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This study evaluates the impacts of machining parameters on the milling of general-purpose poly (methyl methacrylate) (PMMA) with respect to cutting point temperature, maximum machining temperature, and surface roughness. The machining parameters used in the analysis are spindle speed (rpm), depth of cut (mm), and feed rate (mm/min). The extreme ranges of the machining parameters for the material are obtained from trial experiments. From these experiments, four values of each parameter are adopted. This yields 12 experiments, which are divided into three sets. In the first set of experiments, the depth of cut and feed rate are held constant at 0.2 mm and 25 mm/min, while the spindle speed is varied from 1000 rpm to 4000 rpm. In the second set of experiments, the spindle speed and feed rate are held constant at 1000 rpm and 25 mm/min, respectively, while the depth of cut is varied from 0.2 mm to 1.1 mm. In the last set of experiments, the spindle speed and depth of cut are held constant at 1000 rpm and 0.2 mm, respectively, as the feed rate is varied from 25 mm/min to 100 mm/min. Thermal images are obtained during milling, where the cutting point and maximum machining temperatures are obtained. The milled surfaces are then investigated for surface roughness. The chips are also collected from each experiment and used in conducting chip morphology. From the results, it is observed that to obtain the least temperatures and best surface quality, the least machining parameters should be chosen. These parameters are identified as 1000 rpm, 0.2 mm, and 25 mm/min for the spindle speed, depth of cut, and feed rate, respectively. An increase in spindle speed seems to increase the milling temperatures and surface roughness, which is attributed to the reducing chip thickness. An increase in the depth of cut does not affect the generation of chips, and the thickness is relatively constant. However, an increase in milling feed increases the chip thickness, which increases the surface roughness.

This study evaluates CNC milling parameters (spindle speed, depth of cut, and feed rate) on medical-grade PMMA. A single objective analysis conducted showed that the optimal material removal rate (MRR) occurs at a spindle speed of 1250 rpm, a depth of cut of 1.2 mm, and a feed rate of 350 mm/min. The ANOVA showed that feed rate is the most significant factor towards the MRR, and spindle speed (11.83%) is the least contributing. The optimal surface roughness (Ra) occurred at spindle speed of 500 rpm, depth of cut of 1.2 mm, and feed rate of 200 mm/min. The milling factors were insignificant. A regression analysis for prediction was also conducted. Further, a multi-objective optimization was conducted using the Grey Relational Analysis. It showed that the best trade-off between the MRR and the Ra could be obtained from a combination of 1250 rpm (spindle speed), 1.2 mm (depth of cut), and 350 mm/min (feed rate). The depth of cut was the largest contributor towards the grey relational grade (54.48%), followed by the feed rate (10.36%), and finally, the spindle speed (4.28%).

Polymers have been adopted industrially in the manufacture of lenses for optical applications due to their attractive properties such as high hardness, high strength, high ductility, high fracture toughness, and also their low thermal and electrical conductivities. However, they have limited machinability and are therefore classified as hard-to-machine materials. This study conducts a critical review on the machining of various polymers and polymeric materials, with particular focus on poly (methyl methacrylate) (PMMA). From the review it was concluded that various machining parameters affect the output qualities of polymers and which include the spindle speed, the feed rate, vibrations, the depth of cut, and the machining environment. These parameters tend to affect the surface roughness, the cutting forces, delamination, cutting temperatures, tool wear, precision, vibrations, material removal rate, and the mechanical properties such as hardness, among others. A multi-objective optimization of these machining parameters is therefore required, especially in the machining of PMMA.