ADAPTIVE STRATEGIES FORNC MACHINING COMPOUND FREE-FORM SURFACES

This paper treats adaptation to the machining precision and productivity of compound free-form surfaces. The principle of a mixed NC machining method (surface direct interpolating (SDI[1])and discrete NC programming) is introduced- Three adaptive procedures are discussed : ( 1 ) adaptivedivision of the machining areas, (2) adaptive triangulation for generating interference-free tool pathsfrom compound surfaces, (3) machining along surface/surface intersection (SSI ) curves with anadaptive step length. They upgrade the intelligence of machining compound surfaces.

MATHEMATICAL MODEL OF NC MACHINING NONCONVENTIONAL MILLING CUTTERS-FORMING METHOD OF RAKE FACES

How to generate rake faces of nonconventional milling cutters (NCMC) with constant spiral angled and normal rake angled edges on NC machine tools is presented by use of a blunt cup grinder or a cup milling cutter. Motion functions of the NC machining system are mathematically deduced and exam- ed by a experiment. The research will provide theoretical and practical guidance for machining noncon- ventional tools on NC machine tools.

THIRD-ORDER LOCAL CONTACT AND APPLICATION IN 5-AXIS MACHINING OF SCULPTURED SURFACES

In order to increase the efficiency in the machining of the sculptured surfaces, the contact principle of differential geometry is applied to the 5-axis NC machining; The best contact condition between tool and the surfaces is researched. Through analysis the contact degree of the intersection line of the cutter and the surfaces is known. In comparison to previous studies, the theory is more restricted and accurate by going beyond the second-order parameters into the third-order, suiting both the primary surfaces of analytical geometry and the computer-generated surfaces of the computation geometry. It has definite procedure of calculation, and the equations are easy to solve. The thought process is very clear： First, suppose that there is a surface of third-order, the coefficients of which are arbitrary; Then find out the best posture of the circle in order that the circle and the surface will most closely contact with each other at the origin position; Finally, develop the surface into a third-order surface at every point of machining and employ the results mentioned above to find the best cutter posture at every point of machining. As a result, the equations are easy to solve, and the concept is clear.

INTERFERENCE-FREE TOOL POSTURE GENERATION FOR 5-AXIS NC MILLING FREE-FORM SURFACES WITH CYLINDRICAL MILL

The 5-axis NC machining offers the potential of efficient and accuratemachining. However, the present CAM system for 5-axis control is still an unsolved problem due tointerference between tool and surrounding objects. A new method is presented. There are two steps inthis procedure. First, it detects the interference by calculating the shortest distance between thetool-axis and the surrounding surfaces. Then upon the maximum gouging, the interference-free toolposture for 5-axis NC cylindrical milling free-form surfaces is obtained by adjusting tool. Thevalidity of the proposed method has been confirmed by machining an impeller.

Algorithm for Detecting Volumetric Geometric Accuracy of NC Machine Tool by Laser Tracker

Quick and accurate detecting the error of NC machine tool and performing the error compensation are important to improve the machining accuracy of NC machine tool. Currently, there are many methods for detecting the geometric accuracy of NC machine tool. However, these methods have deficiencies in detection efficiency and accuracy as well as in versatility. In the paper, a method with laser tracker based on the multi-station and time-sharing measurement principle is proposed, and this method can rapidly and accurately detect the geometric accuracy of NC machine tool. The machine tool is controlled to move in the preset path in a 3D space or 2D plane, and a laser tracker is used to measure the same motion trajectory of the machine tool successively at different base stations. The original algorithm for multi-station and time-sharing measurement is improved. The space coordinates of the measuring point obtained by the laser tracker are taken as parameter values, and the initial position of each base point can be determined. The redundant equation concerning the base point calibration can be established by the distance information of the laser tracker, and the position of each base point is further determined by solving the equation with least squares method, then the space coordinates of each measuring point can be calibrated. The singular matrix does not occur in calculation with the improved algorithm, which overcomes the limitations of the original algorithm, that the motion trajectory of machine tool is in a 3D space and there exits height difference between the base stations. Adopting the improved algorithm can expand the application of multi-station and time-sharing measurement, and can meet the quick and accurate detecting requirements for different types of NC machine tool.

An Universal Modeling Method for Enhancing the Volumetric Accuracy of CNC Machine Tools

