Papers by Author: Zhan Qiang Liu

Abstract: The purpose of the paper is to investigate the influence of the processing parameters on the surface roughness in rotary ultrasonic burnishing of titanium alloy Ti-6Al-4V plane. A Taguchi orthogonal array for three levels and four factors, which include burnishing depth, feed fate, spindle speed and ultrasonic frequency, are designed. The optimal combination of ultrasonic burnishing process parameters is obtained. Analysis of variance (ANOVA) is applied to determine the most significant processing parameter and to obtain the optimal combination level of processing parameters for the lowest surface roughness. The results show that burnishing depth has the most predominant effect on surface roughness, and spindle speed is the secondary one. Feed rate and ultrasonic frequency are then followed and have no distinct effect on surface roughness in rotary burnishing of Ti-6Al-4V.

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: Fabrication of microchannels on titanium alloy with micro-milling is a tough challenge due to the difficultly to remove the burrs formed in machining process. A novel method to gelatinize workpiece surface to control the generation of burr as well as the optimization of cutting parameters are investigated in this paper. Differences existed between the process of micro-milling and that of traditional milling can be accounted for size effect. Influences of feed per tooth, depth of cut and spindle speed on the formation of burr were taken into consideration respectively by single factor method. The topographies of the machined surface with micro-milling were observed and measured by optical microscope. Results showed that the dimensions of burrs increased with the rise of depth of cut. However, it decreased initially, then increased later with the augment of feed per tooth. Sacrifice layer with PMMA was coated and gelatinized on the workpiece surface, which could restrain the plastic deformation of materials during titanium alloy micro-milling. The experimental results presented that the dimensions of burr could reduce greatly by the proposed PMMA coating method compared to materials without coating.

Abstract: This paper adopts composite structure system analysis method to perform modal analysis of high-speed face milling cutter which is mounted on the machine tool through FEM modal analysis. The key problem of this method is to obtain joint surface parameters between the machine tool spindle and face milling cutter through experimental modal analysis and MATLAB software. The joint surface parameters consist of linear stiffness, linear damping, rotation stiffness and rotation damping. After getting the frequency response function (FRF) at the tool tip of the face milling system through experimental modal analysis, the contact surface parameters can be used to eliminate the influence of the machine tool to get modal parameters of the face-milling cutter itself. Based on the finite element model of face milling cutter, composite structure system analysis method can be used easily to acquire the dynamic performance of the face milling system through FEM modal analysis, greatly to improve the reliability of modal analysis, and is helpful to the dynamic design and the structure improvement of high speed face milling cutter.

Abstract: The paper presents rigorous experimental validation results of the algorithm to predict work-piece surface roughness in face milling operation as developed in the Part 1. The experimental verification system consisting of various devices was established according to the given experimental conditions. Experimental parameters are set for steady face milling. Experimental data are collected through four experiments. These experimental data include the axial and radial run-out errors of each square insert with flat edge, the modal parameters of the face milling system, the Z-axial milling force and the measured surface contour of the milled work-piece. The trajectory of cutting teeth is calculated by the MATLAB software based on the static surface roughness model. Z-axial dynamic relative displacement between the tooth and the work-piece is obtained as the predicted dynamic surface roughness. By integrating the prediction results of static and dynamic models, the surface contour is predicted. Predicted and measured results are compared in the same figure and basically consistent. The work-piece surface roughness prediction model will be useful and valid in high-speed face milling.

Abstract: The determination of the minimum uncut chip thickness is essential in micro machining in order to achieve desired surface integrity and accuracy. The parameters being considered in determination the minimum uncut chip thickness include the cutting tool geometry, workpiece material, cutting parameters and so on. In this paper, five different materials including OFHC Copper, Al 7050, AISI 4340, Ti-6Al-4V and IN 718 with unequal materials’ properties were investigated to find materials parameters’ effect on the minimum uncut chip thickness. An Arbitrary Lagrangian Eulerian (ALE)-based numerical modeling is proposed to determine the minimum uncut chip thickness for the five different materials by changing depth-of-cut. The Johnson-Cook (J-C) constitutive model is employed to describe the work material behavior. Results show that the flow stress of different materials has significant effect on the minimum uncut chip thickness.

Abstract: The work-piece surface quality reflects the cutting performance of face-milling cutter. This paper presents the development of an algorithm to predict work-piece surface roughness in face milling operation. The prediction model is based on the face milling cutter fixed square inserts with flat edges. The static prediction model considers the effects of radial and axial run-out error of inserts, feed per tooth, tooth number, cutting edge length, nose radius, main lead angle, and axial depth of cut. The dynamic prediction model considers the effects of the Z-axial relative displacement between the work-piece and cutting teeth caused by forced vibration. By combining the prediction results of static and dynamic models, the surface roughness of the work-piece in face milling is predicted.

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: The superalloy parts in the aeronautical field demand high reliability, which is largely related to surface integrity. Surface integrity generally includes three parameters, such as geometric parameter, mechanical parameter and metallurgical parameter. The paper presents the influence of cutting speed on surface plastic deformation and white layer formation through orthogonal milling of FGH95 superally material. The influence of cutting speed on grain refinement of machined surface is also investigated. It is found that cutting speed has significantly effect on the surface metallurgical characteristic microstructure. The increasing of cutting speed creates severer plastic deformation. Surface plastic shear strain increases with the increasing of cutting speed, while the depth of plastic deformation decreases on contrary. White layer thickness is increased with the increasing of cutting speed. Through statistical analysis for grains number, it can be drawn that the higher the cutting speed, the more serious grains refinement.

Abstract: Talyor formula is widely accepted to describe tool wear and is employed to optimize cutting parameters. The common test methods and processes of cutting tool wear test are firstly investigated in this paper. The effects of interference factors on different test methods are analyzed by hypothesis test to find the reason that regression generalized Taylor formula is partly invalid or not effective. The meaning of exponentials in generalized Taylor formula is discussed and tool wear test principle for difficult-to-machine materials is proposed at last.