CNC Machining of plastics is growing rapidly because of its high precision and high-quality production. CNC machining is not only restricted to metals but also makes its way into producing many commodities and engineering plastic products. Using thermoplastics and thermosets for CNC machining is becoming common for many applications because of their low-cost and high-quality characteristics.
The use of plastics to process CNC Machining components is increasing immensely. The machining of thermoplastics and thermosetting is quite different regarding process parameters. Considering melting temperature, heat deflection temperature, and degradation temperature is necessary for CNC machining products. The difference in the process parameters, while dealing with thermoplastic or thermosetting polymers, must be dealt with efficiently to optimize the machining product.
Chemical Structure
The main structural difference between thermoplastics and thermoset polymers is the presence of crosslinking regions. Thermoplastics are flexible because of the absence of cross-linking. This crosslinking in thermosetting makes these materials more rigid, stiffer, and brittle.
While on the other hand, thermoplastic polymers offer flexibility, ductility, and tensile properties. Because of its abrupt structural variations, CNC machining of thermoset plastics is difficult to control. The brittleness of these materials has restricted the process from being done at a lower rate as the thermoset changes are observed very quickly, leading to permanent deformation.
Besides, dealing with thermoplastics for CNC machining is quite simple and has wide parameter ranges with more significant optimization and manufacturing of CNC machined parts. As thermoplastics offer higher flexibility, the processing rate may be increased to achieve production on time.
Curing
The curing process of plastics involves the chemical reactions of monomers and their transformation into a three-dimensional matrix of the polymer. This reaction is initiated by heat, light, radiation, or a catalyst. Crosslinking is propagated in response to these polymerization reactions, forming a stiff structural polymer matrix. This behavior is observed chiefly in thermosetting polymers. The strength or intensity of activators, i.e., heat, light, radiation, or catalyst, is essential because of the sensitive responses of these materials.
During CNC Machine Cutting/Drilling, an immense amount of heat energy is produced in response to continuous abrasion that results in a higher temperature gradient affecting the curing of the thermoset. Although, it is confirmed that the thermoset materials can’t be remolded once they are cured. Consequently, this abrupt temperature gradient may affect the curing of material resulting in inaccuracy and imprecision of product shape and physical stability. Considering this fact, the temperature during processing is optimized accordingly to avoid any impact on inherent material properties.
On the other hand, cutting or drilling of thermoplastic materials is easier to handle as thermoplastics provide flexibility in their structure. They may be reused or remolded because of their higher thermal and structural stability. Higher thermal stability makes them able to withstand temperature fluctuations.
Recyclability
Plastics’ recyclability is very important from an industrial point of view. The concept of recycling is only applicable to thermoplastic polymers because of their flexible structure and absence of cross-linking regions. High mechanical strength and thermal stability allow them to be repeatedly applied under higher temperatures for recycling.
However, the quality may only be partially satisfied, but the waste products may be minimized. Same for the case of CNC Machining, thermosets require very precise optimization of parameters. On the other hand, thermoplastics allow some tolerances for high-quality and precision CNC Machining products.
Speed of Cutting/Drilling Head
The speed of the cutting/drilling head plays a vital role in the finalization of characteristics associated with the CNC machined parts or end product. The difference between thermoplastic and thermoset is the same for this factor. The speed of the head must be optimized accordingly, so it may not affect the material thermally, especially in the case of thermosetting materials. The curing of thermosetting is directly affected by temperature and especially by the heat of dissipation during cutting/drilling.
However, they possess high mechanical stability but low ductility. This poor ductility results in brittle fracture during machining services, producing waste and affecting the production rate and economics. Instead, thermoplastic polymers possess lower modulus than thermosets but higher ductility, making them flexible enough against physical and thermal fluctuations during CNC Machining.
Temperature
The temperature values for CNC Machining of polymers are crucial, especially in the case of thermosetting polymers or plastics. The temperature gradient produced during cutting or drilling increases the chain motion inside thermosetting polymers. This increase in temperature supports nucleation of cross-linking, improving the strength of the material but reducing the ductility.
So, a very high rise in temperature may lead to the degradation of polymeric or plastic material. This temperature gradient may be controlled through the speed head or RPM and the medium’s temperature because the speed increase may increase the abrasion, ultimately increasing the heat dissipation or temperature gradient.
The speed or RPM of the cutter may be optimized easily using computer-assisted software simulations. While in the case of thermoplastics, although the heat is produced, these plastics are stable enough to absorb, resist and overcome this temperature or heat energy change. But, the temperature may be optimized so that it may not disturb the thermal properties, i.e., melting temperature, and the glass transition temperature of that particular polymer/plastic.
However, compared to thermosetting polymers, there is an advantage of machining or processing plastic without restricting the curing or cross-linkage of polymer chains. But the temperature should not exceed the melting temperature.
Conclusion
Summarizing the differentiating properties of thermoplastic and thermosetting plastics, it is confirmed that the machining of both types of plastics is quite different from each other. Thermosets are more rigid and require holistic optimization of CNC machining parameters, especially temperature and head speed.
While thermoplastics are pretty flexible, they offer a wide range of machining parameters but are sensitive towards service temperature, significantly above glass-transition temperature and near their melting temperature.