大型复杂薄壁铝合金空心型材挤压成形工艺

目的 解决大型复杂薄壁铝合金空心型材挤压过程中材料流速均匀性控制难,以及模具局部应力集中导致模具寿命低、挤压型材尺寸稳定性差的问题。方法 采用有限元模拟方法对此类典型型材挤压过程进行仿真分析,根据仿真结果中型材出口材料流速分布情况,通过调控不同部位材料流入量及材料流动阻力,并以型材出口流速差和流速均方差（SDV）作为衡量挤压过程中材料流速均匀性的指标,逐步迭代优化模具结构以提高材料流动均匀性;根据仿真结果中挤压模具应力分布情况,以模具最高应力作为衡量模具强度的指标,逐步迭代优化模具结构以减小模具应力。结果 通过迭代仿真依次优化模具工作带长度、分流孔尺寸、阻流块高度等参数,最终型材出口流速差由25.07 mm/s降至2.72 mm/s,流速均方差由9.84 mm/s降至0.72 mm/s;通过迭代仿真优化焊合角度,最终模具最高应力由945 MPa降至863 MPa。采用基于有限元仿真优化结构的挤压模具成功制备了合格的铝合金型材样件,挤压试验结果与数值模拟结果吻合。结论 通过优化模具工作带长度、分流孔尺寸及阻流块高度,调控不同部位材料流入量及材料流动阻力,能够有效解决大型复杂薄壁铝合金空心...     

Influence of the process setup on the microstructure and mechanical properties evolution in porthole die extrusion

Industrial needs are becoming always more complex pushed by an ever more demanding market and an increasingly fierce competition. Innovation and new products are the way forward if customers’ attention has to be captured. On this direction, extrusion processes can be properly designed for the manufacture of complex shape parts. Furthermore, taking into account the current requirements related to the reduction of weights and volumes for fuel saving in the automotive field, the production of components with thinner thickness is increasingly on demand. Therefore, the process complexities have been growing up but, at the same time, companies have to assure quality and productivity in a more and more competitive scenario.In this work, porthole die extrusion was investigated and an “I” shaped section with the welding line in the middle of the tongue was the chosen profile. Different extrusion conditions were experimentally analyzed by changing both the profile thickness and the ram velocity; the impact of these variables on the product quality was evaluated by microstructural observations and tensile tests. The aluminum alloy, AA6060, was the investigated material. The die optimization was carried out by numerical analyses for homogenizing the flow velocity at the die exit; the simulations were also utilized for locally calculate the pressure and temperature distributions in the die and at the exit of the bearing zone for a better explanation of the experimental evidences.A wide discussion on the obtained results is here reported.     

三孔双芯模挤压方管型材的金属流动行为分析

为了分析双芯模挤压铝型材时造成的流动不均匀以及模具结构对该类型材焊合质量的影响,采用DEFORM-3D有限元分析软件,对三孔双芯模挤压6005A铝合金方管型材的金属流动行为进行了分析.模拟结果表明,分流孔面积分布不均易造成方管型材镰刀弯缺陷,当中间分流孔与一侧分流孔的面积比值为0.93～1.03时,型材出口流速均匀、焊缝居中.焊合室高度为13～16mm时焊合良好、成形质量好.挤压力在坯料与焊合室底面碰触后急速上升,在突破模孔时达到最高值.型材出口温度受分流孔面积和焊合室高度影响较小,当坯料温度为480℃时,型材出口温度为546～548℃.在650吨卧式挤压机上进行了挤压实验,实验结果与仿真结果吻合.     

IN690合金管热挤压温升与挤压力的研究

温升和挤压力是影响钢管挤压过程的重要指标,利用热模拟实验获得了IN690合金的热加工本构关系,建立了IN690合金钢管热挤压过程的有限元模型.采用正交实验设计的仿真实验系统分析了坯料温度（T b=1000～1200℃）、挤压速度（v=20～200 mm/s）和模具预热温度（T d=300～500℃）对管材成形过程中温升...     

