Warm Forming Research Articles

Comparative assessment of failure strain predictions using ductile damage criteria for warm stretch forming of IN718 alloy

It is vital to envisage accurately the fracture limits of high strength superalloys when noticeable localized necking or thinning tendency is not observed during sheet-metal stretch forming process. The present study mainly focuses on fracture limits evaluation of Inconel 718 alloy (IN718) in the effective plastic strain (EPS) vs. average triaxiality space. First, uniaxial tensile test, to analyze the material properties, were instigated at different test temperatures (RT-700 °C). Subsequently, stretch forming is performed to evaluate forming and fracture forming limit diagrams (FLD and FFLD) of IN718 using Nakazima test. It is observed that forming and fractured limits of IN718 are significantly influenced by variation of processing temperatures (with approximately 65–70% improvement in major safe and fracture strains) in all deformation regions (with respect to RT). In average triaxiality (η) vs effective plastic strain (EPS) space, higher fracture limits of IN718 are noticed in the entire triaxiality path of deformation region. Seven different ductile fracture models, namely McClintock (M-Mc), Brozzo, Rice-Tracey (R-T), Ko, Oh, Cockcroft and Latham (C-L), and Clift, are formulated so as to foresee the fracture loci of IN718 in EPS vs. triaxiality space. Overall, Oh model, showed best predictability at all temperatures with least Average absolute error (AAE < 13.5%).

Analysis of Sheet Metal Forming (Warm Stamping Process): A Study of the Variable Friction Coefficient on 6111 Aluminum Alloy

Aluminum alloy materials have been widely used in automobile, aerospace and other fields because of their low density, high specific strength and corrosion resistance. The process of the warm forming of aluminum alloy improves the formability of aluminum alloy sheets, reduces the deformation resistance and spring-back and improves the forming accuracy and quality of parts. For these reasons, it is frequently used. In this work, the effects of temperature, sliding speed and normal load on the friction coefficient of 6111 aluminum alloy were studied by using a CFT-I (Equipment Type) friction tester under boundary lubrication conditions. The surface morphology of the sample after the friction test was observed by optical microscopy. The results show that the surface quality of aluminum alloy is better at 200 °C, which was used as the temperature in the experiments. According to the test measurement results, the friction coefficient increases with the increase in temperature and decreases with the increase in sliding speed and normal load. Variable friction coefficient models of sliding speed and normal load were established. Using the optimal parameter combination as the simulation parameter, the established variable friction coefficient models were input into numerical simulation software, and two sets of comparative simulations were established. The thickness distribution of the sheet material obtained through the simulation was compared with the actual test measurement. Further verification was carried out through the amount of spring-back. The results show that the thickness distribution and spring-back of the sheet obtained by the variable friction coefficient model are closer to the actual measurements (the error of the spring-back angle decreased from more than 20% to less than 10%), which verifies the reliability and accuracy of the variable friction coefficient model.

Thermal modeling and experimental investigation on the influences of the process parameters on warm incremental sheet metal forming of titanium grade 2 using electric heating technique

Incremental sheet metal forming (ISMF) is one of the most innovative flexible processes for small volume production of complex sheet metal components. Formability of titanium grade 2 sheets is limited at room temperature and can be improved by forming at elevated temperature. Therefore, warm ISMF process has been explored to enhance the material formability. In this paper, thermal model has been proposed to predict the effect of temperature on the formability of sheet metal in warm ISMF process. Sine law has been used to determine the final thickness of the formed sheets. Experimental investigations on titanium grade 2 sheet at warm temperature has been carried out to study the effects of incremental depth, wall angle, and temperature on formability, geometrical accuracy, and thickness reduction during warm ISMF process using Taguchi L9 orthogonal array. Based on the experimental results, it was found that titanium grade 2 sheets formed with incremental depth of 0.1 mm and temperature of 300 °C showed higher formability with geometrical deviation of 1.52% and thickness reduction of 37.90%. Predictions of thermal model are validated by experimental work, and it has been found that experimental results are in good agreement with the thermal model. Analysis of variance (ANOVA) was used to identify the percentage contribution of each process parameters. To analyze the fracture behavior of the formed component, fractography study has been carried out using scanning electron microscopy (SEM).

