Dongju Chen

Modeling and Simulation of Formed Milling Cutter for Screw Based on Non-instantaneous Envelope Method

According to the shape of screw, the spiral surface equation of screw was established; and through analyzing the relative motion between screw and formed milling cutter, find the contact conditions of screw and cutter, further deduce the meshing conditions of screw and cutter, and the contact line equation was established based on non-instantaneous envelope method. From the axial cross-section shapes which the contact line rotates around the axis of cutter formed rotary surface, the profile equation of formed milling cutter was established. Analyzing the causes of processing error after wear of formed milling cutter, the tooth back curve equation was established, finally got the profile equation of formed milling cutter have constant back edge. By interference checking for profile equation of formed milling cutter, ensure correctness of milling cutter profile.

Characteristics evaluation of gas film in the aerostatic thrust bearing within rarefied effect

The characteristic of gas film is a key factor in the performance of the aerostatic bearing. Because the gas film flow is in the slip regime, influence of the rarefied effect is significant. The modified Reynolds equation suitable for compressible gas in the rarefied effect is deduced through introducing the flow factor in the rarefied effect to the Reynolds equation. Pressure distribution, capacity, and stiffness of the gas film under the rarefied effect are analyzed. With the increase of gas pressure, the gas film capacity and stiffness of bearing would also increase. However, the greater the gas supply pressure, the more intense the gas film vibration, so it was important to select a reasonable gas supply pressure for achieving the optimal gas film characteristic. Finally, the gas rarefied effect is verified by the experiment indirectly, which agreed well with the analytical results and provided a theoretical guidance for the machining accuracy of the machine tool.

A geometric error tracing method based on the Monte Carlo theory of the five-axis gantry machining center

This article proposes a tracing method to identify key geometric errors for a computer numerical control machine tool by cutting an S-shaped test piece. Adjacent part relationships and machine tool errors transform relationships are described by topology of the machining center. Global sensitivity analysis method based on quasi-Monte Carlo was used to analyze machining errors. Using this method, key geometric errors with significant influence on machining errors were obtained. Compensation of the key errors was used to experimentally improve machining errors for the S-shaped test piece. This method fundamentally determines the inherent connection and influence between geometric errors and machining errors. Key geometric errors that have great influence on machining errors can be determined quickly with this method. Thus, the proposed tracing method could provide effective guidance for the design and use of machine tools.

Thermal Influence of the Couette Flow in a Hydrostatic Spindle on the Machining Precision

Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examination of the influence of the temperature distribution, thermal deformation and spindle mode. However, seldom has any research investigated the thermal effects of the associated Couette flow. To study the heat transfer mechanism in spindle systems, the criterion of the heat transfer direction according to the temperature distribution of the Couette flow at different temperatures is deduced. The method is able to deal accurately with the significant phenomena occurring at every place where thermal energy flowed in such a spindle system. The variation of the motion error induced by thermal effects on a machine work-table during machining is predicated by establishing the thermo-mechanical error model of the hydrostatic spindle for a high precision machine tool. The flow state and thermal behavior of a hydrostatic spindle is analyzed with the evaluated heat power and the coefficients of the convective heat transfer over outer surface of the spindle are calculated, and the thermal influence on the oil film stiffness is evaluated. Thermal drift of the spindle nose is measured with an inductance micrometer, the thermal deformation data 1.35 μm after running for 4 h is consistent with the value predicted by the finite element analysis’s simulated result 1.28 μm, and this demonstrates that the simulation method is feasible. The thermal effects on the processing accuracy from the flow characteristics of the fluid inside the spindle are analyzed for the first time.

Carriage Error Identification Based on Cross-Correlation Analysis and Wavelet Transformation

This paper proposes a novel method for identifying carriage errors. A general mathematical model of a guideway system is developed, based on the multi-body system method. Based on the proposed model, most error sources in the guideway system can be measured. The flatness of a workpiece measured by the PGI1240 profilometer is represented by a wavelet. Cross-correlation analysis performed to identify the error source of the carriage. The error model is developed based on experimental results on the low frequency components of the signals. With the use of wavelets, the identification precision of test signals is very high.

Research on General Error Modeling and Instructions Correction Method of Multi-axis CNC Machine Tools

Machine tools has become an indispensable processing tool in industrial field. Especially the appearance of multi-axis machine tools has changed the traditional processing method. This paper focuses on the research of improving the machine accuracy. Based on the general error model which has been established using multi-body theory, it has given the precise NC instructions of multi-axis machine tools. Taking C-A type machine tool for example, the precise NC instructions of circle angular has been given.

