Sculptured Surfaces Research Articles

Generation of kinematic smooth tool-paths in 5-axis milling of sculptured surfaces

This paper addresses the issues of tool-path smoothness and tool-path length (machining efficiency) in the generation of cutter location (CL) paths of 5-axis point milling of sculptured surfaces. In the proposed method, the joint movement between two neighbouring CLs in the machine frame is used to measure the tool-path smoothness and the cutting strip-width to measure tool-path length. In order to generate tool-paths with satisfactory smoothness and good efficiency, two approaches are proposed: 1) a fast repairing approach that modifies CL segments with drastic joint movement; 2) a holistic optimisation approach that considers both objectives simultaneously. For both approaches, corresponding algorithms based on evolutionary algorithms (EAs) have been developed to search for the best posture sequence for the CLs on each path. A case study is presented to show the performance comparison between the two approaches. [Received 18 August 14; Revised 30 April 5; Accepted 18 May 2015]

Research Progress in Tool Path Planning for Five-axis End Milling Machining of Sculptured Surfaces

Research Progress in Tool Path Planning for Five-axis End Milling Machining of Sculptured Surfaces

Reducing fluctuation of machining strip width by tool position modification for five-axis NC machining of sculptured surfaces

This paper presents a method to reduce the fluctuation of machining strip width by modifying tool position. When the machining strip width varies rapidly within a tool path, the fluctuation of cutting force brings negative influence on the workpiece and cutter. Furthermore, as the tool path interval is always defined conservatively to avoid undercut, the machined strips of adjacent tool paths have unnecessary amount of overlap. Rapid changing machining strip width usually creates too much overlap at some location, which causes repeated cutting. A method is proposed to modify tool position and reduce the fluctuation of machining strip width. Besides, tilt angle smoothness along the tool path is also taken into account. The computation result of a blade surface verified the validity of the proposed method.

The estimation of cutting forces and specific force coefficients during finishing ball end milling of inclined surfaces

The majority of cutting force models applied for the ball end milling process includes only the influence of cutting parameters (e.g. feedrate, depth of cut, cutting speed) and estimates forces on the basis of coefficients calibrated during slot milling. Furthermore, the radial run out phenomenon is predominantly not considered in these models. However this approach can induce excessive force estimation errors, especially during finishing ball end milling of sculptured surfaces. In addition, most of cutting force models is formulated for the ball end milling process with axial depths of cut exceeding 0.5mm and thus, they are not oriented directly to the finishing processes. Therefore, this paper proposes an accurate cutting force model applied for the finishing ball end milling, which includes also the influence of surface inclination and cutter's run out. As part of this work the new method of specific force coefficients calibration has been also developed. This approach is based on the calibration during ball end milling with various surface inclinations and the application of instantaneous force signals as an input data. Furthermore, the analysis of specific force coefficients in function of feed per tooth, cutting speed and surface inclination angle was also presented. In order to determine geometrical elements of cut precisely, the radial run out was considered in equations applied for the calculation of sectional area of cut and active length of cutting edge. Research revealed that cutter's run out and surface inclination angle have significant influence on the cutting forces, both in the quantitative and qualitative aspect. The formulated model enables cutting force estimation in the wide range of cutting parameters, assuring relative error's values below 16%. Furthermore, the consideration of cutter's radial run out phenomenon in the developed model enables the reduction of model's relative error by the 7% in relation to the model excluding radial run out.

Modeling and on-line simulation of surface topography considering tool wear in multi-axis milling process

The understanding and prediction of the generated surface topography are very important in milling process. This paper presents a surface topography model and an on-line simulation method of surface topography considering tool wear in a multi-axis milling process. First, the cutting edge equation is established by dividing the cutting edge into a series of cutting edge elements considering tool wear influence and tilt angle of tool axis on each discrete cutting edge element, and an algorithm is proposed to determine the range of divided position angle. Then, the sculptured surface workpiece is divided into a series of elements along the feed direction with the same or less than discrete precision of cutting edge. The intersection points between the discrete cutting edge elements and the planes of both sides of each divided element on workpiece can be obtained based on the established cutting edge equation in the cutting process. The left cutting trajectory points on workpiece are got by reserving the points with the minimum coordinate value in the Z-axis direction under the same coordinate value in the X-axis and Y-axis direction among the intersection points and points on workpiece. Thus, surface topography model can be constructed based on the established cutting edge equation, the determined range of position angle, discrete cutting edge elements, and divided element on workpiece surface. Finally, an on-line simulation algorithm is proposed to simulate the generation process of surface topography in multi-axis milling operation. Experimental work and validation of the established model are performed on a five-axis milling center by using stainless steel 0Cr17Ni12Mo2 and cemented carbides milling cutter. The results about the topography generation of the constructed B-spline surface show that the predictions of the established surface topography model correlate well with the experimental results.

