Punch Displacements Research Articles

Deformation behavior and formability of friction stir processed DP600 steel

Abstract The effect of friction stir processing (FSP) on the formability of DP600 steel was experimentally investigated and the basic relationships between biaxial deformation behavior and FSP-induced evolutions in microstructural and mechanical properties were established. FSP formed a microstructure that consists of lath martensite with increased volume fraction compared to as-received (AR) microstructure that mainly consisted of well-distributed fine martensite particles in a ferrite matrix. Consequently, AR yield strength (301 MPa) and ultimate tensile strength (621 MPa) increased to about 811 and 1054 MPa, respectively. This strength enhancement achieved accompanied by adequate uniform elongation and elongation to failure values of 6.3 and 13.0%, respectively. Under biaxial loading conditions, good strain hardenability of the AR DP600 steel brought about a large membrane stretching regime leading to high punch force for biaxial flow. After FSP, both punch displacements within the membrane stretching regime decreased due to the increased volume fraction of lath martensite leading to higher cracking tendency. In result, cup depth and peak punch force of FSPed DP600 decreased from 8.7 mm and 33.2 kN to 7.1 mm and 28.1 kN, respectively. The obtained results simply indicate that FSP can be employed to enhance the strength of dual-phase steels with a reasonable level of formability.

DETERMINATION OF PRESS BRAKE BENDING PARAMETERS FOR HARDOX 400 STEEL

In the present study, a specific hydraulic press brake based test setup (HPBTS) was designed and manufactured which was used to determine the bending forces and the punch displacements of Hardox 400 steel depending on the plate thickness, plate length and mechanical properties. The setup was equipped with an image processing system to detect the change of the bending angle during forming. Prior to bending tests, tensile tests were carried out and the identified mechanical properties were compared with the ones reported by the manufacturers. The effect of the difference between the mechanical properties on the bending parameters was investigated. Air bending technique was used for bending tests. Experiments were carried out with varying plate thicknesses, plate lengths, bending angles, forming speeds and channel openings using flat materials supplied from two different manufacturers. The effect of these parameters on bending force, displacement and springback angle was revealed. It was shown that the mechanical properties of Hardox 400 steel vary according to the manufacturer. The difference between the measured mechanical properties and the ones obtained from the manufacturers had a direct influence on the bending properties.

Deformation characteristics analysis of the fineblanking-extrusion flanging process

Nowadays, lots of flanging parts formed with the sheet metal have been widely used in the automotive industry. The fineblanked-extrusion flanging process can be used to fabricate the sheet metal flanging parts with high surface quality, high dimensional accuracy and production efficiency when compared with the conventional hole flanging process. In this paper, the process parameters were mathematically analyzed firstly, and the relationship between the punch displacements in fineblanking process H1 and in extrusion process H4 was presented. Then, a finite element model was created and verified by comparing with the experimental result. Using the valid finite element model, the forming load, metal flow, and damage distributions during the forming process were comprehensively analyzed, and the relationship between the workpiece thickness, flange wall thickness and the flange height has been revealed. Based on these simulation results, the deformation mechanism of the fineblanked-extrusion flanging process was revealed.

Industry 4.0 in stamping: A wrinkling indicator for reduced-order modeling of deep-drawing processes

Flange wrinkling is often seen in deep-drawing process when the applied blankholding force is too small. This paper investigates the plastic wrinkling of the flange under a constant blankholding force. The strain and stress state in the flange are first established and a plastic wrinkling reduced-order model is then proposed using energy method. The reduced-order model is implemented to predict the flange wrinkling of AA1100-O sheet by incrementally updating the flange ratio and other material parameters along the drawing process. A finite element model is developed in ABAQUS/standard to verify the results from the reduced-order model. The predicted punch displacements and wave numbers at the onset of wrinkling agree well with the simulated results for different blankholding forces, which demonstrates the accuracy of the reduced-order model and its potential application in fast prediction of wrinkling in deep-drawing process.

