Papers by Author: T. Sun

Abstract: In this paper, a coupled thermo-mechanical FE model is proposed to simulate the cutting temperature’s distribution produced in diamond turning. Simulated results indicate that the heat converting from plastic work has prominent effects on the distribution shape of cutting temperature field, and with an increment in cutting velocity, the locating site of maximal cutting temperature shifts from the contact area between tool tip and chip root to the contact area between rake face and chip. Cutting edge radius has minute influence on the distribution shape of cutting temperature field, but the bigger the cutting edge radius is, the higher the maximum cutting temperature in cutting region. Rake angle also has slight effects on the maximal temperature when it is more than 10○. While clearance angle reaches to 6○, the maximum cutting temperature approaches the smallest.

Abstract: With the development of science and technology, Atomic Force Microscope is widely applied to the field of machining process in nanometer scale. Due to the limitation of the inventive purpose of AFM, only height mode and deflection mode can be applied in AFM-tip micromachining. It can’t control the machining depth during the micromachining process at present. In this paper, a new micromachining system is set up, which composed of a high precision three-dimensional stage, an AFM, a diamond probe and a special control device. By utilizing variation parameters PID algorithm and controlling the machining depth directly, the micromachining system can resolve the problem mentioned above.

Abstract: The measuring system was developed based on a reconstructed atomic force microscope (AFM) combined with the precision rotating air-bearing and assistant transform shaft. By this system the experiment was carried out according to the principle of three orthogonal orientations towards a micro sphere about 0.46 mm in diameter, and nine one-dimensional traces around the sphere were obtained. Analyses on roundness and sphericity are carried out from the measured data.The results show that the maximal roundness is 0.3895 μm, and the sphericity error is 0.3880 μm.These evaluations are significant references to evaluate its fabrication accuracy or to reform its machining processes.

Abstract: In order to investigate nanoindentation data of polymer film-substrate systems and to learn more about the mechanical properties of polymer film-substrate systems, SEBS (styreneethylene/ butylene-styrene) triblock copolymer thin film on different substrate systems have been tested with a systematic variation in penetration depth and substrate characteristics. Nanoindentation experiments were performed using a Hysitron TriboIndenter with a Berkvoich tip. The resulting data were analyzed in terms of load-displacement curves and various comparative parameters, such as hardness and Young’s modulus. The results obtained by the Oliver and Pharr method show how the composite hardness and Young’s modulus are different for different substrates and different penetration depth.

Abstract: Atom Force Microscopy (AFM) can be employed to create surfaces in Si substrate with recessed features. The resulting patterns can serve as masters to make the required elastomeric stamps for soft lithography. Morphology analysis of patterned features on Si substrate and polydimethylsiloxane (PDMS) stamp by AFM imaging confirms that pattern can be successfully transferred from Si substrates to PDMS stamps. It is shown that this method for creating masters can be performed with an AFM, making this method particularly straightforward, economical and accessible to a large technical community that are provided with AFM for measurement.

Abstract: An improved arc welding method was developed to fabricate carbon nanotube probe under direct view of optical microscope. The new fabrication method here needs not coat silicon probe in advance with metal film, which greatly reduces the fabrication’s difficulty. An easy method for shortening the nanotube probe was also developed. The improved fabrication method here is simple and reliable. The fabricated carbon nanotube probe showed good properties of higher length-to-diameter aspect ratio, better wear characteristics than silicon probe.

Abstract: A brittle-ductile transition lapping mechanism is proposed for the mechanical lapping of ultra-precision diamond cutting tools, and then the critical depths of cut for brittle-ductile transition in different orientations and on different planes are deduced in theory. Combined the critical lapping depth with the contact accuracy between rotating scaife and lapped tool surface, the influences of processing factors on cutting edge radius are studied. Both the theoretical analyses and experimental results indicate that the vibration of lapping machine tool and surface quality of scaife have enormous influences on the sharpened cutting edge. And lapping compression force has an optimal value. Lapping rate should be considered when lapping velocity is selected. But the smaller the lapping velocity is, the littler the cutting edge radius sharpened. Finally, the optimal selections are performed for each influencing factor and a perfect diamond tool is lapped in ductile mode with a cutting edge radius of 30~40nm and a surface roughness Ra of 0.7nm.

Abstract: In order to avoid the stochastic damage of micro cleavage on cutting edge, a brittle-ductile transition lapping mechanism is proposed for the mechanical lapping of single crystal diamond cutting tools to direct the tools lapping. As expected, the critical depths of cut for brittle-ductile transition in different orientations and on different crystal planes are calculated. According to the theoretical results, the actual dynamic depth of cut is controlled within the critical depth of cut, which ensures that the tool lapping is carried out in ductile regime and the changes of cutting edge radius characterize with some specific time laws in lapping. Therefore, the time series and nonlinear least square methods are used to analyze the changing laws of cutting edge radius. As a result, a coupled model to build a bridge between the cutting edge radius changes and lapping time is developed. In terms of this developed model, a required cutting edge radius restricts a tool’s lapping time. Above all, the cutting edge radius is known in advance and has no needs measuring. So the production efficiency of diamond cutting tools is improved and its production cost is reduced accordingly.

Abstract: This study aimed to gain an in-depth understanding of the features of AFM micro probe nanomachining. With the aid of the orthogonal test analysis and synthesis method of point rating, factors of influencing the cutting process: the perpendicular load, the feed amount and the cutting speed, were analyzed. The study revealed that the feed amount and the perpendicular load had greater effect on the surface quality and machining efficiency than the cutting speed. The results were also compared with the conventional ultra-precision machining. The optimal machining parameters suitable for two application fields were achieved. This method is a novel and feasible method to perform the nanomachining.