【作者】 严青松；

【导师】 魏伯康； 余欢；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2006， 博士

【摘要】 近无余量、高精度、高性能、复杂薄壁有色合金铸件是21世纪铸造业的发展趋势之一,在航空航天、国防、汽车工业等基础产业具有重要的地位和广阔的应用前景,但现有的精密成形工艺尚不能完全满足质量要求高的复杂薄壁有色合金铸件的生产要求。本研究针对复杂薄壁铝合金铸件的特点,在吸收了真空吸铸、低压铸造、差压铸造工艺优点的基础上,提出了一种在真空条件下低压充型,高压下结晶的新型差压铸造精密成形工艺——真空差压铸造,并探讨了真空差压铸造工艺和理论,开发了具有使用价值的基于智能控制的真空差压铸造设备,解决了国防和民用工业中小批量、铸件质量要求高的复杂薄壁铝合金铸件精密成形问题。本研究提出了真空差压铸造原理及工艺,其采用真空条件下低压充型,高压下结晶的原理,工艺分为抽真空、充型、升压、保压和卸压五个阶段,充型和结晶可在不同压力下进行,具有优越的充型流体力学和凝固的力学条件,解决了一般的反重力铸造工艺在铸造复杂薄壁铸件方面存在的气体反压力和充型等问题,并自行设计和研制了一套VCPC-1型真空差压铸造设备,为真空差压铸造工艺的理论研究和生产应用打下了良好的基础。本文系统地研究了真空差压铸造的智能控制系统,采用MATLAB对真空差压铸造数字PID控制和模糊控制算法进行了仿真分析,在此基础上,确定了真空差压铸造智能控制系统采用模糊控制算法;采用Delphi语言开发了真空差压铸造智能控制的可视化界面,界面以视窗形式弹出,功能齐全,简单实用,具有良好的人-机对话功能;采用串行通信技术,真空差压铸造智能控制系统实现了下位机的近程控制和上位机的远程控制。下位机采用单片机控制,主要便于在现场实时监测整个工艺过程;上位机采用PC机控制,主要用于传输、保存和打印数据,显示和再现整个工艺过程,可以在500m的范围进行控制操作。试验结果表明,研制的真空差压铸造智能控制系统高效可靠,运行良好,完全能够满足工艺要求。系统研究了真空差压铸造工艺的充型理论,自行研制了一套智能化的电极触点法流动形态测试系统,在此基础上,测试了不同壁厚铝合金铸件和不同充型速度下真空差压铸造工艺的充型流动形态,探讨了真空差压铸造铝合金薄壁铸件的充型规律,提出了“临界加压速度”或“临界充型速度”的概念,同时建立了真空差压铸造工艺的“正向充填”和“反向充填”理论,并探讨了金属液的流动形态与铸件质量的关系,为真空差压铸造充型工艺的优化提供了理论依据。系统研究了真空差压铸造工艺的凝固补缩理论,探讨了不同结晶凝固压力下真空差压铸造铝合金试样的致密度和显微组织变化规律,建立了真空差压铸造工艺凝固补缩过程的数学模型,得出晶间不同部位(X处)的补缩速度公式为:指出晶间X处的补缩速度主要取决于结晶凝固时保压压力P保的大小,保压压力P保越大,晶间X处的补缩速度就越快。在此基础上,提出了真空差压铸造工艺的枝晶挤滤渗流补缩理论,并得到金属液的挤滤渗流能力公式为:指出挤滤渗流作用的大小主要取决于保压压力P保,保压压力P保越大,挤滤渗流作用就越强,金属液就能够更顺利的通过凝固枝晶间的狭窄通道向补缩区流动,从而更有利于对固-液界面的凝固补缩。凝固补缩理论的研究为真空差压铸造复杂薄壁铝合金致密铸件提供了理论基础。建立了真空差压铸造工艺参数包括真空度、充型速度、充型压差、升压速度、结晶压力和保压时间等的确定原则,并成功地小批量铸造了最小壁厚0.8mm,最大重量20kg的复杂薄壁铝合金壳体和箱体军品铸件,为航空企业开发了VCPC-2型真空差压铸造系统,表明真空差压铸造技术已具备生产1mm以下的近无余量、薄壁复杂铸件的能力,并适用于熔模精铸型、砂型、金属型、石膏型等多种铸型生产,为我国真空差压铸造技术的推广应用打下了良好的基础,具有广阔的应用前景。更多还原

