Experimental and numerical investigation of anisotropic yield criteria for warm deep drawing of Ti–6Al–4V alloy

Accuracy of the finite element simulation of sheet metal forming is significantly dependent on the correctness of input properties and appropriate selection of material models. In this work, anisotropic yield criteria namely, Hill 1948, Barlat 1989, Barlat 1996, Barlat 2000 and Cazacu Barlat have been implemented for Ti–6Al–4V alloy at 400 °C. Material constants required for the yield criteria have been determined and deformation behavior in deep drawing process has been analyzed in finite element software. Also, deep drawing experiments on Ti–6Al–4V alloy have been performed at 400 °C to validate finite element simulation results. Further, comparison of yield criteria based on thickness distribution, earing profile, complexity in material parameter identification and computational time has shown Cazacu-Barlat to be well suited for deep drawing of Ti–6Al–4V alloy.     

An experimental investigation of forming load and side-wall thickness obtained by a new deep drawing die

Deep drawing is an important process used for producing cups from sheet metal in large quantities. The deep drawing process is affected by many variables such as blank shape, punch and die radii, material’s formability characteristics, and many more. In order to obtain optimal process parameters with regard to part geometry, the blank and die geometry are particularly important factors. In this study, we investigated the effects of blank holder and die shapes, using six different blank holder and die shapes. We measured the distribution of blank holder force (BHF), the forming load at different drawing depths as well as thickness reduction of cup wall thickness for each set of die and punch geometries. The experimental study shows that the angle of blank and die surface influence the forming load and blank holder force distribution. Deep drawing dies with matrix and blank holder angle designed in this study provided deep drawing ratios that are about 25 % larger than those that usually can be obtained by a conventional die.     

Formability of two aluminium alloys

Abstract

The suitability of two recently developed aluminium alloys (an Al–Mg–Mn alloy and an Al–Li–Cu alloy) for press forming applications has been examined. The characterisation involved the experimental determination of microstructural aspects, tensile properties, and formability parameters such as average plastic strain ratio and planar anisotropy. The forming limit diagram has been experimentally evaluated. A detailed analysis of the strain distribution profiles obtained from punch stretching experiments has been attempted. An attempt has been made to correlate the crystallographic texture with the formability parameters. The fracture surfaces of the punch stretched samples were observed using scanning electron microscopy with a view to obtaining a correlation between fracture behaviour and formability. The alloys, in particular the Al–Mg–Mn alloy, have been found to possess good stretchability but both show very limited drawability. Texture analysis indicated negligible earing during deep drawing. These alloys are suitable for stamping applications where stretching constitutes the major proportion of the deformation.     

锥形件拉深智能化控制中压边力的控制规律

法兰起皱、侧壁起皱和侧壁破裂是拉深成形的主要障碍,而合理控制压边力是防止起皱破裂的关键所在.在总结前期研究成果的基础上,结合拉深成形过程的特点,在成形三极限图中给出了圆锥形零件拉深成形的成功区域,并提出了获得最佳压边力控制规律的方法.这为圆锥形零件拉深成形中的模具设计、工艺参数的制定提供了依据,也为拉深智能化控制提供了保证.     

Structure,anisotropy, and properties of hot rolled AA 5083 alloy

Abstract

The changes in structure and substructure occurring during homogenisation and hot rolling of an Al–5Mg alloy (AA 5083) have been investigated. It is shown that a homogenisation treatment is beneficial and that the resulting structure can be related to processing parameters. The results suggest that the substructure morphology is dependent upon the total strain, but this has not been quantified. The development of texture was also studied and it is shown to be almost invariant with temperature, but strongly strain dependent. The anisotropy so produced yielded plastic strain ratios that were found to be strongly dependent upon the rotated copper texture intensity. The deep drawing behaviour of the hot rolled sheet was investigated by employing cupping tests and it is shown that a relationship exists between the earing value and the subgrain size.

