Injection molding and compression molding are two popular processes used for manufacturing plastic products, both of which involve the use of heat and pressure. However, they are different with unique features and benefits. This article will make a comparison between compression vs injection molding in different aspects.
What is Injection Molding ?
Injection molding is a process that involves the injection of raw material into a mold cavity. The material is pulled into a hopper by a screw. The following is the heating process, and then the molten material is injected to the mold. The material cools and solidifies. After that, the mold is opened and the finished part with the desired shape is extracted. The process is ideal for the mass production of complex and intricate parts.
Advantages of Injection Molding
Injection molding has a lot of advantages over compression molding, including:
High volume production of identical parts
Complex shapes and geometries
Less labor is required
Low production costs due to the high levels of automation and rapid manufacturing speed
Shorter cycle times
Large material choice
A high level of precision
Little or no post processing because the parts usually have good aesthetics post production
Versatility and customization are enhanced
Ability to mold in tamper evidence features
Disadvantages of Injection Molding
The followings are some disadvantages of injection molding in comparison with compression molding.
It is usually costly for low volume production runs.
The manufacture of large and thin parts is not always cost-effective.
The cost of the tooling is higher as high plastic injection pressures are required.
Design changes are expensive.
Applications of Injection Molding
Injection molding is a popular process to manufacture plastic parts at scale due to its high quality and effectiveness. It is used in a wide range of industries such as the automotive industry, the medical industry, consumer products and logistics industry. For example, the process can be used to create many things like bottle caps, toys, storage containers, mechanical parts (including gears), and most other plastic products available today. 
What is Compression Molding ?
Compression molding is a molding process that manufacture various plastic or composite parts by utilizing heat and pressure. In the process, the molding material is generally preheated. It is placed into an open, heated mold cavity. The mold is then closed with plugs inserted and the pressure is added to compress the material and take on the desired shape. In this context, the material is forced into contact with all mold areas. The combination of heat and pressure enables the material to conform to the shape of the mold cavity. Once cured, the finished part is removed from the mold. The process requires post-processing to cut off any flash, which is a common defect to be dealt with for compression-molded parts.
Advantages of Compression Molding
Compression molding has some advantages. These advantages include:
Low initial setup cost
Minimal wastage
Compatible with a wide range of materials
Support a wide variety of shapes and sizes
Flexible design
Accommodate varying thickness
Good surface finish
High product uniformity
Ideal for large and intricately shaped components
Produce stronger and durable parts
Cost-effective for high-volume production runs
Disadvantages of Compression Molding
Listed below are some disadvantages of compression molding :
A manual and slow process
Higher labor cost
Mould wear and damage over time
Poor product consistency
Difficulty in controlling flash
A high carbon footprint and energy consumption challenges
Fail to create parts with high levels of complexity
Applications of Compression Molding
Compression molding is well-suited for creating complex parts with a huge variety of applications, from automotive parts to commodities. The common uses for compression molding include automotive parts, electrical components, video games and computer devices, components for medical and dental equipment, and kitchenware. It is greatly used in manufacturing automotive parts such as hoods, fenders, scoops, and spoiler.
Differences Between Injection Molding and Compression Molding

  • Material

    • The common materials used in injection molding include polyethylene, polystyrene, nylon, polypropylene, acrylonitrile butadiene styrene (ABS) and polycarbonate. Compression molding more often makes use of materials like diallyl phthalate (DAP), thermoset polyester, epoxy, sheet molding compound (SMC), vinyl ester, phenolics and silicone. In addition, the two processes also differ in the way the raw plastic material is manipulated into the shape of the mold. Injection molding involves filling cavities with melted plastic materials, while compression molding uses high pressure and heat.

  • Speed

    • Injection molding is much faster than compression molding in that its cycle time can be a few seconds. However, it takes a few minutes for the compression molded parts in terms of cycle times because of the need to cure .

  • Post-processing

    • As for injection molding, there is no need for post-processing. However, post-processing is required for compression molding due to the occurrence of flash.

  • The upfront costs

    • Due to the nature of the manufacturing process, the upfront costs for injection molding are higher than that of compression molding.

  • Application

    • Injection molding is suitable for the high-volume production of more intricate parts with a high degree of accuracy and repeatability while compression molding is ideal for the production of large, simple-shaped and durable ones.

  • Lead Time Length

    • The lead time for injection molding is significantly shorter as opposed to compression molding .
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