Blank Temperature Research Articles

An experimental study on monitoring and early warning of spontaneous coal combustion fires using CPM

At present, the conventional indicator gas has a blank temperature interval in the monitoring of coal spontaneous combustion fire area, and the monitoring accuracy is easy to be interfered by wind flow, which leads to the inaccurate grasp of the situation of the fire area. To solve this problem, the characteristics of condensable particulate matter (CPM) released into the air during spontaneous combustion and heating are analyzed in this paper through a particle collection system. The results showed that the CPM captured by the system gradually increased when the coal temperature rose above 250℃, and the diameter was above 1um. After 300℃, the release of CPM increased significantly, which was more than 10 times that below 300℃. Test analysis showed that these CPMs were mainly phenols and polycyclic aromatic hydrocarbons, which accounted for 22 % and 37 % respectively after 300℃. CPM mainly comes from the pyrolysis stage and the early stage of combustion of coal. Aliphatic macromolecules and polycyclic aromatic compounds generated by pyrolysis are the precursors of CPM. Due to the limitation of oxygen diffusion, these compounds are released into the air due to insufficient oxidation and eventually form CPM. It is worth noting that the release amount and composition of CPM have a good correspondence with coal temperature. The research results can fill the temperature gap of monitoring fire situation by conventional gas, and help to improve the accuracy of monitoring, which is of great significance for the protection of coal resources and safe production.

Experimental performance evaluation of direct cooling of hot stamping dies using fractal cooling channels

Hot stamping is a promising technology to reduce carbon dioxide emissions in the transportation industry by decreasing the weight of components with appropriate strength. However, the low cooling performance of conventional indirect cooling channels degrades the product quality and production rate during hot stamping. This study proposes a novel direct cooling system for hot stamping dies with fractal cooling channels (FCCs). Based on experiments, the cooling performance of the FCC was analyzed at various press holding times, mass flow rates, and cycle numbers. In the FCC, the average blank temperature at a water mass flow rate of 50 kg h−1 was 22 % lower than that at a zero-mass flow rate. At a mass flow rate of 50 kg h−1, the average blank temperature in the FCC increased with the cycle number and converged to 186 °C in the seventh cycle. Additionally, the standard deviation of the temperature distribution in the FCC was on average 39 % lower than that in the straight cooling channel (SCC). Finally, the daily production rate in the FCC was 34 % higher than that in the SCC.

A comprehensive validation of GRA with ant colony optimization for robust optimal design: A case study on the forming process

Sheet metal forming design involves numerous factors and controlling all these parameters to prevent cracks is a major challenge to maintain the quality. Therefore, the careful selection of process parameters is critical for ensuring product longevity. Several researchers employed different techniques for optimal selection of process parameters but consistency among the techniques and validation of results in real time scenarios will play a pivotal role in determining the suitable parameters. Therefore, the current work presents a validation method of Grey Relational Analysis (GRA) results with Ant Colony Optimization (ACO) for the robust optimum design with an illustrative example of forming process. Al 6061 – T6 alloy was chosen as a material for deep drawing process and L27 Orthogonal Array was planned to conduct experiments with four input parameters such as blank thickness, Die and Blank Temperature, Die Speed, Lubrication at three levels each. Punch force and Thickness variation were considered as the output parameters. GRA Technique was implemented to find the best optimal combination and regression equation was developed to predict the nature of objective function. These results were given as an input to ACO, a nature inspired algorithm to search for the optimal solution with in the design space. Sensitivity analysis has also been performed to highlight the effectiveness of the proposed solution in terms of solution quality and computational efficiency. The ACO method, GRA technique and the experimental results are almost similar with a margin of acceptable deviation. The results indicated the robustness of the projected approach in achieving the quality of solution.

Design and analysis of extrusion die for T-shaped sheet materials

Abstract The study explores plastic deformation behavior of T-shaped plates using DEFORM™ 3D, a perfect plastic finite element analysis software that considers T-shaped and double T-shaped extrusion dies as rigid bodies and compares effective strain, effective stress, blank temperature, die wear and temperature conditions. Moreover, the study employed the machine learning step descent method to predict effective stress and effective strain. Furthermore, the Pearson product difference correlation was utilized to examine the relationship between effective stress, effective strain, and temperature in T-shaped extrusion. Lastly, META analysis was conducted to synthesize statistical data on effective stress and temperature from various research.

