基于多界面接触的加工中心紧凑型高速大功率电主轴动力学特性研究

For high speed and high power compact electric spindle in machining center, there are multi-interface contact interaction between cone and end surface of spindle and holder, holder and tool, spindle and bearing, and rolling elements and rings. The contact stiffness of multi interface has an important influence on the dynamic characteristics of the compact and complex structure spindle system. It is difficult to reveal the complex dynamic behavior of the electric spindle by the existing equivalent stiffness model of the interfaces. Thus, the method of improving the dynamic performance of compact motorized spindle is studied based on the theory of dynamics, contact mechanics and tribology. Two-phase bubbly flow and flow solid heat coupling method is proposed, the thermal characteristics model of motorized spindle is established. Based on thermal structure coupling of interfaces and multi scale contact idea, stiffness of interface concept is provided. Nonlinear dynamic model of a compact spindle holder tool system, discover mechanism of the interface parameters and compact spindle structure parameters on dynamic flexibility, nonlinear stability and cutting stability. The dynamic flexibility of compact spindle and cutting stability are chose as multi-objective optimization, then the electric spindle is improved and reproduced. The theories are verified by a high-speed electric spindle test bench and cutting experimental in a machining center. Research results can improve vibration resistance and cutting stability of high-speed electric spindle, providing the new theory and new method for designing of high speed and high power electric compact spindle, and deepen basic scientific research on the dynamics of mechanical systems with multi interface contact.

加工中心紧凑型高速大功率电主轴存在主轴-刀柄、刀柄-刀具、主轴-轴承和滚动体-套圈多界面接触作用，界面间非线性接触特性对紧凑电主轴动特性和切削稳定性有着重要影响，现有结合面等效刚度模型难以揭示该类电主轴复杂的动力学行为。为此，基于动力学、接触力学与摩擦学等理论，研究紧凑型电主轴动力学性能分析与提高方法。提出两相泡状流动结合流固热耦合方法，建立电主轴热特性模型；提出基于热结构耦合、跨尺度接触的界面刚度概念，建立多界面接触紧凑主轴刀柄刀具系统非线性动力学模型，揭示界面参数、紧凑主轴结构对动柔度、切削稳定性的影响机制。提出对界面宏微观参数及紧凑主轴结构优化的概念，建立电主轴动柔度和切削稳定性多目标优化设计模型，改进试制电主轴在加工中心上进行切削实验验证。研究成果能提高紧凑型电主轴抗振性和切削稳定性，形成紧凑型高速大功率电主轴动力学设计的新理论和新方法，深化多界面接触的机械系统动力学基础科学研究。

以加工中心紧凑型高速大功率电主轴为研究对象，建立了两相润滑电主轴流-热-结构耦合模型，发现随着润滑介质进口速度的增加，润滑介质的出口压力和速度增加。随转子转速增加，润滑介质出口压力和速度随之升高。初始气泡直径越大，高速时裂变气泡越多，轴承温升越高。由轴承摩擦功率损耗计算得出各接触区的热流密度，发现高温区域集中在滚道和球接触的部位，油气润滑入口处温度最低。考虑流固热耦合影响后发现温升低于未考虑耦合影响的结果，随转速增大两者之间差别增大。通过电主轴热特性实验验证了内生热源模型的可靠性。考虑跨尺度弹塑性变形作用以及动态切削力，建立了主轴-刀柄和刀柄-刀具界面非线性动态接触刚度。基于有限单元方法建立了考虑紧凑细长主轴和动态切削力的主轴-刀柄-刀具系统整体的非线性动力学模型，考虑界面接触特性建立了主轴-刀架-工具系统的颤振稳定性预测方法，研究发现存在与主轴转速相对应的最佳进给速度，最佳进给速度可通过项目提出的铣削稳定性模型确定，临界轴向切削深度随径向切削深度的增加而减小。为了增加临界轴向切削深度，同时确保切削效率，径向切削深度不应超过临界值。针对紧凑性高速电主轴，对主轴-拉刀材料、轴承预紧力、轴承组跨距、主轴-拉刀接触刚度以及主轴-刀柄接触刚度等参数进行优化设计发现：电主轴静刚度、动刚度分别提高了34.9%、32.3%，静动刚度均满足了技术要求，固有频率提高，电主轴危险频率区间从1100Hz后移至1550Hz，安全工作频率区间增大。对电主轴转子结构进行动平衡改进，改进后主轴转子不平衡质径积下降到1×10-5kg·m，支承轴承预紧载荷增大到500N。优化后转子为一倍周期的振动，振动速度最大为0.35mm/s，临界切削深度增大了30%，满足了使用要求。本课题研究成果提高了紧凑型电主轴抗振性和切削稳定性，对紧凑型高速大功率电主轴动力学设计具有重要的指导意义和应用价值。