Producing Silicone Parts? Compression Molding Could Be For You

Let’s explore why the silicone compression molding production process is so popular for producing silicone parts and products.

You’ll learn about the process itself, its applications, silicone’s benefits as a production material, challenges and considerations, and much more! If you require silicone parts, you’ll be equipped to decide if this process is one you should explore further.

If you prefer listening to reading…

Listen to the audio here.

Here’s a summary of the episode, but listen for full details:

What is the Silicone Compression Molding process?

Silicone compression molding (SCM) uses compression to form the parts, so for the compression aspect you need a top and a bottom (or male and a female) core cavity tool where you put pre-cut silicon inside, the machine then closes the two halves of the mold and the press then shuts it under force. And during that compression, your pre-cut form silicone, whether that be in a circle, round, dog bone shape, is compressed into the final form of the core and cavity taking on its final shape. The machine is then held under compression and heated under specific parameters and time which cures the silicone. The tool opens and the part can be removed, and the final product will probably have flash and excess material around the edge which should be trimmed in post-production finishing. (04:41)

Comparing silicone compression molding to other molding processes.

SCM is most similar to transfer molding which uses heat and pressure to force pre-heated material into a mold, but plastic injection molding is the key other process used and it differs because solid polymer is melted and injected into a mold cavity, cooled, and then ejected to form a specific shape. Liquid Silicone Rubber Molding is more similar to plastic injection molding as just described.

SCM tends to be a more simple process than plastic injection molding because its tooling is less complex and you don’t have all of the sliders and all of the complex aspects that go into making an injection mold tool. The tooling will also commonly be less expensive for that reason.

Unlike plastic injection molding which is usually used for production at scale, SCM is great for low production volumes and product development, but it’s also perfect for mass production because this is something that can be scaled depending on the size of the actual product that’s being produced. You can also have multiple cavities in a tool meaning that you can have one side in use, while the other side is being loaded, ready for the next batch to be produced. This makes it efficient and cost-effective. (09:57)

Silicone’s benefits as a production material.

Silicone provides numerous benefits for products of various applications from medical devices, to automobile parts, to consumer products, largely because it has many beneficial properties, including:

Extreme heat and cold resistance.
Flexible.
Durable.
UV-resistant.
Water resistant.
Electrical insulation.
Non-reactive to most chemicals like acids, etc.
Biocompatible (important for medical devices).
Can take on many colors.
Good adhesive and sealant.
Generally more cost-effective than plastics used in injection molding and SM molds last longer.
Silicone flash can be reused in some cases which reduces waste and improves sustainability. (13:26)

Does compression molding for silicon also allow complex geometries and designs?

SCM generally will only allow simpler designs and geometries. In comparison, with plastic injection molding you can get very clever with sliders and lifters and expandable cores and clever things which yield very complex mold tooling and parts, although they’re expensive. SCM on the compression side is a simpler process and the parts often produced such as O-rings, gaskets, phone cases, and ice trays, are accordingly simple. However, it should be noted that some of these parts will be critical components for very complex devices and machines, such as a commercial jet engine, for example, so it is not only a suitable process for household goods. (22:11)

Industries that rely on silicone parts.

Due to its biocompatibility, the medical device industry is a large user of silicone. It can be heated and sterilized, and it is flexible and soft so is comfortable to be in contact with skin, such as with a prosthesis.

Consumer electronics also use silicone for seals which help them function in different environments and keep out dust, etc.

Silicone kitchenware has become almost ubiquitous in daily life for many households, too, due to it being heat resistant, non-stick, and durable, as well as food safe. (25:14)

Challenges and considerations when producing silicone products by compression molding.

There are limitations and challenges when it comes to silicon compression molding as a process itself:

Design complexity – SCM can’t be used to make parts with very intricate designs and geometries.
Greater draft angles are needed – as silicone tends to stick in the tooling a bit more, and so steeper angles should be added to get them out.
More labor-intensive, longer curing, and increased cycle times – compared to plastic injection molding the operator will need to do more work such as removing parts and the parts take longer to cure, so this increases cycle times.

You should also consider these points when using SCM for product development:

Communication with your supplier is key.
Find a supplier you can rely on who knows what they’re doing.
Get educated about the process yourself.
Understand if the limitations affect your project.
It is good for low-volume product development, but not for fast iterative changes. (27:45)

FAQs and tips.

How long does it take to develop and produce tooling for using SCM? – It depends on the product’s complexity, but to make tooling will generally take 4-6 weeks.
What are the typical tolerances in QC measures? – Around plus or minus 0.1 mm for small parts if the tolerance needs to be strict, but it is larger for larger parts (see standard ISO 3302-1). Plastic injection molding can be higher than this.
How to get the most out of silicon compression molding? – Optimization. You need to look at optimizing your design for the component, making sure that you understand where the component is being used, and making sure you’re selecting the right silicone to apply to that particular part.
You also need to select the right manufacturing partner, so do due diligence in advance to ensure you are working with someone who is reputable and won’t let you down.
Specify your color, silicone grade, etc, requirements to the supplier. – Be clear on the properties required and the silicone type (food grade, medical grade, etc), that you provide a correct 3D file and 2D-dimensional accuracies, and that the color is Pantone referenced. (34:40)

Don't miss a post