Forming limits of magnesium alloy AZ31B sheet at elevated temperatures

Magnesium alloy sheets usually has to be processed by warm forming, and change of strain path and evolution of microstructure can significantly influence their warm formability. Forming limit test for an AZ31B alloy sheet under strain path changes was configured and implemented, and the effects of strain paths and microstructure evolution on the forming limit diagram are investigated. The sheet was pre-strained under in-plane uniaxial, plane strain and biaxial tension loading paths at 150 °C, 200 °C and 300 °C, followed by hemispherical punch stretching experiments at the three temperatures using specimens extracted from the pre-strained samples. A crystal plasticity model that incorporates dynamic recrystallization (DRX) and annealing recovery was combined with the Marciniak-Kuczyński (M-K) approach to calculate the FLDs. The evolution of dislocation density during annealing in the pre-strained FLD test at 200 °C was evaluated, through which the predictions of pre-strained FLDs were considerably improved. The present work provides experimental as well as crystal plasticity based methods for evaluating warm formability of magnesium alloys influenced by temperature, pre-straining, DRX and recovery.

Lithium Carbonate as a Corrosion Inhibitor for Mg Alloy Sheet Metal Product

Reducing the overall mass of transportation vehicles by the use of strong lightweight materials is arguably the best enabling means to improve fuels efficiency and, thus reduce harmful emissions. Wrought Mg alloys with high specific strength, stiffness and warm formability (ZE alloys) provide enabling opportunities as an integral part of lightweight multi-material structural assemblies to achieve this goal. One key technical issue preventing widespread implementation of Mg alloy components is the high rate of dissolution (corrosion) in aqueous environments. This is driven in large part by the inherent reactivity of Mg (lowest standard reduction potential among industrial engineering metals), the high rate of the hydrogen evolution reaction that dominates the cathodic process and the tendency of the native oxide surface film to breakdown and be replaced with a significantly thicker and much less protective corrosion product film. Dissolved Li2CO3 (aq) is being evaluated as an effective corrosion inhibitor for bare Mg alloy sheet metal product (AZ31B and ZEK100) when immersed in 0.1 M NaCl (aq) as a precursor to the development of a conversion coating technology. The extent of corrosion protection is being determined at various Li2CO3 levels (mM) by making volumetric H2 gas evolution and mass loss measurements as a function of immersion time. Complementary potentiodynamic polarization measurements are being conducted to determine the manner in which dissolved Li2CO3 (aq) affects the global anodic and/or cathodic processes that control corrosion. SVP measurements are being made to resolve and track changes in the localized filament corrosion and associated cathodic activation resulting from effective inhibition of dissolved Li2CO3 (aq). Both surface analysis by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) examination of FIB-prepared cross-sections are being utilized to determine the film chemistry and local fine-scale structure involved in the filament corrosion and associated cathodic activation if and when it develops with time. A similar set of measurements is being made with Li(OH)2 (aq) additions (at equivalent pHs) to determine the specific role of Li+ (aq) and CO3 2− (aq) ions in providing improved corrosion control. This paper presents and discusses the results within the context of developing a self-healing conversion coating layer for inclusion in automotive paint schemes.

Influence of processing temperature on formability of thin-rolled DP590 steel sheet

ABSTRACT DP590 steel is used as an alternative material in automobile applications due to its high strength and considerably good other mechanical properties. However, major concern of DP590 steel forming is limited ductility and malleability. Warm forming is used as an effective alternative process to produce complex shape components from such high strength material. The present work is mainly focused on the investigation of processing temperatures (room temperature [RT], 200°C, and 400°C) on stretch forming behavior of DP590 thin-rolled sheet. The formability of the material increased by approximately 26% as the forming temperature increased from RT to 400°C. Further, six ductile fracture criteria were calibrated in order to predict the fracture locus of material in effective plastic strain versus triaxiality space. Oh’s model is found to have best predictability of fracture locus with least average absolute error at RT and 200°C while Cockcroft and Latham model best predicted at 400°C. Furthermore, fracture behavior of DP590 steel has been analyzed in the biaxial, plane strain, and uniaxial regions. The specimens in the biaxial region fractured without any prior hint of necking while predominantly ductile type of fracture has been observed for specimen lying in the uniaxial region.

