Deep Drawing Operations Research Articles

Experimental and Numerical Stress-Strain Analyses of Conventional and Intricate Shapes of LCS (1008-AISI) Sheet Metal Under Deep Drawing Operation

Experimental and Numerical Stress-Strain Analyses of Conventional and Intricate Shapes of LCS (1008-AISI) Sheet Metal Under Deep Drawing Operation

Sustainable tool technology: Wood-based forming tools for deep drawing of sheet metal

In order to improve adaptability to evolving manufacturing processes in an era marked by mass customization and individualization, while also meeting geopolitical climate objectives, it is necessary to employ more sustainable methods in sheet metal forming to enhance flexibility. Metal based rigid tooling systems require a lot of material and energy resources, when aiming for high flexibility and scalability with respect to small batch size production. To reduce the overall resource consumption and to meet climate restrictions, non-metallic tooling approaches can counteract these issues when aiming for individualization in sheet metal forming. Compared to conventional metal-based tooling approaches, wood-based forming tools may enable a potential resource reduction (e.g., carbon footprint) and offer an alternative tooling approach for sheet metal forming. Although the mechanical performance of wood is lower compared to conventional tooling steel, certain wood-based forming tools can potentially be implemented for sheet metal forming. In this work a feasibility study of wood-based tooling materials is executed to investigate the mechanical performance on drawn sheet metal parts in a deep drawing operation. Different composite structures are investigated for wooden forming tools of black locust (robinia pseudoacacia).

Influence of boriding on the tribological behavior of AISI D2 tool steel for dry deep drawing of stainless steel and aluminum

Deep drawing of stainless steel and aluminum is a widely adopted method for manufacturing various industrial goods. However, the wear damage produced to die tools is a recurring problem in these processes. While lubricants are often employed to lubricate and reduce die wear, dry deep drawing is the current best alternative for meeting green manufacturing demands. Hence, enhanced solid lubricants or surface treatments for dies are highly required. This study aims to evaluate and compare the tribological behavior of a heat-treated AISI D2 steel and a boriding AISI D2 tool steel against stainless steel (AISI 304) and aluminum alloy (AA 6061 T6) in the absence of lubricant. The boride coating was formed on the AISI D2 steel by the closed-pack boriding technique, resulting in a tooth-saw morphology with an overall thickness of 33.6 μm. X-ray diffraction analysis confirmed the presence of FeB, Fe2B, and Cr2B3 phases on the surface of the borided AISI D2 tool steel. Notably, the boriding treatment led to a significant increase in the surface hardness of the tool steel, reaching a value of 20.7 GPa. The coefficient of friction (CoF) behavior and wear were evaluated by pin-on-disk tests, simulating conditions similar to those found in cold deep drawing operations. The wear surfaces were analyzed by optical profilometry and scanning electron microscopy (SEM). The results suggest boriding as a suitable treatment to reduce wear damage on the surface of deep drawing dies used for stainless steel and aluminum forming processes in the absence of lubricant. Two-body abrasion and adhesion were identified as the main wear mechanisms in AISI D2 steel against stainless steel and aluminum, with a significant amount of oxidation observed when aluminum was tested. Additionally, a reduction of approximately 20 % in the CoF was observed when employing borided tool steel against stainless steel. However, there was an observed increase of around 75 % in the CoF when the borided tool steel was tested against aluminum.

Analysis of Coefficient of Friction of Deep-Drawing-Quality Steel Sheets Using Multi-Layer Neural Networks

