What Is The Difference Between Injection Molding And Silicone Compression Molding?

Many Silicone products are developed through a process known as Silicone molding. Do you want to know more about the difference between injection molding and compression molding techniques?

We will focus on the differences between silicone injection molding and silicone compression molding, how these techniques work and the main advantages and disadvantages of these techniques.

ZSR Group has the ability to produce silicone consumer products to scale by silicone injection molding and compression molding.

Learn More About Silicone Molding Method And Process

1. What is injection molding?

Injection molding is a manufacturing process that allows for parts to be produced in large volumes. This process involves injecting materials into a closed mold. It is typically used as a mass production process to manufacture thousands of identical items. Injection molding materials include metals, glasses, elastomers and polymers.

An injection molding machine uses terms polymers that are heated up and injected into a mold.

It’s a cost-effective way to mass-produce a silicone or plastic product. It involves the creation of an aluminum or steel tooling, also called a mold, that is inserted into an injection molding machine. The mold has two halves, called a core and a cavity, respectively. The machines exert enormous pressure on these halves to bring them together. Thermoplastic or silicone is then melted and injected into the mold through its gates. The mold can be cooled, or tempered to a certain temperature.

In a Liquid Silicone Rubber molding, you have a “piston”, not a screw, that injects a “cold” silicone material into a very hot mold with very high pressure.

2. How does Liquid Silicone Rubber injection molding work?

Silicone injection molding works by feeding the desired material into a heated barrel; where it is mixed and forced into a mold cavity where it cures and hardens into a specific shape. Molds are usually made from steel or aluminum and are often the most efficient way to mold silicone.

The first stage of injection molding is to create the mold itself. Most molds are made from metal, usually aluminum or steel, and precision machined to match the features of the product they are to produce.

Once the mold has been created by the mold-maker, the material for the part is fed into a heated barrel and mixed using a helical-shaped screw. Heating bands melt the material in the barrel and the molten metal or molten silicone material is then fed into the mold cavity where it cools and hardens, matching the shape of the mold. The cooling time can be reduced through the use of cooling lines that circulate water or oil from an external temperature controller. Mold tools are mounted on plate molds, which open once the material has solidified so that ejector pins can eject the part from the mold.

Separate materials can be combined in one part in a type of injection molding called a two-shot mold. This technique can be used to add a soft touch to plastic products, add colors to a part or produce items with different performance characteristics.

Molds can be made of single or multiple cavities. Multiple cavity molds can have identical parts in each cavity or can be unique to create parts of different geometries. Aluminum molds are not best suited to high volume production of parts with narrow dimensional tolerances since they have inferior mechanical properties and can be prone to wear, deformation and damage due to the injection and clamping forces. While steel molds are more durable they are also more expensive than aluminum molds.

The injection molding process requires careful design, including the shape and features of the part, the materials for the part and the mold and the properties of the molding machine.

3. What are the advantages and disadvantages of Silicone injection molding?

Silicone Injection molding comes with its own unique set of advantages and disadvantages. Here are the main advantages and disadvantages of Silicone injection molding techniques.

Advantages of injection molding

Ease and Experience: We have the unique ability to design, prototype, create the mold for, produce, and fulfill your product to scale right here in China.
Time: Our team has a breadth of experience troubleshooting tooling complications and a quick turn-around time given our in-house tooling shop. This means getting your machine running — and your product to market — as soon as possible. With lower costs and faster cycle times.
Cost: The silicone injection molding require an up-front tooling investment, the price per unit can be extremely low. The more parts are produced, the further that price drops.
Quality: ZSR group is an ISO Certified manufacturer and an FDA-registered silicone products producer. We used Food-grade silicone in our silicone projects and have experience with a variety of polymers as well. We are pleased to offer high-quality parts no matter the project. Low levels of flash.
Consistency: The beauty of our injection molding process is creating millions of identical parts. Whether we are developing a Food application part or, scuba diving equipment, consistency and quality are key.
Waste: Depending on the project, injection molding can produce a low rate of scrap, This diminishes both the financial and environmental cost of production.High dimensional tolerance. Reduced need for secondary trimming.Small amounts of waste.

Disadvantages of injection molding

High tooling cost: Up-front costs can be high for injection molding, particularly with regard to tooling. Before you can produce any parts, a prototype part needs to be created. Once this has been completed, a prototype mold tool needs to be created and tested. This all takes time and money to complete and can be a costly process.
Small runs of parts can be costly: Set-up cost is very higher. In the small quantity, there is much material waste and labor.
More expensive machinery and tooling: The machine and tooling are higher costly.
Producing large parts as a single piece: Because of the size limitations of injection mold machines and the mold tools. Items that are too large for an injection molding machine’s capability need to be created as multiple parts and joined together later.
Large undercuts: Require experienced design to avoid and can add even more expense to your project.