A feasibility study on warm forming of an as-quenched 22MnB5 boron steel

In this paper, the feasibility of a newly proposed forming method, being the warm forming of as-quenched 22MnB5 boron steels, was studied through a series of proof of concept experiments. To assess the material thermo-mechanical behaviours under the proposed forming conditions, first, the as-received 22MnB5 boron steel was austenized and quenched to below the martensite transformation finish temperature to obtain a martensitic microstructure; second, uniaxial tensile tests of the as-quenched steel were conducted under proposed warm forming conditions on a Gleeble 3800 materials simulator. To evaluate the material post-form properties, first, tempering treatments on the as-quenched steel samples were performed to simulate the heat-treating conditions in the proposed warm forming process; second, the mechanical properties (hardness, strength, and ductility) of as-tempered samples were measured and a microstructure analysis was conducted. From the experimental results, it was found that, under the proposed warm-forming process conditions (420 °C–620 °C), the material showed significant strain softening, which would increase the tendency of necking during stamping and adversely affect its drawability. In addition, it was found that the heating of martensite in a 22MnB5 boron steel to higher temperatures (>400 °C) adversely affected its post-form strength and ductility due to the tempering effect. Therefore, according to the results obtained in this study, the warm forming of as-quenched 22MnB5 boron steel may reduce the strength of formed parts by more than 50% in comparison to the possible strength the material could achieve under the investigated process.

Trend Analysis of Maximum and Minimum Temperature over Ebonyi State, Nigeria

This study examined the trend in annual maximum and minimum temperature data in Ebonyi State using data collected from the Nigerian Meteorological Agency of Nigeria. The aim is to reveal the spatial and temporal variation in maximum and minimum temperature from 1984-2015. The study made use of statistical tool like linear regression to depict the trend in annual maximum and minimum temperature over time. Results indicate that maximum temperature possesses steepness in slope of 0.0046? and minimum temperature 0.002?. The maximum temperature equation shows a positive time trend which suggests that maximum temperature of Ebonyi State of Nigeria tends to increase over time. Decadal analysis of the climate variable revealed that the 1994-2003 decade has the highest maximum temperature followed by 2004-2015 decade and then 1984-1993. This shows that the 1984-1993 decade was cooler than the later decade which is a pointer to the increasing temperature being experienced in form of global warming with its attendant environmental consequences. The study therefore recommends that proactive measure like making accurate and appropriate weather and climate data available for planning should be encouraged by all to mitigate these consequences especially on population whose livelihood depends on agriculture that is temperature sensitive.

Differential physiological, transcriptomic and metabolomic responses of Arabidopsis leaves under prolonged warming and heat shock

BackgroundElevated temperature as a result of global climate warming, either in form of sudden heatwave (heat shock) or prolonged warming, has profound effects on the growth and development of plants. However, how plants differentially respond to these two forms of elevated temperatures is largely unknown. Here we have therefore performed a comprehensive comparison of multi-level responses of Arabidopsis leaves to heat shock and prolonged warming.ResultsThe plant responded to prolonged warming through decreased stomatal conductance, and to heat shock by increased transpiration. In carbon metabolism, the glycolysis pathway was enhanced while the tricarboxylic acid (TCA) cycle was inhibited under prolonged warming, and heat shock significantly limited the conversion of pyruvate into acetyl coenzyme A. The cellular concentration of hydrogen peroxide (H2O2) and the activities of antioxidant enzymes were increased under both conditions but exhibited a higher induction under heat shock. Interestingly, the transcription factors, class A1 heat shock factors (HSFA1s) and dehydration responsive element-binding proteins (DREBs), were up-regulated under heat shock, whereas with prolonged warming, other abiotic stress response pathways, especially basic leucine zipper factors (bZIPs) were up-regulated instead.ConclusionsOur findings reveal that Arabidopsis exhibits different response patterns under heat shock versus prolonged warming, and plants employ distinctly different response strategies to combat these two types of thermal stress.

