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In this paper, the conventional hot forming and hybrid quenching hot forming processes of Al-Si-coated 22MnB5 steel sheet were investigated and compared at 0.5 s-15 s holding times in the press tool related to the mechanical properties, microstructure, and dimensional accuracy. The conventional hot forming method is classified as a direct method and an indirect method. Both methods have limitations due to processing time and cooling of the press tool. To speed up the process, an alternative cooling method based on spray or jet cooling was used outside of the die tool. The hybrid quenching method involves hot forming and spray cooling process. This method, using spray parameters, provides more effective control in mechanical properties and microstructure compared to the conventional method by using spray parameters. Vickers hardness tests and tensile tests were carried out to compare mechanical properties. Changes in the microstructure of the materials were investigated using an optical microscope. The results show that spray cooling can be used as part of quenching in the hot forming process by reducing the holding time in the press tool by 97%. However, the microstructure, mechanical properties, and geometry deviations of the stamped parts are still below tolerances after the hybrid quenching hot forming process. The use of the hybrid quenching method with multi-point nozzles in the hot forming process resulted in sheet hardness up to 470 HV1 and 8% elongation with tensile strength of 1500 MPa. [ABSTRACT FROM AUTHOR]

This study's primary purpose is to improve the original krill herd (KH) optimization algorithm by using chaos theory and propose a novel chaotic krill herd (CKH) optimization algorithm. Fourteen different chaotic map functions have been added to the several steps of the KH and CKH optimization algorithms already existing in the literature to improve their performances. Six different well-known benchmark functions have been used to test the performances of the developed algorithm. The proposed algorithm has better performance to reach the global optimum of the objective function which has many local minimums. The proposed algorithm improved the KH and CKH optimization algorithms' performances which already exist in the literature. Proposed novel CKH has been applied to rubber bushing stiffness optimization which is a real automotive industry problem. Obtained results have been compared with KH, CKH, genetic algorithm (GA), differential evaluation algorithm (DE) and particle swarm optimization (PSO). The proposed algorithm has better performance to reach the global optimum of the objective function. The performance and validity of the algorithm have been proved not only by using six different benchmark functions but also by using finite element analysis of rubber bushing. The study is also a unique optimization activity that uses the KH algorithm to optimize rubber bushing by using nonlinear finite element analysis. [ABSTRACT FROM AUTHOR]

In this paper, a three dimensional Computational Fluid Dynamics Model (CFD) model was generated for spray cooling of straight parts by using a single point nozzle. The numerical simulations of spray quenching were performed to investigate the cooling rate of a 22MnB5 hot steel blank commonly used material in the automotive industry. Experiments are carried out to examine infrared thermograph of hot steel blank surfaces during spray cooling process by using infrared thermal camera. Time dependent situations of surface temperatures, surface heat fluxes and cooling areas are investigated numerically. The 3D model with some assumptions is presented to improve the solution of numeric simulation and to meet the most appropriate acceptable results for spray cooling process. The developed 3D model will be used to investigate the heat transfer analysis of hot stamped parts during hybrid quenching to optimize the process parameters. The comparison of the numerical and experimental results showed that the presented approach can be effectively used to evaluate heat transfer during spray quenching with a single nozzle. With this research, it was clearly seen that the estimated cooling rates and the temperatures were in good agreement with the experimental cooling temperature data. By using the numerical results and experimental data obtained in this study, multi-nozzle spray apparatus which will be used to obtain different cooling rates on the parts by changing spray parameters such as spray height, spray angle, mass flow rate, the distance between nozzles and part etc. was developed for hybrid quenching process. [ABSTRACT FROM AUTHOR]