Cooling channel selection for big rectangular plastic parts in injection molding

There are various of types cooling channel designs that have been explored by many researchers to find the best cooling channel that resulted in the optimum results in the injection molding process. The previous research reported that the correct selection of cooling channels in mold design affects the quality of the product and the total cycle time, thus it affected the quality and profit in the manufacturing [1]. The problem in mold design is selecting the correct cooling channel design to ensure the heat transfer distribution is in uniform condition. This paper analysed the effectiveness of four types of different cooling channel designs, the diameter size of the cooling channel, and the variable of coolant temperature in the big rectangular plastic product with the same injection parameters and material type. The objective is to determine the effect of using different cooling channel designs on the cooling time and warpage effect with different coolant temperatures. The commercial mold flow software was used to simulate the injection behaviour to determine the quality of the warpage and total cooling time in the injection molding process. The result found that using a cooling channel type with arrays of the baffle, array bubbler, and conformal cooling channel can reduce the cooling time by almost 50% compared to the conventional cooling channel. The increased coolant temperature in the cooling channel also affects the increase in the cooling time.


Introduction
In the manufacturing industry today, more than one-third of polymeric products was produced through the injection molding process [2].The injection molding process is complicated, where the molten polymer undergoes a complex thermomechanical change, and with the improper setting of the process affects the various defects in the final product thereby increasing the amount of waste [1].In the injection molding process, the part cooling process takes around 50% of the time from the total cycle time during the injection molding process [2].It shows that the cooling process plays a very important role in the total cycle time in the overall injection molding process.Nowadays, many types of cooling channel designs can be used in mold manufacturing.The common type of cooling channel design is the conventional design due to the design's easy and low cost of fabrication.However, this cooling channel design is suitable for mold that produces a flat plastic product without a curved, round, or fillet surface [1].The conventional cooling channel also has lacks heat transfer distribution, contributing to high cooling time.To improve the performance of the conventional cooling channel, the array of baffles and bubbler cooling channel is introduced and normally is applicable in the mold that has a small region shape which has a lack cooling performance.These cooling channels can improve the performance of the heat exchanger in the injection mold and leads to more efficient and uniform control of mold temperature distribution.It is effective for use in 1291 (2023) 012022 IOP Publishing doi:10.1088/1757-899X/1291/1/012022 2 medium and large-sized molds with complex shapes or free-form surfaces [3].The conformal cooling channel has been introduced with the improvement of the fabrication method.This cooling channel has four designs that are the zig-zag type, spiral type, scaffold type, and Voronoi Diagram type [4].The conformal cooling channels can potentially improve the mold performance in terms of less warping and defect and distribution of uniform and fast cooling efficiency into the mold.However, to produce the rectangular plastic product shape, many cooling channel designs can be used, but the wrong selection can cause an increase in the cooling time and warpage of the product, thus can contribute to the increase of mold cost fabrication and reducing the productivity in the production.Therefore, the objective of the study was to determine the effect of using different cooling channel designs on the cooling time and warpage effect with different coolant temperatures.

Model
To get a suitable design cooling channel for the mold that produces big rectangular plastic parts, four cooling channel designs have been modelled.It started with designing the part and gating design.This product consisting a dimension of 4.2mm x 300.6mm x 136.7mm and 2.2mm thickness and use 10 pinpoint gate as shown in Fig. 1.Four types of design of cooling channels have been develop and evaluated to determine the best design of cooling channel that contributes to the shortest cooling time in the injection molding process.It started with the conventional cooling channel design with are designing by following the design from Venkatesh in their study [5].The conformal design also has been taken in the same study because this previous study has been conducted by comparing the conventional and conformal cooling channel designs in the rectangular plastic product.Besides the conventional and conformal design, two types of cooling channels have been highlighted by Tuteski that is the baffles and bubblers types [6].This study also has developed these two designs of cooling channels to compare the effectiveness in the cooling time compared to the conformal design type.Figure 2 show the four cooling channel designs that are modelled and used in this study and the Fig. 3 show the flowchart for this analysis.

Computational Analysis
A further step after designing the various types of cooling channels design is to analysed the cooling time conducted by the Moldex software.Different cooling channels have been designed with Siemens NX11.0 software and a complete CAD file was imported to the MDG file for the mold flow analysis.For the parameter set, ABS Toyolac 100 manufactured by Toray Manufacture was selected as injected material.The processing parameter for this type following the recommendation from the manufacturer which can be referred to in the MFI database is shown in Table 1 below.The flow of boundary conditions in this analysis is divided into two stages.It started with the full-scale analysis that involves filling, packing, cooling, and warping, as in the actual injection molding process

