Warm Forming Research Articles

When good managers face bad incentives: Management quality and fuel intensity in the presence of price distortions

We use unique firm-level data on management practices and fuel expenditures in about 2000 manufacturing firms in central and eastern Europe, Central Asia, and Middle East and North Africa to examine how the quality of management practices relates to the fuel intensity of firms in the presence of fossil fuel subsidies. We use country- and country-sector-level measures of fossil fuel subsidies and distinguish between those that include externalities and those that do not. We find that better managed firms respond to the incentives and increase their fuel intensity if the difference between the supply cost and the consumer price of fuel is relatively large. This is particularly relevant for firms in high energy-intensive sectors. However, in the presence of environmental costs in the form of global warming and local pollution all types of firms tend to reduce their fuel intensity. Findings suggest that the combined effect of these two forces is not statistically distinguishable from zero overall. In high energy-intensive sectors, the polluting effect of fossil fuel subsidies prevails.

Characterization of Ti-6Al-4V alloy in the temperature range of warm metal forming and fracture analysis of the warm capping process

The flow behavior of a Ti–6Al–4V alloy during warm forming was characterized, and the results were analyzed to reveal the causes of fracture during warm forging of a small Ti–6Al–4V alloy bolt. The experimental flow curves obtained by compression test of cylindrical specimens at the warm forming conditions were fitted by a general extended C–m model after post-processed by a high-accuracy temperature correction scheme. Finite element analyses of the compression tests were conducted at various sample temperatures and strain rates using the flow model, revealing that the predicted compression loads were consistent with the experimental results. Flow behavior was also analyzed to reveal the metallurgical and macroscopic instabilities of the Ti–6Al–4V alloy. The flow behavior, macroscopic instability indices, and predicted forming load-stroke curves of Ti–6Al–4V alloy and SCr420H alloy steel were compared. The results study revealed that fracturing of the material in the capping stage during the automatic multi-stage warm forging of the small Ti–6Al–4V alloy bolt was caused by the sharp decrease in the forming load in an unpredictably early stroke from macroscopic instability, as indicated quantitatively by its macroscopic instability index.

Challenges in Tribometry for Warm and Hot Sheet Metal Forming of High Strength Aluminum with Tool Lubrication

For conventional sheet metal forming at room temperature, numerous tribometers were developed in the 20th century. At the present state of the art, unsolved issues for tribometry remain for temperature-supported forming processes of high strength aluminum (e.g. EN AW-7075), in which the sheet is heated to temperatures between 200 and 480 °C. The tribological design of these processes remains a major challenge, which needs to be addressed by investigations with adapted tribometers. In this study, a recently adapted strip drawing test for aluminum warm and hot forming is presented – including a newly developed strip heating unit, a die lubrication system and a die tempering system for efficient tribological testing. The contribution is completed with both, experimental results and a numerical investigation of temperature gradients in the strip drawing test. Finally, it is discussed whether transient process conditions of non-isothermal forming processes with die lubrication should be considered in tribometers for warm and hot sheet metal forming.

Anisotropic damage constitutive model of AA5754 aluminum alloy considering warm forming history

A multipath two-stage loading test for AA5754 aluminum alloy is carried out. In the first loading stage, the tensile tests of big samples were conducted with different preforming conditions. Then small samples were cut off from the pre-strained big samples. In the second loading stage, the mechanical properties of small samples were measured, and the influence of preforming factors such as prestrain value, temperature, strain rate and stress state on the mechanical properties of the sheets has been studied. With increasing prestrain, the yield stress of the sheet increases and the failure strain decreases linearly. The higher the preforming temperature is, the lower the yield strength of the sheet is under the same prestrain, and the greater the hardening index and failure strain. Moreover, the mechanical properties of the sheet are not sensitive to the forming strain rate and stress state. In addition, a transient softening effect appeared during the two-stage loading test. A damage constitutive model considering the history of warm forming is established by VUMAT subroutine of ABAQUS commercial software. The parameters of the constitutive model are determined by the two-stage loading experimental data and a genetic algorithm. This model can describe the transient softening and Bauschinger effect of AA5754 aluminum alloy after preforming at different temperatures. Good agreement is also observed between the stress-strain responses of AA5754 aluminum alloy after warm preforming and the predictions of the model.

