Low-Tonnage SMC/BMC Molding: Efficient Solutions for Small Composite Parts

When it comes to molding smaller, detailed parts from composite materials, full-sized high-tonnage equipment often introduces unnecessary cost and complexity. At Arrowhead, our low-tonnage SMC/BMC molding capabilities give you a smarter, more efficient way to produce intricate composite parts—without sacrificing quality or performance.

This process is well-suited for applications where tight tolerances, clean surface finishes, and production speed matter more than extreme structural strength. By using smaller compression or injection presses with tailored tooling, we’re able to offer a flexible, cost-effective solution that’s ideal for many electrical, automotive, and appliance applications.

What is Low-Tonnage SMC/BMC Molding?

Low-tonnage molding uses less powerful, smaller-footprint machines to mold parts from either Sheet Molding Compound (SMC) or Bulk Molding Compound (BMC). These composite materials consist of a thermosetting resin (often polyester or vinyl ester), combined with fillers, glass fiber reinforcement, and other additives to provide specific mechanical, thermal, or chemical resistance properties.

While high-tonnage machines—sometimes up to 4,000 tons—are required for large body panels or load-bearing components, low-tonnage SMC/BMC molding focuses on the small- to mid-size parts that require precision and efficiency over brute force.

SMC vs. BMC: What’s the Difference?

Both SMC and BMC are versatile and widely used in the composites industry, but they each offer unique advantages depending on the application.

Sheet Molding Compound (SMC):

SMC is a leather-like sheet material reinforced with longer glass fibers (up to 25mm) and a higher fiber content. It offers superior stiffness and strength and is typically used for structural or load-bearing components. However, its flow properties are limited, making it better suited for simpler geometries.

Bulk Molding Compound (BMC):

BMC is a putty-like material with shorter fibers (up to 12.5mm) and better flow properties. This makes it ideal for molding parts with intricate details, complex shapes, or fine surface features. BMC is often more cost-effective than SMC and excels in applications where electrical insulation, flame resistance, or tight tolerances are critical.

Advantages of Low-Tonnage SMC/BMC Molding

Lower Tooling Costs

Because the presses used in low-tonnage molding exert less clamping force, the molds themselves can be smaller, lighter, and less expensive to produce—especially helpful for lower-volume or frequently changing part programs.

Ideal for Small, Detailed Parts

BMC’s excellent flow characteristics allow it to fill detailed cavities, thin walls, and complex geometries that are difficult to achieve with other materials or molding processes.

Fast Cycle Times

Low-tonnage molding supports short molding cycles and is ideal for high-efficiency production, especially when using multi-cavity tools to increase output and reduce per-part costs.

High-Quality Surface Finish

Parts molded with BMC or SMC often exhibit smooth, uniform surfaces right out of the press—reducing or even eliminating secondary finishing steps.

Versatile Material Properties

These materials can be customized with fillers and additives to meet specific performance goals—such as flame retardancy, corrosion resistance, thermal insulation, or dielectric strength.

Typical Applications

Arrowhead’s low-tonnage SMC/BMC molding capabilities are ideal for a wide variety of small-to-mid-sized composite parts, including:

• Electrical Components
  BMC is a top choice for electrical housings, switchgear, meter boxes, and insulators due to its flame resistance and dielectric properties.
• Automotive Parts
  Under-hood brackets, headlamp housings, and sensor covers benefit from BMC’s flow characteristics and thermal stability.
• Appliance Components
  Handles, knobs, heat shields, and internal structural supports for small appliances can be efficiently produced using low-tonnage molding.
• Precision Structural Elements
  Where dimensional stability and tight tolerances are required—without the need for high mechanical strength—this process offers unmatched consistency.