Research On Milling Machining Accuracy Improvement Technologies Of Small Modulus Copper Electrode Gears

Plastic gears are widely used in medical,home,office,transportation and other fields due to their light weight and self-lubricating characteristics.The production of plastic gears by injection molding requires the preparation of non-standard inner gear molds,resulting in the copper electrodes of the EDM inner gear molds becoming nonstandard gears.Gears with arbitrary parameters can be milled by using general milling tools without custom tools.Therefore,it is imperative to carry out research on the milling technology of small modulus CEG.Compared with the general transmission type steel gears,the CEG is made of red copper,which is prone to "sticking" during milling,which makes the mechanism of the milling tool wear(MTW)unclear.Compared with the large-size milling tool,the milling tool deflection(MTD)has a more obvious impact on the machining accuracy of the CEG during milling.These problems limit the application and promotion of the small modulus CEG milling technology.On a four-axis vertical CNC machine tool,a micro-diameter milling tool is used to mill small-modulus CEG.How to ensure the machining accuracy and improve the accuracy of small-modulus CEG needs to be studied in many aspects,including the error traceability of gear,the influence of path planning strategy on gear machining accuracy,the influence of micro-diameter MTW and MTD on gear machining accuracy,and how to compensate for gear errors and many other technical issues to improve gear accuracy.This work studies the milling technology to improve the precision of small modulus CEG,and provides technical support for the application of precision milling technology in small modulus CEG.The research shows that the researched milling technology to improve the precision of the small modulus CEG can realize the precision milling of the small modulus CEG.Based on the above ideas,the main research content of this work are as follows:(1)Traceability and prediction model of machining errors is established.The milling model is deduced,involving the direction of tooth helix,the transition circularity,the normal equidistant surface,the transformation of cartesian coordinates and polar coordinates,and the model unification.The normal equidistant surface provides the running track coordinates for the milling tool and constrains the movement state of the milling tool.The transformation of cartesian coordinates and polar coordinates is studied,which provides a theoretical basis for clarifying the position transformation of the milling tool under the normal equidistant state.The effects of the machine tool positioning error,the workpiece clamping error,the MTD and the MTW on the gear error of small modulus CEG are studied.The prediction model of machining error is established,and the influence of various errors on the machining accuracy of gears is simulated.According to the prediction model,the error is deduced,and the error source in the processing process is clarified.(2)Optimal control method of the constant arc length path trajectory based on the constant scallop height is proposed.The formulation of milling strategy affects the quality of tooth surface and the efficiency of machining.The formulation of the milling strategy mainly includes the cross-section feed strategy,the number of milling lines,the milling trajectory,the indexing method,and the confirmation of the rotation direction.These five aspects involve the specific process of the milling path formulation.When designing the tooth surface quality,it is considered that designing the number of milling lines at the constant angles will easily lead to uneven distribution of the scallop height of the tooth surface and that the number of milling lines at the root of the tooth is too large,resulting in redundancy,which affects the efficiency of processing.The innovative design of the number of milling lines with the constant arc length is proposed,which advantageously improves the problems existing in designing the number of milling lines according to the constant angle,which not only improves the processing efficiency,but also improves the quality of the tooth surface.(3)The milling tool deflection and milling tool wear model are established.The formation mechanisms of the helix slope deviation(HSD),the profile slope deviation(PSD)and the pitch peak are studied,and the mapping relationship between the MTD and the MTW and gear error is conceived.It is clarified that the MTD is the error source that causes the HSD,and the MTW is the error source of the pitch peak and the PSD,which are the result of the combined action of the milling parameters.In order to establish the MTD model of any size,introduces the milling tool radius into the empirical formula of milling force,and fits the MTD model under any size and milling parameters through the orthogonal experimental design.Similarly,the milling parameters and the milling path are connected through the experimental design,and the MTW models of R0.4,R0.3,R0.25 and R0.2mm are established.The establishment of MTD model and MTW model provides technical support for precision milling of small modulus CEG.(4)Inversion compensation technology for milling machining errors of small modulus copper electrode gears is proposed.The reason for the formation of the PSD and the pitch peak is caused by the MTW.Under the condition of certain milling parameters,the MTW increases with the increase of the stroke of the milling path.Through the established MTW model,the MTW can be introduced into the milling program in advance in the process of generating the processing program,and the milling path can be adjusted to achieve the purpose of error compensation.Under the condition of certain milling parameters,the MTD in the milling process is certain,so the milling width and the rotation angle of the motor can be adjusted to achieve the purpose of compensation of the HSD.The compensation of milling error realizes the overall error compensation of machine tool-workpiece clamping-milling tool.The error compensation technology realizes the precise manufacture of CEG with arbitrary gear parameters,milling parameters,and milling tool sizes.(5)G-code generation software for precision milling of CEG is developed.This software has independent intellectual property rights.The software involves workpiece definition,process design,milling tool selection,modification design,and log file generation.It incorporates the key technologies of milling CEG and reduces the requirements for the professional knowledge of skilled workers.The developed software realizes the closed error compensation of the machine tool-workpiece-milling tool system,laying the foundation for the closed-loop manufacturing of small modulus CEG.In this work,the traceability and prediction model of machining error is established by studying the error sources of gear errors.The path planning method of constant arc length is used to realize the optimal control of the milling path,and through the optimal control of the path,the gear errors of the milling process has regularity.According to the regularity,the mapping relationship between MTW,MTD and gear errors are clarified.Based on the replication principle,the MTW and the MTD model are established.The MTW and the MTD model are introduced into the error inversion compensation technology to improve the milling accuracy of small modulus CEG.It has been verified by the milling test that the gear deviation of the small modulus CEG reaches the level 4～5 of GB/T 38192-2019.