镁合金静液挤压和模具结构设计研究

发布时间：2018-06-24 05:22

  本文选题：镁合金 + 静液挤压　； 参考：《南京理工大学》2017年硕士论文

【摘要】：镁合金密度低、比强度高、散热性和减振性好等特性,在轻量化的结构中使用越来越广。但其本身塑性差,在塑性成形方面不理想,静液挤压常用于加工塑性差的材料。文章采用静液挤压的方法研究了管材、棒材和型材的成形。管材成形采用后置模芯和前置穿孔针两种方式,穿孔针分为随动式和固定式两种结构。后置模芯方式中,模芯角度120°比105°需要的挤压力大,挤压力与挤压比的自然对数呈一定的线性关系,挤压筒温度升高可减小挤压力,但减小幅度与模具结构有关;材料流速在模芯处剧烈变化,通过剖视图可看出坯料中间流速快。两种带穿孔针的方式中,挤压比为1.3时,随动式所需的挤压力小。成形中坯料内部应力,随动式最大值191MPa,固定式214MPa。棒材成形先后研究了单孔和多孔模具的成形方法。单孔模具兼顾锥形模和平面模的特点,采用带平台的锥形模结构。通过正交试验确定挤压比为16,模具锥角75°,平台长度2.5mm和定径带长度8mm的设计方案。多孔模具在挤压比为12条件下,发现两孔,三孔及四孔的设计对挤压力和模具刚强度的影响较小。然后针对四孔模具,发现影响挤压力最大的是模具温度,其后是模具入口形状,对流速均匀性影响最大的是模孔的布置,其次是模具入口形状,综合两者确定模孔同心圆直径26mm,模具入口形状为带导流室结构,定径带6mm,模具温度290℃。静液挤压槽型材时,模具设计的关键是使制品同一截面的流速均匀。在挤压比为16的情况下,选用带导流室的模具结构,对其结构尺寸采用神经网络遗传算法进行优化以达到流速均匀的目标,流速均方差优化前后分别为1.03mm/s和0.0674mm/s。型材模具较复杂,对其进行刚强度和磨损的分析,模具受力满足材料要求,磨损主要分析模具硬度和接触摩擦因子的影响。
[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 掳is greater than that of 105 掳, 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 掳, 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，

本文编号：2060213