Cutting Path Planning for Ruled Surface Impellers

At present, most commercial computer-aided manufacturing （CAM） systems are deficient in efficiency and performances on generating tool path during machining impellers. To solve the problem, this article develops a special software to plan cutting path for ruled surface impellers. An approximation algorithm to generate cutting path for machining integral ruled surface impellers is proposed. By fitting sampling data points of an impeller blade into a curve, a model of ruled surface blade of an impeller is built up. Furthermore, by calculating the points where the cutter axis vector intersects the free-form hub surface of an impeller, problems about, for instance, the ambiguity in calculation and machining the wide blade surface with a short flute cutter are solved. Finally, an integral impeller cutting path is planned by way of an integrated cutter location control algorithm. Simulation and machining tests with an impeller are performed on a 5-axis computer numerically controlled （CNC） mill machine, which shows the feasibility of the proposed algorithm.

Machining the Integral Impeller and Blisk of Aero-Engines:A Review of Surface Finishing and Strengthening Technologies

The integral impeller and blisk of an aero-engine are high performance parts with complex structure and made of difficult-to-cut materials. The blade surfaces of the integral impeller and blisk are functional surfaces for power transmission, and their surface integrity has signif- icant effects on the aerodynamic efficiency and service life of an aero-engine. Thus, it is indispensable to finish and strengthen the blades before use. This paper presents a comprehensive literature review of studies on finishing and strengthening technologies for the impeller and blisk of aero-engines. The review includes independent and inte- grated finishing and strengthening technologies and dis- cusses advanced rotational abrasive flow machining with back-pressure used for finishing the integral impeller and blisk. A brief assessment of future research problems and directions is also presented.

Robust Design Optimization Method for Centrifugal Impellers under Surface Roughness Uncertainties Due to Blade Fouling

Blade fouling has been proved to be a great threat to compressor performance in operating stage. The current researches on fouling-induced performance degradations of centrifugal compressors are based mainly on simplified roughness models without taking into account the realistic factors such as spatial non-uniformity and randomness of the fouling-induced surface roughness. Moreover, little attention has been paid to the robust design optimization of centrifugal compressor impellers with considerations of blade fouling. In this paper, a multi-objective robust design optimization method is developed for centrifugal impellers under surface roughness uncertainties due to blade fouling. A three-dimensional surface roughness map is proposed to describe the nonuniformity and randomness of realistic fouling accumulations on blades. To lower computational cost in robust design optimization, the support vector regression（SVR） metamodel is combined with the Monte Carlo simulation（MCS） method to conduct the uncertainty analysis of fouled impeller performance. The analyzed results show that the critical fouled region associated with impeller performance degradations lies at the leading edge of blade tip. The SVR metamodel has been proved to be an efficient and accurate means in the detection of impeller performance variations caused by roughness uncertainties. After design optimization, the robust optimal design is found to be more efficient and less sensitive to fouling uncertainties while maintaining good impeller performance in the clean condition. This research proposes a systematic design optimization method for centrifugal compressors with considerations of blade fouling, providing a practical guidance to the design of advanced centrifugal compressors.

Accurate Evaluation of Free-form Surface Profile Error Based on Quasi Particle Swarm Optimization Algorithm and Surface Subdivision

Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline（NURBS） for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system（DCS） and measurement coordinate system（MCS） for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization（QPSO） is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface.

An automatic grid generation approach over free-form surface for architectural design

An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the main stress trajectories as the representation of force flows on a free-form surface,an automatic grid generation approach is proposed for the architectural design.The algorithm automatically plots the main stress trajectories on a 3D free-form surface,and adopts a modified advancing front meshing technique to generate the structural grid.Based on the proposed algorithm,an automatic grid generator named "St-Surmesh" is developed for the practical architectural design of free-form surface structure.The surface geometry of one of the Sun Valleys in Expo Axis for the Expo Shanghai 2010 is selected as a numerical example for validating the proposed approach.Comparative studies are performed to demonstrate how different structural grids affect the design of a free-form surface structure.

Parametric design of a part with free-form surfaces

3D solid models for parts with regular-form surfaces (PRFSs) are effectively generated using traditional parametric design techniques. A new model is obtained by changing some parameters defining the model. The parts with free-form surfaces (PFFSs), however, cannot be defined by several parameters. Usually they are defined by some geometric elements like profile curves. The traditional parametric design approaches have not easily dealt with the PFFSs. A method for generating a solid model and an engineering drawing for PFFSs is proposed in this paper: First, the new profiles are generated from input point data. Second, the profile information is extracted from the existing model. Last, the old profiles are replaced with the new profiles. This method can preserve the associative information of the existing model and automatically generate the drawing including views, dimen- sions, and annotations. The proposed method has been implemented using a commercial CAD/CAM system, Unigraphics, and API functions written in C-language, and were applied to the blades of a turbine generator. Some illustrative examples are pro- vided in order to show the effectiveness of the proposed method.

Study of the Contact Force in Free-form Surfaces Compliant EDM Polishing by Robot

With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.

