A Study on Dimensional Accuracy of a Vehicle Hood-Catch Considering Material Shrinkage of Polyamide 6 and Length-to-Volume Ratio Characteristic of a Shape

Abstract

A hood-catch is a car part that fixes the vehicle’s hood to its body. This serves as a mechanism for opening and closing the engine bay of an automobile and prevents safety accidents in which the hood is opened while driving due to vibration generated from off-road conditions by firmly latching. Research regarding the overall improvement of products by injection molding, with analysis based on computer-aided engineering, is being actively conducted. However, research on the shrinkage rate considering the characteristics of parts’ shapes, such as length-to-volume ratio, is insufficient. Therefore, in this study, our research is concerned with (1) process improvement compared to the existing process using the design of an experimental method, (2) suggestion of a shrinkage-rate constant, considering both PA6 shrinkage ratio, which is a material characteristic, and length-to-volume ratio, which is a part shape characteristic, and (3) the effect of the proposed shrinkage rate on the accuracy of key dimensions of the hood-catch joint. The results of this study demonstrated that the shrinkage-rate constant needs to be considered simultaneously for both material characteristics and part shape characteristics. In particular, the shrinkage rates of the hood-catch’s pivot sub-assembly and open lever with reinforced PA6, with length-to-volume ratios of 1.24 × 10−3 and 3.10 × 10−3, respectively, are suggested as 0.2% and 0.5%.