Plastic Products Production: Selecting Between Injection and Compression Molding
Plastic Products Production: Selecting Between Injection and Compression Molding
What Is Compression Molding?
Compression molding is a manufacturing technique that utilizes pressure to shape preheated materials into specific forms. In contrast to injection molding, which uses a multi-cavity mold to create multiple parts in one cycle, compression molding features a machine with a carousel containing several single-cavity molds, each producing one closure at a time. The process begins with placing a preheated material, referred to as a charge, into an open mold cavity. Once the mold is closed, pressure is applied to compress the material into the intended shape. After cooling, the mold is opened, allowing for the removal of the finished part.
Advantages of Compression Molding
No gate mark Compression molds do not require gates to allow material flow. The result is that parts produced by compression molding have a surface finish with no visible gate marks.
Fast Color Changes
In a compression molding machine, the extruder feeds directly into each mold without the use of a hot-runner. Injection molding systems, a hot-runner is used to transfer the molten material from the injection unit into the mold cavity. Compression molding can change colors faster without the use of a hot runner.
Lower Energy Consumption
Compression molding uses lower resin temperatures. This means that it takes less energy to heat up and cool down the material in the mold.
Lower Initial Equipment Investment
Initial investment costs are lower for compression molding than injection molding. It may be a benefit to converters who are new in the business of closures, but it is important to consider the total cost of ownership.
Injection Molding vs Compression Molding
When evaluating injection molding in relation to compression molding, it's crucial to recognize that the requirements of your particular application should guide your decision, since both methods offer distinct advantages.
Now, let’s delve deeper into the comparison of injection molding and compression molding specifically for the manufacturing of caps and closures.
Which process is more costly?
Compression molding generally incurs a lower upfront equipment expense compared to injection molding. However, the cost of resin constitutes over 80% of the total part cost, with energy and maintenance expenses being the next most significant factors.
When comparing closures of similar weights, compression molding usually offers a cost advantage of about 5%. Since resin costs are the main driver of expenses, even a slight weight advantage in injection molding can balance out this price difference.
In situations where injection molding is only slightly pricier, the enhanced consumer experience—offered by features such as tethered closures that allow a 180-degree opening and provide audible and tactile feedback—might make the extra expense worthwhile.
While it's challenging to quantify, anyone looking to invest in these technologies should also take into account the potential costs related to licensing fees and additional post-processing steps, like slitting and folding for tethered closures. This includes expenses for systems that orient closures prior to slitting, the cost of specialized knives, and advanced inspection technologies.
Which process provides more flexibility?
A significant benefit of injection molding is its superior design flexibility and versatility. As previously noted, this method is often chosen for projects that require intricate shapes or undercuts. Features such as 180-degree openings and audible clicks—elements praised by leading beverage brands—can only be created using injection molding technology. The level of design freedom and enhancement of consumer experience that injection molding offers far surpasses what compression molding can achieve.
Moreover, injection molding allows for adaptability in the production setting. Manufacturers can utilize the same machinery to create a wide range of closures simply by swapping out the molds, a process that can be completed in just a few hours. Additionally, the injection machine can be repurposed for producing components beyond closures, which increases the overall value of the equipment.
On the other hand, compression molding is more effective for straightforward designs and scenarios where the machinery is dedicated to producing a single type of closure throughout the year.
Which process is more efficient?
Injection molding provides a highly efficient and reliable production method that enhances overall output and effectiveness. Its maintenance requirements are less intensive compared to compression molding, as it involves fewer moving components that operate at slower speeds.
In addition, injection molding streamlines the process by removing the need for extra steps after production, such as slitting and folding, while also significantly reducing the likelihood of generating scrap and dust.
On the other hand, compression molding necessitates that tethered caps and closures be oriented before slitting, which demands a more intricate slitting knife and procedure. Consequently, the inspection process for ensuring slitting quality is also more complicated.
Conversely, closures made through injection molding are fully formed upon exiting the mold, with all shapes precisely crafted within the mold itself, ensuring a high degree of consistency in production.
Which process enhances consumer safety?
The enhanced design flexibility offered by injection molded bands contributes to greater safety for consumers, particularly when considering tethered caps and closure designs. While these tethered components are intended to stay attached to the bottle, consumers can still remove them if desired. In contrast, the restricted design capabilities of compression molding can result in sharp edges and rigid, pointed features when a cap is detached from its band, as illustrated below. Such characteristics could lead to risks of injury to lips and fingers. Conversely, injection molded tethered caps and closures feature softer shapes that create thin, flexible arms, significantly reducing the likelihood of injury.
How to Choose Between Injection Molding and Compression Molding
In the comparison between injection molding and compression molding, it becomes evident that compression molding has benefits like quicker color transitions and reduced energy usage. However, injection molding stands out as a more adaptable and effective method overall. It allows for greater design creativity and production versatility, catering to the requirements of various beverage brands and converters.
To identify the most suitable manufacturing technique for your projects and applications, it is essential to assess their unique needs and limitations. We recommend consulting with our specialists, who can offer valuable information and perspectives to help you make a well-informed choice.
For more information on injection molding, please read the news released on this website on April 10.