Compression Molding vs Injection Molding - Which process will you choose?
- By Echo Engineering
- Oct 5, 2018
The argument over compression molding vs injection molding remains a disagreement among leading manufacturers, but who’s right?
There are advantages and disadvantages to each molding process. Dive into each, then you be the judge. Which technique reigns supreme?
Compression Molding
This method of molding often starts with molding material placed into an open mold cavity. Pressure is applied by a top force to enclose the material within the heated cavity, which begins the curing process. Once cured, the mold is removed by an ejector pin, or through manual extraction and flash trimming.
Compression molding is a popular technique for gaskets, seals, and grommets but isn’t the right choice for all modeling processes.
Advantages of Compression Molding
- Variation of Wall Thickness: This technique allows diversity in wall thickness. Generally, the design can vary between 1.3 mm to an inch.
- Seamless Design: A uniform part is created without any flow lines or knitting. Gaskets are a great example of how compression molding allows for a cohesive part. The part is ejected with a good surface finish immediately.
- Lower Costs: As a low-pressure mold, production of multiple cavities is done at a lower cost.
- More Material Options: Compression molding is suitable for flexible materials, as parts can remain pliable after the curing process. Additionally, thermosets are available to mold multiple cavities, which opens up many options when it comes time to select a molding material. Commonly used materials include silicone, natural rubber, and EPDM.
- Good for High Volume Manufacturing: 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
- Slower Cycle Time: 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.
- Lower Productivity: 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.
- Simple Parts: This technique is best reserved for uncomplicated parts
Injection Molding
A screw feeder quickly extracts an exact amount of material into a hopper or nozzle. The uncured material is then preheated and transferred via runners and sprues into a gate. The rubber then flows from the gate into the mold cavity to evenly fill the part. An injection press holds the mold in place with immense pressure to keep the mold secured during the quick curing cycle. Finally, when the material cures, it’s removed from the mold, and the process quickly repeats.
Rubber injection molding is the best solution for producing components with precision.
Advantages of Injection Molding
- Higher Quality Parts: An elimination of pre-forms allows injection molding manufacturers to quickly produce uniform parts.
- Less Labor Intensive: The absence of pre-forms removes the labor-intensive placement of pre-forms.
- Shorter Cycle Time: Parts with thin walls have cycle times ranging from 2 to 5 seconds.
- High Volume Production: A combination of the molding process and cycle time creates high volume in production. A simpler supply chain and quicker assembly create higher productivity.
- Less Waste: Don’t expect excess flash here, as injection molding produces less scrap and waste.
Disadvantages of Injection Molding
- High Tooling Costs: Each new mold needs its own new tool. Not only can this be expensive, but it can also extend unwanted lead-times.
- Expensive Material Costs: The cost of materials can be as high as 9x more expensive than compression molding silicone
- Part Restrictions: Although it’s possible to produce a large part using injection molding; if the machine needed to create it is large, the tool is extremely expensive to create.
Concluding Thoughts
So, the real question here isn’t WHICH will you choose, it’s WHY will you choose it? 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, Echo Engineering has the capabilities to cover both your compression and injection molding needs.
Reach out if you have a project that needs our expertise and supply chain solutions!