【摘要】：在微機(jī)電、醫(yī)療器械等領(lǐng)域,對(duì)微型異形管件的需求正逐漸上升。液壓成形能夠高效生產(chǎn)微型異形管件,成為研究的重點(diǎn)。由于零件尺寸與晶粒大小接近,微型管件產(chǎn)生了尺度效應(yīng)問題,成形能力降低,制約了其發(fā)展。軸向補(bǔ)料工藝能夠提高管件成形能力,已在常規(guī)異形管件生產(chǎn)中廣泛應(yīng)用。為了提高微型管件成形能力,本文將軸向補(bǔ)料工藝引入微型管件液壓成形中,進(jìn)行了相關(guān)研究。首先,對(duì)微型管件液壓成形導(dǎo)向區(qū)內(nèi)的摩擦特性進(jìn)行了研究。采用自行開發(fā)的實(shí)驗(yàn)裝置,通過測(cè)定初始摩擦力與總推力,并根據(jù)內(nèi)壓大小以及其它尺寸參數(shù),即可計(jì)算出摩擦系數(shù)。分別對(duì)外徑2mm與1mm的304不銹鋼微型管件進(jìn)行實(shí)驗(yàn),結(jié)果發(fā)現(xiàn)隨著尺寸縮小,摩擦系數(shù)顯著上升。造成微型管件摩擦尺度效應(yīng)的主要原因在于管件外表面為曲面,曲率半徑的縮小導(dǎo)致模具表面相對(duì)凹凸不平程度減低,使液體潤(rùn)滑劑存儲(chǔ)困難,摩擦力增大。其次,對(duì)軸向補(bǔ)料工藝進(jìn)行了數(shù)值與實(shí)驗(yàn)分析。利用GTN細(xì)觀損傷模型,直接將外徑2mm,壁厚0.15mm的304不銹鋼微型管件的流動(dòng)應(yīng)力引入到材料屬性當(dāng)中,對(duì)微型管件進(jìn)行建模;同時(shí),基于大量的軸向補(bǔ)料自由脹形實(shí)驗(yàn),通過在線性加載路徑條件下獲得的破裂點(diǎn)壓力值,考察補(bǔ)料量對(duì)成形能力的影響。模擬與實(shí)驗(yàn)結(jié)果表明,軸向補(bǔ)料工藝能夠提高微型管件液壓成形能力,但由于尺度效應(yīng)問題,實(shí)際成形能力受到多種因素影響,從而表現(xiàn)出顯著的工藝分散性。最后,為了考察微型管件實(shí)際成形能力,對(duì)不同尺寸的304不銹鋼微型管件,在不同補(bǔ)料量的條件下,進(jìn)行了 30%脹形率的成形實(shí)驗(yàn)以及等徑T形三通管液壓成形實(shí)驗(yàn)。成形實(shí)驗(yàn)的結(jié)果發(fā)現(xiàn),兩種管件在不同補(bǔ)料量條件下都能實(shí)現(xiàn)成形。T形管液壓成形實(shí)驗(yàn)發(fā)現(xiàn),兩種管件成形后支管最大高度過低,不足以形成完整的支管,這是由于尺度效應(yīng)使材料的應(yīng)變延伸率下降。數(shù)值模擬的結(jié)果則表明,增大補(bǔ)料量能夠改善壁厚減薄,提高成形能力,但由于摩擦力的影響,導(dǎo)致管件兩端壁厚顯著增厚。
[Abstract]:In the field of micro-electromechanical, medical devices, the demand for micro-shaped pipe fittings is increasing gradually. Hydroforming has become the focus of research because it can efficiently produce miniature special-shaped pipe fittings. Because the size of the parts is close to the grain size, the miniature pipe fittings have the problem of scale effect, and the forming ability is reduced, which restricts their development. Axial feeding technology can improve the forming ability of pipe fittings and has been widely used in the production of conventional special-shaped pipe fittings. In order to improve the forming ability of micro tube fittings, this paper introduces the axial feeding technology into hydroforming of micro pipe fittings. Firstly, the friction characteristics in the hydroforming guide zone of micro tube fittings are studied. The friction coefficient can be calculated by measuring the initial friction force and the total thrust force and according to the internal pressure and other dimension parameters. The experimental results show that the friction coefficient of 304 stainless steel pipes with external diameters 2mm and 1mm increases significantly with the reduction of size. The main reason for the friction scale effect of micro pipe fittings is that the outer surface of the pipe fittings is curved surface. The reduction of curvature radius leads to the reduction of the relative uneven degree of the die surface, which makes the storage of liquid lubricant difficult and the friction force increase. Secondly, the numerical and experimental analysis of axial feeding process is carried out. Using the GTN damage model, the flow stress of 304 stainless steel tube fittings with external diameter of 2 mm and wall thickness of 0.15mm is directly introduced into the material properties to model the micro tube fittings. At the same time, based on a large number of free bulging experiments of axial feeding, the flow stress of 304 stainless steel micro-tube fittings with external diameter of 2 mm and wall thickness of 0.15mm is directly introduced into the material properties. The influence of feeding amount on the forming capacity was investigated by the fracture point pressure value obtained under the linear loading path condition. The simulation and experimental results show that the axial feeding process can improve the hydroforming ability of micro pipe fittings, but due to the scale effect, the actual forming ability is affected by many factors, thus showing a remarkable process dispersion. Finally, in order to investigate the actual forming ability of micro tube fittings, the forming experiments of 30% bulging rate and equal diameter T-shaped three-way tube hydroforming experiments were carried out for 304 stainless steel micro-tubes with different sizes under different feeding quantities. The results of forming experiments show that the two kinds of pipe fittings can be formed under the condition of different recharge amount, and the hydroforming experiment of T-shaped tube shows that the maximum height of the branch pipe is too low to form a complete branch tube after the forming of the two kinds of pipe fittings. This is due to the reduction of the strain elongation of the material due to the scale effect. The results of numerical simulation show that the wall thickness can be improved and the forming ability can be improved by increasing the amount of feedstock, but due to the influence of friction, the wall thickness at both ends of the pipe is significantly increased.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG306

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