【作者】 王琳；

【导师】 易幼平；

【作者基本信息】 中南大学 ， 材料加工工程， 2023， 硕士

【摘要】 铝合金薄壁筒形件广泛应用于导弹弹体舱段、筒段等关键结构,具有结构尺寸大、薄壁、弱刚性等特点,是导弹弹体的核心承力构件,工作时受静力、轴弯、冲击等复杂载荷,产品三向力学性能及均匀性要求极高。环形通道转角挤压成形工艺通过两次转角挤压实现薄壁筒形件成形,可获得均匀大变形,细化晶粒组织,提高筒形件力学性能。但该工艺成形所需载荷较大,筒形件成形时易出现开裂、变形不均匀等问题,限制了其在武器装备领域的应用。针对上述问题,本文提出了一种等通量反挤压成形新工艺,并对新工艺的模具结构和工艺参数进行了有限元模拟优化,开展了优化工艺的试验研究。论文主要研究工作及成果如下:(1)提出了一种等通量反挤压成形新工艺,设计了等通量挤压通道,对比分析了不同反挤压工艺成形效果。等通量挤压通道包括通量恒定的下压段、径向挤压段和反向挤压段,下压段、径向挤压段和反向挤压段的通量逐渐减小;在顶出机构上设计分流结构,在不稳定变形区对金属导流;仿真优化了凹模转角,当转角为80mm圆角时变形较均匀、成形载荷较小。不同反挤压工艺成形仿真对比结果表明:等通量挤压通道可以使成形载荷降低26.5%,分流结构可以使成形区应变增大90%;相比于环形通道转角挤压工艺,等通量反挤压工艺成形所需载荷降低了31.5%,成形区域平均应变增加了26.7%,并且更加均匀,流线更加顺畅圆滑,无明显缺陷。(2)进行了2219铝合金薄壁筒形件反挤压成形工艺仿真模拟,探明了成形过程主要工艺参数对等通量反挤压成形工艺影响的规律,优化了成形工艺参数,揭示了成形过程中金属的流动规律。仿真结果表明:在400℃-500℃的范围内,初始成形温度越高,成形过程中凸模载荷越小,成形件应变越大,而损伤会因应变增大而增大,也受到金属塑性的影响,金属塑性越好,发生相同变形损伤越低;随着凸模下压速度增大,成形件应变和损伤都先增大后减小,而载荷先减小后增大。工艺参数优化为:坯料与模具初始成形温度为500℃,锻压机下压速度为1mm/s。在该工艺参数下,等通量反挤压成形所需载荷为505吨;获得的成形件平均应变为7.47,最大应变为62.7,成形部分应变主要在8-11之间;流线整体比较流畅,没有明显缺陷,在成形部分流线分布均匀,可以实现薄壁筒形件的高性能成形。(3)开展了2219铝合金薄壁筒形件反挤压成形工艺试验,探明了等通量挤压通道中的分流结构、径向挤压段和两个转角在成形过程中对金属的影响。试验结果表明:分流结构很大程度上消除了不稳定变形区和成形死区,使成形件获得了效果较好的流线;径向挤压段对心部晶粒影响较小,前中后三个部位平均晶粒尺分别为168μm、165μm、166μm,中部到后部小角度晶界比例从75.71%降至63.31%,中部和后部平均KAM值分别为1.46、1.37,该区域变形均匀性较好;两个转角具有明显的晶粒细化效果,第一转角使晶粒尺寸由214μm变为168μm,第二转角使晶粒尺寸由164μm变为139μm,第二转角对板条状晶粒有钝化效果,并使小角度晶界比例从63.31%增加至81.62%,中部和后部平均KAM值分别为1.89、1.79,变形均匀性变差。图57幅,表5个,参考文献82篇更多还原

