Compression molding is a molding method that utilizes custom machined molds to form parts and products from uncured rubber or plastic. The process involves placing the material into the open mold cavity, closing the mold, and applying heat and pressure to shape and solidify the material into the desired component. It can be used to turn a variety of designs into tangible objects for a wide range of industries and applications. However, while it is an ideal production solution for many projects, it is not suitable for all of them.
Below, we highlight the key advantages and disadvantages of the compression molding process to help you understand if this is the right solution for your needs.
Advantages of Compression Molding
There are many advantages to choosing compression molding for a rubber or plastic component manufacturing project, including, but not limited to, the following:
It is a simpler process.
The compression molding process is relatively simple and straightforward compared to other molding and manufacturing processes. For some part designs this makes it easier for operators to perform, which translates to lower overall production costs.
It involves lower tooling costs.
Compared to injection molding, compression molding does not require special equipment and expensive complex tooling. As a result, the equipment and tools required for the operation are much simpler, which typically means less capital investment. Although it is a labor intensive process, when handled correctly, the wear and tear sustained by the molds during operations is relatively small, which can mean less maintenance needed over time, resulting in lower cost quotes for customers.
It is great for producing large items and thicker parts.
As the compression molding process involves loading the material directly into the mold cavity, it is not subject to part weight limitations except for those imposed by the part design, and equipment (e.g., size and pressure capacities). As a result, it can usually handle the larger amounts of raw material needed to create bigger parts and products.
It can be a good choice for insert molding and multi color molding.
Done in a vertical compression press with the right approach to tooling this process lends itself to some types of insert molding and dual color molding without the high cost of special equipment, very expensive tooling, high set-up and material costs used in liquid injection molding of silicone
It is cost-effective for short production runs.
Due to its lower tooling and setup costs, compression molding is ideal for small to medium production runs. It is often used to create prototypes or samples of designs before proceeding to large-scale production.
Disadvantages of Compression Molding
While the compression molding process carries many advantages for customers looking to start a new part production, it also has a few disadvantages, such as:
It has a higher chance of post molding costs.
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The size (projected area) of the part and its weight must be carefully calculated in relation to the force available from the press used to shut and hold the mold closed during a molding cycle. Even if this is optimal expect more parting line flash and and parting line control issues that may need to be dealt with by hand trimming or nitrogen de-flash of the parts adding cost.
It has slower processing times.
Compared to injection molding, compression molding requires more time to bring materials to cured state. These slower processing times can affect production rates and costs in higher volume projects.
It is not suitable for all complex designs.
The material used in compression molding operations may be subject to some limitations of flow within the mold cavity. As such, it may not reach into more intricate portions of the mold and tooling revisions may be needed to fill some parts. This quality makes the process unsuitable for some complex part and product designs.
Elastomer Technologies, Inc.: Your Partner for Compression Molding Needs
Compression molding can be an effective and efficient manufacturing solution for many projects. By understanding the unique advantages and disadvantages it carries compared to other available solutions, you may find that it is the ideal solution for your project.
Equipped with over 30 years of experience providing precision molded and die cut components to customers in a wide range of industries, the team at Elastomer Technologies, Inc. has extensive knowledge on compression molding and tailoring the process for each project. Check out our compression molding page to find out how we can benefit your next project.
To learn more about compression molding and if it’s right for your needs, contact the experts at ETI today.
“Molding” is an umbrella term encompassing all of the processes that utilize molds to shape material (typically rubber or plastic) into the desired parts and products. Manufacturers are able to employ a variety of molding methods to suit different product and production requirements. One of the most commonly used methods is compression molding.
What Is Compression Molding?
Compression molding of rubber compounds is a technique that involves the compression of pre-formed and/or pre-heated raw material in a heated mold cavity (sort of like making a waffle in a waffle iron). The material experiences high pressures within the closed mold, forcing it to conform to and, once cooled, retain the shape of the die cavity. Below, we provide a more comprehensive overview of the process as well as highlight some of the advantages it has over other manufacturing methods.
An Overview of the Compression Molding Process
While all molding methods operate under the same basic principles, they differ in the exact steps taken to create a molded part or product. Compression molding operations typically follow these steps:
Designing and creating/sourcing the mold. Before the compression molding process can begin, the manufacturer must first obtain an appropriate two-part compression mold to create the desired component.