Experimental testing and Numerical modelling of a Kevlar woven – epoxy matrix composite subjected to a punch test

The paper investigates the penetration mechanics of thick-section composites. For this purpose, a series of quasi-static penetration tests on Kevlar 29 (plane wave) /epoxy panels with a nominal thickness of 6.5 mm (14 layers) were designed and conducted. The experiments were performed at different support spans using a blunt geometry for the punch. During the tests, the punch displacements and the applied force on the punch were measured.Finite element (FE) models were created to replicate the quasi - static punch test using the LS-DYNA solver and exploiting a material damage model that allows the reproduction of all the different types of failure occurring during the tests (fibre failure, matrix failure, delamination). The focus is placed on the capability of the model to mimic the experimental damage in order to have a reliable virtual tool able to provide, with high accuracy, the penetration mechanisms and the trend of the absorbed energy during the different phases of penetration. The comparison between experimental data and numerical results is discussed.

Crack nucleation and propagation in microcrystalline-cellulose based granules subject to uniaxial and triaxial load

Cracking patterns in four kinds of granules, based on the common pharmaceutical excipient microcrystalline cellulose (MCC) and subject to compressive load, were examined. The initial pore structure and the location of initial failure under uniaxial compression were assessed using X-ray micro-computed tomography, whereas contact force development and onset of cracking under more complex compressive load were examined using a triaxial testing apparatus. Smoothed particle hydrodynamics (SPH) simulations were employed for numerical analysis of the stress distributions prior to cracking. For granules subject to uniaxial compression, initial cracking always occurred along the meridian and the precise location of the crack depended on the pore structure. Likewise, for granules subject to triaxial compression, the fracture plane of the primary crack was generally parallel to the dominant loading direction. The occurrence of cracking was highly dependent on the triaxiality ratio, i.e. the ratio between the punch displacements in the secondary and dominant loading directions. Compressive stresses in the lateral directions, induced by triaxial compression, prevented crack opening and fragmentation of the granule, something that could be verified by simulations. These results provide corroboration as well as further insights into previously observed differences between confined and unconfined compression of granular media.

Plastic anisotropy effect on forming kinematics of the hole-flanging process

The plastic anisotropy effect on the forming kinematics of the hole-flanging process was experimentally and numerically analyzed. Firstly, the heterogeneity of the flange thickness and the flange height along the circumferential direction were distinguished experimentally. The measurements were performed from different flanges obtained under various process conditions. In order to explain the experimental results, a 3D finite element model was developed for the different conditions. The zone of the flange in contact with the punch and the zone free from any contact with the tools were distinguished for hole-flanging both with and without ironing. The variation of the contact zone with the punch and the normal contact force were identified along the circumferential direction for selected punch displacements. The profiles of deformed flange obtained on rolling and transverse directions were also characterized. The dependence to the sheet orientation of the clearance thickness ratio (Rcc) which indicates the occurrence of ironing was finally studied. Accordingly, the experimental observations were justified. In some cases, numerical results were validated by experiments. A 0.8-mm 1000 series aluminum alloy was used as typical material.

Fracture toughness prediction of reactor grade materials using pre-notched small punch test specimens

Pre-notched small punch test (p-SPT) samples (10 × 10 × 0.5 mm) have been fabricated to determine the crack initiation toughness. The machined notch profile is fabricated longitudinally from the centre of one side of the sample to the centre of the opposite side, producing a notch depth to thickness ratio a/t = 0.3.Plastic damage analysis of the p-SPT specimen has been performed by Gurson-Tvergaard-Needlemen (GTN) material damage model which shows the distribution sites of maximum equivalent plastic strain and maximum total void volume fraction (TVVF) is found to approximately similar pattern at different corresponding punch displacements. Numerical results show that the maximum equivalent plastic strain and maximum TVVF location is shifting from centre of the p-SPT specimen to the circumference side with the increment of punch displacement. Due to this numerical observation, the initiation of ductile tearing starts away from the centre of the p-SPT specimen.The crack initiation point has been predicted by numerical and experimental methods. The numerical method involves the GTN material damage model to identify crack initiation point. This is observed when first Gauss point failed completely. The GTN parameters which are used to invoke the crack initiation point in the p-SPT specimen were calibrated by experimental results of 3 mm diameter disk SPT specimens. However, the experimental method involves the analysis of the slope just before the maximum load to predict the crack initiation point. The predicted crack initiation points using both methods are utilized to estimate crack initiation toughness of structural steel. The crack initiation toughness values were obtained for two structural steels viz. T91 and SS304LN using the p-SPT test and compared with the standard test. The differences found were duly justified.

