Thin Metal Sheets Research Articles

Rolling of long-length rails with acceleration

The article explains a new temperature-speed mode of rolling long-length rails. Rails up to 50 m long were rolled on linear mills. The production of rails of longer length required the use of larger mass billets and equipment of a new design. At the modern rail-beam rolling mill, the number of stands has increased and some of the stands are combined into a continuous group. Universal rolling stands began to be used not only as calibration stands. Rails with a length of 100 m are rolled from large-mass billets on mills with a continuous reversible group of universal stands. A significant length of the billet leads to the formation of a «temperature wedge» – a decrease in temperature along the length of the rail during rolling in the last stand of the mill. The calculation showed that a decrease in temperature along the rail length can lead to an increase in its height. A similar problem existed in the production of thin sheet metal at continuous broadband hot rolling mill. Rolling the rolled metal in the finishing group of stands with acceleration made it possible to reduce the cooling time of rear section of the rolled metal and warm up the metal due to more intense deformation. The acceleration value is chosen such that at the exit from the finishing group of stands, temperature of the strip is the same along the length of the strip. In this paper, rolling rails with acceleration is proposed. The acceleration value should ensure the same neck temperature along the length of the rail in the mill last stand, which will reduce the height difference along the length of the rolled product. The same rails height along the length will reduce the cost of grinding and accelerate the rail laying, thereby increasing consumer demand and competitiveness of the product.

New shapemeter roll technology based on Fiber Bragg Grating technology for on-line flatness monitoring of thin cold rolled metal sheets

The shape of laminated products is a crucial parameter in high-speed and high-volume finishing lines where they must fulfill tight tolerances. Latent defects are detected by flatness rolls (or shapemeter rolls) inserted in the manufacturing line for online flatness control. A prototype of flatness roll has been developed with high spatial resolution (5 mm) and measurement capability over a thickness range of 0.1–1 mm to evaluate flatness and residual stresses of flat metal strip products manufactured by continuous cold rolling (ultra-thin sheets for packaging and automotive markets). The flatness roll prototype relies on pressure-induced strain sensing on segmented blades using Fiber Bragg Grating technology. Synchronous measurement of the flatness profile across strip width rejects disturbances of strip tension during rolling. We provide a proof-of-concept on pilot lines in both static and dynamic conditions (e.g., roll in rotation and in contact with a strip under tension) and the sensing mechanism shows a capability above 3. This combination of performances remains unique up to now. Interblade crosstalk appears to be an important issue. We propose a crosstalk model that agrees with experimental coupling coefficients. A crosstalk matrix inversion yields the distribution in contact pressure from strain data measured on the reverse side. Additional work will be required to use the flatness roll in industrial conditions.

Efficient cloth simulation based on the material point method

AbstractIn this article, we propose a novel cloth simulation method based on the material point method (abbr. MPM). The response to the cloth strain is characterized by three separated models: the continuous in‐plane hyperelasticity, the discrete bending elastoplasticity, and the continuous frictional contact elastoplasticity. We make use of the moving least squares MPM (abbr. MLS‐MPM) transfer scheme and a discrete bending model to reduce computation overhead. We further extend the hyperelastic bending model to be elastoplastic, which can be further used for the simulation of a wide range of thin shell materials, such as thin metal sheets. A fast and approximate signed distance field generation method for humanoid animation is also proposed. Experimental results demonstrate that our method can efficiently and robustly simulate high‐resolution challenging scenes with hundreds of thousands of triangles.

Assessing the effect of the experimental parameters in the evaluation of the essential work of fracture in high-strength thin sheets

The essential work of fracture methodology (EWF) has been successfully adopted to evaluate the fracture toughness of various metals and polymers. However, some aspects of the methodology are still far less understood, such as the influence of the experimental parameters on EWF measurement in thin metal sheets. In the present paper, the ligament range criterion of the EWF approach was revised for several advanced high-strength steels (AHSS). The validity of the upper and lower ligament length limits given by the ESIS protocol is redefined and rationalized according to the necking capability and the plasticity behaviour of the different AHSS grades. The work provides a new criterion to define the minimum ligament length to be tested, based on the minimum distance required by the crack to fully develop the necking capability of the material. The width constraint is too restrictive and has no effect on the deviation from linearity in the upper range. On the other hand, the maximum ligament length is proven to be controlled by the size of the plastic zone as proposed by the ESIS protocol.

Automatic Calibration of the Adaptive 3D Scanner-Based Robot Welding System.