This article presents the results of an analysis of the influence of friction process parameters on the coefficient of friction of steel sheets 1.0347 (DC03), 1.0338 (DC04) and 1.0312 (DC05). A special tribometer was designed and manufactured in order to simulate the friction phenomenon occurring in the blankholder area in deep drawing operations. Lubricant was supplied to the contact zone under pressure. The value of the coefficient of friction was determined under various contact pressures and lubrication conditions. Multi-layer artificial neural networks (ANNs) were used to predict the value of the coefficient of friction. The input parameters considered were the kinematic viscosity of lubricants, contact pressure, lubricant pressure, selected mechanical properties and basic surface roughness parameters of sheet metals. The value of the coefficient of friction of 1.0312 steel sheets was predicted based on the results of friction tests on 1.0347 and 1.0338 steel sheets. Many ANN models were built to find a neural network that will provide the best prediction performance. It was found that to ensure a high performance of ANN prediction, it is necessary to simultaneously take into account all the considered roughness parameters (Sa, Ssk and Sku). The predictive performance of the ‘best’ network was greater than R2 = 0.98. The lubricant pressure had the greatest impact on the coefficient of friction. Increasing the value of this parameter reduces the value of the coefficient of friction. However, the greater the contact pressure, the smaller the beneficial effect of pressure-assisted lubrication. The third parameter of the friction process, the kinematic viscosity of the oil, exhibited the smallest impact on the coefficient of friction.

Radial clearance influence on strain and stress distribution of the polygonal shape deep-drawing operation

In the existing research, polygonal -shaped dies were manufactured based on the dimensions of the design. These dies were then assembled on the deep-drawing device to create polygonal cups (specifically heptagonal cups) for conducting experimental work tests. The process was achieved via a deep-drawing operation to create heptagonal cups with dimensions (diameter D = 40mm and height L = 31.5 mm). For both experimental work and finite element analysis, the cups of heptagonal shapes were formed from flat circular blanks of Low Carbon Steel (thickness to = 0.7 mm) and diameter D = 80mm. A commercial software program, ANSYS, was employed to perform this finite element analysis. The research aims to study the effect of different radial clearance ( RC = 1.1 to,1.2 to, and 1.3 to) between die and punch for heptagonal shape DD operations on the forming load, the height of the cup, thickness distribution, strain and stress distribution along the cup wall (side-wall and wall curvature). The analysis outcomes indicate that the maximum forming force was 51.250 kN with the wall curvature, the maximum effective strain was 0.8231, and the maximum stress was 676 MPa when the [Formula: see text]1.1 to). Additionally, the squeezing process in the mug wall occurred with [Formula: see text]1.1 to).

Experimental investigation and numerical optimization of sheet metal forming limits during deep drawing process of DD14 steel

This work aims to experimentally study the deep drawability of DD14 hot-rolled steel sheets and to optimize numerically the material formability. The material anisotropy was confirmed by metallographic analysis of the material and tensile tests on specimens taken in three orientations with respect to the sheet rolling direction. Where the stress-strain curves show a sensitivity of material to the Piobert-Lüders phenomenon. The die pressure and the blank holder were considered as controlling factors on plastic instability and the success of the deep drawing operation. The forming limit curves (FLC) were plotted to highlight the different deformation modes that the sheet metal underwent during the deep drawing process. The collected deep-drawn parts observation shows severe plastic instability, until fracture. The initial plastic anisotropy is determined by the Hill48 quadratic criterion and the work hardening by the Hollomon power law. It results, during the experimental tests, that the front bottom corners of the deep drawn part are the areas at high risk of damage. The various numerical simulation scenarios followed by comparisons with the experimental results, allowed us to confirm the optimum conditions that minimize the material's plastic instability risks, forming operation “Step” and BHP “Amplitude”.

Analysis of Surface Topography Changes during Friction Testing in Cold Metal Forming of DC03 Steel Samples

Predicting changes in the surface roughness caused by friction allows the quality of the product and the suitability of the surface for final treatments of varnishing or painting to be assessed. The results of changes in the surface roughness of DC03 steel sheets after friction testing are presented in this paper. Strip drawing tests with a flat die and forced oil pressure lubrication were carried out. The experiments were conducted under various contact pressures and lubricant pressures, and lubrication was carried out using various oils intended for deep-drawing operations. Multilayer perceptrons (MLPs) were used to find relationships between friction process parameters and other parameters (Sa, Ssk and Sku). The following statistical measures of contact force were used as inputs in MLPs: the average value of contact force, standard deviation, kurtosis and skewness. Many analyses were carried out in order to find the best network. It was found that the lubricant pressure and lubricant viscosity most significantly affected the value of the roughness parameter, Sa, of the sheet metal after the friction process. Increasing the lubricant pressure reduced the average roughness parameter (Sa). In contrast, skewness (Ssk) increased with increasing lubrication pressure. The kurtosis (Sku) of the sheet surface after the friction process was the most affected by the value of contact force and lubricant pressure.

