Papers by Author: Xing Ai

Abstract: The first step to predict the milling stability is to identify the dynamic characteristics of cutting process. And the mass loading effects of removal material play an important role on the dynamic characteristics of milling process for thin-walled parts, such as impeller, turbine blades and automobile components, which is changing with cutting time or tool position. Therefore, how to identify the instantaneous dynamic characteristics of milling process is one of the most significant problems. In the paper, a structural dynamic modification method with variable mass to predict the instantaneous dynamic characteristics of multi-axis milling thin-walled workpiece with complex curved surface is proposed. The proposed method takes into account the variations of dynamics characteristics of workpiece with the tool position and material removal. And the material cutting process is regarded as the structural dynamic modifications of cutting system, the instantaneous dynamic characteristics of which can be estimated by the extended Sherman-Morrison-Woodbury formula to obtain the corrected frequency response function (FRF). Experiments were carried out to obtain the instantaneous dynamics of a thin-walled workpiece and the results were verified by finite element method (FEM).

Abstract: Titanium alloy TC25 has been widely used in aircraft industry due to its excellent thermal stability, heat resistance and longer service life. In this paper, cemented carbide tools were applied to carry out orthogonal milling experiments for both titanium alloy TC25 and TC4 with identical cutting conditions. Cutting forces, cutting temperatures and surface roughness were measured to assess the machinability for TC25 and TC4. From the experimental results, the cutting parameters can be optimized to guide efficient machining processing of TC25.

Abstract: The oxide film on implant surface of biomedical titanium alloy is crucial to its bioactivity and biocompatibility in human body. A new method is proposed to obtain titanium oxide film by cutting process in oxygen-enriched atmosphere. A gas mixing system is firstly developed to provide oxygen-argon mixed gas to the flank face of insert during turning. The results show that oxygen-enriched atmosphere promote the oxidation reaction of titanium element. Thicker oxide film can be obtained in oxygen-enriched condition than that in natural atmosphere. The corrosion resistance is also improved significantly by this method in electrochemical test.

Abstract: A generalized cutting mechanics model is proposed for milling processes with solid end mills and inserted cutters. The unified mathematical model is employed for the description of the solid milling flute and insert on a reference tool body. The friction and normal forces acting on the rake face are transformed into milling coordinates using a general transformation matrix by simply assigning operation specific parameters. The generalized model can be used to predict and optimize the machining operations including solid end mills and inserted cutters.

Abstract: Oxide film of biomedical titanium alloy surface is crucial to implants, which plays an important role in their biocompatibility with human body. An oxygen-rich supply system used in machining titanium alloy was developed in this paper, which was able to improve oxide film generation. Pressure and ratio of mixed gas were controlled precisely by detection and programmable logic control logic system. Experimental results revealed that low-pressure oxygen-rich atmosphere greatly decrease the oxidation reaction condition between titanium alloy surface and oxygen. The thickness of the oxide film in oxygen-rich atmosphere was much thicker than that in natural environment.

Abstract: Determination of the surface integrity is of particular importance because of its influence on workpiece service life. The microstructure of 7050-T7451 aluminum alloy under the cutting speed of 3000~5000m/min was observed in this paper. With the increase of cutting speed, microhardness was analyzed to investigate the thermal softening phenomenon engendered, which would affect the surface performance in return. According to the results, influences of cutting speed on microstruceture and microhardness in high speed were explored and further research on temperature in high speed is suggested.

Abstract: This paper presents the experimental results of cutting force and surface roughness of 7050-T7451 aluminum alloy under the cutting speed of 3000~5000m/min. The cutting forces and surface roughness with different cutting parameters were analyzed. Experimental results suggested that increasing cutting speed would engender thermal softening, which would in return affect the cutting force and surface roughness in high speed milling. The cutting force and surface roughness were affected by cutting depth and feed rate obviously. Surface roughness was also affected by cutting width which changed the cutting force slightly. According to the results, proper parameters could be selected and thermodynamic relationship needed to be discussed for further research.

Abstract: This paper presents investigations on turning TC4 alloy with PVD TiAlN coated cemented carbide inserts. The turning test was conducted with variable cutting speeds ranging from 80 to 120 m/min. Wear surfaces of the cutting tools are analyzed to study the wear mechanism of PVD TiAlN coated cemented carbide tools in turning of titanium alloy TC4. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer( EDS) analyses by wear maps indicated that the wear of coated cemented carbide tools was caused by adhesion, coating delamination and mechanical fatigue. The analysis of EDS indicated no oxidation wear generated during the machining. The excellent chemical stability and oxidation resistance performance of TiAlN coating made contribution to prevent oxidation wear.

Abstract: An alternative physical explanation for process damping where a distributed cutting force model, along with a function distribution over the tool-chip interface, is assumed, is described. An exponential shape function is used to approximate the force distribution on the tool-chip interface. The distributed force model results in a more complicated governing equation, a second-order delayed integrodifferential equation, which involves both a discrete and distributed delay. An approach to transform and normalize the governing equation of motion into a third-order discrete system is described and the state-space representation of the new system is obtained. The semi-discretization method is then used to chart the stability boundaries for turning operation.

Abstract: Al₂O₃-TiC-ZrO₂ ceramic composites (ATZ) were fabricated by hot-pressed sintering. The phases and microstructure of the composites were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The relative density and mechanical properties (flexural strength, fracture toughness and Vicker’s hardness) of the composites were tested. The results show that the microstructure of the composites was the gray core-white rim. With the increase of sintering temperature, the relative density and mechanical properties of the composites increased first and then decreased. The composite sintered at 1705°C has the highest synthetical properties, and its relative density, flexural strength, fracture toughness and Vickers hardness are 98.3%,970MPa,6.0 MPa•m^1/2 and 20.5GPa, respectively.