Thermosets Offer Performance + Cost Advantages

Offering the same lightweighting benefits of thermoplastics, thermosets excel in high-heat applications exposed to harsh environments or elements found in automotive applications.

By Spencer Leffelman, Woodland Plastics

With history dating back to Leo H. Baekeland’s invention of the synthetic phenolic plastic, “Bakelite,” in the early 1900s, thermoset materials have been found in a variety of products for more than 100 years. More recently, automotive OEMs and their suppliers are using thermosets to engineer performance-driven components at low manufacturing costs. Despite its “old-technology” reputation, thermoset materials are increasingly providing new-age lightweighting solutions to applications requiring a perfect balance of high performance and low costs.

Whether looking at a metal-to-thermoset conversion of an existing product line or implementing thermosets within a new design, engineers and designers are able to use thermosets to draw out the same lightweighting benefits of thermoplastics, but toward high-heat products exposed to harsh environments or elements. Besides performance, thermoset parts may be molded with Class A surface finishes, proving their worth with not just mechanical, but cosmetic applications, as well. Because of thermoset’s many formulations and material property specifications, engineers can meet particular performance and appearance requirements using low-cost material options to bring a product to market.

What Materials are Thermosets?

Thermoset, or thermosetting plastics, are synthetic materials that strengthen when heated and cannot be remolded or re-melted post-mold. After initial heat forming, the properties of thermosets become “set,” and components are resistant to heat, corrosion and creep. In contrast to thermosets, engineered thermoplastics (nylons, ABS, polypropylene) soften or disfigure when re-heated, jeopardizing the dimensional and chemical stability of a component or product assembly. While a thermoplastic monomer has only two reactive ends for linear change growth, a thermoset monomer must have three or more reactive ends, with its molecular chains crosslinking in three dimensions. Post-mold, thermosets have virtually all molecules interconnected with strong, permanent, physical bonds that are not reversible. Theoretically, the entire molded thermoset part can be a giant, single molecule. In a sense, curing a thermoset is like cooking an egg. Once an egg is cooked, reheating it does not cause melting or disfiguration, and the egg cannot return to its original physical state.

Common thermoset molding materials include phenolic resins or phenolic molding compounds, bulk molding compounds (BMC), sheet molding compounds (SMC), epoxies and diallyl phthalates (DAP). Thermoset materials contain a base resin system that is formulated with added fillers and/or reinforcements, such as glass fibers and minerals, depending on the end-use application or market. Reinforcement fillers provide additional mechanical strength or may improve upon existing performance specifications, such as dielectric strength, UV and flammability resistance, and dimensional/chemical stability.

How Thermosets Differ from Thermoplastics

Manufacturing thermoset materials is similar to thermoplastics, but also a bit different. Thermosets may be injection, compression, injection-compression, insert, or transfer molded, with various benefits pertaining to each molding process. When injection molding thermosets, material is put into a hopper or stuffer and pre-heated at lower temperatures in the barrel of the molding machine. The preheated material is then injected into a hot mold, which is generally between 300 F and 350 F, creating a chemical reaction that “sets” the thermoset’s physical and chemical properties. Thermoplastics, on the other hand, are pre-heated at higher temperatures and then injected into a cooler mold to fill and shape the parts. Another difference between thermoset and thermoplastic materials is how the parts look coming off a press. While excess material flash signifies a “scrap part” in thermoplastics, excess material flash is required in thermoset molding to produce acceptable parts. The excess flash must then be “deflashed” from a thermoset component either manually by using a hand file, dowel or other utensil, or may be deflashed automatically by a Wheelabrator machine, which tumbles parts while simultaneously shooting bits of media at a part to clean away excess material flash in smaller holes or odd dimensions that may be difficult or time consuming to remove by hand.

While excess material flash signifies a “scrap part” in thermoplastics, excess material flash is required in thermoset molding to produce acceptable parts.


Figure 1: Thrust washer for transmission torque converter

Performance-Driven Materials

Thermal and Chemical Performance

With a product life cycle potentially spanning up to two decades or more, automobiles require components that will not disfigure or fail over the life of the product, even within rapidly cycling environments. Thermoset materials offer highly durable material characteristics due to its unique performance advantages. Suitable for automotive applications experiencing high operating temperatures, thermosets provide excellent thermal performance, with heat deflection properties available at more than 450 degrees Fahrenheit. Thermoset components remain dimensionally stable “in the field” because of this high thermal performance, resisting physical degradation despite exposure to high operating temperatures. Aside from dimensional stability, thermosets also provide chemical resistance to automotive and under-the-hood fluids, such as oils, fuel, transmission and brake fluids, power steering fluids, engine cleaners, and other chemicals used in automotive powertrains.


Figure 2: Total shot output of 8-cavity injection-compression molded washers

Durability within Harsh Elements

Along with thermal and chemical performance, many thermoset formulations are UL 94 rated, with either V-0 or 5VA flammability, or flame-retardant ratings from the Underwriters Laboratories (UL). Because electronics are now much more prevalent in vehicles than prior generations due to rising technological advancements, automakers are searching for UL-listed materials with insulating properties to protect electrical wiring or mating assembly parts from damage caused by electrical currents and high voltage. With outstanding dielectric strength and good insulating properties, thermosets are a great option for automotive electronic components or applications requiring good insulation properties. Another big advantage of thermosets over metals for automotive product designs is thermoset’s durability outdoors. Compared to metals, thermosets are highly corrosion resistant, remaining durable despite exposure to a wide range of conditions. While moisture or road salt exposure may eventually corrode metal components, thermosets remain unaffected. By striving to “do more with less,” automotive engineers rely on thermosets as a high-performance material option with all the traditional lightweighting benefits of thermoplastics.

