Since undercut surface of finished product is inclined, not at a 90° angle to mold opening direction, slider's movement direction must be consistent with direction of undercut slope of plastic part; otherwise, plastic part will be damaged. In this case, slider's direction is not perpendicular to mold opening direction, as shown in Figures 9-38 and 9-39.
① When slider's core-pulling direction forms an angle with parting surface, and slider is inclined towards moving mold direction, as shown in Figure 9-38.

 

Figure 9-38 Slider tilted towards moving mold direction
Where H--minimum mold opening distance; H1-actual backward distance of slider in mold opening direction at minimum mold opening distance; L4-relative sliding distance between inclined guide post and slider at minimum mold opening distance; a-tilt angle of inclined guide post relative to sliding direction of slider, generally taken as 15~25; b-tilt angle of slider.
② When slider's core-pulling direction forms an angle with parting surface, and slider is inclined towards fixed mold direction, as shown in Figure 9-39.

 

Figure 9-39 Slider tilted towards fixed mold direction
In formula, H is minimum mold opening distance; H1 is actual backward movement of slider in mold opening direction at minimum mold opening distance; L4 is relative sliding distance between inclined guide post and slider at minimum mold opening distance; a is tilt angle of inclined guide post relative to slider sliding direction, generally taken as 15~25; b is tilt angle of slider.

1) Fixed Mold Angled Spring Slider Structure Analysis
Fixed mold angled spring slider is the most important structural form of fixed mold slider, commonly used in cases where the entire outer shape of product is core-pulled or in cases of large-area core-pulling. In molds for large box-shaped plastic parts, fixed mold angled spring slider core-pulling mechanism reduces the overall mold size and facilitates removal of plastic part from mold. A common fixed mold angled spring slider core-pulling mechanism is shown in Figure 9-40.

 

 

Figure 9-40 Fixed mold inclined spring slider core pulling mechanism
1-A plate; 2-Cavity; 3-Spring; 4-T-shaped guide block; 5, 7-Screw; 6-Positioning pin; 8-Limiting block; 9-B plate; 10-Slider seat; 11-Upper pull hook; 12-Lower pull hook; 13-Slider insert; 14-Core; 15-Wear-resistant plate
Two T-shaped guide blocks are designed on large inclined surface of slider seat for smooth guidance. When glue depth is large, making a T-slot on large inclined surface of slider seat will damage slider strength. In this case, T-slot can be designed on the end face of slider, as shown in Figure 9-41.

 

Figure 9-41 Front mold inclined slide block core pulling
1-A plate; 2-Modifier insert; 3-Spring; 4-Modifier inclined slide block; 5-Ejector plate; 6-Core; 7-Limit block; 8-B plate; 9-Pad; 10-Guide block
When moving and fixed molds separate, slider moves along T-shaped guide blocks under action of upper and lower hooks and spring. When slider moves to a certain stroke (W_o), upper and lower hooks separate, and slider continues to move downwards under action of spring until it hits limit block and stops, at which point slider retracts and finished product is undercut. When slider stroke is large, free length of the selected spring needs to be very long. In this case, a guide rod needs to be added in the middle of spring.
W₁＞W₃＞S,H₁＞H₂＞W₁.a=β
When designing fixed mold inclined spring slider, attention must be paid to positioning of top of slider within cavity. Without a positioning surface, it is difficult to control dimensions during mold assembly. In Figure 9-40, right side of cavity 2 serves as left side of slider insert 13, providing positioning. It is important to note that this positioning surface must be selected on fixed mold cavity; it cannot be solved solely by mutual positioning between sliders.
2) Fixed Mold Inclined Spring Slider Guidance
Figure 9-41 shows a mold diagram for a circular product with two parts, using a split-type half-mold inclined spring slider core-pulling mechanism.
Fixed mold insert 2 provides positioning for two fixed mold inclined sliders 4; this positioning method is commonly known as a servo position. Servo position plays a crucial role in fixed mold inclined spring core-pulling molds and cannot be ignored. Due to nature of plastic part, some mold structures do not have fixed mold inserts; plastic parts are all on sliders. In this case, positioning inserts need to be specially designed at both ends of slider. For molds of small plastic parts, guide blocks 10 can be designed at both ends of slider for positioning and guiding.
Figure 9-42 shows another type of front mold inclined spring half-pulling mechanism, with guide blocks 8 designed at both ends of slider. Bidirectional hooks 7 simultaneously pull fixed mold sliders on both sides. During design, it is important to ensure a 0.5mm gap between top of bidirectional hooks and slider.

 

Figure 942 Front mold inclined spring half-pulling mechanism
1-A plate; 2-Fixed mold half-slider; 3-Limit block; 4-Ejector plate; 5-Ejector plate insert; 6-B plate; 7-Two-way hook; 8-Guide block
3) Design of Large Fixed Mold Inclined Spring Slider
Figure 9-43 shows design of a large fixed mold inclined spring slider. Large mold assembly requires design of process screws 2 and 7 to fix slider, which also facilitates machining during mold fitting and polishing. Fixed mold insert 5 acts as a servo position. Inclined guide post 4 provides guidance for spring while simultaneously opening slider. Wear-resistant block 22 is designed with a 3° slope to reduce sliding resistance of slider during mold opening.

