Plastic injection molding is a common way to make plastic parts. It uses molds to shape melted plastic into products. There are different types of molds, each with its own features and uses. This article will explain the main types in detail. If you need more help with molds, check out https://moldpartner.com/. We will cover the basics and then look at each type step by step.
First, let’s talk about what a plastic injection mold is. It is a tool made from metal that holds the shape for the plastic part. Hot plastic gets injected into the mold, cools down, and then the part comes out. The type of mold affects cost, speed, and quality. Choosing the right one depends on what you are making, how many parts you need, and your budget.
Two-Plate Mold
The two-plate mold is the simplest type. It has two main parts: the core and the cavity. These two plates come together to form the shape of the product. When the mold opens, the part stays on one side and gets pushed out.
This mold is easy to use and costs less to make. It works well for simple parts without complex shapes. For example, it is good for making caps or basic containers. The runner system, which carries the plastic to the cavity, is part of the mold. After the part cools, you remove the runner by hand or machine.
One key point is that it has one parting line where the plates meet. This makes it straightforward to design. However, if your part needs holes or undercuts, you might need extra slides or cores. These add to the cost but make the mold more flexible.
In terms of cycle time, two-plate molds are fast because they are simple. They suit small to medium production runs. If you make thousands of parts, this mold keeps things efficient without high upkeep.
Three-Plate Mold
The three-plate mold adds an extra plate to the design. It has a core plate, a cavity plate, and a stripper plate in between. This setup helps separate the runner from the part automatically when the mold opens.
Why use this? It saves time because you do not need to cut off the runner by hand. The stripper plate pushes the runner out separately. This is great for high-volume production where speed matters.
The mold opens in two stages. First, it separates the runner, then the part. This reduces waste and makes the process cleaner. It works well for parts with multiple cavities, meaning you can make several parts at once.
However, it costs more to build than a two-plate mold. The extra plate adds complexity. You also need a machine that can handle the two-stage opening. Despite the higher cost, it pays off for large runs because it speeds up production.
For maintenance, check the plates often to ensure they align well. Misalignment can cause defects in parts.
Cold Runner Mold
Cold runner molds are the opposite of hot runners. The runner cools with the part and gets ejected as waste. This is common in two-plate and three-plate designs.
They are cheaper to make and maintain. No need for heating elements, so the setup is simple. They work for a wide range of plastics, including those that are heat-sensitive.
The drawback is material waste from the runners. You have to recycle or throw away the solidified runners. This adds to costs over time, especially for big production.
Cycle times might be longer because the runner needs to cool fully. But for low-volume runs or prototypes, this is not a big issue.
In practice, cold runners allow easy color changes. You just flush out the old material. They are reliable and less prone to breakdowns.
Family Mold
A family mold makes different parts in one cycle. It has multiple cavities for various shapes. All parts come out together when the mold opens.
This is useful for sets of products, like a toy with several pieces. It saves time and money by producing everything at once.
The key is balancing the cavities so each fills evenly. If one part is bigger, it might need more plastic, which can cause issues.
Family molds reduce the number of machines needed. Instead of separate molds, one does the job. This is great for small businesses or custom orders.
However, if one cavity breaks, the whole mold stops working until fixed. Also, all parts must use the same material and color.
For design, plan the layout carefully. Place cavities to minimize runner length and ensure even cooling.
Stack Mold
Stack molds have multiple levels or stacks of cavities. They are like having two or more molds in one, increasing output without a bigger machine.
Each stack opens and closes together, doubling or tripling production. This is perfect for high-volume items like packaging or medical supplies.
The benefit is higher efficiency. You get more parts per cycle with the same press size. This lowers cost per part.
But stack molds are complex and expensive. They need precise alignment between stacks. Maintenance is key to avoid downtime.
In operation, cooling systems must work well across all levels. Uneven cooling can lead to warped parts.
Unscrewing Mold
Unscrewing molds handle parts with threads, like bottle caps. They have mechanisms to unscrew the part from the core.
This avoids damage to threads during ejection. Motors or hydraulics turn the core to release the part.
They are essential for threaded products. Without this, threads might strip or deform.
Costs are higher due to the moving parts. But for items like fasteners or closures, it is necessary.
Setup requires checking the unscrewing speed to match the cycle.
Insert Mold
Insert molds place metal or other inserts into the plastic part. The mold holds the insert, then injects plastic around it.
This creates strong bonds, like in tools with metal blades in plastic handles.
It saves assembly time by combining steps. Parts come out ready to use.
Challenges include positioning the insert correctly. If it shifts, the part fails.
For materials, ensure plastic bonds well to the insert.
Overmold
Overmolding adds a second material over the first. It is like insert molding but with another plastic.
Common for grips on tools, providing soft touch over hard base.
It improves comfort and function. Layers can have different colors or properties.
The mold has two stages: first shot for base, second for overmold.
Compatibility between materials is crucial to avoid separation.
Conclusion
There are many types of plastic injection molds, each suited to different needs. From simple two-plate to advanced stack molds, the choice depends on your project. For services like injection moulding tooling services, explore options that fit your requirements. Understanding these types helps you pick the best one for quality and cost. Always consider production volume, part complexity, and budget when deciding. With the right mold, you can make reliable plastic parts efficiently.
