Compression Molding Vs Injection Molding: Which Method is Best for Your Application

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Compression Molding Vs Injection Molding: Which Method is Best for Your Application

Plastic remains one of the most popular materials used in creating a large number of consumer products. The potential uses of this material continue to expand into different industries. Likewise, we can’t ignore the expansion in the number of techniques for this material. Therefore, the need for this compression molding vs injection molding comparison.

Molding is one of the commonest manufacturing processing involving materials like plastic, rubber, and similar polymers. However, it is essential to note that not all molding processes are the same. For instance, injection and compression molding involve contrasting methods. Both of these techniques have their unique features and benefits.

In most cases, the specifications of an application often determine what type of process is best for the product. So, what is the difference between compression molding and injection molding? Let’s dive right into it!

What is Injection Molding?

Injection molding is a process that involves the use of an ‘injection’ technology. The term “injection molding” is due to the procedure which generally involves injecting the raw material into the mold cavity.

the injection molding tool

During the injection molding process, the material is being fed into the hopper by a screw. The heating process follows, and then injection into the mold cavity. The heated material cools and sets in the shape of the mold cavity.

This method offers many benefits in terms of production. It is the best choice for creating complex and intricate parts while also working well with large production runs. If you want consistency, accuracy, and versatility in your work, then injection molding is your best pick.

Advantages of Injection Molding

Some of the advantages of injection molding over compression molding include the following:

  • Efficient and fast production of uniform components
  • Ability to mold in tamper evidence features
  • Enhances versatility and customization
  • Low production costs
  • Solid and durable final products
  • Supports complex mold designs
  • Tolerates a wide range of materials

Disadvantages of Injection Molding

Here are a few cons of injection molding that you need to take note of:

  • High tooling cost
  • Small numbers of productions are usually costly

Tip: We also have an article that introduces injection molding defects and causes, and how to solve them.

Applications of Injection Molding

Injection molding is suitable for a wide range of applications due to its versatility. It helps to create everything ranging from intricate components to appliances. The application of injection molding in automotive parts production is now also widespread.

test tubes made from the injection molding process

Some of its applications include:

  • Medical devices and dental parts
  • Automotive and aerospace components
  • Food and beverage packaging
  • Avionic components
  • Engineering prototypes
  • Cable assemblies
  • Window and door components

What is Compression Molding?

Generally, compression molding is defined by the application of heat and pressure. While this is similar to injection molding, the procedure is quite different.

compression molding process

During compression molding, manufacturers place the raw material in the mold cavity where the heating occurs. After this, the operator inserts the plug onto the top of the cavity to seal it. The plugs also help to apply pressure on the mold cavity further.

The heat and pressure work together to cure the raw material inside the mold cavity, leading to a new component. So, unlike injection molding, compression molding does not fill cavities with melted plastic materials. Instead, it involves placing the material into an already heated cavity.

Advantages of Compression Molding

Some of the advantages of compression molding include the following:

  • Ease of maintaining mold tooling
  • Low initial tooling costs and investment
  • Enables more efficient color changeovers
  • It preserves the mechanical and chemical properties of materials
  • Ensures better visual appearance by avoiding gate vestige

Disadvantages of Compression Molding

It would help if you keep the following downsides of compression molding in mind:

  • It may be slightly less consistent than injection molding
  • Not well suited for complex parts or large production runs
  • Products may show odd parting lines
  • Secondary machining may be required after compression molding
  • Reduced molding depth

Applications of Compression Molding

Compression molding gives strong and durable products. Thus, many industries tend to employ this technique for their applications. Some of the typical applications of compression molding include:

  • Automotive parts
  • Body armor
  • Circuit breakers
  • Plastic dinnerware
  • Electrical and electronic components

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Compression Molding vs Injection Molding: Common Traits and Characteristics

While compression and injection molding are distinct techniques, they come with certain similarities. Both processes involve the molding of plastic materials. Thus, we would expect some common features. Let’s explore these common characteristics

Custom Color

Both injection and molding processes enable the creation of custom colored plastic resins for manufacturing custom parts. Some applications require parts to come in specific colors for aesthetic purposes and to bring the product alive. These processes allow the use of pre-mixed colors for manufacturing purposes.

plastic resins with different colors

They also support masterbatch colors involving mixing with uncolored plastics. In this case, you get up to 2% color by volume. Another popular method involving injection and compression molding is solvent coloring. This process involves mixing pigmented oil with a solvent before spraying over uncolored pellets. Coating here is done prior to injection.

Finally, they also support dry pigment mixing. Here, the operator mixes the plastic resins with dry pigment powder in the hopper. In some cases, there may be a need to dry the pellets first before adding the resin. Hence, both injection and compression molding methods enable you to use your desired color regardless of your application.

Low Labor Costs

Both injection molding and compression molding technologies are very common. Asides from being common, these processes are relatively straightforward. Therefore, operators only require basic technical know-how to complete the processes.

Moreover, both processes support automation. Machines and robotics perform most of the process. This automation ensures a reduction in overall injection molding costs. Since only one operator monitors the operation of the machines, labor costs reduce significantly.

Reduced Part Costs

several parts made from compression and injection molding

Tooling for both processes requires less infrastructure. They usually do not require any additional molding features asides from the cavity features themselves. Molding tools can come from different materials, including aluminum and low-cost steel grades. This generally reduces tooling costs while using high-quality materials.

