Injection Molding vs. Compression Molding

Silicone Injection Molding vs. Compression Molding

Silicone Injection molding is one of the most popular ways to manufacture molded rubber products nowadays. Although compression molding has been used to mold silicone rubber parts since the beginning of the silicone rubber manufacturing industry. It is one of the oldest methods still used to mold rubber parts.

What is Injection Molding: The methodology of injection molding is very straightforward: the hot liquid compound is injected into a closed cavity where it is vulcanized. The result is a dimensionally stable, perfectly cured liquid silicone with no need of much aftercare. Injection molding is ideal for producing high volumes of the product such as LSR Baby Nipple, Breast Pump Duckbill, Medical parts, Automotive parts and Components, gaskets and other Liquid Silicone items. 

What is Compression Molding: The compression molding tool makes even stiff and high durometer rubber materials perfectly vulcanized and dimensionally stable. Compression molding is basically curing in a heated mould cavity under pressure. The preheated material is inserted into mould, closed and then cured under pressure. The result is always a high-quality, long-lasting rubber product that can be used in various industries.

Injection Molding vs Compression Molding for Silicone?

Product Size----Products produced by Injection Molding is High Precision, tolerance can achieve to 0.02mm, and also the flash can be minimum: because the injection molding’s material feeding system is different from compression molding, the temperature, pressure and injection way is controlled by the machine. Compression molding allows creating large silicone rubber products, whereas, injection molding is ideal for smaller parts with tight tolerances.

Product Structure----Injection Molding is suitable for the product with complicated structure: such as silicone forehead pad, bellows, etc. For the product with complicated structure, if produced by compression molding, the product quality probably is well, but after about 1000shots, the quality becomes bad, big flash and parting line will appear, so compression molding is not suitable for this type of product with high production quantity, the mold life is short. So generally simple product will be compressed. Whereas, injection molding enables manufacturing more complex parts.

Production Time----Silicone Injection Mold making time need 45-60 days, silicone compression mold-making time is about 10-20 days. Injection Molding’s production efficiency is higher than compression molding. The production time of compression molding is significantly longer than that of injection molding. Moreover, the excess burrs around the parts must be trimmed manually in case of compression molding, it will slowing down the production cycle even more, and making the process more labor intensive. Injection molding is the more efficient technology because full automation of the process is possible. because there is platinum vulcanization agent, which can speed up the vulcanize time, in this way, the production molding time is shorten; and by LSR injection molding, we can achieve automatic production, some the LSR parts can eject from the mold directly, and sometimes we can use mechanical arm to take the parts.

Production Quantity: When the automation of the injection molding process meets short cycle times, a high-quantity production is possible. Therefore, high-quantity series can be created with injection molding, while compression molding is used rather for low and medium series of large products. For the complex product with high quantity, compression mold tool lifetime is short.

Raw Material Safety----Properties of Liquid Silicone Material is good than solid silicone: the material is more pure, so elongation rate & tear strength is good.

Liquid Silicone Material for Injection Molding is safer than solid silicone for compression molding: 

• LSR is resistant to bacteria growth and won’t stain or corrode other materials. (during production process, solid silicone for compression molding needs to put on the mold manually, and sometimes in order to make the part eject from the mold easier, production people will spray mold release on the mold, while if produced bu injection molding, there won’t be this kinds of concerns, because the whole process is completed by machine. )

• Liquid Silicone Material can be fully cured, so it is more safe, biocompatibility is good. The material can be sterilized via a variety of methods, including steam autoclaving, ethylene oxide (ETO), gamma, e-beam and numerous other techniques, meeting all required approvals such as BfR XV, FDA 21 CFR 177.2600, etc.

• The Liquid Silicone for injection molding possesses a natural transparency and is ideal for direct and indirect food contact because of their inorganic nature. They are heat resistant, easy to clean and satisfy all current food legislation.