Development of a 3D Vibration Assisted Machining System

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.

This instrumentation development project aims to design, fabricate and test a novel 3D vibration assisted machining system for micro milling of sculptured surfaces on hard-to-machine materials. The results from the project will be of benefit to academic and industrial research communities in precision machining, and also benefit to engineering students. The project impact is summarised as follows:

(1) Development of 3D VAM system will have scientific impact in the context of improving machining performance in fabrication of complex shape components on hard-to-machine materials.

(2) The kinematic model and the cutting force model in 3D VAM will help fill the gap in designing such instrument and lead to a better understanding of the vibration assisted process in particular and micro cutting mechanics in general.

(3) The design methodology and outcomes will also benefit research on other related areas, such as micro/nano positioning and control engineering.

(4) The project partners who are acting as the end users will utilise the technology developed in this research to improve their product performance, for example, elongation of the tool life and widening the range of applications. More similar collaborations with industrial companies will be formed during the project period, and implementation of 3D VAM will help them increase machinability of certain hard-to-machine materials which otherwise cannot be processed or are too expensive to be processed by the conventional machining.

(5) The project contributes to training of high skilled researchers in precision manufacturing and design engineering area. The RA who will work on the project will benefit significantly, gaining experience of this interdisciplinary field, incorporating machining sciences, structural dynamics, control engineering and engineering design, and developing a range of practical and analytical skills. 1-2 PhD students working on this project will also gain experience in design/experimental methods and become confident users of many scientific instruments for dynamic testing and surface characterisation.

(6) The educational impact of the project is to train the engineering students, particularly those who are studying engineering design and manufacturing related courses. Bringing vibration assisted machining into the engineering curricula to equip the next generation of manufacturing engineers with the latest technologies will retain the competitiveness of the UK in manufacturing.