Volumetric error modeling method is an important te ch nique for enhancement the accuracy of CNC machine tools by error compensation. I n the research field, the main question is how to find an universal kinematics m odeling method for different kinds of NC machine tools. Multi-body system theor y is always used to solve the dynamics problem of complex physical system. But t ill now, the error factors that always exist in practice system is still not con sidered. In this paper, the accuracy kinematics of MBS (multi-body system) are developed by adding the movement error items and the positioning error items for every couple of adjacent bodies. After make an analysis for different kinds of NC machine tools we can find that NC machine tools can be looked as a kind of sp ecial MBS. It’s main construction only contains two movement branch. the one is from base part to workpiece and the other is from base part to cutter. So an u niversal volumetric error modeling method and the error analysis method for NC m achine tools can be built in this paper based on MBS theory. The essential condi tion for precision machining is derived through mathematics equations and the co ncept of ICCP (inverse changed cutter path ) and ICNI (inverse changed NC instru ction ) are presented in this paper. The numerical solution methods for ICCP and ICNI are also given in this paper which can be directly used to enhance the mac hining accuracy of NC machine tools. In order to verifying the above works, the double frequency laser interface detecting instrument of RENISHAW is used to mea sure the error parameters of the MAKINO 3-axis NC machine tools and the softwar es are developed using C++ developing language to simulate the cutte r trail under different kind conditions in the computer. Latterly the standard w ork parts are selected to be machined on the MAKINO 3-axis NC machine tools bef ore and after use the above mentioned error compensation method respectively. Th e simulation and experiment results show that the volumetric error modeling meth od is effective and the machining accuracy of CNC machine tools can be improved more than 60% after using the compensation method presented in this paper.

MOTION ERROR ESTIMATION OF 5-AXIS MACHINING CENTER USING DBB METHOD

In order to estimate the motion errors of 5-axis machine center, the double ball bar （DBB） method is adopted to realize the diagnosis procedure. The motion error sources of rotary axes in 5-axis machining center comprise of the alignment error of rotary axes and the angular error due to various factors, e.g. the inclination of rotary axes. From sensitive viewpoints, each motion error is possible to have a particular sensitive direction in which deviation of DBB error trace arises from only some specific error sources. The model of the DBB error trace is established according to the spatial geometry theory. Accordingly, the sensitive direction of each motion error source is made clear through numerical simulation, which is used as the reference patterns for rotational error estimation. The estimation method is proposed to easily estimate the motion error sources of rotary axes in quantitative manner. To verify the proposed DBB method for rotational error estimation, the experimental tests are carried out on a 5-axis machining center M-400 （MORISEIKI）. The effect of the mismatch of the DBB is also studied to guarantee the estimation accuracy. From the experimental data, it is noted that the proposed estimation method for 5-axis machining center is feasible and effective.

Bayesian Reliability Modeling and Assessment Solution for NC Machine Tools under Small-sample Data

Although Markov chain Monte Carlo（MCMC） algorithms are accurate, many factors may cause instability when they are utilized in reliability analysis; such instability makes these algorithms unsuitable for widespread engineering applications. Thus, a reliability modeling and assessment solution aimed at small-sample data of numerical control（NC） machine tools is proposed on the basis of Bayes theories. An expert-judgment process of fusing multi-source prior information is developed to obtain the Weibull parameters＇ prior distributions and reduce the subjective bias of usual expert-judgment methods. The grid approximation method is applied to two-parameter Weibull distribution to derive the formulas for the parameters＇ posterior distributions and solve the calculation difficulty of high-dimensional integration. The method is then applied to the real data of a type of NC machine tool to implement a reliability assessment and obtain the mean time between failures（MTBF）. The relative error of the proposed method is 5.8020×10-4 compared with the MTBF obtained by the MCMC algorithm. This result indicates that the proposed method is as accurate as MCMC. The newly developed solution for reliability modeling and assessment of NC machine tools under small-sample data is easy, practical, and highly suitable for widespread application in the engineering field; in addition, the solution does not reduce accuracy.

Bayesian zero-failure reliability modeling and assessment method for multiple numerical control(NC) machine tools

A new problem that classical statistical methods are incapable of solving is reliability modeling and assessment when multiple numerical control machine tools(NCMTs) reveal zero failures after a reliability test. Thus, the zero-failure data form and corresponding Bayesian model are developed to solve the zero-failure problem of NCMTs, for which no previous suitable statistical model has been developed. An expert-judgment process that incorporates prior information is presented to solve the difficulty in obtaining reliable prior distributions of Weibull parameters. The equations for the posterior distribution of the parameter vector and the Markov chain Monte Carlo(MCMC) algorithm are derived to solve the difficulty of calculating high-dimensional integration and to obtain parameter estimators. The proposed method is applied to a real case; a corresponding programming code and trick are developed to implement an MCMC simulation in Win BUGS, and a mean time between failures(MTBF) of 1057.9 h is obtained. Given its ability to combine expert judgment, prior information, and data, the proposed reliability modeling and assessment method under the zero failure of NCMTs is validated.

CAGD AND NC MILLING OF THE CASTING MOULD OF HELICAL INTAKE PORT

A new method of the design and machining the casting moulds of helical intake ports of diesel engines is presented based on CAD / CAM technique. The problems about the smooth continuity between patches, the cutter interference and the determination of the mould split curve are discussed in details.The CAGD system of the intake port has been developed. and the casting mould is machined sucessfully on NC machine.

STUDY ON NEW METHOD OF IDENTIFYING GEOMETRIC ERROR PARAMETERS FOR NC MACHINE TOOLS

The methods of identifying geometric error parameters for NC machine tools are introduced. According to analyzing and comparing the different methods, a new method-displacement method with 9 lines is developed based on the theories of the movement errors of multibody system (MBS). A lot of experiments are also made to obtain 21 terms geometric error parameters by using the error identification software based on the new method.