Compression Experiment and Simulation on Prismatic Lithium-ion Batteries

In order to understand the mechanical characteristics and failure modes of prismatic lithium-ion battery under mechanical loading conditions, flat plate compression and hemispherical punch indentation test were performed on 186570 prismatic LiFePO4 lithium-ion batteries and bare cells (cells without shell casing). Load and displacement of the cells and bare cells were measured in all tests. Additionally, temperature and voltage of the battery cells were also recorded. In flat plate compression condition, the battery shell casing cracked and electrolyte was squeezed from the cells. In hemispherical punch indentation condition, the punch displacements were stopped when a drop in force and voltage of the cell, as well as a rise in temperature indicated an internal short circuit in the cell. From the measured load-displacement data of the bare cell under flat compression condition, the individual compression stress-strain curves were calculated for the bare cells and used to develop a finite element model for the prismatic LiFePO4 battery. The bare cell is modeled as compressible foam material in LS-Dyna. This model can successfully predicted the load displacement relation of the cell under compression condition. On the other hand, this model can closely predict the force and punch displacement corresponding to the onset of short circuit in the cell under hemispherical punch indentation condition. The present tests and simulation can help to understand the deformation shape and internal short circuit mechanism of the prismatic lithium-ion cells under mechanical abuse conditions.

Hybridization effects on quasi-static penetration resistance in fiber reinforced hybrid composite laminates

Abstract Quasi static penetration tests (QSPT) were conducted on fiber reinforced hybrid composite laminates with a circular and cylindrical punch. Woven Carbon, Kevlar and S-glass fibers were used as reinforcing fibers for production of hybrid and non-hybrid composite laminates. Punch shear test procedures were employed until the perforation and complete plugging shear out of the laminate. During QSPT experiments, a flat end punch with diameter of 12.7 mm has been used for two different support spans (25.4 and 63.5 mm) to obtain two different support span (D s ) to punch diameter (D p ) ratios (SPR = D s /D p = 2 and 5). After the experiments, the extent of compression-shear and tension-shear based failure modes were characterized at constant punch displacements of 8 and 10 mm for SPR = 2 and 5, respectively. In addition to visualize of front and back side surfaces, composite samples were half sectioned at damage region to observe the amount of delamination and damage through the thickness of the laminate. It was found that hybridization effects were distinctly observed with dominated tension-shear damage mode at SPR = 5.

Investigations of ductile damage in DP600 and DC04 deep drawing steel sheets during punching

The paper presents numerical and microstructural investigations on a punching process of 2 mm thick steel sheets. The dual phase steel DP600 and the mild steel DC04 exhibit different damage and fracture characteristics. To distinguish the void development and crack initiation for both materials, interrupted tests at varied punch displacements are analyzed. The void volume fractions in the shearing zone are identified by scanning electron microscopy (SEM). The Gurson model family, which is recently extended for shear fracture, is utilized to model the elastoplastic behavior with ductile damage. The effect of the shear governing void growth parameter, introduced by Nahshon and Hutchinson (2008), is discussed.

On the size effects in micro/meso semisolid extrusion–forging of A356 aluminum alloy

Micro/meso forming is an economically competitive process for the fabrication of miniature metallic parts. Scaling conventional metal forming down to micro/meso scale leads to the so-called size effects. In this study, the size effects in micro/meso semisolid extrusion–forging (MSEF) of A356 aluminum alloy were numerically and experimentally investigated. An experimental setup for MSEF was developed, and the mechanical performance of A356 aluminum alloy in the semisolid state was tested. Then, the MSEF with various die-hole diameters and various friction coefficients were numerically investigated to examine the size effects in the processes. With certain punch displacements, it was found that the aspect ratio of the extruded pin decreased and the forging load increased during the miniaturization of the die-hole. In addition, the contact condition and the lubrication became increasing critical when the die-hole got smaller. Furthermore, various experiments were performed using A356 aluminum alloy. When the die-hole shrunk in the experiments, the changes of the pin aspect ratio and the forging load followed similar trends with the numerically simulated results. The size effects in the MSEF experiments mainly belong to the first-order size effect. In addition, no significant defect was found in the formed specimens with a die-hole diameter down to 0.55 mm, indicating great formability of the MSEF. The size effects identified in the MSEF process in this study assist in understanding the material flow and the cavity filling in the micro/meso semisolid forming with complicated geometrical shapes.

