本文選題：鎂合金 + 靜液擠壓　； 參考：《南京理工大學》2017年碩士論文

【摘要】：鎂合金密度低、比強度高、散熱性和減振性好等特性,在輕量化的結(jié)構(gòu)中使用越來越廣。但其本身塑性差,在塑性成形方面不理想,靜液擠壓常用于加工塑性差的材料。文章采用靜液擠壓的方法研究了管材、棒材和型材的成形。管材成形采用后置模芯和前置穿孔針兩種方式,穿孔針分為隨動式和固定式兩種結(jié)構(gòu)。后置模芯方式中,模芯角度120°比105°需要的擠壓力大,擠壓力與擠壓比的自然對數(shù)呈一定的線性關(guān)系,擠壓筒溫度升高可減小擠壓力,但減小幅度與模具結(jié)構(gòu)有關(guān);材料流速在模芯處劇烈變化,通過剖視圖可看出坯料中間流速快。兩種帶穿孔針的方式中,擠壓比為1.3時,隨動式所需的擠壓力小。成形中坯料內(nèi)部應力,隨動式最大值191MPa,固定式214MPa。棒材成形先后研究了單孔和多孔模具的成形方法。單孔模具兼顧錐形模和平面模的特點,采用帶平臺的錐形模結(jié)構(gòu)。通過正交試驗確定擠壓比為16,模具錐角75°,平臺長度2.5mm和定徑帶長度8mm的設計方案。多孔模具在擠壓比為12條件下,發(fā)現(xiàn)兩孔,三孔及四孔的設計對擠壓力和模具剛強度的影響較小。然后針對四孔模具,發(fā)現(xiàn)影響擠壓力最大的是模具溫度,其后是模具入口形狀,對流速均勻性影響最大的是�？椎牟贾�,其次是模具入口形狀,綜合兩者確定模孔同心圓直徑26mm,模具入口形狀為帶導流室結(jié)構(gòu),定徑帶6mm,模具溫度290℃。靜液擠壓槽型材時,模具設計的關(guān)鍵是使制品同一截面的流速均勻。在擠壓比為16的情況下,選用帶導流室的模具結(jié)構(gòu),對其結(jié)構(gòu)尺寸采用神經(jīng)網(wǎng)絡遺傳算法進行優(yōu)化以達到流速均勻的目標,流速均方差優(yōu)化前后分別為1.03mm/s和0.0674mm/s。型材模具較復雜,對其進行剛強度和磨損的分析,模具受力滿足材料要求,磨損主要分析模具硬度和接觸摩擦因子的影響。
[Abstract]:Magnesium alloys are widely used in lightweight structures due to their low density, high specific strength, good heat dissipation and vibration absorption. But it is poor in plasticity and not ideal in plastic forming. Hydrostatic extrusion is often used to process materials with poor plasticity. The forming of pipe, bar and profile was studied by hydrostatic extrusion. Tube forming adopts two ways: post die core and pre-piercing pin. The perforating pin is divided into two kinds of structure: follower type and fixed type. In the post-core mode, the extrusion pressure required by the die core angle of 120 擄is greater than that of 105 擄, and the natural logarithm of extrusion ratio is linearly related to the extrusion pressure. The extrusion pressure can be reduced by increasing the temperature of the extrusion tube, but the decrease is related to the structure of the die. The material flow rate changes dramatically at the core of the die, and it can be seen from the dissection diagram that the intermediate velocity of the blank is fast. When the extrusion ratio is 1.3, the extrusion force required by the follower is small. In forming, the internal stress of the blank is the maximum value of 191 MPa and the fixed type of 214MPa. The forming methods of single hole and porous die have been studied successively in bar forming. The single hole die has the characteristics of both conical die and plane die, and adopts the conical die structure with platform. The design scheme of extrusion ratio is 16, die cone angle is 75 擄, platform length 2.5mm and diameter band length 8mm are determined by orthogonal test. When the extrusion ratio is 12, it is found that the design of two holes, three holes and four holes has little effect on the extrusion pressure and the rigid strength of the die. Then, for the four-hole mould, it was found that the mold temperature had the greatest influence on the extrusion pressure, the mold inlet shape was followed by the mold inlet shape, the layout of the die hole was the most important to the uniformity of the flow rate, and the next was the mold inlet shape. The diameter of the concentric circle of the die hole is 26mm, the inlet shape of the die is the structure of a flow guide chamber, the diameter of the die is 6 mm and the temperature of the die is 290 鈩，

本文編號：2060213