行星滚柱丝杠副小滚柱高效精确滚压塑性成形机制的研究

The ball screw has become a primary functioning unit of the modern machine tool. However, the load transfer is carried out by point contact of ball, which has a limitation on application in a high-load place. The planetary roller screw (PRS) consists of a screw and nut with several rollers parallel to the axis between the screw and nut, which work mechanism is planetary motion with low friction. The rollers have many point of contact with the screw and nut, and a group of rollers bear the load simultaneously, and then PRS provides a load is 3 times greater than that of ball screw, and thus the PRS has become the research focus. The roller is much complicated in structure, which has a thread feature at middle section and spline or gear features at both ends, and the efficiency of production manufactured by conventional machining process is very low. Thus, a novel progressive process is proposed in this project, in which thread and spline shapes of the roller are formed by rolling simultaneously. By using the theories of plastic processing mechanics, differential geometry, plane and space engagement, the meshing equation for rolling die and workpiece and the mechanical model in the process of thread and spline rolling simultaneously are established. The key techniques of finite element modeling for the process of thread and spline rolling simultaneously are solved. The plastic forming mechanism of thread and spline rolling simultaneously is revealed. The influence laws of geometric parameters (blank shape and die structure) and processing parameters (angular velocity of die, infeed speed of die, and decrement of workpiece per revolution) on the rolling process are obtained. The reasonable parameters are determined, and then the relevant experiments are performed to validate the research.

滚珠丝杠副已成为现代机床的基本功能部件，因其是采用钢球点接触传力方式，限制了其在大载荷场合的应用。而线接触传力方式的行星滚柱丝杠副中螺母与大丝杠之间均布多个小滚柱，使用滚动的低摩擦工作方式，承载力高达滚珠丝杠的3倍以上，已成为目前研究的热点问题。该小滚柱结构复杂，中部为螺纹特征，两端为花键或小齿轮特征，采用传统的切削制造方式生产效率极低，本课题提出利用滚压塑性变形同时成形小滚柱螺纹和花键齿形新工艺。应用塑性加工力学、微分几何、平面和空间啮合理论，建立螺纹与花键齿形同时滚压塑性成形中模具和工件的啮合运动方程以及塑性变形力学模型；解决螺纹与花键同时滚压多因素耦合下成形过程数值模拟时的关键技术问题；揭示螺纹与花键同时滚压塑性变形机理；获得几何参数（坯料形状、模具结构）和工艺参数（模具转速、模具进给量、工件每转压缩量等）对螺纹与花键同时滚压成形过程的影响规律，得到合理工艺参数，并进行相关实验验证。

行星滚柱丝杠有标准型和反向式两种，标准型和反向式行星滚柱丝杠副中的滚柱零件同时具有螺纹和小模数花键或齿轮特征，在反向式行星滚柱丝杠副中短丝杠也具有相类似的特征。此外在汽车转向系统、变速器等中也存在类似的同时带有螺纹和花键或小模数齿轮的轴类零件。螺纹与花键同时滚压成形，在一次滚压成形中可同时成形零件上不同部位的螺纹和花键齿形，可有效地减少了成形零件的时间，提高花键段的分齿精度，易于保证螺纹和花键相对位置稳定。本项目对螺纹花键同时滚压成形小滚柱零件的模具结构、啮合特性、成形特征等进行了研究，主要研究内容和重要结果如下：建立了具有普遍性的螺纹和花键滚压前模具相位要求的数学表达式，研究了螺纹花键同时滚压成形前模具相位调整要求，在此基础上确定螺纹花键同时滚压用模具结构；基于平面啮合原理和花键滚压工艺特征，建立了中心距连续变化条件下确定瞬心、传动比、瞬心线的数学模型，分析了渐开线圆齿根花键滚压成形过程中运动特征；基于空间啮合原理和螺纹滚压工艺特征，分析了中心距变化下螺纹滚压过程中工件模具间运动特征，建立了滚压成形过程工件旋转角度、角速度，以及传动比、瞬轴面等相关数学模型，模型应用于渐开螺旋面和阿基米德螺旋面滚压成形分析；基于螺纹花键同时滚压成形工艺特征，进行了适当简化，建立了螺纹花键同时滚压成形过程的有限元模型；研究表明，通过适当的模具结构和工艺过程控制，该成形工艺能够正确成形出零件上不同部位的螺纹牙型和花键齿型；滚压成形过程中存在载荷波动，滚压模具径向进给停止后滚压力开始减少，滚压成形过程中塑性变形仅发生在成形螺纹和花键的部分区域，而且剧烈的塑性变形仅发生在这些区域的表层；螺纹段滚压成形的径向影响区域要大于花键段，不同齿型成形段的变形对轴向影响较小。研究结果为该类零件的塑性成形制造奠定了良好的理论基础。