小型车床内装式电主轴间歇动态热特性研究

发布时间：2018-08-17 17:27

【摘要】：随着驱动技术的发展，机床电主轴已逐步成为现代机床与电气系统之间结合的重要部件，它在数控机床发展中占有重要地位。车床手工装卡时间在整个加工过程中占用比例较大。为了缩短工件装卡时间、提高机床自动化程度，设计制造带有自动夹取功能、用于加工小型盘类零件的专用机床，具有广泛的应用前景。机床电主轴具有结构简单、电机直接驱动主轴等优点，是设计具有自动夹取功能专用机床的首选主轴方案。自动化专用机床电主轴的工作过程使其热平衡过程处在有源传热与无源传热交替进行的状态。专用机床电主轴采用间歇工作制，减轻了主轴自身平均热负荷的同时，也缓解了电主轴温升问题对加工精度影响。主轴加工工件时内装电机处于有源传热状态，内装电机产生的铜耗和铁耗通过各部件之间的热传递散发出去；主轴停机夹取工件过程中，内装电机没有损耗产生，各部件内部储存的热能由于主轴内外温度差的存在而继续进行热传递。因此有效的计算电主轴在自动化专用机床实际加工过程中温升状态是电主轴设计和机床热误差补偿的关键。结合具有自动上下料功能的卡盘倒置立式车床研发项目，，在对机床加工工况、电主轴散热结构及散热过程详细分析之后。以瞬态热网络法建立车床电主轴温升计算模型，并用有限单元法进行模拟，对比验证模型计算结果。对设计方案在多种模拟实际工况下进行了温升校核，并计算了主轴轴向热变形。为了改善卡盘倒置立式车床加工精度，以间歇载荷下电主轴瞬态温升计算为基础提出一种热误差实时补偿方法。最后以车床内装电主轴样机为实验对象进行模拟实际加工工况的温升实验，验证温升计算模型的正确性。研究内容及结论包括以下几个方面：（1）本文对立式车床的动态加工过程、主要加工参数进行了详细分析，确定了在电主轴内装电机的类型及电气参数，运用有限单元法计算了车床电主轴设计过程中主轴刚度及固有频率，进而对设计方案中内装电机散热结构进行分析，最终结合机床整体使用工况，确定了散热方案为自然冷却。对永磁同步主轴散热过程进行了详细分析，利用分离变量法求解了定转子非稳定传热方程级数解，对后续确定边界条件及求解方法提供理论基础。（2）应用传热学理论以瞬态热网络法建立计算模型，分别计算了间歇载荷时高速轻载，低速重载等多种实际工况下电主轴内部各部分温升情况。用有限单元法对相同工况进行分析，初步验证了热网络模型的计算结果。在多种模拟实际工况下对设计方案进行了温升校核，结果表明有限单元法计算结果比热网络法略高。（3）应用热弹性力学及有限元理论，建立了基于热结构耦合的电主轴有限元分析模型，计算了车床电主轴在卡盘倒置立式车床实际加工过程中温度场变化引起的轴向热变形。（4）对主轴加工时热变形进行了详细分析，主轴径向热变形在允许范围内，轴向热变形从加工开始直到主轴到达动态热平衡时持续增大。在加工单个零件时由于加工时间短主轴尚未发生较大热变形，单个零件的加工精度在误差允许范围内。自动化机床加工整批零件时，后加工的零件将由于主轴热变形造成精度超出误差允许范围。针对这种情况，提出了一种基于车床内装电主轴瞬态热特性计算的误差补偿方法，以减小卡盘倒置立式车床主轴热变形引起的轴向尺寸误差。为车床内装电主轴应用于各种不同工况的热误差预测和误差补偿提供了一种新方法。（5）在不同转速及负载转矩下以车床电主轴样机为研究对象，进行了模拟自动化加工过程的瞬态温升实验。用实验数据与热网络模型对应的计算值进行对比，分析表明车床内装电主轴间歇载荷下热传递模型计算结果在误差允许范围内。在参数及边界条件选择正确的前提下，可以有效的计算车床电主轴在自动化加工过程中的瞬态温升。综上所述，本文主要应用热网络法及有限单元法揭示了车床电主轴的结构参数设计及间歇载荷对热态性能的影响机理和规律，以车床电主轴温升实验证实了理论计算结果在误差允许范围内，为电主轴在卡盘倒置立式车床加工过程中热误差补偿研究提供了理论基础。
[Abstract]:With the development of drive technology, the motorized spindle of machine tools has gradually become an important part of the combination between modern machine tools and electrical systems. It plays an important role in the development of CNC machine tools. The machine tool motorized spindle has the advantages of simple structure and direct motor drive. It is the preferred spindle scheme for designing the machine tool with automatic clamping function. The working process of the motorized spindle of the automated machine tool makes its thermal balance excessive. The motorized spindle of the special machine tool adopts the intermittent working system, which reduces the average heat load of the spindle itself and alleviates the influence of the temperature rise of the motorized spindle on the machining accuracy. The heat transfer between the components is emitted; during the process of the spindle stopping and clamping the workpiece, there is no loss of the built-in motor, and the heat stored in the components continues to be transferred because of the temperature difference between the inside and outside of the spindle. The key of shaft design and thermal error compensation of machine tools.
Based on the research and development project of the chuck inverted vertical lathe with automatic loading and unloading function, the working condition of the lathe, the heat dissipation structure of the motorized spindle and the heat dissipation process are analyzed in detail. The calculation model of the temperature rise of the motorized spindle of the lathe is established by the transient thermal network method, and the results of the model are compared and verified by the finite element method. In order to improve the machining accuracy of the chuck inverted vertical lathe, a real-time thermal error compensation method is proposed based on the transient temperature rise calculation of the motorized spindle under intermittent load. Finally, the prototype of the motorized spindle installed in the lathe is used as the experimental object to simulate the actual addition. The temperature rise test of the working condition verified the correctness of the temperature rise calculation model.
