摘要
弯管作为核电、石油天然气、化工等领域中的油、气、液等的输送工具,发挥着重要作用。例如核电站中的主管道是连接蒸汽发生器与反应堆压力容器的大型厚壁弯管,其质量的好坏关系整个核电站的安全。弯管表面质量是决定其整体质量的重要因素,弯管表面加工的难点在于,传统设备加工时会有加工干涉,表面质量一致性差等问题。多轴数控加工技术在复杂曲面的加工方面有巨大优势,能有效解决加工干涉,增加刀具切削稳定性,提高加工表面质量。所以开展针对不同类型弯管利用多轴数控加工技术加工弯管内外表面以及研发高效优质经济专用设备的研究,具有重要理论意义和应用价值。
本文以核电主管道为研究原型,通过分析其几何特性,结合数控铣削加工技术原理和特点,提出了3轴2联动和5轴联动加工主管道样件弯管外表面,4轴联动和5轴联动加工主管道样件弯管内表面的方法以及一种内置平移式专用装置加工主管道内表面的方法。
在进行了如何避免加工干涉和进行均匀切削等理论分析的基础上,在3轴加工中心和5轴加工中心上进行了主管道样件内外表面的铣削试验。试验结果表明：随着转速的提高,进给量的减小,切削深度的减小以及切削行距的减小,外表面质量越来越好；3轴2联动加工相比5轴联动加工表面质量一致性稍差,表面粗糙度范围为Ra3.07um～Ra3.14umm,但加工效率提高了5%：5轴联动加工相比4轴联动加工表面质量一致性更好,粗糙度范围为Ra3.05um～Ra3.10umm,加工效率低了6%。所以采用3轴加工机床加工外表面,5轴联动机床加工内表面是正确的选择。
结合主管道细长等径的特征,设计了内置平移式主管道内表面专用加工装置,采用计算机辅助设计和模块化设计的现代设计方法,进行了装置功能模块划分,详细设计了各个具体模块单元,包括动力系统设计、传动系统设计以及机械模块各部件的结构和尺寸设计,计算了铣削力,并据其确定了驱动电机的功率,完成了关键部件圆弧导轨基座刚度和强度的校核。结果表明,辅助支撑有效减小了导轨基座的变形(无支撑变形为1.82mmm,有支撑变形为0.38mm),圆弧导轨基座最危险截面的应力为94.84MPa,远小于许用应力[σ]=375～500MPa,满足设计要求。
课题研究结果表明,3轴2联动数控加工弯管外表面高效优质,5轴联动数控加工弯管内表面无干涉并且质量可靠,内置平移式专用加工装置加工主管道内表面具有可行性。以上成果为核电主管道以及类似弯管内外表面的加工提供了理论和实践依据。
As transport tools of oil, gas and liquid bent pipes play an important role in nuclear power station, oil and gas industry, chemical industry and other fields. Such as the main pipe of nuclear power station, it is large pipe with thick wall, connecting the steam generator and reactor pressure vessel. Its quality affects the safety of nuclear power station. Its surface quality is important factor to its overall quality. The difficulties to machine its surface are interference, poor quality consistency and inefficiency. Multi-axis CNC technology in the machining of complex surface has huge advantage, which can solve interference, increase cutting stability and improve the machining quality. So it has high theoretical significance and application value to carry out the study on the machining of the bent pipe surface using multi-axis CNC technology and the study on the development of special equipment.
Using nuclear power station main pipe as prototype, this paper analyses its geometrical characteristics and presents new methods for the machining of bent pipe surface, including the methods of3-axis and5-axis machining the external surface of the main pipe sample piece, the methods of4-axis and5-axis machining the internal surface of the main pipe sample piece and the method of machining the internal surface of main pipe for nuclear power station with special equipment inside the pipe.
Based on theoretical analysis, milling experiments are carried out on the internal and external surface of main pipe sample piece using3-axis machining center and5-axis machining center.The results show that, with the improvement of speed, the reduction of feed rate, cutting depth and the row space, quality of external surface becomes better. Compared with5-axis machining, the surface quality consistency of3-axis machining is poorer, the surface roughness range from Ra3.07um-Ra3.14um, but efficiency increases by5%; compared with4-axis machining, the surface quality consistency of5-axis machining is better, the surface roughness range from Ra3.05um-Ra3.10um, efficiency decreases6%. So it is right choice to machining the external surface by3-axis machine tools and machining the internal surface by5-axis machine tool.
The main pipe is long and full bore. According to it special equipment which machining the internal surface of main pipe inside the pipe is designed. With the modern design methods of CAD and modular design, function module partition is finished, each specific module is detailedly designed, including the power system design, the transmission system design and the structure design for all parts of the mechanical module, the milling force is calculated and according to it the motor power is determined, finally the stiffness and strength of base for arc guide are checked. The results show that, auxiliary support effectively reduce the deformation of guide base (the deformation is1.82mm without support and0.38mm with support), the stress in the most dangerous section of arc guide base is94.84MPa, far less than the allowable stress, which meets the design requirements.
The results show that it is a good way to machining the external surface of bent pipe with3-axis machining technology and to machining the internal surface of bent pipe with5-axis machining technology.At the same time, it is a good method to machining the internal surface of main pipe inside the pipe with special equipment.The research results support the machining of main pipe surfaces for nuclear power station and other bent pipes of its kind in theory and practice.
引文
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