Simulation of bridge die extrusion using the finite element method

Abstract

This communication reviews previous work on the extrusion of hollow shapes and uses a three-dimensional (FEM) solution to predict load-required, temperature of the extrudate and material flow during the process. A comparison with experiments is made to assess the relative importance of some extrusion parameters in the extrusion process and to ensure that the numerical discretisation yields a realistic simulation of the process. The usefulness and limitations of FEM when modelling complex shapes is also discussed. Methods to assess the difficulty of extrusion of hollow extrusions in general are presented. The paper also illustrates the essentials of numerical analysis to assist the reader in the comprehension of the thermomechanical events occurring during extrusion through bridge dies. Results are presented for velocity distribution in the extrusion chamber, iso-temperature contours and pressure/ displacement traces. These are compared with experiments conducted using a 5 MN press. It is shown that the finite element program predicts the pressure requirement: the pressure/displacement trace showing a double peak which is discussed in some detail. The finite element program appears to predict all the major characteristics of the flow observed macroscopically.     

Formation of die lines during extrusion of AA6063

Abstract

The die line phenomenon during extrusion of AA 6063 has been investigated and the effects of temperature and strain rate established. The influence of die land length on the surface generated features was also determined. The results indicate that the surface formation mechanism is one of generation and modification; the surface is generated on the leading edge of the die land in the absence of oxygen and interacts thereafter with the remainder of the die land, resulting in material transfer between extrudate and die land, thus increasing the surface roughness. Two mechanisms were identified, both of which involved extrudate die land interaction. The aluminium film on the forward portion of the die land was observed to be more stable and its morphology wasfound to relate directly to the die line features. From these trials, optimum process conditions together with a minimum die land length were identified. Processing at the optimum conditions continued to generate die lines, but these were observed to be finer and less deep, and were termed ‘microdie lines’. The origin of the micro die lines was observed to stem from the structure formed by deformation and the nature of the shear zone.

MST/1108     

铝/钢搅拌摩擦焊对接焊缝组织及机理研究

为了提高Q235钢板和6082-T6铝合金对接的连接强度,采用搅拌摩擦焊进行对接焊接.研究了不同尺寸和形状的搅拌头、转速、焊接速度和偏移量等对铝钢对接焊缝组织的影响,进而优化了搅拌摩擦焊工艺.实验结果表明:不同形状的搅拌头影响接头"钉子"形状,接头的不同位置处由于受到不同热循环和搅拌导致晶粒尺寸不同,从而影响接头的力学性能.当搅拌针旋转速度260 r/min,焊接速度16 mm/min,针头偏向铝侧0.2 mm时,所得焊缝的拉伸强度为141.204 MPa,为最佳工艺参数.在此最优参数下获得过渡层的厚度约为8μm,界面的主要成分是Fe Al3.     

7075铝合金高速搅拌摩擦焊材料流动行为及性能研究

目的 针对7075–O铝合金高焊速、高转速搅拌摩擦焊接缺陷多、质量差等问题,研究焊接接头材料流动对焊缝性能的影响。方法 选用焊接速度1 000 mm/min,搅拌转速分别为1 000、1 200、1 600、1 700 r/min的条件对7075–O铝合金板进行搅拌摩擦焊接,分析不同焊接工艺参数下焊接接头的显微组织及力学性能。同时,利用Fluent软件模拟7075–O铝合金搅拌摩擦焊接过程中的材料流动场分布,分析焊接材料流动与缺陷形成的关系。结果 利用7075–O铝合金三维流动模型,预测出高焊速条件下焊缝前进侧形成一个低压区,孔洞等缺陷易出现在此区域,数值模拟预测与试验结果吻合。在高焊接速度1 000 mm/min、焊接转速1 200 r/min时,焊缝表面光滑平整,焊核区域的硬度分布更加均匀。结论 随着搅拌转速从1 000 r/min增大到1 700 r/min,热输入量逐渐增大,孔洞缺陷由隧道型孔洞转变为不连续的小孔。同时,随着搅拌转速的增大,焊缝高硬度区域的宽度先增大而后降低。当搅拌转速为1 200 r/min时得到了优质的焊接接头,焊缝焊核区硬度分布均匀,硬度值最高为176HV。     

