Blank Holder Force Research Articles

Robust Design of Deep Drawing Process through In-Line Feedback Control of the Draw-In

In the deep drawing process, the scatter of the friction coefficient between blank and tool interfaces as well as of the material properties between blank positions in the coil or between different coils significantly influences the part quality. These uncontrollable fluctuations increase the risk of waste. To avoid this problem, currently, the new era of Industry 4.0 aims at developing control algorithms able to in-line adjust process parameters and always meet the part quality requirements. Starting from this context, in this study a method for process control during the punch stroke is proposed. It assumes the blank draw-in in specific points as the control variable, while the blank holder force is adopted as an in-line adjustable process parameter. The approach was implemented for the deep drawing of a T-shaped component, using a blank in DC05 steel with a thickness of 0.75 mm. The results show that the measurement of blank draw-in is a representative index of the component quality, which in this study is evaluated in terms of formability (thinning) and cosmetic (surface deflections) defects. Once the optimal condition and the corresponding blank draw-in were identified, the feedback control algorithm was able to increase or reduce the blank holder force according to whether the recorded draw-in was higher or lower than the optimal one.

A numerical study on warm deep drawing of polypropylene

AbstractWarm deep drawing of polypropylene, a semi‐crystalline thermoplastic polymer, is studied using finite element analysis. In this process, a circular polypropylene blank is preheated to a temperature much below its melting temperature and deep drawn into the shape of a flat‐bottom cylindrical cup using a punch‐die combination, both initially at 25°C. The material model used for the analysis considers the effects of varying temperature and strain rate during the deep drawing process on the depth of draw. The effects of blank holder force, initial blank temperature, blank diameter, and die and punch corner radii on the depth of draw are determined. Thickness, temperature, and strain variations in the drawn cups, punch forces, and failure modes are also determined.

Investigation of defect behavior during the stamping of a thin-walled semicircular shell with bending angle

Springback, wrinkling, and thinning typically occur during the stamping of thin-walled semicircular shells with bending angle. These defects cause poor forming accuracy of specimens and lead to assemble difficultly; consequently, the produced specimens do not meet requirements. In this work, the defect behavior during the stamping of thin-walled semicircular shells with bending angle is studied via an analytical model, experiments, and finite element (FE) simulation. First, an analytical model is established to predict springback and analyze springback trend. Second, stamping experimental tests of a thin-walled semicircular shell with bending angle are conducted. The influences of blank holder force (BHF) and stamping speed on the springback, wrinkling, and thinning of specimens are investigated. Finally, an FE simulation model is developed to investigate the deformation characteristics and springback of the thin-walled semicircular shell with bending angle. Results show that the maximum springback decreases with increasing BHF. Meanwhile, the results of the analytical model are consistent with the experimental and simulation results. The maximum thinning rate of the specimen increases with increasing BHF, whereas the wrinkling defect exhibits the opposite trend. The maximum thinning rate and wrinkling of the specimen increase with increasing stamping speed. Compared with that of BHF, the effect of stamping speed on defects is smaller.

Impact of Blank Holding Force and Friction on Springback and Its Prediction of a Hat-Shaped Part Made of Dual-Phase Steel.

Formability and its prediction of high-strength steels is an important research subject for forming specialists and researchers in this field. Springback and its accurate prediction of high-strength steels are very common issues in metal forming processes. In this article, the impact of blank holding force and friction on the parts springback made of dual-phase steel was studied. Numerical predictions of the springback effect were conducted using nine combinations of yield criteria and hardening rules. Results from experiments were evaluated and compared with results from numerical simulations. The use of lower blank holding forces and PE foil can reduce springback by a significant amount. Numerical simulations where the Yoshida-Uemori hardening rule was applied produced more accurate springback prediction results compared to simulations that used Krupkowski and Hollomon's isotropic hardening rules in number of cases.

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.

