机床相对动柔度劣化对稳定性Lobe图的影响分析

Effect Analysis of Deterioration of the Relative Dynamic Compliance of a Machine Tool on Stability Lobe Diagram

在机床各种形式的振动中,再生颤振具有最小的稳定极限切削宽度,换言之,机床抵抗再生颤振的能力最差。品质系数(Coefficient of Merit,COM)是切削力和切削表面法向相对位移之间的交叉频响函数最小负实部的函数,其大小直接反映机床抵抗再生颤振的能力。此外,在机床的连续使用过程中,品质系数COM会逐渐减小,进而影响机床再生颤振抗振能力。基于相对激振方法和四自由度立铣加工过程动力学模型,重点分析了机床相对动柔度劣化过程中品质系数COM的变化趋势,以及对加工过程稳定性Lobe图的影响。研究表明:随着机床相对动柔度的劣化,轴向极限切深ap逐渐减小,并有加速递减的趋势,这和机床品质系数的劣化趋势一致。因此,考虑机床相对动柔度对稳定性Lobe图的影响,才能确定更合适的工艺参数,保证切削过程的稳定性,提高加工效率。

In all kinds of machine tool vibrations,regenerative chatter has the minimum stability critical width of cut. In other words,a machine tool has the worst ability to resist regenerative chatter. Coefficient of Merit( COM) is the cross-receptance value between the cutting force and the relative displacement in the direction normal to cut surface,which can reflect the ability of a machine tool to resist regenerative chatter. Otherwise,in the continuous cutting processes of a machine tool,Coefficient of Merit decreases gradually,and then the ability to resist regenerative chatter is weakened. Based on relative excitation method and four-degree-of-freedom dynamic model of end milling,effect of the deterioration of the relative dynamic compliance on the change trend of COM and stability Lobe diagram was focused. Research shows that axial critical depth of cut decreases gradually and the trend is accelerated descending,which is consistent with the deterioration trend of COM. Therefore,considering the effect of relative dynamic compliance of a machine tool on stability Lobe diagram,the high-efficiency cutting parameters can be chosen only by the premise of guarantee of machining stability.