Baohai Wu

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.

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.

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.

Adaptive location of repaired blade for multi-axis milling

Abstract Free-form blades are widely used in different industries, such as aero-engine and steam turbine. Blades that are damaged during service or have production deficiencies are usually replaced with new ones. This leads to the waste of expensive material and is not sustainable. However, material and costs can be saved by repairing of locally damaged blades or blades with localized production deficiencies. The blade needs to be further machined after welding process to reach the aerodynamic performance requirements. This paper outlines an adaptive location approach of repaired blade for model reconstruction and NC machining. Firstly, a mathematical model is established to describe the localization problem under constraints. Secondly, by solving the mathematical model, localization of repaired blade for NC machining can be obtained. Furthermore, a more flexible method based on the proposed mathematical model and the continuity of the deformation process is developed to realize a better localization. Thirdly, by rebuilding the model of the repaired blade and extracting repair error, optimized tool paths for NC machining is generated adaptively for each individual part. Finally, three examples are given to validate the proposed method.

Prediction and Experimental Validation of Cutting Force for Bull-Nose End Mills with Lead Angle

This study focuses on cutting force predictions with the tool-workpiece inclination angle in bull-nose milling based on the semimechanistic force model. By analyzing kinematics and mechanics of the bull-nose end mills during cutting, force expressions including lead angle are stated and the model is exerted on each discrete element as oblique cutting with coordinate transformation and numerical integration to obtain the dynamic cutting force components. An improved identification method considering speed variations along the tool axis is applied to calibrate coefficients. Coefficients are regarded as the function of each elemental elevation. Then, a geometry-based method to acquire cutter workpiece engagement (CWE) is proposed. Also acquisition of accurate start and exit angles on each slice is deliberated elaborately for cutters with lead or tilt angle in milling processes. Thereby, to verify the validity of the force prediction model and start-exit angle acquisition method, experiments with variable lead angles are conducted under different axial immersions. The results reveal that the presented model and approaches can predict cutting forces with high accuracy. Finally, the cutting force components under different cutter postures and conditions are analyzed to provide instructions for parameter selections.

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.

Localization of freeform surface workpiece with particle swarm optimization algorithm

A localization method for freeform surface workpiece with particle swarm optimization (PSO) algorithm is proposed in this paper. This study is the first attempt to use PSO as a matching algorithm in localization based on in situ measuring technology. The performance of the algorithm is studied by a set of simulations and optimal parameters settings are given. To test the performance of PSO and compare it with the classical Iterative Closest Point (ICP) algorithm, a blade model and a free-form surface model are used in this study. Simulation results show that PSO with the proposed parameter settings is appropriate to the localization of different freeform surface workpieces with high accuracy and not dependent on pre-localization condition. This study proves that PSO is a new effective algorithm for the localization of freeform surface workpiece because of its advantage of high global search ability over most existing algorithms.

A Cutting Parameters Selection Method in Milling Aero-Engine Parts Based on Process Condition Matching

An optimal selection method of process parameters based on process condition matching is proposed, for the difficulty of the process parameters selection in the milling of complex structure and difficult-to-cut material parts. The factors of process parameters selection are analyzed, process condition vector and process parameter vector are defined, and their quantitative expressions are proposed. The mapping of existing process condition vectors to the process parameter vectors is established, based on the process data accumulated in practical production. Then, process condition matching degree is defined. In the calculation of the matching degree, Analytic Hierarchy Process (AHP) is adopted to determine the affecting weights of process condition factors, and leveling matrix is adopted to eliminate the differences of dimensions and numerical scales between process condition factors. The optimal process parameters are achieved through matching the actual process condition to the existing process condition. A group of typical aero-engine part milling processes is taken as instance, and the feasibility and effectiveness of this method are verified. A typical aero-engine part CNC machining process database system has been designed and developed based on this method.

Toolpath Generation for Four-Axis Rough Milling of Sculptured Surface Turbine Blade

Presented in this paper is a method for four-axis rough milling of sculptured surface turbine blade. The proposed method consists of two steps, cutter-contact (CC) points generation and tool orientation planning. In the first stage, CC points for trimmed blade surface are generated in the parametric domain and then they are converted into the physical domain to get flow line toolpaths. In the second stage, optimized representative tool orientations are generated first, and then interpolation algorithm is employed to determine all tool orientations. With this method, smooth tool orientations can be obtained. Finally, computational examples were implemented to generate symmetrical spiral four-axis rough milling toolpath for the turbine blade disk. Simulation results show that the proposed method is efficient and it can improve the utilization of four-axis machine tools in the milling of turbine blade.