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The influence of hardening medium in the vacuum carburizing process on the distortion of machine elements used in the automotive industry

Pawęta S., Pietrasik R.

Journal of Achievements in Materials and Manufacturing Engineering

2019

Vol. 94, nr 1-2

32--40

Purpose: As part of this study, the influence of the hardening medium on distortions of FineCarb® carburized rollers used in the automotive industry as elements of fuel pumps has been examined. The analysis was carried out for the process of quenching in gas at different pressure of cooling gas and quenching in oil at variable delay time of oil mixers. Design/methodology/approach: The research was carried out on real elements used in the automotive industry as elements of fuel pumps. FineCarb® vacuum carburizing technology was used in order to obtain optimal parameters of the surface layers. During quenching a variable related to the parameters of the quenching medium was introduced. For quenching in gas it was the pressure at which nitrogen was introduced into the cooling chamber, while for quenching in oil it was the time of mixers delay. The sample batch was laid out in accordance with the PPAP (Production Part Approval Process) requirements for the automotive industry. Microhardness and radial runout measurements were carried out on the samples and subjected to statistical analysis. Findings: The analysis of each hardening processes has showed that depending on the cooling medium used, different distortion values are obtained. The distortion value is significantly influenced by the parameters of the hardening process - gas pressure/oil mixers delay. With the proposed quenching parameters, there is no relationship between the location of the sample in the furnace chamber and the distortion value. The smallest hardening distortions were obtained as a result of the hardening process in gas at a gas pressure of 3 bar. Hardening in gas was characterized by the smallest scatter values of obtained results of radial runout. Research limitations/implications: Basing on the studies and analyses carried out in this work, it can be concluded that the introduction of gas quenching technology instead of oil quenching technology is justified qualitatively and economically alike. Hardening in gas was also characterized by the smallest scatter values of obtained results of radial runout. This is an extremely important technological and economic aspect, due to the cost of grinding processing. Practical implications: The automotive and aviation industries are putting ever greater demands on the quality of manufactured components while reducing costs. It requires optimization of technological processes from co-operators. In the case of hardening plants, the most important aspect is obtaining repeatable, precisely planned parameters of the carburized layer, as well as minimizing the negative phenomena that cause dimensional changes after hardening of elements. The tests allowed to determine the most effective hardening conditions in terms of obtained distortions and costs of eliminating distortions. However, the selection of the optimal parameters depends on whether the core hardness requirements are also determined. Originality/value: The conducted tests allowed to determine the most effective hardening conditions in terms of obtained distortions, costs of levelling distortions and a complete technological process for the automotive industry.

Analiza twardości granicznej warstw nawęglanych hartowanych w gazach pod wysokim cisnieniem

Kula P., Atraszkiewicz R.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

2005

Z. 82

161-168

W artykule przedstawiono omówienie metody określania twardości granicznej warstw nawęglonych po hartowaniu w gazach pod wysokim ciśnieniem, będącej integralną częścią opracowanego w Instytucie Inżynierii Materiałowej Politechniki Łódzkiej systemu FineCarb. Istotą problemu było opisanie modelu matematycznego zmian temperatury w badanym detalu, stworzenie baz materiałowych dla wytypowanych gatunków stali zawierających informacje odnośnie struktury i właściwości, wyznaczenie zależności wielkości wsadu, wielkości komory chłodzenia i ciśnienia gazu od szybkości chłodzenia. Te zależności w połączeniu z wymaganiami odnośnie właściwości warstwy wierzchniej są danymi wejściowymi do symulacji procesu nawęglania próżniowego spełniającego wymagania postawione przez użytkownika systemu.

The method of limiting hardness of carburized and quenched layers analysis has been investigated in the paper. This method is integral part of FineCarb system created at Material Science Institute at Technical University of Lodz. The main goal of investigations and researches was to define a mathematical model of temperature distribution and cooling rate in heat-treated part, create materials database and dependence between charge size, cooling ability of quenching chamber and properties of quenching gases. This assumption leads to perform conditions about surface layer required by users.