Comparative analysis of parameters affecting micro-forming process

This review paper provides a comprehensive analysis of the various factors affecting micro-forming and the parameters involved in manufacturing micro-parts. To ensure minimal wear and tear and error-free products, it is important to optimize both the process parameters and framework. The paper aims to highlight the importance of metal micro-forming technology in designing and manufacturing highly precise micro metallic devices, biodegradable implants, micro-pumps, and gears. Through this review paper, readers can gain a better understanding of metal micro-forming, the variables that influence micro-forming and deep drawing, and the process parameters that affect micro-forming and deep drawing technology. Optimizing the process parameters is crucial for the success of micro-forming and can lead to improved product quality, increased production efficiency, cost reduction, process robustness, and improved material properties. The paper specifically discusses the significance of parameters such as blank holder force and size effects on variables that play an important role in optimizing the metal micro-forming process.

Data-driven Temperature Estimation for a Multi-Stage Press Hardening Process

In a multi-stage press hardening process with a sheet material in a progressive die the material is first rapidly austenitized, pre-cooled, stretch-formed, and finally die bent. The product properties result from the thermo-mechanical history. With the aim to estimate and subsequently to directly control these properties a data-driven estimation of the spatial-temporal temperature distribution in the sheet is developed in this work. Therefore a data-driven dynamical model is designed via the Dynamic Mode Decomposition (DMD) using a Finite Element (FE) simulation as data basis. This model is extended to a parameter-dependent formulation (parametric DMD) capturing the process parameters stroke rate, blank holder force, and austenitization temperature, which serve as inputs to the model. The approach is verified by a comparison of the data-driven model with the original FE model. To estimate the temperature distribution a discrete time system representation is formulated, where the stage dependent and hence time varying output matrix is constructed for thermocouples integrated into the individual stages. Based on this a Kalman filter is designed and evaluated in simulation.

Adaptive metal flow control in stamping through ferrofluidic actuators

Inhomogeneous metal flow in stamping non-axisymmetric parts makes material deformation in the flange critical, resulting in uneven sheet thickness distribution, high blank holder forces or even the need to use draw beads to compensate for large material draw-in. The paper presents an innovative mechatronic system for the adaptive control of the blank holder force, which integrates ferrofluidic actuators and non-contact sensors for the in-line material flow measurement, with the aim of exploring, through laboratory-scale experiments, the feasibility of its implementation in stamping processes and understanding the potential benefits to enable more reliable process design.

Variable blank holder pressure by magneto-rheological actuators in deep drawing

Deep drawing is one of the most used processes in industry, whose reliability is closely linked to the possibility of adequate control of the blank holder force (BHF). To avoid typical failure mechanisms, such as wrinkling and tearing, it is necessary to properly adjust the BHF during the process. The paper presents the design of a new blank-holding set-up based on magneto-rheological actuators, which allow a flexible adjustment of the force during the process. A closed-loop control, based on the direct detection of the metal sheet displacement under the blank holder, is implemented to regulate in real-time the actuator's load. The obtained experimental test results show that (i) the presented set-up allows to apply blank holder pressures with an average error less than 5% with respect of the target forces; (ii) the low latency times to allow the force variations, and (iii) the possibility to vary in real-time the blank holder load response during the deep drawing.

A Study of Stamping Die Design of Autobody Part Using Software Simulation

This paper presents a study of stamping die design of car backdoor reinforcement using software simulation. The existing process of stamping die design and manufacturing in the company being observed involves seven to ten trials before getting an acceptable die and therefore increase the cost of dies. By using software, it is expected that the number of trials is reduced as the design is analyzed in advance to identify unwanted defects in stamping process, such as wrinkle, split, and springback and develop a proper die design. The scenario started with comparing a final stamped part with its design. By using 3D scanner, the final part geometry is obtained and compared with the original 3D CAD model to examine the deviation of the part from its original design. The comparison between the final stamped part and the original design shows discrepancies, it is obvious that most probably the design has been modified to prevent stamping defects. Next, the original design is simulated by applying blank holder force of 109.7 kN. The first simulation on the original design part shows that the minimum thickness strain in -14.4% and has strong wrinkle tendency, therefore the design was modified then run a simulation again on this modified design part. The modification was mainly focus on essential corner radius and increasing blank holder force to 129.2 kN to prevent wrinkle and reduce springback. The second simulation yields a good formability indicated by better forming limit diagram, safety zone, and springback, despite the minimum thickness strain was increased to -19.2%. So, by using software simulation the correct die geometry can be obtained prior to manufacture the dies as to avoid unnecessary cost of modifying the dies during the trial processes. In addition, the number of trials can be minimized resulted in shorter lead time of producing stamping dies.

