Processing-structure-property relationship in injection molding of PP based compounds and composites for automotive applications

Abstract

Plastic as an engineering material is one of the pioneer research topics due to its properties such as lightweigt, recyclablity and easy to process. Therefore, it has been extensively used in the numerous industry from automotive to packaging. As a result of the developments in polymer technology, plastic has risen to the level of engineering and/or high-tech material. Plastic is a promising material to replace many materials such as metals, have high-tech material applications that find applications in the aerospace and defense industries. Injection molding method is an effective method as a fast and economical method in the processing of plastics. Many plastic parts are produced by injection method in the automotive trim parts are exterior components such as bumpers, body panels, fan carrier and vehicle interior components such as dashboard and door panels. Today, when CO2(g) emission, fuel consumption and recycling gain importance, automotive plastics are gaining priority. The process-structure-property behavior of constantly evolving material properties is a subject that needs to be investigated. In the injection molding method, plastic materials are melted by kneading with the help of a screw with the effect of heat and friction forces, and this melt is filled into a mold at high speed and cooled under certain pressure. In other words, injection molding method, solid phase plastic materials into the melt phase; It is a process in which solid phase transformation and crystallization events occur again from the molten phase. Features of plastic injection molded parts (end product); visual quality is expressed by dimensional strength and mechanical property characteristics. In this context, the properties of molded plastics; It is related to the mechanical, physical and optical properties of materials. Therefore, it depends on the crystallinity and microstructure of the materials. During the injection process, the thermomechanical interaction between the plastic material properties and the screw, mold and process conditions determine the properties of the molded part (end product). This interaction affects the molecular arrangement of the molded plastic, namely its crystallinity and microstructure, with the effect of process parameters. On the other hand, thanks to the recent developments in plastic injection technology, many innovative methods are emerging. Current examples such as multi-injection, which allows plastic and/or composite sheets to be shaped and injected, and the microcellular injection method, which enables plastics to be formed into a microcellular structure by foaming, are among these methods. With the physical microcellular injection method developed at MIT University, it is possible to keep the changes in the final product properties at a minimum level by ensuring that the cells obtained are uniformly distributed, in size and density. The targeted uniformity and size control of microcellular structure depends on material properties and process variables. In this context, the effect of the interaction between material properties and process parameters on the molded plastic part properties gains importance once again. In this study which is carried out in the automotive supplier industry, the relationship between "material properties-process parameters-end product properties" in the injection molding of automotive plastics will be examined. In this context, it is important to support the industrial development of plastic injection technologies in our country by considering the innovations in polymer materials and injection technologies at a scientific level, to create the necessary knowledge and to turn university-industry cooperation into added value. This study aims to examine the interaction between material structure and properties and process parameters and the effect on the final product properties in plastic parts shaped by plastic injection molding and microcellular injection molding methods using new generation polypropylene (PP) based thermoplastic materials, also known as automotive plastics. Within the framework of the results obtained, the development of a thermoplastic material proposal for the automotive sector suitable for both methods. In this scope, - To figure out the structure and properties of new generation thermoplastic materials, primarily PP compounds and composites, which are used in the automotive industry. - Injection behavior of novel thermoplastic materials used in automotive applications - The effect of the structure and properties of the materials on the injection process parameters and the physical and mechanical performance of the final product. - The relationship between material structure and properties and process parameters will be examined in the solution of process-related errors. In terms of the microcellular foaming method; - Application and limitation in the automotive trim plastics - Process window which is determined for the PP materials used and data related to process stability will be generated, - Investigation of the effect of microcellular foaming method process parameters on the mechanical properties of the final product are researched. -It is aimed to examine the effect of the PP material type and the amount and size of the additives used in the microcellular foaming method on the distribution, density, and size of the cells, and its relationship with weight reduction