An experimental investigation of the effects of design paramaters of a plastic injection mold on mouldability

Plastics are used in every phase of our daily life. Although there are lots of methods for shaping the plastics, the most widely used method is injection molding. The cost of the production of the plastic products, its quality, the geometric structure, size tolerance and appearance depend on both injection parameters and molding parameters. In the literature, many studies have been conducted about the effects on molded products related to the injection parameters and the studies continue to be performed. However, there are few studies about the molding parameters according to the injection parameters. In this study, the effects of the molding parameters on flow length were analyzed. The effects of the surface roughness of mold cavity, runner profile and mold temperature on flow length were investigated.In order to investigate the molding parameters, an injection mold was designed in accordance with ASTM D 1223. Eight mold cavities were composed in mold core and each mold cavity having different surface roughness were sandpapered. The values of the surface roughness of these mold cavities change between 0,047 µm and 0,481 µm. Moreover, to determine the effects of the runner profiles on flow length, in designed mold cavity four different profiles having the same cross-sectional area and length as semi-circled profile, angled profile, trapezoidal profile and rectangular profile were manufactured. To keep the desired temperature of the mold the mold router was used.In the experiments, four different injection pressures were used as 50, 60, 70, and 80 bar, four different injection temperature were used as 220, 240, 260 and 280 ºC, four different injection speed (flow) were used as 30, 35, 40, and 45 m³/sn and five different mold temperature are used as 20, 30, 40, 50 and 60 ºC. In the first mold cavity, the lowest surface roughness (for the value measured parallel to the flow) with a value of Ra = 0.071 ?m, average 30.94 mm flow length were determined. In the eight mold cavity which has the largest average value of Ra = 0.6 ?m the flow length as 25.55 mm was determined.for the effect of runner profiles on the flow length, the longest flow length was determined in four different runner profiles having average 26,336 mm2 section area, respectively in half round, angled profile, trapezoidal and rectangular profiles. According to the result of the experiment in which the effect of mold temperature on flow length was investigated, the changes of the mold temperature did not affect the flow length significantly. In addition the effect of ironing pressure on the surface roughness of the molded product was investigated and three different pressure values were used as 70, 80 and 90 bar. Accordingly, it was determined that as ironing pressure increased, the product surface roughness decreased.Key Words: Injection , Flow Lenght, Surface roughness, Runnerprofiles