Unsupported machining fixture layout optimisation

Abstract

Abstract It is well established that excessive vibrations in machining operations hinder productivity and quality of the components being made. In these environments it is common to encounter self-excited vibrations due to the dynamic response characteristics of the cutting tool and workpiece; referred to as regenerative chatter. To suppress these effects, conventional practices provide the workpiece with as much support as possible and therefore commonly require custom-built fixturing bases and several manual intervention stages. In contrast, for modern reduced fixturing approaches, the workpiece is minimally-held, with the benefits of reduced setup times, lower fixturing and inventory costs, and improved access to the workpiece thereby avoiding multi-stage setups. However, minimal fixturing reduces support of the workpiece, and so vibration becomes a greater challenge, along with the subsequent detrimental effects to part quality and material removal rate (mrr). This paper sets out to determine an optimisation methodology for layout configurations that maximise milling depths of cut whilst achieving dynamic stability; by means of FEA model-based simulations and particle swarm optimisation (pso) methods. The optimisation algorithm is then tested on simplified setups and compared to exhaustive searches. It is shown that optimal results can differ from standard practice, and despite the comparative reduction in workpiece stiffness to a traditional approach is mostly unavoidable, careful placement of workholding elements can reportedly improve cutting conditions and increase dynamic stability within an unsupported environment.