Cup Drawing Process Research Articles

Numerical and experimental investigation of direct rapid tooling for sheet metal forming using selective laser sintering

The rapid tooling approaches were most sought after for the low-volume production of sheet metal parts within a short duration. This study presents an investigation of direct rapid tools produced with Selective Laser Sintering (SLS) for sheet metal forming. SLS is one of the widely used additive manufacturing techniques to produce polymer parts. The ability to form the sheet metal components using SLS direct rapid tools was assessed through cup drawing from aluminium blanks. A full factorial experiment was formulated to design the tools by varying the punch radius, die radius and draw ratio. The tools were fabricated with SLS using glass bead - filled polyamide material (PAGF) and finite element analysis was employed to study the stress distribution. The stress concentrations were observed at the tool edge radius, yet the PAGF tools sustained the load from the cup drawing process. The inspection of the PAGF tools and drawn cups shows that they are sensitive to the edge radius and draw ratio. Wear at the edge radius was evaluated in terms of percentage deviation from the initial radius. While the designed dimension of the edge radius is a significant factor affecting respective tool edges, the die edge wear was also influenced by the draw ratio. Both the formed parts and the tools exhibit geometrical variations localised to the forming edges and demonstrate good repeatability even up to 200 draw cycles.

Machine learning-based sampling of virtual experiments within the full stress state

This paper presents a new machine learning-based approach to investigate anisotropic yield surfaces of sheet metals by means of virtual experiments. The new sampling approach is based on the machine learning technique known as active learning, which has been adapted to efficiently sample virtual experiments with respect to the full stress state in order to identify parameters of anisotropic yield functions. The approach was employed to sample virtual experiments based on the crystal plasticity finite element method (CPFEM) for a DX56D deep drawing steel and compared with two state-of-the-art sampling methods taken from the literature. The resulting points on the initial yield surface for all three sampling methods were used to identify parameters of the anisotropic yield functions Hill48, Yld91, Yld2004–18p and Yld2004–27p. These parameters were then applied to a cylindrical cup drawing simulation to analyse the effect of the three sampling methods on a typical sheet forming simulation. The results show that the new machine learning-based sampling approach has a higher sampling efficiency than the two state-of-the-art sampling methods. Consequently, fewer computationally expensive crystal plasticity simulations are required. By comparing different variants of the Hill48, Yld91, Yld2004–18p and Yld2004–27p yield surfaces, it was also found that identifying parameters of anisotropic yield functions based on virtual experiments sampled within the full stress state can lead to a degraded representation of the in-plane anisotropy. With respect to DX56D deep drawing steel, this degradation was observed for the Yld2004–18p yield function. The negative implications following from this degraded in-plane representation were further demonstrated by the results of the cylindrical cup drawing process. As a consequence, the representation of the in-plane anisotropy must be carefully reviewed when taking the full stress state into account. In this context, Yld2004–27p was identified as being sufficiently flexible to simultaneously represent the plastic anisotropy of DX56D with respect to the in-plane and out-of-plane behaviour with high accuracy.

Finite Element Simulation of a Multistage Square Cup Drawing Process for Relatively Thin Sheet Metal through a Conical Die

A new manufacturing process has been developed that involves drawing circular sheets of thin metal through a conical die to create square cups. This technique produces deep square cups with a height-to-punch-side length ratio of approximately 2, as well as high dimensional accuracy and a nearly uniform height. The study investigated how various factors, including the sheet material properties and process geometric parameters, affect the limiting drawing ratio (LDR). The researchers used finite element analysis to determine the optimal die design for achieving a high LDR and found that the proposed technique is advantageous for producing long square cups with high dimensional accuracy.

Analysis and Experiment of Blank Holder Gap in the Cylindrical Cup Deep Drawing of Low Carbon Steel to Prevent Cracking-Wrinkling

This paper aims to investigate Blank Holder Gap (BHG) in order to prevent wrinkles and crack defects in the deep drawing process of cylindrical cups with a diameter of 30 mm, using low carbon steel grade SPCC that is 0.7 mm thick. Mathematical and experimental approaches were applied to study the effect of BHG on wrinkle wave height and product quality. The analytical approaches used were the slab method and the Forming Limit Diagram (FLD) to determine the final thickness of the product specimen and the height of the wrinkling wave, respectively. Each method in this study had been compared to each other. Punch-die dimensions were determined based on the standard tool designed. According to the research, BHG is set 100% to 114% of the thickness of the initial material or equivalent about 0.70 to 0.80 mm. By using the value of this gap, the height of wrinkles can be avoided, the magnitude of the drawing force is still below the critical limit, and the product specimen does not experience wrinkles and cracks. The results of this study are applicable to the deep drawing of cup products on SPCC material with a thickness of no more than 1 mm.

