What You Should Know About Injection Molding

by Sachin

Injection molding is used in manufacturing parts, typically when they are produced in large quantities. It is mainly used in occasions where small parts are created frequently, such as thousands of times over and over again. Injection molding offers an array of benefits, such as the ability to produce parts in large quantities. Since the parts are produced in large quantities, the prices per unit can be kept low. 

In short, the more parts that are produced, the lower the price will be. There are many other benefits though. The top ones include: 

Repeatable & Produces Low Scraps

When compared to CNC machining, injection molding produces low scraps. CNC machining tends to cut off too much of a plastic block. Besides that, injection molding is typically a better alternative to 3D printing. 

As for the waste produced in injection molding, there are four different areas where it comes from. Those four areas include ejector pins, the sprue, runner system and gate locations. The runner is made up of channels that connect with the sprue, which is what guides the plastic molten from the molding machine’s spout. 

The molten plastic is guided to the injection molding tool’s cavities. There are runners that lead to the cavities of the part. Solid pieces eventually form along the gates, sprue and runners. They form after the injection process. 

Once the first part is created, the next parts are created. All of the parts after the original part are almost identical to size, shape and everything else. This is important because many companies want to have consistency with their brand, as well as a large amount of parts. This is why injection molding is favored among many companies and brands.

The Downside To Injection Molding 

One of the major downsides is the upfront cost associated with the process. Generally speaking, this upfront price is often very high. This is because of tooling requirements, testing requirements and design requirements. Some brands might find that these costs are way too much, but the benefits tend to outweigh the cons. 

Let’s not forget to mention that all of the other parts have to look similar to the original part. You’ll have to make sure that the first part comes out exactly how you want it to look and function. If the first part is not what you wanted, then hundreds or thousands of parts will not come properly. In order for that first part to come out right, you’ll want to do the following: 

  • Decide what specifications you need. A 3-D printer is what the prototype is typically designed on. However, different materials are used. This may include ABs plastic. 
  • Next, you have to design an injection unit tool. This is for the initial part of the production. If you plan on generating 300-1000 prototypes, then this is required. 
  • The surface finished needs to be refined. This is a must and it needs to be done before mass production occurs. 

With injection molding, wall thickness needs to be uniformed. For example, you would notice that the thickness of the wall is about 0.11 inches, if you were going to cut a cross-section. This prevents part shapes from deforming and it prevents uneven cooling. However, injection molding does have a few negative aspects, such as: 

High Costs And Lead Times 

Tooling is a major process alone. It’s only a small part of the molding process. There is a lot of time required and a lot of costs are involved with tooling. This is in part due to needing to produce the first initial part, and then you can produce the molded part. 

Once the prototype is created and it’s done the right way, you’ll need a molding tool. This is what will produce large quantities of the prototype, all without making any errors. This is why there is a lot of money and time involved with injection molding. 

Hard To Make Changes

You can’t really make changes to these tools, at least not easily. You can create larger cavities if you need to, but you’ll have to either cut through the aluminum or steel. If you need plastic removed, then you’ll have to add metal, as this will reduce the size of the mold cavity. It’s a tremendously difficult task to do. 

Materials That Are Suitable For Injection Molding

The type of material used during injection molding is important. The types of material you use will affect the performance and the overall molding process. In order to choose the material to use in the process, you have to consider both the environment and its function. Other factors include the strength of the material, durability, flexibility and color, as well as cost. 

There are many materials you can use. Some are more common than others. That being said, here are a few of the most commonly used materials: 


Nylon is tough material and it has a high melting temperature. This material is typically used to produce bearings, gears and other similar products. Nylon has a strong resistance to various chemicals, it’s cost effective and it’s not easily subjected to wear and tear. 


Lighting equipment, walls, and window panes are produced with various materials, with one of them like acrylic. It has a good amount of strength, which is why it’s usually a good alternative to glass. Besides that it’s scratch resistance, which is why the material is used to make containers for food. When used to produce food containers, the containers don’t have an odor, which us why acrylic is used to make containers. 


Parts that are made of metal typically incorporates Polyoxymethylene in the manufacturing process. It’s usually used when hardened plastic parts are being created. Chemical compounds that make up the material has made the material extremely rigid, strong and tough. This is another reason why it’s used to make ball bearings, knife handles and gears. 


The above are only a few considerations you’ll want to think about during the injection molding process. Now you know more about the process and what you should consider in regards to what materials you’ll want to use. Good luck on deciding what materials you’ll use for the process.


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