Creating the pre-forms. At the start of the compression molding process, the manufacturer must form the molding material into a pre-form. The carefully weighed pre-form might have the general shape of the desired component but be larger to ensure the material reaches and fills all areas of the mold cavity during the molding process.
Heating the mold. Before the pre-forms are placed in the mold cavity, the mold must be heated to facilitate the curing of the material that has a heat sensitive catalyst milled into it
Placing the pre–forms. The pre-forms are placed into the cavity of the heated mold, and then the mold is closed.
Applying heat and pressure. Heat and pressure is applied to the mold and, consequently, the pre-form. This causes the material to fill and conform to the shape of the mold cavity. Any excess material is free to leak out of the mold cavity.
Ejecting the molded component. Once the component has been formed, it is released from the mold.
Removing excess material. If the molded component has excess material (i.e., flash), it is removed.
Advantages of Compression Molding
Compared to other molding and manufacturing methods, compression molding offers a number of advantages, including the following:
Broad design flexibility. The compression molding process is highly versatile. It can be used to produce a wide range of components in various shapes, sizes, and complexities.
Strong parts. Compression-molded parts generally have little to no residual stress.
Less waste generation. Compared to injection molding and transfer molding, compression can generate less material waste. This quality makes it ideal for molding operations involving expensive materials.
Low tooling costs. The compression molding process requires tooling that is much simpler and, consequently, less expensive than the tooling used in the injection molding or transfer molding processes.
Suitability for large parts. Since material is loaded directly to the mold cavity, the part has less weight limitations except for those imposed by the size and pressure capacities of the press and the way the mold is designed.
Partner with the Experts at ETI for Your Compression Molding Needs
If you’re looking for the right partner for your next compression molding project, turn to the experts at Elastomer Technologies, Inc. (ETI). We are an industry-leading contract molding provider. One of our core service offerings is compression molding. We can compression mold a variety of materials, including butyl, EPDM, nitrile, polyisoprene, silicone, and Viton®, into parts of a wide range of sizes and complexities.
Compression molding uses a heated mold in combination with precise amounts of material and applied pressure to create solid components from a wide range of available and custom formulated materials. In this blog, we offer a concise overview of the compression molding process, its benefits, and its uses for various industries.
What is Compression Molding?
Compression moldingis a highly specialized manufacturing process that uses heated reusable molds and melted thermoset materials to create highly accurate and exceptionally strong components. The process applies intense pressure to force the molten material firmly into all mold cavities, which makes it ideal for producing components with complex geometries or fine details. Compression-molded materials also exhibit an exceptionally high level of strength due to the permanent cross-linking of molecules in the material during the molding process.
The Compression Molding Process
The compression molding process can be broken down as follows:
Design and fabricate a mold around the exact specifications of the desired component.
Heat the mold and and place the specified material into the preheated mold, and close the mold.
Apply extremely high pressure to the material in the mold to remove air and fill all available space, so that even the most detailed components are completed to a high degree of accuracy.
Allow the material to cure and solidify, then remove from the mold cavity.
Compression Molding Uses and Applications
Thermoset materials used in the compression molding process exhibit a favorable strength-to-weight ratio, which facilitates the production of parts that are precise, strong, and low weight. This makes compression molded components ideal for a variety of applications, touching every market segment including:
Material handling tools
Construction and architectural components
Advantages and Disadvantages of Compression Molding
Compression molding offers some unique advantages over other molding processes:
Enhanced component material strength. The combination of heat and pressure result in exceptionally strong components.
Superior detail and accuracy. The application of pressure ensures that every detailed cavity of the mold is filled, resulting in components with a high degree of detail and precision.
Cost-effectiveness. Compression molding creates exceptionally durable, accurate components at a lower overall cost than other production methods. Because the mold is reusable, the process can be used for production runs at relatively low costs.
Metal replacement. Due to their high strength and lightweight nature, compression molded thermosets are often used to replace metal components in various aerospace, industrial, and automotive assemblies and medical components are molded with this method as well.
Although compression molding offers a wide range of benefits, it is not necessarily the best option for all parts. The cycle times are often longer than comparable molding processes, and the cost offset by additional cavities in a mold to make more parts per process cycle which will increase the cost of tooling.
