In-process detection and closed-loop control of the amplitude during ultrasonic vibration superimposed turning for predefined and highly efficient surface microstructuring

对技术系统的效率和功能的要求越来越高，这使得人们更加关注它们的表面特性。微结构表面为改善这些性能提供了特别高的潜力，例如减少滑动摩擦。目前，微结构通常是通过像激光烧蚀这样的附加过程来实现的。这种方法会导致较长的流程链和较高的成本。因此，人们寻求将微结构直接集成到最终加工过程中。在被动力方向上叠加超声波振动进行车削是一种非常高效的加工过程。因此，在最终的加工过程中，每秒可以直接产生20,000多个微结构。然而，对于工作角度快速变化的微结构的产生以及系统的自动控制以确保振动幅度恒定，仍然存在一些悬而未决的基础科学问题。该研究项目的目的是深入了解超声振动叠加在被动力方向上车削时的整体相互作用。重点放在控制超声振动系统以及剪切区的机制上，这取决于工艺参数、材料和工具，包括由此产生的表面微结构。为了实现对超声振动幅度的高精度闭环控制，需要对超声换能器的机械信号而不是电信号进行近过程测量。为此，设计了一种特殊的超声换能器，它具有两个可互换的声纳极，可以通过集成的传感器精确地调节振动幅度。通过应变计、光纤布拉格光栅和加速度计收集有关工具的工作频率、当前振型和当前振动幅度的数据。针对切屑形成和生成表面的运动学模拟的先导实验使得能够设置必要的工艺参数。在实验研究中，使用了一种青铜材料。对所收集的数据、微结构表面的几何分析结果以及产生的切屑进行了分析。在此基础上，加工表面和模拟表面之间的差异与特定的作用机制和从传感器收集的数据有关。此外，还开发了一种包含位于刀具附近的传感器信号的闭环控制。因此，可以评估近程传感器在超声振动系统控制中的适用性。

Increasing demands regarding the efficiency and functionality of technical systems put a stronger focus on their surface properties. Microstructured surfaces offer an especially high potential for improving these properties, for example a reduction of the sliding friction. Currently, microstructuring is usually realised by an additional process like laser ablation. This approach results in longer process chains and high costs. Consequently, a direct integration of the microstructuring into the final machining process is sought. Turning with an ultrasonic vibration superposition in the direction of the passive force represents a highly efficient process. Thereby, more than 20,000 microstructures per second can be generated directly in the final machining process. However, there are still open fundamental scientific questions regarding the generation of the microstructures under consideration of rapidly changing working angles on one hand and the automatic control of the system to ensure a constant vibration amplitude on the other hand.The objective of the research project is to gain an in-depth understanding of the integral interactions when turning with an ultrasonic vibration superposition in the direction of the passive force. The focus is set on controlling the ultrasonic vibration system as well as the mechanisms in the shear zone depending on the process parameters, materials and tools including the resulting surface microstructures. A close-to-process measuring of mechanical signals of the ultrasonic transducer instead of electrical signals is expected to enable a high precision closed-loop control of the amplitude of ultrasonic vibrations.For this task a special ultrasonic transducer with two interchangeable sonotrodes allowing for a precise adjustment of the vibration amplitude by the integrated sensors is designed. Data about the operating frequency, the current mode shape, and the present vibration amplitudes at the tool is collected by strain gauges, fiber Bragg gratings, and an accelerometer. Pilot experiments addressing the chip formation and kinematic simulations of the generated surface enable the setting of the necessary process parameters. For the experimental investigations, a bronze material is used. The data collected, the results from the geometrical analysis of the microstructured surface, and the chips generated are analysed. Based on this, differences between the manufactured surfaces and the simulated ones are linked to specific effect mechanisms and the data collected from the sensors. Furthermore, a closed-loop control including the signals of the sensors positioned near the cutting tool is developed. Consequently, the suitability of close-to-process sensors for the control of ultrasonic vibration systems can be evaluated.