Abstract: Molecular dynamics (MD) simulation can play a significant role in addressing a number of machining problems at the atomic scale. This simulation, unlike other simulation techniques, can provide new data and insights on nanometric machining; which cannot be obtained readily in any other theory or experiment. In this paper, some fundamental problems of mechanism are investigated in the nanometric cutting with the aid of molecular dynamics simulation, and the single-crystal silicon is chosen as the material. The study showed that the purely elastic deformation took place in a very narrow range in the initial stage of process of nanometric cutting. Shortly after that, dislocation appeared. And then, amorphous silicon came into being under high hydrostatic pressure. Significant change of volume of silicon specimen is observed, and it is considered that the change occur attribute to phase transition from a diamond silicon to a body-centered tetragonal silicon. The study also indicated that the temperature distributing of silicon in nanometric machining exhibited similarity to conventional machining.
Abstract: Feed drive system of machine tools may experience serious vibrations or unstable motions during high-speed operation. In this paper, a 6 D.O.F (Degree-Of-Freedom) lumped parameter model was proposed in order to analyze vibrations of a ball screw feed-drive system, which takes planar motion. The equations of motion were derived for the proposed model. Natural frequencies of the system and transient responses due to driving motor speed control input were also analyzed.
Experimental modal analysis and operational vibration measurements of a laboratory ball screw feed drive system were made. Both theoretical analysis and experimental measurement results showed good agreement with each other. Consequently we concluded that the proposed 6 D.O.F model could be well applicable to the vibration analysis of a ball screw feed-drive system.
Abstract: High-speed machining has received important interest because it leads to an increase of productivity and a better workpiece surface quality. However, the tool wear increases dramatically in high-speed machining (HSM) operations due to the high cutting temperature at the tool-workpiece interface and chip-tool interface. Cutting temperature and its gradient play an important role in tool life and machined part accuracy. This paper reviews different methods of the measurements of cutting temperature, which include: (1) thermocouples---tool-work thermocouple, embedded thermocouple, combination thermocouple and compensation thermocouple (2) optical infrared pyrometer, (3) infra-red photography, (4) thermal paints, (5) microstructure or microhardness observation. Each method has its advantages and limitations. The fundamental principles and application fields of each measurement method are presented, which is useful for the selection of the measurement methods for high-speed cutting temperature.
Abstract: Si3N4 ceramic matrix composites toughened with TiC nanoparticles were fabricated by using hot pressing technique with Al2O3 and Y2O3 as sintering aids. The effects of hot pressing temperature on the densification, mechanical properties and microstructure of Si3N4-TiCnano composites were investigated. The experimental results showed that optimum mechanical properties were achieved for Si3N4-30vol. % TiCnano composite hot pressed at 1750°C for 60min, under 30MPa pressure in N2, with the flexural strength, fracture toughness and hardness being 850MPa,
6.7MPa×m1/2 and 16.5GPa respectively. The microstructure and phase composition of the composites were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The analysis results indicated that fine, elongated b-Si3N4 grains and the reinforcements of both intergranular and intragranular TiC nano particles as well as the sub grain boundaries inside the b-Si3N4 grains contributed to the optimum properties of the composite hot pressed at 1750°C.
Abstract: This study deals with the construction of network system for the production site, for the purpose of networking the machine tools as a part of the whole system. The Tele-monitoring for transformation of monitored information was studied. From the point of view of monitoring, the recognition of abnormal is very important in reducing the burden of an operator or for long-time unmanned operations. We then propose a method for the detection of abnormal in cutting process by analyzing the cutting sounds using Fourier transform, filtering, correlation analysis and statistic treatment. For the checking of tool wearing progressing, an experiment was arranged for the
recognition of the sounds from a worn tip in comparison with a new one. On the detection of tipping of the cutter, a new tip is used for a long-time cutting without tool exchanging. The change of worn width and related values were compared with the original standard. It was found that the detection of tipping is possible by continuously sampling the cutting sounds and monitoring their correlation.
Abstract: Industry is looking for practical means to improve the accuracy of the parts machined on CNC machines. Some artificial intelligence (AI) systems have been applied in modeling and compensating manufacturing process errors in CNC machining. However, these systems are not capable of predicting the results of a new operation if no sufficient data on a number of similar operations is available. A generalized AI approach named synergistic interactions amongst modeling, sensing and learning is proposed in this paper. Based on the AI approach, a new strategy of error compensation of workpiece dimension in CNC machining is developed and applied in a CNC turning center. Error compensation results are illustrated the effectiveness of the error compensation strategy. The learning curve shows that the error compensation confidence gradually progresses towards 100% confidence from zero along with the CNC machine operation time increasing.
Abstract: More precise analysis and design of generalized lubrication system with the research results of modern lubrication theories are the effective measures to improve the efficiency and reliability of internal combustion engine. Through discussing and summarizing the development status in this field, a set of systematic methods of integrated analysis and design, and general rules are proposed in this paper. Technical measures for lubrication design of internal combustion engine are given. The database of lubrication design and condition monitoring is suggested to found. The best dispose of lubrication system design will be obtained through modeling, deducing control equation, and numerical simulation, improving and optimizing the coupling relationship among the capacity design, structure design, and lubrication design. Such, the modern lubrication design can be combined with strength design at the period of concert design and scheme design period really.
Abstract: A new intelligent tool condition monitoring technique for metal cutting process is
proposed. Fiest, the frequency spectrum analysis of the audio signal during cutting process, the pixel space projection analysis and equal gray pace analysis of the images of machined workpiece surface are introduced. Then combined the results of the audio signal analysis and the workpiece surface image analysis with artificial neural network, we implemented the intelligent tool condition monitoring based on multi-information fusion. The experimental results indicate that this method can
recognize the tool condition effectively and improve the dependability of tool condition monitoring.
Abstract: A better understanding of the hard-brittle material removal mechanism in wire-sawing provides a basis for optimizing the wire-saw and processing parameters. The maximum cutting depth of each diamond grain in wire-sawing is given. It is proved theoretically that the deformation mode on the machined hard-brittle material surface gradually shifts from brittle fracture to ductile deformation with the increasing of wire-saw velocity, the decreasing of infeed velocity and the decreasing of average grain size. The experimental investigation on the wire-sawing of granite is carried out. It is shown that in the case of wire-saw velocity of 20m/s, infeed velocity of 0.15mm/s and diamond grain size of 200~230#, the removal mechanism in wire-sawing is ductile mode.