High-temperature tribological behavior of Ti containing diamond-like carbon coatings with emphasis on running-in coefficient of friction

Diamond-like carbon (DLC) coatings show a low coefficient of friction (COF) and high wear resistance against aluminum at elevated temperatures, yet they exhibit a high running-in COF (μ R ) prior to reaching a low and stable steady-state COF (μ s ). This study shows that incorporating titanium (Ti) atoms into the DLC structure would reduce the μ R . During pin-on-disk tests conducted on Ti incorporating hydrogenated-DLC (Ti-H-DLC) with 6.2 at.% Ti subjected to dry sliding against 319 Al (Al-6.5% Si), μ s values decreased from 0.27 at 25 °C to 0.11 at 200 °C. The specific wear rate of Ti-H-DLC decreased from 2.44 × 10 −5 mm 3 /Nm at 25 °C to 0.71 × 10 −5 m 3 /Nm at 200 °C. A typical DLC with 40 at.% H (H-DLC) tested at 200 °C showed a low μ s of 0.08 and a wear rate of 1.11 × 10 −5 mm 3 /Nm. However, at 200 °C, Ti-H-DLC showed a lower μ R of 0.16 compared to μ R = 0.78 of H-DLC, and the duration of the running-in period for Ti-H-DLC, t R = 3 revolutions, was shorter than H-DLC with t R of 200 revolutions. Comparisons made with other DLCs, including, NH-DLC, W-DLC, ta-C, and Si-O-H-DLC, in addition to H-DLC, all tested using the same method, revealed that, in the temperature range of 100–250 °C, Ti-H-DLC showed a better running-in behavior making Ti-H-DLC a suitable tool coating for manufacturing processes where high-temperature running-in sliding friction is important, including warm forming and (single-point) turning of aluminum alloys . • High-temperature tribological behavior of Ti-H-DLC against 319 Al was studied. • Low running-in COF and short running-in duration were recorded at 100 and 200 °C. • Compared to other DLC coatings, the lowest μ R and t R were obtained using Ti-H-DLC. • Ti-H-DLC tool coatings are useful for Al warm forming, machining operations ~200 °C.

Effect of process parameters on formability in two-point incremental forming-machining of planar and twisted AA5083 blades

The deformation machining process (DMP) involves machining and incremental forming of thin structures. It can be applied for manufacturing products such as curved-surface blades without using 5-axis computerised numerical control machines. This work presents the effect of tool diameter and forming temperature on spring-back and dimensional accuracy of a simple fabricated part. The results of the first phase of the study are utilised to design the fabrication process of a curved surface blade. A feature-based algorithm is used to design the tool path for the forming process. The dimensional accuracy of the final product is improved through warm forming, two-point incremental forming, and extension of the bending zone to the outside of the product edges. The results show that DMP can be used to fabricate complex curved-surface workpieces with acceptable dimensional accuracy.

Warm sheet metal forming of energy-absorbing elements made 7075 aluminum alloy in the hardened state T6

The article covers experimental research on the forming of products made of 7075 aluminum alloy. This aluminum alloy grade is characterized by high strength, but due to its low formability in T6 temper, its use in the stamping processes of complex structural elements is limited. The authors have manufactured a U-shaped element at an elevated temperature and determined the optimal parameters of the process. Conventional heating of the sheet and shaping it at the temperature of 100 and 150 °C allowed to obtain a product of high strength similar to the T6 state, above 540 MPa. Due to the excessive springback of the sheet during forming, these products were characterized by a large deviation of the shape geometry, exceeding the allowable values of + / − 1 mm. Only the use of an alternative method of heating the sheet to temperatures of 200 and 240 °C (between plates at 350 °C, heating time 2 min, heating rate 1.8 °C/s) allowed to obtain a product that meets both the strength and geometric requirements. The determined optimal process’ parameters were later transferred to the stamping process of elements of a more complex shape (lower part of the B-pillar). The sheet was heated up and formed in the previously pre-heated tools. In the subsequent series of tests, the heating method and the blank’s temperature were being analyzed. In the case of the foot of the B-pillar, it was necessary to lower the initial blank temperature to 200 °C (heating in a furnace with a temperature of 340 °C, heating speed 0.5 °C/s). The appropriate combination of the process parameters resulted in the satisfactory shape deviation and reaching the product’s strength comparable to the strength of the material in as-delivered T6 temper. Using electron microscopy, it was verified that the structure of the finished product contained particles MgZn2 that strongly strengthen the alloy. The obtained results complement the data on the possibility of using 7075 aluminum alloy to produce energy-absorbing elements of motor vehicles.

