Dun Wen Zuo

The Application of FEM Technology on the Deformation Analysis of the Aero Thin-Walled Frame Shape Workpiece

Many thin-walled structure components widely used in aero industries not only have complex structure and large size, but also need high machining accuracy. However, because of their poor rigidity, it is easy to bring machining deformation caused by the existence of the initial residual stresses, the fixing stresses, cutting forces and cutting heat. The difficulty in ensuring their machining accuracy becomes a big problem, so that how to effectively predict and control the machining deformation has become an important subject in the development and production of our national defense weapons. This paper established a 3-D Finite element model with consideration of milling forces, clamping forces and initial residual stress field. By using this model, machining deformation of thin-walled frame shape workpieces has been computed. The simulated results are compared with experimental data, and the correctness of the simulation is verified. The study is helpful to the prediction and the control of machining deformation for thin-walled parts.

Some Key Points for EACVD Thick Diamond Film Preparation

Some key points for thick diamond film preparation by using of EACVD, which is considered as one of the most practical methods, were introduced. The study was focused on the effect of carbon-contained gas supply, the temperature distribution on the substrate surface, the selection of substrate material, and so on. It is found that the maximum diameter of the thick film to be prepared can be predicted according to the filament condition, and it is possible to prepare a film of 150mm diameter under the condition studied. On the basis of the study, some sets of EACVD equipments were developed successfully. Introduction Much attention has been paid to chemical vapor deposition (CVD) thick diamond film in mechanical engineering and other machining fields [1-2], since it can be used as an advanced cutting-tool material. How to prepare the film with a high quality and a high efficiency is the most interesting subject both in academic research and engineering application [3-4]. Nowadays, there are many methods developed to prepare the CVD diamond film, e.g. flame CVD, hot filament CVD (HFCVD), DC arc plasma jet CVD, micro-wave CVD (MWCVD), electron-assisted CVD (EACVD), etc., among of which the EACVD is considered as one of the most practical methods. For its wider application, the cost of CVD thick diamond film and its processing [5-6] is a big problem, and thus high-efficiency preparation of the film and low-cost equipment must be firstly realized. However, the fact is that the equipment for commercial use is too expensive to be acceptable for general use. Trials are still being made on the development of low-cost equipment. In this paper, study is focused on thick diamond film preparation by using of EACVD, where some key points are investigated to develop practical EACVD equipment at low cost. After the mechanism is introduced, the effect of carbon concentration in the mixed gas on the diamond growing is studied. The temperature distribution on the substrate surface is investigated in details theoretically, where the effects of filament diameter, its number and the distance between it and the substrate are made clear. Further, discussion is carried out on the substrate material selection for diamond deposition. EACVD equipment is finally developed based on the study, and thick diamond film is prepared with the equipment. The performance of the equipment is tested, and the film quality is analyzed. EACVD Mechanism and Gas Supply EACVD Mechanism. The CVD mechanism for diamond deposition is well known as shown in Fig.1, where chemical reaction happens between hydrocarbon and active hydrogen atoms and results in activated hydrocarbon radicle. The radicle is then decomposed into new hydrocarbon, new radicle, hydrogen atom and carbon. The carbon deposits onto substrate in both of diamond phase and graphite phase. The graphite phase is further etched by the active hydrogen atoms to produce new hydrocarbon. This process circulates, and the diamond grows up. All the reaction, decomposition and etching need an appropriate temperature and vacuum, so the temperature and vacuum during the process must be controlled well. The difference among the different CVD methods consists mainly in the heating method. In case of Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 517-521 doi:10.4028/www.scientific.net/KEM.259-260.517

Effect of DC-Plasma Arc Behavior on Growth of Diamond Film

DC-Plasma arc behavior is one of the key factors on growth of diamond film. The results show that keeping steady DC-Plasma arc can grow better quality diamond film. In a long-time growth of diamond film, there is sediment carbon on about 5mm border-entad anode annulus, which was proved to be graphite. It results in fluctuating and instability of DC-Plasma arc and in the DC-Plasma density, which causes graphite generation and much stress in the film. By means of adjusting anode annulus assembly, pausing the supply of carbon source and increasing H2, the problem of sediment carbon cab be effectively resolved. Finally, the mechanism of the effect of arc behavior on growth of diamond film is discussed.

Study on EDM Polishing of CVD Diamond Films

Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra<0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.

Study on Mechanical Polishing for CVD Diamond Films of Forming Nucleus Surface and Growing Surface

In the present work, high power DC arc plasma jet chemical vapor deposition (CVD) is used to prepare diamond films with full width half magnitude (FWHM) less than 10 wave numbers at 1332 cm−1 Raman peak. During the polishing process, diamond film is hold against the stainless steel holder, which rotates and swings when the sample comes into contact with the cast-iron plate. Average surface roughness of the forming nucleus polished surface and growing polished surface is 560nm, 90nm respectively. And the materials removal rate is quite different. Fine crystal grain of the forming nucleus surface and the thick column crystal of growing surface are dominant in structure. In the meantime, effects of the size of the abrasive power, the applied force and polishing direction are also discussed. A profilometer, an Raman spectroscopy, X-ray diffraction and a scanning electron microscope have been used to evaluate the surface states of diamond films before and after polishing. This result reveals an. improvement of polishing efficiency and a great potential for commercial application.