MST/I086     

Analytical and finite element simulation studies on earing profile of Ti-6Al-4V deep drawn cups at elevated temperatures

Rolled sheet metal alloys exhibit plastic anisotropy, which leads to the formation of ears during the deep drawing process. An analytical function proposed by Yoon et al. (Int J Plast 27(8):1165–1184, 2011) predicts earing profile based on yield stress and r value directionalities for circular cup drawing. In this study, this analytical approach is applied for a deep drawing of Ti-6Al-4V at elevated temperatures up to 400 °C. Three yield criteria namely, Hill 1948, Barlat 1989 and Barlat Yld2000-2d are used to obtain the directionality inputs for the analytical formula. The analytical model is validated using experimental results and FE simulations and is found to be closely matched while requiring very less CPU time. FE simulation has been also conducted with various yield functions. Barlat Yld2000-2d is considered to be the most suitable yield criterion for very accurate earing prediction in deep drawing of Ti-6Al-4V as the inputs for both the analytical and FEM models.     

Control of microstructure and earing behaviour in aluminium alloy AA 3004 hot bands

Abstract

Control of earing behaviour at the hot band stage is a critical requirement for successful manufacture of aluminium alloy sheet for beverage cans. The present study has combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products. It is shown that optimisation of the product is strongly dependent on (i) iron content of the alloy, (ii) ingot homogenisation temperature, (iii) finish hot rolling temperature, and (iv) heating rate during hot band annealing. Earing level after annealing is shown to depend on the balance between cube (+ Goss) texture intensity and the volume of material having almost randomly spread orientations. Pronounced 0/90° earing tendency is usually associated with coarse and elongated grain structures. A model is shown which represents the microstructure–texture evolution as a competition between cube/Goss grains, which nucleate systematically within transition bands, and randomly oriented grains, which nucleate in the vicinity of coarse second phase particles.

MST/1032     

Failure and formability studies in warm deep drawing of Ti–6Al–4V alloy

Deep drawing experiments have been performed in order to study formability of Ti–6Al–4V alloy sheet at temperature ranging from room temperature to 400 °C. It is found that below 150 °C, formability of the material is very poor and above 150 °C till 400 °C, limiting drawing ratio (LDR) is found to be 1.8 which is substantially lesser than other structural alloys. For better understanding of failures in failed cups, failure regions have been identified in neck and wall which are validated using finite element (FE) simulations. Fractured surface has been examined with scanning electron microscope (SEM) which reveals different types of shallow dimples indicating predominantly ductile failure. Additionally, in the properly drawn cups, thickness distribution has been studied over a temperature range of 150–400 °C and blank diameter 50–54 mm. In order to optimize blank diameter and temperature to obtain uniform thickness distribution of drawn cups, artificial neural network (ANN) and genetic algorithm (GA) have been employed. Thickness distribution for optimized parameters is validated using FE simulation.     

A Study on Estimating Measurement Error in the Measurement of Earing of Pilfer-Proof Caps

The present study was carried out in a reputed Indian integrated aluminum industry. Closure stock, a premiere product of this company, is used as pilfer-proof caps. One important output characteristic was earing percentage, which was basically an undulated edge that emerged during deep drawing due to nonuniformity of metal flow. Earing was defined as the difference between hills and valleys on the cup ring after deep drawing of a circular blank. Plant management was interested in implementing statistical process control (SPC) to control earing. There was a discrepancy in the test results of earing percentage of the product tested in their laboratory and in their customer's laboratory. They were also apprehensive about the presence of considerable error in the measurement system, which might creep into the study and spoil the SPC effort. Before implementation of the SPC, management decided to ascertain the measurement system and have an estimate of measurement error. Therefore, the present study was initiated. Three lots and all three operators were taken into the purview of study. Two cups (closed sample) were drawn from each lot by each of the operators, with 30 cups being drawn. Each cup was measured twice by each operator. Thus, a set of 180 observations was obtained. The data were analyzed using five-stage nested analysis of variance (ANOVA). Error due to repeatability and reproducibility were estimated from ANOVA. Estimate of error of the measurement system was obtained by combining these two components. This error was compared with the international standard. It was recommended to consider this error while reporting the test results to the customer. As a result of implementation, the discrepancy problem of test results of earing percentage was substantially reduced.     

