Materials Science Forum Vols. 836-837

Abstract: The high temperature oxidation phenomenon will occur on the tool-workpiece contact area when machining the superalloy. Two kinds of cemented carbide tools (YG6X, YG8) are selected, the coated carbide tool and coated ceramic tool which are suitable for machining superalloy are selected. The resistance furnace is used for heating tool material, and the oxidation resistance experiments are carried out. The results show that: WC which is included in the cemented carbide tool is oxidized to WO₃ and the Co is oxidized to Co₃O₄, Ti which is included in the coated carbide tool is oxidized to TiO₂. The grain of the tool is smaller, the oxidation resistance is better. The oxidation resistant of coated carbide tool is better than the non-coated tools. The coated ceramic tool is not substantially oxidized in high temperature situation. The merits order of the oxidation resistant properties is that: coated ceramic tool>coated carbide tool > YG6X>YG8.

Abstract: The linear motor feed system can realize high-precision motion with high-speed and high-acceleration, which has a broad application in high-speed machine tools. In its unique zero transmission structure, the motor is connected directly with the mechanical system. The thrust harmonics and other disturbances act on the motor mover directly, which makes the tracking fluctuation more prominent. The traditional accuracy and repeatability of positioning cannot reflect the precision of the linear motor feed system in the process of high-speed movement. In this paper, a novel precision evaluation method which takes the dynamic precision as the index is proposed for the linear motor feed system in high-speed machine tools. The performance and precision of linear motor feed system are evaluated by the transient error, steady-state follow error and tracking fluctuation, respectively. Then the servo control model is established oriented to dynamic precision. The influences of NC instructions, servo system and mechanical system on the dynamic precision are discussed. It can be obtained that this new evaluation method on the precision can evaluate systematically the performance of the linear motor feed system in high-speed machine tools. Meanwhile it can reveal efficiently main factors which lead to the decline of dynamic precision and propose effective improvement methods.

Abstract: Abstract: Corner radius as a non-main cutting parameters, study of corner radius about cutting vibration is relatively small.Turning experiments use PCBN tool in CAK4085 CNC lathe,cutting hardened steel HRC50-52 Cr12MoV and hardened steel HRC62-64 GCr15, eddy current sensor measure the tool vibration amplitude of each group parameters, analysis influence of the corner radius for tool vibration amplitude. With corner radius increases, tool vibration amplitude increases. Research will contribute to the development of high-speed machining of hardened steel.

Abstract: CrN coatings have been widely used in many industrial fields, such as cutting tools, moulds, mechanical components. In this work, CrN coatings were deposited using a high power impulse magnetron sputtering (HIPIMS) with various negative bias voltages. The composition, microstructure, and mechanical properties of the coatings were studied using X-ray diffractometer, scanning electron microscope (SEM) and nanoindenter. The cutting performance of the micro drills coated in CrN was also investigated by high speeding dry drilling printed circuit board (PCB). The results show that the bias voltage has significant influences on the microstructure and properties of the as-deposited films. Increasing negative bias voltages resulted in the microstructures refining of the CrN coatings with columnar grains. Further increasing the negative bias voltage caused the formation of defects in CrN. With optimization of the negative bias voltage, the micro-drills with CrN deposited by HIPIMS exhibited an excellent tool life comparing with the uncoated one.

Abstract: Cutting temperature always highly reaches over to 1000°C when high speed machining with PCBN tools. Diffusion of tool material element may have important influence on tool wear at such high temperature., the diffusion wear and oxidation wear have become the major wear mechanism. In this paper, the rules of diffusion wear and oxidation wear for PCBN cutting tools are proposed and analyzed based on thermodynamics theory. Dissolution concentrations in typical normal workpice materials of PCBN tool material at different temperature are then calculated. Diffusion reaction rules in high temperature are developed and analyzed using Gibbs free energy criterion. The machining tests were conducted using the PCBN tools at different cutting speeds of 50, 95,100 and 180 m/min, feed of 0.1, 0.2mm and depth of cut of 0.1, 0.8, 1, and 1.5 mm respectively on PUMA300LM numerically-controlled lathe. It was found that the theoretical results were uniform with the experimental data; the results will provide useful references for tool material design and selection.

