Machinability of wood-plastic composites from the CNC milling process using the Box-Behnken design and response surface methodology for building applications

This research investigated the optimization of CNC milling parameters on hardness and surface roughness properties resulting from variations in speed (220, 470, and 720 rpm), feed rate (200, 300, and 400 mm/min), and depth of cut (3, 5, and 7 mm) based on experimental design. This study aimed to evaluate the effects and relation of milling parameters using different end mill diameters (8 and 12 mm) for machining wood-plastic composites (WPCs). All of the experimental runs were determined by the Box-Behnken design and optimized using the response surface methodology. The findings from this study revealed that the main milling parameters significantly affected the hardness, average roughness ( Ra), and mean peak-to-valley height ( Rz) of the WPCs. Increasing the speed in a range from 220 to 720 rpm resulted in higher hardness values. On the other hand, the Ra and Rz was decreased. Additionally, this experimental result is different from the morphological structure and surface observation. It was seen that the CNC milling conditions using high speed at 720 rpm displayed smooth surfaces, which resulted in visible evenness on the WPC surfaces. Finally, numerical optimization is a good technique for the experimental results and the predicted values. The predicted conditions for the CNC milling process using end mill diameters of 8 and 12 mm included a speed of 720 rpm, a feed rate of 300 mm/min, and a depth of cut of 3 mm with the best desirability of 0.973 (97.30%). These conditions were verified in the response models and confirmed the optimal values from observed values for the variables included in the models. Also, these optimal conditions for the CNC milling parameters can be used on other types of WPCs with melting points of plastic higher than 180°C.