Vibration analysis of air-bearing work-stage under micro-scale effect:

Vibration is one of the key factors that influences the ultra-precision machining. Taking the air-bearing work-stage for an example, the vertical vibration of the slide plate will directly affect the surface accuracy of machined parts. There are many factors that affect the vibration of precision machine tools, for example, the fluctuation of gas source, noise, environment, and so on. It will affect the machining accuracy and machining efficiency and cannot work in severe cases. Where the lubrication of the gas film in the air-bearing work-stage is in the micro scale category, its flow characteristics are different from the macroscopic gas flow, and it will also affect the stability of the sliding plate. This paper analyzed the vertical vibration characteristics of the air-bearing work-stage by considering the characteristics of gas film in micro scale when the velocity of the slide plate is 0. Based on the Reynolds equation and the characteristics of gas flow, the stiffness (K) and the damping (C) of the gas film are obtained by considering different micro factors. The gas film is assumed as the spring system. Then the stiffness and damping of the gas film are taken into the vibration equation of the slide plate. Through solving the vibration equations, the influence of the micro factor of the fluid on the vibration of the slide plate is researched. The results show that when considering the micro factors of the lubrication gas film, the vibration amplitude of slide plate and the frequency at the maximum amplitude are different from the one in macroscopic without considering any micro factors. At the same thickness of the gas film, the influence of the micro factors on the amplitude of slide plate is largest when three micro scale factors (the first order velocity slip, the flow factor Q and the effective viscosity) are considered. With the increase of the film thickness, the micro scale factors have the little effect on the frequency at the maximum amplitude. By analyzing the dimensionless parameters of the experimental signals and the different simulation signals, we found that when the micro-scale factors are considered at the same time, the vibration amplitude of the slide plate and the frequency at the maximum amplitude are closest to the experimental result. It is proved that combined with the micro scale factor, the analysis of dynamic characteristics of air-bearing work-stage is more accurate.

An evaluation system of the eccentric orbit of shaft with aerostatic bearing in the microscale

In order to improve the machining precision of the aerostatic bearing, an eccentric rotor orbit model considering the microscale effects is established. A flow factor Q embodying the effects in the microscale is introduced into the fluid control equation, the dynamic stiffness, and damping coefficients of bearing are calculated considering the microscale effects. According to the actual working condition of the shaft, the modal analysis in both cases (with and without the microscale effects) is performed. And with the modal information, the dynamic orbit in both states (with and without the microscale effects) is described by the deduced orbit model of the shaft system. Finally, experiments of the frequency by LMS vibration test system and shaft orbit by displacement sensor are measured, and the results indicate that the simulated results considering the microscale effects are more similar with the actual experimental one, which provides a guideline and evaluation standard for further optimization design and precision control of the shaft system.

A prediction model of the surface topography due to the unbalance of the spindle system in ultra-precision fly-cutting machining

In ultra-precision fly-cutting machining, the aerostatic spindle is the key component, which has significant influence on the machined surface quality. The unbalanced spindle directly affects the machining accuracy. In this article, a prediction model of machining surface topography is proposed which involves the effect of the gas film performance of spindle in microscale. With the Weierstrass function, unstable transient response of the aerostatic spindle system is derived by the motion model of the spindle, which response signal represents the surface profile in the ultra-precision machining. Meanwhile, the experiment is performed with different rotation speed of the spindle. And the effect of the unbalanced aerostatic spindle on the surface generation is discussed in time and frequency domain. The conclusion shows that the similar cyclical surface ripple of the workpiece is independent of the spindle speed, and the rotation speed of the spindle and unbalanced spindle directly affects the machining surface topography. This study is quite meaningful for deeply understanding the influence rule of spindle unbalanced error from the viewpoint of machined surface and vibration frequency.

Experimental Analysis of the Gas Film Damping Effect in an Aerostatic Guideway under Microscale

ABSTRACT This article studies the mechanism of gas film damping on the aerostatic guideway system at a microscale with the modified Reynolds equation. The slide film damping force due to the fluid viscous effect is calculated, and the squeeze damping force caused by the gas compression and escape between two plates is analyzed. The damping ratio in the calculation model for the slide film damping is compared with the calculated results from the experiment and the finite element analysis results. Using the results of the study, the optimal supply pressure is designed. The method applied in this article provides the theoretical basis for the analysis and solution of the dynamic performance of an aerostatic guideway.