During production process of plastic molds, mold opening action will cause relative movement between diagonal support pin and slider. This movement includes horizontal movement in mold opening direction so that slider can smoothly detach from undercut structure. For specific situations, please refer to following figure.

 

During mold opening process, slider needs to move a specific distance to ensure that front and rear molds are completely separated, and slider must be able to return to its position safely. After slider returns, it must remain in correct position. If it slides back and forth, it will cause bevel and hole to be misaligned during mold closing, which will cause a collision. Therefore, a positioning device must be installed for slider, device must be flexible and reliable to ensure that slider does not move in place.

 

1) Wave screw positioning
- Advantages: simple processing and intuitive operation.
- Disadvantages: easy to damage.
- Applicable scenarios: commonly used for small-stroke sliders or sliders with larger strokes in X direction (horizontal). It can also assist slider in delaying mold opening, because when bevel is not working, wave ball will hold slider to prevent it from moving.
2) Spring and limit screw positioning
- Advantages: convenient processing, safe and reliable positioning.
- Applicable scenarios: commonly used for sliders in X and Y directions, especially sliders with smaller strokes.
- Spring calculation points: Spring preload means that spring still has preload after mold is opened to overcome gravity of slider to prevent it from returning to its original position. Calculation formula is: (L stroke + 3~5 preload)/40%=L0 (free length). Spring hole depth needs to be determined according to formula H = L0-preload-stroke.

 

 

Case 1:

 

Case 2: Product is an external thread type. Generally, it can be demolded by sliding, but it is not applicable in all cases. Therefore, it is necessary to analyze demolding angle to determine whether there is an undercut in sliding demolding direction and to evaluate degree of undercut. If undercut is small and product tolerance allows, it can be considered to offset undercut effect by tolerance.
To prevent product from sticking to front mold, a delayed mold opening mechanism is designed for slide, that is, front and rear molds have been partially separated but slide has not yet slid, and slide clamps product (using the buckle position) to ensure that product remains in rear mold. Since most of product columns are located on slide, a water cooling system needs to be designed for slide.
Case 3:

 

Case 4: In mold design, special attention should be paid to layout of ejector pins to avoid drilling half of holes between two workpieces for ejection movement, because this may cause ejector pins to be clamped and damaged when workpieces are misaligned. For this reason, a runner ejector sleeve or runner insert can be added to outside of ejector pin to avoid this problem.
When designing ejector mechanism of push plate, it is necessary to ensure that push plate first travels a certain distance before ejecting product to achieve a delayed ejection effect. Since there is a certain space between push plate and product, push plate will travel a certain distance before ejecting product. But sprue ejector is different. Once ejector plate starts to move, sprue ejector will immediately push sprue upwards, while product has not yet started to move, thereby achieving asynchronous ejection of sprue and product, which is convenient for automatic separation.

 

To ensure stability of ejector plate, upper surface of ejector needs to be locked with screws. To prevent ejector from rotating during locking process, ejector head needs to be designed with a positioning structure.