Punch Stroke Research Articles

Simulation of Metal Flow to Investigate the Application of Antilock Brake Mechanic System in Deep Drawing Process of Cup

This paper presents the importance of simulation of metal flow in deep drawing process which employs an antilock brake mechanic system. Controlling the force and friction of the blank holder is imperative to assure that the sheet metal is not locked on the blank holder, and hence it flows smoothly into the die. The simulation was developed based on the material displacement, deformation and deep drawing force on flange in the radial direction, that it is controlled by blank holder with antilock brake mechanic system. The force to blank holder was applied periodically and the magnitude of force was kept constant during simulation process. In this study, the mechanical properties of the material were choses such that they equivalent to those of low carbon steel with its thickness of 0.2 mm. The diameter and the depth of the cylindrical cup-shaped product were 40 mm and 10 mm, respectively. The simulation results showed that the application of antilock brake mechanic system improves the ability to control the material flow during the drawing process, although the maximum blank holder force of 13000 N was applied. The optimum condition was found when the drawing process was performed using blank holder force of 3500 N, deep drawing force of 7000 N, friction coefficient of 0.25 and speed of punch stroke of 0.84 mm/sec. This research demonstrated that an antilock brake mechanic system can be implemented effectively to prevent cracking in deep drawing process.

Earing Prediction in Drawing and Ironing Processes Using an Advanced Yield Criterion

This work aims to contribute to the understanding of the role/influence of advanced yield criteria on the earing profile prediction after drawing and ironing, for a cylindrical cup benchmark proposed at the NUMISHEET 2011 conference [1]. Two typical materials used for can-making were considered and studied: an AA5042 aluminum alloy and an AKDQ steel. The drawing and ironing operations are performed on a special die which allows drawing and ironing in one single punch stroke in order to simplify the real process. The benchmark results report include, for each material: (i) the earing profile after drawing and ironing, presenting the cup height evolution with the angle from the rolling direction, and (ii) the evolution of punch force with punch stroke. This work presents a comparison between experimental and numerical results obtained for the aforesaid benchmark with DD3IMP in-house solver, using two sets of parameters for the Cazacu and Barlat 2001 [2] yield criterion, identified based on uniaxial tensile, equi-biaxial tension and disc compression test results. The first set uses the initial yield stress values while the second one used the flow stress values for an accumulated plastic work of 20 MPa. The results highlight the different impact of the experimental data in the earing prediction for both materials: the results for the second set are slightly improved for the AKDQ steel while for AA5042 the effect is negligible. The improved earing prediction obtained with the second set for the AKDQ steel seems to result from a better description of the stress states that occur in the flange zone.

Control System Algorithm for the Prediction of Sprinback in Air Bending

The phenomenon of springback, which is ruled by strain recovery after removal of forming loads, is of remarkable interest in air bending of metal sheets. In this process, the final angle is affected by a number of parameters related to both process geometry (sheet thickness, die and punch radii) and material properties (elastoplastic stress-strain law); because of this, punch stroke has to be calculated in a nontrivial way and a number of input parameters should be taken into account. In this work the study of total load as a function of displacement is used to collect information about material stress-strain law; using this approach, load data may be exploited to fine tune the mathematical description of the material and, finally, to improve springback prediction. A customized press brake able to measure both displacement and force during bending was fabricated for this purpose. The press brake is equipped with a control system algorithm able to collect material information directly during the initial stage of the bending process. These collected data are used to feed a model based on a FEM simulation and the model output is the final punch displacement suitable to obtained a specific bending angle after unloading. The program utilized for the simulation is Deform 2D. Preliminary tests were executed on metal sheets having different thickness.