Neural and fuzzy model performance evaluation of a dynamic production system

Although mathematical modelling techniques are very well developed, some production processes are difficult to be modelled by these modelling techniques or their math-models are too complex to be used for real-time control due to uncertain, imprecise and vague parameters’ relations. Spray dryers are complex, dynamic and ill-defined production processes. Their product (powder) must have a controllable size distribution consisting of spherical shapes and free-flowing characteristic of particles, which is required for an ideal pressing operation to overcome the product sticking in the dies. The relations of production process' parameters are highly non-linear. In this study, these non-linear parameters were studied and three different soft-computing intelligent models were developed and used to predict uncertain parameter relations. The first is the fuzzy model of the production process; the others are the artificial neural network (ANN) architectures; the back-propagation multilayer perceptron (BPMLP) algorithm and the radial basis function network (RBF). To deal with uncertainty and vagueness of the production system, a method (methodology) based on a fuzzy hierarchical analytic process modelling approach and two ANN approaches was applied. The performance of the BPMLP algorithm was found most vigorous than the RBF and fuzzy modelling approach.     

Thermodynamics of duplex stainless steels

Abstract

The thermodynamic predictions of microstructures in the multicomponent alloys used for duplex stainless steels are discussed in detail in this paper. The production of the duplex ferrite–austenite microstructure by high temperature (1323–1423 K) annealing is considered. Phase diagrams are calculated for Fe–Cr–Ni ternary alloys and the more complex multicomponent systems. It is shown that there is good agreement between the predictions of the thermodynamic models and the measurements carried out on heat treated alloys. The low temperature aging behaviour of Fe–Cr–Ni ternary alloys is discussed and the limitations of activation energy approaches to the modelling of the aging process in these alloys are shown.

MST/1201     

Hot deep drawing of titanium sheet

Abstract

Commercial purity titanium (IMI 125) and a Ti–Cu alloy (IMI 230) in sheet form have been deep drawn at room temperature and at elevated temperatures. Cylindrical cups drawn at room temperature and at temperatures up to about 550°C develop four ear peaks at about 45° to the rolling direction (RD). When drawing is carried out at temperatures above 600°C, two ear peaks are formed at 90 and 270° to RD. The change in anisotropy is attributed to the temperature dependence of crystallographic slip modes, the high temperature behaviour being associated with basal plane slip. Drawing with a temperature gradient (cold punch, heated die) enables high drawing ratios to be achieved.

MST/1352     

Control of earing quality in AA 5052 and AA 5454 aluminium alloys

Abstract

The effect of discrete operations during thermomechanical processing on the earing behaviour of two aluminium alloys (AA 5052 and AA 5454) has been investigated. In the homogenized condition AA 5454 contained a fine dispersoid distribution while AA 5052 was dispersoidfree. It was found that for the dispersoid-containing material the hot-rolling process was less dominant. Nevertheless, for both alloys the earing quality could be adjusted by suitable modifications to hot-rolling, cold-reduction, and annealing cycles. Pole-figure analysis indicated differences in hot-rolled texture caused by variations in processing, which became more significant as the total hot reduction was increased.

MST/41     

飞机铝合金深锥型面零件多道次充液拉深技术

目的随着新一代飞机在隐身和战斗性能方面的提高,飞机钣金零件的复杂程度和制造精度要求也越来越高。对于深型腔复杂型面零件,充液拉深是一种有效的精密制造方法。方法针对难成形、复杂型面的某型飞机铝合金深锥零件,利用理论分析、有限元模拟和工艺试验相结合的方法,设计了多道次充液拉深技术方案,并建立有限元分析模型。基于等裕量函数法和零件锥面特征,分配并优化了不同道次的材料变形量。结果对多道次充液拉深成形过程中出现的起皱和破裂的失效形式进行了研究,分析了预成形高度,液室压力和压边力等关键工艺参数对零件成形质量的影响,获得了优化的预成形高度和液室压力加载轨迹。结论结果表明,提出的多道次充液成形技术能够实现复杂型面,大拉深比的铝合金零件的整体精确成形,采用优化的工艺参数能够成形出壁厚均匀,表面质量好,锥面精度高的零件。     

Assessment of anisotropic hardening models for conventional deep drawing processes

Assessing the predictive capabilities of recent advanced constitutive modelling approaches for processes with industrial complexity is a challenging task. Real process conditions such as blankholder pressure distribution, friction and tool elasticity sensitively affect experimental observations, making the isolation of constitutive effects difficult. A systematic approach is proposed in this work to assess the performance of anisotropic hardening models with the least possible disturbance from process conditions. Two deep drawing examples were used for these purpose (“cross die” and “lackfrosch”) in conjunction with a mild steel (DC05). Optically measured strain distributions have been compared to corresponding simulations, which have been calibrated to accurately match the measured blank draw-in. The effect of initial yield locus shape as well as anisotropic hardening effects have been discussed.     