An advanced automatic calibration procedure and its versatile usage in the context of the adaptive robot welding technology are presented. The 3D scanner-based robot welding system calibration is composed of the measurement of the reference plate and numerical optimization of the hand-eye and intrinsic parameters by minimizing the deviation between the measured and reference plate. The measurements of the reference plate are acquired from various robot poses (typically 15). The shape features of the reference plate are then detected, and finally, the calculation of hand-eye and intrinsic parameters is performed using Powell’s optimization algorithm, where the merit function presents an average deviation between the measured and reference geometry. Validation experiments show appropriate system accuracy which is better than 0.06 mm perpendicular to the scanning direction. This calibration procedure’s important features are complete automation and fast execution times (approximately 90 s). This enables its implementation into a regular daily robot self-maintenance and monitoring plan. The universal use of such a robot welding system is demonstrated in multi-layer heavy-duty welding of thick pipes on cast machined hollow parts and in precise laser welding of thin sheet metal parts.

Identification of fully coupled non-associated-Ductile damage constitutive equations for thin sheet metal applications: Numerical feasibility and experimental validation

Developing an efficient non-associated plasticity criterion fully coupled with isotropic ductile damage is the main contribution of the current research. Two ductile degradation functions with variable degradation exponents are considered in this model, one for elasticity and the other for plasticity. Mixed (isotropic/kinematic) hardening rule and Hill’48 quadratic yield criterion are adopted to describe the elastoplastic material behavior. For this contribution, a VUMAT subroutine including the proposed model has been adopted and implemented in Abaqus/Explicit finite element code. Various experimental tests and finite element simulations are carried out to validate the current model and to predict the damage evolution in notched tensile specimens. In the validation part of this investigation, the quality of the numerical simulation results is assessed by comparison with the experimental ones taking into account the fully coupled non-associated-damage model. The effectiveness of the developed approach is evaluated through comparisons with experimental measurements and numerical models (Hill_S and Hill_R) and show good agreements. This fact indicates that the current model is a useful virtual tool to estimate the formability of anisotropic sheet metals. Numerical prediction is performed in order to reveal the stress triaxiality distributions for single point incremental forming (SPIF). The mentioned study is intended to give a guideline for 5083-aluminum alloy sheet forming.

Study of size effect on anisotropic deformation behavior of rolled α-Ti sheet

Thin metal sheets are widely used in manufacturing miniaturized components through the micro forming process. However, the size effect on the plastic deformation behavior of thin metal sheets is significant, and the plastic anisotropy of rolled α-Ti sheets makes the micro forming process more complicated, which greatly limits the application of micro α-Ti components. A series of in-situ tensile tests were conducted using specimens with different sizes and orientations to investigate the size effect on the anisotropic deformation behavior of the α-Ti sheet. The microstructure and fracture morphology were observed, and the grain-scale deformation behavior of α-Ti was explored through full-field crystal plasticity simulation. The results indicate that the size effect on the tensile deformation behavior of α-Ti is anisotropic. The TD specimen has a greater size effect sensitivity and shows a more considerable fracture stain reduction with the specimen size decreasing. The twinning behavior in terms of types, morphology, and fractions is anisotropic and evolves with the specimen size. TD specimens show a more significant inhomogeneity of strain distribution than that of RD, and the difference increases with specimen size decreasing. More hard-oriented grain and massive local needle-like twins generated in small-sized TD specimens lead to severer strain localization. These findings provide a fundamental understanding of the anisotropic size effect in the micro forming process of α-Ti.

Study on Rubber-Pad Formation for Sheet Metal

This article introduces four rubber-pad formation techniques for the pressing and drawing of components from thin sheet metals. The Guerin process is the simplest technique of rubber formation, which enables the production of shallow sheet metal parts with complex contours and bends. Free formation is another technique used to draw near-hemispherical shells using a rubber medium. Different bending processes can also be conducted using a rubber pad as a flexible die. Multipoint formation is applied to form complex three-dimensional sheet metal parts with discrete dies and rubber cushions. The fundamentals of these techniques as well as the influence of process parameters on the results are investigated in this paper

