In the present study, an algorithm has been developed using the adjoint method to optimise the position and cross-section of an internal cooling channel for a 3D printed tool steel insert for use in ...the aluminium die-casting process. The algorithm enables the development of an optimised complex industrial mould with relatively low computational cost. A transient model is validated against multiple experimental trials, providing an adapted interface heat transfer coefficient. A steady state thermal model, based on the casting cycle and thermal behaviour at the mould surface, is developed to evaluate the spatial distribution of temperature and to serve as the initial solution for the subsequent optimisation stage. The adjoint model is then applied to optimise the cooling channel emphasising the minimisation of the temperature standard deviation for the mould surface. The original transient model is applied to the optimised mould configuration via calibration using experimental data obtained from a dedicated aluminium furnace. The optimised cooling channel geometry, which uses a non-uniform cross-section across the entire pipe surface region, improves the pressure drop and cooling uniformity across the mould/cast interface by 24.2% and 31.6%, respectively. The model has been used to optimise cooling channels for a range of industrial high-pressure aluminium die-casting (HPADC) inserts. This has yielded a significant improvement in the mould operational lifetime, rising to almost 130,000 shots compared to 40,000 shots for prior designs.
•Two-phase refrigerant cooling for hot stamping is proposed for improved quenching.•Experimental and numerical studies on quenching performances are conducted.•R1234yf cooling realizes a better ...cooling performance and higher blank quality.•R1234yf cooling achieves a 9.5–15.3% greater daily production than water cooling.
This study aims to investigate the quenching performance of hot stamping blanks by two-phase refrigerant and conventional single-phase cooling. A low-global-warming potential refrigerant, R1234yf, is used as the working fluid for the two-phase refrigerant cooling. The quenching performance of the water and R1234yf cooling methods is evaluated experimentally and via simulations using a three-dimensional transient thermo-fluid model. The R1234yf cooling method presents a higher cooling capacity and energy efficiency than the water cooling method owing to the effective evaporative heat transfer characteristics of the former. Under the same mass flow rate conditions, the blank hardness and its standard deviation achieved by the R1234yf cooling method are 7.3–31.5 HV higher and 13.1–54.3% lower than those by the water cooling method, respectively. Furthermore, the R1234yf cooling method decreases the hotspot area in the internal lower die and realizes a more uniform temperature distribution compared to water cooling. In addition, the daily production by the R1234yf cooling method is 9.5 − 15.3% higher than that by the water cooling method owing to the shorter approach time to the martensite finish temperature in the former. Accordingly, owing to its higher blank quality and productivity, the R1234yf cooling method has a superior quenching performance than water cooling during the hot stamping process.
This article describes a meter for measuring thermal resistance of power transistors. It was developed to research the thermoelectric properties of power MOSFETs. The research was performed with the ...use of standard thermal resistance measurement methods and with the novel modulation method, which heats the device under test (DUT) with harmonically pulsewidth modulated current pulses. The temperature-sensitive parameter (TSP) was measured in the pauses between pulses. Voltage USD on the closed transistor's channel was used as TSP for power MOSFETs. To eliminate the influence of the delay time on the results of thermal resistance measurements, the TSP values were extrapolated to the end of each heating pulse. For extrapolation, it is proposed to use the root and logarithmic laws of the TSP changing in the process of transistor die cooling after heat impulse. The results of the thermal resistance components measurements obtained by various methods are in good agreement (about 2%) with each other.
The influence of local inner cooling in hot aluminum extrusion dies was investigated. For the manufacturing of the dies with conformal cooling channels, a layer-laminated manufacturing method and a ...laser melting process were applied. Extrusion trials with and without applying die cooling were performed. Numerical and experimental investigations revealed that, while maintaining the exit temperature of the extrudate, a distinct increase of the production speed up to 300% can be realized, while the extrusion force increases only slightly. Visioplastic analyses revealed that the rough surfaces, originating from the laser melting, do not disturb the material flow in the welding chamber.
