Bulk Molding Compounds (BMC) and Sheet Molding Compounds (SMC) are both fiber reinforced materials. So how are they different and how do we choose them? This article will give you a detailed introduction.
What is SMC
Sheet Molding Compound (SMC) is an unsaturated polyester (or vinyl) resin-based, chopped glass fiber (usually 1 inch) or other fiber like natural fiber reinforced composite compound material. Other different functional fillers and agents like shrinkage additive, pigment, release agent, catalyst, etc are added to formulate it to be a stable, moldable material for producing various complex components. (Sheet Molding Compound wikipedia)
SMC has even longer fiberglass which strengthens the material for producing stronger, larger products. In some conditions, continuous glass fiber or even glass fiber mat is used to strengthen SMC material.
SMC Characteristics
The SMC material has light weight, high mechanical strength, electrical insulation, fire resistance, corrosion resistance, heat resistance, weather resistance, low shrinkage, stable dimensional control, and uniform material thickness.
SMC material is the best material for heavy duty truck/body parts (Class A surface) manufacturing.
Main applications of SMC
Sheet Molding Compound （SMC）is widely used for producing electrical insulation, fire, corrosion, or heat resistant components, structural components in various industries like agriculture, automotive, construction, electrical, energy, HVAC, lighting, military, rapid transit, security, solar/wind energy, telecom, etc.
SMC Composites vs Ordinary Composites Comparison Table
Feature
SMC Composites
Ordinary Composites
Material Composition
Oil-free design, no lubrication required
Typically require oil for lubrication
Manufacturing Process
Low maintenance, no oil changes needed
Requires regular oil maintenance and checks
Strength-to-Weight Ratio
Compact and lightweight, ideal for small spaces
Larger and heavier due to oil components
Surface Finish
Superior surface finish, ideal for visible parts
Often requires additional processing for a smooth finish
Applications
Automotive bumpers, construction panels, and electrical housings
Aerospace, sports equipment, and high-performance automotive parts
The table above provides a clear comparison between SMC Composites and ordinary composites, highlighting their unique features, advantages, and common applications.
What is BMC
Bulk Molding Compound (BMC) is an unsaturated polyester (or vinyl) resin-based, short glass fiber (usually 3mm, 6mm, 9mm), or other fiber like natural fiber reinforced composite compound material. (Bulk Molding Compound (BMC) wikipedia)
Other different functional fillers and agents like shrinkage additive, pigment, release agent, catalyst, etc are added and evenly stirred to formulate it to be a stable, moldable material for producing different complex components.
Fiberglass in BMC is shorter than that in SMC, so BMC material flows even better than SMC and can be made for a better finish or more complex.
BMC Characteristics
Lightweight, electrical insulation, fire-resistant, corrosion-resistant, heat resistant, weatherproof, low shrinkage, stable dimension control, superior flowing ability, those varieties of special properties rolled into one, making bulk molding compound (BMC) a most ideal material for making small but more complex, precise products that are used in various industries.
Main applications of BMC
Bulk molding compound (BMC) is a superb material for gaining cost-effective but high-performance products. Usually, you can replace metal, thermoplastic materials, phenolic, or epoxy using BMC if you want to gain the above properties or cut down costs.
It is widely used for producing electrical insulation parts, motor brackets, automotive headlamp housings, and a variety of structural and protective components for different industries.
BMC Composites vs Ordinary Composites Comparison Table
- Here’s an optimized comparison table between BMC Composites and Ordinary Composites
Feature
BMC Composites
Ordinary Composites
Material Composition
Made from chopped glass fibers, thermosetting resins, and fillers
Typically made from continuous fibers like carbon, glass, or aramid with various resins
Manufacturing Process
Low-pressure injection or compression molding, ideal for complex shapes
Varies by type: hand lay-up, vacuum infusion, or autoclave molding
Electrical Properties
Excellent insulation and arc resistance, suitable for electrical enclosures
Electrical properties vary based on resin and fiber combination
Thermal Properties
Heat resistant and thermally stable, ideal for high-temperature environments
Varies by material; some composites are heat resistant, while others may degrade under heat
Environmental Impact
Non-toxic, recyclable, and environmentally friendly
May or may not be recyclable, depending on resin type and manufacturing process
The table above provides a clear comparison between BMC Composites and ordinary composites, highlighting their unique features, advantages, and common applications.
Differences Between SMC & BMC
SMC & BMC Material Properties
Sheet Molding Compounds (SMC) and Bulk Molding Compounds (BMC) are both fiber reinforced materials, typically utilizing glass strand fibers of varying lengths. The difference is that SMC has a higher specific gravity of glass reinforcing fibers and higher stiffness; BMC has a higher specific gravity of the blend filler, so the cost is lower.
The glass fibers in SMC are longer and have higher mechanical properties; the glass fibers in BMC are shorter, have lower relative mechanical properties, and have little difference in insulating properties.
SMC & BMC Material Manufacturing Process
SMC material is made by compressing sheets of resin, glass fibers, and fillers in a heated mold, resulting in stronger, stiffer parts, ideal for automotive and large appliances.
BMC material is produced by mixing resin and glass fibers into a bulk form, then molded through injection or compression molding. It uses shorter fibers, making it more cost-effective but with slightly lower strength compared to SMC material. BMC is ideal for smaller, intricate parts like electrical components.
In short, SMC material is better for large, high-strength parts, while BMC material offers a more affordable option for smaller, complex components.
Which Material is BMC or SMC Suitable for My Project?
In general, when the mechanical properties of the products, including tensile strength, bending strength and impact strength, etc. are higher, the surface area of the products is larger, and the lightweight of the products is higher, SMC will be selected.
In general, the requirements for economic cost control are too high, and the mechanical strength requirements are lower than SMC requirements; When the electrical properties and flame retardant properties of the products are higher; When the surface area of the product itself is small, people usually choose BMC.
At HAMC, we are the main supplier of SMC and BMC materials. And we are also one of the largest composite material manufacturers in China. We can provide the best material for your project and provide the most reasonable solution. If your project needs to use SMC material or BMC material, please contact us. We can help you！