Experimental Study on the Mechanism of Pinching in Cold‐Rolling Processes

Herein, an experimental investigation into the occurrence of “pinching” defects during cold‐rolling of thin metal sheets is presented. Pinched strips are typically characterized by repetitive ripples and local ruptures, which can cause strip breaks. Even though pinches are a widely experienced phenomenon in both hot‐ and cold‐rolling of steel strips, no previous studies are known that have investigated the underlying mechanism for pinching during continuous rolling processes. Therefore, a set of rolling experiments is performed in a single‐stand pilot mill to create pinches by applying sudden perturbations in the process conditions. For the rolling settings chosen in the performed experiments, it is found that disruptions in the lubrication state are a powerful approach to induce shape defects, which develop as pinches. Herein, a first extensive description of the pinching mechanism is provided, as observed during the trials, by monitoring the strip's behavior and analyzing the damaged sheets. It is shown that ripples in these pinched strips are the result of folds, which form in the roll bite. The folds originate from the waviness of the strip upstream of the bite, being created by nonuniform conditions over the width of the strip.

Modeling of self-healing of microcracks in the process of longitudinal electroplastic rolling

Multiscale model to describe the process of self-healing of microcracks in thin metal sheets during longitudinal electroplastic rolling is developed. The simultaneous treatment of a mechanical load and a pulsed high-energy electromagnetic field on the sheet is assumed. Finite element modeling has shown that under certain conditions microcracks and micropores can self-heal partially in the working zone. Impact of external pulsed high-energy electromagnetic field leads to welding of the shores of microcracks by molten metal in their tops, while the length and volume of cracks decrease.

Enhancing cutting performance with an oscillating laser beam

AbstractFiber lasers feature higher energy conversion efficiency than CO2 lasers, which enables a simple structure and energy‐saving design. Consequently, in the laser cutting processes for metal sheets, operators have been shifting usage from CO2 lasers to fiber lasers at an accelerated pace because of their reduced maintenance, improved metal absorption rate due to their wavelength and other advantages. In actual practice, fiber lasers are superior to CO2 lasers in high‐speed cutting processes for thin metal sheets. However, as the thickness of the metal sheet increases, problems arise where fiber lasers have inferior performance to CO2 lasers in terms of dross adhesion, cutting surface quality, and other factors.

All-Metal Wideband Frequency-Selective Surface Bandpass Filter for TE and TM Polarizations

A novel technique to design a low-cost frequency-selective surface (FSS) bandpass filter is presented in this article. Wideband polarization-independent FSS bandpass filters are predominantly made of multiple microwave dielectric substrates or noncommercially available composite materials with or without active components, contributing to a very high manufacturing cost. The presented FSS filter has neither microwave substrates, nor any active devices, while it has a large controllable operational frequency band, which can support all polarizations, due to its symmetrical configuration. To the best of our knowledge, such a polarization-independent wideband bandpass response has never been achieved by any low-cost fully metallic FSS filter. The proposed FSS filter is made of three thin metal sheets composed of an engineered metallic substrate (EMS) and a metallic orthogonal dipole resonator (ODR). The EMS is responsible for ensuring the mechanical integrity of the filter without imposing electromagnetic (EM) restrictions throughout the desired frequency band. The integration of EMS and ODRs realizes a fully controllable wideband bandpass verified thorough circuital and modal analyses. According to the predicted and measured results, the FSS filter has a large bandwidth of around 31%, extending from 8.76 to 11.96 GHz with sharp roll-offs for the normal incidence. Simulated and measured results show a low sensitivity of the FSS filter response to oblique angles of incidence for both TM and TE polarizations.

МЕТОД РОЗРАХУНКУ ЕЛЕКТРОМАГНІТНОГО ПОЛЯ СПІРАЛЕПОДІБНОЇ ІНДУКЦІЙНОЇ СИСТЕМИ ДЛЯ МАНІТОІМПУЛЬСНОГО ОБРОБЛЕННЯ НЕМАГНІТНИХ МЕТАЛЕВИХ СМУГ З ФЕРОМАГНІТНИМ ЕКРАНОМ

Pulsed currents and magnetic forces of an induction system with a spiral winding and a ferromagnetic shield for processing non-magnetic thin-sheet metal strips in order to create magnetoplastic, electroplastic effects due to eddy currents are studied. Under the strip there is the ferromagnetic shield, and above it – spiral winding. The aim of the work is to develop an analytical method for calculating transients of pulsed currents in an electric circuit with the induction system and a capacitor charged to certain voltage taking into account influence of the ferromagnetic shield to perform investigation of time-varying magnetic field. Electromagnetic parameters of the inductor are determined by computer simulation using the finite element method in the mode of harmonic currents. Current transients in the electric circuit are calculated using known in theoretical electrical engineering mathematical dependences and distribution of current density and magnetic forces in the strip is calculated by the finite element method in the mode of transients. Influence of the ferromagnetic shield on electromagnetic processes in the induction system for the set ranges of strip’s thickness, its electrical conductivity and current frequency is established. Electromagnetic force between the spiral winding and the strip, the current density in the strip, as well as the moments of time at which the current and force have maximum values are studied. References 14, figures 6, tables 2.

