Key parameters and optimal design of a single-layered induction coil for external rapid mold surface heating

Abstract

Setting high mold temperatures for injection-molding plastics facilitates favorable flow conditions for filling cavities with melted materials and provides an esthetically pleasing surface as well as a high replication rate of high-quality products; however, the cooling times are typically prolonged. Electromagnetic induction heating incorporating surface heating instead of conventional volume heating for mold-heating processes is advantageous because it provides a rapid heating time and a reduced cooling time, is environmentally friendly, and saves energy; therefore, it has been adopted in various variotherm injection-molding systems. Although previous studies have discussed how induction heating is influenced by major factors, such as the number of coil turns, working frequency, and heating distance, few studies have investigated other crucial factors, such as the thickness of the heated target and the position of the induction coil. In this study, the effects of the thickness of a heated target, pitch of coil turns, heating distance, position of the induction coil, working frequency, and waiting time on the heating rate and temperature uniformity of induction heating on a mold surface by using a single-layered coil were analyzed. In addition, the Taguchi method and principal component analysis were applied to determine the optimal combination of control factors for achieving a high heating rate and low temperature deviation. Both simulation and experimental results indicated that the thickness of a heated target plays a crucial role in affecting the heating rate; specifically, a thicker workpiece slows the heating process and generates rapid heat dissipation after induction heating. Moreover, the position of the induction coil exerts the most notable effect on heating uniformity.