An Investigation into the Friction of Cold-Rolled Low-Carbon DC06 Steel Sheets in Sheet Metal Forming Using Radial Basis Function Neural Networks

This article presents the friction test results for cold-rolled low-carbon DC06 steel sheets, which are commonly processed into finished products using sheet metal forming methods. A strip drawing test with flat dies was used in the experimental tests. The strip-drawing test is used to model the friction phenomena in the flange area of the drawpiece. The tests were carried out using a tester that enabled lubrication with a pressurised lubricant. The friction tests were carried out at different nominal pressures, oil pressures, and friction conditions (dry friction and oil lubrication). Oils destined for deep-drawing operations were used as lubricants. Neural networks with radial base functions (RBFs) were used to explore the influence of individual friction parameters on the value of the coefficient of friction (COF). Under lubrication with both oils considered, the value of the COF increased with decreasing oil pressure. This confirms the correctness of the concept of the device for reducing friction in the flange area of the drawpiece. The developed concept of pressurised lubrication is most effective at relatively small nominal pressures of 2–4 MPa. This range of nominal pressures corresponds to the actual nip pressures when forming deep-drawing steel sheets. Under conditions of dry friction, the values obtained for the COF rise above 0.3, while under lubrication conditions, even without pressure-assisted lubrication, the COF does not exceed 0.2. As the nominal pressure increases, the effectiveness of the lubrication exponentially decreases. It was found that the Sq parameter carries the most information regarding the value of the COF. The RBF neural network with nine neurons in the hidden layer (RBF-8-9-1) and containing the Sq parameter as the input was characterised by an R2 of 0.989 and an error of 0.000292 for the testing set.

Experimental validation of IS2062 deep drawing component

Deep drawing isa leading manufacturing method in which a sheet metal blank is radially stretched into a die by action of a punch to produce various parts of automobiles, computers, electronic items and many other things used in day-to-day life. Optimization of sheet metal forming process parameters was important to reduce the cost of manufacturing a product. Forming a defect-free drawn part is always a challenging task. This work presents analysis and experimental identification of the deep drawing process in order to avoid earring effect and Stretcher strain defect. In our present work, low carbon structural steel (IS2062, Carbon 0.17 to 0.19 wt%) is used for deep drawing application. Factors mainly influencing the friction coefficient, blank holder force, and die nose radius, which are the sheet metal process characteristics that exhibit deformation behaviour. In an experiment, radial clearance between the die and the punch was taken as 0.15 mm on each side. Deep drawing operation was carried out on a 1200 ton hydraulic press with a servo controlled mechanism, a 3 stage forming process was taken and values were compared with the FEA, A cylindrical cup with a LDR of 1.8 has been successfully created experimentally.

Performance of stringer sheet parts under static and dynamic load

The stringer sheet forming process chain enables the cost-effective production of components with significantly increased stiffness for mass markets such as the automotive sector. In the first process step, a stringer is added to a conventional sheet by laser welding. In the subsequent process step, the stringer sheet parts are formed by a deep drawing operation. Previous investigations of component performance focused in particular on the static stiffness of the stringer sheets. The behavior under dynamic load, such as in crash events, has not been systematically investigated to date. Static testing focused on the stringer height as the only influence on part performance. This study characterizes the crash performance of stringer sheet components by means of a drop hammer test. The energy absorption of the components is evaluated in the experiment based on the rebound height of the drop hammer, whereas the structural integrity is characterized based on the maximum dynamic as well as permanent deformation. Furthermore, a quasi-static compression test is carried out to obtain the static stiffness of the parts. In these tests, the geometric design of the stringer sheets as well as two forming process parameters are varied individually. The influence of these parameters on the static stiffness, energy absorption and structural integrity is assessed and discussed on their own and with regard to their influence on the part weight.

