OPTIMAL FEED RATE CONTROL FOR MULTI-AXIS CNC MACHINING OF FREE FORM SURFACES

Considering machining efficiency, surface quality and wear of cutter and machine, it is necessary to maintain high, stable and constant surface feed rate as far as possible.The feed late control strategy for multi-axis CNC machining of free-form surfaces is presented. It comprises: ①the determination of effective feed rate; ②the adoption of suitable approaches to smooth feed rate. This strategy considers path geometry, actuator limitation and machine dynamics. The result shows that machining efficiency is improved effectively.

SOFTWARE-CONTROLLED SYSTEM OF ULTRA-PRECISION MACHINING AXISYMMETRIC ASPHERIC MIRROR

In order to improve machining accuracy and efficiency, a software-controlled system of ultra-precision machining for axisymmetric aspheric mirror, using techniques of error compensation, remote transmission and modularization, is designed based on industrial PC, Windows 2000 work platform and Visual Basic 6.0. By experiments, this system realizes functions of ultra-precision machining, machining error compensation, remote data transmission and automatic data transformation among first machining, compensation machining and accuracy measurement. The actual application shows that error compensation improves machining accuracy, remote transmission improves machining efficiency while modularization avoids repeated work and improves design efficiency. Therefore, the system has met ultra-precision machining need for aspheric mirror.

Study of machining induced surface defects and its effect on fatigue performance of AZ91/15%SiCp metal matrix composite

The quality of surface generated in a peripheral milling of AZ91/SiCp/15%for varying machining conditions and its effect on the fatigue performance are investigated in this study.The machined surface quality was evaluated through roughness measurements and SEM micrographs of ine machined surface.Tensile iesis were pcifumicu io iiieasure the mechanical properties of the composite.Subsequently,fatigue life of milled specimens was measured through axial fatigue tests at four loading conditions.Optical and SEM/EDS micrographs of the fractured surface were studied to identify the crack initiation site and propagation mechanism.Specimens machined at a lower feed rate of 0.1 mm/rev was found to have excellent surface finish and consequently higher fatigue life.At 0.3 mm/rev,the presence of feed marks and other surface defects resulted in a drastic decrease in fatigue life.Five distinct regions were identified on the fractured surface,particle fracture along and perpendicular to the surface,voids in the matrix due to particle debonding and pull out and typical ductile failure of matrix with embedded SiC particles.

Surface defects incorporated diamond machining of silicon

This paper reports the performance enhancement benefits in diamond turning of the silicon wafer by incorporation of the surface defect machining(SDM)method.The hybrid micromachining methods usually require additional hardware to leverage the added advantage of hybrid technologies such as laser heating,cryogenic cooling,electric pulse or ultrasonic elliptical vibration.The SDM method tested in this paper does not require any such additional baggage and is easy to implement in a sequential micro-machining mode.This paper made use of Raman spectroscopy data,average surface roughness data and imaging data of the cutting chips of silicon for drawing a comparison between conventional single-point diamond turning(SPDT)and SDM while incorporating surface defects in the(i)circumferential and(ii)radial directions.Complementary 3D finite element analysis(FEA)was performed to analyse the cutting forces and the evolution of residual stress on the machined wafer.It was found that the surface defects generated in the circumferential direction with an interspacing of 1 mm revealed the lowest average surface roughness(Ra)of 3.2 nm as opposed to 8 nm Ra obtained through conventional SPDT using the same cutting parameters.The observation of the Raman spectroscopy performed on the cutting chips showed remnants of phase transformation during the micromachining process in all cases.FEA was used to extract quantifiable information about the residual stress as well as the sub-surface integrity and it was discovered that the grooves made in the circumferential direction gave the best machining performance.The information being reported here is expected to provide an avalanche of opportunities in the SPDT area for low-cost machining solution for a range of other nominal hard,brittle materials such as SiC,ZnSe and GaAs as well as hard steels.

ENVELOPING THEORY BASED METHOD FOR THE DETERMINATION OF PATH INTERVAL AND TOOL PATH OPTIMIZATION FOR SURFACE MACHINING

An enveloping theory based method for the determination of path interval in three axis NC machining of free form surface is presented, and a practical algorithm and the measures for improving the calculating efficiency of the algorithm are given. Not only the given algorithm can be used for ball end cutter, flat end cutter, torus cutter and drum cutter, but also the proposed method can be extended to arbitrary milling cutters. Thus, the problem how to strictly calculate path interval in the occasion of three axis NC machining of free form surfaces with non ball end cutters has been resolved effectively. On this basis, the factors that affect path interval are analyzed, and the methods for optimizing tool path are explored.