Furthermore, molds tend to last longer in both processes. Therefore, reuse is possible with longer cycle times and multiple part production in the same cycle. Reduced tooling and labor costs combine to make both injection and compression molding cost-effective. At the end of production, components are usually affordable, depending on their complexities.

Differences Between Compression Molding and Injection Molding

While comparing compression vs injection molding, there are several points to consider. It is essential to understand the most efficient of the two methods. Furthermore, your application will determine the best method to choose. While we checked out their similar features, we should also learn more about the difference between compression molding and injection molding. Read on to find out.

Materials

The first point of action for every manufacturing process is deciding the material to use for production. Likewise, material selection is a vital point of consideration when deciding between compression molding vs injection molding.

While both processes support a wide variety of plastics, they have some peculiarities. The following materials are generally the best choices with compression molding:

  • Diallyl phthalate (DAP)
  • Thermoset polyester
  • Epoxy
  • Sheet molding compound (SMC)
  • Vinyl ester
  • Phenolics
  • Silicone

On the other hand, the material options for injection molding include the following:

  • Polyethylene
  • Polystyrene
  • Nylon
  • Polypropylene
  • Acrylonitrile butadiene styrene (ABS)
  • Polycarbonate

Process

The compression molding process is relatively more straightforward. This simplicity may be due to the lesser number of components involved. Such components include the raw material, heated mold, and the upper plug.

compression molding vs injection molding process

As explained earlier, the process begins with heating and compressing the raw plastic material. The material, at high temperature, is transferred to the tooling die with a specific cross-section. The full shape of the component comes out after pressing the upper plug onto the plastic compound. The plug ensures the even distribution of the compound throughout the mold cavity.

Injection molding, on the other hand, needs feed hoppers, an injection and clamping unit, heaters, hydraulic cylinders, and sometimes, other components. The injection molding process begins by transforming the raw materials into machinable pellets or resin before filling them into the hopper.

Consistent heating of the materials helps to melt them. Then, they are transferred carefully into the mold cavity for proper shaping. The resulting product cools before discharging from the die.

Production Capacity

Injection molding is typically ideal for low-volume productions. It would be best to go for injection molding whenever your applications do not rely on several prototypes of the same kind. For instance, among the advantages of injection molding over compression molding is that it allows you to be practical with your options. It is a low-cost option that helps you to identify alterations needed for products before total production runs efficiently.

Meanwhile, compression molding is best suited for high-volume productions. Suppose you look to meet the deadlines of developing many prototypes at once. In that case, you should choose compression molding. It enables you to conduct required quality assurance checks within a short period.

Precision

Another one of the advantages of injection molding over compression molding is that there is no need for post-processing. This is possible as a result of the precision of dimensions. Manufacturers often use durable steel materials to make dies, conferring high strength to the dies. The implication is that they are less prone to defects that could affect the resulting shape of the mold.

Furthermore, the operator can also easily adjust the heat and pressure levels in injection molding. Thus, it becomes easier to make prototypes with more consistent shapes and requiring lesser fine-tuning.

Complexity of Models

As mentioned earlier, injection molding can produce more complex designs and models than compression molding. Therefore, you can easily experiment with different design ideas with injection molding. Furthermore, you can test out your ideas to know how well they will hold up in real life. Compression molding, on the other hand, is better suited for simple designs and less sophisticated components.

Lead Time Length

Although compression molding is best suited for high-volume productions, the lead time for this process is much longer as opposed to injection molding. The process of injection molding is shorter, making it more reliable to clients requiring faster prototype testing. You won’t have to wait before assessing your product for productivity. The shorter lead time of injection molding vs compression molding helps manufacturers focus on other vital operational aspects.

Shape of Final Product

plastic molded parts with different shapes

Injection-molded products are more complex. These products often have different wall thicknesses. They can also be a combination of various shapes. In contrast, compression molding enables manufacturing simple and blocky products. The raw material is simply cut into shapes to resemble the final product for compression.

Should you Choose Injection Molding or Compression Molding

The long-standing discussions on compression molding vs injection molding continue. This is in a bid to find out the most efficient process. You may already have your answer from our comparison above. However, injection molding has the edge over compression molding.

With injection molding, you can create complex parts and test them out within a short period. The shorter lead time of injection molding is an added advantage for both designers and manufacturers. There is also no need for post-processing with injection molding due to the high precision of dimensions.

Your choice between compression vs injection molding will often depend on your specific applications. Our compression molding vs injection molding comparison will help you make informed decisions.

RapidDirect’s Injection Molding Services

A production process is never efficient if you don’t have the best hands working on them. RapidDirect offers the best technicians and processes to help you get the best final products. We provide top-notch custom injection molding services at competitive prices.

rapiddirect provides prototyping manufacturing services

We are an ISO 9001 certified industry with rich experience in producing high-quality injection molded parts. Our advantages include free automated DfM feedback, full dimensional and inspection reports. Get an instant quote today, and let’s get to work.

FAQs

Is injection molding more expensive than compression molding?

When comparing injection and compression molding, it is crucial to consider the cost. Injection molding tends to be less expensive than compression molding. However, both processes are generally cost-effective.

What are the advantages of injection molding over compression molding?

Injection molding easily creates complex parts compared to compression molding. It also allows you to be practical with your options. Prototype testing is also made easy with injection molding with shorter lead times.

What are the suitable volumes for compression molding?

In most cases, compression molding is suitable for high-volume productions. The molds are usually durable and could go on for a long period. Therefore, if you need to produce a large number of prototypes at once, compression molding will be an excellent choice.

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