Spray Cooling of Early Extracted Hot Stamped Parts

Nürnberger, Florian; Diekamp, Max; Moritz, Jörn; Wolf, Lars Oliver; Hübner, Sven; Behrens, Bernd‐Arno

doi:10.1007/978-3-319-48237-8_116

Cited by 7 publications

(2 citation statements)

References 7 publications

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“…The transfer and hot-stamping durations are identical in both processes. Hot stamping takes place at a temperature above 720 °C, which according to Nürnberger et al [12] should result in a fully martensitic microstructure.…”

Section: Resultsmentioning

confidence: 99%

Resistance Heating by Means of Direct Current for Resource-Saving CO<sub>2</sub>-Neutral Hot Stamping

Behrens

Hübner

Albracht

et al. 2022

KEM

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Hot stamping is a well-established and frequently used manufacturing process in automotive body construction. The number of components manufactured in this way is continuously increasing. Hot stamping is used to produce components with a completely martensitic structure, resulting in high strength and hardness. These components are mainly used in safety-relevant areas of the passenger cell, such as the A-pillar, B-pillar, tunnel and sill. For hot-stamping processes, it is necessary to austenitize the blanks. Heating the sheet metal up to 930 °C in a furnace is very energy-intensive. In large-scale industrial applications, the sheets are generally heated in gas-fired roller hearth furnaces up to 60 m long. Apart from the poor energy balance and the high CO2 emissions of such furnaces, they are associated with high investment and maintenance costs, large space requirements and a long heating time. Rapid heating by means of the Joule effect and direct current instead of alternating current offer an energy-efficient and environmentally friendly alternative for sheet metal heating. Therefore, this technology can make a major contribution to environmental protection and resource saving. Within the scope of this work, parts were rapid-heated and subsequently hot-stamped by means of a novel heating system based on direct current with energy savings of up to 80 %. Using electricity guarantees a good CO2 balance. In addition, resistance heating with a new type of DC-heating system and an adapted process chain is compared with conventional furnace heating. In thermographic images and microstructural examinations of the hot-stamped parts, it can be demonstrated that this direct-current technique is well suited for achieving homogeneous hardness and strength in the whole sheet metal. Thus, this new heating system can enhance the efficiency of the hot-stamping technology.

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Section: Resultsmentioning

confidence: 99%

Resistance Heating by Means of Direct Current for Resource-Saving CO<sub>2</sub>-Neutral Hot Stamping

Behrens

Hübner

Albracht

et al. 2022

KEM

Self Cite

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“…Hoffmann et al [19] concluded that the cooling speed of die quenching is influenced by the die pressure and a large holding force is required to increase the cooling speed during die quenching. Nürnberger et al [20] studied the hot stamping of heat treatable steel 22MnB5 using water-air spray cooling. Ota et al [21] improved the formability by partial air cooling of potential cracking regions of blank to harden them before forming.…”

Section: Introductionmentioning

confidence: 99%

Minimisation of Heating Time for Full Hardening in Hot Stamping Using Direct Resistance Heating

Maeno

Mori

Sakagami

et al. 2020

JMMP

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To obtain enough hardness of the die-quenched products after hot stamping using direct resistance heating, the effects of the electrifying condition and initial microstructure of the quenchable steel sheet on hardness were examined in a hot bending experiment. The steel sheet was heated up to 900 °C in 3 to 10 s. The required heating time was shortened by normalising heat treatment due to the fine grain size of the sheet. The standard deviation of the hardness of the sheet heated to 900 °C in 3.2 s without temperature holding at the austenitising temperature was 12 HV, whereas the deviation reduced to 5 HV for temperature holding at the austenitising temperature of 3 s.

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Targeted adjustment of residual stresses in hot-formed components by means of process design based on finite element simulation

et al. 2021

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The aim of this work is to generate an advantageous compressive residual stress distribution in the surface area of hot-formed components by intelligent process control with tailored cooling. Adapted cooling is achieved by partial or temporal instationary exposure of the specimens to a water–air spray. In this way, macroscopic effects such as local plastification caused by inhomogeneous strains due to thermal and transformation-induced loads can be controlled in order to finally customise the surface-near residual stress distribution. Applications for hot-formed components often require special microstructural properties, which guarantee a certain hardness or ductility. For this reason, the scientific challenge of this work is to generate different residual stress distributions on components surfaces, while the geometric as well as microstructural properties of AISI 52100 alloy stay the same. The changes in the residual stresses should therefore not result from the mentioned changed component properties, but solely from the targeted process control. Within the scope of preliminary experimental studies, tensile residual stresses in a martensitic microstructure were determined on reference components, which had undergone a simple cooling in water (from the forming heat), or low compressive stresses in pearlitic microstructures were determined after simple cooling in atmospheric air. Numerical studies are used to design two tailored cooling strategies capable of generating compressive stresses in the same components. The developed processes with tailored cooling are experimentally realised, and their properties are compared to those of components manufactured involving simple cooling. Based on the numerical and experimental analyses, this work demonstrates that it is possible to influence and even invert the sign of the residual stresses within a component by controlling the macroscopic effects mentioned above.

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Spray Cooling of Early Extracted Hot Stamped Parts

Cited by 7 publications

References 7 publications

Resistance Heating by Means of Direct Current for Resource-Saving CO<sub>2</sub>-Neutral Hot Stamping

Resistance Heating by Means of Direct Current for Resource-Saving CO<sub>2</sub>-Neutral Hot Stamping

Minimisation of Heating Time for Full Hardening in Hot Stamping Using Direct Resistance Heating

Targeted adjustment of residual stresses in hot-formed components by means of process design based on finite element simulation

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