Both compression and injection molding come with pros and cons. But how do you know which manufacturing process better suits your food and beverage closure design? There are many factors from the size of the cap to your desired lead time that can make or break your decision. That’s why Silgan Closures experts are always available to walk you through the process, to ensure you choose what yields the best cost and quality combination your closure needs. To get started, here’s a quick rundown of the differences.
IN A NUTSHELL …
Injection molding is the process where plastic material is heated then injected into a mold cavity. This is the perfect molding method for complex shapes. It also is great for easily changing sizes and uptime efficiencies due to independent cavity control. Injection molding is usually the method of choice for a lower volume run because of its easy line changes and multiple material choices.
If you’re looking to run a higher volume, you may want to consider compression molding. This process extrudes plastic material that is melted, cut, and inserted into a cavity. Then, it is molded into its shape under hydraulic pressure.
INJECTION VS COMPRESSION: ADVANTAGES AND DISADVANTAGES
Injection molding provides a faster production changeover time and has the capability to easily change sizes and switch materials in case production changes. Injection molds have a gate which allows the plastic to be injected into the cavity of the mold. The gate can have a huge impact on the design of the cap, such as its aesthetic, part dimensions, and warping.
A great benefit of injection molding, especially for food and beverage closure design, is the ability to mold in a tamper evidence feature (see above), without post-molding operations (like slitting) and increasing lead time. Injection molding also allows for more complex part geometrics and other in-mold actions required to achieve special closure features.
Compression molding provides a low tool maintenance option that makes it easier to run higher volumes with less downtime. Since there is no gate present, as there is with injection molding, gate vestige is avoided and visual appearance is better. Compression also offers the ability to be more efficient with color changeovers. Compression molding is more limited when needing complex geometrics and larger diameter closures that are greater than 48mm.
Below is a direct comparison of Injection vs. Compression molding:
On your next closure project, work with Silgan Closures. We’ll walk you through the process and help you select the manufacturing choice that yields the most cost-efficient and highest quality closure with a low lead time.