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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
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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.