Best of Both Worlds: Injection Molding with Thermosets Combines Strength and Speed

While injection molding is most often associated with thermoplastics, there’s a growing interest in injection molding with thermosets. Thermosets have more commonly been linked to compression molding, but that is an outdated notion. Driven by the desire to replace more metal parts with heavy-duty plastics (such as in automotive and aerospace applications), thermoset injection molding is increasingly becoming a go-to solution for design engineers.

Injection molding process and properties

Thermoset molding technology has been around since the early 1900s, but injection molding with thermoset compounds became truly feasible in the 1970’s. The growth in single-use, disposable products, such as packaging, has led injection molding to be used most commonly with thermoplastics. However, many industries are now turning to thermoset injection molding for the many benefits of thermoset resins, combined with the faster, more cost-effective solution that injection molding delivers.

The injection molding process is similar whether using thermosets or thermoplastics, but the biggest difference is that thermoset resin is injected into a hot mold where it cures and solidifies. In contrast, thermoplastics are injected into a cold mold where the resins quickly cool off and solidify. When the mold opens, parts made with either thermosets or thermoplastics will appear identical in a side-by-side comparison, but their performance capabilities are very different.

Thermoset parts have higher strength, hardness, heat resistance, dimensional stability, UV protection, colorfastness and electric insulation properties compared to thermoplastics. These benefits are the same whether the thermoset parts are made via traditional compression or injection molding. There are multiple thermoset resins that can be used for injection molding, but phenolic and polyester are the two most common.

Thermoplastic injection molding is better for single-use, light-duty and low-cost products that are not subjected to heat.  There are hundreds of thermoplastics available for injection molding. Thermoplastic parts can be produced more quickly – with 50-120-second cycle times for thermoset injection molding (pending wall thickness) versus a 10-30-second cycle time for the average thermoplastics. 

Thermoset compression or injection molding?

When determining if a thermoset part should be made via compression or injection molding, there are many variables to consider.

If a part needs to withstand high levels of force, thermoset compression molding is a better option. This is because in the process of injection molding, the fibers in the thermoset resin orient and weaken slightly, whereas ultra-strong parts may have glass fibers up to an inch long. However, even the shorter fibers in an injection molded thermoset may still be stronger than thermoplastics.

Some part designs may not be conducive to injection molding. These include thick and heavy parts or those with holes or slots in the sidewalls, molded-in inserts, or varying wall thicknesses. In these cases, thermoset compression molding may be necessary.  

Smaller parts, such as wiring connectors, are ideal for thermoset injection molding because they can be produced using a high cavitation mold. This specialized mold contains multiple cavities to produce many parts in a single cycle, which reduces overall production time and costs. When a robotic arm is added to unload those parts, it can lower costs even further.

Larger parts are often more appropriate for thermoset compression molding. Automotive brake components and electrical insulators are examples of large parts that Ci-Dell produces using compression molding.

Expert Consultation

Ci-Dell’s experienced team of talented process engineers that works alongside customer design teams to determine the right material formulations and processing methods best suited for a particular part based on is performance needs and costs.

Ci-Dell takes a scientific approach to develop processes, using data analysis to minimize variability and improve part quality at every stage of processing. This methodology increases production and improves overall quality, so customers get parts on time and on budget.

Ci-Dell Capabilities

Ci-Dell has capabilities to mold a variety of part sizes using thermosets and thermoplastics:

• Thermoset compression molding:  Up to 750 ton press with largest press bed size 72 in. x 54 in. 
• Thermoset injection molding: Up to 200 ton press with largest press bed size 21 in. x 21 in. 
• Thermoplastic injection molding: Up to 200 ton press with largest press bed size 21 in. x 18 in.

Bring your design challenges and parts concepts to Ci-Dell for material and process recommendations that improve your design moldability and lower costs. Contact us.