The injection molding process is very popular due to its cost-effectiveness and repeatability. Right? However, how good a product this process offers depends on the mold it uses. A mold with the wrong dimensions results in poor-quality products. But there is a question: how to make an injection mold perfect in its dimension?
Manufacturing mold seems like an easy task. However, it is one of the most challenging processes, and small mistakes can ruin the mold’s quality. If the mold is incorrect, it is useless and discarded, costing manufacturers extra money. I will explain how a good-quality mold can be made in this article. So, let’s get started!
Basics of Injection Mold & its Importance
Before discussing the manufacturing process, let’s first know what mold is!
An injection mold is a hollow structure with two halves. Inside the hollow box are cavities and channels. The molten material is filled inside those cavities. The channels inside the mold regulate the pressure and temperature. Once the molten material dries, it adopts the shape of the mold, creating the desired product.
This way, the manufacturer gets a product similar to the mold’s shape. Simply put, an injection mold is a tool for making multiple products of identical shapes. For example, you need a mobile cover. In that case, you will have to create a mold similar to your desired shape. Once the mold is ready, you’ll have to fill it with molten plastic.
Once the plastic dries, it adopts the shape of a mold, similar to a phone cover. You can use this single mold to create hundreds and millions of mobile phone covers. These molds are very durable and resistant to extreme temperatures and pressure. So they can remain in good shape and be repeatedly used for years.
So, manufacturers keep using the mold and create identical products in bulk. This not only offers similar products, but those products are also low-cost. The reason is that molds are made only once and can be reused repeatedly. There won’t be any additional cost of mold creation when making bulk products.
Mold is not a machine but plays a role in the manufacturing process. Molds don’t work independently and are only used to fill molten materials. Temperature, pressure, and other parameters ensure the proper working of the mold. The prominent advantage of these tools is that they help create bulk products of identical shapes at low prices.
How Injection Molds Are Made? Step by Step
Have you a basic understanding of mold? I will explain the basics for those new to the molding process. Let’s proceed to our main topic: how a mold is made. In the section below, I will explain mold creation in easy steps. Let’s have a start!
1- Materials Selection
The first step in mold manufacturing is choosing the right materials. Different types of materials are available to help make molds. Molds undergo different pressures and temperatures, so the chosen materials must be durable and robust. Generally, aluminum and steel are popular options for manufacturing an injection mold.
Steel is premium and offers exceptional longevity when used in molds. However, this material is expensive, which is a drawback. Many people consider the higher prices of steel “worth it.” On the flip side, aluminum is an affordable alternative to steel but has some limitations. It is less durable than steel and can wear quickly.
Quick Highlight: The materials selection depends on the manufacturer’s needs and requirements. I recommend choosing steel if you want a mold to make thousands of products. Conversely, an aluminum mold is suitable as a short-term solution. Remember, Using any of these materials will not affect product quality.
2- Mold Designing
Designing the mold is one of the most crucial steps. A slight mistake in this stage will result in the wrong dimension mold. Generally, companies have dedicated designers who take care of mold design. The reason is that laypeople can make mistakes while designing.
The designers generally used CAM and CAD software to create the 3D model. First, the CAM software helps make a mold. This model is similar to the desired shape. For example, if you need a mobile phone cover, the CAM-made model will be identical to the desired shape of the mobile cover.
Once the model is made, it then undergoes the CAD software. This software creates computerized instructions that produce the same shape. These instructions are fed to the computer to get the final product. Remember, mold design should be carefully selected. Your final product will be similar to this mold design.
3- Mold Machining
Once the design is ready, the next step is machining to create the mold. In this step, your chosen material is processed through dedicated machining techniques. Two types of machining are popular when it comes to creating the mold, which is as follows:
- CNC machining
- EDM (Electrical Discharge Machining)
Both of these techniques use computerized systems for excellent precision. In CNC machines, the CAD (Instructions) design is fed to the computer. The machine is then switched on. The computer processes the given coded instructions. As a result, it commands the cutting tools to move so that the desired shape mold is made.
Remember, the movement of the cutting tools is very controlled and automated, so the chances of error are negligible. The cutting tools keep moving, cutting, and shaping the workpiece (material). This way, you get the desired shape mold (similar to the design fed to a computer). The workings of EDM are different as it doesn’t use cutting tools.
Instead, it uses sparks and burns the materials as per computerized instructions. This way, materials cutting and shaping happen without cutting tools touching the workpiece. These machining techniques create the mold of the desired shape. You can use any of these two methods for machining. Both are excellent when it comes to mold precision.
4- Creation of Cavities & Channels (Sprue, Runners, and Gates)
Mold machining involves creating mold cavities and channels. I’d explain the creation of these channels separately for better understanding. Cavities in the mold are hollow structures filled with molten material during product creation. Channels are pathways where fluids flow to enter the cavities.
Channels have different parts, which are as follows:
- Sprue: It is the starting point of channels and can be referred to as an entry for molten materials.
- Runners: These are channels or small tubes inside the mold. The molten materials follow these runners to reach one point to another. For example, molten material uses runners to get the cavities of the mold.
- Gates: Gates are the points where the fluid leaves the channel and enters the cavities. The fluid enters the cavity through gates and fills it.
The design of the mold contains these channels and cavities. So, during the machining, the CNC machine carves out and removes the material to create cavities and channels. The size and diameter of channels require attention. Small mistakes in channel size can result in air bubbles and other defects.
5- Insertion of Ejector Pin
The creation of cavities and channels in the mold is followed by the insertion of an ejector pin. This pin helps eject the plastics that dry inside the mold. Without this ejector, taking the product out of the mold would be impossible. The manufacturer drills a small hole in the mold.
An ejector pin is installed on the hole. The ejection plate is connected to this ejector pin.
Remember, the ejection plate remains at the bottom of the mold. The pin has a spring that allows it to move. As a result, the ejection plate moves due to the act of spring. It results in the ejection of the product (filled inside the mold). Remember, some manufacturers use hydraulic systems to insert ejector pins.
6- Polishing and Finishing
Inserting the eject pin is the final step in creating an injection mold. However, this mold will have a rough surface and uneven edges, which affect its appearance and texture. Different machines are available to smooth and even the surface. Established manufacturers generally use CNC-based grinding machines.
These machines remove uneven surfaces and smooth the edges. Polishing is optional and can improve the aesthetics of mold. Once surface polishing is done, the mold goes for final testing. The companies have a quality assurance team that checks the molds for various parameters. Mold that fulfills the criteria of quality assurance team approval and vice versa.
Conclusion
Molds are essential tools, especially for the injection molding process. They help create products quickly and with exceptional precision. No other method can create identical products with such speed. However, when it comes to mold creation, many have no clue.
Mold creation is a bit technical and requires an understanding of specific machines. In this article, I discussed the easy-to-follow manufacturing of injection molds. Remember, mold quality depends on the mold design. Once the design is ready, CNC-based machines will create the final product precisely.