Limiting Drawing Ratio Research Articles

DETERMINATION OF TECHNOLOGICAL CHARACTERISTICS OF PRESSABILITY

This article deals with the results of technological tests of pressability (Erichsen's - IE index and capping - limit drawing ratio (LDR)). It also presents on which material parameter (ductility, strain hardening exponent, coefficient of normal anisotropy...) should be given more emphasis when choosing a steel sheet, if stretching stress (uniaxial tension, biaxial tension) dominates during the production of stampings, or if dominates the “pull-pressure” technique (pulling out from under the flange).

Prediction of micro/meso scale forming limit for metal foils using a simple criterion

Accurately forecasting the forming limit of metal foils is essential in their micro-forming due to the appearance of necking failure easily. In order to accurately and easily forecast the forming limit of metal foils influenced by size effect, an idea for failure modeling of metal foils using the mechanism that different fracture modes of metal foils are related to shear bands is presented in this work. Based on the idea, a simple ductile failure criterion that considers the maximum shear stress and grain size effect but excludes the stress triaxiality is proposed, motivated by the demand to decrease the complexity of parameter calculation tests in micro-forming failure prediction. The proposed criterion and another criterion called as the μ-DF2022 model are applied to capture the forming limit curves of various thick copper and 304 stainless steel foils with different grain sizes to verify its advantage and performance, and the corresponding mechanisms of their prediction capabilities are also elucidated. Furthermore, the proposed and μ-DF2022 models are applied to forecast the limit drawing ratio of a 304 stainless steel foil to further show its performance and advantage in real micro-forming. The applications show that the proposed failure criterion effectively forecasts the forming limit of metal foils between equi-biaxial tension and uniaxial tension influenced by size effect. Moreover, the prediction accuracies using the proposed model and the μ-DF2022 model are comparable, whereas the proposed model does not require complex micro equi-biaxial tension tests, which are typically unavailable to many engineers and researchers, to calibrate its material parameters. Therefore, it is recommended to utilize the proposed criterion to capture the forming limit of metal foils in micro-forming. This work advances the forming limit modeling method of metal foils and provides insight into the application of uncoupled ductile failure criteria in the micro-forming of metal foils, which contributes to the development of their optimal micro-forming processes.

Microstructure evolution and twinning behavior of AZ31 magnesium alloy sheets with bimodal texture during cold deep-drawing deformation

Cold deep drawing experiments were conducted on AZ31 magnesium (Mg) alloy sheets with bimodal texture, which were prepared by the newly developed equal channel angular rolling and continuous bending and subsequent annealing (ECAR-CB-A) process. The results showed that the sheet could be successfully deep-drawn at a limiting drawing ratio (LDR) of 1.6, and the forming performance was better than that of the as-rolled base-texture sheet at room temperature. The microstructure after deep-drawing deformation was investigated by X-ray diffraction (XRD), optical microstructure (OM), and electron backscatter diffraction (EBSD). A large number of {10−12} extension twins (ETs) are observed in the outer shoulder region. Due to the bimodal texture, the activated {10−12} ET variants and the basal slip within the matrix have a higher Schmid Factor (SF) value when the outer shoulder region is under radial tensile stress, this enables the shoulder of the drawn cup to maintain good deformability. In addition, some {10−11} contraction twins (CTs) and {10−11}-{10−12} double twins (DTs) can be observed in this region, which is activated by the local strain accommodation between the twins and the slip systems, and the multiaxial stress. Due to different stress conditions, the volume fractions of {10−12} ETs in the inner shoulder region are less than that in the outer region. The stress concentration caused by {10−11}-{10−12} DTs that occurred in the edge region is the reason for the fracture of the drawn cups at a drawing ratio(DR) of 1.7.

Study on the hot deep drawing performance and microstructural evolution of AZ91D magnesium alloy sheets

Magnesium alloys are attractive because of their low density and high specific strength and stiffness; however, secondary phase strengthening and the low number of slip systems lower formability especially for the strongest magnesium alloys such as AZ91D. The formability of AZ91D sheets is investigated through orthogonal experiments, which show that AZ91D has no deep drawing properties at room temperature and that plastic forming is only possible under hot forming conditions. When the temperature is increased from room temperature to 400 °C, the limiting drawing ratio of the sheet increases significantly to 1.91, and the thinning rate reaches a minimum value of 6% at approximately 400 °C because of the improved plastic flowability. The optimum process parameters for hot deep drawing are a temperature of 400 °C, blank holder force of 5 kN, and punch speed of 3 mm s−1. The microstructural evolution shows that plastic deformation of the AZ91D magnesium alloy at high temperatures is markedly accommodated by twinning and that, with heating, this twinning deformation mechanism is activated and overcomes the hindrances of the reinforcing phases to achieve better forming properties.

