Ultra-precision Fly Cutting Machine Tool Research Articles

Optimal design of the dynamic performance of the ultra-precision fly cutting machine tool

Optimal design of the dynamic performance of the ultra-precision fly cutting machine tool

A hybrid numerical method for vibration analysis of linear multibody systems with flexible components

This paper presents a novel hybrid numerical method combining the transfer matrix method for multibody systems with the finite element method and the Craig-Bampton reduction method. In the proposed method, the multibody system is divided into two types of subsystems, depending on the shape and stiffness of each component. All the subsystems are independently analysed by the transfer matrix method for multibody systems or the finite element method and the Craig-Bampton reduction method. The whole system is recombined by deriving the relation equations of the connection points amongst subsystems. Then, the overall transfer equation and the eigenvalue equation of the whole system are obtained. Verifications on a simple system and rigid-flexible manipulator system show that the natural frequencies and modal shapes agree well with the finite element method. The dynamic model of the ultra-precision fly-cutting machine tool concerning the linearly elastic deformation of the fly-cutting head is established by the proposed method and validated by the experimental modal test. According to the comparison of computational speed with the finite element method, the proposed method has advantages in easy programming, low matrix order, low computational effort, and high applicability to the linear time-invariant mechanical system with flexible components.

Investigation on dynamic performance of ultra-precision flycutting machine tool based on virtual material method

In the field of ultra-precision machining, the dynamic performance of ultra-precision equipment contributes a lot to the processing accuracy. In this paper, in order to study the dynamic performance of the flycutting machine tool, the virtual material method was adopted creatively to build a machine tool model. This method overcame the complexity of actual structure and obtained more accurate results than traditional methods. Subsequently, the finite element method was applied to analyze the dynamic performance of the virtual material model. Furthermore, the modal test for the flycutting machine tool was performed to verified the simulations by means of the one-point hitting and multi-point measurement. The simulation results indicate that the virtual material model has high comprehensive accuracy, of which the average error of natural frequency is 5.9% and errors are all less than 6% excepting the first order. Moreover, combined with the flycutting experiments, it can be found that the fifth order mode of machine tool contributes a lot to processing quality, which leads to the waviness of 53 mm on the machined surface directly because of the weak stiffness of beam-column joints. By increasing the stiffness of the key joints, the waviness can be eliminated, which greatly improves the surface quality of the workpiece.

Effect of KDP-Crystal Material Properties on Surface Morphology in Ultra-Precision Fly Cutting.

To study the effect of material properties on the surface morphology of potassium dihydrogen phosphate (KDP) crystals, an ultra-precision fly cutting machine tool with a single-point diamond tool was used to perform a cutting experiment on (100) crystal plane of the KDP crystal. The elastic modulus, shear modulus, hardness, and dislocation of KDP crystals are taken into the cutting force model by introducing the strain gradient plasticity theory. Since the size effect and dynamic response will affect the surface roughness during ultra-precision machining, the surface roughness of workpieces in ultra-precision fly cutting is hard to predict. Based on the previously established strain gradient plasticity theoretical model, cutting force model, and the dynamic characteristics of the ultra-precision fly cutting system, a surface morphology prediction model under the influence of KDP crystal material properties was established. Finally, the accuracy of the surface morphology prediction model was verified by ultra-precision fly cutting experiments, and identified the frequency range of the characteristic signal caused by the anisotropy of the KDP crystal from the frequency, thereby verifying the KDP crystal material properties has a significant effect on the surface of the machined workpiece roughness.

Development of an object-oriented framework for the vibration characteristic computation of multibody systems

Vibration characteristic is one of the most important properties for structures and mechanical systems. Transfer matrix method for linear multibody systems (linear MSTMM) is an efficient approach to computing the vibration characteristics of such systems due to its following features: easy to formulate, high programming, and low-order matrix without system global dynamic equations. In this work, a vibration characteristic solver based on linear MSTMM is developed by adopting object-oriented programming (OOP) technique. Binary tree is employed to describe multibody system topology. Then, a novel approach combining sequence and chain storage structures is proposed to store the element data and topology of multibody system. A recursive formula is proposed to derive the overall transfer matrix of multibody system, and its automatic deduction and computation by computer are achieved. The object-oriented framework of the solver is developed to realize the vibration characteristic computation. Furthermore, the numerical study for a Stewart parallel mechanism as well as the practical engineering example of an ultra-precision fly cutting machine tool are performed to validate the solver.

Study on dynamic characteristics of ultraprecision machining and its effect on medium-frequency waviness error

In order to study the influence mechanism of dynamic characteristics on medium-frequency waviness error, the dynamic model of tool tip position of ultraprecision fly-cutting machine tool is firstly established, and the response test of tool tip position of machine tool is also carried out to identify relevant dynamic parameters. Then the dynamic vibration response of the machine tool is obtained by using intermittent cutting forces as input signal. The simulation results of the surface shape characteristics caused by the dynamic characteristics of the fly-cutting machine tool are obtained through the surface simulation. Finally, the simulation surface shape and the experimental surface shape are compared to verify the correctness and effectiveness of the tool tip dynamic model of the fly-cutting machine tool and the arc shape feature in the medium-frequency waviness error.