Free-form contour packing based on material grid approximation and lowest-gravity-center methods

Freeform surfaces, also called sculptured surfaces, have wide applications in clinical prosthesis and manufacturing. The free-form contour of product needs to be packed before it is machined from raw materials. The No-Fit Polygon methods are not suitable to the complex contours packing because calculating No-Fit Polygons for non-convex polygons is time-consuming. A contour packing algorithm for free-form contour machining is proposed in this paper. The parking area of materials is discretized based on a bottom-left and the lowest gravity center strategy. The packing contour is collided in four directions to increase the material utilization. Experimental results show that the packing time is reduced and the material utilization is improved using the proposed algorithm.

A Review of the Main Modeling Methods for Ball Nose End Milling Processes

The ball nose end mills are highly used for complex sculptured surfaces in 3-5 axes milling. The modeling of the cutting process using ball nose end mills is more complex than in the case of simple end mills due to the fact that the cutting speed varies continuously along the cutting edge. By tilting the cutting tool relative to the surface to be machined, the modeling is getting more complicated due to the large number of input variables. This paper presents a review of the main modeling types, underlining the specificity, the advantages and disadvantages for each type in comparison to an own research on a parametric CAD model. There are also recommendations made towards the modeling process, based on the results obtained by the authors.

Efficient NC Tool Path Planning Based on the Subdivision of Sculptured Surface

In this paper, we have presented a method to generate efficient NC tool paths based on the surface subdivision. The main objective is to achieve high efficiency in the machining of sculptured surface. The NC machining efficiency can be improved by segmenting the whole surface into distinct areas according to the characters of sculptured surface and by using different size mills and different tool path planning methods to machine the areas. The iso-parametric method and large mills are used in the curvature changing little areas. While the iso-scallop method and small mills are used in curvatures changing large areas. This can make full use of tool path generation methods and mills, which improve the machining efficiency of sculpture effectively.

Development of a software-automated intelligent sculptured surface machining optimization environment

To ensure the quality of machined products at minimum cost and maximum effectiveness, it is crucial that selection of optimum machining parameters should be done when computer numerically controlled (CNC) machine tools technology is employed. Traditionally, experience of the operator plays a major role in the selection of efficient parameter values; however, attaining optimum ones each time by even skilled end users, is extremely difficult. This paper takes advantage of the possibilities of current computer-aided design (CAD)/computer-aided manufacturing (CAM) technology and implements a genetic algorithm for optimising CNC machining operations mainly for sculptured surfaces. The algorithm has been developed as a hosted application to a cutting-edge CAD/CAM system. Collaboration among applications has been achieved through programming for software automation by utilising the application programme interface of the system. The approach was implemented to a group of test sculptured models with different properties whilst one of them has been actually machined using typical resources. Results obtained after the implementation indicated that the methodology is capable of providing optimum values for process parameters on its way to maintain both productivity and high quality.

Cutting Edge Mathematical Model for Ellipsoidal End Mill

In this paper, a new kind of ellipsoid end mill is proposed in order to improve the quality and efficiency in machining the sculptured surface. An integral ellipsoid end mill parameter optimization system architecture is developed to make the parametric design automatically and efficiently. Then, the mathematical model of continuous blade curve with constant helix angle and normal helix cutting edge of ellipsoid end mill is presented, as well as the cutting edge on the cylinder of cylindrical ellipsoid end mill. And then, all curves are simulated based on MATLAB software. Finally, the ellipsoid end mill is manufactured using a SAACKE UWIF CNC grinding machine to verify the feasibility of ellipsoid end mill.

Optimising tool positioning for achieving multi-point contact based on symmetrical error distribution curve in sculptured surface machining

The multi-point tool positioning algorithms produce much larger machining strip width than the single-point algorithms and apparently reduce the actual machining time. This paper presents a tool positioning algorithm for multi-point machining of sculptured surface, which is excellent at dealing with both of concave and convex surfaces. The proposed method is based on the middle-point error control (MPEC) method, which means the connection point between cutter and surface corresponds to the middle point of error distribution curve. Usually, only one cut contact (CC) point can be obtained with this method. Thus, the proposed method improved the MPEC method for achieving two CC points. At first, the shape of error distribution curve is investigated, and its asymmetry is evaluated. Secondly, the error distribution curve becomes symmetrical after the cutter is rotated with a roll angle, and the cutter is separated with surface at the same time. Finally, the minimum tilt angle is found, and two CC points are obtained without gouging. Machining experiment is conducted to verify the proposed method, and the result reveals that the machining strip width is increased apparently and the tool position is almost unchanged after the adjustment with proposed method. Simulation, measurement, and analysis are also given in the part of the experiment.