Microstructure evolution of warm deformed multilayered Al alloy sheet during brazing

Warm forming can improve the formability of Al alloy sheets that are used in heat exchanger production, but the effect of warm forming on the brazing performance of the sheet is not well understood. This investigation evaluates the brazing performance and corresponding microstructure evolution of a warm formed sheet comprised of an Al-Mn core alloy and an Al-Si clad alloy. Understanding the conditions that lead to the detrimental process of liquid film migration (LFM) during brazing is of particular interest. Warm forming was simulated by tensile tests performed between room temperature and 250 °C, and at strain rates between 7E-4 s −1 to 7E-2 s −1 . A brazing treatment consisting of a 3 min hold at 600 °C was simulated using differential scanning calorimetry. Brazing performance was evaluated by the ratio of the clad alloy solidification energy to the initial melting energy ( i.e. ΔH sol /ΔH melt ). The post-braze microstructure and ΔH sol /ΔH melt depended on strain, strain rate, and forming temperature. ΔH sol /ΔH melt was 0.5 or less when LFM occurred during brazing, but improved to 0.7 when the core alloy recrystallized. The dislocation density in the sheet was calculated using the Bergstrom hardening model; dislocation densities over which LFM and full core recrystallization occurred were distinct from one another. When LFM did not occur, isothermal solidification reduced the amount of clad alloy available for brazing by 23 %. It is concluded that the post-braze microstructure strongly depends on the sheet forming conditions, and that the driving force for LFM is the reduction of stored deformation energy.

Emerging Global Health Crisis of our times- Climate change

The progress of the human race over the last 200 years is unprecedented in recent history. Rapid industrialization, urbanization, and consumerism have made lives easier for humankind. Still, these changes come at a very high price. We never anticipated that we will have to pay the price in the form of climate change and global warming. Our planet, the earth is getting warmer by 0.85 ?centigrde annually for the last one hundred and seventy years. Hence, glaciers are melting faster than ever, water levels are rising, and cities are sinking, while greenhouse gas emission numbers are at their highest points in human history. Unfortunately we humans are living in anthropogenic epoch and are also speeding up the destruction of the earth’s ecosystem by being the dominant cause of the warming observed since the 20th century. Deforestation coupled with increased greenhouse gas emissions has led to a surge of heat-waves globally. These environmental disasters not only affect the environment, plants, and land but also have a profound direct and indirect impact on the health of people. In-fact the health impact has already debuted in the form of worsening key health indicators. In Pakistan alone, the 2015 heat-wave claimed the lives of twelve hundred people in Sindh province. Due to variable rainfall patterns that affect the availability of fresh water, it also affects food production &amp; delivery and brings on the drought. Quality of air, clean drinking water, and availability of food are the top three indicators most influenced by these disasters. Coupled with these, the more than the frequent occurrence of natural calamities; tsunamis, wildfires, snowstorms, and extremes of temperatures has put an extra financial burden on already, stretched to limits budgets of health.

Sustainability aspects in the warm forming of tailor welded blanks

Tailor welded blank (TWB) technology has been used in the manufacture of automobile body-in-white components since a long time. These components consist of different materials/thicknesses. Researchers and manufacturers involved with production of warm formed TWB components failed to address the sustainable issues related to warm forming. Rather they concentrated more on reducing the weld line movement (WLM). The WLM if not arrested shall lead to fracture, due to wrinkles, produced during forming. In this paper, the sustainability aspects involved in the warm forming of TWB were discussed with respect to energy and material savings. The results show a reduction of about 50% punch load in a hydraulic press during deep drawing under warm forming conditions. This paper addresses the questions related to the implications of thickness ratio on the weld line movement and further shows how material savings of nearly 33% has been obtained. It also discusses about the carbon emissions during manufacturing of raw materials and the recycling benefits of stainless steel, so as to minimize emissions at the production stage itself during raw materials production.

