A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the...A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the method of numerical analysis to investigate the boundary points in a series of sections which form the surface of the workspace. That is, to study such points that have the largest polar radius on a certain section in a system of polar coordinates according to conditions of constraint. The constraint conditions considered in the article include the maximum and minimum displacements of each dieblock, the maximum and minimum angles of oscillation in each hinge. By converting the constraint inequalities into constraint equations, the largest polar radius corresponding to every constraint condition can be evaluated and the minimum one is used to decide the boundary point. This algorithm greatly simplifies the computational process and can be used to analyze any section of the workspace. It provides a theoretical basis for the structural design of such a machine tool.展开更多
The dimensional accuracy of machined parts is strongly influenced by the thermal behavior of machine tools (MT). Minimizing this influence represents a key objective for any modern manufacturing industry. Thermally in...The dimensional accuracy of machined parts is strongly influenced by the thermal behavior of machine tools (MT). Minimizing this influence represents a key objective for any modern manufacturing industry. Thermally induced positioning error compensation remains the most effective and practical method in this context. However, the efficiency of the compensation process depends on the quality of the model used to predict the thermal errors. The model should consistently reflect the relationships between temperature distribution in the MT structure and thermally induced positioning errors. A judicious choice of the number and location of temperature sensitive points to represent heat distribution is a key factor for robust thermal error modeling. Therefore, in this paper, the temperature sensitive points are selected following a structured thermomechanical analysis carried out to evaluate the effects of various temperature gradients on MT structure deformation intensity. The MT thermal behavior is first modeled using finite element method and validated by various experimentally measured temperature fields using temperature sensors and thermal imaging. MT Thermal behavior validation shows a maximum error of less than 10% when comparing the numerical estimations with the experimental results even under changing operation conditions. The numerical model is used through several series of simulations carried out using varied working condition to explore possible relationships between temperature distribution and thermal deformation characteristics to select the most appropriate temperature sensitive points that will be considered for building an empirical prediction model for thermal errors as function of MT thermal state. Validation tests achieved using an artificial neural network based simplified model confirmed the efficiency of the proposed temperature sensitive points allowing the prediction of the thermally induced errors with an accuracy greater than 90%.展开更多
Presents an inverse error estimation method for deriving errors of links from cutter head errors to overcome the difficulty in obtaining analystic solutions for new type of machine tools due to the multi solution of d...Presents an inverse error estimation method for deriving errors of links from cutter head errors to overcome the difficulty in obtaining analystic solutions for new type of machine tools due to the multi solution of direct kinematics so that the total dimension chain tolerance of machine tool links can be determined by Monte Carlo random simulation for a certain spindle dimension of the machine tool and the precision requirement specified, and the method of dimensional tolerance allocation developed by analysing the elements of machine tool links and the combination of machine tool precision with actual dimensional tolerance for justification of tolerance design for this kind of machine tools.展开更多
A shield machine with freezing function is proposed in order to realize tool change operation at atmospheric pressure. Furthermore, the transformation project of freezing cutterhead and tool change maintenance method ...A shield machine with freezing function is proposed in order to realize tool change operation at atmospheric pressure. Furthermore, the transformation project of freezing cutterhead and tool change maintenance method are put forward. Taking the shield construction of Huanxi Power Tunnel as an example, a numerical analysis of the freezing cutter head of the project was carried out. The results show that when the brine temperature is-25 °C, after 30 d of freezing, the thickness of the frozen wall can reach 0.67 m and the average temperature drops to-9.9 °C. When the brine temperature is-30 °C, after 50 d of freezing, the thickness of the frozen wall can reach 1.01 m and the average temperature drops to-12.4 °C. If the thickness of the frozen wall is 0.5 m and the average temperature is-10 °C, as the design index of the frozen wall, the brine temperature should be lower than-28 °C to meet the excavation requirements in 30 d. Analyzing the frozen wall stress under 0.5 m thickness and-10 °C average temperature condition, the tensile safety factor and compressive safety factor are both greater than 2 at the most dangerous position, which can meet the tool change requirements for shield construction.展开更多
Five-axis NC machining provides a valid and efficient way to manufacture the mechanical parts with complex shapes,which are widely used in aerospace,energy and national defense industries. Its technology innovations h...Five-axis NC machining provides a valid and efficient way to manufacture the mechanical parts with complex shapes,which are widely used in aerospace,energy and national defense industries. Its technology innovations have attracted much attention in recent years. In this paper,the state-of-the-art techniques for five-axis machining process planning are summarized and the challenging problems are analyzed from the perspectives of tool path generation,integrated geometric/mechanistic simulation and machining stability analysis. The recent progresses in accessibility-based tool orientation optimization,cutter location (CL) planning for line contact and three-order point contact machining,shape control of cutter envelope surface and milling stability prediction are introduced in detail. Finally,the emerging trends and future challenges are briefly discussed.展开更多
