Assessment of tool holder performance in roughing with end mills: Process dynamics and surface formation

摘要

Tool holders are an important power train component of milling with shaft tools having a high impact on dynamic process behaviour and process results. This leads to a significant demand among industrial companies for scientifically proven methods to analyse tool holders which are easy to use as well. Different approaches were applied in order to meet these demands. The dynamic vibrational behaviour of different clamping mechanisms is investigated using tool holders of similar dimensions. First, the resonance frequencies of the tool holders are identified from dynamic compliance measurements in the machine tool. Subsequently, the dynamic process behaviour is investigated by peripheral milling tests in which vibrations of tool and tool holder are detected by acceleration sensors and microphones. Analysis of the sensor data and optical analysis of the manufactured surface reveal a significant influence of the particular clamping mechanism, superimposed by certain geometrical variations of the investigated tool holders. Chatter frequencies occurring during milling tests seem independent of the clamping mechanism respectively the particular tool holder and are caused by the tool or machine-tool components. They correspond roughly with the natural frequencies identified before. Chatter intensity and spindle speeds, at which chatter occurs, are influenced by the tool holders. The occurrence of chatter vibrations correlates with a significant drop in the surface quality of the workpiece. High resonance frequencies of the tool holder excited by chatter and low-frequency waviness observed on the machined surface are related. The well-known phenomenon can be explained under rough milling conditions by a 2D-model-based superposition of subsequent cutting edge engagements. This in turn may enable dynamic analysis and optimisation of rough milling operations by easy to use shop floor equipment in future.