Material saving and cost reduction with hot forming of U‐shaped titanium part

Titanium alloy sheets are widely used for highly loaded components in the aerospace industry as well as spacecrafts. The unique combination of high strength, outstanding corrosion resistance and thermal endurance makes titanium alloys the preferred material for applications with severe requirements. Due to the limited formability at room temperature, forming processes have to be conducted in a multitude of steps what is costly and labour intensive. Additionally, typical titanium alloy sheets show a significant anisotropy of mechanical properties and material flow. Undesired earing, wall thickness variation and residual stresses are the result. Complex shaped parts can be produced at elevated temperatures to avoid named drawbacks. The present work introduces a newly developed hot deep drawing process, applied to titanium sheets at FormTech. In comparison with conventional superplastic forming processes via gas pressure, hot deep drawing comes with a significantly reduced process time and hence, increased output over time. Titanium sheets of the work horse alloy Ti–6Al–4V were formed in a single stroke to a U‐shaped component at process temperatures ranging from 750 to 890 °C. Specimens were extracted to validate the neglectable influence of the hot forming process on mechanical properties and fatigue behaviour. In conclusion, hot deep drawing of titanium sheets offers a cost efficient alternative to a gas pressure superplastic forming process, while maintaining its main benefits such as significantly improved formability, low residual stresses and tight tolerances.     

单晶体材料内应力研究进展

随着科学技术的发展,晶体的力学性质,如弹性、脆性、硬度和解理性等引起了人们的重视。晶体材料应力分布取决于很多复杂因素(加热、退火、提拉、切割、搬运以及生长过程中的各种力学因素)。从应力表征、硬度及断裂韧性的测试方法入手,回顾并总结了晶体材料力学参数的表征手段,阐述了晶体开裂的分布规律及原因。其中光测方法(主要包括光弹法、X射线衍射法等)因其对晶体材料无任何机械损伤、检验灵敏度高而应用广泛:光弹性是光学晶体材料的重要特性,利用光弹仪测定光程差,根据平面光弹性的应力-光学定律确定主应力差;X射线衍射方法测定样品中宏观应力具有无污染、测量精度高等特点。压痕实验和划痕实验是表征晶体硬度的主要手段,结合化学腐蚀和光学观测方法可以有效探讨晶体开裂的微观机理。     

复杂轿车前底板变压边力数值模拟和物理模拟研究

为了有效地解决实际生产中如何优化复杂轿车前底板拉深成形过程中的变压边力工艺,首先基于相似物理模拟理论建立了前底板的简化物理模拟模型,其次通过数值模拟手段从众多典型变压边力模式中得到一条最优化变压边力加载曲线,使拉深件不出现起皱和拉破现象,且厚度分布最均匀.最后通过实际物理模拟实验对比来验证所得结果.数值模拟和物理模拟最终结果均表明:U型变压边力加载模式是复杂轿车前底板拉深成形的较优压边力控制曲线,其状态下不仅拉深工件的厚度最大减薄率最小,而且工件的最终厚度变化率的整体均方差为最小.     

Surface roughness modelling in hard turning operation of AISI 4140 using CBN cutting tool

In this study, the influence of hardness (H) and spindle speed (N) on surface roughness (Ra) in hard turning operation of AISI 4140 using CBN cutting tool has been studied. A multiple regression analysis using analysis of variance is conducted to determine the performance of experimental values and to show the effect of hardness and spindle speed on the surface roughness. Artificial neural network (ANN) and regression methods have been used for modelling of surface roughness in hard turning operation of AISI 4140 using CBN cutting tool. The input parameters are selected to be as hardness and spindle speed and the output is the surface roughness. Regression and artificial neural network optimum models have been presented for predicting surface roughness. The predicted surface roughness by the employed models has been compared with the experimental data which shows the preference of ANN in prediction of surface roughness during hard turning operation. Finally, a reverse ANN model is constructed to estimate the hardness and spindle speed from surface roughness values. The results indicate that the reverse ANN model can predict hardness for the train data and spindle speed for the test data with a good accuracy but the predicted spindle speed for the train data and the predicted hardness for the test data don’t have acceptable accuracy.