The THF Compression Test for Friction Estimation: Study on the Influence of the Tube Material

In the Tube Hydroforming (THF) process, a tube, placed in closed dies, is expanded by a high pressure liquid and two punches push its edges in order to feed the material into the expansion zones. Because of the high pressure and the contact area involved in the process, high friction stresses act on the tube walls restricting the material flow so reducing the amount of fed material, the part formability and affecting the soundness of the final part and its geometry. In fact, previous studies showed that the lower the friction coefficient at the tube-die interface, the more uniform the friction distribution and, therefore, the more uniform the stresses acting on the tube walls. The tube deformation being dependent on the stresses, its final thickness is influenced by friction. Starting from this premise, the authors proposed a reference test which is able to highlight the effect of friction on the final tube thickness. In this test, namely the THF Compression Test, a tube is placed in a cylindrical die having the same diameter as the outside of the tube, it is pressurized and then compressed by the punches. In this way, the tube has no expansion and its final thickness depends on the process parameters (tube material, pressure, punch stroke, tube material and geometry). Using FE simulations, it is possible to express the friction coefficient as a function of the process conditions and to use it in combination with experimental results. In the present paper, the previously validated FE model is used to investigate the influence of the tube material on the compression test results. Therefore, a simulation study was performed using different values of strength and hardening coefficients showing how the method is affected by the tested material thereby giving further indication of the test sensitivity.

End formation of a round tube into a square section having small corner radii

Expansion and reduction are the two common end forming processes for tubes. In the tube end expansion process using a square punch, it is difficult to obtain a small corner radii due to the stretching of the tube around the punch corners. The wall thickness around the corners is small when compared to the side wall. Hence, a tube having a poor square look is formed. In this study, a 2-stage end expansion of a round tube end into a square section having an improved square look i.e. small corner radii and increase in wall thickness around corners is developed. In the 1st stage, the tube end is flared into a cone shape using a 30° conical die by axial compression. In the 2nd stage, the conical end of the tube is drawn through a taper square die using a conical bottom square punch, and a near square section is formed. A 15% ironing ratio is applied during the drawing process to flatten the side wall of the square. Experimental and FEM simulation were performed to evaluate and to verify the forming process. Although the height of the square section increases when the punch stroke at the 1st stage is increased. However, this increase is limited by the buckling of the pipe at the circular section of the thick blank tube. Since the conical end is drawn into a square section having different radial lengths, the bottom of the square section is uneven. The uneven bottom end is trimmed off in the later process. A square section having a maximum height of 32mm after trimming is successfully obtained from the experiment for the punch stroke, S=44mm using an API 5L tube.

Experimental Study and Analysis of the Influence of Drawbead against Restriction and Deep Drawing Force of Rectangular Cup-Cans with Tin Plate Material

Drawbead are often used to control the flow of material, stress and deep drawing force in the flange area. This paper discussed the drawbead (fully, not fully and without drawbead) that combined with variations in the blank holder force against restriction of material flow and drawbead restriction force of deep drawing with palm oil lubrication. In this paper, analytical and experiments are used to predict the drawbead restraining and deep drawing force. The tin steel sheet with a thickness of 0.2 mm is used as speciment. The results obtained, that the application fully drawbead be very effective in controlling the flow of materials in the flange, as compared to not fully and without drawbead. In the beginning of the process (punch stroke < 4 mm), the magnitude of restraining force and deep drawing force can be increased. And, the magnitude of Radial Stress increases, conversely the magnitude of tangential stress decreased. This can prevent the occurrence optimum blank holder force is recommended in range 4394-8788 N. Comparisons of results between the analysis and experiments show the phenomenon is similar.

AZ80 압출재를 이용한 고온단조 윤활특성 분석

This paper demonstrates the lubricant performance in T-shape hot forging of Mg alloys. This processes induces complex plastic material flow of the initial billet such as simultaneous compression and extrusion deformations. Five lubricants with different amounts of graphite are applied to the T-shape forging at temperatures of 300 and <TEX>$350^{\circ}C$</TEX>. As the amount of graphite in the lubricant increases, the extruded depth gradually increases, which improves hot forgeability for Mg alloys. However, the lubricant performance decreases as forging temperature increases from 300 to <TEX>$350^{\circ}C$</TEX>. As the punch stroke increases, forgeability is considerably influenced by the lubricant. Thus, the selection of lubricants in hot forging of Mg alloys is critical when plastic deformation is severe.

