex parts and it enables to produce numerous parts within one cycle. Molding conditions or process parameters are crucial for productivity and quality of desired products. This research aims to investigate the state-of-the-art approach to find optimal parameters characteristics in plastic injection molding process. Fill time, average velocity, pressure, clamp force, cooling time and volumetric shrinkages are selected as process parameters in this research. Nokia 6680 model is used for revealing process optimization. Two case studies based on two plates and three plate moulding layout are conducted to suggest the plastic injection mold optimization process. The process parameters of two proposed layouts are compared based on Mold flow Plastics Insight (MPI) analysis results. Result show that three plate moulding satisfy not only the process quality but also the product quality characteristics in this injection moulding process. Introduction Injection plastic molding is one of the promising methods to meet the never ending demand for a high quality product that have both geometrical and consumption properties under eco-friendly [1]. Due to their numerous advantages such as shorter cycle time, lighter weight and higher surface quality, plastic injection molding is a vital to survive in the highly competitive and demanded today manufacturing industries. Although, it has many advantages, improper material selection, poor mold design and parameter settings will effect severely on process and product characteristics [2]. In principal, the selection of process optimization method mainly depends on individual researchers based on their experience and expertise. Hence, establishment of many optimization methods on analysing the process characteristics and their applications are still significant interest under many limitations. Although there are extensive amount of studies that focused on injection molding process parameters optimization have been done, some of methods are difficult to apply to practice even though their soundness in academically [3]. The author [4] reviewed the many studies in the parameter domain setting for plastic injection molding process such as Taguchi method, mathematical models, Fuzzy logic, Artificial Neural Networks,Case Based Reasoning, Finite Element Method, Principle Component Analysis Non Linear Modeling, Genetic Algorithms, Linear Regression Analysis,Grey Rational Analysis and Response Surface Methodology. However, previous proposed methods are still under challenging task in term of advantages and disadvantages. This study aims to investigate the optimal parameters characteristics in plastic injection moulding process. Fill time, average velocity, pressure, clamp force, cooling time and volumetric shrinkages are selected as process parameters. At first, finite element modelling was done on all cover parts of
the Nokia 6680 model. Secondly, two plates and three plate moulding layout are proposed for optimizing the injection process. Finally, the process parameters of two proposed layouts are compared based on Mold flow Plastics Insight (MPI) analysis results. Proposed method and procedures The whole injection molding process cycle can be divided into post-filling, filling, and mold opening stages. During the molding process, mold cavity determine for residual stress, direction of flow, solidification, and the other product quality characteristics that lead the products quality. Because, the plastic material withstands significant shear deformation under pressure and temperature increases inside the mold cavity, followed by prompt decline of pressure and temperature. Due to thermo-viscoelastic plastic material properties, to receive and maintain desired part quality during the molding process made more complex [5]. FEM modelling of parts. Figure 1 shows the FEM models and meshing of the Bottom casing Phone cover Nokia phone model 6680. That mobile can be divided in to five parts such as upper casing, bottom casing, top casing, transparent key pad and screen. At first, the finite element model or meshing was performed in detail because each design part should be in the most important settings to get an acceptable network in parts. When the surface is imported, there are several other options available to help control the density of the network, including a local network density. While meshing the areas with a lower density network, it was made to ensure very details and properly represented in the model for optimize. Material used for the Nokia 6680 phone cover in this process was Polypropylenes (PP) and its properties are listed in Table.1. Tow plate and three plate mold. After finished the meshing and selecting material properties, the layout of mold was considered. In this research Standard H-type layout (two plate mold) and Radial-star layout (three plate mold) were proposed. Additionally, the suitable gate for each layout was selected before the Mold Flow Insight analysis was conducted. Figure 2 shows the type of gates and their arrangement in this injection moulding process. Submarine Gate was selected for H-type layout and Pin Gate was applied for Radial-star layout respectively. Fig. 1 FEM models and meshing of the Bottom casing Phone cover Nokia phone model 6680 In order to find the most optimize layout arrangement of phone cover mold, the result from two layouts were compared. During the analysis, radial-star and H-type layout are designed to be commonly balanced runner. It provides tight tolerances and high quality products by filling the injected martial equally under the same condition through runner from the spur to all cavities. Optimize flow. Steps required the flow for combined filling and packing optimization is shown in Fig. 3. The flow optimizing within the part is an extension of the filling process that included the additional steps such as balancing the runners and optimizing the cooling. Finally, the packing profile was optimized. After the part filling is optimized, the runner system was designed for their size and balance. In this step, many different, runner and gate sizes were designed and analysed. A cooling analysis also done before the packing is finalized. Heat transfer dominates the packing process. The filling analysis assumes a constant mold temperature. A cooling optimization was
