직접식 쾌속 툴링 기반 다중 재료 적층 방식을 이용한 사출 성형 금형의 냉각 특성 향상에 관한 연구

Abstract

In recent, several research works on the development of the injection mould with a high cooling rate have been actively undertaken in efforts to improve the productivity of injection molding process. Most of those research works have been focused on the development of the injection mould with conformal cooling channels using a direct and indirect rapid tooling (RT) process. The objective of this research work is to develop design technology of mould with rapid and uniform cooling characteristics using the deposition of the multi-materials based on the direct metal rapid tooling process. In order to enhance thermal management characteristics, including the high cooling rate and the uniform cooling, the injection mould was designed as three parts consisted of a base structure, a mid layer and a molding part with P21 injection tool steel. The material of the base structure was selected as Ampcoloy 940 (Cu-Ni alloy) to enhance cooling rate of the mould. The mid layer with Monel 400 was created to reduce a thermal stress induced by a difference of thermal expansion coefficient between the base part and the molding part. Also, the conformal cooling channel was inserted into the mould to increase the cooling efficiency. In order to obtain the optimum material thickness of each layer, transient heat transfer analysis and thermal stress analysis were performed using I-DEAS NX12 ESC module. From the results of the heat transfer analyses, a proper geometrical arrangement of each material was obtained. Through the results of thermal stress analysis, it was shown that the maximum thermal stress of each layer is smaller than the yield strength of each material. In addition, it was found that the thermal management mould with multi-materials and conformal cooling channels can rapidly transfer from the mould surface to the cooling channels in comparison with the single material mould with linear or conformal cooling channels. In order to manufacture the mould with multi-materials, a hybrid rapid tooling technology combining DMT process with a machining process was utilized. The base structure of the designed mould was manufactured from a high speed machining process to shorten the manufacturing time of the mould. The mid layer and the molding part of the designed mould were manufactured from the DMT process. In addition, post processing, including a high speed machining and an EDM and a lapping process, was carried out to improve surface roughness and to implement details of the mould. The designed mould was fabricated within 157 hours. In order to examine the efficiency and the applicability of the mould, several injection molding experiments were performed. From the results of injection molding experiments, it was shown that the cooling time of the developed mould can be shortened to 3 seconds without the decrease of the product quality.