Shear cutting of press hardened steel: influence of punch chamfer on process forces, tool stresses and sheared edge qualities

In order to cope with the difficulties of shearing operations of press hardened steels, this work attempted to optimize these processes. Herefore, it is necessary to reduce the press forces and stresses in tools, while still obtaining adequate sheared edge quality levels. To reach this goal, different punch chamfer angles (0°, 2°, 7° and 20°) and relative cutting clearances (5, 10 and 15 % of the sheet thickness) were tested in a cutting tool, which was adapted in a way that different active elements could be mounted. The tool was equipped with a measurement system, which allowed the determination of the process forces in three dimensions at each punch stroke. Basis was an AlSi coated 22MnB5 sheet with a thickness of 1.5 mm. In addition a finite element model was developed to predict the stress distribution in tools and the sheared edge qualities. According to the experimental results the application of a 20° chamfer angle succeeded to reduce the forces and stresses of tools, but the sheared parts had a poor quality. In contrast, the 7° chamfer angle gave lowest tool stresses and sufficient part qualities, but the forces were very high. The simulation results agreed with the experimental data, except for the prediction of the rollover zone. These deviations were attributed among others to the presence of the AlSi coating, which was not considered.

Numerical Investigation of Fine Blanking of a Helical Gear

Fine blanking, as an effective and economy metal forming process, can be used for the manufacturing of helical gears with inclined forming movement. In the present study, a reliable three-dimensional (3D) rigid-plastic finite element (FE) model is developed on the DEFORM-3D platform for rotational fine blanking of a helical gear. Based on this FE model, distributions of different field variables such as metal flow velocity, mean stress and effective strain are obtained, and cut surface features and punch stroke curve are predicted. The results achieved in this study can not only evaluate the capabilities of the rotational fine blanking process of a helical gear, but also provide valuable guidelines and a better understanding of the deformation mechanism of this process.

Experimental verification of a deep drawing tool system for adaptive blank holder pressure distribution

In deep drawing, the strain path in the blank during the forming process can be significantly affected by application of temporal and spatial variation of the blank holder force. In this study, an active tool system capable of controlling the distribution of the blank holder force is presented which can be integrated into existing stacked deep drawing tools without need for modification of the press.A working system is presented consisting of a controller, designated volume displacement cavity pressure supply units and a shimming plate. It is applied to the deep drawing of a rectangular geometry using a conventional stacked tool design. The shimming plate is used to support the blank holder plate, and has four integrated hydraulic cavities in which the pressure can be controlled individually whereby a controlled deflection of the blank holder plate is achieved analogous to the conventional shimming method using paper or metal shims between the tool plates.The tool system's ability to influence the material flow is investigated by performing a series of deep drawing experiments. Eight different cavity pressure schemes are applied during the punch stroke and the scheme's effects are documented by means of process data and 3D-coordinate measurements of the formed parts demonstrating that both the geometric shape and the thickness distribution in the formed parts can be affected by the shimming system.

A comparison study of sliding friction behavior between two high strength DP590 steel sheets against heat treated DC53 punch: Hot-dip galvanized sheet versus cold rolled bare sheet

Sliding friction tests were performed to compare the friction behaviors of hot-dip galvanized dual phase sheet (GA-DP590) and cold rolled bare sheet (BARE-DP590). The tests were undertaken with sheet specimens slid against heat treated DC53 punch mounted in a self-developed Tribo-tester to simulate the sliding between the sheets and the forming tool. Results show that the friction coefficients of GA-DP590 sheet are higher than those of BARE-DP590 sheet. The coefficient values of both sheets generally decrease with increasing of the loading, the punch stroke and the sliding speed. However, the frictional coefficients of GA-DP590 can be clearly classified into three stages. SEM observations on the slid sheets were performed to facilitate the understanding of the mechanisms affecting the friction behavior.