Result and Discussion
Figure 5 shows the cooling time in different coolant temperatures by using the different diameters of the cooling channel and design of the cooling channel with the (a) conventional cooling channel, (b) baffle cooling channel, (c) bubbler cooling channel and (d) conformal cooling channel.Figure 6 shows the actual part temperature by using the different diameters of the cooling channel and design of the cooling channel with the (a) conventional cooling channel, (b) baffle cooling channel, (c) bubbler cooling channel, and (d) conformal cooling channel.The graph shows that the increase in the coolant temperature affects the increase in the cooling time.This increasing trend is the same for all four types of cooling channels in this analysis.This result also shows that using the other cooling channel types can reduce the cooling time by around 50% reduction compared to using the conventional type.The result between the conformal, baffle, and the bubbler is not contributed to the large difference in the cooling time.The result of cooling time depends on the temperature of the mold cooling channel, which affected the actual part temperature for each cooling channel type with the variable of coolant temperature and diameter cooling channel.Based on this graph, shows that increasing the coolant temperature in the cooling channel affects increasing the actual temperature of the product.The increasing trend also affects the cooling time to increase.Besides that, the difference in the cooling channel design also affected the temperature in the cooling channel.From this, it shows that the conventional cooling channel design contributes to the increase of the actual part temperature almost 40% higher compared to the baffle, bubbler, and conformal cooling channel design.Figure 7 shows the warpage for four types of cooling channel designs using a diameter of 10mm with the variable of coolant temperature.From the result, it can be found that the use of a cooling channel with a type baffle, bubbler, and conformal can reduce the value of the warpage product compared to the conventional cooling channel.The result of these three cooling channels is almost similar to the warpage.Using the bubbler cooling channel type with a 50°C coolant temperature resulted in the minimum warpage compared to another set of coolant temperatures.This paper discussed selecting the best type of cooling channel design for the rectangular plastic product, which includes four types of cooling channels using conventional, baffle, bubbler, and conformal design.The result is focused on two factors that are important in injection molding production that focussed in productivity which focused on the cooling time result and the quality of the product which focuses on the warpage value of the product.From the simulation using software that has been done, the baffle, bubbler, and conformal cooling design can reduce the cooling time by almost 50% compared to the conventional cooling design type.Besides that, the temperature analysis that has been done shows that increasing the setting of the coolant temperature will affect the increase of the cooling time.The result for the baffle, bubbler, and conformal types does not show much difference for the cooling time and warpage result.The actual part temperature also shows that the temperature distribution of these three cooling channels is almost the same.From the warpage result, the conventional cooling channel design will contribute a high value of the warpage compared to the other cooling channel designs.From the previous study that has been done by Lu, conformal design can reduce 18% the reduction of warpage value compared to the baffle type for the circular product [7].The difference with this study is that by using the bubbler type, the warpage is reduced almost 15% compared to the conformal type in setting coolant of 50°C temperature.In terms of low-cost fabrication cost and ease of maintenance issues, the best selection of cooling channel design in the rectangular plastic product mold is by using a baffle and bubbler cooling channel design compared to the conformal design.By study that have been done by Park, it show that the use of a conformal design can reduce 50% of the cooling time compared to the conventional type but the use of Metal 3D printing is required a high cost [8] compared to the baffle and bubbler type that only required CNC straight drilled machine to fabricate this cooling channel.For further study, it suggested analysing the use of the baffle and bubbler cooling design with different shapes from the circular design such as rectangular design, triangle design, or half circular design to compare the optimum performance in the design.Besides that, the different types of material cooling channels also can be applied for further study.

Conclusion
This work shows the simulation result for the cooling channel design in mold manufacturing for the big rectangular plastic product.This study shows that using an array of baffles, bubbler, and conformal designs can reduce the cooling time by almost 50% and reduce the warpage in the product.Besides that, the use of an array of baffles and bubblers contributes almost the same result compared to the conformal design.By this, manufacturing the big rectangular plastic product mold can use the array of the baffle and bubbler design, thus can reduce the manufacturing cost compare to the conformal design.
. The time taken to flow the material is 4.5 seconds with the injection pressure (P) is 300MPa and the melting temperature (T) of the material is 325°C.The second stage involves the flow of coolant in the cooling channel it started with the coolant flow in into the coolant channel (Vin) and flowing out at the end of the coolant channel (Vout) at each cooling channel as shown in Fig. 4. From this figure, for the conventional cooling channel it contains with 5 coolant flow in the cooling channel as indicate V1in until V5in and 5 coolant flow out started with V1out until V5out.The Baffle, Bubbler, and Conformal types contain 4 coolant flow in the cooling channel as indicated V6in until V9in and 4 coolant flow out starting with V6out until V9out.The coolant temperature set start with the temperature of 50°C until 80°C with increasing of 10°C for each setting with the same flow rate (Q) of 120cm³/sec for all flow in Vin and Vout.All setting is the same for each type of cooling channel design with the variable of diameter that started with a diameter of 6mm until 12mm.

Figure 5 .
Figure 5. Cooling time result for the (a) conventional cooling channel, (b) baffle cooling channel, (c) bubbler cooling channel, and (d) conformal cooling channel.

Figure 6 .
Figure 6.Actual part temperature for the (a) conventional cooling channel, (b) baffle cooling channel, (c) bubbler cooling channel, and (d) conformal cooling channel.

Figure 7 .
Figure 7.Total displacement for four types of cooling channels ø10mm.

Table 2 .
Parameter setting in mode analysis.
Figure 4.The example boundary condition for baffle and bubbler cooling channel.