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Everything You Need to Know About Compression Molding

It is a diverse method that is useful to make different parts, from aircraft pieces to little baby-bottle pumps, by small and big production businesses. Thermosetting polymers are made by this method. The substance can be granule or sticky, and it can be free-flowing. The material is poured into a hot mold, which is then sealed with a hydraulic cylinder.

It is a simple technique in which the element is put in an empty, heated mold cavity or form utilizing a two-part mold system. If you want to know about the process and benefits of this type of molding, read the following guide.

compression molding

What Is Compression Molding?

It is a method in which two heated molds compress a defined amount of molding element (known as a charge) into a specific shape.

This is a technique that involves placing a polymer into an empty, heated mold cavity. The mold is then squeezed and sealed with a top cap to ensure that an element contacts all sections. This method may create pieces in a variety of lengths, densities, and complexities. The things it creates are hard, making it suitable for a variety of industries. The most frequent type of element employed in molding is thermoset composite.

Step by Step Compression Molding Process Explained

The technique has four key steps:

1.A two-part metallic element is developed that fits the specifications necessary to manufacture the desired product. Preheat the material and insert it into the machine. Machining, castings, and 3D printing are all options for producing tooling.
2.The suitable composite is pre-shaped into the product’s shape. Pre-forming is a beneficial operation that improves the final part’s efficiency. Washing the mold, switching on the heat, or other set-up operations may be needed based on the equipment or technology you’re operating.
3.The warm mold receives the pre-formed portion. The element is then crushed under high pressure, often between 800 – 2000 psi.
4.After the tension is reduced, the piece is withdrawn from the machine. At this moment, any resin shining around the edges is removed.

Compression Molding vs Injection Molding

These two are different methods. Below is mentioned difference between two:

Compression Molding

It starts with warm plastic being placed in a heated form and being compressed into specific dimensions. The part is taken from the mold and fixed once it has dried to keep its structural stability.

There are so many benefits of using this type of molding:

Compression molding, like most types of injection molding, is a cost-effective technology, but it has several unique benefits, including:

* It will let you accommodate uniform pieces with varying lengths and widths.
* Durability: Compression-molded materials are often more durable.
* Minimal Trash: It generates less plastic pollution, making it more environmentally friendly.
* It may not be the most efficient alternative if the design has complex geometrical patterns and different sizes.

When to Use the Process?

Designers use this process for goods that are subjected to high levels of pressure. As a result, this technology is employed to manufacture appliances and car parts. You can use it to create:
* Circuit breakers or electrical switchgear
* Handles for brushes and mirrors
* Knobs for the stove or cookware

Most of these things have a minimal design, allowing molding appropriate for high-volume manufacture.

Injection Molding

For the creation of plastic pieces, it is the widely used method. Polymer is melted and pumped into a mold, where it acquires shape over time. Once inserted, the plastic starts to occupy the mold’s holes and is allowed to cool and solidify.

What Are Injection Molding’s Advantages?

The injection process, unlike compression molding, is a low-cost way to produce a large number of durable pieces in a short amount of time. It does have a few benefits over compression molding:

* Part Personalization: You can modify the size of pieces and regulate cavities separately.
* Complex Mold Layout: This type of molding is easy, can support different designs and modify molds.
* Material Flexibility: It can work with a variety of thermoplastics.

When to Use the Process?

Because of its adaptability to shape complicated objects, this type of molding is used for different products. The following are some examples of things that gain from the injection molding:
* Components for aerospace, electronics, and automobiles
* Dental and medical lab goods
* Models in engineering
* Windows and doors

Although these two techniques are similar, there are a few differences between these methods. Molds are sealed across the load in compression molding, and the charge is introduced into a sealed mold cavity in injection molding.

Compression or injection molding is commonly used by today’s manufacturers, although for distinct types of materials. Compression molding is a good choice for relatively easy models, like ultra-large shapes that can’t be generated using extrusion methods. Injection molding is a good choice for even more hard elements.