Construction and technological innovations in the field of truck engineering. Part 1. Examples of implementation of general concepts

Abstracts. In the end-to-end process of research, development, design, manufacture, operation and disposal of automotive products and road transport facilities, as in any other field of human activity, in modern conditions of the most serious challenges in the form of global warming and man-made disasters, the optimization of the used technical solutions is of paramount importance. The maximum efficiency of these measures is ensured by their clear consistency and the implementation of constructive and technological innovations. Among them there are multiple manifestations, and the implementation of general layout conceptual solutions is in the lead. Keywords: trucks, structures, technologies, materials, safety, conceptual solutions, research, design, manufacture, operation

“Determinants of Household’s energy consumption preference and its implication to climate changes and economic development of the Kano state of Nigeria”

Energy consumption is always a matter of concern especially to developing and underdeveloped nations throughout the globe. Nigeria and its rural and urban demand for the energy resources is an issue that has similar concerns and challenges. There appears to be a great dilemma of the level of energy demand and its consumption pattern. The positive side of this appears in the form of energy demand of industrialization and production enhancement, whereas the negative side of the same appears to manifest in form of global warming, exploitation and pollution. Thus, it is important for any nation to optimize the consumption pattern for the sake of economic development under the sustainable framework. Although Nigeria is one of the major oil producers and rich in sources of energy apart from oil such as wood, coal, gas, tar sands, and hydro power etc., the optimization of consumption pattern is below par the global levels.This research paper is intended to find out the determinants of energy consumption and its impact over climate with the help of evaluation of the sample from Kano State. The study is based upon direct survey from households using questionnaire. Total sample size was 300 to understand the determinants and consumption pattern in the state. Further, data was analyzed using the required statistical tools and it was extracted that considerably many factors affect the energy consumption preference beside those tested by the one-way ANOVA. Income, education and family size are the tested factors affecting the family energy consumption preference. Beside these, household willingness, occupations, perception of the danger of modern energy to the household as well as the threat of traditional energy sources to climate change were also found to play a significant role in the energy consumption preference.

Accuracy and Sheet Thinning Improvement of Deep Titanium Alloy Part with Warm Incremental Sheet-Forming Process

Incremental forming is a recent forming process that allows a sheet to be locally deformed with a hemispherical tool in order to gradually shape it. Despite good lubrication between the sheet and the tip of the smooth hemisphere tool, ductility often occurs, limiting the formability of titanium alloys due to the geometrical inaccuracy of the parts and the inability to form parts with a large depth and wall angle. Several technical solutions are proposed in the literature to increase the working temperature, allowing improvement in the titanium alloys’ formability and reducing the sheet thinning, plastic instability, and failure localization. An experimental procedure and numerical simulation were performed in this study to improve the warm single-point incremental sheet forming of a deep truncated cone in Ti-6Al-4V titanium alloy based on the use of heating cartridges. The effect of the depth part (two experiments with a truncated cone having a depth of 40 and 60 mm) at hot temperature (440 °C) on the thickness distribution and sheet shape accuracy are performed. Results show that the formability is significantly improved with the heating to produce a deep part. Small errors are observed between experimental and theoretical profiles. Moreover, errors between experimental and numerical displacements are less than 6%, which shows that the Finite Element (FE) model gives accurate predictions for titanium alloy deep truncated cones.

Warm laser shock micro-heading forming (T2 copper): numerical simulation and experimental research

Warm laser shock micro-heading forming (T2 copper): numerical simulation and experimental research

Apnea Spells in a Term Neonate.