Dynamic modeling of ultra-precision fly cutting machine tool and the effect of ambient vibration on its tool tip response

The dynamic performances of an ultra-precision fly cutting machine tool (UFCMT) has a dramatic impact on the quality of ultra-precision machining. In this study, the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems. In particular, the large-span scale flow field mesh model was created; and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique. The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results. In addition, the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time. Applying it to the dynamic model, the dynamic response of the tool tip under ambient vibration was investigated. The results elucidated that the tool tip response was significantly affected by ambient vibration, and the isolation foundation had a good effect on vibration isolation.

Research on the dynamic characteristics of the ultra-precision fly cutting machine tool and its influence on the mid-frequency waviness of the surface

With the increasing demand for machining accuracy of machine tools, the dynamic characteristics of ultra-precision fly cutting machine tool (UFCMT) have increasingly prominent impacts on the machining accuracy. Based on the transfer matrix method for multibody systems (MSTMM), the dynamics model and its topology figure are established, and the dynamic response of the UFCMT is computed. The modal test of the UFCMT and the vibration test of the tool tip are carried out, which verifies the correctness of the dynamics model. To research causes of the formation of the mid-frequency waviness on the machined surface, the machined surfaces at different rotating speeds are measured. By extracting the characteristic frequencies of mid-frequency waviness of the machined surface and comparing with the results from the modal test and the vibration test, the dynamic characteristics of the spindle and the tool holder are main factors that form the mid-frequency waviness. By optimizing the connect stiffness between the tool holder and the fly cutting head, the displacement of the tool tip and the peak to valley (PV) value of the machined surface in the range of mid-frequency waviness is decreased.

Dynamics Modelling and Simulating of Ultra-precision Fly-Cutting Machine Tool

Dynamics modelling and simulating are the significant process to improve the machining accuracy of the machine tool. This paper is aimed to model and simulate the ultra-precision fly-cutting machine tool (UFMT) and find the relations between structure parameters and machined surface. In this paper, the multi-rigid-flexible-body dynamics model of the UFMT is firstly built by using transfer matrix method for multibody systems. After deducing overall transfer equation, overall transfer matrix, eigenfrequency equation and dynamics equations, the vibration characteristics and dynamics response of tool-tip are simulated and validated by tests. The machined surface is simulated by transferring displacement between the fly-cutting tool-tip and the workpiece into 3D curve. According to the simulation results, both the air-bearing stiffness of the flying-cutting head and cutting process parameters have effects on the machined surface.

Dynamic Accuracy Design Method of Ultra-precision Machine Tool

Ultra-precision machine tool is the most important physical tool to machining the workpiece with the frequency domain error requirement, in the design process of which the dynamic accuracy design (DAD) is indispensable and the related research is rarely available. In light of above reasons, a DAD method of ultra-precision machine tool is proposed in this paper, which is based on the frequency domain error allocation. The basic procedure and enabling knowledge of the DAD method is introduced. The application case of DAD method in the ultra-precision flycutting machine tool for KDP crystal machining is described to show the procedure detailedly. In this case, the KDP workpiece surface has the requirements in four different spatial frequency bands, and the emphasis for this study is put on the middle-frequency band with the PSD specifications. The results of the application case basically show the feasibility of the proposed DAD method. The DAD method of ultra-precision machine tool can effectively minimize the technical risk and improve the machining reliability of the designed machine tool. This paper will play an important role in the design and manufacture of new ultra-precision machine tool.

External aerodynamic force on an ultra-precision diamond fly-cutting machine tool for KDP crystal machining

In the ultra-precision fly-cutting machine tool, the speed of the spindle is very high and the distance between the tool holder and the workpiece is small. There will be normal aerodynamic forces below the tool holder and on the workpiece under the influence of external air. The aerodynamic forces will directly result in the vibration of the machine tool and further affect the surface topography of the workpiece. This paper mainly studies the external aerodynamic forces on a fly-cutting machine tool. It results from the periodical and intermittent sweep between the rotating tool holder and the workpiece. The method of computational fluid dynamics (CFD) is adopted to study this phenomenon. Besides, the aerodynamic forces at different spindle speeds are compared. With the increase of the spindle speed, the amplitude and mean value of the aerodynamic force grows regularly. The aerodynamic forces on the slide and below the tool holder when the cutter processes different regions is presented. The aerodynamic force on the slide shows different behaviors at different machining positions along the feed direction. However, the aerodynamic force below the tool holder is identical. The simulated aerodynamic force on the workpiece is well coincident with the experiment results.

Integrated simulation method for interaction between manufacturing process and machine tool

The interaction between the machining process and the machine tool (IMPMT) plays an important role on high precision components manufacturing. However, most researches are focused on the machining process or the machine tool separately, and the interaction between them has been always overlooked. In this paper, a novel simplified method is proposed to realize the simulation of IMPMT by combining use the finite element method and state space method. In this method, the transfer function of the machine tool is built as a small state space. The small state space is obtained from the complicated finite element model of the whole machine tool. Furthermore, the control system of the machine tool is integrated with the transfer function of the machine tool to generate the cutting trajectory. Then, the tool tip response under the cutting force is used to predict the machined surface. Finally, a case study is carried out for a fly-cutting machining process, the dynamic response analysis of an ultra-precision fly-cutting machine tool and the machined surface verifies the effectiveness of this method. This research proposes a simplified method to study the IMPMT, the relationships between the machining process and the machine tool are established and the surface generation is obtained.