Effects of Thermoforming Parameters on Woven Carbon Fiber Thermoplastic Composites.

The quality of woven carbon fiber fabric/polycarbonate thermoplastic composites after thermoforming and demolding was investigated using finite element simulation and the Taguchi orthogonal array. The simulation utilized a discrete approach with a micro-mechanical model to describe the deformation of woven carbon fabric, combined with a resin model. This simulation was validated with bias extension tests at five temperatures. The thermoforming process parameters considered were blank temperature, mold temperature, and blank holding pressure, with three levels for each factor. Optimal values for the fiber-enclosed angle, spring-back angle, mold shape fitness, and the strain of the U-shaped workpiece were desired. The results indicated that the comparison of the stress-displacement curve of bias extension tests verified the application of the discrete finite element method. Results from the Taguchi array indicated that blank holding pressure was the dominant parameter, with the optimal value being 1.18 kPa. Blank temperature was the second most significant factor, effective in the range of 160 °C to 230 °C, while mold temperature had a minor effect. Furthermore, the four quality values are dependent and have a similar trend. The best combination was identified as a blank holding press of 1.18 kPa, a blank temperature of 230 °C, and a mold temperature of 190 °C.

Cryogenic Deep Drawing Tool Design for Reduced Heat Transfer

Subject of this study is the usage of macro-structured tools for deep drawing of aluminum alloys at cryogenic temperatures in order to increase the drawing depth. The advantage of the macro-structure is the reduced contact area, which primarily leads to a reduction in frictional forces in the flange area and also minimizes the heat transfer from the tool to the cooled sheet metal. In addition to the geometry of the tools, the heat transfer is also influenced by the thermal properties of the tool materials. Therefore, the tool must be designed to reduce heat flux and thermal diffusivity. In this regard, substitute materials for the tools, specifically polymer, and steel-shielded polymer, were investigated. In this context, the heat transfer coefficients between the tool material and the aluminum blank are determined experimentally. The influence of thermal conditions on the cryogenic deep drawing process are investigated numerically and experimentally. The result of the study is an improved process understanding to ensure the blank temperature in a cryogenic range and increase the resistance against bottom cracks.

Fast-cooling of aluminium alloy sheet metal for hot-stamping applications

The paper reports an investigation into two rapid sheet metal cooling designs that are suitable for applications in hot-stamping production -air cooling and contact cooling, aiming at improving formability of the high-strength aluminium sheets for the forming of components with complex geometries with enhanced overall process efficiency. The investigation involved both numerical modelling and experimental trials using an in-house developed prototype cooling tools. A series of contact cooling experiments were conducted, considering process variables such as initial blank temperatures, cooling die temperatures, die materials, surface conditions, etc. The results demonstrated that the cooling rate of the aluminium blank could be accurately controlled by both methods with appropriate pre-setting of the equipment and control of the process parameters. The integration of the cooling system into a polit hot-stamping production was also tried, considering industry-scale applications related factors. The results can serve as a design guidance for an industry to introduce such cooling methods and manufacturing facilities.

Metal-Containing Diamond-Like Carbon Coatings with Increased Temperature Stability for Wear Protection of Nitrided Hot Forging Dies

In cold forging processes, diamond-like carbon (DLC) coatings have become established as a wear protection for forging dies, featuring high hardness and advantageous friction properties. This counteracts the particular critical abrasive tool wear and increases tool life. A major disadvantage of DLC coatings is their low thermal stability. In this study, the influence of metallic elements (niobium, tungsten and chromium) in the treatment atmosphere of the coating process is investigated with the aim of increasing the temperature resistance of the DLC coating and enabling its application as a wear-protection measure for hot forging dies. Preliminary studies were carried out to investigate the influence of different treatment atmospheres on wear-reducing properties such as high hardness and coating adhesion depending on prior nitriding processes. The most promising metal-doped DLC coating, with 30 % tungsten in the treatment atmosphere, was used in serial forging tests. At a blank temperature of 1,200 °C and a moderate count of 100 forging cycles, wear was reduced by up to 60 % compared to the nitrided reference tool.