Apnea Spells in a Term Neonate.

Warm Forming Process for an AA5754 Train Window Panel

Abstract A warm forming process is designed for AA5754 to overcome low room temperature formability. The solution includes increased working temperature and is demonstrated with a railway vehicle component. A finite element (FE)-based methodology was adopted to design the process taking into account also the starting condition of the alloy. In fact, the component's dent resistance can be enhanced if the yield point is increased accordingly: the stamping process was thus designed considering the blank in both the H111 (annealed and slightly hardened) and H32 (strain-hardened and stabilized) conditions that were preliminarily characterized. Tensile and formability tests were carried out at different temperature and strain rate levels, thus providing the data to be implemented within the FE model (ABAQUS/CAE): the stamping was at first simulated at room temperature to evaluate the blank critical regions. Subsequently, the warm forming process was designed by means of an uncoupled thermo-mechanical approach. Thermal simulations were run to properly design the heating strategy and achieve an optimal temperature distribution over the blank deformation zone (according to the results of the material characterization). Such a distribution was then imported as a boundary condition into the mechanical step (ABAQUS/Explicit) to determine the optimal process parameters and obtain a sound component (strain severity was monitored implementing a forming limit diagram (FLD))-based damage criterion). The simulation model was validated experimentally with stamping trials to fabricate a sound component using the optimized heating strategy and punch stroke profile.

적층 제조 고분자 금형을 사용한 마그네슘 합금 판재의 온간 굽힘 공정 분석

Research on the application of additively manufactured polymer (AMP) to the conventional manufacturing process is underway. In this study, an additively manufactured die-set (AMDS) was used and applied to the warm forming of the magnesium alloy. Heat transfer and coupled temperature-displacement analysis were conducted in the V-Bending and UBending processes to study the applicability of the AMDS to the warm-forming process of the magnesium alloy sheet (AZ31B). A heat transfer experiment was conducted to determine the thermal contact conductance between the AZ31B material and two types of die-set, the metal and AMP. V-Bending and U-Bending experiments were conducted at 373 and 423 K; reduction in temperature between metal die-set and the additively manufactured polymer die-set were compared. The springback after the bending process with different initial temperatures and die materials was investigated. The simulation model showed good agreement. The springback of AZ31B was more decreased with the additively manufactured polymer die-set than with the metal die-set. The stress of the additively manufactured polymer die-set in the bending process was very small. It was confirmed that in the AZ31B material, the additively manufactured polymer die set helps increase the formability and decrease springback by keeping the temperature of AZ31B better.

Surface quality analysis of AZ31B Mg alloy sheet in ultrasonic-assisted warm single-point incremental forming

With a view to improving the surface quality of the magnesium (Mg) alloy at a warm temperature, the ultrasonic-assisted warm single-point incremental forming (SPIF) is proposed. The surface quality of the Mg alloy during the warm SPIF is primarily affected by two parts: the orange peel patterns of the non-contact surface and the scratches and adhesive wear of the contact surface. In this work, the surface quality of the AZ31B Mg alloy sheet parts at different forming temperatures and ultrasonic amplitudes is evaluated by examining the surface roughness and topography. The results show that the generation of orange peel patterns is significantly affected by temperature. In addition, scratches and adhesive wear of the contact surface increase with the rising temperature. After applying the ultrasonic vibration (UV), the quality of both the non-contact and the contact surfaces of the parts is significantly improved, but too large ultrasonic amplitude slightly reduces the surface quality. Moreover, the microstructural examination results show that UV has a great effect on dynamic recrystallization and grain refinement, which positively affects surface quality improvement.

A Generalized Stress State and Temperature Dependent Damage Indicator Framework for Ductile Failure Prediction in Heat-Assisted Forming Operations.