Dynamic design and thermal analysis of an ultra-precision flycutting machine tool

This article presents the dynamic design and thermal analysis of an ultra-precision flycutting machine tool. The hydrostatic bearings are used both in the spindle and slide to ensure the stiffness of the machine tool. The fluid–structure interaction method is used to obtain the actual clearance changes of the hydrostatic bearing. The dynamic and thermal performances of the machine tool are analyzed considering the effect of hydrostatic bearings. The influence of the thermal effect on the static and dynamic performance of the machine tool is further studied. The prototype machine tool is built. Preliminary machining trials have been carried out and provided evidence of fluid–structure interaction method being helpful to design the ultra-precision machine tool based on the hydrostatic technology.

A novel machine tool design approach based on surface generation simulation and its implementation on a fly cutting machine tool

The paper presents a novel machine tool design approach which is based on the surface generation simulation and evaluation. This design approach bridges the gap between the machine tool performance and the surface topography generation, in view of the machine tool performance realizing the surface topography’s prediction. The main influential factors of surface topography in multi-scale are discussed and modeled by different methods. In addition, by introducing the test software at the early machine tool design stage, the surface topography indicators’ disparity between the simulation results and the design requirements are contrasted, which can indicate directions for the machine parameters’ optimal design, such as the straightness and the dynamic performance. An ultra-precision fly cutting machine tool was designed under the guidance of this approach, and machining trials were carried out to evaluate and validate the approach and simulations presented.

Dynamic error budget analysis of an ultraprecision flycutting machine tool

This paper presents an error budget methodology for designing and characterizing machines used to manufacture or inspect parts with spatial frequency-based specifications. In this methodology, the static and dynamic error are considered in the error budget; the static error affects the figure accuracy, while the dynamic error introduces the spatial frequency domain error. The error caused by the components of the machine tool, the cutting process and the external interference, are considered in this paper. Using the error budget, it is able to minimize risk during initial stages by ensuring that the machine will produce components that meet specifications before the machine is actually built or purchased. This methodology is used to predict and improve the performance of an ultraprecision flycutting machine tool.

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.

A mechanical structure-based design method and its implementation on a fly-cutting machine tool design

The mechanical structure has a main influence of the machining performance and the servo performance. In this study, a mechanical structure-based design method is presented to design and optimize an ultraprecision fly-cutting machine tool. This method takes full account of the influence of mechanical components on the machining performance and servo performance at the design stage. The effect of the components structure on the roughness of machined surface is discussed, and an optimized structural form of the aerostatic spindle is given. The influence of the mechanical structure on the control system and electronic drives is discussed, and an integrated dynamic design model is built and used to optimize the hydrostatic slide. Furthermore, the impact of mechanical system dynamic performance of the machine tool on the processing topography is analyzed by the finite element model of the machine tool. This method provides a theoretical basis for the design and optimization of mechanical components and machine tools stiffness loop.

Modal Analysis of Vertical Spindle Using on Fly-Cutting Machine Tool with Transfer Matrix Method

This paper provides the transfer matrix method to analysis the natural frequency of the vertical spindle using on ultra-precision fly cutting machine tool. Several transfer matrix equations of the typical units of the spindle had been established when considering the effects of the gyroscopic torque as the rotor has a large inertial tensor. And then the natural frequencies and each modal shape of the spindle rotor system were calculated using the transfer matrix model. Also, the modal experimental test had been taken out. The theoretical results from the transfer matrix model are very close to the test results, and the accuracy and the effective of the model was proved.

Design philosophy of an ultra-precision fly cutting machine tool for KDP crystal machining and its implementation on the structure design

This paper presents the design philosophy of an ultra-precision fly cutting machine tool from the machining material properties and the processing requirements points of view. Three configurations of the machine tool are proposed and compared from the aspect of the proposed design philosophy. The design philosophy has been applied to guide the development of the key machine components as well as an experimental prototype. In order to improve the dynamic performances of the machine tool, the influence of the main components on the tool–workpiece structural loop is analyzed, and the weak structural component is optimized. Preliminary machining trials have been carried out. The test results make a further proof and validate that the design philosophy proposed in this article can assure the high performance of the developed ultra-precision fly cutting machine tool for producing large diameter optics.

Research on the Online Test of the Fly Cutting Machine Tool Spindle

The online test system of the vertical spindle motion error of the ultra-precision fly cutting machine tool was established. And then using the online test system established to test and analyze the state of the rotary motion of the spindle under the idling condition. The axial synchronous motion error value of the spindle under 390rpm is about 61 nm, and the asynchronous error motion is about 33nm. The radial error motion value is about 91nm, and the asynchronous error is about 35nm. Through the test, we found that the axial and radial spindle error motion accuracy under idling speed can been improved with the spindle speed increases.