Artificial Neural Networks to the Analysis of AISI 304 Steel Sheets through Limiting Drawing Ratio Test

Artificial Neural Networks to the Analysis of AISI 304 Steel Sheets through Limiting Drawing Ratio Test

PVD coated dies in action: Exploring finite element analyses for sheet metal forming of high‐strength steel

AbstractThis research proposes a complete analysis of the use of physical vapour deposition coated dies in the sheet metal forming process for high‐strength‐steel sheets. The goal of the proposed approach is to investigate how PVD coatings affect die performance and how that affects the formability and quality of the high‐strength‐steel‐sheets that are made. The finite element analyses are used to simulate and evaluate the mechanical behaviour and deformation characteristics during the forming process. Studies to enhance the forming characteristics of these materials, typically denoted by limiting draw ratio and maximum punch force are required. A reduction in punch force required and improved limiting draw ratio is observed that is attributed to the enhanced contact with friction‐conditions in the die‐sheet interfaces. The experimental results are compared with simulation results from DD3IMP, a code used for deep drawing simulations, and it is evident that the experimental outcomes are analysed well with the simulation results.

Improving the Quality of Tantalum Cylindrical Deep-Drawn Part Formation Using Different Lubricating Media-Coated Dies

Lubrication is one of the key factors to improve metal-forming quality. In the process of deep drawing, seizing tumors easily occur on the contact surfaces between the tantalum metal and the mold, which greatly affects the forming quality of the deep-drawn parts. Quality-forming quality problems that occur during the deep drawing of tantalum metal are studied from the perspective of lubrication in this paper. Three lubrication media, caster oil, PE (polyethylene) film, and DLC (Diamond Like Carbon) film, were adopted in the deep drawing of tantalum cylindrical cups. A universal testing machine and microscope were used to investigate the effect of lubrication media on the limit-drawing ratio, maximum forming force, and surface topography quality during the deep drawing process of the tantalum sheet. The results reveal that the lubrication of the PE film and DLC film can greatly improve the forming quality of the tantalum metal sheet, in which the DLC film has higher wear resistance and lower friction coefficient and can be used as the lubricating medium in the industrial forming process of tantalum deep-drawn parts.

Effect of Process Variables on Interface Friction Characteristics in Strip Drawing of AA 5182 Alloy and Its Formability in Warm Deep Drawing

Warm forming is widely used to enhance the formability of aluminum alloy sheets. In warm deep drawing, the process variables significantly affect frictional characteristics at the tool–blank interface. It has been a conventional approach to use a constant value of friction coefficients in the finite element (FE) simulations. However, this can occasionally result in suboptimal accuracy of the predictions. In the present work, strip drawing tests were carried out on AA5182 aluminum alloy sheets to investigate the effect of important process variables, namely, temperature, contact pressure, and drawing speed, on the friction coefficient in the warm forming temperature range (100–250 °C) under lubricated condition. The results obtained from the strip drawing tests were used for defining the friction conditions in the simulation of warm deep drawing of cylindrical cups incorporating the variation of the friction coefficient with contact pressure and speed at different temperatures. The Barlat89 yield criterion was used to define the effect of anisotropy in the material. The Voce hardening law and Cowper–Symonds model were used to incorporate the effect of strain hardening and strain rate, respectively, in the simulation. Drawability and peak force were compared with the predictions when a constant friction coefficient was assumed. Warm deep drawing experiments were conducted to validate the predicted drawability and load–displacement curves. It is clearly observed that the accuracy of prediction of the limiting drawing ratio and peak load through simulations is improved by incorporating the effect of pressure and speed on friction coefficient as it captures the local variations of friction during warm deep drawing precisely, rather than assuming a constant average friction coefficient at all the tool–blank contact areas.