Aluminium production needs the most energy‐intensive technologies among all the metal processing sectors. During the process of aluminium profile extrusion, the whole production line needs bulk ...electricity, and the mold inside the extrusion equipment needs robust cold energy for rapid cooling of the metal surface. This paper presents a new combo‐transmission that can simultaneously deliver cold energy together with electricity to the aluminium profile extrusion line. Thanks to the superiority of virtually zero loss and compact size, the powerful superconducting cable is used to replace the conventional copper cable. The entire superconducting cable assembly is fully installed into a cryogenic pipeline and cooled by liquid nitrogen at 77 K. In addition to keeping a favourable cryogenic environment for the superconducting cable, liquid nitrogen can also provide a large amount of cold energy for cooling the metal surface. For a typical 100 MN aluminium extrusion production line, the design and optimization of 10 kA class superconducting cable with the pipeline cooling system for aluminium production are presented in detail. The simulation results and comparisons show that the total energy loss of superconducting transmission is about 46% of conventional copper cable, and the energy saved in a year can be up to about 240.6 MWh. Moreover, the net profit increases almost linearly along with the increases of the extrusion speed when the liquid nitrogen cooling is applied to the 100 MN production line. For the case of 23% increase in extrusion speed, the net profit can be up to 1.48 M$ in a year. Overall, the novel design, technical evaluation, and economic analysis of the combo‐transmission system (cold energy + electricity) can provide a promising solution for future high‐dense aluminium production sectors.
A new combo‐transmission solution is proposed for enhancing both the energy efficiency and production benefit in an 100 MN aluminium extrusion workshop. The combo‐transmission scheme can transport the liquid‐nitrogen‐based cold energy and the superconductor‐based electric energy using the same cryogenic energy pipeline. The designed superconducting power cable has very superior performance regarding the compactness (83.6% smaller than the copper cable), and energy loss (54% smaller than the copper cable).
Internal die cooling during forging can reduce thermal loads, counteracting surface softening, plastic deformation and abrasive die wear. Additive manufacturing has great potential for producing ...complex geometries of the internal cooling channels. In this study, hybrid forging dies were developed combining conventional manufacturing processes and laser powder bed fusion (L-PBF) achieving conformal cooling channels. A characterisation of the used hot-work tool steel’s AISI H10 powder material was carried out in order to determine suitable parameters for L-PBF processing and heat treatment parameters. Additionally, the mechanical properties of L-PBF-processed AISI H10 specimens were investigated. Furthermore, the influence of different internal cooling channels regarding a possible structural weakening of the die were analysed by means of a finite element method (FEM) applied to a hot-forging process. The numerical results indicated that the developed forging dies withstood the mechanical loads during a forging process. However, during the investigation a large dependency between the resulting stresses and the chosen parameters were observed. By choosing the best combination of parameters, a reduction of the equivalent stress by 1000 MPa can be achieved. Finally, a prototype of the hybrid-forging dies featuring the most promising cooling channel geometry was manufactured.
In this study, the mechanical properties of the extrudate are improved by correcting the defects such as abnormal grain growth (AGG). Die cooling with N
2
gas is conducted to control the extrusion ...temperature during the hot extrusion of Al6061 in order to obtain fine grains of the extrudate. Computational fluid dynamics (CFD) is conducted to evaluate the effect of die cooling with N
2
gas and to determine the relationship between AGG and the extrusion temperature. The optimal cooling channel with a high cooling effect is designed by using the design of experiment (DOE) method, and thermo-mechanical analysis is performed to predict the extrusion temperature. A hot extrusion experiment is also carried out to measure the extrusion temperature and to observe the microstructure of the extrudate. The extrusion temperature predicted from the thermo mechanical analysis is found to be in good agreement with the measured extrusion temperature. The process condition required to reduce the AGG is determined on the basis of the distribution of the evolved microstructure in the hot extrusion experiment. The results confirm the relationship between the distribution of AGG and the mechanical properties of the extrudate. It is confirmed that the mechanical properties of Al6061 can be improved by the application of die cooling with N
2
gas during the hot extrusion process.
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