The die turning injection (DTI) process for the fabrication of hollow parts

The die turning injection (DTI) process, which can fabricate hollow plastic parts with a complex geometry, is proposed in this study. DTI is a new technology, which is accomplished in three steps: (1) the primary injection step, (2) the die turns, and (3) the secondary injection step. Two separate halves of the part are injection molded during the primary injection. The die rotates to align the two halves for the secondary injection. The secondary injection along the aligned surfaces joins the two halves into the final hollow part. The proposed DTI technology provides several advantages. It has the ability to form hollow parts with high dimensional accuracy, the equipment requires a small working space and the machine control is fairly simple. To verify the feasibility of DTI process, industrial trials were performed to manufacture a hollow nozzle part for a washing machine. To optimize the process, a finite element (FE) analysis was performed using the commercial code, Autodesk Moldflow Insight. To design the hot runner system for the primary injection step, two types of hot runner systems, a V-shaped and a T-shaped runner, were investigated. The critical parameter that was measured in these two runner designs was the amount of warpage. An FE analysis for the secondary injection step was also performed to analyze the flow characteristic at the aligned surfaces of the two separate hollow halves. The cooling channel was also designed to cool the mold and control the uniformity of injection temperature. With appropriate control of the injection conditions, a hollow nozzle part having excellent dimensional accuracy was successfully manufactured using the proposed DTI process.