Characterizing and modeling mechanical properties and onset of short circuit for three types of lithium-ion pouch cells

Three types of lithium ion pouch cells ranging from small consumer electric cells with LiCoO2 cathode to large (electric vehicle size) cells with nanophosphate chemistry were tested under several local and global compression scenarios, including compression between two flat plates and local indentation with a flat cylindrical punch, a conical punch, and three hemispherical punches. Load, displacement, temperature, and voltage were recorded in all tests. The punch displacements were stopped when a drop in force and voltage of the cell, as well as a rise in temperature indicated a short circuit in the cell. Finite element models were developed for each cell type. Two tests were used for calibration of the constitutive properties of each type of cell, and the remaining tests served for the validation of the computational model. The models successfully predicted the load displacement relation and contour of deformations in the cells. Additionally, the models closely predict the force and punch displacement corresponding to the onset of short circuit in the cell. The current results are building confidence in robustness and accuracy of the present calibration and modeling approach.

Comparison of Calculated and Experimentally Determined Punch Displacement on a Rotary Tablet Press Using both Manesty and IPT Punches

An indirect method of calculating punch displacement on a rotary tablet press from measurements of the change in punch force with the turret position was in good agreement with direct measurements of punch displacement made using a linear variable displacement transducer (LVDT)-slip ring system. The direct measurements were made during the compaction of three direct compression agents using Manesty punches. However, the agreement between calculated and experimentally determined punch displacements was unsatisfactory when IPT punches were used. The IPT punches have a much flatter punch head profile than the Manesty punches. Due to this difference, the analytic equation does not accurately describe the dynamics of the press under normal operating conditions. Terms in the analytic equation, determined originally under static conditions, were re-evaluated under dynamic conditions for both sets of tooling using the LVDT-slip ring system. Excellent agreement for both IPT and Manesty punches was found between punch displacement calculated using the revised analytic equation and direct experimental measurements. Punch displacements determined from punch head profile and machine geometry only, without taking machine deformations into account, were shown to differ widely from the calculated and experimental values.

Theoretical estimation of punch velocities and displacements of single-punch and rotary tablet machines.

The speed of travel of punches during compaction by a Manesty F3 single punch and D3B Rotary punch tablet machine has been derived from machine dimensions, normal operating speeds and by consideration of the consolidation of a theoretical compact. The analysis may also be used for machines with other dimensions, operating at different speeds with other materials, but would require modification if the punch head design on the rotary machine differed significantly. Punch speeds at the beginning of the compression cycle were similar for the two types of machines, namely 10.36 and 10.24 cm s-1 for the single and rotary machines. The time to reach maximum compression and the total time of contact between punches and powder for the single punch machine was 0.1 s for a compaction force of approximately 40 KN. For the rotary machine operating at approximately the same force, these two parameters were found to be 0.052 and 0.083 s respectively. The additional contact time is associated with a period during which there is no vertical movement of the punch, providing a 'dwell' time of 0.0314 s when the powder is held at a constant volume.

Sensitivity analysis by the adjoint variable method for optimization of the die compaction process in particulate materials processing

Nonuniform shrinkage during sintering results from the nonuniform green density distribution in a compacted powder body and this creates a severe problem in net-shape forming. Therefore, proper selection of the process parameters, such as compaction die design, upper and lower punch displacements, and sequential tool motion, is very important for the optimum design of die compaction processing. Previously, these were guess-estimated based on experience. As a first step in developing a more scientific design technique in powder metallurgy, the equations for the adjoint variable method (AVM) for the non-steady-state uniaxial powder compaction process are derived in detail. The accuracy of the AVM is verified through the comparison of the design sensitivity with calculations performed using the finite difference method.

