Injection Molding vs Compression Molding

You have many options for producing parts, but which manufacturing method is best for you?

Two popular methods that offer unique advantages are injection molding and the compression molding process. While these technologies have similarities, understanding their differences is crucial for making informed decisions. See which one is right for you.

How Injection Molding and Compression Molding Work

Injection Molding

Injection molding is a mass-production process that creates large quantities of identical parts.

It involves designing and building a mold, preparing the material, injecting the molten material under high pressure, cooling and solidifying the part within the mold, and ejecting the finished part.

Compression Molding

Compression molding involves placing a pre-measured material into a heated mold cavity.

The mold is then closed, and pressure is applied to shape the material into the desired form. Compression molds are essential in this process as they shape materials using compressive force. After curing, the mold is opened, and the part is ejected. This process is particularly suited for producing large, durable parts with intricate details.

Design Freedom

Injection molding requires the creation of molds, which restricts design modifications once the mold is produced. This limitation is particularly relevant for complex geometries, undercuts, or frequent design changes. Any design changes may require additional tooling or mold modifications, leading to increased costs and delays.

Compression molding offers greater flexibility in terms of design modifications. Adjustments can be made more quickly than injection molding, allowing for the production of complex and large parts without significant additional costs. Compression molded products are widely used in various industries, including medical and automotive, due to their effectiveness in manufacturing.

Parts made with compression molding. 

Initial Lead Times

Injection Molding: Mold production for injection molding can be expensive and time-consuming, impacting project timelines for initial production. However, this technology can be faster when dealing with large-scale production.

Compression molding typically has shorter lead times compared to injection molding. The molds are simpler and quicker to produce, accelerating the initial setup and production process.

Cost Comparison

Injection Molding: The cost of creating molds for injection molding can be high, especially for intricate designs or multiple cavities. This cost includes mold design, engineering, and precision machining. However, once the mold is created, it can be used for high-volume production, reducing the cost per part due to economies of scale.

Compression molding generally has lower initial tooling costs compared to injection molding. The simpler mold design reduces upfront expenses, making it a cost-effective option for smaller production runs or larger parts.

Strength

Injection molded parts benefit from higher material density and uniformity, resulting in superior strength and structural integrity. The high pressure and temperature in injection molding ensure consistent material distribution, eliminating weak points or variations.

Compression moulding also produces parts with high strength and durability. The process allows for the use of high-strength materials and produces parts with excellent mechanical properties suitable for demanding applications.

Materials

Injection Molding provides access to various materials, including engineering-grade plastics. These materials offer specific properties such as high strength, heat resistance, chemical inertness, or electrical conductivity. Additionally, specialized materials like elastomers and thermosetting plastics are readily available for specific applications.

Compression molding is ideal for high-strength materials, including thermosetting plastics, composites, and rubber. These materials provide excellent heat resistance, chemical stability, and mechanical strength.

Tolerances

Injection molding is known for producing parts with tight tolerances and consistent dimensions. This precision is due to the high pressure used to inject the material into the mold, ensuring that every detail of the mold cavity is filled. At MakerVerse, the tolerance range is as low as ±0.1%.

Compression molding can also achieve good tolerances, but they are generally not as tight as those possible with injection molding. The tolerances for compression molded parts typically range from ±0.25% to ±1%, depending on the material and part design.

Part Sizes

Injection molding is suitable for producing small to medium-sized parts with complex geometries and intricate details. The process can efficiently produce large quantities of these parts, making it ideal for high-volume production runs.

Compression molding excels in producing more significant parts, especially those with thick cross-sections. The process is well-suited for parts that require uniform pressure and material distribution.

Finishing

Injection molded parts. 

Injection Molding: Depending on the part’s requirements, additional finishing operations like trimming, painting, or assembly may contribute to the overall cost. However, injection molded parts often require minimal post-processing compared to other methods, thanks to the smooth surface finish achieved during molding.

Compression molded parts may require more post-processing, such as trimming flash and finishing surfaces. However, the ability to produce large, intricate parts with high detail often justifies the additional finishing steps.

Injection Molding: Depending on the part’s requirements, additional finishing operations like trimming, painting, or assembly may contribute to the overall cost. However, injection molded parts often require minimal post-processing compared to other methods, thanks to the smooth surface finish achieved during molding.

Compression molded parts may require more post-processing, such as trimming flash and finishing surfaces. During the compression molding process, excess material is intentionally used to ensure complete filling of the mold, which results in flash that needs to be trimmed. However, the ability to produce large, intricate parts with high detail often justifies the additional finishing steps.

Advantages of Compression Molding

Compression molding offers several advantages over other molding processes, including:

High strength and durability: Compression molded products are known for their high strength and durability, making them suitable for various applications.

Low weight: These products are often lighter than those produced using other molding processes, making them ideal for applications where weight is critical.

High corrosion resistance: Compression molded products are resistant to corrosion, making them suitable for applications where exposure to harsh environments is a concern.

Cost-effective: Compression molding is cost-effective, particularly for small to medium-sized production runs.

Easy to produce complex shapes: This process is well-suited for producing complex shapes and parts with high precision.

Limitations of Compression Molding

While compression molding offers several advantages, it also has some limitations, including:

Limited flexibility: Compression molding is not suitable for producing parts with complex geometries or intricate details.

High tooling costs: The process requires specialized tooling, which can be expensive.

Limited material options: Compression molding is limited to specific materials, including thermosetting plastics and thermoplastics.

Greater waste: This process can result in greater waste than other molding processes, particularly if the mold cavity needs to be properly designed.

Slower process times: Compression molding can be slower than other processes, especially for larger parts.

Choosing the Right Molding Process

When selecting a molding process, it’s crucial to consider the specific requirements of your project.

Compression molding is a straightforward process that requires minimal tooling and easily sourced materials, making it ideal for short production runs with bespoke specifications. It can achieve good levels of accuracy and quality control, particularly for larger, bulkier components.

However, compression molding may not be suitable for complex applications with several moving parts or intricate details. In such cases, injection molding might be a better option. Injection molding is a faster process that can create more complex shapes and sizes, but it may not be as cost-effective as compression molding for larger components.

Ultimately, the choice between compression molding and injection molding depends on the specific needs of your project, including the type of material, the desired shape and size, and the required level of accuracy and quality control. By carefully evaluating these factors, you can select the molding process that best meets your manufacturing goals.

Getting Started with MakerVerse

Both injection molding and compression molding have their strengths and limitations.

Regardless of what technology you need for your project, MakerVerse is here to help. Choose from the full range of manufacturing technologies and materials. If you’d like, you can work closely with one of our experts to help you choose the best process.