Effect of the yield surface evolution on the earing defect prediction

Although the prediction of earing in the cup drawing process is considerably related to the yield surface shape, the yield surface evolution is also essential for the final ear form. The bending-unbending issue is a fundamental subject occurring on the die and punch shoulders. Since the yield stress is loading path dependent in reversal loadings, the conventional hardening models used in the monotonic loading conditions bring about inaccurate outcomes for predicting the ultimate earing profile, and a kinematic hardening model should be incorporated into the constitutive equations. This study elucidates the yield surface evolution effect involving expansion and translation simultaneously on the ear formation. A sixth-order polynomial yield function was employed to precisely characterize the yield surface shape, while a combined isotropic-kinematic hardening model was implemented to represent the evolution of the yield surface. The translation of the yield surface position was defined by the Armstrong-Frederic hardening model. Punch force-stroke responses and the ear form profiles were predicted by the implemented plasticity model in Marc using the Hypela2 user subroutine and compared with the experimental results. The combined hardening assumption yielded an increase in the mean cup height when compared to the isotropic hardening assumption. Moreover, The HomPol6 coupled with the combined hardening showed a better agreement with the experimental results.

Acoustic emission monitoring for necking in sheet metal forming

There is extensive evidence in the literature that plastic deformation of metals is associated with an increase in Acoustic Emission (AE) activity. Thus, AE measurement techniques have the potential to monitor a forming process in real time and provide a signal for feedback control, to exploit optimum formability. In this work, custom-made AE sensors employing piezoelectric crystals are implemented to measure the emitted acoustic signal during uniaxial tension and cup drawing tests of an AA6013-T4 aluminum sheet (1.5 mm thick). The uniaxial tension tests are conducted with two AE sensors clamped to each end of the specimen gage section, along with full-field surface strain measurement using Digital Image Correlation (DIC) techniques. The AE signals along with the interrogation of the DIC images reveal that the maximum AE amplitude corresponds to the onset of diffuse necking, i.e., when the strain field starts to become spatially inhomogeneous. Interestingly, this onset occurs before the maximum force is attained. Comparing these observations to a model of dislocation activity supports the notion that dislocation is the main driver of AE activity. With these findings, AE measurements are performed in a cup drawing process where a custom-made Marciniak-type punch incorporates three AE sensors. These sensors are used to triangulate and determine the location of necking and eminent fracture based on the time difference of arriving signals to each sensor. The results from the cup drawing tests show that AE signals can identify the onset of necking and accurately predict the location of necking and fracture.

Analysis of Side-Wall Wrinkling in Deep Drawing Processes

Wrinkling, developed due to compressive instability, is one of the main failure modes in deep drawing processes. Depending on the die geometry and blank holder force, it can be observed as flange wrinkling and/or side-wall wrinkling. In this study, side-wall wrinkling in cylindrical cup drawing process is investigated by using different constitutive models that are formed by using CPB06ex2, Hill’48, BBC2008-8p and BBC2008-16p yield criteria with isotropic hardening, and von Mises yield criterion with isotropic, kinematic and combined hardening. Numerical simulations are performed by implementing CPB06ex2, BBC2008-8p and BBC2008-16p models to a commercial finite element code through user subroutines. AA5042-H2 aluminium alloy is selected as a sheet material with 0.2083 mm thickness. In order to verify the developed models, the experimental results of the previous works for wrinkling profile and punch force evolution are employed. The results are compared and presented for the considered yield criteria.