Flat-end cutter orientation on a quadric in five-axis machining

The authors have recently developed methods for cutter orientation and tool path generation in 5-axis sculptured surface machining, where the design surface is approximated locally by a quadric. This paper presents, from a purely geometric perspective, the fundamental theory for optimising the cutter orientation on a quadric, which maximises the machined strip width whilst avoiding local and rear gouging. The analysis focuses on the flat-end cutter which is modelled by a circular cylinder but can be generalised for any fillet-end cutter using an appropriate offset of the design surface and the concept of geometric equivalency. The theory is illustrated by three examples.

Smooth Cutting Operation Strategy for High Finishing Machining

High finishing machining tool path generation methods are usually adopted for five-axis computer numerically controlled machining of sculptured surface parts. The quality of the high finishing machining has an important effect on that of the surface. In this paper, a high finishing machining tool path generation method is introduced to generate an optimal tool path. The initial tool path is firstly created based on the constant scallop height, then the derived tool paths are generated as a kind of the diagonal curve by the initial tool path, and at last, the tool path smoothing algorithm is applied to the generated tool path. This path algorithm can ensure higher level of smooth of the surface been machined. Finally, the results of simulation and experiment of the machining process are given to verify the smooth and applicability of the proposed method.

Evaluation of 3- and 5-axis sculptured surface machining in CAM environment through design of experiments

Sculptured surface machining (SSM) is an operation widely applied to several industrial fields such as aerospace, automotive and mould/die. The number of the parameters and strategies involved to program such machining operations can be enormously large owing to surface complexity and advanced design features. This study focuses on the examination of machining strategies and related parameters for the assessment of roughing and finishing stages. A fractional factorial design implementing an L27 Taguchi orthogonal array (OA) was established to conduct machining experiments with the use of a computer-aided manufacturing (CAM) software. Fractional factorial design specifics involve the statistical elimination of unimportant parameters, thus reducing experimental runs without the loss of useful information. Two scenarios were considered to machine a sculptured part; one involving 3-axis roughing/3-axis finish machining experiments and the other one involving 3-axis roughing/5-axis finish machining experiments. Roughing operation was common for both scenarios. The problem was subjected to discrete technological constraints to reflect the actual industrial status. For each machining phase, two quality objectives reflecting productivity and part quality were determined. Roughing experiments were tested to minimise machining time and remaining volume, whilst finishing experiments were subjected to minimise machining time and surface deviation between the designed and the machined 3D model. Quality characteristics were properly weighted to formulate a single objective criterion for both machining phases. Results indicated that DOE applied to CAM software, enables NC programmers to have a clear understanding about the influence of process parameters for SSM operations, thus generating efficient toolpaths to improve productivity, part quality and process efficiency. Practically the work contributes to machining improvement by through the proposition of machining experimentation methods using safe and useful platforms such as CAM systems; the investigation of approaches to avoid problem oversimplification mainly when large number of machining parameters should be exploited and the evaluation of quality criteria which allow their assessment directly form CAM software.

Study on the cantilever grinding process of aero-engine blade

An aero-engine blade is the typical thin-walled workpiece with low rigidity. The machining accuracy of the aero-engine blade with sculptured surfaces has been a research focus in the aviation industry. This article presents a new cantilever grinding process for the high precision machining of aero-engine blade. Only one end of a blade is fixed and the other end is free in order to eliminate the deformation of blade caused by over-positioning. Moreover, the vibration of aero-engine blade can be reduced so that the surface quality of blade can be improved in the grinding. The grinding parameters are optimized for the low deflections of blade. The types of tool path are also discussed in this article. Finally, the computer numerical control machining examples are implemented. The measurement results show that the profile errors of suction/pressure surface machined by the proposed process do not exceed 0.02 mm. And the machining accuracy of leading/trailing edge with a radius of about 0.05 mm is acceptable.

