Mei Fa Huang

On the Flatness Uncertainty Estimation Based on Data Elimination

Coordinate measuring machine (CMM) plays a more and more important role in the flatness evaluation. The pre-processing for eliminating error data is an important process to improve the quality of flatness evaluation. So, flatness uncertainty estimation becomes a key problem. To solve the problem, a flatness uncertainty estimation method based on data elimination is presented. Firstly, a method for excluding the error data based on statistical theory is expatiated with the consideration of probability theory and mathematical statistics. Secondly, details of calculating flatness uncertainty based on least-square method are analyzed. Then the measured 3-dimensional data are processed so as to put the excluding method into use. So the error data can be deleted and the flatness uncertainty can be decreased and can achieve a good evaluation quality. Finally, an example is given and the result shows that the method proposed in this paper is feasible.

Line to Plane Parallelism Error Evaluation of the New Generation GPS Based on DCWPSO

Currently Least Squares Method (LSM) is commonly applied in the error evaluation, but it is adaptive to the condition of low accuracy requirement. Besides, the error value obtained by LSM is not the minimum. In order to accurately evaluate parallelism error, the minimum zone mathematical model of the parallelism is given based on the new generation geometrical product specification and verifications (GPS). According to the characteristics of parallelism error evaluation, a new adaptive Particle Swarm Optimization algorithm with dynamical inertia weight (DCWPSO) is proposed to solve target optimization problems of the error evaluation. Finally we use the measurement of a line to plane parallelism error evaluation as an example to validate the proposed method. The experiment results show the feasibility and availability of the method．

Finite Element Static Stiffness Analysis of the A/C Axes Bi-Rotary Milling Head

A/C axes bi-rotary milling head is an important functional component in gantry type five-axis CNC machine tool. The static characteristics affect directly the machining accuracy of machine tool. The paper investigates the static stiffness of A/C axes bi-rotary milling head in gantry type five-axis CNC machine tool XK2320-5X developed by a domestic company. Because this product developed depend on the experience of designers, the machining accuracy of A/C axes bi-rotary milling head of primitive XK2320-5X type cannot meet the accuracy requirement under actual working conditions. On the basis of structure design, the static stiffness analysis of the milling head under two working conditions is carried out using finite element method. The deformations of the main mechanical parts in the milling head are obtained. The analysis results indicate that the static stiffness in direction X is the weakest of the milling head and the milling head shell is the most important factor of deformation. The work done provides foundation for further structure design and machining accuracy improvement of A/C axes bi-rotary milling head.

A Fast Retrieval Method Based on K-Means Clustering for Mechanical Product Design

Radius Angle Histogram (RAH) is useful method of retrieving 3D mechanical models. This method, however, not completely uses the information of radius angle histogram of the model. As a result, the retrieval precision is not very high enough. To improve the retrieval efficiency, K-means clustering method (KMM) is proposed in this paper. The radius angle histograms of the models are established first and then be served as inputs as KMM, respectively. By using KMM, the models can be classified and the results can be obtained. To validate the proposed method, an experiment is given. The results show that the retrieval precision of the proposed method is higher than that of single using RAH method.

On the Generation of the Specification Surface Model of Planar Feature with Flatness

The new-generation standards of Geometrical Product Specifications (GPS) take the measurement and verification of manufactured parts according to the duality principle. The Specification Surface Model (SSM) is a simulation model of the actual manufactured part which plays a decisive role in the process of duality verification. The existing methods, however, have not been found to carry out much related research on the generation of SSM. This paper presents a method to generate the SSM for the characteristic of planar feature with flatness under the standards of GPS. The mathematical model of the flatness tolerance is firstly established. Secondly, in order to get the simulation points to simulate the actual characteristics of the manufactured parts, both of the functional requirements of the parts and the influences of the manufacturing process are considered. And then the simulation points under the normal distribution are generated within their tolerance zone by computer. By using the approximation method of the least-squares SSM is then obtained. Finally, an example is used to illustrate the proposed method.

