Punch Displacement Research Articles

Influence of the material properties on the clinching process and the resulting load-bearing capacity of the joint

This study focuses on the phenomenological change in material strength caused by a specific heat treatment and the subsequent analysis of the influence on the clinching process and the resulting joint properties. For this purpose, three series of tests were performed. In the first series of tests, the influence of heat treatment up to 340 °C on the mechanical properties of an age-hardenable AlMgSi alloy was investigated. Holding time and temperature were varied and the material strength was evaluated by tensile and hardness tests. Two strength-increasing and two strength-reducing heat treatment parameters were identified. In the second series of tests, selected heat treatment parameters were applied to a larger number of specimens and the joint strength was investigated by shear and head tensile tests. In the shear tensile test, mainly the properties of the punch-side material have an influence on the resulting joint strength. A change in strength of the die-side material can be neglected. In contrast, the properties of both sheets are important in the head tensile test. The strength of the joint will only increase if the strength of both sheets is increased. In general, a strength increasing heat treatment resulted in higher joint strength. In the third series of tests, the factor of punch displacement was considered, which was demonstrated to directly influence the formation of the clinched joint geometry.

The effect of deformation rate on the process of hot extrusion with dispensing of round hollow semi-finished products

Background. Stamping of round hollow semi-finished products by hot reverse extrusion is one of the initial operations in the manufacture of hollow products for special purposes. The force and shape change of the metal during hot plastic forming is significantly affected by the deformation rate or the speed of movement of the deforming tool. For special-purpose products, certain mechanical properties are required in the wall height and bottom part. The wall height properties are ensured at subsequent stretching transitions with thinning of the semi-finished product obtained by hot extrusion, which involves working out the metal structure by plastic deformation to achieve the required properties. Therefore, it is an urgent task to study the effect of the deformation rate on the force and shape change of the metal during hot reverse extrusion of hollow semi-finished products.Goal. To determine the influence of the deformation rate on the parameters of hot reverse extrusion with the dispensing of hollow semi-finished products from round and square billets by means of finite element method (FEM) modeling and to compare the results of theoretical researches.Methodology of implementation. Theoretical researches of extrusion power modes, specific forces, and the stress-strain state of metal were carried out by modeling using the FEM in the DEFORM software environment.Results. The FEM was used to model the process of hot reverse extrusion with dispensing of round hollow semi-finished products from mild steel with protrusions at the end of the bottom part on the side of the cavity and on the outer surface. The deformation rate was in the range of 20 to 80 mm/sec. Round and square cross-sectional blanks were used. The dependence of the extrusion force on the punch displacement was determined. The distribution of specific forces on the deforming tool was determined. The stress-strain state and temperature distribution in the deformed metal at the end of extrusion were determined. The development of the metal structure by hot plastic deformation was evaluated and the results obtained were comparedConclusions. The effect of the deformation rate on the parameters of hot reverse extrusion with dispensing of round hollow semi-finished products was determined

Examination of the Forming Properties of Vehicle Body Panels

During vehicle design, the mass of the components and their resistance to collision are important criteria, as they affect fuel consumption and make the vehicle safer. In this study, we examined the deformation of high-strength materials commonly used in the automotive industry in the form of tailored welded blanks. Tests were conducted both in an experimental environment and in a simulation environment, measuring the punch displacement associated with the specimens to characterize the deformation. In designing the specimens, the weld seam was placed perpendicular and parallel to the rolling direction, thus creating different deformation states.

Effect of meshing technique and time discretization size on thickness strain localization during hole-flanging simulation of DP980 sheet at high strain level

In the simulation of the hole-flanging process, many had reported that the effect of mesh sensitivity on strain localizations is insignificant. In this study, mesh layouts including the number of elements along the hole circumference (CD), element sizes in radial directions (R1) and the time discretization (or increment) sizes (T) are varied in the 3D FE simulation of 10-mm hole flanging process of DP980 thin sheets using a conical punch. Its effect on wall thickness distributions and forming load profiles are investigated. Also, the effect of punch surface meshing techniques i.e., analytical and discrete rigid on the distributions is investigated. The simulation results showed that the largest % wall thinning range around the expanded hole edges for punch displacement, S = 15 mm and 20 mm are 25.8–29.2% and 33.3–64.2%, respectively. The load-displacement curves during the continuous hole expansion are not linear for R1 ≥ 0.5 mm. For CD70 & R1 = 0.1 mm, the increase in T values from 0.1 s to 1.0 s has significantly increased the total simulation time by 25% due to the convergence problems. The automatic time increment mode in each step at T = 1.0 s has failed to reduce the total simulation time. The discrete rigid punch surface produces more concentrated wall thickness distributions than the analytical one, leading to higher amount of wall thinning, particularly for high S values. Since the model stiffness reduces with decreasing mesh size. It is recommended to match the simulated peak load with the experimental peak under the instability condition with a smooth hole e.g., a laser cut hole to determine the appropriate meshing method for the mesh sensitivity study. With that, the stiffness of the simulation model is calibrated with the experiment.

