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What Is Sheet Molding Compound (SMC)?

Sep 28, 2021 ·
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There are many materials and composites used in the manufacturing of automotive parts. They offer different benefits in terms reinforcement and protection in the event of an accident.

From fiber-reinforced plastics (FRP) to bulk molding compound (BMC) to sheet molding compound (SMC), each has its own use in the automotive space. In this article, we’ll focus on what SMC is and what makes it suitable for the industry.

How Is SMC Made?

SMC is a reinforced polyester material that features carbon or glass fibers that are typically an inch or more in length. These long strands of fiber are suspended or spread out in a resin bath made of a mixture of vinyl ester, polyester or epoxy.

The combination of the resin and long fibers produces a strong final product. SMC is typically sold in rolls that can be cut into smaller pieces known as “charges.”

Production of SMC occurs to ensure the fibers and resin are fully integrated. Resin gets applied to a film in the form of a paste. Fibers are then cut and added to the resin.

Next, this mixture is squeezed and compacted between two pieces of film. Once the right texture and thickness is reached, it gets stored for several days. Heat and pressure are then applied in a process called compression molding, which cures the SMC and creates the final product.

Compression Molding

The process of compression molding allows SMC to be formed into a range of parts that vary in thickness, length and detail. From simple to complex parts, compression molding takes preheated SMC and uses a hydraulic press to compress it to the desired shape.

The hydraulic press typically features the upper and lower half of a mold between two heated plates. SMC is poured into one of the mold cavities, and the upper portion of the mold is lowered. Pressure of up to 2,000 pounds per square inch (PSI) is applied.

Advantages of SMC

There are several benefits to using SMC for manufacturing different car parts. One of the advantages is that SMC is lightweight compared with other materials.

This has caused SMC to replace different metal components and become one of the primary materials used on auto parts. In fact, when SMC was introduced, it was seen as a revolution in parts manufacturing and shifted the industry to metals vs. polymer-based compounds.

Even though SMC is lightweight, it’s still a durable material that works to resist impact.

SMC can also be easily produced at a high volume. The compression molding process is straightforward and provides a short production cycle. This makes it a cost-effective, reduced-waste choice for manufacturers.

SMC FAQs


What car parts commonly use SMC?

Several outer-vehicle body parts utilize SMC — this goes for passenger vehicles and lightweight trucks. SMC parts include door assemblies, body panels, roof panels, spoilers, fenders and bumpers.

What damage does SMC experience in an accident?

During an accident, the most common damage to SMC is cracking. In severe situations, part of the panel might be torn off completely.

What does FRP mean?

FRP is an abbreviation for fiber-reinforced plastics. They are composite substances that are made of a polymer matrix and strengthened by fibers. SMC is a type of FRP.

How is SMC repaired?

When repairing SMC, a repair adhesive specifically designed for it can be used. It can either be a two-part urethane or epoxy adhesive. Loose or damaged fibers are removed and, in the case of a hole, a piece of scrap material can be used as a patch it if it’s the same kind of material. Proper sanding techniques are then used to ensure a quality repair.

What’s the difference: SMC vs. fiberglass?

SMC is a combination of glass-fiber and polyester material molded into panels using a compression process. Fiberglass is glass strands that are woven into cloth or matted together. The fiberglass matting or cloth is placed in a mold, then pure resin with a hardener is applied to form the part.

Learn All About Collision Repair at UTI

Accidents happen every day, which means there are plenty of opportunities for those interested in pursuing a career as a collision repair technician.1

The Collision Repair & Refinish Technology (CRRT) program offered at Universal Technical Institute (UTI) helps teach students the skills necessary to restore and repair a wide variety of vehicles.

Courses cover a range of topics, including sheet molding compound. Though SMC repair isn’t a subject that’s taught in one of UTI’s hands-on labs, students still learn the basics of how the process works and how to repair it during a course module and presentation.

The CRRT program is available at UTI campuses in Long Beach, California, and Houston, Texas, and can be completed in just 51 to 54 weeks. The program can provide the foundational knowledge needed for an entry-level career in the collision repair industry. Find out more here.

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By submitting this form, I agree that Universal Technical Institute, Inc., Custom Training Group, Inc., and their representatives may email, call, and / or text me with marketing messages about educational programs and services, as well as for school - related communications, at any phone number I provide, including a wireless number, using prerecorded calls or automated technology. I understand that my consent is not required to apply, enroll or make any purchase.

By submitting this form, I further understand and agree that all information provided is subject to UTI's Privacy Policy available at uti.edu/privacy-policy

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