Experimental Investigations of Hydrodynamic Deep Drawing of Galvanized Steel to Form a Hemispherical and Complex Cup

In this work, a blank of galvanized steel blank with 80 mm diameter and 0.7 mm thickness and the hydromechanical deep drawing process to make a hemispherical and complex cup. Hydraulic oil was used to apply different amounts of fluid pressure. The work of this study was done in the following three states: In the first state, the experimental work was done without fluid pressure, so the product has wrinkles. In the second state, flaws like wrinkles were fixed by adding 1N/mm2. At a pressure of 1.7 N/mm2, the third state was done. The results show that a product with a blank holder force (BHF) that is neither too high nor too low may be free of defects. When BHF is low, faults in the cylinder cup look like wrinkles, and when BHF is too high, the cylinder cup breaks. So, the BHF value should change depending on the material, thickness, and nature of the product.

Estimating Forming Conditions for Deep Drawn SUS304 Square Cups Having no Delayed Cracks Using FE Simulation

Forming conditions for deep drawn SUS304 square cups having no delayed cracks are determined using finite element (FE) simulations based on the threshold % of wall thickening for delay cracking obtained from deep drawing tests of SUS304 cylindrical cups. The maximum drawing ratio and the initial blank thickness are fixed at 1.87 and 0.8 mm, respectively in this study taken into the considerations of the capacity of the press machine i.e., 100 kN. The blank holding forces (BHF), punch corner radius, rp and die corner radius, rd are varied to obtain 75 mm x 75 mm square cups having % of local thickening less than the threshold value i.e., 47% in the cracking zones located adjacent to the top corners of the cups. A quarter 3D FE simulation model of the deep drawing process is constructed, the wall thickness distributions of the cups are calculated. The simulation results showed that the forming conditions for the crack-free cups could be obtained with BHF ≥ 47 kN, rp ≥ 8.5 mm and 6.8 mm ≤ rd ≤ 9.5 mm. A method for designing the forming conditions of deep drawn SUS304 square cups is proposed in this study.

Experimental Investigation on the Formability of Al-Mg Alloy 5052 Sheet by Tensile and Cupping Test.

Aiming at the enhancement of the lightweight formability potential of aluminum alloy, the bulging and tensile properties of a 5052 Aluminum alloy sheet were tested on a microcomputer controlled sheet metal forming tester and tensile testing machine. The effects of different blank holder force, punch velocity and lubrication conditions were investigated on bulging properties by the experimental analysis. The cupping values (Erichsen Cupping Index: IE) of sheets with a thickness of 1.2 mm at room temperature were obtained under different process parameters. Meanwhile, the anisotropic property of the material was analyzed in different rolling directions. The results show that the sheet cupping values increase with the increase of blank holder force and punch velocity, and the stress state was changed due to the changing of the blank holder force and strain rate. Moreover, the use of lubricating conditions with a lower coefficient of friction allows the sheet to exhibit a larger cupping value. The effect of rolling direction on the anisotropy of 5052 aluminum alloy sheet is distinct, which means in the aluminum alloy sheet forming process the anisotropy factor should be carefully considered.

