Showing papers on "Stamping published in 2019"

Bifacial stamping for high efficiency perovskite solar cells

Abstract: We report a novel approach for a fast phase transition of FAPbI3 (FA = formamidinium) at low-temperature and the effective removal of interfacial recombination in MAPbI3 (MA = methylammonium). This method also allows for printing (patterning) of the perovskite on a desired area. The pre-annealed MAPbI3 and δ-phase FAPbI3 films were prepared by spin-coating DMSO and a polar aprotic solvent admixed precursor solution at 65 °C and 100 °C for about 1 min, respectively, to form adduct films containing DMSO. Two films were sandwiched without pressure by a method called bifacial stamping, and annealed at 100 °C for 9 min, which resulted in complete δ → α phase transition of FAPbI3 and led to a power conversion efficiency (PCE) of 18.34%. The stamped MAPbI3 demonstrated a PCE of 20.18% that was much higher than the conventionally annealed MAPbI3 (∼17.4%) mainly due to a much higher fill factor and open-circuit voltage. Optical and structural studies revealed that DMSO-mediated ion exchange plays a vital role in the phase transition of FAPbI3 and the surface modification of MAPbI3. Theoretical calculation results further support the role of DMSO in the phase transition at low temperature. Stamping was applied to EAPbI3 (EA = ethylammonium), where photoinactive yellow EAPbI3 changed to photoactive EAPbI3 with a PCE of 13.02% after stamping with MAPbI3. The DMSO-mediated EA/MA ion exchange reaction during the stamping process created a new layer having a gradient solid solution of EAPbI3 and MAPbI3, which was responsible for the abnormally high PCE of the EAPbI3 based perovskite solar cell. Facilitated ion transport by a Lewis base (such as DMSO) reservoir in the perovskite adduct film is suggested to be involved in the bifacial stamping procedure.

Development of the Metal Rheology Model of High-Temperature Deformation for Modeling by Finite Element Method

Abstract: It is shown that when modeling the processes of forging and stamping, it is necessary to take into account not only the hardening of the material, but also softening, which occurs during hot processing. Otherwise, the power parameters of the deformation processes are precisely determined, which leads to the choice of more powerful equipment. Softening accounting (processes of stress relaxation) will allow to accurately determine the stress and strain state (SSS) of the workpiece, as well as the power parameters of the processes of deformation. This will expand the technological capabilities of these processes. Existing commercial software systems for modeling hot plastic deformations based on the finite element method (FEM) do not allow this. This is due to the absence in these software products of the communication model of the component deformation rates and stresses, which would take into account stress relaxation. As a result, on the basis of the Maxwell visco-elastic model, a relationship is established between deformation rates and stresses. The developed model allows to take into account the metal softening during a pause after hot deformation. The resulting mathematical model is tested by experiment on different steels at different temperatures of deformation. The process of steels softening is determined using plastometers. It is established experimentally that the model developed by 89 ... 93 % describes the rheology of the metal during hot deformation. The relationship between the components of the deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation. As a result, the number of iterations and calculations has significantly decreased.

Improving The Operational Reliability Of Stamped Parts Of Electrical Engineering Machines And Electrical Products

Abstract: The durability and operational reliability of electrical machines, electronic and electrical engineering products in almost all cases can be achieved by imparting special properties to the materials used. In addition, it is extremely important to choose the most rational, economical method of treating materials that provide a high operational reliability and quality of the produced parts. Among a large variety of physico-chemical nature of the impact on the material of a workpiece, the stamping methods have received very a intensive development in the field of influence on the structure and operational properties of the latter. The performance characteristics of the parts of electrical machines and electronic products from a thin-sheet material largely depend on the accuracy of punching and the size of the burr. In addition to the traditional technologies for cutting and punching in hard dies, and with the help of the elastic or liquid media the explosive forming is also used.The advantages of the explosion forming when performing the dividing operations are due to the absence of a gap between the deforming medium and the die. The use of the pulsed metalworking methods in the cutting operations of the sheet metal forming eliminates the nonflatness of parts during the cutting, the formation of burrs and sinkers, forms in terms of the use of the overlaid explosives, a fine and ultrafine-grained material structure. This increases the electrical resistance of steel, reduces the parasitic eddy current losses and the efficiency of the electrical heating elements

