Changfeng Yao

Influence of high-speed milling parameter on 3D surface topography and fatigue behavior of TB6 titanium alloy

High-speed milling of titanium alloys is widely used in aviation and aerospace industries for its high efficiency and good quality. In order to optimize the machining parameters in high-speed milling TB6 titanium alloy, experiments of high-speed milling and fatigue were conducted to investigate the effect of parameters on 3D surface topography and fatigue life. Based on the fatigue fracture, the effect mechanism of surface topography on the fatigue crack initiation was proposed. The experiment results show that when the milling speed ranged from 100 m/min to 140 m/min, and the feed per tooth ranged from 0.02 mm/z to 0.06 mm/z, the obtained surface roughness were within the limit (<0.8 μm). Fatigue life decreased sharply with the increase of surface equivalent stress concentration factor. The average error of fatigue life between the established model and the experimental results was 6.25%. The fatigue cracks nucleated at the intersection edge of machined surface.

Surface integrity and fatigue behavior in shot-peening for high-speed milled 7055 aluminum alloy

The influence of shot-peening parameters on surface integrity of 7055 aluminum alloy is investigated based on shot-peening experiments. Surface integrity measurements, fatigue fracture analysis and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that surface roughness increases significantly, and irregular pits and bumps appear on surface after shot-peening; grain on subsurface is refined and produces a shift and distortion in the pellets hit direction; compressive stress can be detected on all machined surfaces. Shot-peening parameters have significant impact on micro-hardness. In comparison with the milled specimen, fatigue life of peened specimens is improved by about 23.8, 3.96 and 1.01 times. Fatigue source zone transfers from stress concentration location on surface to subsurface due to the lower surface roughness and lager residual compressive stress.

Control rules of surface integrity and formation of metamorphic layer in high-speed milling of 7055 aluminum alloy

Orthogonal experiments were conducted to investigate the effects of parameters on surface integrity in milling 7055 aluminum alloy. In order to correlate metamorphic layer with thermal and mechanical phenomena developed during milling, milling force and temperature fields of machined surface were obtained with finite element method, while milling speed and feed per tooth were paid particular attention to study formation of metamorphic layer. Experiment results show that when milling speed, feed per tooth, milling depth, and milling width are 1100 m/min, 0.02 mm/z, 0.7 mm, and 6 mm, respectively, obtained surface roughness, surface residual stress in X direction, surface residual stress in Y direction, and surface micro-hardness are Ra 0.258 µm, −123 MPa, −137 MPa, and 193.76 HV0.025, respectively. From precision machining to rough machining, depth of compressive residual stress layer increases from 35 to 45 µm, and the depth of plastic deformation layer increases from 5 to 20 µm. Finally, the formation of metamorphic layer can be explained by thermo-mechanical coupling effects.

Surface integrity and fatigue analysis of shot-peening for 7055 aluminum alloy under different high-speed milling conditions

To study the effect of different milled surfaces on shot peening surface integrity (roughness, residual stress, hardness, and microstructure), research on the change of surface integrity is carried out using the same shot peening process for different milling surfaces of 7055-T77 aluminum alloy. Surface integrity measurements, fatigue fracture analysis, and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that shot peening can reduce the dispersion and instability of surface integrity brought by milling processing, although it increases the surface roughness; the maximum residual compressive stress and depth of residual stress layer increase significantly after shot peening, and the residual stress and hardening distribution are very good; larger surface roughness and irregular surface scratches of milling samples before shot peening easily lead to cracks and gouges produced on shot peening surface.

Effect of cutting parameters on machinability characteristics in milling of magnesium alloy with carbide tool

Magnesium alloy has attracted more attentions due to its excellent mechanical properties. However, in process of dry cutting operation, many problems restrict its further development. In this article, the effect of cutting parameters on machinabilities of magnesium alloy is explored under dry milling condition. This research is an attempt to investigate the impact of cutting speed at multiple feed rates on cutting force and surface roughness, while a statistical analysis is adopted to determine the influential intensities accurately. The results showed that cutting force is affected by the positively constant intensity from feed rate and the increasingly negative intensity from cutting speed. In contrast, surface roughness is determined by the gradually increasing negative tendency from feed rate and the positive effect with constant intensity from cutting speed. Within the range of the experiments, feed rate is the leading contribution for cutting force while the cutting speed is the dominant factor for surface roughness according to the absolute intensity values. Meanwhile, the trends of influencing intensities between cutting force and surface roughness are opposite. Besides, it is also found that in milling magnesium alloy, chip morphology is highly sensitive to cutting speed while the chip quality mainly depends on feed rate.

