Silicone Compression Molding Introduction

Compression molding has been used to mold rubber parts since the beginning of the rubber manufacturing industry. It is one of the oldest methods still used to mold rubber parts. Albright Technologies is a silicone molding company that has utilized compression molding since the year 2000. Silicone compression molding offers Albright’s customers an effective and efficient way to manufacture their liquid silicone rubber prototypes and low-volume production parts.

silicone compression molding diagram

The compression molding process is quite simple when compared to injection molding, transfer molding or extrusion molding. Albright will manufacture a compression mold tool which requires CNC machining and hand polishing. Once the tool is ready for engineering samples, then each plate is loaded with liquid silicone rubber. Simple part designs typically only require a two plate mold, which includes a cavity side and a core side. After the material is loaded, the mold plates are assembled and inserted into a compression molding press between the two platens. Next the press is clamped to a set pressure to produce high quality parts. Heat and pressure are applied for a given amount of time allowing the liquid silicone to spread throughout the mold cavity and cure. Then pressure is released from the press, which then opens and the compression mold is removed. Then the plates are separated using hand tools and finally the silicone part is removed. This completes a normal compression molding cycle for a simple silicone part design.

Albright Technologies has a range of differently sized compression molding presses in both our controlled environment room and on our production floor. This ensures that we can run small to large sized parts and single cavity molds, as well as multi-cavity ones in either space. If needed, we can easily configure our molding equipment and space to meet our customers’ demand for production.

Compression Mold Tooling

Albright typically manufactures its silicone prototype compression molds out of Aerospace Grade Aluminum 7075. The main reasons we manufacture tools out of Aluminum 7075 is that it can be machined and polished faster than steel and has a higher heat transfer rate for mold processing. This allows us to provide a mold tool capable of 10,000 plus shots in as little as 5 business days. Typical lead time on an Aluminum compression mold is 15 business days, however we can provide 5 and 10 business day expedites if you need your engineering samples fast!

compression mold

Whether it be your preference or your volume demands it, we can manufacture your compression mold out of steel. Low-volume production parts often require multi-cavity molds where steel can be more suitable than Aluminum. Steel compression mold tools typically take about 20 to 25 business days to complete, due to the additional time required to machine and polish the mold.

Albright also provides liquid injection molding tools for manufacturing your production parts. Silicone injection molding tools are only necessary when your volume becomes high enough that it is justified and a lower piece price is desired. If you require several thousand pieces or more on an annual basis, then an injection mold tool will be better suited than a compression mold. To learn more about our liquid silicone injection molding services, please contact our sales department at 978.466.5870 or by email at info@albrightsilicone.com.

Compression Mold Design

Simple parts, even ones with mild undercuts, can typically be de-molded from a two plate compression mold thanks to the high elongation percentage of liquid silicone rubber. Parts with complex geometries often require a pick-apart compression mold that can be made up of as few as three different plates or actions, but may have as many as eight or more different plates. The plates and cores are assembled together to contain and form the liquid silicone to mold the part. This can cause de-molding to be significantly longer when compared to the liquid injection molding process, where an action(s) would be used to remove the part. The pick-apart mold must have all of the plates unbolted and disassembled so that the silicone part can be removed.

Benefits for Using Compression Molds over Liquid Injection Molds for Silicone Prototypes

Albright Technologies utilizes compression molds to mold silicone parts, because the tooling is faster and less expensive to machine. In addition, process development time is significantly shorter as compared to liquid injection molding. This allows many part iterations to be completed in a very short time span. Compression molds can often be modified for different part revisions as well. Another advantage is that there are no gate vestiges since compression molds do not require gates. The time to setup and breakdown a compression mold is significantly shorter than an injection mold allowing multiple materials to be used without all the messy material changeovers. De-molding and part inspection are easier to complete since the compression mold plates are separated on a nearby workbench rather than within the molding press. Compression molds can be manufactured to be family tools, which include different part designs in each cavity, far more easily than injection tools.

Compression Molding Press

Compression molded prototypes are capable of having the same quality, surface finish, parting line locations and flash tolerances as a prototype from an injection mold would. High Consistency Rubber (HCR) can be easily molded with compression mold tools, while injection molding HCR requires careful handling and specialty delivery equipment, which results in a more expensive and difficult product development cycle. Compression molding allows for insert, fabric and encapsulating molding for prototypes with simpler handling and faster process development, when compared to liquid injection molding. Prototyping of silicone micro molded parts is ideal for compression molds thanks to controlled handling, shorter tooling and process development times, and lower overall costs.

Silicone Compression Molding at Albright

The Albright team is pleased to share decades of experience and silicone molding know-how with our customers to ensure that they receive only the highest quality silicone molded prototypes and production parts. We will use compression tools of varying complexity to mold your high consistency rubber and liquid silicone rubber parts. To learn more about silicone compression molding, please contact the world’s expert silicone molding company by phone at 978.466.5870 or via email at info@albrightsilicone.com.

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