Characterization of the Tribological Behavior of Different Tool Coatings and Dry Lubricant for High‐Strength Aluminum Alloys at Elevated Temperatures

The use of high‐strength aluminum components in automotive manufacturing offers the opportunity to reduce vehicle weight significantly and provide new lightweight potentials. In the past, the so‐called hot forming and quench process (HFQ) successfully demonstrates the potential for the production of complex‐shaped components made out of age‐hardenable high‐strength aluminum alloys. Currently, no method permits wear‐free quench forming without the use of lubricants. To fulfill the increasing ecological and economic requirements, it is necessary to identify wear‐reducing techniques to promote this forming technology in the future. This contribution investigates the interaction of lubricant and tool coatings on the tribological performance during quench forming of the high‐strength aluminum alloy AA7075 at elevated temperatures. For this purpose, the tribological behavior is investigated using both, flat strip drawing tests and deep drawing operations. Subsequently, the component quality is compared and discussed. The results demonstrate that tool coatings are effective for the production of high‐strength components in the HFQ process with minimal or even no lubrication and thus provide ecological as well as economic advantages.

Sheet-Metal Formability Study on a Circular Tube with a Folding Bottom Feature

The formability of sheet-metal with a folding-bottom circular hollow tube has been studied both by numerical simulation and experiment. A mesh-convergence analysis has been carried out to determine an optimum element size for purposes of numerical simulation. The geometry and dimension of the dies and of the punch are designed to simulate the multi-stage deep drawing operation to take place. During the deep drawing operation, the strains of the sheet blank are always located in the second quadrant of the forming limit diagrams, and it continuously moves in a linear state to the left side of the diagram. At the final stage, the tube is drawn to a certain height without evidence of fracture. In order to obtain a quality product, an optimization of input parameters for the deep drawing operation is conducted using Taguchi method. Finally, a validation test is also employed to demonstrate the accuracy of forming processes. The result reveals sufficient agreement in both geometry and dimension between simulated and actual tubes to meet a good quality standard.

Critical Aspects Concerning Large-scale Production of a Batch-annealed Medium-Mn 780 MPa Grade for Automotive Applications

This article presents the results of the development of a medium-Mn780 grade at large scale production via conventional LD-converter route at the voestalpine steel plant in Linz. It highlights the property profile of the newly developed grade—being a well-balanced global-formability type for demanding deep drawing operations and crash applications. Furthermore, it offers the possibility of weight reduction by replacing grades with lower strength levels.The article highlights critical aspects of the application of the material that had to be overcome. The first aspect addresses the often-observed presence of extensive yield point elongation (YPE) in medium-Mn steels. This contribution clearly shows that YPE can be avoided by a two-step heat treatment. The second aspect concerns the robustness of the manufacturing process and refers to the sensitivity of mechanical properties to the intercritical annealing temperature, which is a concern for industrial scale production. Based on the large-scale material, this contribution can emphasize that, with a precise temperature control during a batch annealing cycle, stable mechanical properties throughout an entire coil can be achieved. The third aspect addresses the necessary suitability of the material for the resistance spot welding process. In our first investigations, the material revealed rather low cross tension strength (CTS) after welding with standard parameters. Therefore, the chemical composition was adjusted and a double-pulse regime was established to vastly increase CTS.Considering all the above-mentioned aspects, this contribution represents a compilation of critical points and possible solutions towards the large-scale implementation and subsequent use of the present material by the automotive industry.

