Enhancement of induction heating efficiency on injection mold surface using a novel magnetic shielding method

Mold temperature is a major factor in the quality of injection molding process. A high mold temperature setting is feasible to enhance the molding quality but prolongs the cooling time. Induction heating is the method currently used to heat the mold surface without increasing the molding cycle. However, one unresolved problem of induction heating is the proximity effect resulting from two adjacent coils with different current directions. The proximity effect substantially decreases heating efficiency, which then causes non-uniform heating. This effect is difficult to avoid in a single-layer coil. The most common solution, which is to use magnetic concentrators to reduce the proximity effect, does not obtain satisfactory results. In the novel magnetic shielding induction heating method developed in this study, heating efficiency and temperature uniformity are enhanced by using ferrite materials to separate the conflicting magnetic fields caused by the repulsive proximity effect. Three typical single-layer coils are investigated in this study, including a reciprocated single-layer coil, a single-layer spiral coil, and a rectangular frame coil. Appropriate placement of ferrite materials on these induction coils successfully eliminated the proximity effect, increased the heating rate, and improved temperature uniformity.