本文關(guān)鍵詞：智能控制的薄壁鋁合金鑄件真空差壓鑄造工藝與理論，由筆耕文化傳播整理發(fā)布。

華中科技大學(xué)博士學(xué)位論文摘要；近無余量、高精度、高性能、復(fù)雜薄壁有色合金鑄件是；本研究提出了真空差壓鑄造原理及工藝，其采用真空條；本文系統(tǒng)地研究了真空差壓鑄造的智能控制系統(tǒng)，采用；系統(tǒng)研究了真空差壓鑄造工藝的充型理論，自行研制了；華中科技大學(xué)博士學(xué)位論文法流動形態(tài)測試系統(tǒng)，在此；系統(tǒng)研究了真空差壓鑄造工藝的凝固補縮理論，，探討了；?δ2G?G2σ8βμXu()

華 中 科 技 大 學(xué) 博 士 學(xué) 位 論 文 摘 要

近無余量、高精度、高性能、復(fù)雜薄壁有色合金鑄件是21世紀(jì)鑄造業(yè)的發(fā)展趨勢之一，在航空航天、國防、汽車工業(yè)等基礎(chǔ)產(chǎn)業(yè)具有重要的地位和廣闊的應(yīng)用前景，但現(xiàn)有的精密成形工藝尚不能完全滿足質(zhì)量要求高的復(fù)雜薄壁有色合金鑄件的生產(chǎn)要求。本研究針對復(fù)雜薄壁鋁合金鑄件的特點，在吸收了真空吸鑄、低壓鑄造、差壓鑄造工藝優(yōu)點的基礎(chǔ)上，提出了一種在真空條件下低壓充型，高壓下結(jié)晶的新型差壓鑄造精密成形工藝——真空差壓鑄造，并探討了真空差壓鑄造工藝和理論，開發(fā)了具有使用價值的基于智能控制的真空差壓鑄造設(shè)備，解決了國防和民用工業(yè)中小批量、鑄件質(zhì)量要求高的復(fù)雜薄壁鋁合金鑄件精密成形問題。

本研究提出了真空差壓鑄造原理及工藝，其采用真空條件下低壓充型，高壓下結(jié)晶的原理，工藝分為抽真空、充型、升壓、保壓和卸壓五個階段，充型和結(jié)晶可在不同壓力下進(jìn)行，具有優(yōu)越的充型流體力學(xué)和凝固的力學(xué)條件，解決了一般的反重力鑄造工藝在鑄造復(fù)雜薄壁鑄件方面存在的氣體反壓力和充型等問題，并自行設(shè)計和研制了一套VCPC-1型真空差壓鑄造設(shè)備，為真空差壓鑄造工藝的理論研究和生產(chǎn)應(yīng)用打下了良好的基礎(chǔ)。

本文系統(tǒng)地研究了真空差壓鑄造的智能控制系統(tǒng)，采用MATLAB對真空差壓鑄造數(shù)字PID控制和模糊控制算法進(jìn)行了仿真分析，在此基礎(chǔ)上，確定了真空差壓鑄造智能控制系統(tǒng)采用模糊控制算法；采用Delphi語言開發(fā)了真空差壓鑄造智能控制的可視化界面，界面以視窗形式彈出，功能齊全，簡單實用，具有良好的人－機(jī)對話功能；采用串行通信技術(shù)，真空差壓鑄造智能控制系統(tǒng)實現(xiàn)了下位機(jī)的近程控制和上位機(jī)的遠(yuǎn)程控制。下位機(jī)采用單片機(jī)控制，主要便于在現(xiàn)場實時監(jiān)測整個工藝過程；上位機(jī)采用PC機(jī)控制，主要用于傳輸、保存和打印數(shù)據(jù)，顯示和再現(xiàn)整個工藝過程，可以在500m的范圍進(jìn)行控制操作。試驗結(jié)果表明，研制的真空差壓鑄造智能控制系統(tǒng)高效可靠，運行良好，完全能夠滿足工藝要求。

