Yazhou Sun

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.

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.

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.

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.

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.

Modeling and simulation of the interaction of manufacturing process and machine tool structure in flycutting machining

The process machine interactions in the flycutting machining are presented by integrating the state-space method and finite element method. The prediction of the cutting force fluctuations in the machining process caused by the compliance of machine tool structure is achieved. Furthermore, the relationship between the dynamic performance of the machine tool structure and the machining speed is discussed, which has great influence on the root mean square of waviness and flatness on the machined surface. The simulation results are validated by experiments.

A novel dynamic modeling method for aerostatic spindle based on pressure distribution

The pressure distribution in an aerostatic bearing has an important effect on the performance of the associated mechanical equipment. To more accurately predict performance, a new dynamic modeling method has been developed that takes into account the pressure distribution in the bearing by integrating the principle of flow equilibrium and finite element theory. The direct corresponding relationship between the fluid film characteristics and spindle dynamic performance is established using this method. The simulation and experimental results show that the new dynamic modeling method for the aerostatic bearing is more efficient and reliable than traditional modeling methods.

Study on different behaviour of poly(vinylidene fluoride)-polyhedral oligomeric silsesquioxane nanocomposites in mechanical properties and nano-tensile testing

Nanocomposites consisting of a poly(vinylidene fluoride) (PVDF) matrix and 0, 3, 5 and 8 wt-% fluoropropyl polyhedral oligomeric silsesquioxane (FP-POSS) were prepared using the solvent evaporation method. The mechanical properties of nanocomposites were investigated by universal mechanical testing and nano-tensile testing. The results derived from two different scales testing both indicated that a small addition of FP-POSS exhibited a positive reinforcement effect of mechanical properties. Meanwhile the reason of the different variation trend of mechanical properties derived from testing standards under different scales was analysed, and the specific role and multi-performance of POSS were estimated.