【Abstract】 Near net shape,high accuracy,high performance,complicated and thin-wall nonferrous alloy castings is one of developing trend of foundry industry in the 21st century,and have important status and broad application prospect in basic industries such as aviation,airsPace,national defense,car and automobile industry fields. But existing processes have not satisfied producing demand of high-qulity,complicated and thin-wall nonferrous alloy castings completely. In the Paper,according to the characteristics of complicated and thin-wall aluminum alloy castings,a new counter-pressure casting process named vacuum counter-pressure casting was presented on the basis of suction casting,low-pressure casting and counter-pressure casting process,which adopted to low-pressure fill mould under the condition of vacuum and crystallize under high pressure. Meanwhile,its principle and theory were investigated,and its equipment based on intelligent control was developed,which solved middle or short run,high-qulity, complicated and thin-wall aluminum alloy castings forming accurately in national defense and civilian industries.First of all,vacuum counter-pressure casting process and principle were presented,and its technology principle adopted to low-pressure fill mould under the condition of vacuum and crystallize under high pressure. Meanwhile,its process wsa divided into five stages:vacuumizing,filling mould,rising pressure,keeping pressure and releasing pressure,additionally,filling mould and crystallization could carry on at different pressure. So it had predominant filling hydrodynamics and solidification mechanics condition,and it solved the problem of gas counter pressure and filling mould which existed in general counter-gravity casting complicated and thin-wall aluminum alloy castings. meanwhile,a set of VCPC-1 vacuum counter-pressure casting equipment was designed and developed by oneself,which had laid a good foundation for theory research and producing application of vacuum counter-pressure casting process.Intelligent control systems of vacuum counter-pressure casting were studied systemically. Through simulation analyses of vacuum counter-pressure casting digital PID control and fuzzy control algorithm based on MATLAB,its intelligent control systems were comfirmed to adopte fuzzy control algorithm. Meanwhile,visual interface of its intelligent control systems was developed by using Delphi language,which appeared in the form of window,and its functions was multiple,simple and practical,moreover , it had good persons-machine dialogue functions. Through serial communication technique,intelligent control systems of vacuum counter-pressure casting realized short range control of hypogynous machine and long-distance control of epigynous machine. Hypogynous machine adopted the single-chip computer to control,which was convenient to monitor the whole process course real-time at the scene. Additionally,epigynous machine adopted PC computer to control,which was used mainly to transmit,save and print data,and show and reproduce the whole process course,moreover,it could control on the range of 500m. Results indicated Intelligent control systems of vacuum counter-pressure casting developed were high efficient and reliable,and run well. Morover,they could meet process demand completely.Filling mould theory of vacuum counter-pressure casting process was studied systemically. Through a set of testing systems of intelligent electrode contacting method developed by oneself,filling mould flow morphology of vacuum counter-pressure casting aluminum alloy was tested under condition of different thick castings and filling velocity. Meanwhile,its filling regulation was investigated,and the concept of critical pressurizing velocity and filling velocity was presented. Additionally,obverse and inverse filling mould theory of vacuum counter-pressure casting process was established,and relation of flow morphology and castings quality was discussed,which had provided theoretical foundation for filling process of vacuum counter-pressure casting.Solidification feeding theory of vacuum counter-pressure casting process was studied systemically,and changing regulation of the density and microstructure of vacuum counter-pressure casting aluminum alloy sample under different crystallization and solidification pressure was investigated. Meanwhile,mathematical model of its solidification feeding course was established,and feeding velocity equation of X location between dendrite was obtained and shown below:It was pointed that feeding velocity equation of X location between dendrite depended on magnitude of keeping pressure Pk mainly,moreover,the higher keeping pressure Pk was,the quicker its feeding velocity was. On this basis,dendrite extrusion and infiltration feeding theory of vacuum counter-pressure casting process was presented,and extrusion and infiltration ability equation of molten metal was obtained and shown below:It was pointed that extrusion and infiltration effect depended on magnitude of keeping pressure Pk mainly too,moreover,the higher keeping pressure Pk was,the stronger its effect was,which could make molten metal Pass through narrow Passage between solidification dendrite to flow toward feeding area successfully. Therefore,it benefited from solidification feeding for interface between solid and liquid. Study of solidification feeding theory provided theoretical foundation for vacuum counter-pressure casting complicated,thin-wall and sound aluminum alloy castings.Finally , determinate principle of vacuum counter-pressure casting process Parameters such as vacuum degree,filling velocity,filling pressure difference,rising pressure velocity,crystallization pressure and keeping pressure time were established. Meanwhile,short run complicated and thin-wall shell and box body aluminum alloy military castings which the smallest wall was 0.8mm and the biggest weight was 20kg had been produced successfully,and VCPC-2 vacuum counter-pressure casting systems had been developed for aviation enterprise. Results indicated vacuum counter-pressure casting technology had possessed ability of producing near net shape,thin-wall and complicated castings under 1mm,and was suitable for many kinds of moulds such as investment casting,sand mould,permanent mould and gypsum mould,which had laid a good foundation for popularizing application of vacuum counter-pressure casting technology,and has broad application prospects.更多还原