SMC (Sheet molding compounds)

SMC or Sheet Molding Compounds consists of the molding of a thermostable resin generally reinforced with fiberglass in the form of cut or continuous threads, obtaining the final piece through polymerization of the resin by applying pressure and temperature.

This manufacturing method has a preliminary stage in which the prepreg is created that will later be used to make the desired final piece. This pre-process is based on using fiberglass rovings in continuous cords that are cut into pieces (about 5cm) on a layer of resin filling transported on a polyethylene film. Subsequently, once the lower layer has all the fibers distributed, another layer of resin filling is placed on top of the first, forming a sandwich. This sandwich is compacted and rolled on calibrated packaging rollers.

The prepreg rolls will be stored to let the fiber settle with the thermoset matrix.

Glass fibers can be presented not only as cut fibers, but there are also cases in which continuous threads are used or as a mixture of both (continuous threads and cut fibers), in the latter case the best mechanical properties would be obtained.

Finally, the rolls of composite material are taken to a press, where they are cut with the appropriate configuration for the part to be obtained and placed in a tight, heated metal mold. Subsequently, the hydraulic press is closed and the SMC flows uniformly under pressure throughout the mold, forming the final product.

The main features are:

It is a process that, due to its high automation capacity, is mainly used in large series production, with the automobile being its main sector (hoods, front panels...). This phenomenon makes SMC currently the most used method in the manufacture of composite materials with thermoset resins.

Injection

Infiltration of composite materials by injection uses the same technology as traditional plastic injection molding. But unlike introducing only a polymer (either thermoplastic or thermoset) into the mold, the polymer plus a reinforcement is introduced.

The most used fibers are glass, carbon and aramid. These reinforcements significantly affect the mechanical properties of the final material. But on the other hand they present some drawbacks such as:

Pultrusion

It is a very versatile automatic process through which constant section profiles are obtained.

A fiber embedded in a thermostable resin is used, which reacts when heat is applied. The material is pulled (pull) to avoid breaks and misalignment of fibers.

Through this process any complex section can be produced as long as its thickness is constant. Furthermore, due to the precision of the mold surface, high quality finishes are obtained.

However, the process speed is relatively low (3 m/min) compared to the extrusion speed (30 m/min). Furthermore, it is very difficult to orient the fibers at optimal angles.

Description of the process:.

The pultrusion process consists of several stages:

RTM (Resin Transfer Molding)

It is a closed mold manufacturing process at low pressure. It can be summarized in five stages:

Due to the possibility of molding the fibers dry before injecting the resin, a better orientation of the fibers is achieved, increasing the mechanical properties of the material.

SMC (Sheet molding compounds)

SMC or Sheet Molding Compounds consists of the molding of a thermostable resin generally reinforced with fiberglass in the form of cut or continuous threads, obtaining the final piece through polymerization of the resin by applying pressure and temperature.

This manufacturing method has a preliminary stage in which the prepreg is created that will later be used to make the desired final piece. This pre-process is based on using fiberglass rovings in continuous cords that are cut into pieces (about 5cm) on a layer of resin filling transported on a polyethylene film. Subsequently, once the lower layer has all the fibers distributed, another layer of resin filling is placed on top of the first, forming a sandwich. This sandwich is compacted and rolled on calibrated packaging rollers.

The prepreg rolls will be stored to let the fiber settle with the thermoset matrix.

Glass fibers can be presented not only as cut fibers, but there are also cases in which continuous threads are used or as a mixture of both (continuous threads and cut fibers), in the latter case the best mechanical properties would be obtained.

Finally, the rolls of composite material are taken to a press, where they are cut with the appropriate configuration for the part to be obtained and placed in a tight, heated metal mold. Subsequently, the hydraulic press is closed and the SMC flows uniformly under pressure throughout the mold, forming the final product.

The main features are:

It is a process that, due to its high automation capacity, is mainly used in large series production, with the automobile being its main sector (hoods, front panels...). This phenomenon makes SMC currently the most used method in the manufacture of composite materials with thermoset resins.

Injection

Infiltration of composite materials by injection uses the same technology as traditional plastic injection molding. But unlike introducing only a polymer (either thermoplastic or thermoset) into the mold, the polymer plus a reinforcement is introduced.

The most used fibers are glass, carbon and aramid. These reinforcements significantly affect the mechanical properties of the final material. But on the other hand they present some drawbacks such as:

Pultrusion

It is a very versatile automatic process through which constant section profiles are obtained.

A fiber embedded in a thermostable resin is used, which reacts when heat is applied. The material is pulled (pull) to avoid breaks and misalignment of fibers.

Through this process any complex section can be produced as long as its thickness is constant. Furthermore, due to the precision of the mold surface, high quality finishes are obtained.

However, the process speed is relatively low (3 m/min) compared to the extrusion speed (30 m/min). Furthermore, it is very difficult to orient the fibers at optimal angles.

Description of the process:.

The pultrusion process consists of several stages:

RTM (Resin Transfer Molding)

It is a closed mold manufacturing process at low pressure. It can be summarized in five stages:

Due to the possibility of molding the fibers dry before injecting the resin, a better orientation of the fibers is achieved, increasing the mechanical properties of the material.