Effects of process variables on the uniformity of Al-St and Al-Mg laminated composite cups produced by hydro-mechanical deep drawing operation

Hydro-mechanical deep drawing (HMDD) process is comparatively a new technique in sheet metal forming. The present study focuses on the use of HMDD for bimetallic components comprising aluminum and steel sheets as well as aluminum and magnesium blanks. Carrying out both experiments and numerical simulations, the effects of process parameters such as drawing depth, the fluid pressure inside the die and the process temperature were profoundly investigated. To study the effect of the process temperature on the quality of the product, the specimens were formed at both the room temperature and 200°C. Considering the maximum thickness strain and thickness variation of the specimens as measures of product quality, various results, including those obtained from the design of experiments (DOE), illustrated significant impacts of all the considered factors on the quality of the final product. The findings also showed that for the bimetallic aluminum/steel specimen, the Al/St layer sequence offered a higher quality compared with the St/Al arrangement under the same process conditions. The amount of thickness strain and thickness variation in the Al/St arrangement, compared with the St/Al sequence, were respectively improved by 27.4% and 12.6%, for the optimal value of the maximum fluid pressure (150 bar). Moreover, the thickness variation of the Al/Mg specimen was smaller than that of Al/St bimetallic cup, regardless of the drawing depth.

Digital Twins in deep drawing for virtual tool commissioning and inline parameter optimization

Fluctuating boundary conditions and the highly nonlinear process behavior of deep drawing operations make experience-based selection of suitable control parameters difficult. Nowadays, commissioning deep drawing tools, i.e., die spotting and identification of suitable control parameters for defect-free parts, is conducted on real world try-out presses. Transferring the tools to production machines entails adaption of these initial parameters. Once production is ramped up, any changes to material properties, lubrication and press behavior require continuous manual machine parameter tuning. Virtual tool commissioning and utilizing these simulation models in the production phase to adapt control parameters would reduce time and cost over the entire life cycle of the machine and the tool sets. The virtual representative, which provides services for a plant over several life cycle phases, is also referred to as Digital Twin. In this paper, the authors present a Digital Twin concept for deep drawing presses to predict the state of the system and optimize the control parameters during the production. The integration of all involved subsystems into one system simulation and its efficient calculation is the biggest challenge. The authors combine a virtual commissioning simulation tool with a finite element model to implement all relevant properties of the deep drawing press and the interaction of its subsystems. It is shown, how the idea of a system simulation makes predictions of system parameters specific to a production situation possible, and therefore, can help to select suitable control parameters that leads to a reduction of the error rate in deep drawing.

Study on size-related product quality of multiscale central-punched cups fabricated by compound forming directly using brass sheet

Meso/microforming has gained much more attention in the last decades and is widely used as a reliable method to fabricate meso/micro-scaled metallic components. In this research, a compound meso/microforming system which combines deep drawing, punching, and blanking operations was developed to fabricate multiscale central-punched cups by using brass sheets. The parts with three scales were produced by using the brass sheets with various thicknesses and grain sizes to investigate geometrical and grain size effects on the deformation behaviors, dimensional accuracy, and material flow behaviors in the forming process. Through physical experiments and finite element simulations, it is revealed that the ultimate deformation load in the drawing-punching stage is smaller than that in the single deep drawing stage under microscale, but the results in the meso-scaled scenarios are opposite. In addition, the thickness variation is increased with grain size, but the variation of the normalized thickness variation does not show an obvious tendency with different size scales. In the bending area, the material flow is tangential to the thickness direction, leading to the formation of thinning area. In addition, the material flow is almost opposite to the punching direction in the punching area, avoiding the expanding deformation of the hole. Thus, the punching operation barely affects the dimensional accuracy including the thickness and hole diameter of the formed parts. Furthermore, the micro-scaled cups with finer grains have a better surface quality. These findings enhance the understanding of size effect in compound meso/microforming with the combined deep drawing and punching operations.

