Papers by Author: Y. Gao

Abstract: Nano structures such as CNTs were proposed to be directly used as cutting grains to fully utilize the nice mechanical and thermal properties for nano machining. To further understand the CNT abrasive tool, a theoretical study of the CNT uncut chip model was conducted together with preliminary experimental tests to investigate the chip generation in the nano machining process. We found that the CNT distribution was not even in the CNT layer of the wheel. Based this finding, a grain spacing model and a feed of workpiece per cutting edge model were developed. Theoretical results were all very small. It was also found that individual workpiece chips were difficult to find due to small sizes. Further work is necessary. Furthermore, Chip gelling effect was found. The reasons were due to agglomeration and epoxy melting. Experimental results were found agree with our theoretical results.

Abstract: The opaque coolant used in the removal machining processes has an inaccessibility problem for the form error in-process optical measurement. The water beam assisted approach should be one of the possible solutions for the problem. In this project, we propose to study the measurement process using the computational approach for better understanding of the process and for validating the models and settings. The experimental results and the Computational Fluid Dynamics (CFD) results are found close to each other. This gives us confidence in using the proposed CFD models and settings. The proposed new transparent window definition is suitable. The models and settings established include geometric model, mesh adaption model, domain settings, coolant concentration representation, expressions, boundary conditions, and CFX solver settings. The developed CFD models and settings will be useful in our further studies of the form error measurement method.

Abstract: In precision machining, it is desirable to measure the workpiece form profiles to provide feedback for control to maintain machining quality. A water beam assisted form error in-process optical measurement approach has been proposed to solve the opaque coolant problem to permit form error in-process optical measurement. To have more comprehensive understanding of the method, factorial and preliminary parameter tests were conducted. It was found that the water flow rate Qw and the height of medium hm are the two most important parameters affecting the transparent window size At. For Qw, there is a transition of flow state changing from laminar to turbulent. Increasing hm generally gives smaller At. The preliminary parameter test results also show that the conditions Qw[0.6-0.75ml/s] and hm [0.3-0.4 mm] give better stability for At.

Abstract: Optical profiler is a typical modern device for precision form error measurement. In our use of the equipment, we found that the surface form profile after stitching is ambiguous if the lens magnification is changed. The error in terms of PV value can be up to 3200% when the lens magnification changes from 2.5 times to 30 times. This has been confirmed by the equipment supplier. It is worthwhile to offer a comprehensive study as many users may use the instrument of the kind straightforward without detailed investigation of the performance. We found that, among the 6 key parameters studied, 3 independent parameters are more important. For the 3 independent parameters, we recommend to set the magnification A=2.5 times, the resolution r=0.5, and the overlap p=20%. With the recommended settings, the measurement error can be less than 0.5%. Backscan and length for scanning in the vertical direction, and cut off frequency for delivering form profile are less critical compared with the three independent parameters.

Abstract: To allow better machining heat transfer through mist evaporation, a new active cooling method is proposed. It is based on variable strength activation of coolant together with active cooling. A key issue in the proposed method is the use of multiple actuators of high frequency vibration for extra strength increase. This will rely on the idea of focusing and superposition. In this project, experimental tests were conducted to test the idea for the proposed variable strength activation of coolant in precision machining. Experimental test results show that the effects of ejection distance de on the vibration sensor output amplitude Aa and output frequency fa are not significant. The output amplitude Aa has a linear relationship with the number of actuator na. The effects of na on fa is not obvious. Based on the results, the idea of using multiple actuators for focusing and constructive superposition in variable strength activation is confirmed.

Abstract: A new active cooling method is proposed for increased cooling effectiveness of coolant in grinding. It is based on variable strength activation of coolant together with active cooling to allow better machining heat transfer through mist evaporation. Multiple actuators are used through superposition and focusing. A device of variable strength coolant activation has been developed. Preliminary experimental tests were conducted to test the feasibility of the proposed cooling method. It is found that, using the proposed variable strength activation, an improvement of 87.6% in Ra value and 71.9% in Rq value were obtained when compared with the existing activated and cooled coolant cooling method.

Abstract: We propose to use nano structures directly to fully utilize the nice mechanical and thermal properties for nano machining. In this project, CNTs were directly used as cutting grains. For the CNT grains, we use epoxy as one of the bonding materials of our choice. A series of CNT grinding wheels were fabricated to demonstrate the effectiveness of the proposed new type of abrasive tool. Preliminary experimental tests were conducted for the proposed method of abrasive tool making. The CNT wheels are made of 1% MWCNTs or Multi Wall CNTs. Preliminary test results show that CNT wheels without functionalization or chemical treatment give the best average results. In the developed abrasive tool, CNT nano cutting edges are clearly seen in the TEM image. Carbon nanotubes can be used as cutting grains for nano machining. Further experiments are necessary.

Abstract: In order to enhance the cooling performance, better understanding of the effects of coolant parameters is necessary. In this project, a total of five input parameters for actively cooled and activated cutting fluid were studied. An aerosol spectrometer was used to measure the particle size spatial distribution of the cooling mist in the fluid. Taguchi method was used in the design of experiments. It was found that the unit volume net specific particle counts exhibit the behavior of oscillation and attenuation of a second order dynamic system. Cooling mist particle spatial frequency ranges from 0.01269/μm to 2.5/μm, the weighted average size ranges from 0.3051μm to 3.714μm and the particle size difference for 99.8% count attenuation ranges from 0.5μm to 19.7μm. The order of importance of the input parameters was studied and the coolant concentration was found as the most important input parameter for the unit volume net particle counts.

Abstract: An actively cooled and activated cooling approach is proposed and examined in this project in order to deal with the problems associated with methods such as the cryogenic cooling method. It is also aimed to further improve the surface quality of the workpiece after grinding by combining the advantages of the existing cooling methods. Both computational and experimental studies were conducted for grinding the brittle materials with the proposed approach. Optical examinations were used to study the surface morphology. The experimental results show that the surface quality can be improved by up to 23.75% on average in terms of surface roughness Ra. The computational test reveals that the heat can be taken away more effectively by the proposed approach.

Abstract: In order to allow optical signals to reach the workpiece surface to realize in-process optical measurement through an opaque coolant, a locally transparent region generated by use of an air beam is examined to allow better understanding of the fluid assisted in-process optical measurement approach. With the air beam used, the problems associated with the diluting effect on coolant concentration and the measurement error due to the optical transmittance through multiple media can be avoided. The working principle and the experimental results for testing the proposed method are presented and discussed.