The effect of hot form quench (HFQ®) conditions on precipitation and mechanical properties of aluminium alloys

Abstract: Hot form Quench (HFQ®) represents a leading-edge hot sheet stamping technology for manufacturing complex-shaped high strength aluminium alloy panel components. Transfer of sheet blank from the furnace to the press is the first crucial step in the process. This paper reports work in which the effects of the blank transfer on the deformation of material during pressing and on the final properties after ageing through thermal-mechanical testing and microstructural observations. Two aluminium alloys are investigated, 6082 and 7075. Hardness, quasi-static uniaxial tensile measurements and TEM microstructure observations provide evidence that post-treatment properties and the underlying microstructure are strongly influenced by the blank transfer step. Severe deterioration in the post-treatment strength was observed for blank transfer temperature, ranging from 250 °C to 400 °C. The temperature-time-property (TTP) diagrams showed that 350 °C was the most sensitive temperature that reduced the post-treatment strength by 45% within 10 s holding. As evidenced by TEM, typical coarse η and S precipitates at high temperatures were identified, which resulted in different post-treatment properties and hot deformation behavior. Finally, the results from HFQ® technology processed aluminium alloys 7075 and 6082 were compared with conventional TTP diagrams, enabling comparison with conventional scientific understanding of quenching effects.

Hot incremental forming of titanium human skull prosthesis by using cartridge heaters: a reverse engineering approach

Abstract: The single-point incremental forming process is an emerging process, which presents an alternative to the conventional sheet metal-forming processes like stamping and drawing. It is known to be perfectly suited for prototyping and small series. The incremental forming process offers the possibility of manufacturing medical prosthesis or implants specific to each patient, which are more comfortable and guarantee better performance. A reverse engineering approach associated with single-point incremental forming process in order to produce a titanium prosthesis of human skull is developed. It allows guaranteeing the high degree of customization required. In this paper, several novel warm forming experimental setup equipped with instruments to measure efforts and temperature monitoring is proposed. This new warm setup is feasible and makes it easy to monitor force and temperature sheet at forming; it gives it the ability to be exploited in the industry of manufacturing titanium alloy medical shapes. The real geometry of a skull prosthesis is re-constructed from a laser scanning technique, and specific treatments are performed until a CAD model is obtained. From it, the forming punch trajectories have been defined, and skull prostheses are manufactured using the technology of single-point incremental forming in titanium material at different temperatures.

Numerical and experimental investigation on the forming behaviour of stainless/carbon steel bimetal composite

Abstract: Bimetal composites have wide applications due to their excellent overall performance and relatively low cost. In this study, the formability of stainless/carbon steel bimetal medium-thick composite in the stamping process without blank holder was investigated by finite element (FE) simulations and experiments. Uniaxial tensile tests on substrate metal (carbon steel) and clad metal (stainless steel) were first conducted, respectively, in order to obtain the material properties of each metal layer required in the FE simulation. Processing variables, including the layer stacking sequence, relative thickness ratios of two layers and friction conditions, were considered, and their effects on the magnitude of press load and distributions of thickness strain for predicting the high-risk region of necking during stamping were discussed. Experimental tests were carried out to verify the simulation results. It is indicated that simulation results can be used as an evaluation indicator to ensure the bimetal medium-thick composite can be safely formed.

Springback analysis of 6016 aluminum alloy sheet in hot V-shape stamping

Abstract: Springback behavior of 6016 aluminum alloy in hot stamping was investigated by a series of experiments under different conditions using V-shape dies and a finite element model which was validated reliable was used to further elucidate the springback mechanism. The effects of initial blank temperature, blank-holding force, die closing pressure and die corner radius were studied. It is found that springback decreases remarkably as the initial blank temperature rises up to 500 °C. The springback also reduces with the increase of die holding pressure and the decrease of die corner radius. Under different initial temperatures, the influence of blank-holding force is distinct. In addition, the bending and straightening of the side wall during the stamping process is found to interpret the negative springback phenomenon.

