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Open AccessArticle

Effect of the Martensitic Transformation on the Stamping Force and Cycle Time of Hot Stamping Parts

1
Metallurgy Research Centre IK4 AZTERLAN, Aliendalde Auzunea 6, 48200 Durango, Spain
2
Department of Mechanical Engineering, University of the Basque Country (UPV/EHU), Plaza Ingeniero Torres Quevedo 1, 48013 Bilbao, Spain
*
Author to whom correspondence should be addressed.
Metals 2018, 8(6), 385; https://doi.org/10.3390/met8060385
Received: 26 April 2018 / Revised: 22 May 2018 / Accepted: 24 May 2018 / Published: 26 May 2018
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PDF [5516 KB, uploaded 26 May 2018]
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Abstract

Stamping dies perform two functions in the hot stamping process of body-in-white components. Firstly, they form the steel sheet into the desired shape and, secondly, they quench the steel at a cooling rate that leads to hardening by means of the austenite-γ to martensite transformation. This microstructural change implies a volume expansion that should lead to a force peak in the press, which has yet to be detected in industrial practice. In this study, a set of hot stamping laboratory tests were performed on instrumented Al–Si-coated 22MnB5 steel flat formats to analyze the effect of the stamping pressure on the detection of the expected peak. Plotting the sheet temperature and pressure curves against time allowed us to identify and understand the conditions in which the force peak can be detected. These conditions occurred most favorably when the stamping pressure is below 5 MPa. It is thus possible to determine the exact moment at which the complete hardening transformation occurs by monitoring the local pressing force of the tool in areas where the pressure exerted on the metal format is below 5 MPa. This information can be applied to optimize the time needed to open the dies in terms of the complete martensitic transformation. View Full-Text
Keywords: hot stamping; press hardening; martensitic expansion; force peak; cycle time hot stamping; press hardening; martensitic expansion; force peak; cycle time
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Muro, M.; Artola, G.; Gorriño, A.; Angulo, C. Effect of the Martensitic Transformation on the Stamping Force and Cycle Time of Hot Stamping Parts. Metals 2018, 8, 385.

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