Ontology-Based Assembly Design Representation for Model Reuse

Assembly is an important part in production and development of complex products. Flexible assembly retrieval is one of the key issues to find the reusable model. The main objective of this paper is to extend the model of ontology-based assembly design for model reuse. Firstly, we propose a representation of assembly structural data including topological structure, assembly semantics, and geometrical information. Secondly, we enrich assembly design (AsD) ontology for knowledge captured and shared in Web Ontology Language 2 Description Logic (OWL 2 DL) and Semantic Web Rule Language (SWRL). And then, we define the matching strategies and similarity assessment for two matched models. Finally, we illustrate the validity of assembly design representation for model reuse through experiments.

Research on the Evaluation of Plane Orientation Error Based on Uncertainty Theory

Based on coordinate measuring machine (CMM) the given part is measured in any orientation, and then the least square evaluation mathematical model of plane orientation tolerance is established. What’s more, the uncertainty evaluation method of orientation error is proposed according to the uncertainty theory of new geometrical product specification (GPS). The face-to-face angularity is taken as the example to present the effectiveness of the proposed uncertainty evaluation method. The result shows that the uncertainty evaluation method not only meets the requirements of new GPS standard, but also ensures the integrity of the flatness inspection results. As a result, the accuracy of the workpiece inspection can be improved.

Thermal Characteristics Analysis of Mill Head of Five-Axis CNC Mill Machine Based on Finite Element Method

Machine tool is the foundation of manufacture，then, five-axis CNC machine is the sophisticated equipment of CNC machine. During the practical work，there is an thermal deformation in a CNC machine because of many kinds of heat sources . This deformation affects the relative displacement between the work piece and the cutter, caused the manufacturing errors, and influences the machining accuracy of the part. So is of great importance to research the thermal characteristics. In this paper, thermal characteristics of CNC milling machine are simulated by analyzing the thermal boundary condition and using the finite element software-ANASYS Workbench. Get the temperature field cloud picture of A/C axes bi-rotary mill head of five-axis CNC machine. Weakness of Thermal Characteristics will be found out. This research provides the theoretical fundamentals for improving the accuracy of the mill head.

Minimum Zone Evaluation of Symmetry Error for Flatness to Flatness Based on the New Generation GPS

Least square method (LSM) is the most popular method used to evaluate machining error nowadays. However, LSM is likely to overestimate the error value, therefore its solution is only approximate and rather than minimum. In order to obtain the minimum, we study the principle of the minimum zone tolerance method (MZT), analyze the characteristics of the new generation GPS, and give the minimum zone mathematic model of the symmetry error for flatness to flatness. For the purpose of optimizing the mathematical model, this paper describes the application of adaptive genetic algorithm to achieve the best estimation. Simultaneously, the process of optimization is realized by MALTAB. Finally, the experiment shows that the evaluation results of MZT is better than evaluation results of LSM.

Kinematic Analysis and Simulation of an A/C Axes Bi-Rotary Milling Head with Zero Transmission

Because of the flexible kinematic characteristic of five-axis-linkage machining center it is widely used to process complex parts. The milling head is the key functional component of the five-axis machining center, therefore study of the milling head is of vital importance. The A/C axes bi-rotary milling head is the most common used structures. The current mechanical A/C axes bi-rotary milling head is mostly with large volume and small rotation range. This paper presents an A/C axes bi-rotary milling head with zero transmission in small volume. To understand the kinetic characteristics of the A/C axes bi-rotary milling head with zero transmission, we apply D-H parameter method to establish displacement equations, speed equations, and acceleration equations. SolidWorks is then utilized to build the virtual prototyping model of the designed mechanism. Motion module of SolidWorks is also used to carry out the kinematics simulation. The experimental results show that the mechanism could achieve the rotation of A/C axes and smooth motion trajectory. The rotation range of A-axis could reach ±120°.