Study on formability and microstructure evolution of hot deep drawing manufactured 7005 aluminum alloy sheet metal

The hot deep drawing process with an in-die heating system was proposed on the forming of 7005 aluminum alloy to improve the formability due to the limitation of ductility during severe plastic deformation at room temperature. The feasibility of hot deep drawing AA7005 sheet (only 0.8 mm) was investigated and evaluated by Swift cup tests from RT to 450 °C. The priority of main process parameters, namely temperature, blank holder force, and stamping speed, on sheet metal forming limit were discussed by analysis of range and variance. Experimental results indicated that elevating the temperature could fundamentally improve the deep drawing performance of the alloy, which is manifested by the revolutionary change in sheet metal behavior — from the failure of deformation at lower temperatures (RT-200 °C) to achieving a limiting drawing ratio of 2.19 at 450 °C. The optimal process parameters under HDD conditions are given as drawing temperature of 400 °C∼450 °C, BHF of 3 kN, and punch speed of 15–20 %. The thickness variation increases with rising temperature corresponding to the formability enhancement during the process within acceptable limits. DRV and DRX are the flow softening mechanism under the high temperature and large strain in HDD process obtained from the analysis of microstructure and texture evolution. The elongation and rotation of grains further substantiated the interrelationship between drawing performance and microstructure evolution. Improving the deep drawing performance through HDD process can provide practical guidance for the application of AA7005 sheet metal.

Application of an Oleophobic Coating to Improve Formability in the Deep-Drawing Process

The competition among sheet-metal-forming manufacturers in recent years has become more severe. Many manufacturers have survived by cutting their production costs. Increasing the formability, which could reduce the production costs, is the focus of many manufacturers and engineers. In the present research, to increase the formability over the limiting drawing ratio (LDR) in the cylindrical deep-drawing process, the application of oleophobic coating is proposed. An SUS304 (JIS standard)-stainless-steel cylindrical deep-drawn component was used as the investigated model. First, we applied the oleophobic coating in the sheet-metal-forming process, and tribology tests were carried out to examine the friction coefficients, which were reduced by approximately 60% compared with those of standard lubricant use (Iloform TDN81). Next, deep-drawing tests were performed to investigate the drawing ratio (DR). The LDR recommended in the past could be overcome, and it increased by approximately 12% with the oleophobic coating use. Finally, the deep-drawing mechanism using an extremely low friction coefficient was clarified as well. Based on these results, an oleophobic coating could be applied in the cylindrical deep-drawing process to increase the LDR. The results also clearly expose the multidisciplinary approach that combines an oleophobic coating application and the sheet-metal-forming process.

Deep drawability of electron beam welded tailored blanks of commercially pure titanium thin sheets

In this work, commercially pure titanium tailor-welded blanks (TWBs) were fabricated from sheets of thicknesses 1.0 mm (Ti1.0) and 1.2 mm (Ti1.2) using electron beam welding (EBW). It was observed that the titanium base materials had an equiaxed microstructure, whereas the FZ of the weld consisted of coarsened prior β grains with internal α substructures. Transverse and longitudinal tensile tests were conducted to evaluate weld integrity and weld properties, respectively. The deep drawing behaviour of both the base materials and TWB had been investigated by conducting laboratory-scale deep drawing tests. The limiting drawing ratios (LDR) of the Ti1.0 and Ti1.2 base materials were 2.14 and 2.21, respectively. The LDR of TWB was 2.14, which was same as that of the Ti1.0 base material. The CPB06 yield criterion and weld properties were incorporated in the FE modelling to study the deep drawing behaviour of the TWB for the first time. The FE model successfully predicted the non-uniform material flow and thickness distribution in the deep drawn TWB. Moreover, the weld line movement was found to be towards the Ti1.0 side at the cup top region and towards the Ti1.2 side at the cup bottom of the TWB deep-drawn cup.

底面集合組織の形成を抑制したAZ31Bマグネシウム合金板材の室温深絞り成形性に及ぼすプロセス因子の影響

The effects of process parameters on room-temperature (RT) deep drawability were investigated for AZ31B magnesium alloy sheets, in which the formation of basal texture was suppressed by high-temperature rolling. When the blank holder force was set to the minimum value to prevent wrinkling, high RT drawability was obtained. In particular, a significantly high limiting drawing ratio (LDR) of 1.83 was obtained by the optimization of the process parameters of the servo-press machine. At higher punch speeds, the drawability tended to be deteriorated; however, a high LDR of 1.72 was obtained even at a high punch speed of 50mm/s by the optimization of the process parameters of the servo-press machine. Furthermore, when the punch speed in the initial stage of deep drawing was reduced, it was possible to perform deep drawing without fracture even if the punch speed in the later stages was increased. The results of the study of the effect of lubricants indicated that relatively high RT drawability was obtained when molybdenum disulfide was utilized. It was also suggested to be important to select a lubricant that reduces punch load and does not delaminate during deep drawing.

