Injection molding engineered mold made of several key components, each of which plays a vital role in shaping, cooling, and releasing the final part.
Understanding the basic parts of an injection mold can help you design better products, perform troubleshooting, and improve product quality.
In this guide, we’ll break down the main parts of an injection mold, how they work, and why each one matters in the process.
Introduction to Injection Molding
Injection molding is a manufacturing process used to produce large quantities of plastic parts. It works by melting plastic pellets, injecting the liquid plastic into a mold, and cooling it to form a solid shape.
This method is fast, efficient, and great for making strong, lightweight, and detailed parts. It’s commonly used to produce everyday items like bottle caps, phone cases, car parts, toys, and medical devices.
Because the mold can be used repeatedly, injection molding is ideal for high-volume production where consistency and quality are important.
Key Parts of an Injection Mold
Injection molds comprise several key components that work together to shape, cool, and eject plastic parts. Let’s look at the most important injection mold components:
1. Clamping Plate / Mold Base
The clamping plate, often part of the mold base, is the foundation of the injection mold. It holds the mold securely in the injection molding machine and provides structural support during operation.
It has two sides: the stationary plate (attached to the machine) and the moving plate, which opens and closes. These sides ensure the mold aligns properly and withstands the high pressure during injection.
If the mold base isn’t strong enough, the mold could shift or break during production.
2. Cavity and Core
The cavity and core are the heart of the mold as they form the actual shape of the plastic part. Together, they define the part’s size, design, and surface finish.
- A cavity is the hollow part where plastic is injected, forming the outer shape of the product.
- The core is the raised section that fits inside the cavity to create the inner surfaces.
Example: In a plastic cup mold, the cavity shapes the outer walls, while the core creates the hollow inside.
3. Runner System
The runner system is a set of channels that guides the molten plastic from the injection nozzle into the mold cavity. This system includes three components:
- Sprue: Main vertical passage from the nozzle.
- Runners: Horizontal channels that distribute plastic to each cavity.
- Gates: Small openings that control the flow into the cavity.
The runner system is important because it reduces waste, ensures an even flow, and improves part quality.
4. Cooling System
The cooling system helps solidify the molten plastic after it enters the mold. It uses channels inside the mold that circulate water or oil to absorb heat. Proper cooling is crucial to avoid warping, sink marks, or long cycle times.
Moreover, it directly affects the speed and consistency of the product. With efficient cooling, your parts will be of better quality, and the production time will be greatly reduced.
5. Ejection System
Once the plastic part has cooled and solidified, the ejection system separates it from the mold quickly and cleanly without damaging the product. Key components of this part include:
- Ejector pins: Push the part out of the core.
- Ejector plate: Moves all ejector pins at once.
- Return pins/springs: Reset the system for the next cycle.
6. Venting System
The venting system allows trapped air and gases to escape from the mold during the injection procedure. It has tiny gaps or grooves near the cavity edges to allow air to escape without letting plastic leak out.
Without proper venting, air pockets or burn marks can appear on the final part. This also ensures smooth surfaces for the plastic parts and prevents any defects.
Optional or Advanced Parts of an Injection Mold
While basic injection molds work well for simple parts, complex designs often require extra components. Some of these injection mold parts include:
1. Slides Cores / Side Actions
Slide cores or side actions are moving injection mold parts that are used to create features like holes, undercuts, or side slots—things that can’t be manufactured with just the cavity and core moving up and down.
They slide in from the side when the mold closes and move out when it opens. This part is used for molded-in hooks, holes through the side of a part, or snap-fits.
2. Lifters
Lifters are injection mold components that move at an angle when the mold opens to release parts with angled or curved undercuts. They rise and pull away from the part before ejection.
This part is used when features are not reachable by a slide or would complicate the mold design. It’s commonly applied to angled locks, tabs, or clips on a product’s interior.
3. Hot Runner System
A hot runner system keeps the plastic inside the runner channel hot and molten throughout molding. Unlike a cold runner, it reduces material waste because there are no leftover runners after each cycle.
It includes heated nozzles and manifolds to keep plastic flowing until it reaches the gate. Additionally, the benefit of using this part includes faster cycle times, better temperature control, and higher part quality.
4. Insulator Plates
Insulator plates are placed between the mold and the injection molding machine’s platens. They help reduce heat transfer from the mold to the machine. This helps maintain stable mold temperature, especially during long production runs.
This part matters because it improves energy efficiency and reduces wear on machine components.
Need Precision in Injection Mold Design?
Understanding the parts of an injection mold is important for improving product quality, efficiency, and cost-effectiveness in manufacturing. From basic parts like the cavity and runner system to advanced features like the lifter and hot runners, each component plays a role in shaping the final product.
If you want to optimize your mold design or start a new project, we’re here to help. At Fecision, we specialize in designing and manufacturing high-performance injection molds exactly as you want them.
Get in touch with Fecision today, and let us help bring your plastic parts to life!
