Problem of guiding and positioning is repeated staggered actions when injection mold is closed and opened. When closing mold, guide pin and guide sleeve are the first to guide, to ensure that mold parts have correct initial movement trajectory. After orientation is over, positioning comes into play. Due to different structure of plastic parts, each plastic part will have lateral force more or less during injection molding. Deep cavity plastic parts and asymmetric plastic parts have the largest lateral force. There is a gap between guide posts and guide sleeves, and its working state is actually line contact. Therefore, in injection mold, huge lateral force during injection cannot be withstood only by guide post and guide sleeve. Positioning system must be designed to withstand lateral force. Structure of injection mold to ensure that moving parts move according to established trajectory is called guiding system; structure to ensure relative position accuracy between front and rear molds, between movable parts is called positioning system. As an important part in mold production process, guide post is used for guiding, supporting and positioning. Support means that guide post needs to bear weight of mold plate.
Small molds have low lateral force, positioning problem can be solved by using four corners of mold core to design tiger's mouth. Small molds can also take advantage of structural characteristics of plastic parts to design corresponding tightening systems for front and rear molds. Small mold is locked by parting surface as shown in Figure 1.

 

Figure 1 Typical parting surface locking form
When four corners of front and rear mold cores are designed for positioning of tiger's mouth, inclined angle of tiger's mouth should be smaller, generally 5゜～10゜. A small angle can effectively protect penetration surface of mold from damage. Disadvantage of positioning of die core four-corner tiger mouth is that it has high requirements for processing. Tiger mouth generally needs CNC machine tool processing. Processing accuracy is easily limited by accuracy of machine tool and tool, and it often fails to meet accuracy requirements. For example, fit of inclined plane must be above 80% for reliable precise positioning.
Figure 2 shows two-way interlocking of mold cores. 5゜ inclined plane A and 5゜ inclined plane A'cooperate with each other; 5゜ inclined plane B and 5゜ inclined plane B'cooperate with each other. All mating surfaces can be ground by a grinder, positioning accuracy is significantly higher than that of four-cornered tiger's mouth. When plastic part is in a small and medium-sized mold where cavity and core glue position are roughly symmetrical, design of two-way interlocking of mold core can effectively improve clamping accuracy of dynamic and fixed mold. Therefore, this positioning method is widely used in European molds.
Figure 3 shows slope positioning block showing edge of mold base. When designing slope positioning block, it is necessary to pay attention to middle of edge of mold base, so as to resist thermal expansion caused by thermal expansion and contraction.

 

Figure 2 Two-way interlocking of mold cores

 

Figure 3 Slope positioning block of edge of mold base
Positioning of mold base positioning block is usually called secondary positioning. Secondary positioning is precise positioning of front and rear mold bases. Positioning accuracy of zero-degree positioning block is much higher than that of guide post and guide sleeve. Matching groove of positioning block on mold base should be processed in mold base factory as far as possible to ensure matching accuracy of front and rear mold bases. Positioning block material adopts alloy steel heat treatment or copper and graphite material, and there should be a lubricating oil groove on friction surface of positioning block. Zero-degree positioning block has two functions of guiding and positioning, which can effectively protect weak penetrating surface on mold core. Mold base positioning block is very important for precision molds. Therefore, zero-degree positioning block is a must in North American molds.

 

 

Figure 4 HASCO zero-degree positioning block Z085
Mating height of two sides of zero-degree positioning block determines length of positioning effect. After zero-degree positioning block is designed, movable and fixed molds produce a certain distance of precise guidance and positioning before mold is closed. Therefore, in mold with more insertion positions, zero-degree positioning block can effectively protect insertion position from damage. Figure 4 shows HASCO zero-degree positioning block Z085.

Figure 5 shows edge interlocking of large mold base

 

Figure 5 Interlocking edges of large mold base
Four-corner interlocking is another form of interlocking for large mold bases, as shown in Figure 6. Interlocking angle of four corners of the mold base is 10゜～15゜. Corner interlocking can be applied to all molds, especially in molds where there are large sliding blocks on four sides and it is not convenient to design edge interlocking. When inspecting mold base after processing, it can be inspected by painting to ensure that contact rate of inclined surface is not less than 80%.

 

Figure 6 Interlocking of corners of large mold base