Novel forming process for aluminum alloy thin shells at ultra-low temperature gradient

The occurrence of wrinkling and splitting in forming integral aluminum alloy thin shells using traditional forming processes is extremely difficult to preclude. Accordingly, a novel forming process at ultra-low temperature gradient is proposed in this paper. The process leverages the abnormal ‘dual enhancement effect’ of hardening and ductility at ultra-low temperatures. In this proposed approach, the risk unsupported region is fundamentally cooled to ultra-low temperatures to avoid splitting, and the tension-compression stress state is then adjusted by ultra-low-temperature gradient cooling and blank-holder force to control wrinkling. Hyper-hardening and high-ductility properties at ultra-low temperatures are simultaneously utilised to adjust the deformation considering these properties. Mechanical and numerical analyses were conducted to reveal the deformation mechanism, and the effects of ultra-low-temperature gradient, blank-holder force and thickness-to-diameter ratio were studied. The forming defects, thickness, and stress and strain distributions were determined to reflect the deformation behavior. The blank needs to withstand larger deformation to form the thinner components without wrinkling. The maximum radial strain increases by 50% when the thickness-diameter ratio decreases from 13.3% to 3.3‰. A smaller temperature gradient and larger blank-holder force can be used to reduce hoop compressive stress and prevent wrinkling defects. A bigger temperature gradient may be used to increase the stress difference between flange and unsupported regions to further improve forming limit or deformation uniformity, accompanying with easier engineering implementation for large-sized components. An ultra-low temperature forming device was developed to verify the feasibility of this new forming process. The forming limit was significantly improved by cooling the unsupported region, and a more uniform thickness was obtained at a larger ultra-low temperature gradient. The depth of the hemispherical specimen improved by 54.5%, and the average thickness deviation was only 6.9%. Through fundamental research, an integral dome with a diameter of 2.25 m was formed at an ultra-low temperature gradient, surpassing the wrinkling limit and overcoming splitting. The new forming process has considerable potential to fabricate large thin-shell components made of aluminum alloy.

Research on stamping forming prediction of aluminum alloy sheet based on RBF neural network

In order to accurately predict and reduce the possible defects in the stamping process of an aluminum alloy sheet, the simulation data of the sheet thickness for the 6016 aluminum alloy in the stamping process were obtained by the Hill’48 yield criterion based on finite element ABAQUS/Explicit solver. Taking blank holder force, friction coefficient, stamping speed, and die clearance as input parameters, the radial basis function (RBF) network model for predicting the maximum thinning rate of the stamping aluminum alloy sheet was established. The results show that the RBF network model constructed in this paper has high precision and can reflect the complex relationship between the stamping process parameters and the maximum thinning rate well by comparing the finite element simulation and neural network prediction results. It is of great significance to improve the optimization efficiency of the stamping process of the aluminum alloy sheet and reduce the actual experimental cost.

Study on the key process parameters of hydrodynamic deep drawing on the stainless steel single sink with countertop

Stainless steel single sink with countertop (SC) has the characteristics of large depth and asymmetric countertop. Its traditional stamping process is mainly realized by the combination of multi-stage deep drawing and annealing process, which leads to the complex manufacturing process, long production chain and poor consistency of products. Based on finite element analysis software (Dynaform) with nonlinear dynamic display algorithm, numerical simulation analysis and research are carried out on the parameters of hydrodynamic deep drawing. First, the sink and the part of countertop are preformed into a cylinder shell, and then the excess of the cylinder shell is drawn back to the countertop. The research results show that the hydrodynamic deep drawing process can effectively improve the flow uniformity of stainless steel sheet, increase the forming of stainless steel tank, drawing a more uniform wall thickness, thus effectively improve the quality of single tank with countertop by setting up reasonable preform structure, controlling the liquid pressure and its loading paths and blank-holder force.

Die design for fine micro-blanking process

As the increase in demand for microparts of metal foil, the micro-blanking process with many advantages of plastic deformation has been widely applied on microparts manufacturing area. But the fracture zone of shearing surface is always present and affects the service life of the part. This paper proposes a new micro-blanking die based on fine blanking technology. In this die, the rubber as the power transmission device is selected to provide a blank holder force and counter force. In the FEM simulation, the influence of a few key die parameters is considered such as punching clearance and fillet radius of female die and punch. And the fine micro-blanking experiments for superalloy foils were conducted to evaluate the feasibility of the die designs. The results had shown the fine micro-blanking die proposed was able to be used for micro-blanking and obtain metal microparts.