Ultrahigh strength-ductile medium-Mn steel auto-parts combining warm stamping and quenching & partitioning

Abstract: A novel application of quenching and partitioning (Q&P) treatment to warm stamping of a warm-rolled medium Mn steel was investigated. The results show that Q&P could improve yield strength of auto-parts from the formation of carbides and twinned martensite, and reduce the yield point elongation for carbon partitioning during Q&P process and a higher dislocation density. Regardless of stamping temperature either the single austenite or dual-phase region, an extraordinary product of strength and ductility (≥24 GPa·%) was achieved, which is two or three times higher than those of hot-stamped boron steels. The combined warm rolling and warm stamping process with Q&P treatment may have potential to implement the application of medium Mn steels for ultrahigh strength-ductile auto-parts.

Resist-Free Direct Stamp Imprinting of GaAs via Metal-Assisted Chemical Etching.

Abstract: We introduce a method for the direct imprinting of GaAs substrates using wet-chemical stamping. The predefined patterns on the stamps etch the GaAs substrates via metal-assisted chemical etching. This is a resist-free method in which the stamp and the GaAs substrate are directly pressed together. Imprinting and etching occur concurrently until the stamp is released from the substrate. The stamp imprinting results in a three-dimensional anisotropic etching profile and does not impair the semiconductor crystallinity in the wet-chemical bath. Hole, trench, and complex patterns can be imprinted on the GaAs substrate after stamping with pillar, fin, and letter shapes. In addition, we demonstrate the formation of sub-100 nm trench patterns on GaAs through a single-step stamping process. Consecutive imprinting using a single stamp is possible, demonstrating the recyclability of the stamp, which can be used more than 10 times. The greatest benefit of this technique is the simple method of patterning by integrating the lithographic and etching processes, making this a high-throughput and low-cost technique.

Rapid manufacturing of woven comingled flax/polypropylene composite structures

Abstract: The use of natural fibre reinforced composites such as flax fibre / polypropylene is in a constant expansion particularly in automotive and marine industries due to their good mechanical properties, low density and thus, lightness, low environmental impact, low cost, recyclability, renewable properties of flax fibres and a minimum energy intake during their process. One of the major challenges of thermoplastic composites for the automotive industry is to manufacture finished parts in a single processing step within a minimum amount of time. For this purpose, a stamping airflow device was specifically developed. It is designed to produce woven comingled composite parts from comingled woven fabrics such as flax/polypropylene in only 200 s. Firstly, preliminary tests and the optimization of processing parameters were performed. Then, a quasi-static mechanical characterization of the formed parts was realized. By using criteria based on mechanical properties, the optimal process parameters such as the level of pressure, temperature, holding time and cooling rate so that to obtain the lowest voids rate were determined. Finally, a comparison of the mechanical properties of parts obtained from using the new manufacturing process and a conventional thermo-compression process is presented to demonstrate the interest and the level of performance achieved by this original and fast manufacturing device.

Investigation of springback during electromagnetic-assisted bending of aluminium alloy sheet

Abstract: Electromagnetic-assisted forming (EMAF) combining quasi-static stamping and electromagnetic forming (EMF) is a potential method for controlling the springback of aluminium alloy materials. In this study, to further promote the application of EMAF in the high-precision forming of aluminium alloy sheet parts, the springback during electromagnetic-assisted bending of aluminium alloy sheet was investigated using a custom-designed U-shaped bending tool with the optimised curved spiral coils. Two types of conditions to control springback were designed: gapless and gap conditions, and the springback under these conditions was studied both experimentally and using numerical simulations. In addition, the effects of the discharge parameters on springback were analysed. Finally, the mechanism for controlling springback under different forming conditions was revealed. The results showed that the efficiency of springback control was significantly higher under gap conditions compared with gapless condition. With increasing gap, the springback angle decreased, but negative springback easily occurred when using excessively wide gaps. As the discharge voltage or number of discharges increased, the tangential stress of the fillet area decreased, thereby reducing the springback angle. Stress oscillations under the gapless condition reduced the tangential stress of the fillet area to a certain extent, while inertial motions under gap conditions greatly reduced the tangential stress, which were the essential mechanism for the observed springback reduction.

