The Research On The Time Delay Effect And Process Damping Of Milling

Milling chatter is one vital restriction for the manufacturing quality and production. Chatter usually leaves inclining vibration marks on the machined surface, which can deteriorate the surface quality. Besides, the vibration marks are usually required to be removed manually, which may reduce the manufacturing production. The chatter is more likely to occur in the cutting of the difficult-to-cutting material such as titanium alloy due to the large unit cutting force and low modulus of elasticity. The milling of titanium alloy and the corresponding thin-walled workpiece is one difficult problem for aeronautical manufacturing. The research aim of the thesis is to solve the problem, thus the following work are completed:The physical natures of milling chatter are explored. The influence of time-delay effect on the damping and stiffness of milling system are studied. The Routh Criterion is introduced to explain that the occurrence of the chatter is caused by the added elements, especially the crossed ones in damping and stiffness matrices. The crossed elements are increased as the cutting depth increasing, which result in the negative coefficient in Routh Table and the occurrence of chatter. The mechanisms of the occurrence of chatter are different in variable unstable types. The above ideas are verified by the comparisons of computational and experimental results. Based on the above ideas, the damping mechanism of variable pitch cutters and variable speed cutting are studied deeply. It is pointed out that the two methods can all suppress chatter by changing time-delay of milling system to eliminate crossed damping elements, and one simple optimization object objective is proposed. The optimal pitch of cutters and modulate parameters can be obtained based on the objective soon. The validity of the analytical methods are verified by the examples in classical references.The process damping play a vital role in suppressing milling chatter, which arises from the interference between the flank face of tool and machined surface. The mechanisms of process damping are researched deeply and the occurrences conditions of interference are given, and the influence of cutting speed and relief angle on process damping are studied. The nonlinear dynamic model is established to analyze chatter stability, which considers the process damping and tool separating from workpiece. The model can reflect the practical manufacturing conditions roundly and provided one method to descript the surface vibration marks and calculate the indentation area. The typical titanium alloy Ti6AL4 V are used as the experimental material. The comparison of computational and experimental results indicates that the model can predict the stable region caused by process damping at low speed. The anti-vibration relief angle designed can increase the process damping and expand stable region further.The process damping is applied to the milling of thin-walled made of titanium alloy. The improved model is established to descript the surface wave marks caused by vibration of workpiece, and the indentation area and process damping forces are calculated, thus the chatter stability analysis of milling of thin-walled workpiece can be achieved. The comparison of computational and experimental results indicates that the model can predict the stability limits at low speed in milling of thin-walled workpiece made of titanium alloy. The anti-vibration relief angle designed can increase the process damping and expand stable region effectively.