Surface metrology as a tool in surfboard manufacturing to assess machinability of expanded polystyrene blanks via CNC milling

Abstract

Although most of the current surfboards are manufactured industrially, the use of rigorous surface metrology is scarce to control the surface finish of CNC-milled expanded polystyrene (EPS) blanks. The present study aimed to evaluate the surface finish of EPS blanks machined by a CNC milling machine with a diamond disc tool, designed for surfboard manufacturing. Four EPS blanks of different brands and densities were characterized, machined at two feed rates: (a) 10 m min−1 and (b) 5 m min−1, and the quality of the surface finish was evaluated. Scanning electron microscopy as well as a confocal laser scanning microscope were used to evaluate the surface morphology. A range of topographical parameters was proposed and assessed. The structural characteristics of the EPS blanks demonstrated that the machined material is easily mouldable, not causing damage to the tool, thus requiring little maintenance for tool periodic replacement. The use of confocal microscopy proved to be efficient for the evaluation of the quality of the surface finish of EPS blanks and a set of topographical parameters was chosen. The higher density blanks showed better surface finish after machining at the feed rate of 5 m min−1, while the lower density blank had a better surface finish when machined at the feed rate of 10 m min−1. The parameters Sq, Sz, Sdq, Spk and Svk could not differentiate well the quality of the machined EPS surfboards under different conditions due to the large deviations of the measured values, probably resulting from the occurrence of through-bead cutting and bead removal. The parameters Ssk and Sku could detect problems in the surface morphology resulting from machining EPS blanks, enabling to differentiate between the through-bead cutting and bead removal mechanisms. When bead removal occurred significantly, Ssk values became more negative and Sku values were lower than 3.