SUNConferences, RAPDASA 2014

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DETERMINATION OF COOLING RATES DURING LASER BEAM MELTING OF ALUMINIUM ALLOY EN AW 7075 USING HIGH SPEED PYROMETRY
K. Krag, Oliver Hentschel, Bhrigu Ahuja, Michael Schmidt

Last modified: 2014-11-02

Abstract


Additive Manufacturing of Aluminium cast alloys via Laser Beam Melting in powder bed (LBM) is now industrially used for functional prototypes and small series production. The choice of processable alloys is currently limited to silicon based Aluminium cast alloys such as AlSi10Mg. Geometric Freedom of Laser Beam Melting offers future potential for topology optimized lightweight structures which could be produced with less design compromises compared to other manufacturing technologies. The Mechanical properties depend on the microstructure, which is formed during melt solidification under key influence of the cooling rate. In LBM the cooling rates are several orders of magnitudes higher than in conventional production processes such as die casting. They have so far been estimated a posteriori by analysis of resulting microstructures or by numeric simulations that could not be validated directly. In this paper a high-speed pyrometer with a sampling rate of 100 kHz is used in a lateral setup to measure radiation emitted by a stationary spot, through which the laser focus passes. Signals were obtained from simplified geometries such as thin walls and cubical blocks in different vertical build heights made from Aluminium wrought alloy EN AW 7075 under variation of scan speed and laser power. Furthermore the findings were related to metallographic microsections of the generated test structures. The results improve the fundamental understanding of solidification phenomena and their dependencies on part geometry and scanning speed for Aluminium wrought alloys such as EN AW 7075, which is a challenge to be processed using Laser Beam Melting because of their characteristic poor weldability.

 




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