사출 금형의 밸브 게이트 순차 제어 적용을 위한 피드 시스템 최적화

Abstract

Recently, multi points injection are used to reduce high molding pressure occurred by enlargement of injection molded products and high viscosity characteristic of plastic resin. And then, Weld line defects caused by the multi-component injection molding can be eliminated by a sequential valve gating technology which successively controls of open close time of gates. However, the original sequential valve gating technology has a limit that the response of the injection system is delayed. This limit causes rapid changes of the flow front velocity, which have negative effects on the quality of molded products. Thus, in this study, a new molding feed system is established as a measure of guarantee of the exterior quality of products to supplement the limitation of responsibility of the injection system without application of costly additional control systems. The feed systems consists of 3 stages, which are applied in order, of overlap molding technology, diagonal gates, auxiliary runners. The analysis conditions were designated as a total of 10 cases according to the application of each stage, and the analysis was performed by Moldflow injection molding analysis program. As a result of temperature distribution at a flow front, all cases except Case 1 which is applied by original sequential valve gating technology were suitable for the criteria for evaluating the excellent quality. Then, as a result of analyzing the distribution flow front velocity within the fill time, when overlap molding was applied, the rapid hesitation was relatively reduced. And when diagonal gate was applied at intervals of 10mm in length of the gates, the molding pressure was decreased. Finally, a phenomenon of rapid acceleration could be alleviated by application of auxiliary runners according to the shape. Based on the results of temperature distribution at a flow front and fill time of the products, it was found that Case 9 was the optimum condition. This study could suggest composition of the new feed system as a measure of exterior quality of molded products. |사출 성형 제품의 대형화 및 용융 수지의 높은 점도 특성으로 인해 높은 사출 압력이 요구됨에 따라 다 점의 Gate 를 활용하게 되는데, 이때 생성되는 Weld Line(외관 결함)을 줄이기 위하여 Gate 를 순차적으로 개방하는 Sequence Control 을 적용하고 있다. 그러나, 사출기 응답성 지연으로 인한 유동선단속도가 급격하게 변화하여 제품 외관 품 질에 부정적인 영향을 주는 한계점이 발생한다. 본 연구는 기존의 Sequence Control 시스템의 한계점을 고가의 추 가 정밀 제어를 적용하지 않고 보완할 수 있는 새로운 금형 Feed System 을 구축함으로써 사출 제품의 외관 품질 제 어 방안을 확보하고자 하였다. 이를 위하여 새로 개발한 구성요소 총 3 단계 ‘Overlap 성형’ 기술, 사선 Gate, 보조 Runner 순으로 적용하였다. 해석 조건은 단계 별 기술 적용에 따라 총 10 가지로 지정하여 Mold Flow 사출 성형 해 석 프로그램을 통해 해석을 수행하였다. 충전 시간 내 유동 선단 속도 분포를 분석해본 결과, ‘Overlap 성형’ 기술을 적용 시 급 정체 현상이 현저히 감소하였고 사선 Gate 길이 10 mm 간격으로 적용 시 Overlap 성형 거리가 동일한 길 이만큼 감소함을 알 수 있었다. 또한 보조 Runner 적용 시 급가속 현상의 정도가 0.5 배로 줄어든 것을 확인할 수 있 었다 이로써 Overlap 성형 기술, 사선 20 mm Gate, 보조 Runner 두께 5 mm, 저항 요소 두께 1 mm 를 적용한 조건을 최적의 조건으로 도출하였다.