Key Engineering Materials Vols. 315-316

Abstract: Austenitic stainless steel is a kind of difficult-to-cut material widely utilized in various industry fields. But cutting tools is the uppermost obstacle in the application of high efficient and precise machining of austenitic stainless steel. Drill is the one of the most complicated universal cutting tools, whose geometry structure influences greatly on drilling performance. So the development of special drills is imperative for high-efficient drilling. This paper presented the optimal geometrical characteristics of the special drills, with138° point angle and 38° helix angle, for high-efficient drilling austenitic stainless steel. The drilling performance has been evaluated completely and comprehensively through the experiments including measuring cutting deformation coefficient, thrust force, torque, cutting temperature near the cutting point, cutting tool life, drill wear mechanism and so on. The special drill indicated appreciated cutting performance during drilling austenitic stainless steel with high efficiency. Compared to the commercial available standard drill with 118° point angle and 32° helix angle, the cutting tool life of the special drill was 1.6 times of the standard drill and the special drill yielded good performance of chip evacuation, good wear resistance and great drilling quality.

Abstract: Coating is an effective method to solve the contradiction between the wear resistance and the toughness for tool materials and the coated tool can yield satisfied cutting performances. Now the coated high-speed steel (HSS) drill is widely used in drilling of stainless steel. This paper studied the tool life of the TiN, the TiAlN and the TiCN coated special drills in drilling austenitic stainless steel 1Cr18Ni9Ti through contrastive experiments. The tool life of the TiN coated drill was only 81.5% of TiCN, and 66% of TiAlN because of its low oxidization resistance and hardness. The wearing features of TiAlN and TiCN coating were also studied by experiments and the different wear mechanisms were revealed. Finally the comparison of cutting performance was given between TiAlN and TiCN coated drills and recommendation of coating selection for drilling austenitic stainless steel was also presented. TiCN coating is suitable for HSS cutting tool base, which is often used for drilling austenitic stainless steel at low speed. TiAlN coating is appropriate for tungsten carbide cutting tool base, which is used for drilling austenitic stainless steel at high speed. The special designed drill with optimal geometrical structure plus appropriate coating can yield long tool life and high material removal rate in high-efficient drilling austenitic stainless steel.

Abstract: Improving adhesion and surface roughness of diamond films on WC–Co substrate is the key factor of the widespread application of diamond coated tools. A new pretreatment method has been performed for smooth Co-cemented carbide inserts in order to lower the surface roughness of diamond films under the premise of good adhesion between diamond films and substrates. The effect of the new pretreatment on the adhesion of the diamond films is investigated. Research results show that the boronization pretreatment can effectively suppress cobalt diffusion to the surface and avoid catalytic effect of Co at high temperature. This new pretreatment can avoid the surface roughening of inserts and ensure the deposition of smooth diamond films. Investigation shows that the optimum boronization compounding is a powder mixture of 70%B4C+15.5%KBF4+1.5% La2O3+13%Na2CO3. Adhesion between substrates and diamond films is evaluated by Rockwell A indentation tests and the cutting performance of the diamond-coated tools is investigated by the cutting tests. Diamond films on smooth cemented carbide inserts with cobalt boride interlayer have high adhesive strength and low surface roughness. Diamond-coated tools with boronization pretreatment have a 5-fold increase in tool life compared with untreated ones.

Abstract: The bearing support implement is the key component in the precision process of bearings. Diamond films are deposited on Co-cemented carbide bearing support implements using the acetone and hydrogen as the gas source by the bias–enhanced hot filament chemical vapor deposition (HFCVD) technique. Diamond-coated bearing support implements are fabricated and used in the precision grinding of bearings. The research results show that the appropriate pretreatment methods and CVD process can effectively control the morphology, chemical quality, surface roughness, and adhesion of diamond films. As compared with the cemented carbide bearing support implements, the diamond-coated bearing support implements have obviously better wear resistant properties and working performance. It is of great significance for improvement of the bearing processing quality and raising of the bearing processing level.

Abstract: 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.

Abstract: The design for orthogonal cutting experiment is made according to the characteristics of a new kind of nickel-based super alloy. The machinability of this new material in milling and drilling operations, including cutting force and tool wear, has been researched through experiments and then the empirical formulas of cutting force in milling and drilling have been presented. The research is useful in selecting the tool geometry and cutting parameters for machining the new material in practice.

Abstract: The state of the passivating film is a key factor affecting ELID grinding. In the paper the state of the passivating film on the grinding wheel surface was characterized by the loop current, the strategies actively controlling the film state, discontinuous in-process electrolyzing and intermittent grinding were put forward, and the ELID grinding tests under the conditions of actively controlling of the film state and the traditional dynamic balance of the film state were respectively performed and contrasted with each other. It is indicated that by real-time monitoring of the film state with the loop current, the film state variation could be controlled to a narrow scope with the strategies of discontinuous in-process electrolyzing and intermittent grinding, as a result the ELID grinding kept at a fine quality and a high efficiency.

Abstract: This paper presents an electronic subdviving method for linear encoder of high speed position detection. The method aims to enhance the resolution of position measurement and improve the precision of noncircular component cutting system. A 20-subdividing circuit based on resistor chain phase shift is researched and implemented, and some key technologies are discussed. The method is proved to be successful in raising the resolution and precision with a high speed response. The experiment result proves that electronic subdividing method is doable and effective to raise the resolution of the existing system.

Abstract: The presence of residual stress in aircraft aluminum components can give rise to distortion after machining. Excessive distortion may result in the rejection of a part or the need for costly and time-consuming rework prior to placement in service. The purpose of this research was to develop a methodology for the prediction of machining-induced distortions of residually stressed aircraft aluminum components. Numerical simulation results show that the magnitude of machining distortion is strongly related to the square root of Stain Energy Density W or Stress Range σ . The experimental results demonstrate good agreement with the predicted machining distortions of 7075T73 bulkheads. It included that the original residual stress in the blocks of aircraft aluminum component is one of key factors to cause machining distortion.

Abstract: Experimental study on the laser direct fabrication (LDF) of stainless steel powder is carried out. Microstructure and properties of the deposited components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) etc. Cracking generation mechanisms of this material are investigated, corresponding cracking control strategies have been proposed. Finally, fully dense stainless steel components free of defects and with perfect comprehensive mechanical properties have been produced.