Two-Step Tool Setting Method with Progressive Accuracy Levels in Ultra-Precision Turning
Objective The traditional circular groove tool matching method which requires two trial cuts to complete tool matching in the height direction and feed direction is not efficient.Meanwhile,experience in first-line machining shows that the Z-direction cutting depth error can affect the circular groove width.Additionally,the measurement results of the circular groove width are not unique true values,with significant selection errors introduced to the fitting and data processing.This method may result in tool alignment errors of several micrometers,making the ultra-precision turning accuracy of optical components unable to meet the accuracy requirements.Therefore,our tool alignment method aims at further improving the machining accuracy of single-point diamond ultra-precision turning,thus meeting the high-precision manufacturing requirements for optical components.Methods Firstly,based on the turning machining principle,we analyze the influence of tool setting errors on the surface shape accuracy of the machined optical components.Meanwhile,theoretical analysis of the factors that affect the shape of the surface error curve is conducted to determine the curve shape that different types of surfaces will exhibit under different tool alignment errors,with the relationship between curve shape and tool alignment error size presented.Secondly,many fundamental errors in traditional tool alignment methods result in tool alignment errors of several micrometers in production practices,making the ultra-precision turning accuracy of optical components unable to meet the accuracy requirements.Therefore,we theoretically analyze the shortcomings of traditional circular groove cutting methods and optimize them.Then,based on the analysis results of error influence theory and the optimized circular groove tool matching method,a tool matching method of two-step progressive precision level is designed and the overall processing flow is solidified to improve production efficiency.Finally,we carry out experiments to explore whether the proposed method can improve the manufacturing accuracy of optical components and further enhance the machining accuracy of single-point diamond ultra-precision turning.Results and Discussions Firstly,based on the turning machining principle,the influence of tool setting error on the surface shape accuracy of machining is analyzed.The shape of the surface shape error curve caused by the tool setting error is determined by both the surface type of the workpiece and the tool setting error.Since different surface types will produce"W"or"M"fitting error curve shapes in different error conditions,the type of tool alignment error can be determined by the shape of the fitting error curve.Additionally,theoretical analysis shows that the difference between the horizontal coordinates of the left and right curves of the actual generated surface cross-section is equal to twice the tool deviation value.On this basis,a precise adjustment method of tool positions based on the machining surface error results is proposed,which is called the spherical surface matching tool method.Secondly,the traditional groove cutting method is optimized to improve the accuracy and efficiency of tool alignment in principle to complete tool alignment in two directions by a single trial cut.This is called the optimized circular groove cutting method.Finally,to solidify the overall processing flow and improve production efficiency,we put forward a two-step knife alignment method with progressive precision levels.Experiments prove that the RMS and PV values of the surface shape of the spherical reflector machined by the proposed two-step precision leveling method have been reduced by 52.03％and 58.86％respectively.The application of this knife pairing method plays an important role in improving the manufacturing accuracy of optical components,with the overall goal of further improving the machining accuracy of single-point diamond ultra-precision turning.Conclusions A high-precision tool alignment method is an important prerequisite for SPDT technology to achieve efficient and high-precision machining of optical components.The existing groove-to-tool method exerts a significant influence on the groove width due to the Z-direction cutting depth error,and the measurement results of the groove width are not unique true values.Therefore,significant selection errors are introduced to the fitting and data processing.To further improve the tool alignment accuracy,we propose a two-step tool alignment method to guide the progressive accuracy level of ultra-precision tool alignment based on the feedback of machining surface shape error results.Theoretical analysis of the adverse effects of different tool errors is as follows.The tool error on the Y-axis can cause cylindrical/conical residues in the machining surface center,while that on the X-axis can result in surface shape errors on spherical workpieces with"W"or"M"shapes.A precise adjustment method of tool positions based on the machining surface shape error results is proposed by combining it with the traditional groove-to-tool method.Compared with the traditional circular groove tool matching method,the RMS and PV values of the surface shape of the spherical reflector machined by the proposed method have been reduced by 52.03％and 58.86％respectively.Finally,we verify the accuracy of the tool alignment method and the effectiveness of improving the ultra-precision turning accuracy of optical components.
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