Go with the gas flow

We caught up with Benedikt Roidl and Thomas Fauner to find out more about their technical white paper that explores innovations in gas flow for additive manufacturing.

Left: Benedikt Roidl | Right: Thomas Faunder
Q&A Dr. Benedikt Roidl and Thomas Fauner, GE Additive

Q: When our industry talks about innovation in additive - is it fair to say that gas and gas flow doesn’t always get the airtime it deserves? 
Benedikt: Kind of, yes. In the early days of laser additive manufacturing, the focus was more on the fundamental machine architecture and how to control the manufacturing process in general. Look, there were just so many other challenges. Also, single laser machines were more common back then, and a simple gas flow concept was somehow sufficient enough to get rid of the soot.

Thomas: However, with the advent of multi-laser machines and steadily increasing part requirement levels imposed by our customers, gas flow has found itself increasingly in the spotlight. And today it is one of the key systems to ensure high part quality and repeatable results. 
Q: When it comes to gas flow, you sometimes use the analogy of a Laundromat – why?
Benedikt: On a classic M2 machine a simple and robust gas flow design with only one inlet was selected. The flow is oriented in the process chamber such that is keeps the optical components clean but also transports off all the soot & spatter from the build plate. This was accomplished by a gas flow path that rotated by 180° in the process chamber, giving it the nickname Laundromat.

Thomas: This kind of flow configuration delivered results which satisfied part requirements in the past. However, higher requirement levels narrowed down the opportunities where to improve the machine after optimizing scanner and laser systems and powder bed, for example. So, the laundromat-like gas flow was a candidate for further improvement.
Q: Why is the gas flow over the build plate so important to the laser additive manufacturing process? 
Benedikt: To transport soot and spatter efficiently off the build plate without spending too much time in the process chamber. Since any interaction of the laser beam with soot and spatter particles are potentially influencing the part quality in a quite negative way. 

Thomas: Actually, that has been the goal for years. So, yes, you want to have a clean, recirculation-free gas flow in your process chamber. Recently, focus has shifted to achieve improved control over the gas flow, to accommodate the use of high-power lasers and advanced laser scanning strategies for example. 
Q: Could you tell us more about soot & spatter? 
Benedikt: Spatter and soot are created when the laser melts and partially evaporates the metal powder. While spatter particles have the size of up to several hundredth microns and are spit out mainly from the liquid melt pool, metal vapor shoots upwards from the melt pool surface, condensating to blackish nano-particles, called soot. 

Thomas: We have been successfully working together our own global research center (GRC) at GE for several years now to understand the mechanism of the soot and spatter generation and the impact these have on the part quality through extensive experiments and simulations. This research & understanding drives our gas flow designs and, for example, our scanning strategies.
Q: You talk about continuous improvement in the field. Where are you turning your attention to next? 
Benedikt: Short term, we are wrapping up the validation of the M Line gas flow on our machines. In general, we are continuously looking into methods to even further improve the flow distribution and increase the robustness of the flow system to minimize part quality variations over the build plate and to eliminate machine-to-machine variation.

Thomas: We are also working on improved gas flow concepts for new machine architectures using novel gas flow concepts. We also exploring how gas flow can unlock maximum productivity of multi-laser machines.