VARIATION OF PRESSURE WITH RAM SPEED AND DIE PROFILE IN HOT EXTRUSION OF ALUMINUM-6063

Prediction of extrusion pressure, especially in the case of complex die geometries, is an area of continued research interest. Die complexity, usually defined by “shape factor” (the ratio of the perimeter to the cross-sectional area of the profile), critically affects the flow of metal and the pressure required to extrude a given product. Applied strain rate (related directly to the ram speed of the extrusion press) also alters the product quality significantly. The current paper presents results of an ongoing study about effects of ram speed and die profile on extrusion pressure. Experiments were conducted using dies of different complexity to track the effects of ram speed variation and changing die profiles on extrusion pressure. Al-6063, the most popular commercial variety of structural aluminum, was used as the billet material for all experiments.     

异种铝合金MIG焊工艺研究

目的 研究汽车用铸铝和铝型材MIG焊接头质量特性.方法 对铸铝AlSi10MnMg和铝型材6005A-T6进行MIG搭接焊,探讨焊接速度对焊缝成形的影响规律,研究接头的显微组织.结果 其他焊接参数相同,焊接速度为4 mm/s时,易导致压铸铝合金产生氢气孔.MIG搭接焊接接头型材和铸材的熔合区晶界均有不同程度的粗化,铸材...     

三基发射药单螺杆压伸模具流场仿真及实验验证

为了实现三基发射药生产工艺中的连续化压伸,同时避免模具内部螺旋状流道造成的三基发射药成型的质量和安全问题,应用ANSYS软件模拟了发射药物料在模具内的挤压过程及模针的受力情况。分析了收缩角、出料方向和模具结构对物料在模具中的温度、模具壁面压力、模针表面受力和物料出料速度分布的影响规律,并通过实验进行了验证。结果表明:模具收缩角越大,模具内压力越大,物料温度也越高,且越容易形成热点,同时模针外表面受到的挤压力和摩擦力也越大,模针越容易出现变形和断裂;竖直挤出过程中,模具壁面压力及模针受力均远大于水平挤出中的相应参数,且容易造成挤出后物料的弯曲;增加多孔板有利于物料在挤出模具中的整流和取向,大幅减少物料的径向流动,降低模针在挤出过程中的受力,且成型质量更好。     

Numerical investigation of an arc inlet structure extrusion die for large hollow sections

This paper aims to improve the working life of extrusion dies by optimal structure design, which plays an important role in mass production. First, an arc-shaped inlet die structure for an aluminum large-hollow-section profile was developed. Second, a three-dimensional finite-element model of the porthole extrusion process was established using an arbitrary Lagrangian-Eulerian method. Third, the comparison of the formability was analyzed and discussed, including the diversity of extrusion forces and uniformity properties between the proposed design and two traditional design schemes using the same extrusion process. A group of square-profile extrusion dies was used to set up a L16_4_3 orthogonal experimental scheme, considering the side length of profiles, L, with four levels, 110, 100, 90, and 80 mm; inlet angles, α, of the porthole bridge of 0°, 10°, 20°, and 30°; and profile wall thicknesses, t, of 1, 1.5, 2, and 2.5 mm. The results of the orthogonal tests were similar to those of the actual production die model. Two different analysis models reached the same conclusion: the inlet angle or the arc inlet structure has a small effect on the metal flow and the forming distribution, but the arc inlet structure can alleviate the stress load of the dies. The die testing and production validation results indicate that the novel structural design of the arc inlet die will have a long working life.     