conducted to receive more accurate packing analysis result of the mold surface temperature distribution. Finally, packing of the part system was investigated. The significant parameters of gate and runner freeze time were optimized in order to obtain the high accuracy of packing analysis. Table.1 Properties of material used in injection moulding process Family Name Polypropylenes (PP) Trade Name Polyflam PRP 1058 UHF Manufacturers A Schulman Mold surface temperature (Recommendation) 80 0 C Melt temperature ( Recommendation) 230 0 C Solid density 0.92889 g/cm 3 Melt density 0.7751 g/cm 3 Absolute maximum melt temperature 320 0 C Ejection temperature 93 0 C Maximum shear rate 2400 1/s Maximum shear stress 0.26 MPa Elastic module 1340 Mpa (0:3e + 006) Poisson ratio 0.392 (a) (b) Fig. 2 (a) Two plate mold (H-type) layout with submarine gate and (b) Three plate mold (Radial-Star layout) with pin gate Optimize flow Optimize fill Balance /Size runner Cooling Analysis No Optimize packing profile Yes Optimize Cooling Analysis End Fig. 3 Steps required optimizing the flow for combined filling and packing
Results and discussions Each result was interpreted and discussed in term of fill time, average velocity, pressure, cooling time, and volumetric shrinkage process parameters. The Mold flow insight analysis diagrams show the different colours mapping that represent the condition of injected plastic into the mould cavity part. The variation of colour defines the different conditions inside of mold and no colour represent there is not plastic material existence. Fill time. Figure 4 shows the fill-time position of the flow as the cavity fills at regular intervals for both layouts. Although the fill time of both layouts are not significant different, radial-star layout takes the most balanced with all the part filled almost uniformly. The H-type layout got some flashing defect in some particular parts. Pressure result.the Pressure result represents the pressure distribution through the flow path inside the mold generated from a fill-time analysis results. The compared analysis result of the radial star layout and H-type layout is shown in fig. 5. Radial star have lower pressure and better pressure distribution than H-type layout. Because of the radial star layout have bigger runner size and volume than the rest type. Clamp force. Flashing defect can be able to reduce by lowering the packing pressure of the machine[6]. According to the results from Fig. 6, it can see clearly that radial star layout required just 28 tonne clamp force than the H-type that required the 38 tonne clamp force. Hence, the parts of radial star layout have lower defect of flashing. Cooling time. Melt temperature and mold temperature are major factors that affect the cooling time. To obtain high quality products and process capability, both parameters need to be optimized. Decreasing either the melt or mold temperature decrease the cooling time because it takes shorter time for the frozen layer to achieve the desired thickness. Figure 7 revealed the different cooling time of both layouts. Radial-star type has comparatively lower cooling time than standard H-type mold. Fig. 4 Fill time result comparison Fig. 5 Pressure result comparison
Fig. 6 Clamp force result comparison Fig. 7 Cooling Time (time to reach ejection temperature) result comparison Fig. 8 Volumetric shrinkage result comparison Volumetric shrinkage. The variation of volumetric shrinkage percentage is determined by many process parameters. Hence, significant influences factors on the volumetric shrinkage are needed to optimize. There are many techniques for optimization of those parameters [5]. The volumetric shrinkage distribution in both two plates and three plate injection and their improvement is shown in Fig. 8. Detail analysis and comparison of process parameters between proposed layouts are listed in Table 2.0. Filling time in two plate mold and three plate mold is almost same although the average velocity is higher in two plate mold. Other important process parameters such as clamp force, pressure,colling time and volumetric sharinkage are improved with the three plate mold arangement.
Table.2 Comparison of process parameters between two plate mold and three plate mold Paramaters Standard H-type layout (Two Plate Mold) Radial-Star layout (Three Plate Mold) Fill time (time in seconds) 3.146 3.176 Average velocity (cm/s) 953.40 754.30 Clamp force (tonne) 38 28 Pressure (Mpa) 33.30 32.78 Cooling time (s) 50.05 30.19 Volumetric shrinkage (%) 12.19 10.84 Conclusions In this study, process parameters of two proposed layouts are compared and optimized based on Mold flow Plastics Insight (MPI) analysis results. The process quality and the product quality characteristics in this injection moulding process have analysed based on the selected parameters of fill time, average velocity, pressure, clamp force, cooling time and volumetric shrinkages are selected. Results show that three plate moulding satisfy both process quality and the product quality characteristics in this injection moulding process. The radial star layout was the better layout for parts injection molding process. Although this optimization study only emphasis in the runner layout and product configuration in the mold, the proposed approach is feasible and effective to assist the today manufacturing industry needed for complex shape. References [1] Stanek, M., et al.: International Journal of Mathematics and Computers in Simulation 5.5 (2011) 413-421. [2] Chen, W. C., & Lin, S. B.: International Journal of Applied Physics and Mathematics, Vol. 3, No. 6, (2013) 373-375 [3] Dang, X.P.: Simulation Modelling Practice and Theory 41 (2014) 15-27., [4] P.K. Bharti et. al. : International Journal of Engineering Science and Technology Vol. 2(9), (2010) 4540-4554 [5] Shen, C., Wang, L., & Li, Q Journal of Materials Processing Technology 183.2 (2007) 412-418. [6] Tang, S. H., et al.: Journal of materials processing technology 171.2 (2006) 259-267.