May 27, 2016 | By Alec

While no manufacturing process is perfect, metal 3D printing solutions are very close to reaching perfection. Capable of realizing miniscule details and extremely complex geometric shapes at fast rates, it could be the technology that takes mankind to Mars. But like components made with any other manufacturing process out there, 3D printed metal parts can exhibit small levels of porosity, consisting of very tiny defects and gaps. Fortunately, researchers from the Lawrence Livermore National Laboratory (LLNL) have been able to answer the crucial question of what causes that porosity, paving the way for an optimized laser powder-bed fusion metal 3D printing process.

This discovery was made by a team of researchers led by Lawrence Livermore National Laboratory (LLNL) researcher Ibo Matthews, and has just been published in the latest edition of the journal Acta Materialia Online. The team also includes Gabe Guss and Phil Depond.

As the researchers explain in the paper, the problem is a denudation phenomenon caused by the laser used in laser powder-bed fusion 3D printing. As the laser moves over the bed to irradiate the metal powder, it produces a driving force that clears away some of the nearby powder particles. After several runs, this slightly reduces the amount of available powder, causing very tiny gaps and defects in a finished part.

As Matthews explained, this is the first time the metal vapor caused by 3D printing was studied. “During this process you get to temperatures that are near or at the boiling point of the metal, so you have a strong vapor flux emitted from the melt pool,” he explained. “Prior to this study, there wasn’t an understanding of what effect this flux of metal vapor had on the powder bed.”

To study this phenomenon, which takes place on a microscopic level, the LLNL researchers acquired a laser-based powder bed fusion R&D platform from the Fraunhofer Institute in Aachen, Germany. Using a custom-made microscope setup, a vacuum chamber and an ultra-high-speed camera (borrowed from the LLNL High Explosives Applications Facility), they were able to observe the ejection process of the metal powders as the laser passes by. Through computer simulation and fluid dynamics principles, they were subsequently able to build models that recreate the particles’ movement.

While the researchers haven’t discovered a solution yet, their breakthrough provides them with a greater understanding of the metal 3D printing process, and obviously paves the way towards technological improvements. “[They have] discovered a phenomenon that we didn’t know was present in metal powder-bed additive manufacturing, and this is an effect that has important implications for part quality and build speed,” Chris Spadaccini, director of LLNL’s Additive Manufacturing Initiatives, said. “It is also something we now know we will have to capture with our models, so new physics is being added to the simulation codes.”

According to Wayne King, LLNL‘s director of the Accelerated Certification of Additively Manufactured Metals project, this is a crucial breakthrough for the metal 3D printing industry. “It’s one of those things that nobody really had a clue about why it happened,” King said. “What this does is bring us closer to an understanding of the process, which will eventually lead to a reduction in defects of parts. The models should help us optimize the process and give us the best chance at getting the best part.”

Matthews and his team are now working on the next steps of their research: studying how porosity develops in real-time during 3D printing, and exploring steps to counter it. To do so, they will be using advanced diagnostics and process modifications to try and optimize 3D printing quality. “Now having the physics better understood, we can simulate the process more accurately and make enhancements to our manufacturing efforts,” Matthews said. “In the end, we want to be able to use simulation to build the confidence that we’re making parts with little or no defects.” Metal 3D printing, it seems, is about to become even more accurate than ever before.



Posted in 3D Printing Technology



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krosstoph wrote at 6/6/2016 11:22:05 AM:

This is acutally old news. And I have to agree with BStott that this kind of experimental and analytical costs was kind of overkill for figuring out a problem every manudfacturer knows about. Everyone who has such a machine can see the genarated vapour through the looking glass and knows about the connected difficulties. Furthermore, its not only material the gets blown away that generates defects, but also material that is not transported away properly because the ventilation in any manufacturers machine is never perfect. So some burnt material will allways stay in the printing area and consequently be fused in the next layer. Just visit one of them 3D printing trade fairs and look for yourself. Also I have to add: 3D printing is maybe one of the manufacturing processes that is LEAST perfect, not NEARLY perfect. Nearly perfect are conventional processes like grinding, drilling, milling, turning etc. So far, all we have achieved in 3D-printing is generating parts that all have to be post-processed by conventional methods, because the quality is nowhere near the specified properties. Except of course you just want to generate parts that just have to look good. But even there you will have to apply some kind of polishing or infiltration process.

BStott wrote at 6/2/2016 9:57:30 PM:

The laser acts as a hose collecting and blowing material off the previous layer solid table. Once you start thinking the actions involved the study is not required only to view and practice with advanced tools. This is a fundamental reminder of what high energy light is: waves and particles. Don't need to analize or quantify. Solution: Angle laser backwards from direction of motion. Then, powder material is pushed into solidified layer and eliminates voids. Easy! Realize/Remenbere lasers emits energy and push materials and you don't need so many expensive studies and time. But, duh!

BStott wrote at 6/2/2016 9:06:55 PM:

Excellent! The laser acts like a blow torche pushing material. Now, they can counteract this effect by angling the laser backwards to its direction of motion. This way tha laser pushes powder into the melted part region creating a fully dense material across each entire part layer. This is likely a simple technician's mechanical adjustment to the existing machine's laser mount.

James K McMahon wrote at 5/28/2016 1:57:33 PM:

Excellent research work. Very impressive that someone has looked closer at this 3D technology. I believe all of the 3D technologies require investigations to better understand how they work and if there should be concerns. I see small company startups duplicating 3D machines and selling them at low cost. Sales or marketing is driving these businesses and few if anyone understands the technology. 2D Inkjet thermoplastic printing evolved into 3D printing in much the same way. These small inkjet fluid delivery passages are seeing thermal effects that were not anticipated with 2D printing and the printing materials are going through changes to satisfy customer demands for color and speed. The original 2D invention disclosures never mentioned 24 hour printing cycles and the 3D printing machine designers have no history of the first inventions. More work needs be done and the customers need to understand they are experimenting with these new 3D printers.

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