Dinghua Zhang

Milling Force Modeling of Worn Tool and Tool Flank Wear Recognition in End Milling

The wear state of a cutting tool is an important factor which affects machining quality. Therefore, monitoring tool wear is extremely essential to ensure workpiece quality and improve tool life. This paper models the milling forces of a worn tool and proposes a recognition method of milling tool wear state based on the influence relationships between the milling force features and tool wear. In the milling force model, the friction effect force and the shearing force are treated separately, and the friction stress distribution on tool flank is described. Then the force model is calibrated and verified through experiments. In the tool wear recognition method, the relationship between the milling force feature vector and tool wear is investigated. On this basis, the tool flank wear recognition method is proposed. A tool wear experiment is performed using superalloy material. In the experiment, the recognition results are expressed in confidence intervals which can represent the recognized tool wear more effectively and accurately. Finally, the scheme of tool flank wear online monitoring is proposed.

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.

Material removal process optimization for milling of flexible workpiece considering machining stability

The material removal process of a flexible workpiece has a great effect on the stability limits and chatter-free machining time, as the sequence of material removal can be altered to obtain a better workpiece dynamic behaviour. Therefore, the uncut material can be better designed to get chatter-free machining conditions and a shorter machining time. With this as the objective, a material removal process optimization method is presented to design the uncut material distribution. Different from existing methods, the presented approach begins from the last machining step, the maximum stable cutting depth is calculated, and the removed material is virtually added to the design model. Therefore, beginning from the design part, the material is virtually added to the part and the stock model of the part is finally obtained. Based on this approach, the optimized uncut material can provide support for the part in the semi-finish or finish machining processes, and the machining process is stable. Optimization results show that while machining plate-like structures, step removal methods can be used and the arc or triangle shape machining allowance can be used to get better machining results. Cutting experiments were carried out to show the effectiveness of the presented approaches.

Effects of cutting parameters on tool insert wear in end milling of titanium alloy Ti6Al4V

Titanium alloy is a kind of typical hard-to-cut material due to its low thermal conductivity and high strength at elevated temperatures, this contributes to the fast tool wear in the milling of titanium alloys. The influence of cutting conditions on tool wear has been focused on the turning process, and their influence on tool wear in milling process as well as the influence of tool wear on cutting force coefficients has not been investigated comprehensively. To fully understand the tool wear behavior in milling process with inserts, the influence of cutting parameters on tool wear in the milling of titanium alloys Ti6Al4V by using indexable cutters is investigated. The tool wear rate and trends under different feed per tooth, cutting speed, axial depth of cut and radial depth of cut are analyzed. The results show that the feed rate per tooth and the radial depth of cut have a large influence on tool wear in milling Ti6Al4V with coated insert. To reduce tool wear, cutting parameters for coated inserts under experimental cutting conditions are set as: feed rate per tooth less than 0.07 mm, radial depth of cut less than 1.0 mm, and cutting speed sets between 60 and 150 m/min. Investigation on the relationship between tool wear and cutting force coefficients shows that tangential edge constant increases with tool wear and cutter edge chipping can lead to a great variety of tangential cutting force coefficient. The proposed research provides the basic data for evaluating the machinability of milling Ti6Al4V alloy with coated inserts, and the recommend cutting parameters can be immediately applied in practical production.

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.

An approach for machining allowance optimization of complex parts with integrated structure

Abstract Currently composite manufacturing process, such as linear friction welding plus NC machining, is the main method for the manufacturing and repairing of complex parts with integrated structure. Due to different datum position and inevitable distortion from different processes, it is important to ensure sufficient machining allowance for complex parts during the NC machining process. In this paper, a workpiece localization approach for machining allowance optimization of complex parts based on CMM inspection is developed. This technique concerns an alignment process to ensure sufficient stock allowance for the single parts as well as the whole integrated parts. The mathematical model of the constrained alignment is firstly established, and then the symmetric block solution strategy is proposed to solve the optimization model. Experiment result shows that the approach is appropriate and feasible to distribute the machining allowance for the single and whole parts for adaptive machining of complex parts.

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.

Optimisation of spiral tool path for five-axis milling of freeform surface blade

This paper deals with optimisation of five-axis tool paths in the context of milling of turbine blade. The purpose is to generate tool paths that respecting kinematical performance of machine tool while ensuring the geometrical conformity of the machined part. To achieve this object, outer transverse curves are created at the leading edge and trailing edge of the blade while generating spiral tool path, it allows the machine tool to maintain the programmed feed rate while respecting the kinematical limits of the machine tool. As for the leading and trailing edges of the blade, they are machined along height direction of the blade. Machining experiments showed that machine tool moved smoothly and no overcut or dot marks would occur with the proposed method, thereby demonstrating the feasibility of the presented approach.