This paper proposes a new iterative compensation methodology of geometric errors to improve the machining accuracy of a non-orthogonal five-axis machine tool (NOFAMT). Firstly, based on homogeneous ...transform matrix (HTM) and multi-body system (MBS) theory, the relative motion constraint equations (TRMCEs) of the tool tip position and tool orientation vector related to a NOFAMT with a nutating rotary B axis are established. Then, by utilizing TRMCEs, the mapping relationships between tool path and the numerical control (NC) command without and with considering the geometric errors are constructed respectively. In order to truly reproduce tool motion trajectory of the machine tool driven by the given NC command, the mapping relationship between the NC command and tool cutting trajectory is also established. Meanwhile, procedures of iterative compensation are described by using the aforementioned mapping relationships without the traditional inverse calculation, and the actual NC code is generated in self-developed compensation software. It is not difficult to find that the new approach takes the difference between tool path and tool cutting trajectory as the control objective and can directly obtain the actual NC code controlling the machine tool to achieve the desired machining accuracy. Finally, a cutting test is carried out on the DMU60P NOFAMT. Experimental results show the developed iterative compensation methodology is precise and effective for NOFAMTs. Therefore, compared with the existing methods, the new method is more direct and accurate. And its basic idea can be applied to other type of machine tools.
•First, the relative motion constraint equations of a non-orthogonal five-axis machine tool are established.•Second, the mutual mapping relationships between tool path, NC command and tool cutting trajectory are established respectively.•Third, a new iterative compensation methodology is presented.•Fourth, a cutting experiment is proposed to verify the machining accuracy improvement of the researched machine tool.
•The influence mechanism of geometric errors on the form errors of S-shaped test piece is investigated.•The quantitative interval sensitivity analysis method for identifying key geometric errors at ...different intervals is proposed.•The compensation for the identified key geometric errors is conducted and verified by the simulation and experiment.
Error compensation is a common method to improve the machining accuracy of five-axis machine tools (FAMTs). Before that, in order to identify the key geometric errors that affect the machining accuracy, sensitivity analysis (SA) in entire machining region or a specified point is usually used. However, since the influence of geometric errors on form errors is different in each interval, the result of SA would be affected, which decreases the compensating accuracy. For this reason, a new approach for accuracy enhancement of FAMTs based on quantitative interval sensitivity analysis (QISA) is presented in this paper. First, based on multi-body system theory and homogeneous transform matrix, the volumetric error model of the FAMT is established. Then, the geometric error model of the FAMT is formulated. Second, development of form error model is involved in this paper to clarify the effect law of geometric error on form error. Moreover, the machining region of S-shaped test piece is divided into five intervals. Then, the QISA method is presented to calculate the sensitivity index of each geometric error and identify key geometric errors at different intervals. Finally, simulations and experiments are conducted to validate the feasibility and effectiveness of the presented method.
In order to study the influence mechanism of the motion accuracy of the air static pressure guide system, this article combines the internal transmission law of the driving part of the table and the ...coupling analysis of solid damping and micro-scale gas damping and establishes the stepping motor, ball screw, nut, and motion table. The four-degree-of-freedom operation model was used to study the response simulation and dynamic characteristics of the entire table under the influence of various components. Combined with the damping characteristics extracted from the experiment, the influence mechanism of micro-gap solids and gas damping on the motion accuracy of the air-floating table is analyzed, and the optimal structural scheme that can effectively improve the accuracy and stability is proposed to improve the performance of the air-floating table and ultra-precision machine tools, processing accuracy to solve key technical problems in improving nano-machining accuracy.
Sulfonated poly(ether ether ketone) (C-SPEEK) membranes with pendent carboxylic acid groups are prepared and first investigated for vanadium flow battery (VFB) application. The introduction of ...carboxylic acid groups can effectively improve the ion conductivities of C-SPEEK membranes, while, keep their ion selectivities. The prepared C-SPEEK membranes exhibit excellent performance under VFB operating condition. VFB single cell assembled with C-SPEEK-50 membranes shows much higher energy efficiency (85% Vs 82%) and columbic efficiency (97.3% Vs 94.6%) than that assembled with Nafion 115. The membrane keeps a stable performance after more than 180 cycles charge-discharge test, showing good stability.
