Junxue Ren

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.

Feedrate scheduling for multi-axis plunge milling of open blisks

Multi-axis plunge milling has an increasing application in the manufacturing industry to rough machine open blisks. Its objective is to remove mass stock material with high efficiency and machining stability. In multi-axis plunge milling, cutting parameters are usually determined conservatively as constants to prevent excessive cutting forces and unexpected tool breakage. This is an obstacle to improve the cutting efficiency of rough machining. To address this issue, this article proposes an original approach to schedule the feedrate in multi-axis plunge milling of open blisks based on material removal rate. The material removal rate in plunge milling is directly proportional to the area of the cross section on the removed stock material. According to different types of the cross section, one feeding phase in plunge milling of open blisks is divided into three feeding stages. The cross section in each feeding stage is then identified with a mathematic and geometric method. Its area is then calculated by its constituting elements, such as a polygon, circular arches, and elliptical arches. After that, the feedrate is regulated to guarantee a constant material removal rate in the entire feeding phase. Experimental tests are conducted to verify the proposed feedrate scheduling method. This approach can reduce the cutting time and smooth the variances of cutting forces and torque in multi-axis plunge milling of open blisks.

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.

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.

Cutting forces, tool life, and size effect of passivated cutters in milling of Inconel 718

An experimental study is conducted to research the passivation effects of cutters on cutting forces, tool life, and size effect in milling of Inconel 718. Cutting forces and tool life of passivated cutters with different cutting edge radiuses are measured and compared in plunge milling. The results show that, with the increase of the cutting edge radius, cutting forces keep increasing while tool life increases first and then decreases. When the cutting edge radius is 7.9 μm the tool life of passivated cutter reaches its maximum under experimental conditions. The unit cutting force per cutting area on the tool edge is adopted to evaluate the size effect of passivated cutters in end milling. The results show the effect size of tool edge is obvious when the cutting depth is less than the cutting edge radius. This effect is more significant with the decrease of the cutting depth.