On the temperature distributions and thermal stresses induced in laser solid freeform fabrication of multi-material structures

This paper presents a numerical-experimental investigation on the effects of preheating the substrate on the potential delamination and crack formation across the parts fabricated using the Laser Solid Freeform Fabrication (LSFF) process. For this purpose, the temperature distributions and stress fields induced during the multilayer LSFF process, and their correlation with the delamination and crack formation are studied throughout the numerical analysis and the experimental fabrication of a four-layer thin wall of SS304L. A 3D time-dependent numerical approach is used to simulate the LSFF process, and also interpret the experimental results in terms of the temperature distribution and the thermal stress fields. The numerical results show that by preheating the substrate prior to the fabrication process, the thermal stresses throughout the process domain substantially reduce. Accordingly, this can result in the reduction of potential micro-cracks formation across the fabricated part. Preheating also decreases the transient time for the development of a proper melt pool which is an important factor to prevent poor bonding between deposited layers. The experimental results are used to verify the numerical findings as well as the feasibility of preheating on the reduction of the micro-cracks formed throughout the fabrication process.

Download Full-text

Effect of Thermal and Stress Fields on the Microstructure of a Thin Wall Built Using Laser Solid Freeform Fabrication Process

Volume 10: Mechanics of Solids and Structures, Parts A and B ◽

10.1115/imece2007-42921 ◽

2007 ◽

Cited By ~ 1

Author(s):

Masoud Alimardani ◽

Christ P. Paul ◽

Ehsan Toyserkani

Keyword(s):

Temperature Distribution ◽

Stress Field ◽

Thermal Stresses ◽

Solid Freeform Fabrication ◽

Experimental Results ◽

Thin Wall ◽

Stress Concentrations ◽

Aisi 304L ◽

Freeform Fabrication ◽

Laser Solid Freeform Fabrication

Temperature distribution and consequent rapid cooling determine the microstructure and final physical properties of a part fabricated using laser solid freeform fabrication (LSFF). As well, in this technique, thermal stresses are the main cause of any possible delamination and crack formation across deposited layers. In this paper, the temperature distribution and the stress field induced during the LSFF process are studied throughout the fabrication of a thin wall up to four layers. The thin wall is fabricated of stainless steel AISI 304L using a 1 kW Nd:YAG pulsed laser. Variations of the microstructure and geometry of the wall are studied. A 3D dynamic numerical model of the multilayer LSFF process is used to interpret the experimental results in terms of the temperature distribution, stress field and microstructure. The experimental results show that the stress concentrations at the end points of the wall, which are due to the higher temperature gradient at these regions, are the locations for possible delaminations and crack formations. Different types of microstructures are observed at the various locations within the same layer due to the different cooling rate. While numerical results confirm the experimental findings, they also show that it is possible to reduce the maximum stress by preheating the substrate.

Download Full-text