Using differential ejection to cut off condensate in side gate pouring system means staggering ejection time of product and ejection time of gate runner condensate. When mold is opened and ejected, product is ejected first, and gate runner condensate remains in moving mold. After product is separated from gate runner condensate under action of ejector, runner ejector ejects runner again, that is, gate runner condensate is ejected.
Following is an example of a three-way pipe plastic part. As shown in Figure 1, three-way pipe plastic part is made of POM. Round tube shape cannot be used for latent gates; POM material is not suitable for point gate pouring systems; from a cost perspective, it is not suitable for hot runners and three-plate molds. After comprehensive consideration, product should adopt side gate feeding method. Layout of product in mold and opening of pouring system are shown in Figure 2.

 

Structure of three-way pipe injection mold using differential ejection is shown in Figure 3. As can be seen from Figure 3 (a), there is a pin 5 under cup head of runner ejector 4, which is fixed on movable mold base plate 8. When mold is closed, ejector panel 6 and pin 5 fix position of runner ejector 4. A travel expansion hole for ejector cup head is opened on ejector support plate 7 directly below runner ejector 4 to delay ejection. Function of positive conical runner undercut at A is to pull runner and separate runner and product when product ejector ejects product and runner ejector is delayed. Figure 3 (b) is the first ejection. Product is first ejected and separated from runner. Runner does not move due to undercut and expansion position until ejector plate completes expansion stroke of runner ejector, realizing separation of casting system condensate from product. When expansion stroke is completed, second ejection begins, as shown in Figure 3 (c). Runner ejector starts to work and ejects runner condensate, and ejection ends.
Differential ejection method is currently the simplest side gate automatic cutting method, but due to uneven cross-section of product gate, gate residues are often left on product, affecting product appearance. Therefore, this solution is only used for products with low appearance requirements.

During injection to pressure holding process, ejector rod of ejector shaft can realize function of moving forward and backward. When any time has passed since injection molding machine started to shoot, pre-ejection rod can move forward to gate and cut it off. Gate shearing needle in mold will compress (cut off) gate part of molded product, thereby separating molded product and runner. Forrward time of gate shearing needle is freely adjusted by time controller. Figure 4 shows parameter setting of injection molding machine control panel with pre-ejection gate cutting function.
How to set pre-ejection on injection molding machine:
(1) Set pre-ejection mode ON/OFF to ON.
(2) Set pre-delay time (try to use 0.01 seconds as unit).
Pre-delay time is start time of pre-action, which is set from start of injection to start time of each action. General setting is: injection time + about half of holding time. If pre-ejection action is performed during injection process, gate is in a closed state, which may cause damage to mold; if cooling time is too long, plastic solidifies, gate is blocked, gate shear pin is overloaded and may break.

 

(3) Setting of pre-advance position, speed, and advance stop time
For setting of "pre-advance position", it is necessary to have a good understanding of mold structure, gradually increase it from about half of expected ejection stroke, and finally confirm molded product in units of 0.01mm.
For setting of "pre-ejection advance speed", first set speed to a slower 5mm/s, then gradually increase it according to molding conditions.
For setting of "stop time", stop time is the time when gate cut-off pin just cuts off gate. It is generally effective when gate is cut off in a relatively soft state.
(4) Pre-retract position setting
Set return position after gate cutting is completed. Generally, it is set to same position as start of pre-ejection. Retract speed is generally slower than forward movement.
Set parameters are shown in Figure 5.

 

In-mold gate shearing process is shown in Figure 6. As can be seen from figure, in order to realize pre-ejection function, in addition to having a pre-ejection function on injection molding machine, it is also necessary to pay attention to design of mold structure. On mold, bottom of all other ejector pins except runner shear pin must be enlarged to ensure that ejector pin has a certain stroke. Enlarged hole distance is pre-ejection distance of runner shear pin.

 

Not all injection molding machine controllers have a pre-ejection function. If pre-ejection function needs to be added, controller software needs to be upgraded, injection molding machine must have a CNC control device and an AC servo motor. At the same time, ejection structure of traditional mold needs to be modified. Ejection structure of mold before and after modification is shown in Figure 7.

 

Characteristic of cylinder slider cutting method is that two movable inserts are made on movable and fixed mold plates at gate. Mold is opened twice, and fixed mold is opened only once. Fixed mold plate and fixed mold base plate are separated. Gate insert in fixed mold plate is fixed on fixed mold plate. When mold is opened for the first time, it does not move with fixed mold plate. Fixed mold plate retreats with movable mold to make room for cutting gate runner. After the first mold opening is completed, injection molding machine temporarily stops opening mold. Cylinder drives slider to push gate runner condensate away from product, then continues second mold opening and finally ejects it. Figure 8 is a schematic diagram of layout and feeding method of a certain product and mold structure.

 

Mold action sequence is shown in Figure 9 (a) and (b).
(1) When fixed mold side is opened for the first time, fixed mold gate runner insert is fixed on fixed mold plate, and fixed mold plate retreats a distance. Fixed mold gate runner insert is separated from runner cold material to make room.
(2) After the first mold opening action is completed, cylinder pushes forward to push movable mold runner insert to cut off gate.
(3) After cylinder slider cuts off gate, injection molding machine continues to complete mold opening action and then ejects product.
Characteristic of this solution is that gate cut surface is flat, and it is generally used for products with higher requirements. The only disadvantage is that cost is high and processing is difficult.

 

In summary, methods of automatic cutting of side gate pouring system have their own characteristics. Differential ejection method is currently the simplest automatic cutting method for side gate, but product appearance quality is poor; pre-ejection method requires injection molding machine to have a pre-ejection function, and in mold structure, bottom of all other ejector pins except runner shear pin must be expanded to ensure that runner shear pin can have a certain pre-ejection distance; gate cut surface of cylinder slider cutting method is flat, and product appearance quality is high, but disadvantage is that cost is high and processing is difficult. Therefore, when designing mold, we should consider various factors comprehensively according to characteristics of product and requirements of customer, and choose a more appropriate solution for automatic cutting off of condensate in side gate pouring system.