The research contents and conclusions include the following aspects:
(1) In this paper, the dynamic machining process of the vertical lathe, the main processing parameters are analyzed in detail, the type of motor installed in the spindle and the electrical parameters are determined, the spindle stiffness and natural frequency in the design process of the spindle are calculated by the finite element method, and then the heat dissipation structure of the motor installed in the design scheme is analyzed. The heat dissipation process of permanent magnet synchronous spindle is analyzed in detail, and the unsteady heat transfer equation of stator and rotor is solved by the method of separation of variables, which provides a theoretical basis for determining boundary conditions and solving methods.
(2) Based on the theory of heat transfer, the transient heat network method is used to establish the calculation model, and the temperature rise of each part of the motorized spindle is calculated under various practical conditions, such as high speed, light load, low speed and heavy load. The results show that the finite element method is slightly higher than the thermal network method.
(3) Based on thermoelasticity and finite element theory, the finite element analysis model of the motorized spindle is established, and the axial thermal deformation of the motorized spindle caused by the change of temperature field in the actual processing of the chuck inverted vertical lathe is calculated.
(4) The thermal deformation of the spindle during machining is analyzed in detail. The radial thermal deformation of the spindle is within the allowable range, and the axial thermal deformation increases continuously from the beginning of machining until the spindle reaches the dynamic thermal balance. In order to reduce the axial dimension error caused by the thermal deformation of the spindle of a chuck inverted lathe, an error compensation method based on the calculation of the transient thermal characteristics of the spindle installed in the lathe is proposed. A new method for predicting and compensating the thermal errors of lathe with motorized spindle under various working conditions is provided.
(5) Taking the prototype of lathe motorized spindle as the research object under different rotational speeds and load torque, the transient temperature rise experiment of simulating the process of automatic machining was carried out. On the premise of choosing the correct parameters and boundary conditions, the transient temperature rise of lathe motorized spindle in the process of automatic machining can be calculated effectively.
In summary, this paper mainly uses the thermal network method and the finite element method to reveal the mechanism and law of the structure parameter design of the lathe motorized spindle and the influence of intermittent load on the thermal performance. The temperature rise experiment of the lathe motorized spindle confirms that the theoretical calculation results are within the allowable error range and the motorized spindle is in the process of the chuck inverted vertical lathe. Thermal error compensation provides a theoretical basis.
【学位授予单位】：沈阳工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG51

【参考文献】