ADAPTIVE MEASUREMENT METHOD BASED ON CHANGING-CURVATURE FOR UNKNOWN FREE-FORM SURFACE

Current measurement method for unknown free-form surface has low efficiency.To acquire given precision, a lot of null points are measured. Based on change surface curvature, anew measurement planning is put forward. Sample step is evaluated from the change curvature and thelocally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient andlocal camber coefficient, are used to optimize sampling step. The first coefficient is computed toavoid sampling-point exceeding the measurement range and the second control sampling precision.Compared with the other methods, the proposed planning method can reduce the number of themeasuring-point efficiently for the given precision. Measuring point distributes adaptively by thechange surface curvature. The method can be applied to improve measurement efficiency and accuracy.

NEW VISUAL METHOD FOR FREE-FORM SURFACE RECONSTRUCTION

A new method is put forward combining computer vision with computer aidedgeometric design (CAGD) to resolve the problem of free-form surface reconstruction. The surface isfirst subdivided into N-sided Gregory patches, and a stereo algorithm is used to reconstruct theboundary curves. Then, the cross boundary tangent vectors are computed through reflectance analysis.At last, the whole surface can be reconstructed jointing these patches with G^1 continuity(tangentcontinuity). Examples on synthetic images are given.

Research on the Fault Monitoring System in Free-form Surface CNC Machining Based on Wavelet Analysis

Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let decompose. According to the feature of transient fault, the author proposes for the first time the automatic determination technology of the threshold by us e of the adaptive filter characteristic of wavelet transform. Based on profound researches on steady fault feature, this dissertation makes an effective token o f steady fault feature by using wavelet energy method, and proposes the new idea to identify cut-in case and cut-out case, thereby successfully gives an uniqu e description quantitatively on the characterization of the variation of fault a nd cutting condition in the monitoring system.

Real-time accurate Free-Form Deformation in terms of triangular Bézier surfaces

We implemented accurate FFD in terms of triangular Bezier surfaces as matrix multiplications in CUDA and rendered them via OpenGL. Experimental results show that the proposed algorithm is more efficient than the previous GPU acceleration algorithm and tessel- lation shader algorithms.

Tool-path planning for free-form surface high-speed high-resolution machining using torus cutter

In CNC machining, two essential components decide the accuracy and machining time for a sculptured surface: one is the step-size interval, the other is the tool-path interval. Due to the limitation of the conventional method for calculating the tool-path interval, it cannot satisfy the machining requirement for high-speed and high-resolution machining. Accordingly, for high-speed and high-resolution machining, the current study proposes a new tool-path interval algorithm, plus a variable step-size algorithm for NURBS. Furthermore, a new type cutter, which can improve the cutting efficiency, is investigated in the paper. The transversal equation of the torus cutter onto the flat plan is given in this paper. The tool-path interval is calculated with the transversal equation and the proposed algorithm. The illustrated example shows that the redundant tool paths can be reduced because an accurate tool-path interval could be calculated.

Tool selection and collision-free in 5-axis numerical control machining of free-form surfaces

The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high precision. The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface. Several larger cutters are selected to machine the surface in order to find the interference-free area. The difference of machining time for this area between the optimal small cutter and the large cutters is calculated. The functional relationship between the machining time and the radius of a cutter is established, by which the optimal number of cutters is obtained. The combination of cutters, which possesses the minimum overall machining time, is selected as the optimal cutter sizes. A case study has demonstrated the validity of the proposed methodology and algorithms.

A Computer Vision Method for 3D Reconstruction of Curves-Marked Free-Form Surfaces

Visual method is now broadly used in reverse engineering for 3D reconstruction. The traditional computer vision methods are feature-based, i.e., they require that the objects must reveal features owing to geometry or textures. For textureless free-form surfaces, dense feature points are added artificially. In this paper, a new method is put forward combining computer vision with CAGD. The surface is subdivided into N-side Gregory patches using marked curves, and a stereo algorithm is used to reconstruct the curves. Then, the cross boundary tangent vector is computed through reflectance analysis. At last, the whole surface can be reconstructed by jointing these patches with 1Gcontinuity.

A Real-time NURBS Surface Interpolator for 5-axis Surface Machining

A real-time non-uniform rational B-spline （NURBS） surface interpolator is proposed and 5-axis machining method with a flat-end cutter is discussed. With the Taylor expansion and the coordinate transformation, the algorithms of NURBS interpolation, cutter effective machining radius, cutter offsetting and.inverse kinematics are deduced and implemented, respectively. Different from the conventional free-form surface machining, the proposed interpolator can real-time generate the motion commands of computer numerical control （CNC） machines with CC feedrate, rather than that of CL. An example part surface is demonstrated and the results of simulation show that the proposed method can be applied in actual 5-axis surface machining.

