For previous reading, please refer to Mold Design Guide 4 (Molding Part Design).

Mechanisms with side parting and core pulling are collectively called slide mechanisms. There are many types of slide mechanisms, and various classification methods exist. Based on usage characteristics of various slide structures, common slide mechanisms can be summarized into following categories:
(1) Front mold slide mechanism (2) Rear mold slide mechanism (3) Internal slide mechanism (4) Huff mold mechanism (5) Lifter and rocker arm mechanism (6) Hydraulic (pneumatic) slide mechanism

(1) Each component of slide mechanism should have reasonable machinability, especially molding part. General requirements:
a. Avoid slide clamping lines as much as possible. If unavoidable, clamping line should be located in an inconspicuous position on plastic part, and clamping line length should be as short as possible. At the same time, a combined structure should be used as much as possible so that slide clamping line part and cavity can be processed together. As shown in Figures 7.2.1a and 7.2.1b.
b. To facilitate processing, molding part and sliding part should be made into a combined form as much as possible. As shown in Figure 7.2.2.

 

(2) Components and assembly parts of sliding mechanism should ensure sufficient strength and rigidity.
Sliding mechanism is generally designed based on experience, but simplified calculations can also be performed (see Section 5.3 of Chapter 5 for calculations). To ensure sufficient strength and rigidity, following is generally adopted:
A. Maximum structural size. When spatial location allows, sliding component adopts maximum structural size.
B. Optimized design structure. For example, following situations:
1) Positioning end of a longer sliding pin to avoid bending, as shown in Figure 7.2.3.

 

2) Increasing cross-sectional size of lifter and decreasing guide slope of lifter to avoid bending of lifter rod, as shown in Figure 7.2.4. When structural space "D" of plastic part allows, increase cross-sectional dimensions "a" and "b" of lifter, especially dimension "b". At the same time, while satisfying side core pulling requirement, decrease angle "A" to avoid bending of rod under lateral force.

3) Changing structure of ejector to enhance strength of mold at assembly part. As shown in Figures 7.2.5a, 7.2.5b, 7.2.6a, and 7.2.6b.

 

4) Increase locking to improve strength of shovel. (See Chapter 5, 5.3)
(3) Movement of sliding mechanism should be reasonable.
To ensure normal operation of sliding mechanism, it should be guaranteed that sliding mechanism does not interfere with other structural components during mold opening and closing process, movement sequence is reasonable and reliable. Following points should generally be considered:
A. When using a front mold sliding mechanism, mold opening sequence should be guaranteed. As shown in Figure 7.2.7, during mold opening, parting should begin at point A-A, followed by point B-B.

 

B. When using a hydraulic (pneumatic) sliding mechanism, parting and resetting sequence of sliding mechanism must be well controlled; otherwise, sliding mechanism will be damaged. In Figure 7.2.8, sliding mechanism can only part after locking block 2 leaves sliding mechanism. Before mold closing, sliding mechanism must be reset, and after mold closing, locking block 2 locks sliding mechanism. In Figure 7.2.9, because sliding pin passes through front mold, it must be pulled out before mold opening so that sliding mechanism can be reset after mold closing and locked by hydraulic cylinder pressure.

 

C. During mold closing, sliding mechanism should prevent interference with ejector mechanism.
When projections of sliding mechanism and ejector mechanism in mold opening direction coincide, a reset mechanism should be considered to allow ejector mechanism to reset first. (See Chapter 8.6 for reset mechanism.)
D. When inclined guide pillar or inclined slide of driving sliding mechanism is long, length of guide pillar should be increased.
Guide pillar length L>D+15mm is shown in Figure 7.2.10. Purpose of lengthening guide pillar is to ensure that mold is fully guided by guide pillar and guide sleeve after inclined guide pillar or inclined slide, avoiding damage to sliding mechanism during mold closing.

 

(4) Ensure sufficient slide travel to facilitate demolding of plastic parts.
Slide travel is generally taken as side hole or concave/convex depth plus 0.5~2.0mm. Use a smaller value for lifters and rocker arms, and a larger value for other types. However, when using a combination mold to form plastic parts such as coil frames, travel should be greater than side concave depth, as shown in Figure 7.2.11. Travel s is calculated using following formula.

 

(5) Slide guide should be smooth and reliable, and should have sufficient service life. Slide mechanism generally uses a T-shaped guide groove for guiding. Figure 7.2.12 shows several commonly used structural forms.

 

When slide mechanism completes side parting and core pulling, length of slide block remaining in guide groove should not be less than 2/3 of the total length. When mold plate size cannot meet minimum fitting length, an extended guide groove can be used, as shown in Figure 7.2.13.

