粘性介质反向压力胀形对5A02铝合金板成形性的影响

粘性介质压力成形(ViscousPressureForming,VPF)是一种适合于难变形材料板金零件制造的软模成形工艺。采用粘性介质胀形实验研究了反向压力对5A02铝合金板料成形性能的影响,结果表明在一定范围内的反向压力有利于抑制板料的平面各向异性,而在更高的反向压力条件下板料具有更好的成形性。     

板料粘性介质胀形过程应变速率变化的模拟研究

采用半固态、具有应变速率敏感性的粘性介质作为板料软模成形传力介质, 这种粘性传力介质的抗力可随板料发生局部变形而迅速增加, 建立起适应于板料变形的压力, 对提高板料成形性十分有益。本文针对板料粘性介质胀形, 采用有限元模拟方法研究了板料与介质应变速率变化, 模拟结果显示介质应变速率与相接触的板料应变速率是一致的, 解释了粘性传力介质变形抗力 “自适应”于板料变形的原因。     

Effects of process parameters on warm and electromagnetic hybrid forming of magnesium alloy sheets

As the lightest structural metal, magnesium (Mg) is attracting increasing interest from both the industrial and academic fields. Magnesium alloy parts are mainly processed by die casting due to their poor sheet formability at room temperature. Warm forming is a popular method of forming; Mg alloy sheets produced in this manner show excellent formability around 200-400 °C. Electromagnetic forming (EMF) can improve the formability of metal sheets without the need for lubricants. In this paper, a new approach, called warm and electromagnetic hybrid forming (WEMF), is presented. The effects of voltage, capacity, and temperature on the bulging height of Mg alloy sheets are investigated. Results show that the bulging height of Mg sheets increases with moderate discharging energies. Enhancing the discharging voltage is also a more efficient method for increasing bulging height compared to simply increasing the capacity. When the discharging energy is kept constant, the bulging height first decreases (<150 °C) and then increases (>150 °C) from room temperature to 230 °C. The formability of Mg alloy sheets improves with increasing temperature, while the forming efficiency of WEMF decreases under similar conditions.     

板材软模成形过程有限元与无网格伽辽金法耦合的数值分析(英文)

提出一种板材变形和软模体积变形耦合的数值分析方法。基于更新的拉格朗日(UL)列式,板材的弹塑性变形采用有限元法(FEM)分析,软模的体积变形采用无网格伽辽金法(EFGM)分析,板材和软模之间的摩擦接触通过罚函数法来处理。利用开发的有限元-无网格法耦合算法程序(CDSB-FEM-EFGM)分析板材弹性软模胀形过程。同有限元软件DEFORM-2D得到的数值解以及实验结果相比,验证了所开发程序的有效性。这种方法为分析板材软模成形提供了一种适合的数值方法。     

Viscous warm pressure bulging process of AZ31B magnesium alloy with different ellipticity dies

Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging (VWPB) of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram (FLD) of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.     

Deformation behavior of TC 1 titanium alloy sheet under double-sided pressure

In order to investigate the influence of normal stress through thickness on the formability of sheet metal, the viscous pressure bulge（VPB） tests of an annealed TC1 titanium alloy sheet were carried out under two different conditions： double-sided pressure bulging and conventional single-sided pressure bulging. The automated strain analysis, measurement environment （ASAME） and scanning electron microscope（SEM） were used to study the strain distributions and the fracture morphology of bulged specimens. It is found that thickness strain is increased for double-sided pressure bulging specimens, and the limiting dome height（LDH） of double-sided pressure bulging specimens is increased by 31.8% compared with conventional single-sided pressure bulging specimens. The dimples in fracture surface for double-sided pressure bulging specimens are larger and deeper than those for conventional single-sided pressure bulging specimens. The results indicate that normal stress through thickness is helpful in improving the formability of titanium alloy sheet metal.     

