Influence of electrical discharge machining of the molding cavity on the surface condition of filled polymer moldings.

In order to obtain the desired surface roughness of the injection molding, the surface of the mold cavity is shaped by selecting appropriate technological processes and machining parameters. However, the roughness of a plastic product is also significantly affected by a number of other factors, such as: process parameters, type of polymer material, material of the mold cavity and construction of the injection mold. The influence of process parameters or the surface condition of the molding cavity on the roughness of molded parts was extensively described in scientific literature. However, mainly cavities with low roughness, obtained as a result of milling, grinding and honing processes were concerned. It is suspected, that the reflection of the molding cavity by the material is affected by the process parameters in a different way for surfaces with low roughness than in the case of complex surfaces with high roughness, obtained e.g. in the process of electrical discharge machining. The purpose of the conducted research was to determine the relationship between the material and temperature of the injection mold, the roughness of the surface of the molding cavity, obtained in the EDM process and the level of polyamide filling with glass fiber. As a result of the conducted research, a significant influence of the surface roughness of the mold cavity on the ability of the polymer material to reproduce it in the injection process was discovered. In addition, a different effect of the injection mold temperature on the roughness of molded parts was found in the case of molding cavities with low roughness (Sa<9 µm) than in the case of cavities with higher roughness (Sa>14 µm). No unequivocal tendency was found describing the influence of the content of glass fibers on the surface roughness of polyamide injection mouldings. [ABSTRACT FROM AUTHOR]