Numerical Study on the Formability of Metallic Bipolar Plates for Proton Exchange Membrane (PEM) Fuel Cells

Abstract: Thin stamped bipolar plates (BPPs) are viewed as promising alternatives to traditional graphite BPPs in proton exchange membrane fuel cells. Metallic BPPs provide good thermal/electrical conductivity and exhibit high mechanical strength, to support the loads within the stack. However, BPPs manufactured by stamping processes are prone to defects. In this study, the effect of the tool’s geometry on the thin sheet formability is investigated through finite element simulation. Despite the broad variety of flow field designs, most of BPPs comprise two representative zones. Hence, in order to reduce the computational cost, the finite element analysis is restricted to these two zones, where the deformation induced by the stamping tools is investigated. The channel/rib width, the punch/die fillet radii, and the channel depth are the parameters studied. The analysis is conducted for a stainless steel SS304 with a thickness of 0.15 mm. The results show that the maximum value of thinning occurs always in the U-bend channel section, specifically in the fillet radius of the die closest to the axis of revolution.

Springback Calibration of a U-Shaped Electromagnetic Impulse Forming Process

Abstract: A three-dimensional (3D) finite-element model (FEM), including quasi-static stamping, sequential coupling for electromagnetic forming (EMF) and springback, was established to analyze the springback calibration by electromagnetic force. Results show that the tangential stress at the sheet bending region is reduced, and even the direction of tangential stress at the bending region is changed after EMF. The springback can be significantly reduced with a higher discharge voltage. The simulation results are in good agreement with the experiment results, and the simulation method has a high accuracy in predicting the springback of quasi-static stamping and electromagnetic forming.

A Quick Cycle Time Sensitivity Analysis of Boron Steel Hot Stamping

Abstract: Several vehicle platforms involving the hot stamping of manufactured parts are launched every year. Mass production represents a key step in the manufacturing process of an actual hot stamping part. In this step, the cycle time (consisting of cooling time (t1) and handling time (t2) components) must be optimized. During t1, the stamping tool (punch and die) is closed, for cooling of the part. The t2 components (i.e., inlet transfer time, press forming time (closing and opening), and outlet transfer time) define the production output that ensures process performance. However, cost is the main driver in automotive applications. Here, a cycle-time calculation based on the design of experiments (DOE) is proposed for formulating cost-effective formulas. An iterative one-dimensional heat transfer model for each DOE step is set up to simulate 10 hot stamping cycles; the part temperature after quenching in cycle number 10 (where steady conditions are achieved) was selected as the process output variable to be controlled in the DOE. Several DOE variables were considered. The DOE results were employed for the proposal of a simplified formula, which helps in assessing the cycle time with its excellent trade-off between calculation cost and reliability. The formula was validated by laboratory tests.

3D Metal Printing from an Industrial Perspective : Product Design, Production, and Business Models

Abstract: This paper is focused on automotive stamping tools and dies as well as the impact of 3D metal printing and metals related 3D-printing on design and production of such tools and dies. The purpose has been to find out the current industrial potential of 3D-printing as far as lead time, costs, shapes, material usage, metal piece size, surface roughness, hardness, strength, and machinability are concerned. The business transformational impact of 3D-printing is also addressed in this paper. The obtained results show that the lead time can be halved, the costs are somewhat higher, and the strength, hardness, surface roughness, and machinability of the 3D-printed metallic tools and dies are as good as those of the conventionally made. The maximum size of a metal piece that can be 3D-printed today by Powder Bed Fusion (PBF) is, in the best case, 500 mm × 500 mm × 500 mm. 3D-printing can also be used for the pattern to make the mold box in iron and steel casting. It is also possible to eliminate the casting pattern, since the mold box can be 3D-printed directly. All this has started to have a large business impact, and it is therefore of great significance to outline and execute an action plan almost immediately.

Quality and productivity driven trajectory optimisation for robotic handling of compliant sheet metal parts in multi-press stamping lines

Abstract: This paper investigates trajectory generation for multi-robot systems that handle compliant parts in order to minimise deformations during handling, which is important to reduce the risk of affecting the part’s dimensional quality. An optimisation methodology is proposed to generate deformation-minimal multi-robot coordinated trajectories for predefined robot paths and cycle-time. The novelty of the proposed optimisation methodology is that it efficiently estimates part deformations using a precomputed Response Surface Model (RSM), which is based on data samples generated by Finite Element Analysis (FEA) of the handled part and end-effector. The end-effector holding forces, plastic part deformations, collision-avoidance and multi-robot coordination are also considered as constraints in the optimisation model. The optimised trajectories are experimentally validated and the results show that the proposed optimisation methodology is able to significantly reduce the deformations of the part during handling, i.e. up to 12% with the same cycle-time in the case study that involves handling compliant sheet metal parts. This investigation provides insights into generating specialised trajectories for material handling of compliant parts that can systematically minimise part deformations to ensure final dimensional quality.

