Toyota interior accessories products are shown in Figure 1. Maximum outer dimensions of product are 315.90 mm * 15.58 mm * 22.57 mm; average glue thickness of plastic parts is 1.00 mm, plastic part material is PP, shrinkage rate is 1.014, and plastic part weight is 7.42 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling, flow lines, pores, warping deformation, silver streaks, cold materials, jet lines, etc. and they must comply with ROSH environmental requirements.

 

Figure 1 Toyota interior accessories product map

 

Figure 2 Analysis diagram of three elements of mold design
As can be seen from Figure 1, shape of plastic part is a curved irregular plastic part with undulating heights. Inside of plastic part contains 4 pairs of raised buckles, forming a demoulding undercut. These undercuts appear in pairs, and a forced demoulding mechanism needs to be designed to achieve demoulding. Plastic parts are irregular plastic parts, which brings great difficulties to mold design. Difficulty of mold design for this kind of plastic parts is selection and design of parting surface.

 

Figure 3 3D diagram of mold
Before mold design, mold opening direction needs to be analyzed first. Analysis and selection of mold opening direction is the most important step in determining mold design plan. The three elements of mold design plan are gate, ejection and parting surface. Mold opening direction analysis is closely related to plastic part ejection and gate design. Selection of mold opening direction is basis and premise of parting surface design. Only when mold opening direction is correctly selected can parting surface be selected correctly. For parts with same shape and different sizes, size values will affect selection of parting surface. Selection of parting surface is related to mold structure. Qualitative analysis can only summarize general rules, while quantitative analysis needs to be combined with size of plastic part.
For some plastic parts, selection of parting surface is not complicated. Parting surface is even a plane in the middle of product. Difficulty lies in choice of mold opening direction, that is, which side of plastic part is placed on movable mold and which side is placed on fixed mold? This problem is sometimes difficult to judge, and even experienced engineers may make misjudgments. Correct judgment will leave side with greater mold adhesion force in movable mold to facilitate ejection and demoulding of plastic parts, and design gating system on the other side. We call this problem choice of mold opening direction. Sometimes the simpler shape of plastic part, the more difficult it is to judge mold opening direction. For round products, products with seemingly simple shapes have more complicated mold opening direction choices. Plastic parts of this set of molds are irregular strips, and analysis of the three elements of parting surface is shown in Figure 2.

 

Figure 4 3D view of rear mold core and parting surface

 

Figure 5: Lifter comes out and buckles

 

Figure 6 Small lifter view
The three elements that determine mold design plan are gate, ejection and parting surface. Mold design is a systematic design. Only by considering the three elements comprehensively and analyzing them comprehensively can we find a reasonable mold design plan. As mentioned before, before parting surface is determined, mold opening direction should be determined first. In this set of molds, side with undercut is placed in movable mold, so that plastic parts can remain in movable mold after mold is opened. On both sides of parting surface, arrows are used to mark fixed mold and movable mold respectively. They are often replaced by letters. CAV represents fixed mold and CORE represents movable mold. Dividing line is parting surface, small triangles are marked on both sides to make parting surface intuitive, eye-catching, and clear at a glance. PL is marked on parting surface. Parting surface is a complete and closed parting line on product. This line cannot intersect with itself. Therefore, no matter how complex plastic part is, resulting in a complex parting surface, or undulations, or curved surfaces and gaps, etc., expression of parting surface should be complete, correct, and unique. There should be no room for ambiguity or ambiguity.
On parting surface expression diagram, dividing line of slider should also be drawn in detail. If slider does not affect parting surface, for example, buckle position of plastic part is below parting surface, mark slider with an arrow and mark Out SLIDE1, 2, 3... At the same time, also add position of ejector pin and gate. If necessary, position of large inserts should also be drawn on this picture.
Due to structure of plastic part, mold design cavity arrangement is 2 cavities. There are 5 sliders on the side and end face of plastic part, and there are 6 sliders in total for the two plastic parts. Mold design fully considers position of slider. Mold base is a standard mold base CI3560, and gate is a side gate with two points for glue injection. On parting surface, an exhaust groove is ground to facilitate injection molding.
Rear mold can be buckled by force removal or by designing a lifter. Actual mold design adopts lifter method. Structure of lifter is shown in Figures 5 and 6. Since stroke of lifter is very small, a small lifter with a small stroke can be designed and manufactured using quenched steel. Plastic parts are ejected using a combination of straight ejection and inclined ejection.