Effect of Drilling Speed and Task Duration on Discomfort Score and Metal Removal Rate on Workers Performing a Drilling Task

Abstract

Work related musculoskeletal disorders (WMSD’s) have been reported by industrial workers performing various kinds of manual tasks. Heavy workload, awkward postures, repetitive nature of tasks and working conditions were responsible for WMSD’s in workers. Manual drilling was one such task in which the workers have reported various kinds of disorders. Manual drilling is either performed by a hand held drilling machine or by a bench drilling machine. In the present work, the drilling operation being carried out on a bench drilling machine was studied. The task was to perform drilling operation on a mild steel block of dimensions 60 mm x 60 mm x 30 mm. The drilling speed at two levels (300 RPM and 700 RPM) and task duration at three levels (5, 10 and 15 minutes) were selected to determine material removal rate (MRR) and discomfort score. The two way ANOVA of the data collected showed that the task duration and drill speed both were significant in the context of MRR and discomfort score. It was found that at both the drill speeds (i.e., 300 and 700 RPM) the material removal rate decreased with the increase in task duration. Results also showed that the perceived discomfort score was found to be minimum at a drill speed of 700 rpm when the drilling task was performed for 5 minutes while the average maximum discomfort level was found at a drill speed of 300 rpm when the drilling task was performed for 15 minute duration.