Research On Eccentricity Mechanism Of BTA Boring Machining System Induced By Cutting Fluid Coupled Eccentric Pilot

This paper researched dynamic characteristics of BTA deep hole boring-bar with nonlinear considering cutting fluid’s free surface, which included eccentricity, sensitivity, frequency and stability. The cutting fluid of BTA deep hole machining system was the most key factors affecting the stability of the boring-bar. The influence factors to the eccentricity and frequency characteristic on machining accuracy of the inner hole were analyzed using the comparison method. Then the influence factors of the systemic sensitivity were investigated using numerical simulation method. Dynamic stability of inner cutting fluid was analyzed based on the stability theory. The research aimed at providing theoretical support for the actual production. The main results in this study were shown:1. The eccentricity model of BTA boring-bar was established based on the radius equation of inner cutting fluid’s free surface in boring-bar when there was the free surface association with the geometric error of pilot, and the analytic solution was also obtained. Meanwhile the various trends of influence factors on BTA boring-bar eccentricity were gained too.2. The equations of eccentricity and vortex frequency of BTA boring-bar were simulated synchronously, and the sensitivity weight analyzed considering influence factors. The sensitivity weights of influence factors to the processing accuracy of the system were obtained through establishing the relationship between the eccentricity and vortex frequency of BTA boring-bar.3. The frequency response of cutting fluid on the boring-bar was studied in the BTA deep hole machining system. The results showed that the downtrend of the frequency in two types of equations would appear as a whole with free surface, but the contrary phenomenon would happen in the scope of cutting fluid with vertical small flow. Under the condition of the same simulation input parameters, the influence of both inner cutting fluid and the outer on the frequency equation of the boring-bar was bigger when the pressure was low in the system, while the influence of inner cutting fluid on the frequency equation of the boring-bar was bigger when the pressure was high. Through the analysis of sensitivity of two kinds of frequencies, it was indicated that the inner cutting fluid was the key factors affecting the frequency characteristic in the processing.4. The stability of the BTA deep hole machining system was investigated when there was inner cutting fluid. The critical position of boring-bar’s instability was obtained through the contrast among the speed ratio, liquid filling ratio and frequency ratio. Boring-bar’s critical condition to avoid the chaos phenomenon, was analyzed, which indicated that the critical curve of chatter instability of the boring-bar would happen and so did the heteroclinic orbits of the jump point whose trajectory had no longer determinacy.The conclusions of this study provided the theoretical support for the optimal design of BTA system structure and the choice of operating parameters, gave process parameters’ operation interval that avoided chatting region to improve the machining accuracy of hole, and provided guiding significance for the actual production.