Preparation of Nanocrystalline Diamond Films on Molybdenum Substrate by Double Bias Method

The synthesis of nanocrystalline diamond film on polycrystalline molybdenum substrates was carried out by using of self-made hot filament chemical vapor deposited (HFCVD) system. Positive bias voltage on the grid electrode on top of hot filaments and negative bias voltage on the substrate were applied. High purity and extremely smooth nanocrystalline diamond films were successfully prepared by using the double bias method. Raman, SEM, XRD and AFM results show that the diamond films obtained have grain sizes less than 20nm, nucleation density higher than 1011cm-1. The mechanism of double bias is also discussed in this paper. The positive grid bias increases the active, decomposition and ionization of hydrogen and methane molecules, while negative substrate bias helps positive carbon-containing ions bombard the substrate that leads to the high nucleation density of the diamond film.

Smoothing of Thick Diamond Film Prepared by Electron-Assisted CVD

This paper focused on the smoothing of thick diamond film prepared by electron-assisted chemical vapor deposition (EACVD), whose equipment was developed by the authors. CO2 laser and YAG laser were used to scan the film surface. It is shown that CO2 laser is not suitable to the surface smoothing, while YAG laser is effective to remove the salience on the film surface, though thermal damage occurs in the surface to some extent. A final mechanical lapping was introduced to remove the damaged layer occurred in the laser smoothing. The results showed that a low roughness Ra 0.1μm could be obtained with a high efficiency. Introduction Low processing efficiency is an important problem left in the application of CVD thick diamond film in engineering, although its super performance enables it to have so wide range of application not only in mechanical engineering but also in electronical and aeronautical ones. Generally, cutting-off, grinding, lapping, polishing and brazing are needed when the thick film is applied to some cutting tools or mechanical parts, where it will take much time to smooth the film because of its super hardness. As a result, a high processing cost plus the high cost of the film itself become restriction to its popular application. Much attention has been paid to the smoothing of CVD diamond film, and some new methods were applied to the smoothing, such as ion beam irradiation, hot-iron-metal polishing, etc [1-3]. Attention was also paid to precision micro-machining for the film [4]. In this paper, experiments were conducted on smoothing of thick diamond film prepared by EACVD [5], and the effects of laser scanning and mechanical lapping condition on the surface roughness and surface quality were investigated [6]. For the thick film used, it had an initial diameter of about 100 mm and a thickness of 0.6 mm. It was cut into small circle pieces by using of YAG laser for smoothing experiments. A special set-up was designed to adjust the incident angle of laser beam when scanning the film surface. Holing experiments were firstly made as pretest to investigate the effect of laser power on the diamond removal. The surface roughness was measured and compared under different conditions, and the smoothed surface was observed by using of SEM. Raman spectrum analysis was conducted after laser smoothing and mechanical lapping. Laser Processing CO2 Laser Processing. Laser is a typical kind of the beams that have high-density power, and it has been applied widely in material removing, not only for metal materials but also for non-metal ones. CO2 laser is powerful and able to show high efficiency in cutting-off of thick steel plates, and it is also effective to process difficult-to-machine materials such as ceramics. For the reason, in this study trials were made to use CO2 laser as a pre-smoothing method for the initial rough surface of thick diamond films as shown in Fig.1a. Experiments were made in Engineering Center of Laser & Advanced Manufacturing, Jiangsu University. The laser power, its spot diameter and scanning speed were changed in the experiments, and the incident angle of laser beam , as shown in Fig.1b, was adjusted by using of the specially Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 507-511 doi:10.4028/www.scientific.net/KEM.259-260.507

Effects of Processing Parameters on Energy Efficiency of Squash Presetting Laser Cladding

The green presetting of powders was performed on the substrate by introducing a novel technique namely squash presetting method, and cladding coatings were prepared by crosscurrent CO2 laser in this work. Based on the concept of laser energy efficiency which being accepted generally by insider, the energy efficiency of squash presetting laser cladding was determined. Meanwhile, effects of processing parameters including specific energy, laser power, scanning speed and spot diameter on energy efficiency were investigated through an orthogonal test. The results show that the energy efficiency increases at first and then decreases with the increase of specific energy, and the energy efficiency is relatively higher when laser specific energy ranged from 90 J/mm2 to100 J/mm2. Among three single-factors, the effects of spot diameter on energy efficiency are most significant, laser power takes second place, and scanning speed comes next. It is considered through analysis that the relationship between energy efficiency and processing parameters is closely related to powders melting and heat-conduction course of squash presetting laser cladding.

Green, Flexible, Intelligent: Clamping System Based on Thermal Sensitive Material with Volume Effect

Nowadays, the research on the greenization of clamping technology obviously lags the research of green cutting, green machine tool etc. This paper provides a new clamping system to clamp the workpiece by the green fast heating/cooling adverse-change semiconductor technology and temperature controllability to thermal sensitive medium with volume effect. This clamping system has a low speed operating part, few moving parts, low medium leakage and noise pollution and it is convenient to be flexible configuration of multi-place, multi-workpiece and multi-direction clamping. Furthermore, the clamping system can use the sensors of temperature, pressure and displacement to collect the relative data and process them by computer, then intelligently control the clamp force and clamping displacement.

The Design of Noncircular Gear of Constant Pressure Angle and the Realization of Its Wire-Electrode Cutting

This paper brings forward a new type of the tooth profile of noncircular gear—constant pressure angle involute tooth profile, and realizes its wire-electrode cutting. By the design of CAD and CAM, this paper shortens the design time of the noncircular gear and improved the design accuracy of the noncircular gear. By the research of the constant pressure angle involute tooth profile of noncircular gear, this paper has improved the transmission accuracy of the noncircular gear. By the research of the technology of wire-electrode cutting, this paper has improved the manufacturing accuracy of the noncircular gear.