Investigating of Plastic Injecting Molding Process Optimization in

Complex Shape Product

Ahmad Aizuddin Bin Abd Aziz1,a*, Shamsuddin Bin Sulaiman2,b, Aung Lwin Moe1,c, Kano Fukuda1,d and Aminudin Bin Abu1,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, caunglm@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 0C

Melt temperature ( Recommendation) 230 0C

Solid density 0.92889 g/cm3

Melt density 0.7751 g/cm3

Absolute maximum melt temperature 320 0C

Ejection temperature 93 0C

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

Fig. 3 Steps required optimizing the flow for combined filling and packing

No

Yes

Optimize flow

Optimize fill

Balance /Size runner

Cooling Analysis

Optimize packing

profile

Optimize Cooling

Analysis

End

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

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