Forming process prediction of a self-piercing riveted joint in carbon fibre reinforced composites and aluminium alloy based on deep learning

As a mechanical internal locking structure, the forming process of a self-piercing riveted (SPR) joint is currently mainly investigated through riveting interruption experiments and finite element simulation. To solve the problems of complex simulation modelling processes, high experimental costs, and low efficiency, an SPR process prediction method based on deep learning was proposed to predict the deformation process and damage of SPR joints in carbon fibre-reinforced composites and aluminium alloys. The original images of the model dataset were obtained based on the simulation results, and image segmentation technology was used to classify the cross-section and damage morphology of the joint. A deep learning model based on a convolutional neural network and conditional generation antagonism model architecture was established, and the section shape and damage morphology of the joint were predicted by inputting the percentage of punch displacement. The k-fold cross validation method was used for model training, and the untrained data were used as the test set to verify the predictive ability of the model by comparing the forming section parameters of the SPR joint. The results show that the deep learning model used can accurately predict the deformation state and damage evolution of riveted materials at different joining stages. The average prediction accuracies of the height of the riveted head, residual thickness, and rivet spread are 95.80 %, 95.68 %, and 92.40 %, respectively.

Solving three-dimensional contact problems for foundation design in green building

Design of foundations on an elastic base is carried out using the solution of three-dimensional problems of contact interaction. Improving the accuracy of engineering calculations is necessary to ensure economic efficiency and increase energy savings in green building. The problems of indentation of punches with a flat base bounded by doubly connected close to polygonal contact areas are researched in the present work. Small parameter method is used to obtain explicit analytical expressions for the contact pressure distribution and the punch displacement dependence in a simplified form, which is convenient for engineering practice. The found load-displacement dependence satisfies the known inequalities that are valid for an arbitrary contact domain. Also a numerical-analytical method is in consideration. It uses the simple layer potential expansion and successive approximations for the problems accounting roughness of the elastic half-space. Roughness coefficient is considered as a parameter of regularization of the integral equation for the smooth contact problem. The results of both methods coincide with sufficient accuracy.

Experiments and simulations of the drawing envelope of commercially pure aluminum

The range of blank-holding force (BHF) for which deep drawing of AA1100-H24 is successful is investigated using a combination of experiments and simulations. The experiments involve circular blanks of three different diameters: 35 mm, 37 mm and 40 mm. The thickness of the blanks is 0.51 mm. These are drawn with a punch of 20 mm diameter, i.e., at drawing ratios of 1.75, 1.85 and 2.0, respectively, using a custom, modular forming apparatus where the BHF can be controlled at will, between 0 and 2,400 N. The experiments are performed in an Instron 8872 servo-hydraulic frame that allows precise measurements of the punch force and displacement. The working envelopes are determined experimentally in the space of BHF and draw depth, which can be categorized into three regimes: wrinkling, safe and tearing. It is found that grey zones exist between the three regimes. These experiments are then simulated in Abaqus/Standard, using two types of elements: axisymmetric and shell. In the latter case, plastic anisotropy is introduced, using the Yld2000-2D anisotropic yield function. Wrinkling and tearing failure are triggered by inducing suitable geometric imperfections. It is shown that the models are able to reproduce the experiments well. This serves as a verification of the modelling framework, which can then be used for the simulations of more complex forming processes.