An investigation on the size-effects on thickness-distribution of directionally rolled multi-stage deep-drawn copper cups through finite element analysis, and its validation through experimentation employed scaling law

Most sectors are moving towards downsizing products that retain high standards of quality and satisfy customer needs. Miniaturisation of components typically makes use of scaling rules. In this work, we use the idea of similarity theory to investigate the micro-and nano-scale thinning behaviours of multi-stage deep-drawn cups. Deep drawing with a limiting draw ratio (LDR) of 1.69 was used to shape ETP copper sheets into cylindrical cups via annealing and directionally rolling. Each rolling pass consists of nine incremental passes that result in a 50% reduction in thickness. The influence of scaling laws for uni and bi-directional rolling was studied, and scaled dies and punch sets were employed to create scaled cups of five different thicknesses, each 50% of the original 6 mm. For this simulation, we used Altair INSPIRE, a sort of explicit finite element analysis that uses real-world material test data. To investigate the impact of thickness variation across all scaled cups, measurements of the thickness were taken at three points on multi-stage deep-drawn cups. Bi-directional rolling produced cups with less thickness variance than uni-directional rolling. All the scaled cups had a consistency greater than the mean at the lip point and less at the cup base for both ways of rolling, it was also noticed. Physical evaluations of the drawn cups for extreme values verified that the inferred variations lie within ±15% of their original thickness for all cups, and the mean thickness likewise has 50% of its multi-stage-drawing, proving the applicability of the scaling rules.

Study of the limiting parameters of deep drawing of sheet blanks made of heat-resistant copper alloys

This article studies the mechanism of thin-walled workpiece deep drawing in the mould with a conical die and determines the forming limit state that occurs at the time of the bottom detachment in the radius part of the punch when stresses in the meridional direction reach their maximum value. This condition is determined by a decrease in the workpiece edge size at the stage of slow material hardening and a decrease in the workpiece flange area that are main factors hindering the process. This condition makes it possible to establish a criterion used to determine the limiting drawing ratio (ratio of the diameter of the workpiece to the diameter of the part), namely: equality of meridional stresses in the punch radius rounding area and the material tensile strength. The paper establishes the effect of the workpiece material strength properties, friction and die taper on the limiting drawing ratio. A change in the plastic and strength properties of the BrKh08 heat-resistant copper alloy (tensile strength, yield strength) does not affect the material hardening constant values and practically does not affect the limiting drawing ratio. The paper uses a comprehensive research method including theoretical analysis and modeling in the ANSYS/LS-DYNA software with input data for the 1.35 mm thick workpiece 100 mm in diameter made of BrKh08. The article presents computer simulation stages indicating main process parameters such as the workpiece material model, mechanical properties, type of elements, kinematic loads, conditions of contact interaction between elements, etc. Process simulation results confirmed theoretical conclusions necessary for the process implementation without part defects.

Strip Casting of Al-4.7%Mg with Impurity Fe Using a Single Roll Caster with a Scraper

Fe was added to Al-4.7%Mg to make model alloys of recycled Al-Mg alloy. The effect of Fe addition on the mechanical properties of the Al-4.7%Mg strip cast using a single-roll caster equipped with a scraper was investigated. The added Fe content was 0.2, 0.4, 0.6, and 0.8%. The as-cast strip cast at 30 m/min was cold rolled down to a thickness of 1 mm thick annealed to conduct a tensile test and a cup test. The as-cast strip could be cold rolled without cracking. The tensile stress and the 0.2% proof stress were only slightly affected by the addition of Fe. The elongation gradually decreased as the Fe content increased. When the Fe content was 0.8%, the elongation in the casting direction was 27.7%. The limiting drawing ratio did not deteriorate until the Fe content was 0.4%. When the Fe content was 0.4% and 0.8%, the limiting drawing ratios were 2.0 and 1.7, respectively.

