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The selection of the injection mold gate design depends on a number of factors, such as the volume of production, budget, time restraints etc. Mold plates are used to support molds and tools. They are made of metals such as aluminium and steel. The mold types can be classified into two-plate mold and three plate mold. Let us know more about both of them.
What is a Two Plate Mold?
Two plate mold is one of the most reliable and simplest mold designs. It has very few moving parts making it more straightforward to run in the production of injection mold slide design. Owing to its simple and straightforward design, it is cheaper than its counterparts.
Two plate molds consist of a single parting plane from where the mold splits. In the case of a multi-cavity two-plate mold, the gate and runner is present in the parting plane. They make sure that the gate and the runner eject while the mold splits.
Here are some of the advantages as well as disadvantages of two plate mold:
Advantages Of Two Plate Mold
- The design is simple and cost-efficient
- It has a lower time cycle when compared to the three plate mold
- Reduced lead time
Disadvantages Of Two Plate Mold
- In the case of multi-cavity injection mold gate design, balancing the molten plastic flow is a very challenging task.
- In a multi-cavity two plate injection mold, the parting line needs to be aligned with the gate.
Two Plate Mold Design
Two plate mold design is one of the simplest injection mold structures that has several advantages. Two plate molds consist of two main parts – side A and side B. When there is a load on the injection machine for injection molding products, side A is held still and fixed while side B remains movable. Here are some of the parts in the two plate mold design:
- Return Pin: it makes sure that the ejector pin is pulled back before the mold is closed. It also protects the products made by injection molding from getting damaged.
- Spurs: it allows the melted material to flow into the cavity.
- Ejector guide pin: The ejector Guide Pin acts as a guide to make sure that the ejection process is accurate.
- Guide bushing / Guide Pin: Guide Pin and Guide Bushing are made for precision guiding.
- Location of the ring: It locates the hole between the spur and injection nozzle. It is generally made from S55C.
Two Plate Mold Diagram
The structure of the two plate mold is divided into two parts. As discussed above, one part is fixed, whereas the other is moving. The cavity side of the mold design remains fixed, and the core side moves.
In the fixed mold, there is a runner, which is placed on the parting surface. Once the molding process is completed, the runner and the injection-molded product stay in the moving part of the mold. The runner and the injection part are later removed from the parting surface.
What is a Three Plate Mold?
A three-plate mold consists of two parting planes and its mold splits into three sections. For a three-plate plastic molding design, the runner is present on the second parting plane that runs parallel to the main parting plane. The second parting plane allows the sprue and runners to get expelled when the mold is open.
This type of plate has three main plates or parts that are separated from each other at the opening. Pin-point gate is one of the significant advantages of this type of mold and it can be used for making multi-impression molds.
Advantages Of Three Plate Mold:
- Is flexible in gating location
- It is an alternative to the hot runner mold.
- Eliminate gate removal operation.
Disadvantages Of Three Plate Mold:
- Higher ejection time because of the ejection of the runner system.
- Consists of a more complex design.
- Requires high ejection pressure.
- High material wastage.
Three Plate Mold Design
The three plate mold can serve as a go-to option and help you save costs.
When using three-plate advanced prototype molding for round parts, you need to ensure that the part is evenly filled. It is critical to make sure that the spaced gates are placed evenly around that particular part and have been evenly filled all around.
As the mold of the three plates opens up, the A and B halves are held together with releasable plate locks. The sprue is then released, and then the gate breaks away from that part. Under-cut pins hold the sprue back in another floating plate. When the tooling of the A-side is hit, a set of stop bolts. These two events occur successively.
Then the A and B halves of the part get separated, and the pins get pulled from the Sprue, enabling it to drop from the mold. The part can get ejected off after the mold gets completely opened, just like normal two-plate plastic injection products.
Three Plate Mold Diagram
The three plate mold has three cavities that are filled through a centrally located pinpoint gate. The mold is typically divided into three sections:
- The first part is the feed plate assembly.
- The second part is the intermediate or cavity plate, and;
- The third part is the core plate assembly.
The general construction of the three plate mold is built about the opening sequence of the molding product. Understanding the complete design of the mold is required to know how the mold functions. The mold opens in three different stages.
- Stage 1: As the plates of the machine opens, the intermediate plate gets pulled away from the first plate or the feed plate assembly. The runner system gets retained in the feed plate assembly by sucker pins or runner puller. This process of retaining the runner helps to break the gate while being fully supported by the other components. This stage is hence known as the breaking first stage.
- Stage 2: The gates get parted from the mold, and the runner clearance daylight completely extends. The molding product is then ready for the second stage, which is the runner stripping and ejection. The daylight is extended completely on the runner, and then the runner stripper plate is pulled forward with the engagement of the second plate’s intermediate shoulder bolts. The length of the stroke by stripping the runner is determined by the height of the engagement of the runner plate.
- Stage 3: The ejection of the molding takes place upon opening the core. It takes place once the movement of the intermediate and the feed plate assemblies get arrested. When the molding has sufficient daylight, the molding, either gets ejected traditionally or is stripped off the core. The explanation of opening the three plate mold highlights one of the drawbacks of the design of the three plate mold. It is wise to calculate the required daylight before getting started with the selected course of action.
To gain more control on the desired mold opening sequence, it is also required to set the movement accurately. The closing of the mold is obtained by the closing action of the molding machine.
Compared to the two plate mold, the three plate mold has an additional plate that is found floating on the moving and fixed plates. The fixed plate and the center plate have a feed system in between to form injection molding products. The closing of the molding machine is usually achieved by the closing action that picks up progressively and closes the sections as they move forward.
What are the Differences Between Two Plate And Three Plate Mold
The selection of the molding product type depends on several factors like components design, budget, and production volume. One of the significant questions that remain in the manufacturer’s mind during new product development is what type of mold is required?
Two Plate Mold | Three Plate Mold |
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The application of three plate mold requires the runner system to be positioned among different planes to automatic degating and injection location. The stripper plate is one of the significant differences between the two plate mold and the three plate mold used for plastic molding products. The significant difference also lies in the structure, orientation, and guide pin location. The three plate mold exists mainly to respond to the appearance and the production requirements. The injection pressure on the three-plate mold is not higher than the two-plate mold when a complete filling situation is concerned.
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Final Word
Two plate molds are the most frequently used in plastic injection molding service. They include a parting plane where the mold divides into two halves. In a mold that has multiple cavities, the gate and the runner must be located in the parting planes to ensure that ejection takes place when the mold divides into two.
Three plate injection mold design engineering consists of two parting planes, and the mold divides into three parts. Thus, runners and components can be located on different parting planes. In three plate injection mold, the runners are generally ejected separately to the molded part. Therefore there is a probability of automatic degating. We hope that by now you are aware of the key differences in between the two types of mold. Hence, choose one that is best suited to your project requirements.