Rate-dependent JKR-type decohesion of a cylindrical punch from an elastic substrate

Recently published experimental data on non-quasistatic detachment of a flat-ended cylindrical punch from an adhesive rubber layer are analyzed in the framework of axisymmetric rate-dependent JKR-type model. The functional dependence of the work of adhesion on the velocity of the contour of contact area is assumed according to the known Gent–Schultz model. The evolution of the variable contact radius as a function of the punch displacement is described by a first-order ordinary differential equation, which possesses the localization property for its solutions, meaning that the detachment occurs at some nonzero contact radius. To facilitate the model fit to experimental force-displacement curve, a computationally efficient analytical approximate solution is suggested. A parametric analysis of the basic case (when the rubber layer is approximated by an elastic half-space) is presented.

A Vector Equation Method for Analyzing Kinematics and Kinetostatics of Toggle-Type Transmission Mechanism

With the help of vector equations and MATLAB software, this paper studied the kinematics and kinetostatics of toggle-type transmission mechanism (hereinafter referred to as “toggle mechanism” for short) and attained the analytical expressions of displacement, speed, and acceleration of slider punch, and the force and moment balance equations of each component in the toggle mechanism with their inertia force taken into consideration. Then, the toggle mechanism was compared with conventional crank-link mechanism and their kinematic characteristics were comparatively analyzed. The proposed kinematics analysis method of toggle mechanism could figure out the kinematic characteristics of the target mechanism and reveal its operating advantages on the basis that its functional requirements are met, in this way, the research purpose of optimizing the design of the mechanism could be realized, and the attained conclusions could provide useful evidence for the design of other types of transmission mechanisms.

Study of the influence of current density and displacement rate on hydrogen embrittlement using small punch tests

Susceptibility to hydrogen embrittlement was studied on quenched and tempered 42CrMo steel with Small Punch Tests (SPT) using different punch displacement rates. Hydrogen was cathodically charged using an electrolyte composed of 1 M H2SO4 with 0.25 g/l As2O3, and two different cathodic current densities (0.50 and 1.00 mA/cm2). The results were analysed using different embrittlement indices: related to the energy consumed at maximum load, to the equivalent biaxial deformation at failure location and to the failed diameter. Failure location is directly related to punch displacement and, consequently, to embrittlement.All embrittlement indices increase as the punch displacement rate decreases (longer time for hydrogen diffusion) and as the cathodic current density increases (higher hydrogen concentration in equilibrium with the hydrogenated medium). On the other hand, the use of a pre-charging time before the start of the in-situ hydrogen charged test produces no change in the results, as most hydrogen enters the sample due to the high plastic deformation induced on its surface in the course of the mechanical test.

Numerical modelling of the KOBO extrusion process using the Bodner–Partom material model

Numerical simulations of the extrusion process assisted by die cyclic oscillations (KOBO extrusion) is presented in this paper. This is highly non-linear coupled thermo-mechanical problem. The elastic-viscoplastic Bodner–Partom-Partom material model, assuming plastic and viscoplastic effects in a wide range of strain rates and temperatures, has been applied. In order to perform simulations, the user material procedure for B–P material has been written and implemented in the commercial FEM software. The coupled Eulerian–Lagrangian method has been used in numerical computations. In CEL method, explicit integration of the constitutive equations is required and remeshing is not necessary even for large displacements and large strains analyses. The results of numerical simulations show the heterogeneous distribution of stress and strain inside container and the non-uniform distribution of strain in the extruded material. The increase of material temperature has been noted. The results obtained (stress, temperature, location of plastic zones) qualitatively confirm the results of experimental investigations. The application of the user material procedure allows accessing all material state variables (current yield stress, hardening parameters, etc.), and therefore it gives detailed information about phenomena occurring in extruded material inside recipient. This information is useful for a proper selection of parameters of the KOBO extrusion process e.g. synchronization of the punch displacement with the die oscillations frequency to avoid the saturation of material isotropic hardening, which blocks the progress of extrusion.

Bendability assessment of high strength aluminum alloy sheets via V-die air bending method

The bendability of high-strength aluminum alloy (AA) sheets for two different thicknesses was experimentally evaluated by the V-die air bending method and the numerical simulation procedure was attempted to comprehend the characteristics of the V-die air bending method. Despite similar bendability along the material direction for a given punch radius in the experiment, the distinguished fracture strains were predicted for each direction based on the punch force and displacement information. For the numerical simulation, V-die air bending was modeled with the full 3D non-quadratic anisotropic yield criterion and compared with the results of the isotropic yield function estimating that bendability along the rolling direction is higher than those along the transverse direction. The thinner material showed higher anisotropy in bendability and the characteristics of V-die air bending were also discussed suggesting a maximum value as an upper bound of the bendability. As a comparison, an anisotropic analytical formulation was also newly developed combined with the kinematic assumption and the limitation was also covered in the study. The analytical fracture strain was discussed as the equivalence to the maximum value suggested in the research.