New attempt to wrinkling behavior analysis of tailor welded blanks during the deep drawing process

Tailor welded blanks (TWBs) are steel sheets of different characteristics welded into a single flat blank prior to pressing in order to achieve the optimal material arrangement and weight reduction for cars, and to increase process efficiency and machine flexibility. The problem in regard with these blanks is their low formability, which defects like wrinkling occur prematurely. Developing a model to assess the wrinkling initiation of these blanks during forming processes enables one to arrange the forming parameters to enhance the formability. In this research, wall wrinkling tendency of a TWB consisted of interstitial free (IF) steels with different thicknesses (0.8 and 1.2mm) was analyzed analytically, numerically and experimentally. Due to more formability of thin segment with respect to weld and thick segments which results in deflection of the thin segment, the principal stress directions were assumed to be deviated from the principal curvature axes. “Autogrid” software was applied to measure the geometrical data and strains during the experiments. The predicted results about punch stroke value and critical strain at onset of wrinkling were in good agreement with experimental results. The results also showed that wrinkle waves just formed in thin segment of TWB, and wrinkling initiated by development of three wrinkle waves.

Investigation into the effects of weld zone and geometric discontinuity on the formability reduction of tailor welded blanks

Numerous advantages of application of tailor welded blanks (TWBs) in automobile industry, namely reduction of weight, fuel consumption and air pollution, have made the manufacturers eager to investigate in this field. On the other hand, while experiments generally provide valuable information in regard with mechanical behaviors, but utilization of simulation methods has extended vastly due to time and cost saving issues. One challenging issue in numerically analyzing the forming behavior of transversely welded TWBs, welded by laser welding methods, has been the presence of weld zone. While some researchers believe that during simulation, the weld zone can be neglected due to its minority and consequently the simulation time will be less, the others confess that the consideration of weld zone increases the accuracy of the results although the time of simulation enhances. In this research, the effect of weld zone presence on the formability of transversely CO2 laser welded TWBs was studied experimentally and numerically (FE-method). The studied TWBs were consisted of IF-steels with different thicknesses (0.8 and 1.2mm), and limiting dome height as well as forming limit diagram were used for formability assessment. Experiments in regard with limiting dome height test showed that the decisive factor in decreasing the dome height is geometric discontinuity and the effect of weld zone is about 6%. Moreover, simulation results indicated that the consideration of weld zone did not have any observable effect on limiting strains, although tearing occurred at lower punch stroke.

Bending Testing Rig Development through CAE Tools Application

Bending can be considered one of easier sheet metal forming processes. In fact, it represents one of the basic variants of applied deformations to metal blanks. However, the numerous research contributions dedicated to sheet metal bending that have been published over the past decade and the constant stream of announcements by R&amp;D departments of machine constructors are strong indications that not all research challenges related to sheet metal bending have been done. This paper reports the developed activity carried out to design a bending testing rig characterized by: a working horizontal axis, a maximum bending length equal to 200 mm, a maximum applicable force equal to 80 kN. A partitioned blankholder has also been designed to allow bending operations on tailored blanks. Moreover, a Graphical User Interface hollows to set up the process parameters and the acquisition of testing data (Temperature and/or Force as function of the process time or punch stroke). CAE tools application had a strategic role to develop the best layout and to find the optimum solutions for the process variables tuning. CAE techniques have allowed to investigate and verify different layout solutions both for the bending process and the structural components of the tooling.

Anisotropic Plastic Behavior of TRIP 780 Steel Sheet in Hole Expansion Test

Plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy in different stress states. Additionally, disk compression test was performed for obtaining the balanced r-value. According to the different yield criteria, yield stresses and r-values were calculated for different directions and then compared with experimental data. To verify the modeling accuracy, a hole expansion test was carried out experimentally and numerically by FE simulation. Stress-strain curve from the biaxial test was described using voce and swift hardening models. Punch load and stroke, final hole radius, and strain distribution on specimen surface along the hole circumference and the specimen diameter in rolling and transverse directions were determined and compared with the experimental results. It was found that the simulations applying Yld2000-2d yield function provided an acceptable agreement. Consequently, it is noted that the anisotropic yield potential significantly affects the accuracy of the predicted deformation behavior of sheet metal subjected to hole expanding load.

