Papers by Author: Xun Chen

Abstract: Cutting processes in machining involves the elastic and plastic formation where a layer of material is removed by a cutting tool to be removed from the workpiece in forms of various types of small chips. In this paper, a series of finite element simulations of 2D chip formation with various parameters are presented. Different types of chip shapes, such as continuous, discontinuous and serrated shape, are simulated under different conditions. A damage evolution technique based on fracture energy dissipation during material damage progression is used to demonstrate the influences on chip formation. It is concluded that the fracture energy in damage evolution is a crucial factor for the determination of chip shape. Further the influence of depth of cut and rake angle are considered in the simulations.

Abstract: The multi-pass nanometric machining of copper with diamond tool was carried out using the Molecular Dynamics (MD) simulation. The copper-copper interactions were modelled by the EAM potential and the copper-diamond interactions were modelled by the Morse potential. The diamond tool was modelled as a deformable body and the Tersoff potential was applied for the carbon-carbon interactions. It was observed that the average tangential and the normal components of the cutting forces reduced in the consecutive cutting passes. Also, the lateral force components are affected by atomic vibrations and the cross sectional area during the cutting process.

Abstract: This paper presents recent development in acoustic emission (AE) technique for grinding process monitoring. It demonstrated the similarity of thermal acoustic emission feature existing in grinding processes and laser irradiation tests. An innovative concept that grinding process can be monitored by using thermal AE signatures from laser irradiation tests has been proposed. Based on such idea, an artificial neural network (ANN) was built and the results showed that grinding performance variation due to wheel wear can be identified by using the ANN. This development could bring great benefits by reducing experimental works in the preparation of an ANN for grinding monitoring.

Abstract: The paper presents an investigation of grinding material removal mechanism using finite element method. Understanding of grinding removal mechanism relies on the investigation of material removal by each individual grain. Although some analytical formulations have been developed to predict and to quantify the machining events in grinding, they do not illustrate every stage of abrasive actions. Finite element analysis provides good facility to present details of physical behaviour in grinding. In this research, material removal mechanism of grinding, namely rubbing, ploughing and cutting, is discussed with the variation friction coefficient. The major emphasis here is on the ploughing. Total force variation exerted during indention and sliding of a grain is also presented along its path.

Abstract: Traditionally, abrasive finishing process only focused on producing excellent surface finish on regular form shapes. Ever increasing demands in freeform features in aerospace, energy and medicine applications require abrasive finishing technology not only provides excellent surface finish but also is capable to correct the errors on freeform surfaces. The paper presents current development of corrective polishing technology for freeform surfaces.

Abstract: This paper looks at the multiple characteristics and investigations of two grinding anomalies: grinding burn and grinding chatter. A genetic programming (GP) of multiple classifications was investigated for different machining strategies and associated anomaly phenomena. Such a GP paradigm could evolve rules to provide the correlation between monitored signals and grinding phenomena. The investigation also looks at both Short-Time Fourier Transforms (STFT) and Wavelet Packet Transforms (WPT) to convert the raw acoustic emission (AE) signal into a time based frequency signal, segmented into different frequency bands. A set of encouraging results is presented.

Abstract: The material removal in grinding involves rubbing, ploughing and cutting. For grinding process monitoring, it is important to identify the effects of these different phenomena experienced during grinding. A fundamental investigation has been made with single grit cutting tests. Acoustic Emission (AE) signals would give the information relating to the groove profile in terms of material removal and deformation. A combination of filters, Short-Time Fourier Transform (STFT), Wavelets Transform (WT), statistical windowing of the WT with the kurtosis, variance, skew, mean and time constant measurements provided the principle components for classifying the different grinding phenomena. Identification of different grinding phenomena was achieved from the principle components being trained and tested against a Neural Network (NN) representation.

Abstract: The paper presents a method that identifies and extracts features of chips on loading grinding wheel using image processing technology. The Sobel operator is adopted to detect chips edge. The segmenting threshold was obtained by applying Otsu's method. Image dilation connects the discontinuous segments to yield continuous and close shapes of chips. Erosion removes the noise from the image. The different optical characters between metal chips and abrasive grains are analysed. The ratios of chips are calculated and displayed to monitor the wheel surface working status. The toolbox of the MATLAB is used for image processing.

Abstract: Finite element (FE) analysis is very useful in the early stage of a fixture development in order to reduce or eliminate design problems. Accurate prediction of fixture-workpiece deformation requires an appropriate representation of the contact relationship between fixture elements and workpieces. The paper addresses the special features of the deformation analysis between complicatedly shaped components and fixture elements. The effectiveness and the scope of applicability of commonly used methods are analysed. The verified FE analysis is used to predict surface error arising from deformations, and to evaluate the deformation distributions from fixture elements and workpiece. Based on the FE analysis, the tolerance can be allocated to the fixture elements and the workpiece. The development of a turbine blade fixture is provided as case study.

Abstract: Grinding burn is a common phenomenon of thermal damage that has been one of the main constraints in grinding in respect of high efficiency and quality. Use of acoustic emission technique for identifying grinding burn was reported before. However, the AE features of grinding burn are relatively weak and easily merged by other AE sources. This paper presents an investigation of the AE features of the thermal expansion induced by laser irradiation, which was designed to simulate grinding thermal behaviour. By means of the wavelet packet transforms, AE features at the grinding burn temperature can successfully be extracted without other mechanical interferential factors. These clean features can provide a firm foundation for analysing the real grinding burn AE features and for monitoring grinding burn.