A CNC simulation system based on intemet for operation training of manufacturing facility and manufacturing process simulation is proposed.Firstly,the system framework and a rapid modeling method of CNC machine tool a...A CNC simulation system based on intemet for operation training of manufacturing facility and manufacturing process simulation is proposed.Firstly,the system framework and a rapid modeling method of CNC machine tool are studied under the virtual environment based on PolyTrans and CAD software.Then,a new method is proposed to enhance and expand the interactive ability of virtual reality modeling language(VRML)by attaining communication among VRML,JavaApplet,JavaScript and Html so as to realize the virtual operation for CNC machine tool.Moreover,the algorithm of material removed simulation based on VRML Z-map is presented.The advantages of this algorithm include less memory requirement and much higher computation.Lastly,the CNC milling machine is taken as an illustrative example for the prototype development in order to validate the feasibility of the proposed approach.展开更多
Surface roughness is one of the most important evaluation indexes in machine cutting. In order to analyze how the tool path affects the roughness of the surface after milling, series of simulations are implemented in ...Surface roughness is one of the most important evaluation indexes in machine cutting. In order to analyze how the tool path affects the roughness of the surface after milling, series of simulations are implemented in MasterCAM. We set up the same processing conditions with same parameters such as speed, material and feed rate etc. in these simulations, but different processing paths are used. We choose three paths: the parallel milling along the X-Y axis direction, the parallel milling along the Z-X or Z-Y axis direction and the streamline processing in the simulations. At the same time, end miller, arc miller and ball miller are respectively selected in the software. So there are totally 9 simulations of the milling process that are performed. Then the experimental cutting processes are performed correspondingly and the surface roughness and the accuracy are measured. The results show that the milling effect of the arc is better and the waste is minimal in the parallel milling along the Z-X or Z-Y axis direction with the end mills.展开更多
A combined FDM/FEM software system was developed to analyze the temperature and stress distributions in castings. The FDM was used to calCulate the temperature distribution while the FEM was used for the stresssimulat...A combined FDM/FEM software system was developed to analyze the temperature and stress distributions in castings. The FDM was used to calCulate the temperature distribution while the FEM was used for the stresssimulation. For practical application, a machine tool bed iron casting was selected and the high temperature mechanical properties of the cast iron were measured. The FDM/FEM simulation results of the temperature and stressdistributions of the solidification process of the casting using current production technology agreed well with the measured temperature and residual stress results. A modified production technology was then proposed. The numericalsimulation results showed that the temperature distribution of the modified production technology was more uniformand the distribution and value of residual stresses were more favorable to dimensional stability of the machine tool.展开更多
基金Ministerial Level Foundation(96J185 .1BQ0150) Fund for Reasearch on Doctoral Programs in Institutions of Higher Learning(1997000716)
文摘A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the method of numerical analysis to investigate the boundary points in a series of sections which form the surface of the workspace. That is, to study such points that have the largest polar radius on a certain section in a system of polar coordinates according to conditions of constraint. The constraint conditions considered in the article include the maximum and minimum displacements of each dieblock, the maximum and minimum angles of oscillation in each hinge. By converting the constraint inequalities into constraint equations, the largest polar radius corresponding to every constraint condition can be evaluated and the minimum one is used to decide the boundary point. This algorithm greatly simplifies the computational process and can be used to analyze any section of the workspace. It provides a theoretical basis for the structural design of such a machine tool.
文摘The dimensional accuracy of machined parts is strongly influenced by the thermal behavior of machine tools (MT). Minimizing this influence represents a key objective for any modern manufacturing industry. Thermally induced positioning error compensation remains the most effective and practical method in this context. However, the efficiency of the compensation process depends on the quality of the model used to predict the thermal errors. The model should consistently reflect the relationships between temperature distribution in the MT structure and thermally induced positioning errors. A judicious choice of the number and location of temperature sensitive points to represent heat distribution is a key factor for robust thermal error modeling. Therefore, in this paper, the temperature sensitive points are selected following a structured thermomechanical analysis carried out to evaluate the effects of various temperature gradients on MT structure deformation intensity. The MT thermal behavior is first modeled using finite element method and validated by various experimentally measured temperature fields using temperature sensors and thermal imaging. MT Thermal behavior validation shows a maximum error of less than 10% when comparing the numerical estimations with the experimental results even under changing operation conditions. The numerical model is used through several series of simulations carried out using varied working condition to explore possible relationships between temperature distribution and thermal deformation characteristics to select the most appropriate temperature sensitive points that will be considered for building an empirical prediction model for thermal errors as function of MT thermal state. Validation tests achieved using an artificial neural network based simplified model confirmed the efficiency of the proposed temperature sensitive points allowing the prediction of the thermally induced errors with an accuracy greater than 90%.