Due to the effect of gravity on machine tools, the small deformations inevitably exist. The existing tolerance allocation methods are based on the rigid body assumption, which ignore the small ...deformations. It will make optimization results inaccurate and increase manufacturing cost. Therefore, a new optimal tolerance allocation method, which integrates the small deformations, is presented in this paper. The establishment of a geometric error model based on tolerance is involved at first. Based on this model and multi-body system theory, the mapping relationship between tolerance and volumetric error of the five-axis machine tool (FAMT) is formulated. Secondly, the small deformations of the FAMT are obtained based on finite element analysis. Then, the optimal tolerance allocation model is established by integrating the small deformations into the constraint conditions. Thirdly, simulation analysis is carried out with this model by using a genetic algorithm. Then, the optimal tolerance allocation scheme is obtained, and the total manufacturing cost after optimization is reduced by approximately 11.5%. Finally, the volumetric errors of the FAMT are calculated based on the two tolerance allocation schemes. The results show that the volumetric errors are within the permitted ranges. Therefore, the proposed method in consideration of the small deformation is feasible and effective.
As an additive manufacturing technology, selective laser melting (SLM) can form any complex metal parts, which has unparalleled advantages compared to traditional processing methods. However, there ...are still some problems such as accuracy and non-repeatability to overcome to apply SLM to production practice. The high-precision monitoring and degradation feedback technology of SLM equipment is the future development direction. The real-time monitoring machine can repair itself and avoid the tedious detection in the post-processing stage. The researchers mainly monitor the quality of the forming process by molten pool signal, temperature signal, sound signal, and scanning track. The forming process is monitored using coaxial detection or paraxial detection through a high-speed camera, pyrometer, and other equipment. This paper can provide theoretical support for the SLM intelligent monitoring field.
The existing aerostatic spindle dynamic model only analyses the effects of mass imbalance and external load, ignoring the influence of cutting system on the spindle dynamic characteristics under ...cutting conditions. In this paper, a 5-DOFs aerostatic spindle dynamic model is established considering the influence of the micro-scale non-linear dynamic performance of the aerostatic spindle and cutting process damping. First, an analytical identification model of process damping with blunt circular cutter is established. Then, the micro-scale dynamic characteristics of the aerostatic spindle are analyzed and a 5-DOFs aerostatic spindle dynamic model is established considering the influence of process damping. Finally, the model is simulated and the influence of process damping on the dynamic characteristics of aerostatic spindle is analyzed. The simulation results show that the process damping of the cutting system has a significant influence on the dynamic characteristics of the aerostatic spindle. This study can provide theoretical guidance for coupling research of cutting system and spindle system.
In this paper, a 3D surface topography model for ultra-precision turning is proposed, in which the coupling effect of turning dynamics and dynamics of the aerostatic spindle in microscale is ...considered. Firstly, the identification model of the tool-workpiece interference area is established by the analytical method, and then the accurate process damping coefficient is obtained. Meanwhile, considering the influence of the dynamic characteristics of the aerostatic spindle on the formation of the workpiece surface morphology, a 5-DOF aerostatic spindle dynamic model is established under the influence of the process damping effect in the cutting process and the microscale effect of the gas film. Then, based on the dynamic model of turning and aerostatic spindle, the surface topography model of ultra-precision turning is established. The effects of spindle speed, cutting width, and feed rate on the surface topography of ultra-precision turning are also analyzed. Finally, the cutting experiment is carried out, the surface morphology obtained from the simulation and experiment is characterized by three-dimensional surface roughness parameters, and the error between the simulation and experimental results is analyzed. The results show that the 3D surface morphology model built in this paper matches the experimental results better, which proves the effectiveness of the model.