Heat-assisted forming processes are becoming increasingly important in the manufacturing of sheet metal parts for body-in-white applications. However, the non-isothermal nature of these processes leads to challenges in evaluating the forming limits, since established methods such as Forming Limit Curves (FLCs) only allow the assessment of critical forming strains for steady temperatures. For this reason, a temperature-dependent extension of the well-established GISSMO (Generalized Incremental Stress State Dependent Damage Model) fracture indicator framework is developed by the authors to predict forming failures under non-isothermal conditions. In this paper, a general approach to combine several isothermal FLCs within the temperature-extended GISSMO model into a temperature-dependent forming limit surface is investigated. The general capabilities of the model are tested in a coupled thermo-mechanical FEA using the example of warm forming of an AA5182-O sheet metal cross-die cup. The obtained results are then compared with state of the art of evaluation methods. By taking the strain and temperature path into account, GISSMO predicts greater drawing depths by up to than established methods. In this way the forming and so the lightweight potential of sheet metal parts can by fully exploited. Moreover, the risk and locus of failure can be evaluated directly on the part geometry by a contour plot. An additional advantage of the GISSMO model is the applicability for low triaxialities as well as the possibility to predict the materials behavior beyond necking up to ductile fracture.

Investigation of formability, microstructures and post-forming mechanical properties of heat-treatable aluminum alloys subjected to pre-aged hardening warm forming

Currently, the hot forming of aluminum alloys has garnered significant attention for overcoming poor formability at room temperature (RT). However, the current hot forming technique is facing problems such as time-consuming procedures and high economic cost. To improve forming efficiency, we herein propose a novel forming technique for heat-treatable aluminum alloys, termed pre-aged hardening warm forming (PHF) process. An Al–Zn–Mg–Cu alloy is used to investigate the flow behavior, drawing formability, and post-forming mechanical properties during the aforementioned process. Uniaxial tensile tests and Erichsen tests are conducted to evaluate the plastic flow behavior and drawability, respectively. Stamping tests are performed on a cap beam component to verify the engineering feasibility of the forming technique. Optical microscopy (OM) and transmission electron microscopy (TEM) are performed to characterize the microstructure evolution during the PHF process. The tensile test results show that the pre-aged alloys exhibit true fracture elongation similar to the fracture elongation of the O-temper alloy at RT, and that the Erichsen values of the pre-aged alloys are 5%–16% higher than that of the O-temper alloy at 200 °C. The results of the stamping tests for the cap beam component indicate that the optimal final strength of the stamped component achieves σ/σ0.2 = 566 MPa/500 MPa, exceeding the strength of the AA7075-T6 alloy. OM observations show that the stamping process does not significantly affect the grain sizes of the pre-aged alloys. TEM results show that numerous thermostable GPⅡ zones exist in the pre-aged alloys, and that the stamping procedure transforms the GPⅡ zones to dispersed η′ phases and results in the entanglement of numerous dislocations. The dual effects of phase transformation and plastic deformation during the PHF process contribute to the desirable mechanical properties of the stamped components.

Prediction of forming limits and microstructural evolution during warm stretch forming of DP590 steel

Prediction of forming limits and microstructural evolution during warm stretch forming of DP590 steel

Prevalence of Bone Marrow Fibrosis in 47 Cases of Autoimmune Hemolytic Anemia Patients: Clinical and Biologic Relationships