Spark plasma sintering of W-30Si refractory targets: Microstructure, densification and mechanical properties

W-30Si refractory targets were widely used as gate materials in the field of semiconductor integrated circuits. This work aimed to study the microstructure, densification mechanism, and mechanical properties of W-30Si targets prepared by spark plasma sintering (SPS). The results manifested that the punch displacement and relative density rose as temperatures increased, and the sintering route processed at 1200 °C included four parts. A fully dense target can be obtained at 1200 °C, while part of Si would volatilize at 1220 °C. No significant variation was observed in grain sizes from 1000 to 1200 °C, thus it was believed that the consolidation predominated over this temperature range. The effective stress exponent (n) was generally regarded as a parameter closely related to the densification mechanism. At the initial stage of 1000 to 1200 °C and the late stage of 1000 °C (n < 1), the particle rearrangement had a major influence on the densification. At the late stage of 1050 to 1200 °C (1 < n < 2), the grain boundary diffusion was a significant factor for consolidation, and the activation energy (n = 1.5) was estimated to be 931.40 kJ/mol. Besides, the microhardness rose with increasing temperatures. The present study laid the groundwork for future research on the fabrication of W-30Si targets by SPS.

A horizontal punch on a layered and orthotropic composite system with negative Poisson’s ratio

This paper studies the problem of a layered and orthotropic material with a negative value of Poisson’s ratio under a horizontal punch through a rigid line. Full-field solutions near the edge of the rigid line are developed and expressed in terms of the relevant values of the stress intensity factor and energy release rate. The Influences of Poisson’s ratio, orthotropicity orientation and the difference between the properties of the layered materials on the stress field and energy absorption are identified. The results show that materials with a negative value of Poisson’s ratio have a great potential to reduce the stress concentration and to increase punch resistance. If the punch load is maintained constant, the punch edge stress will increase with the layer thickness. However, if the punch displacement is maintained, the punch edge stress will decrease with layer thickness.

Characterization of mechanical properties for tubular materials based on hydraulic bulge test under axial feeding force

A T-shape tube hydraulic bulge test under axial feeding force is carried out to characterize the mechanical properties of EN AW 5049-O and 6060-O aluminium alloys. The punch displacement, T-branch height and axial compressive force are recorded online during the experiment. An intelligent inverse identification framework combining the finite element method and numerical optimization algorithm is developed to determine material parameters by fitting simulated results to the experimental data iteratively. The identified constitutive parameters using the inverse modelling technique are compared with those determined by the theoretical analysis and uniaxial tensile test. The comparison shows that the predicted bulge height and punch force based on the material parameters obtained by the three methods are different and the inverse strategy produces the smallest gap between numerical and experimental values. It is possible to conclude that the hydraulic bulge test can be applied to characterize the stress-strain curve of tubular materials at the large strain scope, and the automatic inverse framework is a more accurate post-processing procedure to identify material constitutive parameters compared with the classical analytical model.

Diagnosing Extrusion Process Based on Displacement Signal and Simple Decision Tree Classifier.

The article presents an extensive analysis of the literature related to the diagnosis of the extrusion process and proposes a new, unique method. This method is based on the observation of the punch displacement signal in relation to the die, and then approximation of this signal using a polynomial. It is difficult to find in the literature even an attempt to solve the problem of diagnosing the extrusion process by means of a simple distance measurement. The dominant feature is the use of strain gauges, force sensors or even accelerometers. However, the authors managed to use the displacement signal, and it was considered a key element of the method presented in the article. The aim of the authors was to propose an effective method, simple to implement and not requiring high computing power, with the possibility of acting and making decisions in real time. At the input of the classifier, authors provided the determined polynomial coefficients and the SSE (Sum of Squared Errors) value. Based on the SSE values only, the decision tree algorithm performed anomaly detection with an accuracy of 98.36%. With regard to the duration of the experiment (single extrusion process), the decision was made after 0.44 s, which is on average 26.7% of the extrusion experiment duration. The article describes in detail the method and the results achieved.

