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 compression molding. 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. 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.

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-molded parts also exhibit 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.

Getting Started with MakerVerse

Both injection molding and compression molding have their strengths and limitations. Injection molding excels in high-volume production, superior strength, and material options. Compression molding offers flexibility, shorter lead times, and cost efficiency for smaller production runs or larger parts.

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.