Advantages & Disadvantages of Compression Molding vs Injection Molding

There are many benefits to using it for latex or plastic parts operations:

It Is a Less Complicated Process

In comparison to other molding and manufacturing methods, this method is comparatively simple and uncomplicated. It makes things easy for workers to complete some layouts, resulting in cheaper total production costs.

It Entails Cheaper Tooling Expenses

It does not necessitate the use of specialized equipment or tooling. As a result, the project’s necessary equipment and instruments are simpler, requiring less capital expenditure. Even though it is a lengthy method, when done correctly, the damage on the molds during processes is minimal, leading to less maintenance over time and reduced cost estimates for customers.

It’s a Great Option for Multi-Color Molding or Inserts Molding

This method includes different kinds of insert molding and dual-color molding without the cost of specific equipment, replacement parts, high set-up, or manufacturing costs utilized in silicone when performed with the proper solution to tooling.


This method is appropriate for small and medium manufacturing runs owing to its low equipment and installation costs. It’s utilized to make models or samples of concepts before moving forward with full-scale production.

Because compression molding involves feeding the piece into the mold cavity, there are no part mass restrictions other than those given by part form and equipment. As a result, it can handle the higher quantities of raw resources required to produce larger products and materials.

Although compression molding has several benefits for customers wishing to build a new production line, it has certain drawbacks, including:

It Is More Likely to Incur Post-molding Expenditures

The stuff’s size and mass should be examined to the pressing force needed to shut and maintain the mold closed throughout a molding cycle. Even if it is great, expect control concerns, which may need cutting or nitrogen deflashing of the parts, which will increase the costs.

It Takes Longer to Process

When opposed to other methods, it takes longer to cure the elements. In higher-volume operations, these lengthier processing times can have an impact on production rates.

The Applications of Compression Molding

It is a high-pressure casting technique used to create complicated, high-strength fiberglass reinforcements. Unidirectional tapes, knitted textiles, arbitrarily oriented fiber mat, and diced strands can all be used to compression mold composite materials thermoplastics. This process has the advantage of being able to shape complex pieces. As compared to other molding procedures, it is one of the most cost-effective. It wastes very little material, providing it an edge when dealing with valuable compounds.

The process may result in uniformity and trouble controlling blinding, and it is not appropriate for all parts. Fewer knit lines are formed and less fiber length deterioration is apparent. It can be used to make ultra large shapes. It was invented to build composite elements for metal substitution applications. It’s commonly applied to make bigger flat or curved sections.

You can use this method in the production of automobile parts like hoods, bumpers, scoops, spoilers, and other smaller, more complicated elements.

Materials for Compression Molding

Polyester fiberglass resin materials (SMC/BMC), Vespel, PPS, and types of PEEK are commonly made by this method. A thermoplastic polymer composite is crushed to fill each aspect of the mold, providing things with different thicknesses, widths, and detail.

There are six crucial aspects that a designer should remember when compression molding:

* Choosing the right volume of material
* Identifying the energy needed to burn the material
* Calculating the shortest time to melt the element
* Choosing the most appropriate method
* Estimating the force needed to make sure that the projectile is shaped correctly
* After the substance has been crushed into the cast, the mold should be designed for fast cooling

Factors Affecting the Process

Compression molding, like other manufacturing techniques, is affected by a variety of parameters.

If the polymer isn’t melted to the proper temperature, it can fail to occupy the mold’s hole. If the thermoplastic polymer is overheated, it may cause large pressure and necessitate a prolonged cooling period. Variable compression heating techniques are available, which will alter the process’ efficiency. Due to its potential to mass-produce synthetic plastics and objects with minimum wastage, it’s a favorite choice between industrial companies.


The process can be beneficial to different industries. The process can manufacture detailed designs and layouts. It is a cost-effective method for creating different elements. The possibilities are nearly unlimited, as it is well-suited to many industries.

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