Finite Element Analysis of the Axially Non-symmetrical Piercing Punches Performance for Belt Perforation

Modification of the punch geometry can greatly reduce the force necessary to perform the perforation of the belt. This paper presents research on axially non-symmetrical piercing punches – double sheared one and one with a cylindrical bowl. FEM analysis was performed for a variable tip angle β in the 60-150° range for a double sheared punch or a variable bowl radius R in the 5.25-10 mm range and for a constant punch diameter D = 10 mm and TFL10S belt. Based on the obtained results, the influence of the tip angle β (for the double sheared punch) and the bowl radius R (for a cylindrical bowl punch) on the perforation force FP and pneumatic cylinder stroke increase Δs was determined. FEM analysis was used to obtain the perforation force in function of punch displacement characteristics for various tool geometry. Based on the results, the characteristics of the perforation force in function of punch geometrical parameters were determined. Additionally, their application in the punching die design process, where the effective geometrical features of the tools are desired, is presented.

Application of Machine Learning to Bending Processes and Material Identification

The increasing availability of data, which becomes a continually increasing trend in multiple fields of application, has given machine learning approaches a renewed interest in recent years. Accordingly, manufacturing processes and sheet metal forming follow such directions, having in mind the efficiency and control of the many parameters involved, in processing and material characterization. In this article, two applications are considered to explore the capability of machine learning modeling through shallow artificial neural networks (ANN). One consists of developing an ANN to identify the constitutive model parameters of a material using the force–displacement curves obtained with a standard bending test. The second one concentrates on the springback problem in sheet metal press-brake air bending, with the objective of predicting the punch displacement required to attain a desired bending angle, including additional information of the springback angle. The required data for designing the ANN solutions are collected from numerical simulation using finite element methodology (FEM), which in turn was validated by experiments.

High-temperature mechanical properties of preceramic paper-derived Ti3Al(Si)C2 composites obtained by spark plasma sintering

In the present work, the flexural strength of Ti3Al(Si)C2-based composites was investigated at 25, 800 and 1000 °C using small punch technique. The composites were spark plasma sintered at 1150 °C and 50 MPa from preceramic paper with Ti3Al(Si)C2 powder filler. Sintered composites represent a multi-phase system with secondary TiC and Al2O3 phases and have more than 900 MPa of flexural strength at room temperature. It was revealed that at 800 °C the flexural strength of composites decreases to 690 MPa. At 1000 °C, the flexural strength of composites further decreased to 620 MPa, however, an anomalous displacement of punch was detected during the fracture test attributed to the Ti3Al(Si)C2 brittle-to-plastic transition of the fracture mechanism.

Numerical Simulation and Parameter Analysis of Electromagnetic Riveting Process for Ti-6Al-4V Titanium Rivet

Electromagnetic riveting process (EMR) is a high-speed impact connection technology with the advantages of fast loading speed, large impact force and stable rivet deformation. In this work, the axisymmetric sequential and loose electromagnetic-structural coupling simulation models were conducted to perform the electromagnetic riveting process of a Ti-6Al-4V titanium rivet, and the parameter analysis of the riveting setup was performed based on the sequential coupled simulation results. In addition, the single-objective optimization problem of punch displacement was conducted using the Hooke–Jeeves algorithm. Based on the adaptive remeshing technology adopted in air meshes, the deformation calculated in the structural field was well transferred to the electromagnetic field in the sequential coupled model. Thus, the sequential coupling simulation results presented higher accuracy on the punch speed and rivet deformation than the loose coupling numerical model. The maximum relative difference of electromagnetic force (EMF) on driver plate and radial displacement in the rivet shaft was 34.86% and 13.43%, respectively. The parameter analysis results showed that the outer diameter and the height of the driver plate had a significant first-order effect on the response of displacement, while the platform height, transition zone height, angle, and transition zone width of the amplifier presented a strong interaction effect. Using the obtained results on the optimal structural parameters, the punch speed was effectively improved from 6.13 to 8.12 m/s with a 32.46% increase. Furthermore, the displacement of the punch increasing from 3.38 to 3.81 mm would lead to an 80.55% increase in the maximum radial displacement of the rivet shaft. This indicated that the deformation of the rivet was efficiently improved by using the optimal rivet model.