Extension of Process Limits in High‐Strength Aluminum Forming by Local Contact Heating

The aluminum alloy EN AW‐7075 T6 is used in the automotive sector for its favorable strength‐to‐weight ratio. However, the limited cold formability is currently addressed by energy‐ and time‐consuming temperature‐assisted processes. In order to limit the effort to critical forming areas only, the state‐of‐the‐art shows promising results for increasing the blank temperature in the range of warm forming. The design of new processes in an industrial context requires appropriate numerical simulation with inherent complexity due to time‐ and temperature‐dependent effects. Herein, the potential of a newly developed tool setup and process chain with integrated local contact heating of the EN AW‐7075 T6 blank is investigated on the basis of a curved hat profile. A thermomechanically coupled FE model of the process is developed and validated. The influence of the local heating layout is analyzed in experimental forming tests and a corresponding process window is derived. The influence of local heating on the occurring failure mechanisms is discussed based on simulation results. The equivalent plastic strain evolution is successfully used to evaluate the local heating dependent failure behavior. A significant increase in the overall formability of the part is achieved by the proposed process chain.

A numerical study on warm deep drawing of polypropylene

AbstractWarm deep drawing of polypropylene, a semi‐crystalline thermoplastic polymer, is studied using finite element analysis. In this process, a circular polypropylene blank is preheated to a temperature much below its melting temperature and deep drawn into the shape of a flat‐bottom cylindrical cup using a punch‐die combination, both initially at 25°C. The material model used for the analysis considers the effects of varying temperature and strain rate during the deep drawing process on the depth of draw. The effects of blank holder force, initial blank temperature, blank diameter, and die and punch corner radii on the depth of draw are determined. Thickness, temperature, and strain variations in the drawn cups, punch forces, and failure modes are also determined.

Investigation into a comprehensive forming limit curve considering multi-parameters effects for semi-cured FMLs through uniform pressure loading test

Recently, hydroforming has paid dividends in composite forming due to its uniform pressure distribution, which helps in reducing the delamination defects. Considering the need to develop an appropriate criterion for evaluating the formability of FMLs, inspired by sheet metal forming and testing, the uniform pressure loading test was adopted to characterize the formability of semi-cured FMLs by forming limit curve ( FLC). In this paper, both theoretical analysis models considering and ignoring the tangential cohesive effect were established, and the stress expression of the critical zone was given. The results show that the tangential cohesive stress demonstrates a non-negligible influence on the FLC. A new form of comprehensive FLC was given by defining global equivalent strain and global strain ratio and analyzed by the finite element method. In addition, the numerical simulation model and the experimental parameters were verified. A simplified Hashin criterion was proposed and developed into the numerical simulation as a subroutine based on theoretical analysis. Parameters such as blank holder pressure, pressure rate, and temperature were considered both in experiments and simulation. Only fiber stretching damage was distinguished in the cross, single, and arc crack but no wrinkling. As predicted theoretically, a lower forming limit is expected when FMLs are subjected to greater tangential cohesive stress. Finally, with the help of numerical simulation, the influence of different boundary conditions on the comprehensive FLC was studied. Instead of a simple evaluation of FMLs, this comprehensive FLC could be used directly to optimize hydroforming processes in the engineering field.

Multi-Objective Optimization of Process Parameters in 6016 Aluminum Alloy Hot Stamping Using Taguchi-Grey Relational Analysis

The hot stamping technology of aluminum alloy is of great significance for realizing the light weight of the automobile body, and the proper process parameters are important conditions to obtain excellent aluminum alloy parts. In this paper, the thermal deformation behavior of 6016 aluminum alloy at a high temperature is experimentally studied to provide a theoretical basis for a finite element model. With the help of blank stamping finite element software, a numerical model of a 6016 aluminum alloy automobile windshield beam during hot stamping was established. The finite element model was verified by a forming experiment. Then, the effect of the process parameters, including blank holder force, die gap, forming temperature, friction coefficient, and stamping speed on aluminum alloy formability were investigated using Taguchi design, grey relational analysis (GRA), and analysis of variance (ANOVA). Stamping tests were arranged at temperatures between 480 and 570 °C, blank holder force between 20 and 50 kN, stamping speed between 50 and 200 mm/s, die gap between 1.05 t and 1.20 t (t is the thickness of the sheet), and friction coefficient between 0.15 and 0.60. It was found that the significant factors affecting the forming quality of the hot-stamped parts were blank holder force and stamping speed, with influence significance of 28.64% and 34.09%, respectively. The optimal parameters for hot stamping of the automobile windshield beam by the above analysis are that the die gap is 1.05 t, the blank temperature is 540 °C, the coefficient of friction is 0.15, stamping speed is 200 mm/s, and blank holder force is 50 kN. The optimized maximum thickening rate is 4.87% and the maximum thinning rate is 9.00%. The optimization method used in this paper and the results of the process parameter optimization provide reference values for the optimization of hot stamping forming.