Electro-hydraulic forming of sheet metals: Free-forming vs. conical-die forming

This work builds upon our recent advances in quantifying high-rate deformation behavior of sheet metals, during electro-hydraulic forming (EHF), using high-speed imaging and digital image correlation techniques. Aluminum alloy AA5182-O and DP600 steel sheets (1 mm thick, ∼152 mm diameter) were EHF deformed by high-energy (up to ∼34 kJ) pressure-pulse in an open die (free-forming) and inside a conical die. The deformation history (velocity, strain, strain-rate, and strain-path) at the apex of the formed domes was quantified and analyzed. The data shows that the use of a die in the EHF process resulted in an amplification, relative to free-forming conditions, of the out-of-plane normal velocity and in-plane strain-rate at the dome apex. This amplification is attributed to the focusing action of the die on account of its conical geometry. Further, while the strain-path at the dome apex was generally linear and proportional, the use of a die resulted in greater strain at the apex relative to the strain during free-forming. The sheet deformation profile in the EHF process was found to be different from that previously observed in electromagnetic forming (EMF) and, thus, the two processes are expected to result in different strain-paths and formability. It is anticipated that quantitative information of the sheet deformation history, made possible by the experimental technique developed in this work, will improve our understanding of the roles of strain-rate and sheet-die interactions in enhancing the sheet metal formability during high-rate forming.     

Flexible die drawing of magnesium alloy sheet by superimposing ultrasonic vibration

Combining solid granule medium forming technology with ultrasonic vibration plastic forming technology, ultrasonic vibration granule medium forming (UGMF) technology was proposed. To reveal the effect of ultrasonic vibration on flexible-die deep drawing, an ultrasonic vibration with a frequency of 20 kHz and a maximum output of 1.5 kW was on the solid granule medium deep drawing of AZ31B magnesium alloy sheet. The results revealed that ultrasonic vibration promotes the pressure transmission performance of the granule medium and the formability of the sheet. The forming load declines with the ultrasonic amplitude during the drawing process as a result of the combined influence of the “surface effect” and the “softening” of the “volume effect”.     

Effect of pressurization profile on the deformation characteristics of fine-grained AZ31B Mg alloy sheet during gas blow forming

The deformation characteristics of a 0.6 mm-thick, fine-grained AZ31B Mg alloy sheet were investigated with the intention of reducing forming time during gas blow forming. The sheets were successfully deformed into hemispherical domes at 300, 370, and 420 °C under various pressurization profiles. The results show that the proposed pressurization profiles could achieve the goal of reducing forming time. A stepwise pressurization profile may be a suitable process at lower temperatures, whereas a constant or near constant pressure imposed during forming is a better method at higher temperatures. The pressurization profiles used in this study were not restricted to providing the optimum constant strain rate, which is often used in the traditional superplastic forming. Under the proposed pressurization profiles, maximum stress in the range of 23.5–45.6 MPa and resultant average strain rate in the range of 6.63 × 10⁻³ to 1.56 × 10⁻² s⁻¹ were imposed on the deforming sheet at the apex of the dome. The pressurization profile might not be one of the major factors influencing formability at the same forming temperature but it can significantly affect the forming time. Deviation of the bulged shape from the perfect sphere shape increased with increasing forming temperature.     

Numerical simulation of influence of viscous adhesive stress on viscous pressure bulging process of hemispherical sphere

1　INTRODUCTIONViscouspressureforming(VPF)isanewdevel opedtechnologyforsheetmetalflexibleforming ,whichusesakindofsemi solid ,flowableandviscousmediumaspressure carryingmedium[15] .Sheetmet alisaffectednotonlybynormalpressureofviscousmediumbutalsobytangentadhesivestressofviscousmediuminVPFprocess.Theactionofviscousmedi umonsheetmetalimprovessheetmetalformability .Itcanpostponelocalneckinginthesheetmetalandcanmakethethicknessdistributeuniformly[6 9] .Theviscosityofviscousmediumisoneofth…     

Experimental characterization of sheet metal deformation during electro-hydraulic forming