Common Rubber Materials in Compression Molding
Compression molding can be used to create components from a wide range of polymers, including:
What is the Difference Between Injection Molding and Compression Molding?
Although injection molding and compression molding are similar, they exhibit some distinct differences:
Injection molding is ideal for small parts, while compression molding can be used for much larger components.
Injection molding is faster, as it does not require the same amount of finishing work.
Compression molding equipment has excellent production capacity and gains economies of scale through multi cavity tooling, which makes it better for high-volume production runs.
Compression molding equipment is easier to repair and maintain than injection molding.
Compression Molding Services at Elastomer Technologies
With more than 40 years of experience, Elastomer Technologies is a leading expert in compression molding and fabrication services. We pride ourselves on providing quality manufactured products using equipment and processes that meet and exceed even the most stringent industry standards.
Rubber molding is a manufacturing process that uses pre-shaped molds to create parts and components from uncured rubber. Depending on the product and specifications, there are several different rubber molding method options—such as compression molding, transfer molding, and injection molding—each of which comes with unique considerations and best use cases.
In the following blog post, we offer an overview of the above three methods, outlining their process steps, tooling considerations, design and material considerations, and applications.
Overview of Liquid Injection Molding
Liquid injection molding (LIM) is a highly versatile and cost-effective rubber fabrication method that involves injecting liquid silicone rubber (LSR) compounds into a high quality injection mold. Once injected into the heated mold and cured, the material maintains the shape of the mold, thereby producing a detailed component. The process readily accommodates automation, enabling it to be used to complete large production runs in a short period of time.
Tooling Considerations for LIM
Although LIM is quick and efficient, it is not ideal for all applications. For example, the process may not be suitable for producing prototypes for manufacturing operations. The upfront cost of creating the mold, lead times, set-up cost, process validation cost and material costs can be limiting factors.
Design and Material Considerations for LIM
Liquid injection molding operations utilize liquid silicone rubber. The material is particularly useful because it is consistently produced and has a useful range of temperature and mechanical properties. Its shrink rate is fairly predictable but as it cures after ejection may continue to shrink so it is important to consider shrinkage when designing a liquid injection molded part.
Silicone likes to move into spaces in a mold so its flow characteristics can be of benefit when filling very thin walls and other complex geometry. However, this same characteristic can create flash issues at parting lines of molds. It is also important to note that when variable geometry in a part is required it can create pressure variations as the liquid silicone moves through a mold. It is important for LSR molding that gate locations, gate sizes and venting in molds be used to optimize the process.
There are many suppliers and distributors of liquid silicone rubber to be found and they all have many pre-designed and manufactured compounds that can be employed. Custom compounding of liquid silicone material is rare, but in the right application it can be done. However the cost is usually quite high and the lead time can be very long.
Be aware that the cost, availability and use of liquid silicone should be part of the research done by a designer or customer. Molders can be of great assistance in narrowing the field of available materials and suppliers and all have preferences based on experience but picking a material for a product and process is ultimately the customer’s decision.
Applications and Uses of LIM
By altering injection pressure and speed, process temperatures, and clamp pressures, industry professionals can easily tailor the LIM process to suit a wide range of part and production needs. They can also integrate automation components to increase the level of precision and accuracy achievable and decrease the need for post-molding operations, saving manufacturers both time and money.
The LIM process can be a cost effective method of manufacturing high volumes of simple geometry and complex products. Typical parts produced include electronic components, isolators, O-rings, and seals for use in the aerospace, medical, consumer and automotive industries.
Liquid silicone rubber is a versatile material that has low surface energy and a broad temperature range. This along with other properties makes it an excellent choice for medical device components. It can be formulated to be both conductive and non-conductive allowing it to be useful in electrical applications. Silicone can be colored and this along with its finish gives it aesthetic appeal. Its elasticity provides an avenue for designing specific mechanical applications.
Overview of Compression Molding
Compression molding involves the compression of specific compounds of catalyzed rubber between two halves of a heated mold while applying tremendous pressure. Once released from the mold by hand, the cured material holds the internal shape of the mold producing a specific part.