Phase change flattening process for axial grooved heat pipe

A novel processing technique named phase change flattening process has been developed to fabricate the flattened grooved heat pipes, which are in high demand for electronics cooling. The phase change vapor pressure in the flattened heat pipe is analyzed on the basis of its operating principle. An elasto-plastic FEM simulation is proposed to analyze stress and strain distribution for the flattening process. An experiment is also set up to verify this elasto-plastic deformation of axial grooved heat pipe (AGHP). Results show that the vapor pressure is determined by the saturated vapor pressure equation of heat pipe. Punch load of the upper plate greatly increases due to its higher vapor pressure and the buckling phenomenon can be well eliminated when the vapor pressure reaches 1.002MPa at vapor temperature 453K. The maximum equivalent plastic stress and strain distribute on the maximum bend points at the bending wall of heat pipe when the punch stroke is over 3mm. The width, vapor area and grooves of flattened heat pipe change greatly as the flattening proceeds.

Study on Working Hardening for the Sheet with Different Hardening Index by Fine-Blanking with Negative Clearance

The hardening layer of blanking boundary could enhance structure intensity and wear resistance of blanking work piece evidently. Therefore it could enhance fatigue strength and the working life of work piece greatly. This paper carried through fine-blanking with negative clearance processing experiment for the sheet with different hardening index and measured the blanking force and the punch stroke relations curves. The micro hardness of the blanking work pieces sheared surface were measured by Vickers Hardness instrument(MH-6), which obtained the relations curves of punch stroke and the micro hardness of the blanking work pieces. The level of working hardening were compared with different hardening index materials by fine-blanking with negative clearance, and the blanking work pieces working hardening were enhanced evidently by fine-blanking with negative clearance.

Lateral Extrusion of Gear-Like Components with Radial Tooth Profile: Metal Flow Simulation and Analysis

The process of lateral extrusion of gear-like components with radial tooth profile has been studied in this paper. The material flow in extrusion die cavity has been simulated using the SuperForge of FVM simulation package. The results of simulation have shown that the material fills the die cavity in two stages: Parallel movement to the end of toothed die cavity and fills the rest of shaped die cavity. Each stage of deformation has been analyzed by using slab method of analysis and the extrusion load values for each punch stroke have been estimated. Finally, comparisons between present theoretical results and experiments of other researchers’ work have been carried out to illustrate the validity of this proposed model.

Plate forging of tailored blanks having local thickening for deep drawing of square cups

A plate forging process of tailored blanks having local thickening for the deep drawing of square cups was developed to improve the drawability. A sheet having uniform thickness was bent into a hat shape of two inclined portions, and then was compressed with a flat die under restraint of both edges to thicken the two inclined portions. The bending and compression were repeated after a right-angled rotation of the sheet for thickening in the perpendicular direction. The thickness of the rectangular ring portion equivalent to the bottom corner of the square cup was increased, particularly the thickening at the four corners of the rectangular ring undergoing large decrease in wall thickness in the deep drawing of square cups became double. The degree of thickening can be adjusted by controlling the punch stroke in the bending. By using the tailor blanks having local thickening, not only the decrease in wall thickness at the bottom corner of the square cup was prevented, but also the limiting drawing height of the cup without fracture was increased to 28.3 mm, whereas that for the uniform blank was 21.3 mm.

Size effects in micro blanking of metal foil with miniaturization

Miniaturization of micro blanking process caused changes in the relative contribution of relevant process parameters and the grain size of metal foil reaches the same order with the blanking clearance. As a result, the size effects occur, which is different from the other micro forming processes, such as micro upsetting, micro tensile, and micro bending. In the paper, the size effects of micro blanking of metal foil with miniaturization were investigat- ed. Similar to the traditional blanking process, the micro blanking process is still composed of three stages of elastic deformation, plastic shearing deformation, and fracture separation. However, the maximum blanking force appeared at punch stroke of foil thickness, which is much larger than the transitional blanking process of 1/3 of work material thickness. The cross section of micro-hole is also composed of rollover, smoothly shearing zone, fraction zone, and burr. But the distribution of the fraction zone and burr is uneven, which is caused by the influence of the material anisotropy with the decreasing of the foil thick- ness. The results show that the ultimate shear strength of micro blanking is decreasing with the increasing of the length scale l, not only for the brass foil, but also for the stainless steel foil. The fracture mechanism of micro blanking of brass foil is significantly changed from shear dimple to slip separation with the decreasing of length scale l, but the fracture mechanism of micro blanking of stainless steel is not changed and kept ductile fracture with equiaxed dimples