 

Inner sliding mechanism is mainly used for molding concave or convex inner walls of plastic parts. During mold opening, sliding mechanism moves towards "center" of plastic part. Its typical structure is as follows:
(1) Structure 1: As shown in Figure 7.5.1, inner sliding mechanism molds concave inner walls of plastic part. Inner sliding mechanism 1 moves under action of inclined pin 3, completing parting of concave inner wall of plastic part. After inclined pin 3 disengages from inner sliding mechanism 1, inner sliding mechanism 1 is positioned under action of spring 4. Because an inclined hole needs to be machined on inner sliding mechanism 1, width of inner sliding mechanism is required to be relatively large.

 

(2) Structure 2: As shown in Figure 7.5.2, an inclined tail is directly machined on sliding mechanism 1. During mold opening, inner sliding mechanism 1 moves under drive of inclined surface A of insert 5, completing parting of concave inner wall. This structure is compact, width of inner sliding mechanism is not limited, and it occupies little space.

 

(3) Structure: As shown in Figure 7.5.3, inner sliding protrusion is formed. In this type of structure, to avoid rear mold scratching formed protrusion when plastic part is ejected, dimension D shown in figure is generally required to be greater than 0.5mm. Note that a1 should be greater than a.

 

A half mold is a sliding mechanism consisting of two or more sliders that combine to form a cavity, where sliders simultaneously achieve lateral parting during mold opening. Lateral stroke of a half mold is generally small. Typical half mold structures are as follows:
(1) Structure 1: As shown in Figure 7.6.1, cavity consists of two inclined sliders located on the front mold side. During mold opening, under action of pull hook 1 and spring, inclined slider 3 moves along inclined groove to complete lateral parting. After parting, inclined slider 3 is positioned by spring 2 and limiting block 4. Structure and assembly form of pull hook 1 usually adopt two methods shown on the right side of Figure 7.6.1. Angle A of inclined slider generally does not exceed 30°.

 

(2) Structure 2: As shown in Figure 7.6.2, cavity consists of two inclined sliders located on the rear mold side. During ejection, inclined slider 3 moves along inclined groove under action of ejector rod 5 to complete lateral parting, while simultaneously ejecting plastic part. Angle A of inclined slider should generally not exceed 30 degrees.

 

Lifter and swing rod mechanism is mainly used for molding side concavities and convexities inside plastic parts, and also has an ejection function. This mechanism has a simple structure, but poor rigidity and a small stroke. Commonly used typical structure is as follows:
(1) Structure 1 Lifter Mechanism
Figure 7.7.1a shows the most basic lifter mechanism. During ejection process, lifter 1 moves along rhomboid hole of rear mold under action of ejection force to complete lateral molding. Root of lifter requires assembly structure shown in figure. Figure 7.7.1b shows disassembly diagram of its assembly.

 

In lifter mechanism, in order to ensure stable and reliable operation of lifter, following points should be noted:
(A) Rigidity of lifter. To enhance rigidity of lifter, following methods are generally adopted:
1. When structure allows, try to increase cross-sectional size of lifter. (See Chapter 7, Section 7.2)
2. When lateral ejection is feasible, draft angle "A" of ejector should be as small as possible, generally not exceeding 20°. Lateral stress point of ejector should be moved downwards, for example, by adding insert 2 as shown in Figure 7.7.1a. Insert can also have higher hardness, improving mold life.
(B) Lateral movement space of ejector. As shown in dimension "D" of Figure 7.7.1a, to ensure that ejector does not interfere with other structures on plastic part during ejection, lateral parting distance and draft angle "A" of ejector should be fully considered to ensure sufficient lateral movement space "D".
(C) Reset of ejector in mold opening direction. To ensure that ejector returns to predetermined position after mold closing, following structural form is generally adopted, as shown in Figures 7.7.2a and 7.7.2b.

 

 

(D) Sliding of bottom of lifter on ejector plate should be smooth and stable.
(2) Structure 2: Rocker arm mechanism, as shown in Figure 7.7.3.
During ejection process, when head of rocker arm 1 (range shown in L1) exceeds rear mold core, rocker arm 1 swings upward under action of inclined plane A, completing parting.
When designing rocker arm mechanism, it should be ensured that: L2 is greater than L1; E2 > E1.
Disadvantage: Area "B" in figure is prone to wear, and hardness of this area must be increased. Generally, it is required to design this area as an inlay structure.

 

Utilizing pressure of liquid or gas, through piston of oil cylinder (pneumatic cylinder) and control system, lateral parting or core pulling is achieved. Characteristics of hydraulic (pneumatic) sliding mechanism are long sliding stroke, large parting force, parting and core pulling are not limited by mold opening time and ejection time, with smooth and flexible movement. Typical structural forms are shown in Figures 7.2.8 and 7.2.9.