Metal forming defect detection method based on recurrence quantification analysis of time-series load signal measured by real-time monitoring system with bolt-type piezoelectric sensor

In recent years, research related to smart manufacturing processes, which aim to advance production technology through productivity improvement and manufacturing technology innovation, has been actively pursued. In the field of sheet metal press forming, intelligent process management is required to improve productivity and reduce costs. In this field, a method of indirectly monitoring signals generated in the forming process without the need to modify existing tools is advantageous, as it can be easily applied to the mass-production process. In this study, a monitoring system for a laboratory-scale cup drawing process was established that uses a bolt-type piezoelectric sensor. First, a numerical analysis was conducted to select the location where the sensor was to be installed in the tool, and the feasibility of load monitoring was confirmed. Then, the forming load of the cup drawing process using a servo press was measured according to process variables such as holding force, specimen size, and initial specimen position. Forming defects such as wrinkles and fractures occurred according to process variables, and it was confirmed that the measured load had a specific pattern. To quantitatively analyze the time series data of the measured load, recurrence quantification analysis was used, and a system for real-time monitoring of formability was developed based on the structural shapes formed by the resulting recurrence plots.

On the reliability of yield functions in deep drawing simulations

In sheet metal forming simulations, the yield functions are usually calibrated based on experimental data, and validated by comparing the modelled and measured r-values and (in more advanced models) yield stresses along various in-plane directions. The fitted yield function should ideally reproduce (or interpolate) all the experimental values used for the fitting. However, this requirement does not guarantee accurate results in a forming process simulation, and it can even lead to unexpected results. The performance of a yield function, in addition to the fitting procedure, depends on the active loading modes which the material experiences during the simulation. The active loading modes are in turn determined by the die geometry as well as the process parameters like blank holder force and lubrication. As a consequence, the performance of a yield function, which is fitted to simple experimental data, is not identical for different forming conditions. Therefore, the application of each model is usually limited to a range of materials and processes, and this applicability is often evaluated based on experience. In the present study, we examine three phenomenological yield functions and a new crystal plasticity based material model for cup drawing process simulation with an AA6016-T4 aluminium alloy. These functions are different in their input data types used for the calibration. The results surprisingly shows that the models with more experimental data (in particular, yield stresses in different directions) in their formulation not only predict unexpectedly wrong results, but also show strong sensitivity to some of those additional input data and even to modelling parameters like the friction coefficient.

Evaluasi Kekuatan Resistance Spot Welding pada Proses Tailor welded blankss Menggunakan Mill-steel Beda Ketebalan

This paper presented the test of cup drawing, and the tensile ability of tailor welded blanks (TWBs) used to join the resistance spot welding a variety of different parameters. This study used SPCC-SD (JIS 3141) material with a material thickness of 1.0 mm and 1.2 mm. This research is focused on obtaining the highest tensile-shear strength of resistance spot welding and how it affects the results of the drawing cup process. This study used an experimental research method using six samples of RSW parameters. RSW parameters used are welding current, welding time, and squeeze time. This research was achieved the highest tensile-shear strength value of 5.09 kN and the lowest 4.15 kN which was achieved in the 5th and 1st samples respectively. The results of the cup drawing test using RSW parameters in the 5th and 6th samples showed no TWB failure in the welded area. Further research will be carried out by performing Taguchi optimization using RSW and TWBs parameters in the cup drawing process.

Buckling and post-buckling of an elastica under a lateral restraining force

Buckling of structures under lateral load restraint has been found to differ from the conventional bifurcation problems and cannot be handled with conventional analysis. Towards a better understanding of this type of unconventional buckling problems, this work investigates the upheaval buckling of an elastica resting on a smooth surface and restrained by a lateral constant force. Analytical solutions for the Mode-1 and Mode-2 post-buckling responses and configurations of the elastica are established. Stability of the post-buckling configurations under force-control are investigated via the energy method. An energy barrier is found to exist and the buckling load depends on the restraining force and perturbation energy. The imperfection sensitivity of the system is different from the conventional buckling ones, and a characteristic imperfection is found to exist that can transform a snap-through instability into a bifurcation buckling. As a first attempt to address the problem of flange wrinkling under a constant blank-holding force during the cup-drawing process, the fundamental solutions are extended to study the wrinkling of a shrinking elastic annulus under a constant lateral restraining force. The post-wrinkling responses are established and an energy barrier is found to exist for each wrinkling mode. A characteristic imperfection is also found to exist for each mode, which eliminates the energy barrier and enables bifurcation wrinkling. The linear relationship between the critical restraining force that prevents the wrinkling of the elastic annulus and the imperfection amplitude is established, which is also verified by numerical simulations. This study contributes to a better understanding of load-restrained buckling problems and is expected to shed light on the elastoplastic buckling of plates and shells under lateral load restraints in general, and on the wrinkling of a thin sheet during cup-drawing in particular.

