Development of a 3D Vibration Assisted Machining System

在加工过程中，工件和刀具之间的振动会降低加工精度和表面质量。然而，受控的小幅度(几微米)高频(几十千赫)振动可以促进机械加工过程。这称为振动辅助加工(VAM)。VAM结合了刀具与工件之间小幅度振动的精密加工，在适当的加工和振动参数设置下，刀具可以周期性地与切屑失去接触，从而改变了切割运动学和力学，从而提高了加工性能。报道的好处包括：减少了加工力；提高了表面光洁度和成形精度；抑制了毛刺的形成；减少了刀具磨损和延长了刀具寿命；等等。在车削过程中，由于刀具是固定的，振动辅助相对容易实施。一维振动辅助系统和二维振动辅助系统在车削加工中都得到了成功的应用，其中一维振动辅助系统是指在加工方向上的线性辅助振动，而二维振动辅助系统是指在加工方向和深度方向上的椭圆运动。由于磨削过程运动学和动力学的复杂性，振动辅助磨削在磨削加工中的应用还很少受到重视。目前对振动辅助磨削的研究都是纯经验的，缺乏精确的运动学和动力学模型来设计最优的VAM系统，而且所有的二维振动辅助磨削的研究都局限于低频，不适用于微细粉碎操作。此外，为了获得复杂的形状几何，铣削过程需要在空间中的任意方向上的进给矢量，即对于3D端铣来说，进给矢量的垂直和水平分量都是必需的。然而，目前还没有3D VAM系统的报道。为了克服这些技术上的局限性，利用振动辅助的优势，本项目将开发一种新型的紧凑型三维振动辅助加工系统，用于对难加工材料上的自由曲面进行微细加工，并通过加工实验对其性能进行评估。在生物工程、MEMS、光学等各种应用中，由半导体材料、压电材料、玻璃等难加工材料制造精密微型产品的需求越来越大。该项目的成功将为以更具成本效益的方式加工此类材料开辟新的工业途径。然而，为了在实践中实现这一点，迫切需要开发三维振动辅助加工系统及其相关的设计和建模方法。

Vibrations between the workpiece and the cutting tools in machining processes can deteriorate machining accuracy and surface quality. However controlled small amplitude (several microns) high frequency (tens of kHz) vibrations can facilitate machining processes. This is called vibration assisted machining (VAM). VAM combines precision machining with small amplitude vibration between tool and workpiece, and for appropriate machining and vibration parameter sets, the tool can periodically loses contact with the chip, which changes the cutting kinematics and mechanics, and can improve machining performance. Reported benefits include: reductions in machining forces; improved surface finish and form accuracy; suppression of burr formation; reduction of tool wear and extension of tool life; etc. In turning process, the vibration assistance is relatively easy to implement as the tool is stationary. Both 1D vibration assisted system, i.e. linear vibration assistance in the cutting direction, and 2D vibration assisted system, i.e. elliptical vibration motion in the plane of cutting direction and depth of cut direction have been applied in turning processes with success. Due to the complexity of kinematics and dynamics of the milling process, application of vibration assistance to milling has received little attention. Currently efforts on vibration assisted milling are purely empirical and lack accurate kinematic and dynamic models to design an optimal VAM system, and all 2D vibration assisted milling studies have been limited to low frequencies which are not applicable to micro milling operations. In addition, to obtain complex shape geometry, the milling process requires a feed vector in arbitrary direction in space, i.e. both a vertical and horizontal components of feed vector are necessary for 3D end milling. However, currently no 3D VAM systems have been reported. To overcome these limitations on the state-of-the-art and make use of the advantages of vibration assistance, this project will develop a novel compact 3D vibration assisted machining system for micro milling of free-form surfaces on hard-to-machine materials, and evaluate its performance through machining experiments. Fabrication of precision micro products from hard-to-machine materials, such as semiconductor materials, piezoelectric materials, glasses, is increasingly in demand in various applications such as bio-engineering, MEMS, optics, etc. Success of the project would open new industrial avenues for processing such materials at a more cost-effective manner. However, to achieve this in practice, development of a 3D vibration assisted machining system and its associated design and modelling methodology are urgently needed.