AIHA is an uncommon and heterogeneous disease caused by autoantibodies directed against erythrocytes and classified as warm (direct antiglobulin test DAT typically positive with anti-IgG antisera and seldom with anti C3d), cold (CAD, usually IgM driven with DAT positive for C3d), mixed (DAT positive for both IgG and high titer C3d), and atypical (DAT negative and IgA driven) forms. The disease is generally benign, but some cases show refractoriness to/relapse after first and further therapy lines, with a correlation with low Hb and inadequate bone marrow compensatory response at onset. Here we aimed to evaluate bone marrow histology (BMH) in 47 primary AIHA patients followed at our Institution, focusing on fibrosis, cellularity, dyserytrhopoiesis, and lymphocyte infiltrate, and their relationship with clinical, laboratory and immunological parameters, collected at enrolment (from January 2017), along with informed consent. BMH samples were revised by an expert hemopathologist and fibrosis graded (MF0 to MF3) according WHO 2016. The number of therapy lines (steroids, immunesuppressors, rituximab, splenectomy) were retrospectively collected. Serum levels of TGF-beta, IL-6, IL-10, IL-17, TNF-alpha, and IFN-gamma were evaluated in patients and in 40 age and sex matched healthy controls, using ELISA kits. Statistical analysis was performed using Student' t test for continuous variables and chi-square or Fischer exact probability test for categorical ones. Figure 1 shows main data of patients (14 males and 33 females; mean age 57 years; 26 CAD, 4 warm, 7 warm with C3d+, 5 mixed, and 5 atypical AIHA), divided according to bone marrow fibrosis (BMF) grade: BMF MF1 was observed in 36% of cases with no relationship with AIHA type, nor with mean Hb values, LDH levels, and the presence of splenomegaly; reticulocyte counts were higher in MF1 cases (p=0.02), although the incidence of inadequate reticulocytosis was comparable in the two groups (82% vs 93%). MF1 cases showed significantly increased cellularity (p=0.005) and dyserythropoiesis (p=0.04), without differences in lymphocyte infiltrate. Concerning cytokine levels, MF1 patients showed increased TGF-beta serum levels and reduced IL-6 (p=0.033), IL-10, IL-17, TNF-alpha, and IFN-gamma compared with MF0 cases. As regards treatment, no differences were observed among MF0 and MF1 cases considering the frequency of steroid and rituximab administration and their efficacy. Splenectomy was performed in 3 cases, all MF0, with 100% response, and cytotoxic immunesuppressors were given to both MF0 and MF1 with a response in the former patients only (67% vs 0%). Of note, MF1 cases more frequently required 2nd or further therapy lines (70 vs 53%), and displayed AIHA related complications (infections, acute renal failure and concomitant thrombocytopenia); at variance the occurrence of thrombosis was more common in MF0 cases.This is the first observation of BMF MF1 in more than 1/3 of AIHA cases. Although the number of patients is limited and the results preliminary, our data suggest that this subgroup is characterized by a hypercellular dyserythropoietic bone marrow and a higher rate of relapse and treatment requirement. Consistently, in MF1 cases, TFG-beta was the only cytokine increased among those tested. These chronic refractory cases may show clinical/pathologic features similar to low-risk myelodysplastic syndromes and recently described idiopathic cytopenia/dysplasia of unknown significance. On the other hand, MF0 AIHA patients seemed to present with a more florid hemolytic disease characterized by increased immune activation and cytokine release, more frequent thrombotic events, and a better response to immunesuppression.Figure1. Clinical and laboratory features of AIHA patients divided according to bone marrow fibrosis grade. Upper panel consists of a table showing clinical and laboratory parameters at diagnosis, therapy lines and complications. Lower panel consists of a graph showing cytokine levels in patients with or without bone marrow fibrosis. Data are given as median (range), if not better specified. TGF-β transforming growth factor beta; IL interleukin; TNF-α tumor necrosis factor alpha; IFN-γ interferon gamma. [Display omitted] DisclosuresBarcellini:Alexion: Honoraria; Agios: Honoraria, Research Funding; Novartis: Honoraria.

Temperature-controlled tools for multi-stage sheet metal forming of high-strength aluminium alloys

The high-strength aluminium alloys EN AW-6082 and -7075 possess great light-weight construction potential due to their high specific strength. However, their range of applications is limited by the low cold formability and high springback in the ultra-high-strength T6 state. To extend formability, either preconditioned semi-finished products, requiring a subsequent heat treatment or temperature-supported process routes such as warm forming or hot forming die quenching (HFQ) are used. If the forming degrees achievable with these methods are not sufficient, multi-stage forming is required. The forming degrees are limited by strain hardening in case of a cold forming operation of preconditioned semi-finished products and by heat transfer between the component and the tool parts in case of temperature-supported process routes. In order to reduce or even eliminate the cooling of the component in the subsequent forming stages, a four-stage forming tool with temperature-controlled active parts was developed and its influences investigated in more detail. The paper will demonstrate how precise temperature control of the tool components contributes to an extension of the formability. In addition, reproducible and robust process conditions can be guaranteed throughout the entire process chain.