Jae Hyuk Choi

This paper presents a novel method to eliminate halo gloss transition surface defects commonly found on large-scale injection-molded parts. Due to the increasing importance of product appearance and its influence on consumer decisions, the halo defects that deteriorate surface appearance and quality should be eliminated. The effect of the main injection molding process parameters on the halo defects was compared and investigated by correlating the injection molding simulations and defect specimens. It was found that a drastic increase in flow front speed (FFS) is the main cause of the halo defects. A multi-step injection speed approach that minimizes a drastic increase of FFS due to the reduction of flow front area according to the filling patterns is proposed. The proposed approach was experimentally validated for a simple test part and a real-world, commercial home appliance part, respectively. This approach can contribute to reducing the time for setting defect-free injection molding conditions before mass production.

In this study, an evolutionary cooling channel, a new methodology for designing a conformal cooling channel, was proposed. This methodology was devised by imitating the way that a plant’s roots grow towards a nutrient-rich location. Additionally, Murray’s law was applied to increase the cooling efficiency through minimizing the pressure loss of the cooling water inside the cooling channel. The proposed method was applied to the specimen shape to verify the concept, and it was confirmed that efficient cooling was achieved by applying it to the headlamp lens cover part of an actual vehicle. When this methodology was applied, the temperature deviation of the part could be improved by about 46% in just third generations, and the pressure loss could be reduced by about 10 times or more compared to the result of applying the straight-line cooling channel.