Major Performance Benefits:

  • Chemical Stability
  • Corrosion Resistance
  • Dimensional Stability
  • High Dielectric Strength
  • High Strength-to-Weight Ratio
  • Low Creep/Shrink
  • Thermal Performance
  • UL Listed for Flammability

High Volumes, Low Costs

Regardless of the performance a material offers, it must be cost effective to mass-produce components that may potentially require up to millions of parts annually. Similar to thermoplastics, thermoset components have lower part weights over metal counterparts, saving costs in shipping and improving fuel economies. Additionally, using thermoset plastics instead of metals in a product produces major part consolidation benefits, limiting the total number of components in an assembly and lowering total manufacturing costs of the product assembly. Thermosets also offer available molded-in color and surface finishes that can be matched to nearly any color or surface, drastically reducing or eliminating secondary operations and machining typically required with metal components. When mating parts is required, thermosets allow for molded-in inserts, reducing hardware costs and enabling designers to easily integrate multiple parts of a product assembly. Due to high manufacturability, thermosets may be molded into intricate geometries and designs, and injection molded—offering low cycle times with very high product yields in production. Thermoset tooling can be built with one or multiple cavitation, boosting production capacity and lowering unit-part costs. This is favored within the automotive market as components may have high part-volume requirements, with thousands, or even millions, of a component or assembly being used in vehicles each year.

Fig. 3 Interior automotive ashcup


Lowering Total Manufacturing Costs

While some advanced thermoplastics, such as carbon-fiber reinforced plastics (CFRP), polyphenol-sulfides (PPS), polyamides and polyamide-imides (PAI), offer similar performance characteristics to thermosets, the raw material costs of these advanced thermoplastics are generally much higher than common thermoset materials such as bulk molding compounds (BMCs) and phenolic resins. Many automotive-grade thermoset materials are available in the $1 to $3.50 per pound range, making thermosets a viable option for both short and long production runs. Implementing thermosets may also provide up-front savings in tooling, as well. Compared with metal components, thermoset tooling with hardened steel is generally less expensive. Additionally, thermoset tooling for high-volume applications can provide up to 1,000,000 cycles per mold, thereby producing more parts before the program requires re-tooling. Along with high-volume quantity programs, thermoset tooling may also be built strictly for prototyping purposes, lowering tooling costs for sampling and testing analysis.

Major Cost Advantages:

  • High Product Yield
  • Limited Machining
  • Limited Secondary Operations
  • Low Raw-Material Costs
  • Lower Capital Tooling Expenses
  • Lower Overall Part Weight
  • Part Consolidation

 Lightweighting Applications for Thermosets

While lightweighting efforts have been championed in the automotive industry due to rising regulatory and environmental standards, such as the Corporate Average Fuel Economy (CAFE) fuel economy regulations, the all-around performance, cost and manufacturability benefits enable thermosets to cross over into other industry markets for lightweighting applications. There is not a limit to what could use thermoset materials. Generally, most potential thermoset applications will have some degree of heat or high temperatures applied to the operating product. Along with high-heat stability applications, thermosets are also common in metal-to-plastic conversions to consolidate multiple parts of an assembly, further lightweighting a component or product assembly without sacrificing performance. Here are some applications that are using thermosets.


Thermosets are currently used in a variety of automotive bearing or wear applications. Besides lightweighting benefits, using thermoset materials for bearings, thrust washers and slip rings may provide higher impact strength, dimensional stability, heat resistance and can last longer than metal or thermoplastic-bearing components. Thermoset materials may also be formulated with a self-lubricant, eliminating the need for oils or other lubricants required with metal bearings or washers.

Figure 4: High-strength component resistant to automotive fluids


Using a variety of processing techniques, thermoset materials are showing up in automotive interiors. Ash cups and trim panels for cigarette lighters are perfect examples of interior components requiring high-quality surface finishes and heat/flammability resistance. Additionally, thermosets are very common in headlamps, or parabolic reflectors, which require extremely high surface-finish quality, coupled with electrical properties, such as dielectric strength and insulation performance.

Figure 5: High-volume transmission component

Powertrain and Under the Hood

Automotive powertrain components, such as oil pans or oil pan blockers, pump housings, pulleys and valve covers, are prime applications for thermosets due to requirements for chemical resistance toward under-the-hood oils and fluids, and high heat deflection properties. Other under-the-hood uses, such as smaller transmission components and electronic throttle controls, may also incorporate thermosets for the same thermal and chemical performance requirements.

Figure 6: Injection molded pulley with molded-in inserts

Structural and Body

Thermosets are generally geared for compression-molded sheet molding compounds (SMC). Automotive body frames, panels and pillars may use thermoset materials due to the material’s high strength-to-weight ratio, dimensional stability, and improved tensile and flexural strength over certain thermoplastics or metals.



About Woodland Plastics

Woodland Plastics Corporation is a custom thermoset molder, specializing in injection molding of bulk molding compounds (BMCs) and phenolic resins for the automotive, appliance, electrical and lighting, and energy markets. As an ISO 9001:2008 & ISO/TS 16949:2009 certified thermoset molder, Woodland offers extensive thermoset molding experience and expertise to assist a wide range of automotive customers, including OEMs and Tier 1/Tier 2 automotive suppliers. In addition to custom thermoset molding, Woodland Plastics provides engineering and tooling-design services, along with a number of available assembly and secondary operations. For more information on Woodland Plastics’ capabilities, please contact Spencer Leffelman at 630-543-1144, or







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