Influence of heating mode on orange peel patterns in warm incremental forming of magnesium alloy

Orange peel patterns on the surface of the magnesium alloy generated in warm incremental sheet forming significantly affect the appearance of the products. In this work, the influence of the heating modes on this phenomenon is investigated. Two heating methods, i.e., hot air heating and carbon fiber electric pipe heating, were developed for the warm incremental forming respectively. An octagonal pyramid is taken as example and four different forming temperatures are set for the two heating systems. The results indicate that the occurrence of orange peel patterns is strongly affected by the temperature distribution. The surface quality of the parts formed with the hot air heating system is generally better than that with the electric pipe heating system. The influence of the forming temperatures is also discussed based on the microstructural observation.

Study on warm formability of aluminum alloy 2219 in hemispherical part conventional spinning

To obtain the warm spin-ability of the thin-walled hemispherical part, the conventional spinning of aluminum alloy 2219 sheets with a thickness of 2mm is studied in this work. A spinning machine equipped with induction heating was set up, and a thermo-mechanical coupled spinning simulation of the AA2219 hemispherical part was developed. And the deformation temperature of about 250 ℃ can be realized for the AA2219 sheet. The effect of the deformation temperature on the spin-ability of the spun part has been studied by experiment and numerical simulation. The experimental results show that a stable and uniform temperature on the blank flange can be achieved via induction heating, and the developed numerical model is reliable for simulating the induction heating spinning process. Compared with the cold spinning, the warm spinning heated by induction coil causes the decrease of the flange anti-wrinkling and the increase of the thinning of the spun parts, but a less shape error in a single pass process.

Monitoring and Analysis of Water Quality Parameters for Diagnosis of Safe Drinking Purpose using Wireless Sensor Network

In the 21st century, the world had advanced through lots of innovations; its parallel impact in the form of pollutions, global warming and climatic change crisis are being raised. These crises create a gap in terms climatic changes, poor air quality, and unsafe drinking water for the population around the world. Among all pollutants, water pollution is a thrust area as it is a prominent parameter in the food chain of living things. There are huge numbers of diseases that are attributed due to polluted water. The water sources are mainly polluted due to untreated sewage and industry discharges. But mainly industrial wastewater discharge contributes to the accelerated pollution in the water bodies. The proposed design focuses on monitoring the water quality parameters like pH, TDS, TOC, and Chlorine content, conductivity etc., using wireless Sensor Nodes around open ponds and wells near tannery units. The data is transmitted to the cloud, and further information is given to the people through GSM. Repository of data is maintained in order to take it for further analysis. Results obtained from the model indicate the values of the above mentioned parameters.

Hot and warm cross-wedge rolling of ball pins – Comparative analysis

Cross-wedge rolling is a process conducted mainly in hot forming conditions. Warm forming is a compromise between hot and cold forming. This paper presents the results of a comparative analysis of warm and hot rolling of ball-shaped pins. Rolling process was controlled in terms of energy consumption, load and abrasive wear of tools. Warm cross-wedge rolling is more economical due to the low energy consumption required to heat the billet. Warm rolling can be less cost-effective due to faster tools wear. Faster tool wear during rolling in warm conditions may generate additional cost connected to regeneration and more frequent tool replacement. The stress and strain during the rolling at different temperatures was analysed. The variable nature of stress during cross-wedge rolling is more advantageous during hot rolling due to the lower amplitude of stress changes. Particular attention was paid to the quality of elements and difficulties resulting from rolling at lower temperatures. The influence of the rolling temperature on the quality of the microstructure of the rolled products was demonstrated. It was proved that during the warm rolling, the material may be strengthened due to deformation.

The exploitation of western and southern deserts in Iraq for the production of solar energy