On the use of fixed point translations as input variable for digital twins in deep drawing compared to current methods

Recent work aims at the inverse parameter estimation in deep drawing using pretrained surrogate models for the detection of the current process, material or tool parameters. The use of the methodology requires the definition of state variables to describe the current process state. Whereas our recent work makes use of draw-ins and local blankholder forces, other approaches from the literature also use skid-lines measured after the deep drawing process. For the future, the solution with even higher information content would be to detect the global strain distribution on the final part and use it as a state variable for process detection, which has not been documented in the literature to the best knowledge of the authors.In this work, we present a first step into this direction by comparing the surrogate model based parameter estimation by using draw-ins and by using the movement of material fixed points on the blank over the deep drawing process. The result shows that the mathematical methods used for parameter prediction based on draw-ins can directly be used for the prediction with fixed point translations as reference. For the investigations, a cup drawing process is used.

Analysis of rectangular cup drawing considering anisotropic hardening and cyclic effect for orthogonal anisotropic materials

An anisotropic plasticity model is developed based on the non-associated flow rule with anisotropic hardening. The model combines non-quadratic yield function and quadratic plastic potential function for orthogonal anisotropic sheet metals. The model is also expanded to properly reproduce the cyclic effect during forming processes. The simple formulations can contribute to cost saving in the parameter acquisition process and implementation. The developed model was implemented into the finite element code ABAQUS as a user material subroutine under a general three-dimensional condition. To evaluate the capability of the plasticity model, different loading conditions and prediction of the yield surface were considered. A multi-step rectangular cup drawing process with the AA5182-O and DP600 sheets including draw/re-draw effects was applied to evaluate the performance of capturing complex plastic behavior by finite element simulation. The results show that the anisotropic plasticity model is capable of describing the anisotropic behaviors including anisotropic hardening and cyclic hardening with high accuracy and efficiency.

A novel hydrodynamic deep drawing utilizing a combined floating and static die cavity

A novel method named hydrodynamic deep drawing process utilizing a combined floating and static die cavity (HDDC) was proposed in this research, in order to depress wrinkling during hydrodynamic deep drawing process to form a conical cup with higher height. A special experimental setup of a combined die cavity, which a static chamber inlaid with an inner floating die cavity, was designed to implement the modified hydrodynamic deep drawing experiments. At first, the feasibility of the modified method was evaluated in detail by numerical analyses and experimental tests. Then, the effects of the liquid counter pressure in die cavity on the forming process were also studied. It was found that the proposed method HDDC was feasible and the suppressing wrinkling effect dramatically came into being by using a floating die cavity during the hydrodynamic deep drawing process for conical cups of higher height. The rigid contact between the crater corner of the floating cavity and the blank contributes to the suppressing wrinkle effect during the hydrodynamic deep drawing process utilizing a combined floating and static die cavity. The hydrodynamic deep drawing process of conical cups utilizing a combined die cavity becomes more robust compared with the conventional hydromechanical deep drawing process.

Experimental and numerical analysis of aluminium alloy cylindrical cup using novel deep drawing technique

ABSTRACT In the traditional deep drawing process, a blank holder is required to press the blank over the die to prevent wrinkling and to control the material flow into the die cavity. But, this important tool responsible for fracture on the sheet and the optimisation of blank holder pressure is very critical. This present study introduces a new technique for the deep drawing process of cylindrical cups through a conical die without a blank holder. In this new technique, cylindrical cups are produced by pushing a circular blank using a flat-headed cylindrical punch through a conical die with a cylindrical throat in a single punch stroke. A 3-D parametric FE model was built using the commercial FE package ANSYS/APDL-19. A die with a half cone angle of 18° has shown the best drawability for the new technique. A flat-headed punch was used for forming of AA8011 & AA1200 with 1 to 2 mm initial thicknesses and diameters varies from 45 to 65 mm in experimental analysis. 100-ton hydraulic press used for deep drawing setup. Finite element model results showed good agreement with experimental results. Experimentally, a cylindrical cup with a LDR of 2.5 has been successfully achieved.