A novel experimental technique, that combines high-speed imaging and digital image correlation techniques, has been developed and applied to investigate the high-rate deformation behavior of aluminum sheet during electro-hydraulic forming (EHF). Aluminum alloy AA5182-O sheets (1 mm thick and ∼152 mm diameter) were EHF deformed by high-energy (up to ∼21 kJ) pressure-pulse and the time-evolution of sheet-displacement, velocity, strain and strain-rate quantified. The data shows that different locations on the sheet undergo unique deformation history that is not apparent from the conventional post-mortem strain measurement (using etched circle/grid pattern) approach. Under the experimental conditions used in this work, the sheets were formed into domes and the maximum strain-rate observed was ∼664/s. Further, this maximum strain-rate was observed at an off-apex location and was ∼2.5 times greater than the maximum strain-rate at the dome apex. The maximum velocity observed was ∼100 m/s and the velocity-time data showed evidence of pressure-wave reverberations during the forming process. We believe that knowledge of such time-evolution of sheet deformation is necessary for a better understanding and accurate modeling of sheet formability that has often been reported to exceed quasi-static forming limits under high-rate forming conditions.     

铝合金圆锥形零件粘性介质温成形研究

采用热力耦合有限元数值模拟方法对铝合金圆锥形零件粘性介质温成形过程进行了模拟分析,研究了成形过程粘性介质和板材的温度分布、不同温度条件下成形零件壁厚分布、成形载荷等.结果表明,圆锥形零件的底部圆角区域为成形危险区域.非等温粘性介质温成形过程中,在粘性介质内部形成的非均匀温度场影响了板材的温度分布.当粘性介质温度略低于板材温度时,坯料中心区域温度较低,有利于延迟底部圆角成形时的破裂,提高了零件壁厚的均匀性.分别进行了室温和加热时铝合金圆锥形零件粘性介质压力成形试验,试验结果与数值模拟具有相同的规律.     

半球形件粘性压力成形的实验研究

本文对半球形件的粘性介质胀形进行了实验研究。充分利用实验设备的特点 ,分析了背压、介质排放口等粘性压力成形中的工艺参数对板材成形性能的影响。实验结果表明 ,粘性压力成形中背压及介质排放口分布的变化可以引起模腔中介质压力场的变化 ,在板材表面形成不同的压力分布 ,进而改变了板料的流动模式及应力状态 ,选取合适的背压及介质排放口的分布可以改善板材的成形性能     

Experimental Observations of Quasi-Static-Dynamic Formability in Biaxially Strained AA5052-O

To establish the efficacy of electromagnetically assisted sheet metal stamping (EMAS), a series of combined hydraulic bulging and electromagnetic forming (EMF) experiments are presented to evaluate the biaxial quasi-static-dynamic formability of an aluminum alloy (AA5052-O) sheet material. Data on formability are plotted in principal strain space and show an enhanced biaxial formability beyond the corresponding experimental results from conventional forming limit diagram. The plastic strains produced by the combined process are a little larger than or at least similar with those obtained in the fully dynamic EMF process. In addition, the biaxial forming limits of aluminum sheets undergoing both very low and high quasi-static prestraining are almost similar in quasi-static-dynamic bulging process. Limit formability seems to depend largely on the high-velocity loading condition as dictated by EMF. It appears that in quasi-static-dynamic forming, quasi-static loading is not of primary importance to the material’s formability. Based on these observations, one may be able to develop forming operations that take advantage of this formability improvement of quasi-static-dynamic deformation. Also, this could enable the use of a quasi-static preform fairly close to the quasi-static material limits for the design of an EMAS process.     

超声振动效应对TA2钛合金板材力学及胀形性能影响

针对钛合金板材塑性变形能力差的问题,进行了超声振动辅助成形工艺的研究,分析超声振动对钛合金TA2板材力学性能及与接触面之间摩擦系数的影响。在此基础上进行了不同宽长比坯料的超声振动辅助胀形实验,分析超声振动对TA2板材胀形力、极限胀形高度的影响。同时,基于网格应变原理,通过不同宽长比坯料极限应变的测量,建立TA2板材的成形极限图。研究结果表明,选择合适的超声振动辅助成形工艺参数, 不仅可以提高TA2板材变形能力,还可以减小摩擦对板材成形性能的影响,从而有效提高了TA2板材的成形极限。     

Improving formability due to an enhancement of sealing limits caused by using a smart fluid as active fluid medium for hydroforming