&lt;span&gt;We have, an overview is presented of the potential future demands and possible supply of solar energy to Iraq. Solar energy, which is clean, unlimited, and environmentally friendly, is presented as a renewable energy resource. Many problems such as CO&lt;sub&gt;2&lt;/sub&gt; emissions, industry, human activities, and electricity distribution grids have attracted much attention because of the current state of crude oil production and its prices. Moreover, estimations of solar radiation levels and of the efficiencies of photovoltaics (PVs), concentrated solar power (CSP), and solar chimney towers, have all been investigated. Those systems that combine various sources of energy are called hybrids and they have received much attention in recent decades. The basic features of solar radiation in Iraq are outlined, and the selection of those sites with potential for development of solar plants is based on the local largest solar radiation. Moreover, longitudinal and latitudinal orientation, wind, solar intensity, dust, temperature, rain, humidity, and pollution factors are all considered in the calculation of PV/CSP efficiencies. We know there is an abundance of fossil fuels in Iraq, energy shortages began in 1991 because of the perturbation caused by the full ruin of the country. The obvious renewable energy resource available in Iraq is the solar energy, and its exploitation would provide a means to reduce CO&lt;sub&gt;2&lt;/sub&gt; emissions from the burning of fossil fuels and to achieve self-sufficiency of electric energy and export the rest to neighboring countries. Solar energy is becoming increasingly important because of the climatic change in the form of global warming.&lt;/span&gt;

Mechanical properties of ultra-high-strength steels at elevated temperatures

ABSTRACTThis paper presents an experimental study on the mechanical properties of ultra-high-strength steels at elevated temperatures. Tensile tests were carried out at 300–600°C on Docol 1200M and Docol 1400M steel samples. The results indicate that as the temperature increases Young’s Modulus, yield strength (YS) and ultimate tensile strength (UTS) display a decrease. YS/UTS ratios at 300°C are lower than those at room temperature, they make peaks at 400 and 500°C for Docol 1400M and Docol 1200M, respectively, and then decrease again beyond those temperatures. While total elongation continuously increases, uniform elongation slightly decreases with increasing temperature. Present carbides in tempered matrix continue to grow and new carbides are observed at the grain boundaries. Considering all roll forming parameters, 300°C seems the most convenient temperature for warm forming. In this sense, the warm roll forming has a potential for forming complex-shaped parts by reconciling strength with formability.

Assessment of solutions to reduce wear with the warm forming of aluminum

Aluminum warm forming can be used to form very hard sheet materials and reduce the weight of the parts produced, helping to lighten cars. While many studies have focused on the aluminum warm forming technique, few examine the effects of temperature on sheet - tool contact conditions during repetitive parts making. The purpose of this study is to focus on the different sheet/tool contact configurations with the warm forming of aluminum based on 2 types of tests: tribological testing for an initial range of contact configurations and press testing of the forming tool for the final evaluation of a range of configurations. 18 configurations, involving various materials, tool coatings and lubricants, were initially evaluated using a warm pin test on an AW5083 H111 sheet. According to the analysis of wear surfaces, adhesion/galling type damage occurred on pins and highlights the importance of lubricating with a beneficial influence of tool coatings. The analysis of the coefficient of friction alone cannot explain the degraded aspect of the pins obtained. Then press tests with a tunnel-shaped part were carried out on 4 selected configurations. If the coated and lubricated configurations are satisfactory, the uncoated and lubricated configurations are surprisingly good and better than the tribological results have shown. In addition to the risks of pick-up and galling, the deposits of residues on the tool are compared for the lubricants tested.

Warm Forming Simulation of a ZEK100 Magnesium Door Panel

The warm forming of a door panel made of commercial grade ZEK100 magnesium alloy sheet was modelled using finite element techniques (Autoform). The operation consisted of a heating step, a forming step and a cooling/springback step. The material properties of the ZEK100 blank were modelled using a set of temperature- and strain rate-dependent stress-strain curves, which were derived based on a Zerilli-Armstrong constitutive model. In order to simplify the material model to enable its complex response to be represented within a commercial finite element code, the anisotropy of the magnesium sheet was approximated using a Banabic-2005 yield surface and yield asymmetry was neglected, a reasonable approach for warm forming. Necking was predicted using a set of forming limit curves obtained at different isothermal temperatures. The entire forming model was run at a punch speed of 160 mm/s, and two initial blank temperatures: 215 and 230 °C. The tooling was initially at room temperature. The model predicted that the blank cracked when its initial temperature was 215 °C due to excessive cooling. The best formability (lack of wrinkling and necking) was predicted when the blank was heated to 230 °C. These predictions agree well with the forming trial outcomes.