ract—In this paper,  the structural feature and forming technology of two automobile engine covers are analyzed. The mould structure with two cavities is designed and the working process of the injection mould is discussed.。The mould structure is complicated. The core-pulling mechanisms are designed reasonably in one mould and demoulding of the plastic parts is realized. Many inserts and standard parts are used in the injection mould, so the economical efficiency of the injection mould is well and the injection mould can be maintained conveniently. The injection mould is already in mass production. Industrial practice proves that the action of the core-pulling mechanisms, ejector mechanisms and resetting mechanisms is stable and reliable. The plastic parts produced can meet the customers’ technical requirements.9840
Keywords- injection mould; core-pulling mechanism; slide; Demoulding
I. INTRODUCTION
Two automobile engine covers are shown in figure 1. The plastic parts are in mass production and the two plastic parts are asked to be moulded in one mould. The plastic parts are made of polypropylene (PP). The molding shrinkage is 0.95%. The outline dimensions of two plastic parts are 124.26mm×219.16mm×78.6mmａｎｄ174.58mm×221.67mm×146.32mm. The basic wall thickness　of the two plastic parts is 1.8mm. The appearance of the　plastic parts should maintain perfect. The mark of pouring　and ejecting is not allowable to appear on the plastic part.　The disfigurement of injection such as weld lines, sink mark,　flashing, splay, etc. is not allowable to appear either. Design　of the parting surface of the two plastic parts is difficult. The　parting surface is complicated curved surface and it has　uneven step shape. The side gate is adopted. There are two　reentrant structures in the area of A and B of the plastic part　1, the draft angle is zero in the area of C of the plastic part 1　and there are six reentrant structures within the limit of D　and E of the plastic part 1. The corresponding core-pulling　mechanisms should be designed in the five places. There are　three reentrant structures in the area of F, G and H of the　plastic 2 and there are six reentrant structures within the limit　of I and J of the plastic part 2. The corresponding core-pulling　mechanisms should be designed in the five places also. Then　ten core-pulling mechanisms will be placed in one mould. So　the reasonable design of the core-pulling mechanisms is the　most important in the course of designing the injection　mould.
 
II. DESIGN OF ANGLE PIN CORE-PULLING MECHANISMS
According to the structure feature of the plastic parts, six angle pin core-pulling mechanisms are designed in the area　of A, B and C of the plastic part 1 and in the area of F, G and　H of the plastic part 2. The mechanisms are distributed in　Figure 2.
 
Taking the angle pin core-pulling mechanism 1 shown in　Fig.2 for example, the mechanism is mostly composed of　slide 1, angle pin 4, positioning screw 6, slide wedge 8, wear　plate 5 and wear plate 7. The mechanism is shown in figure 3.　When the mould is opened, the angle pin fixed in the　fixed half of the mould guides the slide in the moving half of　the mould. The slide moves outward along the slide way.　The inclined plane of the cavity plate which is mated with　the slide can ensure wedging the slide when the mould is　closed.Considering the mould structure and process　parameters, the inclined angle of the angle pin is 13°and the　inclined angle in the cavity plate is 15°. The slide and the　components which are in touch with the slide are easy to　wear because the slide moves frequently. In order to　postpone wearing the components, the two steps are adopted　as follow: The slide is made of 718H and is quenched to　50HRC around. The wear plates are laid on the bottom of the　slide and on the back of the slide. The wear plates are made　of GS2510 and are quenched to 60HRC around. The slide　way is formed by the slide wedge and the core plate. The　slide way is easy to machine and to maintain. 抽芯机构在注射模设计中的应用英文文献和中文翻译:http://www.youerw.com/fanyi/lunwen_8695.html