系統(tǒng)研究了真空差壓鑄造工藝的充型理論，自行研制了一套智能化的電極觸點

華 中 科 技 大 學(xué) 博 士 學(xué) 位 論 文 法流動形態(tài)測試系統(tǒng)，在此基礎(chǔ)上，測試了不同壁厚鋁合金鑄件和不同充型速度下真空差壓鑄造工藝的充型流動形態(tài)，探討了真空差壓鑄造鋁合金薄壁鑄件的充型規(guī)律，提出了“臨界加壓速度”或“臨界充型速度”的概念，同時建立了真空差壓鑄造工藝的“正向充填”和“反向充填”理論，并探討了金屬液的流動形態(tài)與鑄件質(zhì)量的關(guān)系，為真空差壓鑄造充型工藝的優(yōu)化提供了理論依據(jù)。

系統(tǒng)研究了真空差壓鑄造工藝的凝固補縮理論，探討了不同結(jié)晶凝固壓力下真空差壓鑄造鋁合金試樣的致密度和顯微組織變化規(guī)律，建立了真空差壓鑄造工藝凝固補縮過程的數(shù)學(xué)模型，得出晶間不同部位（X處）的補縮速度公式為：

?δ2G?G2σ8βμXu()ρ=+P?R?g?? 保2D12μ?T?η??Tηδ(1?β)δ?

指出晶間X處的補縮速度主要取決于結(jié)晶凝固時保壓壓力P保的大小，保壓壓力P保越大，晶間X處的補縮速度就越快。在此基礎(chǔ)上，提出了真空差壓鑄造工藝的枝晶擠濾滲流補縮理論，并得到金屬液的擠濾滲流能力公式為:

K(P保+2σ?P靜?P氣)F??τ μ?L?G=

指出擠濾滲流作用的大小主要取決于保壓壓力P保，保壓壓力P保越大，擠濾滲流作用

就越強(qiáng)，金屬液就能夠更順利的通過凝固枝晶間的狹窄通道向補縮區(qū)流動，從而更有利于對固-液界面的凝固補縮。凝固補縮理論的研究為真空差壓鑄造復(fù)雜薄壁鋁合金致密鑄件提供了理論基礎(chǔ)。

建立了真空差壓鑄造工藝參數(shù)包括真空度、充型速度、充型壓差、升壓速度、結(jié)晶壓力和保壓時間等的確定原則，并成功地小批量鑄造了最小壁厚0.8mm，最大重量20kg的復(fù)雜薄壁鋁合金殼體和箱體軍品鑄件，為航空企業(yè)開發(fā)了VCPC-2型真空差壓鑄造系統(tǒng)，表明真空差壓鑄造技術(shù)已具備生產(chǎn)1mm以下的近無余量、薄壁復(fù)雜鑄件的能力，并適用于熔模精鑄型、砂型、金屬型、石膏型等多種鑄型生產(chǎn)，為我國真空差壓鑄造技術(shù)的推廣應(yīng)用打下了良好的基礎(chǔ)，具有廣闊的應(yīng)用前景。

關(guān)鍵詞：真空差壓鑄造，薄壁鑄件，鋁合金，智能控制，充型，凝固補縮

華 中 科 技 大 學(xué) 博 士 學(xué) 位 論 文 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

華 中 科 技 大 學(xué) 博 士 學(xué) 位 論 文 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：

?δ2G?G2σ8βμXu()ρ=+P?R?gk?? 2D12μ?T?η??Tηδ(1?β)δ?

It was pointed that feeding velocity equation of X location between dendrite

華 中 科 技 大 學(xué) 博 士 學(xué) 位 論 文 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：

K(Pk+2σ?Ps?Pg)F??τ μ?L?G=

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.

Keywords：vacuum counter-pressure casting，thin-wall castings，aluminum alloy，

intelligent control，filling mould，solidification feeding

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  本文關(guān)鍵詞：智能控制的薄壁鋁合金鑄件真空差壓鑄造工藝與理論，由筆耕文化傳播整理發(fā)布。