Plastic injection moulding (PIM) is a widely used manufacturing process for producing high-precision plastic

components. Among various process parameters thermal condition particularly core and cavity temperatures and

their respective cooling rates significantly affect the volumetric shrinkage of moulded parts. Non-uniform

cooling due to imbalanced temperature profiles can lead to percentage volumetric shrinkage, causing residual

stresses, dimensional inaccuracies, and warpage. This study investigates the effects of core temperature, cavity

temperature, and cooling time on volumetric shrinkage in the injection moulding process. A statistical approach

using Design of Experiments (DOE) based on the Response Surface Methodology (RSM) was employed to

analyze the relationships and interactions among these parameters. The results indicate that core temperature has

only 1.43% compared to experimental results. These findings highlight the critical role of thermal management

and parameter interactions in minimizing volumetric shrinkage in plastic injection moulding.

Keywords—Plastic injection moulding, volumetric shrinkage, core temperature, cavity temperature, cooling

variation

Plastic injection moulding (PIM) is a widely adopted manufacturing technique for producing complex plastic

components with high dimensional accuracy and repeatability. However, one of the critical challenges in the

process is controlling volumetric shrinkage, which affects the dimensional stability, surface finish, and overall

[4].

According to Isaza et al. [5], a higher cavity temperature tends to delay polymer solidification, increasing

shrinkage and cycle time, whereas a lower core temperature accelerates cooling but may induce internal stresses.

Cooling time is another parameter with a significant yet complex influence on shrinkage. A study by Kosciuszko

et al. [6] demonstrated that prolonged cooling time allows more time for heat dissipation and crystallization,

reducing shrinkage variability. However, excessively long cooling cycles may not yield proportional

improvements and can negatively affect production efficiency.

To optimize these variables, researchers have employed statistical and simulation-based methods. Response

Surface Methodology (RSM) has been widely used to model and analyze the influence of multiple variables on

relatively fewer focusing exclusively on volumetric shrinkage in relation to differential core and cavity cooling.

Moreover, limited research has addressed the interaction effects between thermal parameters, such as how core

temperature might influence the effect of cooling time, leaving a research gap in comprehensive thermal

optimization strategies.

Therefore, this study aims to fill this gap by systematically investigating the individual and combined effects of

core temperature, cavity temperature, and cooling time on volumetric shrinkage. By employing experimental

design and optimization techniques, this work seeks to contribute to improved control over part dimensional

accuracy and to enhance the understanding of thermal dynamics in plastic injection moulding.

while oil was utilized to achieve elevated temperature settings, enabling accurate control of the mould thermal

environment.

Three key process parameters were investigated: core temperature, cavity temperature, and cooling time. These

parameters were selected based on their significant influence on the cooling profile and consequent volumetric

shrinkage of the moulded parts. Table 1 shows the process parameters and levels for each input parameters.

using a precision digital scale as shown in Figure 1. The theoretical volume of each cavity was obtained through

CAD modelling using CATIA software, and volumetric values were calculated based on the known material

comparison between the experimental results and the modelled predictions was conducted to validate the

reliability and accuracy of the proposed model in assessing part quality and dimensional stability.

Table I Process Parameters And Their Levels

Fig. 1 Dumbbell plastic part measurement using weighing scale

This section presents and discusses the experimental results, main effect plots, one-way ANOVA analysis, the

detailed analysis of variance (ANOVA). Further, 3D surface plots, contour plots, the developed mathematical

model, and the optimization of volumetric shrinkage were performed.

selected based on a design matrix developed through Response Surface Methodology (RSM).

TABLE II EXPERIMENTAL RESULTS OF PERCENTAGE VOLUMETRIC SHRINKAGE

Nashiro et al. [15], who noted that while cooling time affects overall cycle performance, its influence on

volumetric shrinkage is relatively minor unless paired with other thermal parameters.These results emphasize

that thermal parameters, especially core temperature must be tightly controlled to minimize shrinkage and

improve part quality.

Two 3D surface plots were generated to visualize the interaction of process parameters. Figure 3 illustrates the

relationship between core temperature and cooling time, with cavity temperature held constant at 77.5 oC. It

reveals that shrinkage increases significantly with rising core temperatures, while cooling time has a minimal

effect within the tested range.

These findings align with earlier research, where higher mould temperatures were shown to reduce cooling

gradients and delay solidification, leading to increased shrinkage [18]. Although cooling time is often cited as

an important factor for thermal stabilization [19], its limited impact in this study suggests that shrinkage

The contour plot in Figure 4 illustrates the combined effect of cooling time and core temperature on volumetric

shrinkage, with cavity temperature held constant at 77.5 °C. The results indicate that shrinkage increases

significantly with higher core temperatures, whereas the influence of cooling time within the studied range is

comparatively minimal. Lower core temperatures (20 to 60 °C) consistently yield the lowest shrinkage values

(<15.5%), regardless of cooling time. This finding aligns with previous studies showing that core temperature

has a dominant influence on shrinkage due to its direct effect on polymer solidification, crystallization rate, and

thermal contraction, whereas cooling time beyond the required solidification point provides diminishing benefits

[20], [21].

Fig. 4 Contour plot based on cooling time and core temperature

A regression-based mathematical model was developed to quantitatively describe the relationship between the

volumetric shrinkage values, calculated using the regression equation in uncoded units, were compared with the

experimental results to evaluate model accuracy. After calculated the percentage differential of volumetric

shrinkage, It was found that run 5 shows the highest percentage different at 3.26%, while run 15 had the lowest

at 0.43%. The comparison, illustrated in Figure 5, demonstrates good agreement, with an average differential of

volumetric shrinkage was 1.43%.

Fig. 5 Percentage differential between experimental versus mathematical

This reflects an estimated improvement of approximately 36.59%, highlighting the critical role of thermal

management and parameter interaction in enhancing dimensional accuracy during plastic injection moulding

[22].

Fig. 6 Optimization plot

This study has demonstrated that the variation in core and cavity temperatures, as well as cooling time,

significantly affects volumetric shrinkage in plastic injection moulding. Through the application of Response

Surface Methodology (RSM), it was found that core temperature exerted the most substantial influence, followed

by cavity temperature, while cooling time exhibited a notable interaction effect with core temperature. The

developed regression model provided accurate predictive capability, with an average error of approximately

0.02% when compared to experimental results. Optimization of process parameters yielded optimal settings at a

core temperature of 15.0 °C, cavity temperature of 60.45 °C, and cooling time of 12.5 s, resulting in a predicted

and ADTEC JTM Tangkak Campus, Johor, for providing the necessary facilities and support that contributed to

the successful completion of this work