Multi-Objective Optimization of Process Parameters in 6016 Aluminum Alloy Hot Stamping Using Taguchi-Grey Relational Analysis

The hot stamping technology of aluminum alloy is of great significance for realizing the light weight of the automobile body, and the proper process parameters are important conditions to obtain excellent aluminum alloy parts. In this paper, the thermal deformation behavior of 6016 aluminum alloy at a high temperature is experimentally studied to provide a theoretical basis for a finite element model. With the help of blank stamping finite element software, a numerical model of a 6016 aluminum alloy automobile windshield beam during hot stamping was established. The finite element model was verified by a forming experiment. Then, the effect of the process parameters, including blank holder force, die gap, forming temperature, friction coefficient, and stamping speed on aluminum alloy formability were investigated using Taguchi design, grey relational analysis (GRA), and analysis of variance (ANOVA). Stamping tests were arranged at temperatures between 480 and 570 °C, blank holder force between 20 and 50 kN, stamping speed between 50 and 200 mm/s, die gap between 1.05 t and 1.20 t (t is the thickness of the sheet), and friction coefficient between 0.15 and 0.60. It was found that the significant factors affecting the forming quality of the hot-stamped parts were blank holder force and stamping speed, with influence significance of 28.64% and 34.09%, respectively. The optimal parameters for hot stamping of the automobile windshield beam by the above analysis are that the die gap is 1.05 t, the blank temperature is 540 °C, the coefficient of friction is 0.15, stamping speed is 200 mm/s, and blank holder force is 50 kN. The optimized maximum thickening rate is 4.87% and the maximum thinning rate is 9.00%. The optimization method used in this paper and the results of the process parameter optimization provide reference values for the optimization of hot stamping forming.

Influence of alloy composition and lubrication on the formability of Al-Mg-Si alloy blanks

The formability of 1.0 mm-thick Al-Mg-Si alloy blanks with different Si and Mg contents was numerically and experimentally investigated using two deep drawing tools: (i) a cross-shaped tool with open die and (ii) a complex-shaped panel tool with closed die. For the cross-shaped tool, forming velocity and blankholder force were constant and the formability was characterized based on the maximum drawing depth at crack initiation. For the complex-shaped panel tool the forming velocity and the drawing depth was constant and the formability was characterized based on the maximum blankholder force at crack initiation. Two types of commercial lubricants were applied on the blank surfaces. In order to investigate critical forming conditions, numerical models of both deep drawing processes were built using the AutoForm finite element (FE) software. Parameters required as input for these models were experimentally determined. The flow curve and the anisotropy of each of the aluminum alloys were determined using uniaxial tensile tests. Based on the results of pin-on-plate tests an advanced friction model which considers different contact pressures and sliding velocities was created using the TriboForm software. Good agreement between deep drawing simulations and experiments was achieved in terms of forming force, local thinning and strains. Experiments and simulations confirmed that the maximum drawing depth or blankholder force, respectively, tended to increase with increasing Si and Mg contents. However, the influence of lubrication on the formability of the Al-Mg-Si alloy blanks was much more significant than the influence of the alloy composition.

Springback Behavior of Aluminum/Polypropylene/Aluminum Sandwich Laminates

The springback of sheet metals after forming has been widely studied for decades using numerical and experimental methods. Many of these springback studies involve aluminum alloys. This study aims to understand the springback behavior of aluminum-polypropylene-aluminum laminates as they are being used increasingly in automotive and other applications because of their weight saving potential. A finite element model of the draw bending of a U-channel based on Numisheet’93 benchmark study is built using LS-DYNA. First, the model is validated and studied for springback prediction of single AA5182-O aluminum alloy sheets, and then it is extended to the study of the springback behaviors of AA5182-O/polypropylene/AA5182-O laminates with various combinations of core and skin thicknesses. The numerical model is also validated by experiment. Effects of various tool design and process parameters, such die radius, punch radius and blank holder force, on the springback of the sandwich laminates are studied. The effect of numerical modeling parameters is also considered.