Development of variotherm extrusion blow molding technology to produce high-gloss automotive spoilers

The surface quality of plastic parts produced by the conventional extrusion blow molding (EBM) process is usually poor, especially for those made of engineering thermoplastics. To achieve a high-gloss appearance, some costly and pollutive post-treatments (e.g., painting, polishing, etc.) have to be employed to hide or eliminate surface defects. Herein, a variable mold temperature EBM (i.e., variotherm EBM) technology with electric heating and water cooling, which has the potential to directly yield high-gloss parts, was developed. First, the process principle was designed and presented. Then, an complex industrial plastic part, i.e., automotive spoiler, was selected as a molding case to be studied, in which the variotherm blow mold of the spoiler was designed and especially the design rationality of the mold electric-heating and cooling systems was then examined by numerically evaluating the mold thermal response in the respect of cavity surface heating/cooling efficiencies and uniformity. Finally, the variotherm EBM experiments based on the manufactured prototype spoiler mold were conducted. The results showed that the developed technology can realize high-temperature blow molding with both the molding cycle time and energy consumption in an acceptable range compared with the conventional EBM. Moreover, the surface quality of the molded spoilers is largely improved and the surface defects that are generally appearing in the conventional EBM process can be fully eliminated. Thus, the feasibility and effectiveness of developed technology in yielding high-gloss blow-molded parts are demonstrated.