Tooling Considerations for Compression Molding
The tooling for compression molding typically consists of two pieces of steel or sometimes aluminum that, when put together, form an enclosed space that creates a part. One side of the mold may be machined to create the outside geometry of a desired part and the other side might contain the details of the inside of a part.
The costs associated with building the mold are directly related to the amount of complexity required to be machined into the mold to make the desired design. The more complex or the larger the part, the number of cavities that are requested to be made that make individual parts in a mold, the time and type of material used to make the mold all go into the cost.
Additionally there is a cost to set-up and test new molds that is usually folded into the mold cost. This would include press time, material cost and any additional cost estimated by a molder.
Material and Design Considerations for Compression Molding
Compression molding can be used to manufacture a startlingly wide variety of products. The diversity of compounds within the types of material is nearly limitless allowing it to be designed to make parts that can perform with specific mechanical requirements, chemical resistance properties, and environmental qualifications.
The compression molding process may not display the same level of accuracy and precision, which makes it less suitable for products where tight dimensional tolerance is critical and where flash and parting line shift may cause issues. This makes trimming of parts, and nitrogen de-flashing of parts a go–to solution for some of these issues.
Applications and Uses of Compression Molding
The compression process is useful for the production of large or small parts with varying degrees of complexity usually lending itself better to smaller quantities of parts as it is slower and more labor intensive than injection molding of rubber. Designers and engineers often employ it for prototyping and sample production operations to test out new part or product designs. However, this process can be used successfully to make high quantities of parts.
Any industry can benefit in the use of compression molding rubber parts. Medical, oil and gas, aerospace, electronics, automotive and other consumer products companies all use products made with compression molding.
Overview of Transfer Molding
Similar to compression molding, the transfer molding process requires the use of pre-measured and positioned material. However, it offers greater precision and is less prone to flash on parting lines as the two halves of the mold that contain the part geometry are closed together before material enters the part detail in the mold. Compared to injection molding, it is much slower since the material is placed by hand in the mold and the part removed by hand forms the mold once molded.
Tooling Considerations for Transfer Molding
While tooling is similar to compression molding it has some advantages for specific parts. The pot and piston design allows better efficiency and precise distribution of material in the mold. This can be beneficial for parts where gate location may be critical to effectively fill a thin wall or in a larger part that might require a pressurized distribution of material to fill more effectively or a multiple cavity mold saving time in loading many individual cavities with material.
Choosing the right material can be very important. Aluminum molds can have problems with parting lines when molding some materials and the constant opening and closing of molds can create wear and tear. Steel is preferred for production tooling and different types of steel including pre-hardened alloy, hardened material, stainless steel and even more exotic material such as titanium can be employed in specific applications.
Design and Material Considerations Transfer Molding
Compared to both compression molding and injection molding, transfer molding usually generates less material waste because overflows in the mold are usually not needed. It does produce waste in the form of leftover material in the transfer pot and sprues leading to the gates where the material enters the cavity in the mold. After the molded product solidifies, this material must be removed and discarded as it is a thermoset material and cannot be reused.
When designing a transfer mold, it is important to consider the above. Ideally, the mold should produce the highest quality part in the shortest cycle time with the least amount of scrap. Partnering with an experienced mold maker can help achieve this goal.
Material used in transfer molding is usually the same range of materials used in compression molding.
Applications and Uses of Transfer Molding
Transfer molding is faster than compression molding and less expensive than injection molding, qualities that make it ideal for use in the manufacture of parts in small production runs. However, like compression molding it produces an amount of waste, and this has to be measured against the cost of the material being employed.
As with compression molding, any industry can benefit in the use of transfer molding of rubber parts. Medical, oil and gas, aerospace, electronics, automotive and other consumer products companies all use products made with compression molding.
Molding Services at Elastomer Technologies, Inc.
Liquid injection molding, compression molding, and transfer molding are three commonly employed rubber production methods. Each offers unique benefits and limitations that suit them for different applications.
At Elastomer Technologies, Inc. (ETI), we are well-versed in all three methods, enabling us to meet a wide range of rubber molding needs. Our customer base is highly diverse, ranging from aerospace and automotive to food processing and medical. By partnering with us, they benefit from our:
Over 35 years of industry experience
Commitment to superior customer service
Continuous improvements to our molding techniques and technologies
To learn more about rubber molding or our services and capabilities, reach out to us today.