基于直驱机床的航空整体叶轮加工效率优化方法研究

为解决航空叶轮在复杂五轴联动加工过程中的效率和精度控制难题,本文基于直驱机床围绕加工参数对表面粗糙度和加工时间的影响进行了深入分析。首先通过与传统机床进行加工对比,证明了直驱机床的精度与速度方面的优势;其次针对原点坐标的研究揭示了原点位置对加工效率的影响,尤其是当原点接近A、C轴中心时,加工效率显著提高;最后通过正交试验法研究了转速、每齿进给量、切宽这3个关键因素,并发现每齿进给量是影响表面粗糙度的主导因素,其次是切宽,而转速的影响较小。在保证粗糙度小于1.6μm的前提下,以转速20000 r/mim、每齿进给量0.03 mm、切宽0.6 mm的参数组合获得最优结果。基于优化的工艺参数不仅提升了加工效率,节约了43.3%的加工时间,还确保了加工质量,为航空叶轮的精密加工提供了重要的技术参考,同时为基于直驱机床的复杂零件高效加工提供实践指导和理论依据。

钛合金离心叶轮多工艺状态下的疲劳特性研究

离心叶轮叶片的疲劳强度是叶轮叶片表面完整性各特征量的综合作用结果,不同工艺参数的叶片表面完整性状态也不相同,带来不同的疲劳特性。本文重点研究精密切削和喷丸强化对钛合金(TC11)离心叶轮叶片疲劳特性的影响规律,根据不同工艺状态下叶轮叶片疲劳强度试验反馈数据,开展基于离心叶轮结构特征的形性优化设计,并通过振动疲劳试验,采集循环次数3×10^(7)的叶轮叶片疲劳强度值,试验结果表明优化设计后的叶轮叶片疲劳强度提升15%,对新研型号的离心叶轮加工参数优化和结构设计优化具有重要指导意义。

基于HyperMILL的叶轮五轴数控编程及加工表面质量控制

在HyperMILL软件中,对半开式整体叶轮进行五轴数控编程,编程得到的刀位轨迹经过内部机床模拟加工验证,用后置处理器将刀位轨迹文件生成机床可识别的NC加工指令代码。在HURCO-VMX42Ui五轴加工中心上对6061铝合金整体叶轮进行加工,并通过结合设备准备功能G代码,对加工表面质量控制。加工结果表明,通过对HyperMILL软件五轴数控编程与刀轨文件的模拟,可避免加工过程中容易出现的干涉、过切、欠切等问题,提高叶轮加工的质量与生产效率;分析VMX42Ui五轴加工中心准备功能G代码参数的修改,工作面的加工精度和表面质量有较明显提升。该研究为其他同类复杂零件的编程加工提供参考依据。

Multi-parameter optimization of machining impeller surface based on the on-machine measuring technique

Selecting the optimal machining parameters for impeller surface is a challenging task in the automatic manufacturing industry, due to its free-form surface and deep-crooked flow channel.Existing experimental methods require lots of machining experiments and off-line tests, which may lead to high machining cost and low efficiency. This paper proposes a novel method of machining parameters optimization for an impeller based on the on-machine measuring technique. The absolute average error and standard deviation of the measured points are used to define the grey relational grade for reconstructing the objective function, and the complex problem of multi-objective optimization is simplified into a problem of single-objective optimization. Then, by comparing the values of the defined grey relational grade in a designed orthogonal experiment, the optimal combination of the machining parameters is obtained. The experiment-solving process of the objective function corresponds to the minimization of the used errors, which is advantageous to reducing the machining error. The proposed method is efficient and low-cost, since it does not require re-clamping the workpiece for off-line tests. Its effectiveness is verified by an on-machine inspection experiment of the impeller blade.

TC11钛合金整体叶轮铣削加工表面完整性研究

考虑叶轮真实加工参数,探究了切削速度、每齿进给量、行距、切深、冷却液对整体叶轮叶片的表面完整性(包括表面粗糙度、表面形貌、表面显微硬度、金相组织、残余应力)的影响。结果表明:行距和每齿进给量对叶片表面粗糙度影响最大,行距和每齿进给量越小,叶片表面粗糙度越小,当行距从0.3 mm减小至0.16 mm时,平均粗糙度Ra从0.64μm减小至0.48μm,当每齿进给量从0.1 mm减小至0.06 mm时,平均粗糙度从0.62μm减小至0.4μm;行距和每齿进给量对表面形貌影响最为明显,随着行距和每齿进给量的增大,叶片表面的残留高度增大;切削参数选取相对合理,叶片表面没有产生划痕、划伤和毛刺等缺陷;在合理的参数条件下,叶片表面的力热水平较低,使得叶片表面的显微硬度变化不明显,各切削参数下表面平均硬度在335HV左右浮动,同时也没有产生区别于基体的变质层;叶片表层残余应力均表现为压应力,行距、切深对残余应力的影响较小;随切削速度和每齿进给的增大,表层压应力先增大后减小,沿深度方向表现出先微弱减小再增大到峰值最后到达基体的趋势,平行和垂直进给方向上最大残余应力分别可达275 MPa和400 MPa;水基冷却液在加工表层达到远大于油基冷却液的残余压应力,但残余应力在深度方向下降明显。