FEM analysis to predict development of structure during extrusion and subsequent solution soak cycle

Abstract

Materials which form the surface and subcutaneous layers of an extrudate experience large deformations when they traverse the die land, which, added to the inhomogeneous caused by the dead metal zone, leads to considerable modifications to the deformation parameters when compared with the remainder of the extrusion. The distribution of structure is therefore greatly inhomogeneous. Reference to both empirical and physical models of the recrystallisation process indicates that nucleation and growth will differ at these locations in those alloys that are usually solution treated and aged subsequent to the deformation process. Since static recrystallisation (SRX) has a significant influence on many of the properties of the extrudate, it is therefore essential to provide the methodology to predict these variations. In the present work, a physical model based on dislocation density, subgrain size and misorientation is modified and integrated into the commercial FEM codes, FORGE2 and FORGE3 to study the changes of the microstructure. Axisymmetrical and shape extrusion are presented as examples. The evolution of the substructure influencing SRX is studied. The metallurgical behaviours of axisymmetric extrusion and that of shape extrusion are compared. The predicted results show an agreement with the experimental measurement. The distribution of equivalent strain, temperature compensated strain rate and temperatures is also presented to aid in interpretation. Importantly the properties of hard alloys improve with the increase in the temperature of the extrusion. This phenomenon is discussed and theoretically justified.     

凸模结构对大截面带筋方筒件挤压力的影响研究

目的 解决大截面铝合金带筋方筒构件在反挤压过程中成形力大的难题,实现在3 000 t压力机下成功制备内孔为665 mm×665 mm的大截面带筋方筒形构件。方法 提出了一种使用新型棱台凸模结构代替平凸模结构的方法,用主应力法得出了棱台凸模结构与平凸模结构的挤压力计算公式,对比分析了2种凸模结构反挤压成形力的大小,并用DEFORM有限元软件模拟分析了不同结构参数下的棱台凸模反挤压过程,最终进行工程试制,验证了反挤压工艺的可行性。结果 通过主应力法得出了方筒形件的变形力计算公式,得出棱台凸模结构反挤压成形力小于平凸模结构反挤压成形力,经模拟分析得出在反挤压过程中棱台凸模结构的最优结构参数为棱台斜角15°、棱台高度40 mm,并在3 000 t压力机上成功制得内孔为665 mm×665 mm的大截面带筋方筒形构件。结论 通过数值模拟分析可知,与采用平凸模结构相比,采用棱台凸模结构时的反挤压成形力降低了约13%,同时减少了挤压变形过程中的金属流动“死区”。经实验验证,在3 000 t压力机上成形了内孔为665 mm×665 mm的大截面带筋方筒形构件,实现了省力挤压。     

Continuous resistance welding of thermoplastic composites: Modelling of heat generation and heat transfer

A process model composed of electrical and heat transfer models was developed to simulate continuous resistance welding of thermoplastic composites. Glass fabric reinforced polyphenylenesulfide welded in a lap-shear configuration with a stainless steel mesh as the heating element was considered for modelling and experimental validation of the numerical results. The welding temperatures predicted by the model showed good agreement with the experimental results. Welding input power and welding speed were found to be the two most important parameters influencing the welding temperature. The contact quality between the electrical connectors and the heating element was found to influence the distribution of the welding temperature transverse to the welding direction. Moreover, the size of the electrical connectors was found to influence the achievable welding speed and required power input for a certain welding temperature.     

A study of surface fracture in paste extrusion using signal processing

Gross circumferential fracture (GCF) is a surface defect sometimes observed during the extrusion of particulate pastes. In this study particular attention was paid to the frequency of fracture in pastes undergoing ram extrusion through dies with circular, square and rectangular slot cross section. Three methods for estimating the fracture frequency were employed. The first was determined from the observed fracture periodicity, the second was determined from the application of short time Fourier transformation (STFT) techniques to the pressure signal measured at the die plate and the third was the application of the geometrical result first reported by Domanti and Bridgwater (2000). All were found to be in agreement within experimental error where failure was observed. In some materials the fracture frequency was still observed in the frequency domain after fracture ceased in the extrudate, indicating the existence of a flow instability in the paste: if the extrudate was smooth throughout the process STFT detected no peak. Fracture was more pronounced with short dies and/or where the paste experienced high wall shear stress. Square dies were more prone to fracture than circular dies (corner effects) and the fracture spacing could be related directly to the hydraulic diameter. Rectangular slot dies were more prone to irregular fracture. It was shown that lowering the die wall friction by using Teflon-lined dies reduced the propensity of the paste to fracture for all die geometries tested.     

