摘要
锻造生产是在高温和动载荷条件下进行的,由于生产条件复杂,操作机夹持界面的接触状态容易发生改变,会影响夹持稳定性。因此对锻造操作机夹持界面的力学性能进行研究显得尤为重要。
本文通过数值计算,对锻造操作机夹持界面的静动态力学特性进行了研究。重点对钳口与锻件接触界面的力学行为进行了探讨,为解决夹持稳定性问题及锻造操作机的结构设计和运动控制提供参考依据。
本文主要工作有:
(1)首先,建立了二维夹持界面有限元模型,利用静力隐式算法,探讨了接触压力沿锻件周向的分布形式;并对材料本构模型、锻件不圆度、夹持界面摩擦系数、钳口角度、锻件大小等系列参数进行了研究分析,确定这些参数对接触压力分布和接触力大小的影响;考虑到锻件重力会对钳口中心产生较大的力矩,在二维研究的基础上,讨论了三维夹持界面在锻件位姿变换时接触压力沿锻件长度方向的分布形式。
(2)其次,考虑到操作机整机在锻锤冲击作用下将受到影响,夹钳会产生回弹趋势,钳口夹持力也会发生改变,本文对锻造过程中夹持界面的动态力学特性进行了探讨分析。在对整机物理模型分析简化的基础上,利用动力显式算法重点研究了锻打速度、弹簧刚度、锻锤质量对夹钳回弹量、锻件最大塑性应变的影响;探讨了钳口夹持力在锻打作用下的变化情况,为进一步研究近恒力输出夹持系统的驱动策略提供参考。
Forging manufacturing is conducted in dynamic loads cases and under high temperatures. For the complex manufacturing conditions, the contact mechanical behavior between clamps and workpiece is changeable, and subsequently affecting the stability of the interface. It is necessary and significant to analyze the mechanical properties for those contact mechanical behavior.
Accordingly, this thesis mainly concerns with both the static and dynamic mechanical properties between clamps and workpiece through numerical analysis. It provides practical guidelines for the structure design and motion control of forging manipulator; also it gives useful suggestions for solving the stability problem.
This thesis mainly concerns with the following areas:
Firstly, the circumferential distribution of contact pressure along the workpiece was discussed by using the implicit algorithm for the established 2-D grasping FE model. Also, series factors that would influence the contact mechanical properties, such as the constitutive model, the roundness and size of the work piece, friction coefficient of the contact interface, the angle of clamps were investigated. In addition, as the gravity of the work piece will generate large moment for the clamp center, based on the 2-D model analysis, the axial distribution of contact pressure along work piece in 3-D model under different conditions was discussed in detail.
Secondly, since the manipulator will have a rebound behavior for the forging impact, and thus the clamping force will change accordingly as well, the dynamic contact mechanics during the forging operation is studied. Based on the simplified physical model, the influence of velocity, mass of the forging hammer, the stiffness of the manipulator, the spring back of clamp and maximum plastic strain of work piece have been discussed by using explicit dynamic algorithm. Moreover, from the grasping stability perspective, the change of contact force between the contact interfaces under forging impact is discussed. The discussion can provide with useful suggestions for the study of constant force output grasping system.
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