Publication

Modélisation quantitative du procédé de frittage sélectif par laser : relation paramètres/microstructure

Cédric André
2007
Theses

Abstract

The Direct Metal Laser Sintering process (DMLS) is a Rapid Manufacturing (RM) technique. A 3D object is built layer by layer through laser consolidation of metallic powders. Several industrial DMLS stations are commercialised. The current performances of the parts manufactured by this process remain insufficient. Hybrid processes were developed. The DMLS process is then coupled to other technologies in order to post-process DMLS parts. The quality of the parts is improved but the post-processing stage slows down the manufacture. The main goal of this Ph.D. work was to increase the understanding of this laser manufacturing process in order to be able to make DMLS parts that could be used without post-processing. The powder used in this work is a 316L grade Stainless Steel powder. Particles are spherical and have a diameter between 11 and 45 µm. The powder has a good flowability, leading to good powder layer quality after deposition (before laser consolidation). Many monolayer samples were built, using more than seventy sets of process parameters. For each set of parameter, a specific microstructure is obtained. A microstructural index η was defined. The index is an adimensional number between 0 and 1 and represents the degree of sintering (η is close to 0 if the sintering process just began, η tends towards 1 if the sample's density is close to full density). This index allows us to characterize quantitatively the microstructure of all the parts we built. Three key parameters were identified : the pulse duration τP, the energy density of the laser Eρ and the powder bed density ρlit. Thanks to the relation η = η(τP, Eρ, ρlit) established, we estimate quantitatively that Eρ is the process parameter which has the largest influence. Qualitatively we developed phenomenological models predicting locally that the microstructure of a monolayer is becoming finer if the pulse duration as well as the powder bed density increase and if the energy density of the laser decreases.

Official source

https://infoscience.epfl.ch/entities/publication/0d4b5607-aee4-4720-b059-272c64d3f9c0

Cédric André
2007
Theses

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/0d4b5607-aee4-4720-b059-272c64d3f9c0

Related concepts (31)

Powder metallurgy

Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product. Powder metallurgy is also used to make unique materials impossible to get from melting or forming in other ways. A very important product of this type is tungsten carbide.

3D printing

3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer control, with material being added together (such as plastics, liquids or powder grains being fused), typically layer by layer. In the 1980s, 3D printing techniques were considered suitable only for the production of functional or aesthetic prototypes, and a more appropriate term for it at the time was rapid prototyping.

Manufacturing

Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary sector of the economy. The term may refer to a range of human activity, from handicraft to high-tech, but it is most commonly applied to industrial design, in which raw materials from the primary sector are transformed into finished goods on a large scale.

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