Microstructural correlation with formability aspects of low carbon steels during deep drawing operations

Mechanical and fluid assisted (hydro-mechanical) deep drawing operations were performed on drawing quality (DQ) and interstitial free (IF) steels at various forming depths. The evolving microstructure in terms of textural developments, in-grain misorientations and residual stresses measurements were significantly different between the two grades and deep drawing processes. In all the deformed microstructures, however, clear formation of near boundary gradient zones (NBGZs) was observed, quantified from electron backscattered diffraction (EBSD) data. The effective presence and extent of the NBGZs appeared to be the primary source of differences in deformed microstructure developments leading to changes in strain distributions between two different forming processes. It was observed that the formation of NBGZ was lower in hydro mechanical deep drawing (HMDD) operations. Moreover, the estimated statistical parameter strain non-uniformity index (SNI) confirmed the development of uniform strain distributions during HMDD operations. The determined correlation coefficient R2 values showed best fit for HMDD operations.

The Interaction between the Sheet/Tool Surface Texture and the Friction/Galling Behaviour on Aluminium Deep Drawing Operations

The increasing demands for lightweight design in the transport industry have led to an extensive use of lightweight materials such as aluminium alloys. The forming of aluminium sheets however presents significant challenges due to the low formability and the increased susceptibility to galling. The use of tailored workpieces and controlled die roughness surfaces are common strategies to improve the tribological behaviour, whilst galling is still not well understood. This work is aimed at analysing the interplay between the sheet and tool surface roughness on the friction and galling performance. Different degrees of Electro Discharge Texturing (EDT) textures were generated in AA1050 material strips, and tooling presenting different polishing degrees were prepared. Strip drawing tests were carried out to model the tribological condition and results were corroborated through cup drawing tests. A new galling severity index (GSI) is presented for a quick and quantitative determination of both galling occurrence and severity. The present study underlines the key role of die topography and the potential of die surface functionalization for galling prevention.

Studying Formability Limits By Combining Conventional and Incremental Sheet Forming Process

In this work it is assessed the potential of combining conventional and incremental sheet forming processes in a same sheet of metal. This so-called hybrid forming approach is performed through the manufacture of a pre-forming by conventional forming, followed by incremental sheet forming. The main objective is analyzing strain evolution. The pre-forming induced in the conventional forming stage will determine the strain paths, directly influencing the strains produced by the incremental process. To conduct the study, in the conventional processes, strains were imposed in three different ways with distinct true strains. At the incremental stage, the pyramid strategy was adopted with different wall slopes. From the experiments, the true strains and the final geometries were analyzed. Numerical simulation was also employed for the sake of comparison and correlation with the measured data. It could be observed that single-stretch pre-strain was directly proportional to the maximum incremental strains achieved, whereas samples subjected to biaxial pre-strain influenced the formability according to the degree of pre-strain applied. Pre-strain driven by the prior deep-drawing operation did not result, in this particular geometry, in increased formability.

The Procedure of Experimental Work and Finite Element Simulation to Produce Spline Shape Multi-Stage Deep-Drawing Operation

This research deals with a multi-stage deep-drawing operation. The research aim is to produce spline shapes using two methods (direct and indirect) for three-stages based on experimental work and FE model procedure. The direct method was performed to produce spline shapes from the blank for the first stage, while the second and third stages from shapes of the first and second stages, respectively. The indirect method was performed to produce spline shapes from the cylindrical shapes of three-stages. The multi-stage deep-drawing was completed to perform the experimental procedure required to produce a spline shape with inner dimensions of major axis D = 41.5,33.3,28.8, and miner axis d = 34,27.2,23.6 mm for the first, second, and third stages, respectively. Flat circular blanks (diameter Db = 80 mm and thickness t = 0.7mm) of low carbon steel (1 008 - AI S I) used in this research. FE analysis based on the ANSYS workbench program was used to model the multi-stage deep-drawing operation. The comparisons between results showed that the direct method was successful with the first stage, while it was failed with the second and third stages. For the three-stages, the maximum drawing force required to produce spline shape by the direct method is greater than the maximum drawing force required to produce spline shape by the indirect method. The maximum drawing force values equal to 41.650 kN, 33.175 kN, 33.11 kN for the first, second, and third stages, respectively, Also, for the three-stages, it was observed that it is possible to produce a complete spline shape without defects in the indirect method when comparing with the direct method.