Plastic injection molded door handle cooling time reduction investigation using conformal cooling channels

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Abstract

Cycle time is a significant parameter in injection molding process as it affects the rate of production and governs the quality of part produced. The cycle time can be reduced by minimizing the cooling time. Cooling time contributes to the majority of the cycle time and it can be effectively reduced by proper heat dissipation. The heat of the melt should be dissipated efficiently by the cooling channel. Therefore, design and placement of cooling channel is a major factor contributing to the cycle time reduction. The improper positioning of channels for cooling leads to uneven cooling and results in defects like sink marks, warpage and thermal residual stresses. Hence, there are channels that conform to the shape of the part, allowing the part to cool uniformly with minimum defects and thus lead to the minimum cycle time. In this paper, an investigation of cooling time has been done for a door handle. The cooling pattern for the conventional cooling channels and the parameters affecting cooling time has been studied. The mold and cooling channels have been designed of U-shaped cooling channel and conformal cooling channel in SolidWorks software. The results showed a reduction of cooling time by 18.2% over U-shaped cooling channel.

Introduction

Plastic manufacturing has its global share among the other manufacturing processes. Injection molding process is the second major contributor to the plastic manufacturing globally. Injection molding technique is used to produce parts of various shapes and sizes along with parts having intricate and complex geometries. This process is used to make parts for automotive and aerospace industries for aesthetics of interiors and various assembly parts for medical equipment, in electronic equipment, packaging industries, household products and toys. Injection-molded parts are used in construction purposes for its strength, durability and aesthetics. Injection molding process comprises of melting the plastic material and subsequently injecting into the cavity created within the mold. The melt is allowed to solidify in the cooling stage and after it has reached its ejection temperature, the part is ejected. The important phases in the process are injection of plastic melt, packing phase, part cooling phase and part ejection. Amongst all processes, cooling of melt contributes to 50 to 70 percent of the cycle time [1]. So the cooling time accounts for two – third of the cycle time which can be controlled as compared to the injection time, packing time and ejections times which are considerably small. Despite the various advantages and applications of injection molding, various other factors to be considered are coolant channel design for mold and cavity, plastic melt temperature, injection pressure, mold temperature, temperature of coolant, method of ejection from mold, etc. to ensure a good quality of the product.

Mostly mold cooling processes are being carried out by creating cooling channels into mold or core by drilling straight holes. But this straight drilling process is good for component with simple design and straight surface. For components having complex shape having curved surfaces, these straight drilled channels are inefficient to uniformly cool the mold [2], [3]. As cooling of mold is not uniform it causes various defects like warpage, sink marks, weld lines. These defects reduce the quality of the product. So for uniform temperature distribution in mold conformal cooling channels can be created. These cooling channels are placed close to the cavity so that the channel conforms to shape of the mold or cavity and cool the mold uniformly and reduces warpage, shrinkage, sink lines etc., thus increasing the quality of the product.

The injection molding process consists of four stages: First is the filling stage, in which the plastic material is injected in the cavity. After the filling is complete, some extra melt material is injected at high pressure to compensate for shrinkages. This stage is called packing stage. The mold is allowed to cool in the cooling stage and as the part reaches the ejection temperature, it is taken out in the ejection stage.

Section snippets

Background

Many researches done for plastic injection molding process, focus on minimization of cycle time for the sake of maximization of rate of production and subsequently reduced part rejections. Since cooling of the injection mold takes most of cycle time, so the literature reviewed are mostly based on the reduction of cooling time.

Sun et al. (2004) [1] proposed the cooling channels made from milling process. They have taken a household iron for study and they have generated milled grooves in the

Governing equation and boundary conditions

The heat transfer takes place from the melt to the mold, from mold to the cooling channels and then from channels to the mold again and then to the atmosphere. The heat dissipation process is mainly governed by the convection and conduction equations. [1] and [2] assumed heat transfer between the mold and the cooling channels to be steady and to be taking place in one direction. The heat transfer analysis has been done with different boundary conditions. The first condition is considering the

Simulation of door handle and input parameters

To analyze cooling system for U-shaped and conformal cooling system process parameters such as filling time, packing pressure, injection location were fixed. Channels are made on the core and cavity side of the mold having Steel 420SS material. A comparative study is done for U-shaped and conformal cooling channels for a door handle using SolidWorks Plastics software. The analysis includes calculation of cooling time and warpage. It can be seen that warpage is directly affected by the residual

Results and analysis

The results obtained from the simulation indicate the time required to reach ejection temperature right from the start of fill are discussed below along with volumetric shrinkage and heat flux.

The flow results for the U- shaped conventional and conformal cooling channels have been indicated. A comparative analysis has been done between both. The time to fill the cavity was 9.9 s for U-shaped channel and 10.8 s for conformal cooling channels. The filling time has been shown in Fig. 3 and Fig. 4.

Conclusion

From the thermal analysis, it has been seen that time required to cool the part has significantly reduced from 1890 s for U shaped channels to 1546 s for conformal cooling channels. So there is a change of 18.2% in the cooling time. The time to fill the cavity is 9.9 s in U-shaped channels and 10.8 s in conformal channels. Also with the use of channels that conform to shape of part, heat dissipation can be improved thus leading to a homogeneous cooling. The results obtained from thermal

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