Within this paper a new approach to enhance the process window in sheet metal hydroforming processes will be presented. The key idea of the technology is the local adaption of the properties of the active fluid medium. In this case the magnetorheological fluid (MRF) Basonetic^® 5030 is used and the fluid behavior is changed due to a partially applied external magnetic field. Based on the new property distribution the medium can be used as forming and sealing medium at the same time. The results are compared to the values reached with mineral oil. The presented work covers all necessary steps for a successful application of the technology. After the presentation of the used fluids, a material characterization and the tools, which are developed for this reason, as the sealing limits for two different configurations are determined. Based on these investigations forming operations are carried out at the related process parameters to show up the potential of the MRF. At the end a numerical model is built up and validated for both fluids used to offer a qualified tool for process design.     

DC04钢板胀形-渐进复合成形锥形件成形能力的实验研究

为了提高渐进成形过程中板料的成形极限和加工效率,提出了胀形-渐进成形的复合成形方法,通过胀形-渐进成形复合成形锥形件实验,研究了DC04钢板胀形-渐进成形复合成形锥形件和纯渐进成形锥形件的成形极限角和应变变化以及壁厚分布规律。结果表明:预成形高度为h=15 mm和h=25 mm时,复合成形零件的成形极限角分别为α极=66°和α极=69°;采用胀形-渐进成形复合成形锥形件,当胀形的最大减薄量发生在局部渐进成形区内,并且胀形和渐进成形的最大减薄量位置方向相反时,锥形件壁厚趋于均匀,提高了胀形-渐进成形的复合成形能力。     

基于固体颗粒介质的板材软模成形工艺

选用非金属颗粒(NMG)作为研究对象,通过体积压缩试验和NMG在高应力水平下的物理性能试验,得到NMG体积压缩曲线和扩展的Drucker-Prager线性模型参数;通过摩擦强度试验,得到NMG的Mohr-Coulomb模型参数,并与扩展的Drucker-Prager线性模型参数比对基本吻合;测定了NMG与板材在不同正压力下的摩擦因数曲线。以材料性能试验为基础,对基于固体颗粒介质的板材软模成形工艺进行数值分析;设计制造固体颗粒介质板材成形试验模具,成功制出抛物线形零件。结果表明：固体颗粒介质与板材表面作用所表现出的显著摩擦性能,可以极大限度地发挥板料的成形性能;其工艺控制简便,模具结构简单;成形工件具有表面质量好、贴模性好、精度高等优点,为板材的加工和制备提供了新的方法和手段。     

不等厚高强钢激光拼焊板焊缝组织及胀形性能分析

采用激光焊接方法,针对1.8mm厚的SAPH440与2.2mm厚的DP600高强钢实施激光拼焊.测试了不等厚拼焊板焊接接头的金相组织以及显微硬度,然后通过杯突试验对所得到的不等厚高强钢拼焊板的胀形性进行了研究,进一步与母材的胀形性相比较.结果表明,焊缝的金相组织为针状铁素体和板条马氏体,焊缝两侧硬度分布不同,焊缝处的硬度要高于母材.拼焊板的杯突值低于任何一侧母材的杯突值,焊缝的位置对不等厚拼焊板的胀形性有一定的影响,薄板所占比例越大拼焊板的胀形性越好,在胀形成形过程中焊缝向厚板侧移动.     

金属板料幂指型硬化模型应变强化系数K值研究

应变强化指数n值因同时体现金属板料胀形、压延等成形性能优劣,甚至与材料的宏观断裂和疲劳特性也存在一定关系,故已成为评价其冲压成形性能的主要材料参数而获得广泛关注。而幂指型硬化模型的另一重要参数——强化系数K值,前期研究虽表明其对板料的冲压成形性能也有重要影响,但目前对其在冲压成形性方面的研究甚少。文章以金属板料单向拉伸塑性失稳点特性为基础,结合硬化模型在该点附近较好地与板料真实应力-应变曲线相符合的基本假设,详细推导了K值与抗拉强度σb和n值之间解析关系,并基于该解析关系讨论了K值与n值在评价板料成形性能方面的一致性。结果表明,K值可作为衡量板料成形性能的综合指标,为研究金属板料成形能力评价方法打开了新的思路。通过实验证明了该解析结果的正确性及其工程适用性。