Effects of the cooling system in plastic injection moldson the quality of the produced parts

Plastic injection is a widely used method for mass production of plastic parts in many industries. In this production process, the raw material is injected into the molds by means of an injection machine and then hardened by cooling. The cooling system plays a critical role in controlling and optimizing this curing process. This method allows plastic parts to be produced quickly and efficiently. It is widely used in plastic injection, automotive, electronics, medicine, packaging, toys and many more industries. It can be used in the injection molding process for various plastic materials, different designs and sizes. The plastic injection method is known for its advantages such as high precision, fast production, repeatability and use of various materials. However, factors such as mold design, material selection and process control can affect quality and efficiency. The cooling system is designed to provide rapid, homogeneous and controlled cooling of the plastic part in the mold. This system is usually provided with water channels or cooling circuits integrated into the mold. Cooling water or suitable coolants circulate through these channels, lowering the temperature of the material and accelerating its hardening. Different cooling systems are used depending on the geometry, dimensions and properties of the produced part. These systems are often designed by adding additional channels to the molds. However, creating these additional channels is labor-intensive and can also increase the cost of the system. For these reasons, some businesses may prefer to produce without using a cooling system. Especially in the production of small-sized parts, not using the cooling system is usually not a problem. However, in the production of large-sized parts, the situation can become more complex. Inhomogeneous cooling rates occur between the thicker regions and the thinner regions of large parts. This causes changes in the physical properties and dimensional accuracy of the part. This study aimed to examine the possible effects of using a cooling system on large plastic parts. The effects of cooling rates in different parts of the part on important properties such as mechanical strength, dimensional consistency and surface quality were investigated. The results of this study can offer a valuable perspective on the design and optimization of cooling strategies in the production of large parts. Production carried out Özgürmetal Plastik ve Kalıp San. company. The focus of the study is to examine the effects of using and not using the cooling system on the part properties in the plastic injection production process. This review focuses on the "plastic seat rib (PSR)" part, which is one of the company's chronic problems. When the PSR part is produced without using the cooling system, the geometric and dimensional problems that occur in the hole part are an important challenge for the xxvi company. In this context, the company supported this study in order to investigate how effective the cooling system is on these faults. Within the scope of the research, the same piece was produced using polypropylene material. While rapid cooling conditions were applied in one set, no cooling system was used in the other set. The properties of the parts produced in both sets, such as mechanical durability, dimensional accuracy, and crystal structure, were characterized in detail. Dimensional measurement, hardness test, XRD analysis and Moldflow analysis were carried out, respectively. In the dimensional measurements, 2 samples were taken from the parts produced with and without the cooling system, and 7 critical dimensions were measured based on the values in the technical drawing. According to the measurement point, measurements were made using digital caliper and CMM. As a result of the measurement, the critical dimension (hole diameter) of the parts produced without the use of a cooling system was out of tolerance. If the cooling system is not used, the plastic material cools more slowly and unevenly. In this case, the part stays in the mold longer and the temperature distribution is not homogeneous. This causes the part to shrink in size. Shore hardness test was applied to 2 samples taken from both sets. Measured 55 Shore with the cooling system connected and 60 shore disconnected. The Shore hardness scale usually takes a value between 0 and 100. A hardness change of 5 Shore means a difference of 5 units. However, such a change usually does not make a noticeable difference, either visually or physically. Therefore, a hardness change of 5 Shore is not considered a big change and does not usually make a noticeable difference in part properties. However, in any case, the intended use and requirements of the part must be considered. The hardness tolerances required for a particular application may be where a 5 Shore variation can be significant. In particular, in some sensitive applications, the hardness sensitivity can be higher and even smaller hardness variations can be significant. The XRD analysis made in the study was made by taking two regions of the parts. As a result of the XRD analysis of the sections taken from the ear part of the PSR part, if we compare the ear and hole parts of the production without the use of a cooling system, it is seen that the ear part will cool faster than the hole part because it is relatively thinner, different crystal structures are not formed. Since the only variable factor in our study is the presence of the cooling system, there is no factor that will create different crystal structures. XRD analysis is a technique that determines the existence and properties of crystal structures. In XRD analysis, material samples are exposed to X-rays and these X-rays are scattered by the crystal structures. The scattering patterns of X-rays provide information about the crystal structure of the material. Although uncontrolled cooling and rapid cooling methods produce different crystal structures, the scattering patterns of crystal structures measured during XRD analysis may be similar. Therefore, XRD analysis of polypropylene samples produced as a result of uncontrolled cooling and rapid cooling gives similar results. At the same time, Moldflow analysis was performed. In this analysis, the situations of using and not using the cooling system are simulated. After the analysis, the volumetric shrinkage differences are higher in the production using the rapid cooling system than in the production made with uncontrolled cooling. It is important to note that the volumetric shrinkage is not uniform throughout the entire piece. Different areas of the part may experience varying levels of shrinkage due to variations in cooling rates, part thickness, and part geometry. xxvii This non-uniform shrinkage can cause part distortion, warping, or dimensional changes in different parts of the part. The results support the literature research. The shrinkage rate in the production using the cooling system is higher than the production without using the cooling system. However, this difference is at a level that does not affect the geometry of the part. In the moldflow analysis, which shows the surface and mold temperatures of the two productions, the surface temperature is lower as a result of the production using the cooling system. As a result of both production, there was no visible warping or distortion in the part. According to the results of the moldflow analysis of the surface temperature differences of the two productions, when the cooling system is not used, the part will cool uncontrollably, and regional temperature differences occur in the part. This difference now causes stress. This causes shrinkage in the part with high wall thickness. By simulating the injection molding process using Moldflow analysis, manufacturers can predict and analyze residual stress in PP parts and adjust the mold design and injection molding process to minimize its impact. This can result in high quality parts with minimal defects, reduced bending and improved dimensional accuracy. The research findings show that the use of cooling system can significantly improve part quality. The cooling system reduces the temperature difference between the inner and outer parts of the parts and reduces undesirable deformations such as shrinkage and warping. In addition, the use of the cooling system balances the stresses in the part and prevents deformations depending on the thickness and geometry of the part. On the other hand, if the cooling system is not used, the cooling time of the part is prolonged and it cannot be cooled homogeneously. This can cause problems such as shrinkage, bending and deformation. Also, die cycle times can be longer and have a negative impact on productivity. The findings presented in this article show that the use of cooling system in plastic injection improves part quality and reduces undesirable deformations. Effectively designing and optimizing the cooling system is an important factor in the part manufacturing process and should be considered for better results in the injection molding industry.