Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are maintained until the molding material has cured; this process is known as compression molding method and in case of rubber it is also known as ‘Vulcanisation’. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms.

Compression molding is a high-volume, high-pressure method suitable for molding complex, high-strength fiberglass reinforcements. Advanced composite thermoplastics can also be compression molded with unidirectional tapes, woven fabrics, randomly oriented fiber mat or chopped strand. The advantage of compression molding is its ability to mold large, fairly intricate parts. Also, it is one of the lowest cost molding methods compared with other methods such as transfer molding and injection molding; moreover it wastes relatively little material, giving it an advantage when working with expensive compounds.

However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection molding. Compression-molding is also suitable for ultra-large basic shape production in sizes beyond the capacity of extrusion techniques. Materials that are typically manufactured through compression molding include: Polyester fiberglass resin systems (SMC/BMC), Torlon, Vespel, Poly(p-phenylene sulfide) (PPS), and many grades of PEEK.

Compression molding is commonly utilized by product development engineers seeking cost effective rubber and silicone parts. Manufacturers of low volume compression molded components include PrintForm, 3D, STYS, and Aero MFG.

Compression molding was first developed to manufacture composite parts for metal replacement applications, compression molding is typically used to make larger flat or moderately curved parts. This method of molding is greatly used in manufacturing automotive parts such as hoods, fenders, scoops, spoilers, as well as smaller more intricate parts. The material to be molded is positioned in the mold cavity and the heated platens are closed by a hydraulic ram. Bulk molding compound (BMC) or sheet molding compound (SMC), are conformed to the mold form by the applied pressure and heated until the curing reaction occurs. SMC feed material usually is cut to conform to the surface area of the mold. The mold is then cooled and the part removed.

Materials may be loaded into the mold either in the form of pellets or sheet, or the mold may be loaded from a plasticating extruder. Materials are heated above their melting points, formed and cooled. The more evenly the feed material is distributed over the mold surface, the less flow orientation occurs during the compression stage.^[3]

Compression molding is also widely used to produce sandwich structures that incorporate a core material such as a honeycomb or polymer foam.

Thermoplastic matrices are commonplace in mass production industries. One significant example are automotive applications where the leading technologies are long fibre reinforced thermoplastics (LFT) and glass fiber mat reinforced thermoplastics (GMT).

In compression molding there are six important considerations that an engineer should bear in mind:

Determining the proper amount of material.
Determining the minimum amount of energy required to heat the material.
Determining the minimum time required to heat the material.
Determining the appropriate heating technique.
Predicting the required force, to ensure that shot attains the proper shape.
Designing the mold for rapid cooling after the material has been compressed into the mold.

Compression mold making is a manufacturing process used to produce parts and products by compressing a material, typically a thermosetting plastic or rubber compound, within a mold cavity under high pressure and heat. This process involves several steps:

Preparation of Materials: The raw material, usually in the form of pellets, powders, or preforms, is prepared and placed into the mold cavity.
Closing the Mold: The mold, consisting of two halves, is closed under high pressure, clamping the material between them.
Applying Heat and Pressure: Heat and pressure are applied to the mold, causing the material to soften and flow to fill the cavity completely.
Curing or Solidification: The material undergoes a curing process, where it hardens or solidifies into the desired shape.
Cooling and Removal: After the material has solidified, the mold is cooled, and the part is removed from the mold cavity.

Compression mold making is often used to produce parts with intricate shapes, high strength, and dimensional stability. It is commonly employed in industries such as automotive, aerospace, electrical, and consumer goods manufacturing.

Compression Mold Making Materials

Compression mold making typically involves materials that can be molded under pressure and heat. Some common materials used in compression molding include:

Thermosetting Plastics: These are polymers that, once cured, cannot be remelted or reshaped. Examples include:
- Phenolic resins
- Epoxy resins
- Polyester resins
- Polyurethane resins
Composite Materials: These are materials made from a combination of different constituents, such as fibers and resins. Examples include:
- Fiber-reinforced plastics (FRP)
- Carbon fiber composites
- Glass fiber composites
Rubber: Some types of rubber can also be compression molded, such as:
- Silicone rubber
- EPDM rubber
- Nitrile rubber
Bakelite: Bakelite, a type of phenolic resin, was historically one of the first materials used in compression molding and is still used in some applications today.

The choice of material depends on the specific properties required for the molded part, such as strength, durability, heat resistance, and chemical resistance.