Investigation of Multiple Contact Interaction of Elements of Shearing Dies

Abstract: When justifying the design parameters, it is necessary to carry out the analysis of the strain-strain state of individual elements of technological systems, which are sets of parts under contact interaction conditions. These problems are nonlinear, and the principle of superposition does not apply to them. For this reason, the amount of calculations increases dramatically. To overcome this drawback, methods and models for the rapid and precise study of the strain-strain state of complex objects, taking into account contact interaction are developed. The feature of the problem statement is that the solution of contact problems under certain conditions linearly depends on the load. The patterns of contact pressure distribution are determined. It is concentrated in the areas of constant shape and size. Only the scale of contact pressure distribution varies.This gives an opportunity to significantly accelerate design studies of die tooling while preserving the accuracy of numerical modeling of the stress-strain state.The developed approach involves a combination of advantages of numerical and analytical models and methods for analyzing the stress-strain state of elements of shearing dies, taking into account contact interaction. This concerns the possibility to solve problems for a system of complex-shaped contacting bodies, which is impossible with the use of analytical models. On the other hand, the possibility of scaling the solutions of these problems with the stamping force is substantiated, which is generally not performed for nonlinear contact problems. So, it is sufficient to solve the problem of determining the strain-strain state of elements of such a shearing die. For the other value of stamping force, the proportionality rule is applied. Thus, the efficiency of research sharply increases and high accuracy of the obtained results is ensured.

A new design method based on feature reusing of the non-standard cam structure for automotive panels stamping dies

Abstract: The cam die is one of the most complicated types of automotive panel stamping dies. It is hard to achieve parametric and automated design of the non-standard cam, which determines the quality and cost of die design. The cam design process is extremely complex and requires a great deal of professional knowledge. A new design system for non-standard cams based on the feature reuse and group assembly technology was researched and developed in this paper for automotive panel dies. Taking the advantage of the well-organized historical knowledge base and features database of non-standard cam design cases and the seamless integration with the NX platform, the system was able to generate designs of the die substructure with cam in the form of assembly, including the driver, slider, stripper, cam base, and types of standard components such as nitrogen cylinders, guide plates, stopper seats, return hooks, safety pulling plates, and other parts. Finally, an engineering example of a cam trimming die for body side outer panel verified the feasibility and validity of this system. Comparisons with different design methods demonstrate that the newly developed system shows excellent performance in the design of complex non-standard cams for automotive panels.

Improvement of sheet metal formability by local work-hardening with punch indentation

Abstract: To improve the formability in stamping, a blank was locally work-hardened by indentation with a punch. Local strength expressed as a product of flow stress and thickness is increased up to a certain punch stroke by indentation, because the influence on the local strength contributed by the flow stress increase is larger than that by the thickness reduction. The effects of the indentation ratio, the number of punches and blank materials on the deformation behaviour in stamping were evaluated. The formability was increased by indenting thinning portions of the blank. The approach is effective for a sheet metal having a high work-hardening exponent such as stainless steel.

Hot stamping forming and finite element simulation of USIBOR1500 high-strength steel

Abstract: Flow stress curves of USIBOR1500 high-strength steel at high temperatures were obtained by tensile test. A constitutive model of high-temperature deformation of the material was established at 300–600 °C and 500–800 °C for one- and two-stage hot-forming processes, respectively. On the basis of the established constitutive equation, the one- and two-stage hot-forming methods were simulated, and the best process was determined. Results showed that the parts with simple shape and structure adopted the one-stage hot stamping technology, whereas the complicated parts adopted the two-stage hot stamping technology. The process parameters of the one-stage hot stamping technology are as follows: heating of the sheet material to more than 850 °C through an electric furnace, initial die temperature of 100 °C, stamping speed of 50 mm/s, pressing force of 1.28 kN, and punching pressure of 19.8 kN.