【Abstract】 Aluminum alloy thin-walled cylindrical parts are widely used in missile body cabin,barrel section and other key structures,with the characteristics of large structural size,thin wall,weak rigidity and so on.It is the core load-bearing component of missile body,which is subjected to complex loads such as static force,shaft bending,impact and so on.The requirements of three-dimensional mechanical properties and uniformity of the products are extremely high.The annular channel angular extrusion process realizes the forming of thin-walled cylindrical parts by twice angular extrusion,which can obtain uniform and large deformation,refine grain structure and improve the mechanical properties of cylindrical parts.However,this process requires a large load,and it is easy to crack and uneven deformation during the forming of cylindrical parts,which limits its application in the field of weapons and equipment.In order to solve the above problems,a new process of equal flux backward extrusion is proposed in this thesis,the die structure and process parameters of the new process are simulated and optimized by finite element method,and the experimental study on the optimization process is carried out.The main research work and achievements of this paper are as follows:(1)In this thesis,a new process of equal flux backward extrusion is proposed,the equal flux extrusion channel is designed,and the forming effects of different backward extrusion processes are compared and analyzed.The equal flux extrusion channel includes the lower compression section,the radial extrusion section and the backward extrusion section with constant flux,and the flux of the lower compression section,radial extrusion section and backward extrusion section decreases gradually;the shunt structure is designed on the ejection mechanism to guide the metal in the unstable deformation zone;the rotation angle of the concave die is simulated and optimized,and the deformation is more uniform and the forming load is smaller when the corner is 80 mm fillet.The simulation results of different backward extrusion processes show that the equal flux extrusion channel can reduce the forming load by 26.5%,and the shunt structure can increase the strain in the forming zone by 90%.Compared with the annular channel corner extrusion process,the load required by the equal flux backward extrusion process is reduced by 31.5%,the average strain in the forming area is increased by 26.7%,and it is more uniform,the streamline is smoother and smooth,and there are no obvious defects.(2)The backward extrusion process simulation of 2219 aluminum alloy thin-walled cylindrical parts is carried out,the law of the influence of the main process parameters on the equal flux backward extrusion process is found out,the forming process parameters are optimized,and the change law of metal in the forming process is revealed.The simulation results show that in the range of 400 ℃-500 ℃,the higher the initial forming temperature is,the smaller the punch load is,the greater the strain of the formed part is,and the damage will increase with the increase of strain,and also affected by metal plasticity,the better the metal plasticity is,the lower the damage of the same deformation occurs;with the increase of the punch pressing speed,the strain and damage of the formed part increase at first and then decrease,while the load decreases at first and then increases.The process parameters are optimized as follows: the initial forming temperature of billet and die is 500 ℃,and the pressing speed of forging press is 1mm/s.Under this process parameters,the load required for equal flux backward extrusion is 505 t,the average strain of the forming part is7.47,the maximum strain is 62.7,and the strain of the forming part is mainly between 8 and 11.The overall streamline is relatively smooth,there are no obvious defects,and the streamline is evenly distributed in the forming part,which can realize the high performance forming of thinwalled cylindrical parts.(3)The experiments of backward extrusion of 2219 aluminum alloy thin-walled cylindrical parts are carried out to find out the effects of shunt structure,radial extrusion channel and two angles on the metal in the process of equal flux extrusion.The test results show that the shunt structure eliminates the unstable deformation zone and forming dead zone to a great extent,and makes the formed parts obtain better streamline.The radial extrusion section has little effect on the core grains.The average grain sizes of the front,middle and back parts are 168μm,165μm and166μm respectively,and the proportion of small-angle grain boundaries from the middle to the rear decreases from 75.71% to 63.31%.The average Kam values in the middle and rear are 1.46 and 1.37 respectively,and the deformation uniformity in this region is good.The two corners have obvious grain refinement effect.The first corner changes the grain size from 214μm to 168μm,the second angle makes the grain size change from164μm to 139μm,and the second angle passivates the lath grain.The proportion of small-angle grain boundary is increased from 63.31% to81.62%,the average KAM values in the middle and rear are 1.89 and 1.79 respectively,and the deformation uniformity becomes worse.更多还原