A new partitioned 1D LTNE continuum model for the simulation of 3D-shaped honeycomb absorbers

Porous absorber structures intended for open volumetric receivers of central tower power plants are receiving significant attention in current research. Due to the geometric complexity, volume-averaged continuum models are a common tool for the simulation of volumetric absorbers. Widely established for the investigation of ceramic foams, existing continuum models are less suitable for the simulation of honeycomb absorbers. 3D-shaped honeycomb absorber designs, i.e. absorbers with varying cross-sections, can pose additional challenges in the form of internal front-like surfaces, which are oriented perpendicular to the main channel axis. Due to the importance of the internal front-like surfaces w.r.t. absorption of solar radiation and convective heat transfer, a new partitioned 1D LTNE continuum model is proposed. The key innovation is the division of the absorber geometries into distinct sections forming a set of coupled LTNE models.The new 1D continuum model has been successfully validated against a 3D CFD model. For nine compared simulation cases, the calculated thermal absorber efficiencies differ on average 0.81 percentage points between the two models. Simulations have been conducted for the state-of-the-art HiTRec absorber and two new absorber geometries. The StepRec absorber, a monolithic channel design with characteristic step-pins created, via ceramic 3D screen printing out of SiSiC, reaches a thermal efficiency of up to 89.5% for an air outlet temperature of 700°C. A volumetric effect is predicted by for the new Emitec absorber, a channel geometry made of thin metal sheets, depending on the incident irradiation with efficiencies of up to 85.8% at 700°C.

Extending the potentials of draw-forging

Composite components combine the benefits of different materials, leading to improved product properties, enhanced resource- and energy efficiency and widening the product spectrum. Draw-forging is the unique combination of deep-drawing and cold forging, where a core material is encapsulated within a thin sheet metal blank. Previously, the basic draw-forging process only allowed covering of the shaft tip, and the covered length was limited by the maximum drawing ratio of the sheet. In this work, the different failure types, including tearing of the sheet, asymmetric encapsulation, and the development of a gap in the transition zone were investigated numerically and experimentally and the axial encapsulation length is increased significantly. The usage of anisotropic sheet material leads to a form fit and enhances the bond strength in draw-forged hybrid components. An alternative process route in which a pierced sheet is utilized to partially cover a specific section of a shaft was also developed. The process route was stabilized with a novel contoured counter holder to ensure high repeatability.

Bending properties of sandwich sheets with metallic face sheets and additively manufactured 3D CFRP lattice cores

• Sandwich sheets with representative shell-lattice, truss-lattice and plate-lattice cores are proposed. • Effects of core topologies on mechanical properties and bendability of sandwich sheets are clarified. • Theoretical predictions of failure modes during bending of sandwich sheets with 3D lattice cores. • Bendable sandwich sheets with 3D lattice cores are successfully designed and produced. • Bendable sandwich sheets with multifunctional application potentials. To improve structural performance, bendability and potential functionality of metal-based sandwich sheets, the 3D lattice cores were sandwiched between thin metallic face sheets. The bending properties of sandwich sheets with 3D printed carbon fiber reinforced plastic (CFRP) lattice cores originating from basic topologies of spherical shell, tetrahedral truss and tetrahedral plate were systematically investigated. The effects of core topologies, core relative densities, core heights, face sheet thicknesses on structural properties were clarified. The common failure modes during bending of sandwich sheets, such as face buckling and shear failure of core, were deeply investigated by theoretical models and experimental tests. At a prescribed radius of 60 mm, the sandwich sheets with the bilayered dome, octet truss and plate lattice cores of relative density of 50 %, height of 6 mm and face sheet thickness of 0.5 mm are bendable. This study demonstrates the feasibility of design and production of bendable sandwich sheets with 3D lattice cores based on the theoretical and experimental validations. The designed bendable sandwich sheets can be adopted to replace conventional heavy monolithic metal sheets in various engineering applications, which is anticipated to fulfill the high demand for lightweight functional materials.

