Polipropilen malzemelerde mekanik özellikler ve geometrik boyutlandırma için proses parametrelerinin deney tasarımı, duyarlılık analizleri, istatistiksel analizi ve optimizasyonu

Ballı, Yasin
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Plastic materials are in a large part of our lives with the advantages and various disadvantages they provide in today's industrial components. With the growing interest in the products offered by the plastics industry, studies on technologies related to the production of plastic materials have increased and production methods that provide different advantages have been developed. It has become one of the most preferred production methods thanks to the ease of production provided by plastic injection molding and the possibilities it provides with mass production possibilities in high quantities. In the plastic injection molding method, which is based on the principle that the plastic raw material in granular form is melted and takes the shape of the closed volume it fills, the production process is completed when the product becomes solid. The structure in which the molten material solidifies and takes the shape it is in is called the injection mold. Although the mold designed for each product is different, the molds can be used in different injection machines. Mold design can be manufactured from different steels depending on the desired quality in the final product. In summary; it is expected that there is a cavity in the form of the desired part in the injection mold and that the melt is injected into this cavity in a fast and uniform manner, cooled and taken out of the mold. The effect of the process that takes place in the mold and on the injection bench is great in terms of the geometric dimensions, mechanical properties and desired quality of the product coming out of the mold. Therefore, the process must be kept under control in order to provide the desired properties of the final product. In order to control the process, it is necessary to understand the effect of the parameters used on the product and to understand the nature of the process. Although these processes are modeled with various simulation programs today, it can be seen that the models and the real product do not act conjugately, and it is seen that there are more deviations in this approach if the part sizes are large. In the studies conducted in the literature, they mentioned that real PvT variation diagrams cannot be measured during part production with plastic injection molding and they aimed to examine the effect of process conditions on distortion and PvT variation diagrams based on PvT measurements made under standard conditions. During the study, the injection temperature, the holding pressure, the temperature at the end of the holding pressure and the cooling liquid flow rate were investigated with an experimental design at 4 levels. Simulation was carried out with the generated DOE and it was claimed that while the injection temperature had a high effect on the specific volume, it had little effect on the distortion, and the specific volume decreased non-linearly due to the decrease in the cooling flow. In another study, it was aimed to determine the best alternative for plastic injection moldability index with polypropylene raw material. For the DOE created in the study, using the Taguchi and FAHP methodology, the case of warping, cloaking and underfilling on the piece was examined. The study was carried out in a simulation environment for a 1 mm thick plate and was experimentally controlled. The runner inlet type, injection time, cooling time, ironing pressure and melt temperature were controlled at 3 levels, and it was claimed that the moldability index of 10 trials for simulation and 5 trials in experimental trials was high in 18 trials. In the study carried out in 2020, life calculation under static and dynamic loads under notched and unnotched condition with short fiber reinforced PA6-20CF raw material on a thin-walled piece was investigated. The study was carried out by comparing simulation and experimental studies with two different model proposals. After the study, it was observed that there was a 13.7% deviation between the simulation and experimental trials. Front-loading washing machines are widely used in today's world. It aims to meet customer demands with the capacities and spin cycles it provides, and customer satisfaction and product demands are increasing with new technologies added day by day. In order to meet the increasing demands, the producers are increasing their capacity and the competitive market is getting harder day by day with the emergence of new producers. Therefore, manufacturers should update themselves in accordance with current technology and production standards. In this study, it is aimed to come to the forefront in the competitive market by improving production. With this study, it is aimed to improve the production conditions of the plastic part in the drive group in order to avoid contact with the bellows, which provides the connection between the drive group and the body group for the washing machine. It is aimed to examine the mechanical effects of the behavior of the plastic parts in the drive group under production conditions and the reactions they show under operating conditions with an optimization approach, to compare them with each other and to optimize the production parameters and take the most suitable sample. In this way, it is targeted to optimize the mechanical behavior and the change in geometric dimensions on the part, and to eliminate the situations such as abrasion, laundry tear or smoke formation that the customer may encounter. When the process parameters studied in the literature research and the previous studies of our production unit are evaluated, the parameters to be examined in this study are determined as cooling time, ironing pressure, injection speed and speed-pressure transition time. The lower and upper limits determined for the cooling time were 40 sec and 50 sec. It was observed that when the pressure was taken under 40 seconds, the part was bled, and when it was exceeded 50 seconds, the cycle time was unnecessarily prolonged. Ironing pressure limits are determined as 60 bar and 75 bar. When the production is made under 60 MPa, the volumetric shrinkage has distorted the part size. The injection speed was chosen between 30 mm/s and 38 mm/s. Incomplete injection occurred when the pressure was below the lower limit, and when the pressure was over 38 mm/s, burns occurred on the part. It is determined as 45 mm and 60 mm for the velocity-pressure transition position. The experimental design undertaken in this study was created by the response surface experimental design method. The analyses were carried out with the statistical approaches and relations obtained by Minitab. Optimization study was carried out in line with certain objectives by evaluating the parameters and the interactions between the outputs as a result of the study. The outputs obtained at the end of the study were compared with the situation before the study and the improvement levels were revealed. It is an experimental design used to determine the most important factors that are effective during a process. With the scan design, fewer attempts can be made to isolate fewer parameters that affect process quality. They are experimental designs that include the estimation of complex relationships among the identified factors and the main factor effects. The importance of factors and interactions can be understood with full factorial designs. In the experimental design known as response or response surface designs, instead of linear models to make the outputs more understandable, curvilinear models are created depending on the factors used and the surface optimization of the response output can be performed. The most commonly used response surface is the experimental design. Center response surface designs are factorial or fractional factorial design with center points enriched with a group of axial points (also called star points) that allow you to estimate curvature. The Box-Behnken design is a type of response surface design that does not include the previously studied factorial design. In the simplest mixing test, the response (product quality or performance according to some criteria) depends on the relative proportions of the ingredients (ingredients). A Taguchi design is a designed experiment that allows you to choose a product or process that works more consistently in the work environment. Taguchi designs recognize that not all factors that cause variability can be controlled. These uncontrollable factors are called noise factors. Taguchi designs attempt to identify controllable factors (control factors) that minimize the influence of noise factors. It has been revealed that the most effective single parameter in dimensional changes is the injection speed, and it has been shown that the effect of cooling time, holding pressure and velocity-pressure transition position respectively decreases. It was determined that the most effective bilateral relationship was multiplication of cooling time parameter and holding pressure parameter. It has been shown that multiplication of cooling time and injection rate is a factor in the interaction at a similar rate. It has been shown that the most effective single parameter on the mechanical properties is the velocity-pressure transition position, followed by the effect of injection speed, holding pressure and cooling time, respectively. It has been revealed that the most effective dual relationship is multiplication of cooling time and speed-pressure transition position. When all the requirements are taken into consideration, it has been shown that the most effective single parameter is the injection speed, and then the efficiency of the speed-pressure transition position is stated proportionally. It has been revealed that the most effective bilateral relationship is multiplication of cooling time and holding pressure. In the dimensional changes, it was observed that the values went to the undesirable region in some regions, while an improvement was observed at variable rates in certain regions. While the greatest improvement in mechanical properties was observed in the modulus of elasticity by 11%, no significant difference was observed in the impact energy. When the process duration before and after optimization is compared, the process cycle time was reduced from 73.5 seconds to 63.1 seconds, resulting in 14% improvement.
Thesis (M.Sc.) -- İstanbul Technical University, Graduate School, 2023
Anahtar kelimeler
polipropilen, polypropylene, plastik malzemeler, plastic materials