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Polymeric materials have attracted applications in various industries, especially the medical field, due to their desirable properties such as high strength and low weight and biocompatibility with human tissues. However, the manufacture of components from these materials has faced several challenges, including their poor machinability leading to the generation of poor surfaces and low production rates (Yan et al., 2021). These challenges necessitate the evaluation of the primary machining parameters (spindle speed, depth of cut, feed rate, nose radius, tool geometry, tool vibrations) and their impact on the quality of products to identify the optimal parameters for production (Aslaliya et al., 2014).
Various researchers have conducted studies on optimizing the material removal rates and surface quality of different materials. These optimization studies involve selecting the most common machining parameters and determining the most suitable combination for the highest material removal and the least surface roughness. For example, in most milling processes, the most common machining parameters are spindle speed, cutting speed, feed rate, and depth of cut (Ribeiro et al., 2017; Ratnam, 2017). In addition, the parameters tend to largely influence the surface roughness and material removal of milled components (Sakthivelu et al., 2017).
In a study conducted by Lazarević et al. (2012) on the optimization of cutting parameters for the least surface roughness of polyethylene, it was found out that the feed rate was the most significant factor. The authors concluded that the optimum parameters for the least surface roughness were approximately 213 m/min, 0.049 mm/rev, 2 mm, and 0.8 mm for the cutting speed, feed rate, depth of cut, and nose radius, respectively. Similar findings were presented by Hamlaoui et al. (2017) during the machining of polyethylene, where the feed rate was identified as the most significant parameter towards the surface roughness. Tamiloli & Venkatesan (2016) investigated the impact of milling parameters on surface quality and heat generation. They found that high spindle speed and low feed and depth of cut were most preferred for a better surface finish. Low speeds and feeds were also desired for low heat generation.
Further, Ali et al. (2012) found out that during the micro-milling of PMMA, the feed rate and depth of cut were the most significant parameters towards the generation of machining vibrations, while for the minimum surface roughness, the spindle speed was the most significant. In a PMMA facing operation conducted by Dhakad et al. (2017) to optimize the cutting parameters for the best surface finish, it was found out that the feed rate was the most significant parameter followed by the cutting speed and depth of cut. Therefore, the authors recommended the maximum cutting speed, minimum feed rate, and a moderate depth of cut. Similar results were also identified by Korkmaz et al. (2017) in the micro-milling of PMMA, where the feed rate and spindle speed were the most significant factors towards the surface finish. On the other hand, the depth of cut had a negligible influence on the surface roughness. Additionally, during the CNC milling process, Pant et al. (2017) found out that the material removal rate was affected mainly by the cutting speed and depth of cut.
Thermoplastic polymers, such as PMMA, have been considered hard-to-cut materials due to their mechanical and chemical properties, such as poor thermal conductivity and chip formation, among others (Yan et al., 2021). These properties affect machining processes such as heat dissipation which leads to high machining temperatures. High machining temperatures impact the tool wear, which affects the tool's cutting ability, affecting the surface quality and removal of chips. This also increases the machining forces, translating to workpiece fracture and delamination (Arhamnamazi et al., 2021). As a result, these materials have been machined using non-conventional methods such as laser-assisted machining and ultrasonic-assisted milling, among others. However, these machining methods involve complex procedures and requirements, limiting the polymers' application in high precision fields such as in medical and aerospace (Halim et al., 2017; Bharat & Bose, 2020).