What's The Difference Between LSR Injection Molding And Compression Molding?

Aug. 16, 2022

Difference Between LSR Injection Molding And Compression Molding

As a professional LSR injection molding manufacturer, Hopewell would like to share the difference between LSR injection molding and Compression molding. There are four four aspects in their differences. We will give your more detailed explanation. First we gonna know what are liquid injection molding and compression molding:

▼ Liquid Injection Molding

Liquid injection molding, LIM in short, uses liquid silicone rubber (LSR) or similar elastomeric material to manufacture wide ranges of products to demonstrate excellent durability and flexibility. Seals and sealing membranes, electrical and electronic components, such as connectors and cables, medical and sterile devices, kitchen goods, infant care products and other products are produced by LIM.

Due to its use of LSR, liquid injection molding relies on a more streamlined and consistent mechanical mixing process rather than a labor-intensive one (such as is used in compression molding). The closed-loop process employs a pump and mixing unit to mix and dispense the liquid material into a molding press. Once the curing stage is complete, the press opens and ejects the finished component, allowing it to be manually or robotically removed. Liquid injection molding is one of the most cost-effective and versatile manufacturing methods currently available. It is applied towards any industry or market, including: Aerospace and aviation, Automotive, Electronics, Food and beverage, Medical and dental, and etc..

▼ Compression Molding

Compression molding involves placing a thermosetting resin into a heated mold cavity and applying pressure to force it down and compress it in the mold. Material temperature and pressure levels are regulated throughout the process from dispensing to curing to facilitate precise part production.

Compression molding is highly flexible and versatile. It is suitable for producing parts of various sizes, thicknesses and complexities and addresses certain manufacturing challenges such as production operations requiring exotic materials, difficult-to-manage inserts or unique part shapes.

While compression molding is suitable for high-volume production, liquid injection molding offers faster processing with greater repeatability and consistency, requiring little labor. Compression molding offers faster production changeover times, cheaper tooling in some cases, lower upfront material costs and greater production flexibility.

Difference Between LSR Injection Molding And Compression Molding

◆ Raw Material

The raw material of Compression molding is solid, and the solid silicone needs to be mixed manually. Our staff will pick raw materials from the warehouse according to the order situation, then add the corresponding agents into solid silicone while in mixing, such as: vulcanization agent (divided into: high temperature and low temperature, platinum and peroxide, etc.), coloring agent, anti-bacteria agent and so on. The agents added into solid silicone vary from different products, our engineers will validate while in prototyping, and they are also carried out according to the order situation. After mixing, the raw materials will be cut and packed for hot pressed.

The raw material of LSR injection molding is liquid, it will be mixed by the LSR injection molding machine's feeding system, and agent A and agent B to be mixed at the ratio of 1:1. For customized colors, there will be agent C to be added separately at a certain ratio, depends on different customized silicone products.


Difference Between Injection and Compression Molding

Difference Between Injection and Compression Molding
Solid Silicone         Liquid Silicone


◆ Process

The process of compression molding is rough as below:

Raw Materials Preparing- Compression Molding- Sampling Inspection- Deflashing- Secondary Vulcanization (Baking is for high temperature deodorization)-Full Inspection- Packing- OQC- Shipping

These processes will also be applied according to the characteristics of different products, and some products will also have the step of punching. The defective products generated in the process of compression molding are mainly caused by the following 6 factors:

  • People, the speed of each person will be different, and the speed of placing the product and taking the product will directly affect the product.

  • Machine, it is also very important for the machine to be adjusted to the appropriate parameters.

  • Material, when the weight of the raw material exceeds the positive or negative values, it will also lead to the defective product.

  • Method, the method of placing materials and taking products, improper operation will also affect the quality of the product.

  • Environment, which means that the environment within the production and operation range should be clean, and if the dirt is attached to the product, it will produce defective products.

  • Measurement, the QE must be careful when measuring.


Process of LSR Injection Molding:

LSR Injection Molding → Sampling Inspection- LSR Deflashing- Full Inspection- Packing- OQC - Shipping

Unlike solid raw materials, the liquid does not require manual mixing and can be directly collected from the warehouse. Liquid raw materials have different degrees and properties, and they are selected according to customer requirements or product needs. Special attention should be paid to: A and B agents work at the same time when feeding, so if one agent is short of material, it will lead to poor products, so it should be replenished in time.

The difference from the solid state is the material weight. The liquid silicone is adjusted by the machine while the solid material weight is manually weighed, and it does not need manual placement, which can reduce time thereby making it more efficient.

The liquid injection molding machine mainly produces silicone valves, silicone optics, silicone covers, medical silicone seals and other customized LSR overmolding waterproof silicone products.


◆ Molding Temperature

For the compression molding, the molding temperature is controlled between 165±5℃. While for the LSR injection molding, the molding temperature is controlled between 135±3℃. 


◆ Mold Structure

Due to the molding machines for these two processes are different, the mold of compression molding, it is composed of 1 upper mold and 1 lower mold. As to the mold of LSR injection molding, for vertical injection machines, the mold is composed of 1 upper mold and 2 lower mold, while for horizontal injection machines, the mold is composed of 1 upper mold and 1 lower mold, but the mold of LSR injection molding are more precise than the mold of compression molding.

Difference Between LSR Injection Molding and Compression MoldingDifference Between LSR Injection Molding and Compression MoldingDifference Between LSR Injection Molding and Compression Molding
 Compression Molding MachineVertical LSR Injection Molding MachineHorizontal LSR Injection Molding Machine

LSR Deflashing Process     

LSR deflashing, also known as Liquid Silicone Rubber deflashing, is a process used to remove excess flash or burrs from liquid silicone rubber molded parts. Flash and burrs are tiny pieces of silicone rubber that can form as a result of the injection molding process. These extra bits can affect the function and appearance of the finished part.

During the LSR deflashing process, molded parts are placed in a tumbling machine along with abrasive materials. The machine rotates the parts, causing them to rub against the abrasive materials, which remove any excess flash or burrs. This process enables manufacturers to create high-quality liquid silicone rubber parts that are free from any blemishes or deformities.

This process is commonly used in the production of medical devices, automotive parts, and consumer products. It helps improve the integrity, precision, and overall quality of the final product, making it an essential step in the manufacturing process.


For better understanding, we've also taken a video for an explanation

Click Video Center for more info

HopeWell Silicone is a professional LSR injection molding manufacturer and supplier, if you still have questions on the difference between LSR injection molding and compression molding, want to know more information or if you have a design or customize liquid injection molding products, please feel free to contact us.

Difference Between LSR Injection Molding and Compression Molding

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