Influence of Macro-Structured Tools on the Formability of Aluminum Alloys in the Cryogenic Temperature Range

Aluminum materials are popular materials for research in terms of lightweight construction. How cryogenic forming can be used to increase material utilization in terms of resource efficiency is one of the areas being investigated. Subject of this study are numerical and experimental investigations regarding the formability of the aluminum alloy AA6014-T4 with macro-structured deep drawing tools at cryogenic temperatures. The macro-structure of the deep drawing dies significantly reduces the heat flux between the dies and the blank due to the reduced contact area. For this reason, active cooling or heating of the dies is not required. The process of heat conduction between the tool and the blank, as well as the deep drawing process, is calculated using the FE-method and compared with the experimental investigations. In addition, the induced residual stresses are determined using the hole-drilling method and compared with the computational solution. The presented examination shows an improved deep drawing ratio of the aluminum alloy AA6014-T4 at cryogenic blank temperature without active tool cooling. Additionally, the influence of the blank temperature on the forming regarding the residual stresses in the cups is analyzed and discussed.

Numerical analysis of non-isothermal warm deep drawing of an Al-Mg alloy using different yield criteria and experimental validation

Finite element analysis of non-isothermal warm deep drawing of AA5083-O aluminum alloy sheets has been carried out using a coupled thermomechanical numerical model. Two different yield criteria, namely Hill's and Barlat's criteria have been used to define the yielding behavior in the simulations. Using cold punch in combination with hot dies significantly improved the drawability of the sheet material but at the same time resulted in a large thermal gradient and strain rate variation during the process. Therefore, for a better predictive accuracy, the effect of strain rate and temperature has been incorporated into the simulations by defining the stress–strain curves at various temperatures and strain rates. Numerical simulations have also been carried out at different initial blank temperatures and punch speeds to study the influence of temperature and speed on drawability, thinning, and drawing load. The predicted drawability, thinning, and drawing load are found to be in good agreement with the experiments.

Temperature and strain dependent fracture of AlSi coating in hot stamping of press hardening steel

In hot stamping severe tool wear occurs. The main tool wear mechanism is the so-called compaction galling, in which fractured particles from the coating of the part (blank) being build-up and become compacted upon the tools. Since fractured particles play an important role in the wear mechanism, fracture of the AlSi coating is investigated. For this purpose, simplified B-pillar parts are pressed at several temperatures to investigate the effect of temperature, strain and tool contact on the fracture behavior of the AlSi coating. Three positions which exhibit different strain modes are analysed by means of optical topography and optical microscopy measurements. The results indicate a strong correlation between the AlSi coating fracture, strain and temperature. For instance, at relatively low forming temperatures (i.e. 650 ºC), mode I fracture as well as spallation of the coating and at higher temperatures (750 and 800 ºC) mainly mode I coating fractures are observed. Interestingly, this type of mode I coating fractures are found to widen, eventually giving rise to mode II coating fractures along the coating-substrate interface. The onset strain of coating fracture is low and approximately at strains of 0.017, coating cracks are observed at all start temperatures. At contact-dominated regions, additional coating cracks are observed mainly due to a drop in blank temperature and added shear stresses due to the relative sliding between the blank and tools.

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.