4. What is compression molding?

Compression molding is a tried-and-true method of manufacturing simple silicone rubber parts. It is a simple, high-pressure situation where vulcanized silicone rubber is transformed into a strong, useful rubber part. that’s added to an open mold. The mold is closed and placed under great heat and pressure. The pressures on the top plate force the casting material to fill all mold areas and dispel air. Heat and pressure are held until the material is cured. After the parts have been cured, the silicone products are removed from the mold.

Compression molding is ideal for applications where the durometer is low and tolerances tight – and where the cost of injection molding is an issue. With over more than 10 years of experience, we have the expertise to create fairly intricate parts using compression molding.

5. How does compression molding work?

Compression molding works by combining heat and pressure to mold Silicone rubber into a shape.

Once all of the above elements are in place, vulcanized Silicone rubber is subject to compression on prepared molds.

Here are the steps of the Silicone rubber compression molding process:

The mold is prepared by being heated and sealed.
Uncured rubber (preform) is placed in the mold cavity- it is prepared to be formed, or molded. Every mold will have a different shape and size preform that works best. When the optimal preform has been determined, it is important to have a tolerance on both its size and shape to ensure the part forms correctly. Too much material is wasteful and can cause the flash to become too thick, while too little material can cause voids in the part.
The mold is closed-Heat and pressure is applied in a compression molding press. Presses used in production utilize a programmable logic controller to monitor and control critical parameters like temperature, pressure and time to ensure molding takes place within a prescribed tolerance window.
Heat and pressure are applied (according to programmable logic controls and in accordance with temperature and pressure parameters) with the mold closed.
The mold is opened and the cured Silicone rubber is removed along with its flash.
The silicone rubber products are then moved through the manufacturing operation to undergo Post-molding processes including deflashing, inspection, post-curing, etc.

6. What are the advantages and disadvantages of Silicone compression molding?

Compression molding is a popular technique for gaskets, seals, and grommets but isn’t the right choice for all modeling processes because its advantages and disadvantages.

Advantages of compression molding

Minimal lead time- Short set up a time
Easy to prototype- Minimal wastage
Widest range of part sizes- Perfect for the manufacturing of parts with a very large cross-section
Dimensional stability- Capacity to process stiff, high durometer materials, Excellent for low quantities of parts requiring a long cure time
Low tooling and equipment costs- Tooling is simpler and more cost-effective than injection molding, Although this technique has a longer cycle time, it is a low-pressure mold, which means it’s inexpensive to produce a variety of cavities without high tooling costs.

Disadvantages of compression molding

Produces only intermediate tolerances- Parts can be less consistent
Parts may require deflashing-When flash (the resin that escapes between two parts) occurs, it must be manually trimmed, thus slowing down productivity. Additionally, you’re unable to regrind this excess material, which creates more waste.
Higher Human Capital Investments: As previously mentioned, flash is removed manually on compression molds, which generates higher labor costs.
Longer cure times: The time needed to start and repeat the sequence of operations is between 1-6 minutes for compression molds; a much slower cycle time than injection molding.
Does not all work well for complicated part configurations-This technique is best reserved for uncomplicated parts
Coloured Silicone can be easily contaminated
Transfer or injection molds may be required
Coloured Silicone can be easily contaminated

7. Silicone Injection molding VS Compression molding

ZSR Group has the knowledge and expertise to help you understand which silicone manufacturing process is best suited to your needs. They explain that the choice between rubber compression molding or injection molding largely boils down to cost, volume and time pressures. Compression molding and injection molding each have their advantages and disadvantages, but who reigns supreme depends on what you’re producing.

It’s important to select a manufacturer who understands which technique best suits your part, as that should be the deciding factor. Regardless of which one is better suited, ZSR Group has the capabilities to cover both your compression and injection molding needs.

"Whilst neither technique is better than the other, the choice between injection or compression molding relies heavily on the requirements of your product and its application".

8. Conclusion

Any Silicone products or Silicone project need technical support, you also can custom Silicone products at ZSR Group. We will support your Silicone products from idea to life.

If you like the article or you need more information from us, please leave a message or contact us by [email protected], Any inquiry from you is welcome.

Reach out if you have a project that needs our expertise and supply chain solutions!

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About Author: Z.S.R International Group

Z.S.R International Group(Hong Kong) co., Limited, is a one-stop supplier for molded silicone products and silicone products molding solution provider in the consumer products field. We offer OEM services from product design to Silicone products contact manufacturing. We have the capability for LSR molded silicone products, solid silicone molded products, molded silicone multi-colored products. We also can custom molded silicone, custom molded LSR, custom molded dripping injection dispensing (co-injection) silicone multi-colored products, custom tooling.