文摘Presents an inverse error estimation method for deriving errors of links from cutter head errors to overcome the difficulty in obtaining analystic solutions for new type of machine tools due to the multi solution of direct kinematics so that the total dimension chain tolerance of machine tool links can be determined by Monte Carlo random simulation for a certain spindle dimension of the machine tool and the precision requirement specified, and the method of dimensional tolerance allocation developed by analysing the elements of machine tool links and the combination of machine tool precision with actual dimensional tolerance for justification of tolerance design for this kind of machine tools.
基金Project(2014FJ1002)supported by the Science and Technology Major Project of Hunan Province,ChinaProject(2012AA041803)supported by National High Technology Research and Development Program of China。
文摘A shield machine with freezing function is proposed in order to realize tool change operation at atmospheric pressure. Furthermore, the transformation project of freezing cutterhead and tool change maintenance method are put forward. Taking the shield construction of Huanxi Power Tunnel as an example, a numerical analysis of the freezing cutter head of the project was carried out. The results show that when the brine temperature is-25 °C, after 30 d of freezing, the thickness of the frozen wall can reach 0.67 m and the average temperature drops to-9.9 °C. When the brine temperature is-30 °C, after 50 d of freezing, the thickness of the frozen wall can reach 1.01 m and the average temperature drops to-12.4 °C. If the thickness of the frozen wall is 0.5 m and the average temperature is-10 °C, as the design index of the frozen wall, the brine temperature should be lower than-28 °C to meet the excavation requirements in 30 d. Analyzing the frozen wall stress under 0.5 m thickness and-10 °C average temperature condition, the tensile safety factor and compressive safety factor are both greater than 2 at the most dangerous position, which can meet the tool change requirements for shield construction.
基金supported by the National Basic Research Program of China (2005CB724103)the National Natural Science Foundation of China (50835004)
文摘Five-axis NC machining provides a valid and efficient way to manufacture the mechanical parts with complex shapes,which are widely used in aerospace,energy and national defense industries. Its technology innovations have attracted much attention in recent years. In this paper,the state-of-the-art techniques for five-axis machining process planning are summarized and the challenging problems are analyzed from the perspectives of tool path generation,integrated geometric/mechanistic simulation and machining stability analysis. The recent progresses in accessibility-based tool orientation optimization,cutter location (CL) planning for line contact and three-order point contact machining,shape control of cutter envelope surface and milling stability prediction are introduced in detail. Finally,the emerging trends and future challenges are briefly discussed.
基金Selected from Proceedings of the 7th International Conference on Frontiers of Design and Manufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50775047)Scientific and Technological Foundation of Guangdong Province,China(No.2004B10201032).
文摘A CNC simulation system based on intemet for operation training of manufacturing facility and manufacturing process simulation is proposed.Firstly,the system framework and a rapid modeling method of CNC machine tool are studied under the virtual environment based on PolyTrans and CAD software.Then,a new method is proposed to enhance and expand the interactive ability of virtual reality modeling language(VRML)by attaining communication among VRML,JavaApplet,JavaScript and Html so as to realize the virtual operation for CNC machine tool.Moreover,the algorithm of material removed simulation based on VRML Z-map is presented.The advantages of this algorithm include less memory requirement and much higher computation.Lastly,the CNC milling machine is taken as an illustrative example for the prototype development in order to validate the feasibility of the proposed approach.
文摘Surface roughness is one of the most important evaluation indexes in machine cutting. In order to analyze how the tool path affects the roughness of the surface after milling, series of simulations are implemented in MasterCAM. We set up the same processing conditions with same parameters such as speed, material and feed rate etc. in these simulations, but different processing paths are used. We choose three paths: the parallel milling along the X-Y axis direction, the parallel milling along the Z-X or Z-Y axis direction and the streamline processing in the simulations. At the same time, end miller, arc miller and ball miller are respectively selected in the software. So there are totally 9 simulations of the milling process that are performed. Then the experimental cutting processes are performed correspondingly and the surface roughness and the accuracy are measured. The results show that the milling effect of the arc is better and the waste is minimal in the parallel milling along the Z-X or Z-Y axis direction with the end mills.
文摘A combined FDM/FEM software system was developed to analyze the temperature and stress distributions in castings. The FDM was used to calCulate the temperature distribution while the FEM was used for the stresssimulation. For practical application, a machine tool bed iron casting was selected and the high temperature mechanical properties of the cast iron were measured. The FDM/FEM simulation results of the temperature and stressdistributions of the solidification process of the casting using current production technology agreed well with the measured temperature and residual stress results. A modified production technology was then proposed. The numericalsimulation results showed that the temperature distribution of the modified production technology was more uniformand the distribution and value of residual stresses were more favorable to dimensional stability of the machine tool.
