Guoda Chen

Dynamic design approach of an ultra-precision machine tool used for optical parts machining

The article presents a dynamic design approach of an ultra-precision machine tool based on the morphology requirements of the workpiece. Compared with common parts, optical parts not only have as many high requirements for surface finish and flatness, but also topographic properties, which leads to a big difference in design with traditional machine tools. This approach, from the topographic properties and functional requirements of the workpiece, demonstrates how to design and analyze the kinematic chain and configuration of the machine tool. Then, a finite element model and mathematical model are established to predict the topographic properties of the workpiece. The design and optimization of an ultra-precision flycutting machine tool is employed as a case study to elaborate the approach in detail. Preliminary machining trials have been carried out and provided evidence of the approach being helpful to design and optimize the ultra- precision machine tool used for optical parts machining.

An integrated method for waviness simulation on large-size surface

The surface waviness of the KH2PO4 crystal has important influence on its optical performance, but it is difficult to simulate by the current simulation models. This article presents an integrated machining performance forecasting method, which considers the interaction between manufacturing process and machine tool and integrates the cutting simulation, machine tool dynamic performance simulation and the control system. The profile and waviness prediction on the large area are achieved by this method with short time and high accuracy. The machining trials on a fly cutting machine tool are carried out to demonstrate the effectiveness of the proposed approach.

Investigation of the tool-tip vibration and its influence upon surface generation in flycutting

Flycutting is a major machining process for flat-surface machining, which is a typical intermittent-machining process. This paper is dedicated to study the influence of the intermittent-machining force on the workpiece surface generation. In the present study, some defects are identified on the machined surface and found to be corresponded to the tool-tip vibration by the dynamic analysis and the surface-generation simulation. A theoretical model is proposed to capture the dominant factor based on the characteristic. It reveals that the defects are attributed to the changing period of the intermittent-machining force and the dynamic performance of the machine tool. Hence, a surface-generation model is proposed to take account of the tool-tip vibration and the changing of the cutting locus. The simulation results have been found to agree well with the experimental results.

Measurement and analysis for frequency domain error of ultra-precision spindle in a flycutting machine tool:

The ultra-precision spindle is the key component of ultra-precision machine tool, which largely influences the machining accuracy. Its frequency characteristics mainly affect the frequency domain error of the machined surface. In this article, the error measurement setup for the ultra-precision aerostatic spindle in a flycutting machine tool is established. The dynamic and multi-direction errors of the spindle are real-time measured under different rotation speeds. Then, frequency domain analysis is carried out to obtain its regularity characteristics based on the measurement result. Through the analysis, the main synchronous and asynchronous errors with relatively large amplitude of the spindle errors are found, and the amplitude change law of these main spindle errors is obtained. Besides, the cause of the main synchronous and asynchronous errors is also analyzed and indicated. This study deepens the understanding of ultra-precision spindle dynamic characteristics and plays the important role in the spindle frequency domain errors’ control, machining process planning, frequency characteristics analysis and oriented control of the machined surface errors.

An experimental and theoretical investigation into multimode machine tool vibration with surface generation in flycutting

Relative vibration between the cutting tool and the workpiece plays an important role in the surface generation in ultra-precision diamond machining. High-frequency vibration of the cutting tool has important influence on the surface roughness error, while the low-frequency vibration of machine tool structure affects the figure error. The previous related researches mainly focus on the first-mode frequency vibration of the machine tool. However, its multimode frequency vibration is rarely discussed. In this article, the multimode frequency vibration of the machine tool and its influences on the surface generation in flycutting are studied. The experimental results have been found to agree well with the simulation results.

Investigation of the influence of constant pressure oil source fluctuations on ultra-precision machining

The waviness errors on the machined surfaces have significant impact on the performance of optical components. Mid-spatial frequency errors (amplitude near 10 nm, wavelength about 1 mm) are found on the machined surfaces along feeding direction, and the oil pressure fluctuations of the hydrostatic slide are confirmed to be the main source which produces such waviness errors. In this article, the influence of oil pressure fluctuations on the machined surface is studied quantitatively for the first time, and the corresponding experiments are carried out. Besides, the three-dimensional surface profile simulations of workpieces considering the oil pressure fluctuations are achieved. The simulation results have been verified by the experiments on an ultra-precision flycutting machine.

Flatness improving method of KDP crystal in ICF system and its implementation in machine tool design

The flatness of the KH2PO4 (KDP) crystal has important effect on the inertial confinement fusion system. The method to improve the flatness of KDP crystal and its implementation in the machine tool design is presented in this paper. The finite element model of the whole machine tool is built up to describe the tool tip displacement with the cutting force along the cutting path. The influence of the axial and radial bearing stiffness of the aerostatic spindle on the machined surface flatness is discussed. Furthermore, a novel adjusting mechanism which is used to adjust the squareness between the spindle and the slide is designed, and a new machining process is proposed to improve the flatness of the machined surface. The machining trials are carried out to evaluate and validate the effectiveness of the presented approach and simulation.

A new static accuracy design method for ultra-precision machine tool based on global optimisation and error sensitivity analysis

Ultra-precision machine tool is indispensible in many cutting-edge manufacturing fields. Static accuracy design is the important content of its design, the main problem of which is the trade-off between the accuracy and cost. A new static accuracy design method based on global optimisation and error sensitivity analysis is proposed, which has good robustness, global optimality, high portability and less dependence on the engineering experience. This method transforms the problem of static error allocation of the machine tool to that of multi-objective optimisation with nonlinear constraints. The objective functions simultaneously consider the optimisation of cost, balance and robustness. Besides, the sensitivity analysis is used in the stages of optimisation and post-optimisation respectively, and the global optimisation algorithm is applied for the optimisation. A case study of five-axis ultra-precision machine tool is carried out to demonstrate the detailed process of this method. The results show the feasibility of the proposed method.

Fourier transform based dynamic error modeling method for ultra-precision machine tool

In some industrial fields, the workpiece surface need to meet not only the demand of surface roughness, but the strict requirement of multi-scale frequency domain errors. Ultra-precision machine tool is the most important carrier for the ultra-precision machining of the parts, whose errors is the key factor to influence the multi-scale frequency domain errors of the machined surface. The volumetric error modeling is the important bridge to link the relationship between the machine error and machined surface error. However, the available error modeling method from the previous research is hard to use to analyze the relationship between the dynamic errors of the machine motion components and multi-scale frequency domain errors of the machined surface, which plays the important reference role in the design and accuracy improvement of the ultra-precision machine tool. In this paper, a fourier transform based dynamic error modeling method is presented, which is also on the theoretical basis of rigid body kinematics and homogeneous transformation matrix. A case study is carried out, which shows the proposed method can successfully realize the identical and regular numerical description of the machine dynamic errors and the volumetric errors. The proposed method has strong potential for the prediction of the frequency domain errors on the machined surface, extracting of the information of multi-scale frequency domain errors, and analysis of the relationship between the machine motion components and frequency domain errors of the machined surface.