​Additive Manufacturing (AM) is an emerging part production technology that offers many advantages such as high degree of customization, material savings and design of 3D highly complex structures. However, AM is a complex multiphysics process. Therefore, only a limited number of materials can already be commercially used to produce parts and a handful of others are being studied or developed for such process. Consequently, limited knowledge on this process is available, especially concerning materials that present thermomechanical challenges such as brittle materials.
The research I did during my PhD studies focuses on additive fabrication of silicon pillars on a monocrystalline silicon wafer by Direct Laser Melting (DLM) with a pulsed 1064 nm laser beam. The simple geometry of pillars allowed for the first determining steps into process understanding. Several results were achieved through this PhD work. First, crack-free silicon pillars were successfully built onto monocrystalline silicon wafers. With the help of in-situ process monitoring and sample characterization, wafer substrate temperature and laser repetition rate were found to be the main influential parameters to obtain crack-free samples, as minimum substrate temperature of 730°C and a minimum repetition rate of 100 Hz were necessary to reach this goal (for a feed rate of 15 g/min and a pulse duration of 1 ms). The influence of secondary process parameters such as feed rate and energy per pulse were also discussed. A simple Finite Element Modeling (FEM) model validated by the experiments was used to explain crack propagation in the samples. Then, process monitoring of the DLM process was realized. High-speed camera image analysis revealed that vertical stage speed and powder feed rate should match to obtain a constant pillar building rate. As all pillars presented necking at their base, estimations of the thermal characteristics of the pillar during growth were carried out by FEM simulations. They were more used to explain the pillar final shape. Finally, the microstructure of the pillars built was characterized by the Electron Back-Scattering Dif-fraction (EBSD) technique. In the conditions presented in this work, the microstructure of the pillar was found to be in the columnar growth mode. The feed rate was identified as the most influential parameter on the microstructure, followed by the stage speed, the impurity content of the powder and the crystallographic orientation of the substrate. Epitaxial growth was achieved on more than 1 mm with a feed rate of 1.0 g/min, a stage speed of 0.1 mm/s, a powder with purity of 4N and a <111> oriented wafer substrate. This work could be further continued by making improvements to the DLM setup, studying the influence of additional process parameters on the thermomechanical behavior and the microstructure control of the pillars, and/or using these results to realize more complicated shapes, either with this setup or by using a powder bed technique.
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L'Hebdo, le monde des ados. I even managed to get an internship for a week there!
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L'Hebdo, le monde des ados. I even managed to get an internship for a week there!
Responsible production and transparency
I am aware of the impact I have on the environment and on people when I create a product. Also, I commit to be as responsible as possible in my mode of production. The world of production is very complex, so I am doing my best every time I develop a new project!
Natural and more ecological textile fibers
In the textile industry, the difficulty of traceability comes from the many stages of production. From the cultivation of the raw material, to spinning, to weaving, to printing, to assembly... Each of these stages requires the extraction of materials, chemical processes and human labour. The choice of a material must also take into account its use during its lifetime, as well as its end of life. There is no ideal solution at present. But the good news is that there are better solutions! For fabrics intended for fashion, I only use Tencel, EcoVero Viscose, linen and GOTS certified organic cotton. These are all fabrics with lower ecological impacts than conventional cotton, polyester or viscose for example. I also want to limit my use of cotton because this material is used too much in the fashion industry, which prevents the reconstitution of the soil by favoring monoculture. Unfortunately, I had to use polyester thread to sew the first collection of long-sleeved T-shirts, but this is necessary for the solidity of the garment.
FSC certified and/or recycled paper
The paper industry is also complex. In particular, I have to be careful that the paper I use does not come from ancient forests. That's why I only use FSC certified and/or recycled paper. For the moment, I print on at least FSC Mix certified paper (which guarantees that at least70% of the content comes from sustainably managed forests), but I am actively looking for solutions that guarantee 100% certified content and remain affordable in terms of price, because who says small production, says bigger costs!
When it comes to packaging, I use recycled, reusable or upcycled materials.
An ethical production as local as possible
I try to keep the production as local as possible for three reasons. First, it allows me to communicate much more easily with my partners and to go on site. Labor regulations are also stricter in Europe, which allows me to guarantee fair wages and good working conditions. And of course, the carbon footprint generated by transport is minimized. The raw materials cannot all come from Europe (cotton does not grow there, nor Eucalyptus, the raw material for Tencel), and it is difficult to trace all the manufacturing stages of a material. Currently, my Tencel fabrics are printed in the Netherlands, my long sleeve shirts are made in Switzerland, the T-shirt fabric is made in Portugal, and the T-shirts are sewn and printed in France.
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Photo by Social Fabric
Your purchase contributes to social projects
I am committed to giving more value to my products by contributing to social and/or environmental projects. My first series of long-sleeved tops is produced in Zürich by Social Fabric, an association that promotes the integration of people in a migration situation by giving them opportunities to network and learn about textile production.
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Photo by Social Fabric
