Car interior panel product diagram is shown in Figure 1. Maximum outer dimension of product is 301.44 mm * 159.96 mm * 65.94 mm; average thickness of plastic parts is 2.35 mm, plastic part material is FPP TSOP-AT5HF, and shrinkage rate is 1.009. 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. Note that all dimensions in 3D drawings are in imperial units and have not been adapted in order to maintain style of original drawings.

 

Figure 1 Car interior panel product diagram

 

Figure 2 3D diagram of car interior panel mold

 

Figure 3 Mold parting surface design

 

Figure 4 3D diagram of rear mold core
As can be seen from Figure 1, shape of plastic part is a U-shaped flat shell folded into a V shape, outer surface is polished, and head has a rectangular sunken glue position, where front and rear mold cores are inserted and punctured. There are 10 buckles on the two sides and one end face on the back of plastic part, and it is necessary to design a lifter for demoulding.
Plastic part is a large plastic part. Mold design cavity ranking is 1 cavity. Plastic part is V-shaped. Correspondingly, mold parting surface is V-shaped. Design of mold parting surface is shown in Figure 3. This type of parting surface is an irregular parting surface, and distribution of lateral forces is very unbalanced. Therefore, mold is designed with a three-level positioning structure. That is, positioning of guide pillars and bushings, positioning of zero-degree positioning block in the middle of four sides of mold base, and positioning at four corners of front and rear mold core. Positioning accuracy of zero-degree positioning block is very high, and it needs to be processed together with mold base at mold base manufacturer to ensure its accuracy. Zero-degree positioning blocks are the most preferred precision positioning method for European and American mold customers. Considering thermal expansion and contraction of mold, zero-degree positioning block generally needs to be designed at the center of mold base. If there is interference from slider, it can also be moved to an off-center position. The biggest role of zero-degree positioning block is to ensure repeated mold closing accuracy of mold. It needs to be matched with a high-precision injection molding machine so that role of zero-degree positioning block can be effectively exerted. For example, in a mold with many weak insert insertion positions, zero-degree positioning block can ensure that small inserts are not broken by lateral force because mold closing angle is smaller than insertion angle of small inserts, effectively extending life of mold.

 

Figure 5 lifter view of front end face

 

Figure 6 Structural diagram of lifter
Size of plastic parts is large, and design of pouring system of plastic parts is very critical. Outer surface of plastic part is appearance surface, and gates cannot be designed. Considering structural characteristics of plastic part, gate can only be designed on inner edge of sunken gate. Gate is a horn gate, see 3D diagram of mold. Horn gate is a variant of latent gate. Gate is connected to inner surface of product in the form of a hook runner, and can feed glue at same height as PL surface. It is mainly used in situations where gates are not allowed to exist on exterior and side surfaces of plastic part. It is usually designed at the bottom of side of plastic part or on inside near edge. It is suitable for products that require automatic removal of runner condensate and do not allow gate traces in appearance. This form of gate is used for some products with special needs. For example, there is no place to add bone on inner surface of product or bone is not deep enough. Horn gates and latent gates are both gates that can be automatically cut off in mold to facilitate automated injection molding, so they are very popular among European and American customers.
Its main feature is that there are no gate marks on appearance, it is easy to realize automated production, and there is no need to trim gate. Key points of its design are as follows:
1. For materials such as PS, gate ripple marks are easy to occur.
2. Horn gates cannot be used for hard and transparent materials such as PMMA.
3. Spray produced during injection molding may cause marks on outer surface of product.
4. Horn gate is a gate formed by processing two inserts separately and then fitting them together. Now with emergence of 3D printing technology, it can be made as a whole.
5. Horn gates can also be used when gates of two-color products overlap.
6. For large plastic parts, multiple horn gates can be designed. Cross-section of horn gate of large plastic parts is flat. Horn gate is also suitable for small plastic parts. Cross section of horn gate for small plastic parts is oval.
As can be seen from mold diagram, size of plastic part is larger, molten plastic process is longer, and pouring system is a needle valve hot runner system with a corner gate. Problem of gate eccentricity is solved through manifold of hot runner.
Difficulty in designing this set of molds also includes design of lifter. Undercuts on both sides need to be designed with lifters. At the same time, when demoulding lifters on both sides, care must be taken to prevent plastic parts from being caught by lifters and making it difficult to demould. For this type of buckle, lifter can also be designed in another direction, so as to avoid problem of product clamping. Readers are advised to analyze and think about it.