Numerical simulation of warm compacted synchronous pulley

Abstract A new mechanical model for warm powder compaction was presented. Warm compaction process of iron-based powder was investigated to deal with the existence of elastic, plastic and thermal strains. A coupled mechanical and thermal model was developed based on ellipsoidal yield criterion and continuum theory. The constitutive equations were integrated into the constitutive integral arithmetic and solved employing incremental iterative solution strategy. The flow stress model of iron powder was nonlinearly fitted according to uniaxial warm compaction. The constitutive model was implemented into user-subroutines of MSC.Marc. With the equations, algorithms and programs developed, the compaction procedures of a complex synchronous pulley were simulated. Two different compaction schemes with different punch displacements were tested and the relative density distribution was obtained. Comparison with experimental data shows that the homogeneity of green compact is greatly affected by the compaction mode. The simulation results agree with the experiments very well.

Thermodynamic analysis of compact formation; compaction, unloading, and ejection: I. Design and development of a compaction calorimeter and mechanical and thermal energy determinations of powder compaction

The aim of this investigation was to determine and evaluate the thermodynamic properties, i.e. heat, work, and internal energy change, of the compaction process by developing a ‘Compaction Calorimeter’. Compaction of common excipients and acetaminophen was performed by a double-ended, constant-strain tableting waveform utilizing an instrumented ‘Compaction Simulator.’ A constant-strain waveform provides a specific quantity of applied compaction work. A calorimeter, built around the dies, used a metal oxide thermistor to measure the temperature of the system. A resolution of 0.0001°C with a sampling time of 5 s was used to monitor the temperature. An aluminum die within a plastic insulating die, in conjunction with fiberglass punches, comprised the calorimeter. Mechanical (work) and thermal (heat) calibrations of the elastic punch deformation were performed. An energy correction method was outlined to account for system heat effects and mechanical work of the punches. Compaction simulator transducers measured upper and lower punch forces and displacements. Measurements of the effective heat capacity of the samples were performed utilizing an electrical resistance heater. Specific heat capacities of the samples were determined by differential scanning calorimetry. The calibration techniques were utilized to determine heat, work, and the change in internal energies of powder compaction. Future publications will address the thermodynamic evaluation of the tablet sub-processes of unloading and ejection.

Axi-symmetric bodies of equal material in contact under torsion or shift

Two axi-symmetric bodies are pressed together, so that their axes of symmetry coincide with the contact normal and the normal force is held constant. A small torque about the contact normal or a small tangential force is applied. For bodies of equal material, the normal and tangential stress states are uncoupled, and can solved separately. The surfaces of the bodies are thought as a superposition of infinitesimal rigid flat-ended punches. Consequently, the normal stress distribution can be calculated as a summation of differential flat punch solutions. A formula results, which is identical with the solution of Green and Collins. After application of a torque an annular sliding area forms at the border of the contact area. For reasons of symmetry, the common displacement of the inner stick area must be a rigid body rotation. Similarly to the normal problem, the solution can be thought as a superposition of rigid punch rotations. The tangential solution can be derived analogically, in form of a superposition of rigid punch displacements. The present method also solves the problem of simultanous normal and torsional or tangential loading with complete adhesion. As an example, Steuermann's problem for polynomial surfaces of the formA2nr2nis solved. The solutions for constant normal forces can be used as basic functions for loading histories with varying normal and tangential forces.

Calibration of a compaction simulator for the measurement of tablet thickness during compression.

For the calibration of a compaction simulator for punch displacement measurements, the displacement of the punch must be related to the voltage output of a linear variable displacement transducer (LVDT) which is attached to the punch via its movable core, with correction for any deformation of the machine parts which are inherently incorporated in the LVDT readings. Contrary to common assumptions the relationship between the displacement of the movable core and the voltage output of the LVDTs used is not linear. Similarly, the deformation of the machine parts did not follow Hooke's law of linear elasticity but exhibited characteristics of nonlinear elasticity. The data demonstrate the need for careful validation of the calibration of a compaction simulator when accurate punch displacements are required.