Development Of A Three-Dimensional Elliptical Vibration Assisted Diamond Cutting Apparatus

Diamond cutting is an important method in precision and ultra-precisionmachining. There are still, however, some difficulties, one of which is that materialsmachined by diamond cutting are restricted. For example, diamond tools’ cuttingperformance can be very poor when cutting ferrous metals like Hardened steel orbrittle materials like Silicon carbide, resulting serious tool wear and deterioration ofsurface quality. Vibration cutting especially the three-dimensional elliptical vibrationcutting is considered to be the most effective method to solve the problems mentionedabove for its advantages such as reducing the cutting force and the tool wear andimproving the surface quality. However, current research into three-dimensionalelliptical vibration cutting is far from perfect and existing devices used to generatethree-dimensional elliptical vibration are far from enough. Therefore, it is ofsignificance in both the theory and the practical application to develop a novelthree-dimensional elliptical vibration diamond cutting device.The dissertation focuses on development of a three-dimensional ellipticalvibration cutting device whose main structure is designed by using flexure hinge.Three PZT stacks which are perpendicular to each other are adopted to drive theflexure hinges as well as the diamond tool in three axes. Each axis’s displacement andstiffness are designed to be10μm and50N/μm respectively. Three capacitivetransducers from Microsense are used to detect displacement of the three axes.The vibration device is mainly composed of a3-DOF flexure hinge structurewhose three directions are alone X-axis, Y-axis and Z axis separately. Mainadvantages of this design are as follows:(1) Fixed parts and moving parts aremanufactured by EDM as a whole and so there are no assembly errors and movingclearance;(2) Each axis is guided by several pairs of flexure hinges and so there is nolateral movement;(3) Force coupling and kinematic coupling are not serious and sothere is no need to design a special controller to remove them;(4) vibration directionin X-axis, Y-axis and Z-axis are just along with the Normal, Principal and Thrust direction in actual cutting process and so it is easy to analyze how the vibrationconditions in the vibration cutting device affect the experiment results.In order to obtain the response characteristics of the device, offline tests arecarried out in a testing system established by a Newport RS4000air bearing table,PMAC multi-axis motion controller, industrial PC and so on. Through the offlineexperiments, stiffness of X-axis, Y-axis and Z-axis are50.93N/μm,39.42N/μm,40.36N/μm respectively, the stroke8.63μm,10.37μm,10.21μm and the resonancefrequency2879Hz,1717Hz,1748Hz. After that, the three PZT stacks are driven bythree sinusoidal voltage signals in different phase and capacitance sensors are used tomeasure the output displacement of each PZT. Composite motions of every two of thePZT stacks are elliptical trajectory in XY plane and YZ plane or reciprocating lineartrajectory in XZ plane.The3D elliptical vibration cutting device is installed into a precision CNC latheon the slide and the workpiece is clamped in the spindle chunk. Turn the workpieceby using the vibration cutting device under different oblique angles of the ellipticalvibration trajectory while other conditions including the workpiece material(6061aluminum alloy), cutting tool(PCD) and cutting parameters of the lathe remainunchanged. Compare the obtained workpiece surface and the cutting chip, it is foundthat with the oblique angle increases, the surface becomes more and more finishing,the surface roughness value(Ra) gets smaller and smaller, the cutting chip curls moreand more evident and the chip length appears longer and longer.