Implementation of Interference Checking Based on Construction Space Concept

Methods of interference checking in NC programming are briefly discussed. A new approach for interference detection in 3-axis NC machining of sculpture surface based on the concept of construction space is introduced. The space is firstly divided into millable space and gouge one and then the toolpath segments in the gouge space are checked and eliminated. The algorithm described in this paper is stable and reliable, and is suitable for ball-end，round-end and flat-end cutters.

The Application of the GM(1,1) Metabolism Model to Error Data Processing of NC Machine Tools

This paper applied the gray system theory to error data processing of NCmachine tools according to the characteristic. It presented the gray metabolism model of error dataprocessing. The test method for the model needs less capacity. Practice proved that the method issimple, calculation is easy, and results are exact.

YKJ3180H Economy NC Gear Hobbing Machine

The YKJ3180H Economy NC GearHobbing Machine is a new variety,developed recently by the ChongqingMachine Tools Works to meet clients’demands. Its most prominent feature is its highproduction efficiency ( able to complete awork cycle automatically), high processingprecision (Grade 7 or higher according to theGB 10095) and its cost competitiveness. This product is used in the machinetool and machinery industries at automobiles,tractors, gears and gear box factories. It canbe used for processing spur gears and helicalgears, automatic radial feed wormwheels,tapered gears and crowning gears; so it isespecially applicable in factories usingcrowning gear couplings, such as metallurgy,mining, lifting transport and the chemicalmachinery.

METHOD OF ENHANCING THE POSITIONING ACCURACY FOR NC MACHINE TOOLS

Based on the kinematics of the multi-body system , a general model for the positioning errors of NC machine tools by means of the lower numbered body array and the geometric constraint is presented. The parameters identification of geometric errors by an improved 22-line method is discussed. Moreover , an intelligent error compensation controller has been developed. All these are verified by a series of experiments on XH714 machining center. The results show that the prosition- ing errors with compensation have been reduced to ±7 μm from 50 μm.

Error Analysis and Its Offset on the NC Lathe Machine in Cutting a Semi-Sphere Surface

This paper analyzed the errors that occurred by leaving the shape of the cutting edge out of consideration on a NC lathe machine in cutting a semi-sphere surface and brought forward a method to offset these errors and the correct calculated formula for some parameters on the basis of experiments. It has increased the manufacturing accuracy of the semi-sphere surface on the NC lathe machine.

ESTIMATING THE CUTTER＇S MAXIMUM DIAMETER IN 5－AXIS NC FACE MILLING OF TURBINE BLADES

Based on the principles of differential geometry,the basic equations are derived for generating gouging free tool path in 5-axis NC face milling,the influence of surface's local geometry is discussed,and the conditions of using cutter with reasonable diameter are presented.

A review of recent advances in machining techniques of complex surfaces

Complex surfaces are widely used in aerospace,energy,and national defense industries.As one of the major means of manufacturing such as complex surfaces,the multi-axis numerical control(NC)machining technique makes much contribution.When the size of complex surfaces is large or the machining space is narrow,the multi-axis NC machining may not be a good choice because of its high cost and low dexterity.Robotic machining is a beneficial supplement to the NC machining.Since it has the advantages of large operating space,good dexterity,and easy to realize parallel machining,it is a promising technique to enhance the capability of traditional NC machining.However,whether it is the multi-axis NC machining or the robotic machining,owing to the complex geometric properties and strict machining requirements,high-efficiency and high-accuracy machining of complex surfaces has always been a great challenge and remains a cutting-edge problem in the current manufacturing field.In this paper,by surveying the machining of complex parts and large complex surfaces,the theory and technology of high-efficiency and high-accuracy machining of complex surfaces are reviewed thoroughly.Then,a series of typical applications are introduced to show the state-of-the-art on the machining of complex surfaces,especially the recently developed industrial software and equipment.Finally,the summary and prospect of the machining of complex surfaces are addressed.To the best of our knowledge,this may be the first attempt to systematically review the machining of complex surfaces by the multiaxis NC and robotic machining techniques,in order to promote the further research in related fields.

CAX-A Domestically Developed CAD/CAM System

This paper introduces a domestically developed CAD/CAM system,CAX,which is able to meet the needs of small and medium sized enterprises.Firstly,the motivations and principles for the developing of the system are presented.Then,the functions and features of CAX are described.In the 3rd section,the algorithms for generating blending surfaces with both constant radius and variant radii are detailed.Six color plates showing the applications of CAX are included in section 4.Finally,dis- cussed are some enhancements being added to CAX in th future.

AUTOMATIC PROGRAMMING SYSTEM WITH NURBS METHOD ON PC

This paper presents an automatic programming system on PC, it has also solved the technic problem in the combination of different curves or surfaces. The NURBS is applied to modeling and fitting complicated curves and surfaces. The circular spline is combined with the NURBS to determine the cutter path in accordance with the features of the interpolation movement of NC machine tool. Three methods have been developed to solve the overcutting problems.