Evaluation of the possibility of deep drawing of aluminium cylindrical drawpieces from sheets at different relative rolling reductions

In the paper, experimental results of research into a multi deep drawing process of cylindrical drawpieces are discussed. The investigations aimed to evaluate of the possibility of deep drawing of aluminium cylindrical drawpieces from sheets and analysis of experimentally obtained changes of forces at different relative rolling reductions. For the purpose of research, EN AW-1050A aluminium blanks with constant diameter and different thicknesses were examined. The material was prepared by longitudinal rolling with different relative rolling reductions (z = 10÷50%) and blanking process. Before deep drawing, some specimens were heat-treated to increase their plasticity. The material was annealed at 300-440°C for a period of 0.3 h. A special stand was utilised during the research. The experimental results on forces and displacements were recorded and processed using a computer stand with Test&Motion software. Selected parameters of the deep drawing process, including forces and limit deformations in four drawing steps, were determined. The results may be used as boundary conditions to perform an in-depth numerical analysis of the deep drawing process of aluminium cups without inter-annealing of material in the course of the production.

Experimental investigation of forming parameters for square cup deep drawing process

Abstract Manufacturing a defect free drawn part is always challenging task. This paper presents numerical analysis and experimental validation of deep drawing process in order to avoid thinning and wrinkles. Numerical and experimental approaches are used to analyze the effect of different drawing parameters such as blank shape, blank thickness, load, dry/wet lubrication on square cup drawing process using extra deep drawn steel (EDD) sheet material. Results of simulation through computer aided engineering (CAE) software are validated through experimentation. Formability analysis on the laser engraved circular grids formed on the blank surface is carried out using forming limit diagram (FLD). The optimized process parameters helped to form a square cup without any defects such as thinning, wrinkling, etc. Experimental and formability analysis showed that for considered process parameters, formability of material having a blank thickness of 2 mm is better as compared to a blank thickness of 1 mm and 0.8 mm, for load of 100 kN with dry lubrication. This work highlights the significance of forming limit diagram technique in strengthening numerical and experimental investigation of deep drawing process. In overall, this parametric study leads to prediction of final geometry of sheet blank accurately and distribution of strain and stresses, for the development of quality product through forming process.

Development a new methodology for measuring deep drawing forces based on dimensionless evaluation

In this research work, dimensionless models based on geometric parameters have been developed for the deep drawing process of rectangular cups to reduce the manufacturing costs on a large scale of application in a noticeable way. In the following, geometric parameters were given in dimensionless form by the Π-Buckingham dimensional analysis method and a series of dimensionless groups were found for both circular and rectangular initial blank. To find the best group of dimensionless geometric parameters, different cup scales 1:1, 2:1, 4:1 and 5:1 are evaluated numerically by ABAQUS Finite Element (FE) software, validated by experimental work. After all effective geometric parameters have been analyzed, the best fitting relational model of dimensionless parameters is found for rectangular and circular blank separately. Various thicknesses of St12 sheet metals were used for experimental validation, which were formed at room temperature. Also, results and response parameters were compared in the simulation process, experimental tests and dimensionless models. By looking at the outcomes, it is demonstrated that the geometric qualities of a large scale can be predicted by a small scale, utilizing the proposed dimensionless model. A comparison of the outcomes for dimensionless models and experimental tests shows that proposed dimensionless models have a high degree of precision in determining geometrical parameters and the prediction of drawing force. Furthermore, the dimensionless analysis was generalized to ensure high precision estimation of geometric values for large geometric scales.

Measurement of Weld Zone Properties of Laser-Welded Tailor-Welded Blanks and Its Application to Deep Drawing

Weld zones in tailor welded blanks have different mechanical properties than the base metals and thus have significant effects on formability. In this work, flow stresses of weld zones in laser-welded dissimilar dual-phase steels were measured. Strains at the weld zones of notched specimens were measured using the digital image correlation method and the flow stress data were corrected considering the anisotropy. For validation, finite element simulations were performed for the cup drawing process by considering the measured weld zone properties, and the weld line movements were compared with the measurements.

Deformation behaviour during deep drawing operation under simple loading path: A simulation study

Deep drawing is a significant metal forming process which is used in sheet metal forming operations. By this process complex shapes can be manufactured with significant accuracy. In this study, the prediction of deformation behaviour of aluminium alloy during an axi-symmetric cup drawing operation is studied numerically. For this purpose, 3D Finite Element (FE) simulation of a simple cup drawing process has been conducted using ABAQUS software. The simulation is done by considering the isotropic hardening and von Mises stress criteria. As the deep drawing process commences, the variation of generated von Misses stresses and plastic equivalent strain are observed at different stages of deformation and the change in strain energy generation of aluminium alloy sheet have been analyzed.