Wanqun 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.

Modeling the Influence of Tool Deflection on Cutting Force and Surface Generation in Micro-Milling

In micro-milling, cutting forces generate non-negligible tool deflection, which has a significant influence on the machining process and on workpiece accuracy. This paper investigates the tool deflection during micro-milling and its effect on cutting force and surface generation. The distribution of cutting forces acting on the tool is calculated with a mathematical model that considers tool elasticity and runout, and the tool deflection caused by the cutting forces is then obtained. Furthermore, an improved cutting force model and side wall surface generation model are established, including the tool deflection effect. Both cutting force and surface simulation models were verified by the micro-end-milling experiment, and the results show a very good agreement between the simulation and experiments.

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.

Hydrostatic spindle dynamic design system and its verification

A design system for hydrostatic spindle is presented in light of the dynamic synthesis, which is based on the laws of the fluid mechanics, engineering thermodynamics and rotor dynamics. The finite element theory and hydrostatic principle are integrated into the design process, which provides not only the analyses and determination of the stiffness and temperature rise of the hydrostatic bearing but also the dynamic performance optimization. The proposed design system was implemented through a hydrostatic spindle on ultra-precision machining tools with the flycutting process.

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.

Optimal design of an aerostatic spindle based on fluid–structure interaction method and its verification

The aerostatic spindle is made up of the structure components and the fluid film. The interaction between them has important influence on the comprehensive performance of the spindle. This paper presents a new design method of aerostatic spindle based on the fluid–structure interaction method. The changes of bearing clearance caused by the structure deformation under high-pressure fluid film are considered, and the static performances of the bearing are obtained. In order to improve the performance of the spindle, the structural parameters of the bearing are optimized. The proposed design method is implemented through a self-developed aerostatic spindle.

A two-round design method for ultra-precision flycutting machine tools with stringent process requirements

In order to achieve the special functional surfaces machining, a two-round design method for the ultra-precision machine tool design is proposed in this article. This method starts from the engineering design experience; by alternately using the simulation and experiment, the “design-simulation-experiment-simulation-redesign experiment” strategy is employed to the machine tool design. The main influence factors for all of the specifications are determined by this alternating strategy. The analysis of the machine tool performance and the surface generation simulation are well integrated, and the test software is used early at the design stage to estimate the predicted surface. This design method is used for an ultra-precision flycutting machine tool design for potassium dihydrogen phosphate crystal machining, and the results show that by the two rounds of design and modification, the final machine tool meets the processing requirements well. It is believed that the proposed model can be successfully applied to an ultra-precision machine tool designed for achieving strict processing requirements.

Aerostatic thrust bearing performances analysis considering the fluid-structure coupling effect

This article presents a novel calculation method for the bearing performance of the aerostatic thrust bearing. This method is provided while taking the fluid-structure coupling effect into account. High pressure air film leads to the structure deformation, thus the bearing clearance after deformation is utilized to estimate the real bearing performance. Furthermore, the influencing factors on the bearing performance, the thrust plate’s thickness, and the orifices’ location, are investigated on the basis of the fluid-structure coupling effect. The calculation method of the best gas film thickness is deduced and presented. Experimental results for validation highlight the reliability of this method.