Abstract: The tool edge preparation has a significant influence on the quality of the workpiece surface, the stability of the cutting process and the tool life. In order to investigate the effect of the tool edge preparation, the impact on the cutting force components, the roughness and the residual stress is analyzed through the response surface methodology. The paper presents experimental results of turning tests with different edge radius and changing the cutting speed, the feed amount per tooth, the axial depth, and the radial depth. The research results will put forward theoretical value and practical significance to develop the processing technology of high-speed and efficient cutting, improve the metal cutting theory and prompt the development of the manufacture industry.

Abstract: In order to improve the working efficiency of a manufacturing system, tool life estimation is very essential. In this paper, the dominant factors affecting tool life are analyzed by theoretical analysis. According to the nonlinear relationship between affecting factors and tool life, a tool life prediction model based on BP neural network, which is optimized by genetic algorithm (GA), is built up. 15 network patterns are trained to get the best network structure. The accuracy of GA-BP model is verified through computing and compared with the standard BP model. The results show that GA-BP model prediction value is exactly closed to the expected value of tool life and the prediction accuracy can be improved more than 5% compared than the standard BP model. The model is proved to be accuracy and it can be used as an effective method of tool selection decision.

Abstract: This Research is Focused on the Chemical Mechanical Sharpening of CVD Diamond Micro Tool, which has High Strength and Good Wear Resistance. the Diamond Grinding Wheels were Usually Used for Sharpening, but this Method could Not get High Quality Surface of the Diamond Efficiently and Small Cutting Edge Radius. in Order to Seek a Better Mode for Sharpening, the Copper Based Tungsten Carbide Disc and Abrasive were Used for Grinding. for Better Understanding the Effects of Different Parameters on the Grinding Process and Optimizing them, the Orthogonal Method was Used to Design the Experiments. Grinding Direction, Feed Rate and the Grinding Velocity were Investigated to Obtain Sharper Cutting Edge and Smooth Flank Face. Analysis of Range was Also Introduced to Evaluate the Contribution of each Parameter in Orthogonal Experiment. the Results Showed that down Grinding, Medium Feed Rate and Low Velocity could Achieve a Better Sharpening Result.

Abstract: Cutting tools play an important role in the cutting process of titanium aircraft components, but it is difficult to comprehensively evaluate the cutting tool performance, so the selection of appropriate cutting tool becomes extremely important. In this paper, an evaluation method using grey relational analysis for cutting tool performance was proposed. Meanwhile, in this method, a test benchmark with some typical difficult-to-machined features extracted from titanium aircraft components was designed, and the processing route was developed. Grey comprehensive evaluation models of cutting tool performance were established for the rough and finish machining respectively. Finally, the grey comprehensive evaluation models were used to evaluate the cutting tool performance in the milling experiments of the benchmarks. The results show that the grey relational comprehensive evaluation method is convenient and effective to evaluate milling tools performance for titanium aircraft components.

Abstract: Cutting tool is the executor and core element of machining, and tool material is of decisive significance for the development of high-speed machining technology. For a particular workpiece material, to select the appropriate tool material is an important prerequisite to increase the machining productivity and to improve the machined surface quality.In this paper, a weighting method of subjective judgment was utilized to conduct criteria weighting in the tool materials selection when machining Al-Si piston alloy. The analytic hierarchy process (AHP) method was used to subjectively judge the significance of the material properties and determine their criteria weight. The hierarchical structure model, with the objective layer, the criterion layer, and the alternative layer, was established. The performance of tool materials was set as the objective layer. Seven property indexes, such as density, Young's modulus, hardness, fracture toughness, thermal stability, thermal conductivity, thermal expansion coefficient, were chosen as the criterion layer in comparative judgment of the alternatives and criteria. And five kinds of tool materials, YG6X Cemented carbide, YG8 Cemented carbide, PCD, CBN, and Ceramic were chosen as the alternative layer. Then the pairwise comparison matrix of the material property index was constructed to compare a set of criteria pairwise according to their relative importance weight. The comparative weights were derived by finding the largest eigenvector with respective of the matrix. Finally, the consistency index and consistency ratio were calculated to ensure the consistency of the subjective perception and the accuracy of comparative weights. Then the weights of the material properties were determined, and the synthesis scores of the different tool material candidates were obtained.Results revealed that PCD was found as best materials for Al-Si piston alloy machining, and YG8 is slightly more suitable than YG6X for machining Al-Si piston alloy. In short, the qualitative problems in tool material selection were realized systematically and hierarchically by quantitatively calculation and analysis. This provides a new thinking in tool materials selection for high efficiency machining of difficult-to-machine materials.