Taguchi based GRA-PCA hybrid optimization for the forming of AL6061 alloy in automotive applications

Current study researches the impact of material and forming factors on punch force and sheet thickness in sheet forming of Aluminum 6061 composites. The particular properties of aluminum make it the most excellent candidate to replace the heavier materials in the vehicles which act as reaction to the mass drop interest inside the car area. As of now, the high-heat treatable composites Al 6000 series alloys are applied to broad applications. The forming tests were directed depending upon L27 orthogonal array (OA) planned by taking into account about temperature, die speed, sheet thickness and type of lubricant as input for process parameters. Multi target improvement was done to decide the individual significance of every reaction through Taguchi based Grey Relational Analysis (GRA) along with Principal Component Analysis. The procedure provide the ideal parameter condition for example sheet thickness of 2mm, die and blank temperature of 300oC, die speed of 0.4 mm/s , with Boric Acid lubrication that results in 25.96% decrease in Punch power and thinning improved by 50.74%. ANOVA is valuable to make out the significance and furthermore the result of each cycle factors on response parameters. Though, considerably all the parameters play important role, the die and blank temperature affects 80.11% of the reaction parameters as that of forming factors whereas die speed turned to be the slightest significant factor. Confirmation test was performed for approving the best blend.

Cryogenic deep drawing of aluminum alloy AA6014 using macro-structured tools

For functional lightweight construction, 6xxx aluminum alloys are essential materials for exterior components due to their low weight to stiffness ratio and acceptable formability. The formability of the 6xxx alloys is lower compared to other aluminum alloys but they are free of flow lines. MOUSAVI ET AL. [1] demonstrate an alternative method of improving the forming limit with a deep drawing process using macro-structured tools. Another approach increasing the formability of aluminum alloys is forming at cryogenic temperatures [2]. This paper presents an advancement of deep drawing on macro-structured tools at cryogenic temperatures. This assumes a lower heat flux due to the reduction of the contact area between the blank and deep drawing tools, enabling forming at cryogenic blank temperature. After characterization of the material, experimental investigations are carried out on a cup test geometry. In addition to the required punch force at different temperatures, this paper presents the influence of macro-structured tools at cryogenic temperatures on springback and hardness distribution. Finally, the extension of the process limits and options by cryogenic macro-structured deep drawing are discussed.

Design analysis for thermoforming of thermoplastic composites: prediction and machine learning-based optimization

The correct prediction of a composite parts’ final performance is of paramount importance during the initial design phase of the manufacturing process. To this end the correct evaluation of the most effective process parameters and their influence on the parts performance is key for the success of the manufacturing process. Our aim with this paper is to provide methodologies for the prediction of the temperature field in thermoplastic composites during thermoforming and to propose a strategy for process parameter selection. We measured the temperature variations over the different thermoforming stages and compared these values with analytical and finite element results. Our results show the accuracy of the predictions and the importance of the correct laminate temperature with respect to the prediction of the parts’ spring-in angle. We discuss the essential features needed for accurate predictions of the temperature fields over the whole thermoforming process at an early design stage and the potential of a Machine Learning procedure based on Artificial Neural Network to aim for the optimum range of process parameters for a desired part performance outcome. In conclusion, we provide essential guidelines for blank temperature predictions, and the benefit of a machine learning-based tool over traditional approaches.

Low temperature exerts protective effects by inhibiting mitochondria-mediated apoptosis pathway following pressure injury to rat muscle.

We aimed to determine the effect of different low-temperature range interventions at different time-points in a rat model of pressure injury (PI) produced by Ischemia/Reperfusion (I/R) injury. Sprague-Dawley rats were randomly assigned to blank control, injury control, and temperature intervention groups. Rats in the injury control and temperature intervention groups (involving exposure to different temperature range at different time-points) were subjected to three cycles of I/R injury with 2-h ischemia and 0.5-h reperfusion to induce PI. The muscle tissues exhibited degenerative changes after compression. Low temperature intervention of 16-18°C in the ischemia period resulted in the lowest degree of tissue damage and significantly decreased levels of Bcl-2-associated X protein (Bax), caspase-9, and caspase-3. Moreover, it resulted in the highest expression level of B-cell lymphoma 2 (Bcl-2) and lowest expression levels of Bax, caspase-9, and caspase-3 in muscle tissues among all intervention groups. Low-temperature intervention at 16-18°C during the ischemia period showed optimal effects on the expressions of apoptotic factors during the development of PI with I/R-induced tissue damage.