Investigation on improvement of limit drawing ratio in two-stage hydrodynamic deep drawing of cylindrical cups

Investigation on improvement of limit drawing ratio in two-stage hydrodynamic deep drawing of cylindrical cups

A new ductile failure criterion for micro/meso scale forming limit prediction of metal foils considering size effect and free surface roughening

For the establishment of reliable micro/meso scale forming processes, it is essential to accurately predict the forming limits of metal foils under different deformation paths. However, existing uncoupled ductile failure criteria cannot accurately forecast the micro/meso scale forming limits of metal foils affected by size effect in the whole strain path range of forming limit curve (FLC). To deal with the issue, a new ductile failure criterion is proposed in this paper based on the theoretical analyses of size effect affected void nucleation, growth, and coalescence, as well as free surface roughening affected critical damage of metal foils. A method for identifying the material parameters of the proposed ductile failure criterion coupled with a modified Yld2000 yield criterion is provided, and the size effect on micro/meso scale FLCs forecasted by the proposed ductile failure criterion is discussed. In addition, the forming limit strains of SUS304 and pure copper foils with different thicknesses and grain sizes are employed to reveal the prediction capability of the new ductile failure criterion. Comparisons between the experimental results and the FLCs constructed by the proposed failure criterion demonstrate that the proposed failure criterion can accurately predict the forming limits of metal foils affected by size effect between uniaxial tension (UT) and equi-biaxial tension (EBT). To further show the prediction capability of the proposed failure criterion in actual micro/meso scale forming processes, the limit drawing ratio of a SUS304 foil and local maximum forming heights in micro-channel hydroforming for pure copper foils are predicted using the new failure criterion combined with the finite element method, and the predicted results are compared with experimental results. Comparative research demonstrates that the proposed ductile failure criterion can accurately forecast the forming limits of metal foils affected by size effect in actual micro/meso scale forming processes.

Drawing Capability of High Formable Packaging Steel: Comparison of Limiting Drawing Ratio and Forming Limit Curve

To assess the suitability of different packaging steels for complex deep drawing applications, nowadays, the total elongation and the Lankford coefficients in simple tensile tests are used. However, the simple use of uniaxial tensile tests is not supposed to predict the limiting drawing ratio precisely and thus the suitability for deep drawing applications. At the same time, the conduction of limiting drawing ratio experiments is extensive and requires a high testing effort. Therefore, in this work, the correlation between the forming limit curve results were compared to the results of limiting drawing ratio experiments to predict the formability of packaging steel by a much simpler criterion. At the same time, different approaches to calculate the plane strain forming limit by tensile test data were used to assess the drawing capability of packaging steel. Results revealed a strong correlation between the measured plane strain forming limit and the limiting drawing ratio at a fixed blank holder force. However, calculation methods based on tensile test data were not able to predict the drawing capability sufficiently.

Evaluating the influence of the deformation of the forming tools in the thickness distribution along the wall of a cylindrical cup

The Swift cup drawing test has been adopted for evaluating sheet metal deformation properties, namely the material formability assessed through the limiting drawing ratio. Since the strain path of the points located on the flange is between uniaxial compression and pure shear, this region is subjected to thickening. If the thickness of the drawn flange is larger than the gap between the punch and the die, cup wall ironing will occur. Therefore, the ironing forces can lead to significant elastic deformation of the forming tools (punch and die). The main objective of this study is to evaluate numerically the deformation of the forming tools during the deep drawing-ironing process of a cylindrical cup. Then, the effect of that deformation on both the earing profile and the evolution of thickness along the circumferential direction, at different heights, is analysed. The material studied is the AA 6016-T4. Since both the thickness strain and the earing profile are strongly influenced by the adopted yield criterion, the study considers the classical quadratic one proposed by Hill and a non-quadratic proposed by Cazacu and Barlat. The process conditions considered are the ones from EXACT, the ESAFORM Benchmark 2021, enabling the comparison with experimental results.

Twin-Roll Casting of Al-4.8%Mg Alloy with Added Fe

Fe (0.2, 0.4, 0.6, and 0.8 %) was added to roll-cast Al-4.8%Mg alloy to create a model of recycled Al-4.8%Mg and its effect was investigated. An unequal-diameter twin-roll caster was used. The roll speed was 20 m/min. An as-cast strip was cold-rolled down to 1 mm and annealed. Its mechanical properties were then evaluated. The surface condition of the as-cast strip was not influenced by the Fe content. The thickness of the as-cast strip decreased with increasing Fe content. The tensile strength and 0.2% proof stress increased with Fe content up to 0.4%Fe and then decreased. When 0.8% Fe was added to Al-4.8%Mg, the tensile strength and 0.2% proof stress became higher than those for Al-Mg. Elongation and the limiting drawing ratio gradually decreased with increasing Fe content. When 0.8% Fe was added, elongation in the lateral direction was 19.6% and the limiting drawing ratio was 1.7.