Influence of heat treatment on the suitability for clinching of the aluminium casting alloy AlSi9

In many manufacturing areas, multi-material designs are implemented in which individual components are joined together to form complex structures with numerous joints. For example, in the automotive sector, cast components are used at the junctions of the body and joined with different types of sheet metal and extruded profiles. To be able to join structures consisting of different materials, alternative joining technologies have emerged in recent years. This includes clinching, which allows assembling of two or more thin sheet metal and casting parts by solely cold forming the material. Clinching the brittle and usually less ductile cast aluminium alloys remains a challenge because the brittle character of the cast aluminium alloys can cause cracks during the forming of the clinched joint. In this study, the influence of the heat treatment time of an aluminium casting alloy AlSi9 on the joinability in the clinching process is investigated. Specific heat treatment of the naturally hard AlSi9 leads to a modification of the eutectic microstructure, which can increase ductility. Based on this, it will be examined if specific clinching die geometries can be used, which achieve an optimized geometrical formation of the clinched joint. The load-bearing capacities of the clinched joints are determined and compared by shear tensile and head tensile tests. Furthermore, the joints are examined microscopically to investigate the influence of the heat treatment on the failure behaviour during the load-bearing tests as well as crack initiation within the joining process.

An efficient multiphysics solid shell based finite element approach for modeling thin sheet metal forming processes

The main objective of this paper is to provide a numerical approach to study thin sheet metals involved in multiphysics manufacturing processes. The proposed approach also accounts for anisotropic plastic deformations in the context of modeling of deep drawing process. In this work, different constitutive models are implemented with a prismatic solid shell element to simulate these applications. Moreover, a new element assembly technique has been developed to permit the assembly of prismatic elements in a tetrahedral element-based finite element code. This technique splits the prism into multiple tetrahedral elements in such a way that all the cross terms are accounted for. The numerical approach has been validated using multiple tests that involve different non-linearities: geometric, material and contact. Then, more complex sheet metal processes have been simulated. The performance of the solid shell element with one element through the thickness is very comparable to the results obtained with more refined mesh of a tetrahedral element. This reduction in the number of elements accelerates the simulation, especially in the deep drawing problem and the coupled magnetic-mechanical simulation used for the magnetic pulse forming process. • Solid shell finite element implementation in tetrahedral based finite element software. • Prism division algorithm into multiple overlapping tetrahedral elements. • Solid-shell element showed better performance than MINI element in modeling thin structures problems. • Incorporate anisotropic plastic behavior in the simulation of deep drawing process. • Electromagnetic pulse forming simulation using solid shell element reduces time of simulation and maintain good accuracy.

Kinematic Simulation of Automatic Conveying and Stamping Machine based on UGNX

This paper designed a kind of automatic conveying and stamping machine, which was mainly used for drawing thin sheet metal. UGNX software was used to design the motion law of the mechanism and the simulation mechanism. The time displacement diagram obtained by theoretical calculation and simulation was compared to verify the correctness of theoretical analysis and the rationality of the design. The comparison shows that the device meets the requirements of theoretical calculation. The device has the characteristics of simple structure, high efficiency and easy operation, which provides a reference for the subsequent realization of conveying and stamping devices with different requirements.

The improvement of bolted joints model via finite element model updating method

Efficient schemes to represent mathematical model of thin-sheet metal structures jointed by bolted joints for accurately predict the structure dynamic behaviour has been a significant unresolved issue in structural dynamics community. The biggest challenge is to efficiently incorporate the joints local deformation effects on the developed mathematical model via finite element (FE) method. Generally, the joints local deformation typically exerts on the joints mating area. To solve this issue, this paper proposes efficient schemes to represent mathematical model of thin-sheet metal structures jointed by bolted joints with application to accurately calculate the structure dynamic behaviour using FE model updating method. The initial FE model of the assembled structure was developed by employed Fastener Connector (CFAST) in MSC NASTRAN software to represent the bolted joints while, the inclusion of the local deformation effects at the bolted joints mating area was represented by contact elements. Then, the responses obtained from the FE model was evaluated by weight up with experimental data. FE model updating (FEMU) method then was utilised for minimising prediction discrepancies originated from the initial FE model based on the experimental data. The proposed scheme shows the accuracy of the initial prediction was improved from 25.03 % to 14.65 % while the accuracy of the predicted mode shapes via modal assurance criterion (MAC) analysis were above 0.8. Therefore, the findings offer useful schemes for improving the quality of predicted dynamic behaviour, particularly in the thin-sheet metal jointed structure and the developed model can be used with confident for any subsequence dynamic analyses.