Developing a system to build lightweight, efficient structures in orbit will revolutionize space travel. It is nontrivial and the efficiency of launch, deployment, and employment in space is a key objective and challenge.
Structures built for use in space must meet vastly different requirements than terrestrial structures. Where temperature variations occur on earth, they are negligible compared to the variations a space vehicle may see in orbit. The force of gravity is negligible in space while significant on earth. Getting any structure engineered and manufactured on earth into space adds extraordinary requirements to withstand the loading and g-forces placed on the structure to withstand a space launch. The answer to that challenge is to transport only the tooling and raw materials and tools needed to manufacture all the structural elements in space.
To that end, 3D printing holds much promise. NASA already has several plastic printers in orbit and has been ramping up research for metal-based systems. One promising metal-based additive technology is Ultrasonic Additive Manufacturing (UAM) . Instead of fusing metal powders, UAM welds foil at (near) room temperature.
When considering manufacturing in space, some critical considerations must be addressed.
- Welding in space is subject to small gravitation forces. A small gravitational force greatly affects the mechanisms necessary for successful fusion-based welding processes.
- Welding in space has almost no atmosphere. The lack of interaction with gasses can cause process instability in traditional fusion processes. Arc-based processes require gas ionization to function, while laser/EB processes rely on atmospheric pressure for developing beam keyholing.
- Welding in space requires accounting for wild temperature variations. While terrestrial welders can control thermal fluctuations to within tens of degrees, structures in space can experience fluctuations of several hundred degrees.
- Welding processes in space must use significantly less power due to limited power sources. Fusion-based welding systems can require hundreds of kilowatts of power to heat and melt metal. Terrestrial power sources can easily accommodate such power requirements. However, systems in space run on extremely tight power budgets.
The fundamental characteristic separating UAM from other metallic additive manufacturing technologies is that UAM is a solid-state welding process . Metals remain in their solid state, and melting does not occur at any time during the process. All the attendant impacts of high-temperature welding and the effects on the properties of the metal do not occur.
The results and advantages of employing UAM in space manufacturing include low power consumption as most welding heads use much less power; as a solid-state process, the feedstock retains 97 percent of its original properties; operates without (and with) an atmosphere, does not require any welding filler material; does not cause heat-affected zones; does not require post-process stress relieving.
The nature of the solid-state ultrasonic bonding process used in UAM will enable the building of space flight components without the complexity of molten metals or difficult-to-manipulate powders.
Several NASA programs have contributed toward the use of UAM for welding in space. Through Phase I and II SBIR programs, Fabrisonic built a welding system that met the in-orbit manufacturing requirements. The standard (terrestrial) Fabrisonic industrial metal 3D printers have been in production since 2011. They can weigh up to 35 tons and use over 10kW of electrical power.
NASA presented these challenges to Fabrisonic:
- Can the UAM welding assembly be scaled down to save power, weight, and size?
- Can a concept be designed to fit the bounds of NASA requirements?
- Can the UAM system be remotely controlled to build practical structures in low-Earth orbit?
The goal was to shrink a full UAM system to reduce overall system weight and power usage. Fabrisonic answered through the PH II program:
Fabrisonic designed and built a small-scale UAM system that would accommodate the geometric constraints of current ISS project lockers and reduced the welding power requirements to under 1kW.
To minimize cost and proving-out the space and energy savings, Fabrisonic built a demonstration platform. While the in-flight system did not have the accuracy or speed of a Fabrisonic industrial (terrestrial) system, it allowed the team to address the challenges of NASA. As a result, a new low-cost system was realized that would support many customers’ 3D printing needs that did not require the higher power and accuracy of the original (industrial) design.
As the Phase II program progressed, several customers were able to see the new small-scale 3D printer and expressed an interest in the ability to work with UAM in a smaller form factor and lower cost. After receiving such a high degree of interest, Fabrisonic directed its efforts toward developing this new design.
Fabrisonic modified the NASA SBIR system to include required safety and human-interface upgrades that would allow any knowledgeable CNC operator to run the new 3D printer. This became the newest model in the Fabrisonic lineup, the SonicLayer 1200 (video ). As a hybrid manufacturing center, the UAM system combines traditional CNC milling with integrated UAM printing capability. This creates a hybrid additive-subtractive process, where swapping from additive to subtractive is as easy as a tool change.
This article was written by Mark Norfolk, CEO, Fabrisonic (Columbus, OH). For more information, visit here .