| Optical free surface with its superior performance plays a more and more important role in the aerospace, aviation and military industries. It's increasingly obtained concerns in other industries faced with consumers, such as digital cameras, fax and other optoelectronic products of key components. Compared with rotary symmetrical optical surface, the Non-Rotationally Symmetric (NRS) optical surface can overcome kinds of optical aberration of optical system, improve optical properties and lightweight the optical system. Due to the superior performance of NRS optical surface, it makes the breaking- through optical design become possible. Whether the NRS optical surface can be successfully applied to every field of consumption industry, the key lies in whether the high precision curved NRS and low cost of processing can be achieved or not, but so far the processing capacity of NRS optical surface is still very limited. Based on FTS(Fast Tool Servo), the manufacturing of NRS with high efficiency, accuracy and low cost raises growing concerns on FTS turning NRS optical surface. Due to machine system which contains geometric errors and physical errors caused by the force between the tool-workpiece system, the turning process will produce processing error inevitably and affect machining precision of parts. In order to study the influence of the tool and cutting parameters on the machining error, the FTS turning processing error model must be established.This paper takes the FTS device and CNC machine tools as research object, establishing the diamond turning FTS processing error model which includes the spindle's gyration error model, tool-workpiece system dynamics model, and cutting force deformation error model. By homogeneous transformation methods, the processing error including geometry and physical factors can be unitily expressed by processing error model. Besides, analyzes the influence of the processing error caused by tool and cutting parameters, achieving error compensation and improving the processing precision.Firstly, in the ultra-precision processing, the spindle's gyration error makes a great influence on the machining accuracy. This chapter analyzes the causes of the spindle's gyration error, classification of spindle's gyration error and measurement methods of spindle's gyration error. Using Fourier transform to express the spindle's gyration error signal, we will get the axes trajectory of spindle axis under the situation of radical derection pulsatile. The x, y, z axis errors and the math expression of the swinging angle of spindle and axial playing error can be obtained by the polar equation of the axes trajectory spontaneously. Setting up spindle's gyration error model, introducing errors of the radical derection pulsatile, swinging Angle and axial playing make preparatins for the FTS diamond turning processing error model of the fourth chapter.Secondly, the establishment of the cutting force deformation error model. First of all, analyze the affect of cutting force to processing error and establish a cutting force model. General point of view, cutting force is directly proportional to cutting area. This paper begins with the calculation of the cutting area, establishing and upgrading the cutting area of the model. Moreover, it also establishes the tool-workpiece system dynamics model and makes the dynamic model non-dimensional. From the tool - workpiece system dynamics model, obtained the vibration change of tool - workpiece system in the x and z under the conditions of the tremor so that establish the cutting force deformation error model.Thirdly, Homogeneous transformation is a simple and practical method to solve multi-body dynamics of the campaign which can connect tool coordinate system, inertial coordinate system, the principal axis coordinate system and workpiece coordinate system. In this paper, homogeneous transformation method taken to make tip-to-Process datum center coordinate transformation process baseline matrix equation and introduce the spindle cutting force error model and deformation error model to unify the diamond turning machining error FTS major factor in spindle error and cutting force deformation error. In that way, the diamond turning FTS processing error model is established.Finally, simulate of the establishment of turning processing error model of the FTS. As FTS cutting process turns in two direction of fx and fz, we can discuss the processing errors of x and z axis in the text for variable spindle rotation. Concentrated on the analysis of the conditions of cutting parameters (cutting depth, feed volume, speed, etc.), cutting tool parameters (tool angle, tip radius), such as the impact of processing errors made by changes of the machining error in x (Δx ) and z(Δz )to. Error Analysis of the specific processing principle illustrate as follows: Error Analysis of the FTS diamond turning of the processingThrough the above analysis, the followings can be concluded:1. Through the establishment of diamond turning processing error model of FTS, the main error sources of FTS diamond include the impact of the geometric processing error(spindle and processes systems) and physical processing error factors (deformation caused by cutting force).Meanwhile, the introduction of tremor disturbance in the cutting tool under the conditions of tool- workpiece system dynamics model, can then be integrated to take into account all the relevant factors having an impact on processing error.2. Through MATLAB simulation analysis, we can draw geometry parameters and cutting tool parameters on diamond turning FTS error as follows: Corner Radius increases, processing errors are inclined to increase; the velocity of cut increases, processing errors tend to enlarge; tool angle increases, x to the machining error tends to increase, z to the machining error are inclined to decrease; cutting speed increases, the processing error tends to decrease.3. By analyzing FTS error processing through modeling, we can be targeted through the control system to adjust the turning parameters and reduce the tremor to lower the effect on the surface quality in order to improve the machining accuracy and reduce the role of error processing. |
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