Multiobjective Optimization of Surface Integrity in Milling TB6 Alloy Based on Taguchi-Grey Relational Analysis

This paper studied an effective method based on Taguchis method with the grey relational analysis, focusing on the optimization of milling parameters on surface integrity in milling TB6 alloy. The grey relational grade that is derived from the grey relational analysis is mainly used to determine the optimum cutting process operations with multiple performance characteristics. Specifically, surface roughness (Ra), hardness, and residual stress were important characteristics in surface integrity of milling TB6 alloy. Based on the combination of these multiple performance characteristics, the feed per tooth, cutting speed, and depth of cut were optimized in this study. Additionally, the analysis of variance (ANOVA) was also applied to determine the most significant factor for the surface integrity of milling TB6 alloy according to the contribution of the ANOVA, and the most significant factor is the cutting speed in this paper. Based on the analysis, the experimental test results have been improved prominently through the grey relational analysis. Hence this method can be an effective approach to enhance the surface integrity of milling TB6 alloy.

Empirical modeling of compressive residual stress profile in shot peening TC17 alloy using characteristic parameters and sinusoidal decay function

This article introduces two comprehensive experimental models to predict the compressive residual stress profile induced in TC17 alloy after shot peening. Experiments are carried out utilizing one of experimental design techniques based on response surface methodology. Shot peening intensity and coverage are considered as two input parameters affecting compressive residual stress profile. The characteristic parameters model is created by regression analysis, which has the capability of predicting the four main characteristic parameters of a typical compressive residual stress profile. Based on this model, the absolute sensitivity of characteristic parameters with respect to shot peening intensity and coverage is analyzed. The sinusoidal decay function model is created with a proposition of that the compressive residual stress profile is a sinusoidal decay function of the depth beneath surface and the coefficients of this function are, in turn, functions of the two input shot peening parameters. The main advantage of sinusoidal decay function model over characteristic parameters model is that it provides the effect of shot peening parameters on the shape of the compressive residual stress profile. The two models have been checked for accuracy by two extra tests. The results show that the prediction errors of the four main characteristic parameters are within 20%, and the compressive residual stress profiles predicted by the sinusoidal decay function model are in consistent with experimental data.

Surface characterization of Ti1023 alloy shot peened by cast steel and ceramic shot

To optimize the surface properties such as surface roughness, residual stress, and micro-hardness of Ti1023 titanium alloy, the effects of shot peening on Ti1023 alloy were investigated. Surface roughness, surface topography, residual stress, micro-hardness, and micro-structure were carried out at different shot-peening parameters. The results demonstrate that the increased peening intensity enhances the surface roughness, compressive residual stresses, and hardness in subsurface, which is mainly due to the plastic deformation in the near surface layer. Specimen 11 has a low surface roughness of Ra = 1.91 μm, well-developed dimple topography, higher compressive residual stress layer depth of 143 μm, and higher hardened layer depth of 200 μm. The ceramic shots with a diameter of 1.08 mm and peening intensity of 0.18 mm A are the optimal shot-peening conditions.

Experimental study on cutting force of face-turning Inconel718 with ceramic tools and carbide tools:

In the process of face-turning high-temperature alloy Inconel718 with carbide tools and ceramic tools, the change rules of cutting force were studied and the empirical models of cutting force on the cutting parameters were established. For the tools, the main cutting force has positive relation to both the feed rate and the turning depth. Variation trends of the axial force are in accordance with the increase in these two parameters. During the increasing process of the cutting speed, the feed force changes slightly while the main cutting force decreased about 96 N when using the carbide cutter. For the ceramic cutter, the main cutting force and the axial force increased to about 380 N first and then decreased when the cutting speed increased. The axial force affected not only the processing parameters but also the geometrical parameters of the cutter. There exist some relationships between component forces.

Surface integrity in high-speed milling of Titanium alloy TC11

The study focuses on the machined surface integrity of titanium alloy TC11 under different cutting conditions. Residual stress, surface roughness and microstructure were investigated. Three cutting speeds were selected as 376.8 m/min, 471 m/min, and 565.2m/min. In addition, three different cooling methods including dry, emulsion liquid and oil mist were selected. The results show that the surface residual stresses are compressive under all cutting condition. The compressive residual stresses decrease with the milling speed increasing both in feed and stepover directions. When the milling speed increases, surface roughness increases obviously. The lowest residual stress and surface roughness are obtained when the emulsion liquid is used as cooling method. The microstructure of surface layer is not obvious changed; phase transition and undesirable deformation of grain are not found under all cutting condition. Emulsion liquid cooling is the best cooling method in high-speed milling of titanium alloy with uncoated cemented carbide tool.