 

Figure 9-43 Design of Large Fixed Mold Angled Spring Slider
1. 6. 16. 23 - Screw; 2. 7 - Process Screw; 3 - Pressure Plate; 4 - Angled Guide Post; 5 - Fixed Mold Insert; 8 - Fixed Mold Base Plate; 9. 19 - Fixed Mold Angled Spring Slider; 10 - Wear-resistant Plate; 11 - Hook; 12 - Spring; 13 - Pressure Plate; 14 - Locking Block; 15 - B Plate; 17 - Spring Block; 18 - Core; 20 - Extrusion Block; 21 - Guide Block; 22 - Wear-resistant Block
Due to large size of mold, limit block screw specification should be M10 or higher.
Due to large size of slider and significant depth of precision frame within fixed mold base plate 8, ensuring accuracy of inclined surface during machining is challenging. Therefore, while maintaining sufficient inclined surface length, top of slider can be angled to allow for clearance, ensuring precision frame functions as a positioning, guiding, and mold-locking element.
4) Fixed Mold Slider Stability Mechanism
In recent years, for large molds, hydraulic cylinders and nitrogen springs have been used as ejection elements, overcoming limitations of springs in terms of length and elasticity. Figure 9-44 shows a mold design with a vertically mounted spring and a DME tiger buckle for slider limiting; after mold opening, slider exhibits good stability.
Refrigerator's bottom drawer, as shown in Figure 9-44, has external dimensions of 429.51mm x 227.53mm x 176.5mm. Product structure is a single-sided open, non-closed type with undercuts at both ends requiring a large slider. Large side cavity insert at handle position needs to extend into moving mold, necessitating overcoming insufficient strength to prevent burrs.

 

For large molds such as box-type molds, fixed-mold core pulling has significant advantages. After mold opening, core pulling mechanism remains in fixed mold, plastic part moves with moving mold and eventually remains on moving mold. After ejection, whether part is removed by a robot or manually, there is no core pulling mechanism around plastic part to obstruct its removal.
There are many design methods for fixed-mold side core pulling mechanisms. For large sliders, refrigerator drawer molds use a fixed-mold inclined spring structure. Slider is driven by a spring 9 and a pull hook 18. A guide bar 29 is designed at the center of wedge 14, and there are T-shaped inserts 30 and 31 on each side. T-shaped inserts mate with T-slots on slider. A limit block 16 is installed on each side of wedge 14. Back of slider has two limit surfaces, A and B. After slider moves to limit surface and contacts limit block, it stops moving. At this time, limit pin 12 on slider contacts limit clamp 15 and is fixed. Limit clamp, commonly known as a "tiger buckle," is a standard part of DME (DME code PSM0001). Limit clamp provides safe and reliable positioning of slider after it opens.
During mold opening, mold opens along parting surface. Moving mold moves backward under drive of injection molding machine. Pull hook 18, fixed to mold core plate, pulls pull hook slots on both sides of slider. Under action of T-slots, slider gradually disengages from undercut of plastic part. Slider stops moving after being fixed by limit clamp. Plastic part continues to move backward with moving mold core 21. Upon reaching mold opening stroke, mold opening action stops, and hydraulic cylinder drives push plate 20 to eject plastic part. Plastic part is then gripped by robotic arm and moved to conveyor belt next to machine. During mold closing, hydraulic cylinder first drives push plate back to its original position, then moving mold moves to parting surface to close.

 

Figure 9-44 Refrigerator Drawer Mold Diagram
1 - Heat Insulation Plate; 2 - Cavity Plate; 3, 2, 6 - Extrusion Block; 4 - Diverter Plate/Pressure Plate; 5 - Diverter Plate; 6 - Positioning Ring; 7 - Hot Nozzle; 8 - Pressure Plate; 9 - Spring; 10 - Pop-out Pin; 11 - Cavity; 12 - Limiting Pin; 13 - Slider; 14 - Wedge; 15 - DME Limiting Clip; 16 - Limiting Block; 17 - Wear-resistant Plate; 18 - Pull Hook; 19 - Push Plate Insert; 20 - Push Plate; 21 - Core; 22 - Core Plate; 23 - Base Plate; 24 - Positioning Ring; 25 - Push Plate Insert; 27 - Cavity Insert; 28 - Adjusting Block; 29 - Guide Strip; 30, 31 - T-shaped Insert
This vertically mounted spring can be replaced with a hydraulic cylinder or a nitrogen spring to increase mold opening force.

Moving mold's angled core-pulling mechanism is shown in Figure 9-45. Angled slider 5 is connected to slider seat 7 by a T-slot. Under action of angled guide post 3, angled slider 5 is pulled through slider seat 7. Slider seat is positioned within DME tiger buckle by a locating pin at the bottom.

 

Figure 9-45 Moving mold oblique core pulling
1. Fixed mold base plate; 2. A plate; 3. Angled guide post; 4. Cavity; 5. Angled slider; 6. Core; 7. Slider seat; 8. Angled wedge; 9. B plate; 10. Positioning clamp