MACHINING MECHANISM OF MIRROR-LIKE SURFACE OF ADVANCED CERAMICS

The conditions of convertion from brittle removal mechanism to plastic removal mecha-nism are studied through analysis of ecramic microstructure and the relatiotship between the ma-terial renicval form and machining unit. By the rabonal technology program worked out, theplane and cylindrical mirror-like surface machining is successfully achieved and its surfaceroughness Rais 0.01 ￣0.03 m after many times of expenmental study.

Experimental Research on the Surface Quality of Milling Contour Bevel Gears

Contour bevel gears have the advantages of high coincidence,low noise and large bearing capacity,which are widely used in automobile manufacturing,shipbuilding and construction machinery.However,when the surface quality is poor,the effective contact area between the gear mating surfaces decreases,affecting the stability of the fit and thus the transmission accuracy,so it is of great significance to optimize the surface quality of the contour bevel gear.This paper firstly analyzes the formation process of machined surface roughness of contour bevel gears on the basis of generating machining method,and dry milling experiments of contour bevel gears are conducted to analyze the effects of cutting speed and feed rate on the machined surface roughness and surface topography of the workpiece.Then,the surface defects on the machined surface of the workpiece are studied by SEM,and the causes of the surface defects are analyzed by EDS.After that,XRD is used to compare the microscopic grains of the machined surface and the substrate material for diffraction peak analysis,and the effect of cutting parameters on the microhardness of the workpiece machined surface is investigated by work hardening experiment.The research results are of great significance for improving the machining accuracy of contour bevel gears,reducing friction losses and improving transmission efficiency.

Status of research on non-conventional technology assisted single-point diamond turning

With the increasing use of difficult-to-machine materials in aerospace applications,machining requirements are becoming ever more rigorous.However,traditional single-point diamond turning(SPDT)can cause surface damage and tool wear.Thus,it is difficult for SPDT to meet the processing requirements,and it has significant limitations.Research indicates that supplementing SPDT with unconventional techniques can,importantly,solve problems due to the high cutting forces and poor surface quality for difficult-to-machine materials.This paper first introduces SPDT and reviews research into unconventional techniques for use with SPDT.The machining mechanism is discussed,and the main advantages and disadvantages of various methods are investigated.Second,hybrid SPDT is briefly described,which encompasses ultrasonic-vibration magnetic-field SPDT,ultrasonic-vibration laser SPDT,and ultrasonic-vibration cold-plasma SPDT.Compared with the traditional SPDT method,hybrid SPDT produces a better optical surface quality.The current status of research into unconventional techniques to supplement SPDT is then summarized.Finally,future development trends and the application prospects of unconventional assisted SPDT are discussed.

Research on feed-pulse collaborative control method in micro-electrical discharge machining

Reducing the short-circuit rate and increasing the effective discharge rate are important targets for improving the servo control effect of micro-electrical discharge machining(micro-EDM),as these two indicators are closely related to the machining efficiency and quality.In this study,a feed-pulse collaborative control(FPCC)method is proposed for micro-EDM based on two dimensions(space and time).In the spatial dimension,a feed control strategy with a discharge holding process is adopted.Meanwhile,in the time dimension,a forward-looking pulse control strategy is adopted,in which the pulse interval is adjusted based on a sequence analysis of feed commands and discharge states.Process experiments are carried out to determine the key parameters used in this method,including the discharge holding threshold and pulse interval adjustment value(T_(off_(adj))).The feed smoothness and discharge sufficiency analyses of the experimental results show that compared to the traditional double threshold average voltage method,the FPCC method reduces the number of long-distance retreats by 64%and improves the effective discharge time by 40%.

A novel algorithm of normal attitude regulation for the designed end-effector of a flexible drilling robot

An end-effector for a flexible drilling robot is designed, and a novel four-point algorithm of normal attitude regulation for this end-effector is presented. Four non-coplanar points can define a unique sphere tangent to them in spatial geometry, and the center point of the sphere and the radius can be calculated. The shape of a workpiece surface in the machining area is approximately regarded as such a sphere. A vector from the machining point to the center point is thus approximately regarded as a normal vector to the workpiece surface. By this principle, the algorithm first measures four coordinates on the curve in the drilling region using four sensors and calculates the normal vector at the drilling point, then calculates the error between the normal vector and the axis of the spindle. According to this error, the algorithm further figures out the angles of two revolving axes on the end- effector and the displacements of three linear axes on the robot main body, thus it implements the function of adjusting the spindle to be perpendicular to the curve at the drilling point. Simulation results of two kinds of curved surfaces show that accuracy and efficiency can be realized using the proposed algorithm.