Research on Cutting Force Simulation for Francis Hydro Turbine’s Blade Based on VERICUT

Hydro turbine blade is a very complex body closed by sculptured surface, and reasonable cutting parameters are very important for the quality of Francis Hydro Turbine blades and machining efficiency. An implementation method of digital cutting force simulation was proposed in this paper for Francis Hydro Turbines Blade based on VERICUT. Firstly ,cutting parameters can be extracted by the secondary development of VERICUT, and the forecasting process of cutting force have been established under the different parameters in theVERICUT. Then we can obtain the change of cutting force by adjusting cutting parameters in the process of digital machining simulation, and the influence of cutting parameter on cutting force was analyzed. Finally, the case study on the Hydro turbine blade has been conducted, and its application results are remarkable.

Complexity analysis and calculation for sculptured surface in multi-axis CNC machining based on surface subdivision

Complexity of sculptured surfaces has a great influence on multi-axis computer numerical control (CNC) machining performances such as processing efficiency, surface quality, and energy consumption. A term called surface machining complexity (SMC) is first presented to describe the complexity level of surface geometrical shape features, and its influence on CNC machining performance. Shape features of sculptured surfaces are classified into seven categories based on surface curvature. An innovative method for quantifying SMC using surface subdivision is proposed. Firstly, representation of sculptured surfaces is introduced. Then, three processes of surface subdivision are presented, which are surface discretization based on iso-parameter line sampling, rough partitioning based on surface shape categories, and region grouping based on two criteria. After that calculation, formulas of SMC including formulas of local SMC and global SMC are developed. The proposed formulas utilize three correction factors to describe the influences of surface size, cutter diameter, grouping order, and mode of different surface shape categories. Finally, the proposed method is applied to calculate SMC for a typical sculptured surface and multi-axis CNC machining experiments to demonstrate the ability of our method, which can form a foundation for further research.

Optimum Material Evaluation for Gas Turbine Blade Using Reverse Engineering (RE) and FEA

Gas turbines play a major role in the field of aviation owing to their high power to weight ratio and being self-contained, as compared to other conventional power generating units. The main function of the blades in gas turbines is imparting energy to, or extracting it, from a fluid stream. Since the underlying function of the blades is to smoothly change the velocity of fluid flow, they are generally comprised of parametric sculptured surface models. In absence of design data, the reverse engineering process can be considered as a major tool for modeling. Reverse engineering process involves sensing the geometry of existing part, creating a geometric model of the part from the sensed data and passing this model to an appropriate CAD/CAM system for manufacturing. This paper mainly deals with the modeling and analysis of gas turbine blades. The design data for a turbine blade is obtained using Reverse Engineering technique. Using the data so obtained, a model of the turbine blade is created in ANSYS FEA package. For the given loading conditions, the blade is analyzed for static structural analysis for different materials at varying centrifugal loads and different materials and a safe and feasible material is suggested.

Face-milling spiral bevel gear tooth surfaces by application of 5-axis CNC machine tool

In order to solve some common problems of CNC-machined spiral bevel gears such as small cutting strip width and poor surface quality, while milled by the ball-end, a machining method of face milling using a disk cutter with a concave end is presented. The research theories are based on the foundation of spiral bevel gears’ geometry structure. Firstly, a bigger diameter disk cutter with a concave end is selected. Then, change the setting order of cutter orientation angles. The functions of cutter tilt and yaw angle are separated, and tooth surfaces machined with big cutting strip width and no bottom land gouge can be expected. Since the cutter yaw angle, determined firstly by cutting contact point, positions in the tooth surface machine, the bottom land gouge interference can be avoided effectively. Then, the tilt angles of the gear pair, both side tooth surfaces, are determined by the theory of sculptured surfaces machined by the flat-end cutter, respectively. As a result, the improved cutting strip width and machining efficiency can be realized. Finally, feasibility of this method is verified through machining experiment and measurement of a spiral bevel gear pair.

Offline flexible optimisation of feed and speed in computer numerical control machining of sculptured surfaces exploiting dedicated cutting force metamodels

An intelligent offline optimisation system for feed and spindle speed in three-axis machining of sculptured surfaces is presented. Optimisation is performed by a standard genetic algorithm seeking, in this instance, to minimise machining force variation along designated sections of the tool path. Machining force is modelled realistically, rather than mechanistically, by dedicated artificial neural networks trained with a low number of experimental data that are obtained from the very equipment on which machining is to be carried out. The artificial neural networks employ the material volume removed per tool revolution as calculated using a standard solid modelling engine. The artificial neural network model architecture is optimally determined in a rigorous way as opposed to often followed trial-and-error approaches, and it is made use of directly in the evaluation function of the optimiser. This framework is flexible enough to enable definition of constraints, additional evaluation criteria and desirable force patterns to guide optimisation. Effectiveness of the approach is successfully demonstrated for finish machining a hemispherical part.