Metal flow behaviour of wide flat bar in the spreading extrusion process

Abstract

To examine metal flow behaviour experimentally in the spreading extrusion process, a round billet is spread by means of a spread ring and extruded through a die opening wider than the internal diameter of the container. In spreading extrusion, the extrusion load is reduced by about 30% in comparison with basic extrusion. However, the metal flow balance in spreading extrusion worsens, because of the high frictional force generated at the interface of the billet and spread ring during the filling process. When the profile is wide or when spread ring height is low, the geometry of the plastic deformation zone on the die face changes from an ellipse into a figure of eight at the wide zone at both ends of the die opening. As a result, the metal flow balance markedly worsens, due to an increase in the size of the plastic deformation zone and frictional resistance acting on the spread ring wall.     

颤振激励条件下的反挤压有限元模拟分析

目的 针对“难成形零件”提出的电液颤振挤压成形技术,理论研究颤振对冷挤压成形的影响规律。方法 通过离散化处理颤振速度,对挤压筒和顶杆分别施加颤振激励,利用DEFORM-3D软件有限元模拟,分析比较不同颤振激励下的行程载荷、摩擦力、速度场和应力应变场。结果 在挤压成形过程中,材料流动规律会由于颤振激励的存在而发生改变,在局部区域,材料流动速度较传统挤压时有较大提高;当颤振最大速度小于挤压速度时,颤振对挤压力、摩擦力、等效应力和等效应变的影响并不显著,当颤振最大速度大于挤压速度时,颤振可降低挤压力与摩擦力,改变等效应力和应变分布,但并不影响最大等效应力值。结论 颤振激励影响材料流动规律,对挤压力、摩擦力和应力应变场的影响存在一个拐点,为电液颤振冷挤压成形技术的推广应用提供了一定理论依据。     

凹模转动挤压成形过程的有限元分析

降低能耗及提高制品性能是当前挤压加工技术领域的一个共性问题,采用数值模拟方法对转模挤压成形过程进行研究,结果表明:随着凹模转速的增加,塑性区范围显著地扩大,转速由0增加到0.314 rad/s时,挤出速度均值增大了1.5倍,成形载荷极值降幅达40%;当挤压速度由0.157 mm/s增大至0.628 mm/s时,挤压载荷峰值增大了38.6%,挤出速度均值增大了1倍.当其他条件不变时,应综合考虑挤压速度及凹模转速之间数值的合理匹配关系.     

变论域模糊PID控制微流挤出型3D打印机的挤压力研究

为了提高微流挤出型3D打印机的打印精度，针对其挤压力控制在挤出成型过程中存在时变性和非线性等典型特性，基于挤压力模型分析打印材料的挤出成型过程，并提出了一种变论域模糊PID（proportion integration differentiation，比例积分微分）控制策略，以实现挤出成型过程中挤压力不规律变化时的快速调节功能。同时，利用MATLAB软件建立挤压力控制系统仿真模型以开展不同控制策略的仿真分析，并利用自主搭建的实验平台进行实物打印，以验证所提出控制策略的可行性。仿真和实验结果表明，变论域模糊PID控制策略对改善成型坯体表面质量和提高成型精度有显著效果。所提出的变论域模糊PID控制策略可为挤出型3D打印机挤压力的稳定控制提供一定参考，也可为类似时变和非线性控制系统提供一定的借鉴。