Hardening Effect on Machined Surface for Precise Hard Cutting Process with Consideration of Tool Wear

During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12MoV. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.

A novel method to improve interfacial bonding of compound squeeze cast Al/Al-Cu macrocomposite bimetals:Simulation and experimental studies

A facile and innovative method to improve bonding between the two parts of compound squeeze cast Al/Al-4.5 wt.%Cu macrocomposite bimetals was developed and its effects on microstructure and mechanical properties of the bimetal were investigated.A special concentric groove pattern was machined on the top surface of the insert(squeeze cast Al-4.5 wt.%Cu) and its effects on heat transfer,solidification and distribution of generated stresses along the interface region of the bimetal components were simulated using ProCAST and ANSYS softwares and experimentally verified. Simulation results indicated complete melting of the tips of the surface grooves and local generation of large stress gradient fields along the interface. These are believed to result in rupture of the insert interfacial aluminum oxide layer facilitating diffusion bonding of the bimetal components. Microstructural evaluations confirmed formation of an evident transition zone along the interface region of the bimetal. Average thickness of the transition zone and tensile strength of the bimetal were significantly increased to about 375 μm and 54 MPa, respectively, by applying the surface pattern.The proposed method is an affordable and promising approach for compound squeeze casting of Al-Al macrocomposite bimetals without resort to any prior cost and time intensive chemical or coating treatments of the solid insert.

Hierarchical planning for a surface mounting machine placement

For a surface mounting machine (SMM) in printed circuit board (PCB) assembly line, there are four problems, e.g. CAD data conversion, nozzle selection, feeder assignment and placement sequence determination. A hierarchical planning for them to maximize the throughput rate of an SMM is presented here. To minimize set-up time, a CAD data conversion system was first applied that could automatically generate the data for machine placement from CAD design data files. Then an effective nozzle selection approach was implemented to minimize the time of nozzle changing. And then, to minimize picking time, an algorithm for feeder assignment was used to make picking multiple components simultaneously as much as possible. Finally, in order to shorten pick-and-place time, a heuristic algorithm was used to determine optimal component placement sequence according to the decided feeder positions. Experiments were conducted on a four head SMM. The experimental results were used to analyse the assembly line performance.

RESEARCH ON MODELING AND CHARACTERISTICS OF THE SPINDLE DYNAMIC COUPLING ABSORBERING SYSTEM OF A SUPER-PRECISION SURFACE GRINDING MACHINE

The bearing is described by constrain matrix, and the spindle system of a NCsurface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is usedto establish the dynamic model of beam. Moreover, the response of the end of rotor is analyzed, andthe natural frequency, principle mode and other dynamic characteristics of the coupling system arestudied, the law of bearing stiffness to coupling frequency and amplitude of rotor is also found.Finally, according to the actual condition, a dynamic absorber is designed. The simulation andexperimental results show that the amplitude of spindle can be declined effectively when the dynamicabsorber is attached.

Heat Transfer of Boiling R134a and R142b on a Twisted Tube with Machine Processed Porous Surface

The objective of this work was to investigate nucleate pool boiling heat transfer performance and mechanism of R134a and R142b on a twisted tube with machine processed porous surface （T-MPPS tube） as well as to determine its potential application to flooded refrigerant evaporators. In the experimental range, the boiling heat transfer coefficients of R134a on a T-MPPS tube were 1.8-2.0 times larger than those of R134a on a plain tube. In addition, the developed experimental correlations verified that the predictions of the heat transfer coefficients of boiling R134a and R142bon a T-MPPS tube at the experimental conditions were considerably accurate.

Experimental Study of Machinability in Millgrinding of SiCp/Al Composites

An attempt was made to investigate the machinability of Si Cp/Al composites based on the experimental study using mill-grinding processing method. The experiments were carried out on a high-speed CNC machining center using integrated abrasive cutting tool. The effects of combined machining parameters, e g, cutting speed（vs）, feed rate（vf）, and depth of cut（ap）, with the same change of material removal rate（MRR） on the mill-grinding force and surface roughness（Ra） were investigated. The formation mechanism of typical machined surface defects was analyzed by SEM. The experimental results reveal that with the same change of material removal rate, lower mill-grinding force values can be gained by increasing depth of cut and feed rate simultaneously at higher cutting speed. With the same change of MRR value, lower surface roughness values can be gained by increasing the feed rate at higher cutting speed, rather than just increasing the depth of cut, or increasing the feed rate and depth of cut simultaneously. The machined surface of Si Cp/Al composites reveals typical defects which can influence surface integrity.

Vibration reliability analysis for aeroengine compressor blade based on support vector machine response surface method

To ameliorate reliability analysis efficiency for aeroengine components, such as compressor blade, support vector machine response surface method(SRSM) is proposed. SRSM integrates the advantages of support vector machine(SVM) and traditional response surface method(RSM), and utilizes experimental samples to construct a suitable response surface function(RSF) to replace the complicated and abstract finite element model. Moreover, the randomness of material parameters, structural dimension and operating condition are considered during extracting data so that the response surface function is more agreeable to the practical model. The results indicate that based on the same experimental data, SRSM has come closer than RSM reliability to approximating Monte Carlo method(MCM); while SRSM(17.296 s) needs far less running time than MCM(10958 s) and RSM(9840 s). Therefore,under the same simulation conditions, SRSM has the largest analysis efficiency, and can be considered a feasible and valid method to analyze structural reliability.

A Generic Kinematic Model for Three Main Types of Five-axis Machine Tools

Material removal is one of the most used processes in manufacturing. Five-axis CNC machines are believed to be the best tools in sculptured surface machining. In this study, a generic and unified kinematic model was developed as a viable alternative to the particular solutions that are only applicable to individual machine configurations. This versatile model is then used to verify the feasibility of the two rotational joints within the kinematic chain of three main types of a five-axis machine-tool. This versatile model is very useful applied to the design of five-axis machine tools.

Efficient cutting path planning for a non-spherical tool based on an iso-scallop height distance field

Iso-scallop height machining means,when machining a freeform surface,the scallop height between any two neighboring tool paths on the surface will be a constant(i.e.,the given threshold),which is preferable among various freeform surface machining strategies due to its high machining efficiency as well as better machine tool’s dynamics.However,all the existing iso-scallop height path planning methods pertain to only the ball-end or flat-end types of tools.In recent years,the non-spherical cutting tool has become more and more popular,especially for five-axis machining of complex freeform surfaces,majorly owing to its non-constant curvature which can be utilized to adaptively fit the tool to the surface to both avoid the local gouging and enlarge the cutting width.However,there have been no reported works on iso-scallop height five-axis tool path generation for a non-spherical tool,and,in this paper,we present one.Specifically,we first define and construct two fields on the surface to be machined-the collision-free tool orientation field(vector)and the iso-scallop height distance field(scalar).The iso-lines of the scalar field and their associated tool orientation field vectors then naturally serve as potential iso-scallop height five-axis tool paths,and we present a propagation-based algorithm to construct the desired tool path from the iso-lines.The computer simulation and physical cutting experiments confirm that everywhere on the surface,except maybe near the saddle curves of the scalar filed,the scallop height is exactly the given thresh-old.By adding the saddle curves as extra tool paths,the final machined surface then is assured of the required scallop height requirement.

A new localization theory of adaptive machining of near-net-shape blades

In the fabrication of aero-engine blades,a great deal is gained when massive material removal is avoided at the end of the process,and as little as possible material is left on the blade billet.Due to the uncertainty of pre-process,the billet shapes are inconsistent.Sometimes,the near-net-shape billet doesn’t cover the blade design surface to be cut.Therefore,blade localization is necessary for these billets before the machining.In conventional localization methods,the design surface’s location focused on guaranteeing enough material to be cut.However,because the to-becut surface is in near-net and free-form shape,it is difficult to find a valid localized surface model to generate the tool path.Different from the localized surface is taken as rigid in previous investigation,it is allowed to deviate from the design surface no more than the tolerance band.In term of this principle,the tolerance band is utilized to promote localization ability.A series of optimization models with different priorities is established to avoid the abandonment expensive blade billet.Finally,with the experiments performed on the near-net-shape blades,the blade localization theory and the promotion of localization ability are verified.