Friction Stir Additive Manufacturing (MELD)
Huge metal components print in a solid state - completely without melting or distortion.
1. Introduction: Additive manufacturing through friction
When we think of metal 3D printing, we usually think of lasers, electric arcs or electron beams that transform metal powder or wire into a liquid melt. Friction Stir Additive Manufacturing (MELD or FSAM) completely breaks this paradigm: It prints metal in a solid state - without melting.
This white paper highlights the revolutionary MELD technology, which is based on the principle of friction stir welding and enables gigantic components without thermal distortion.
How does MELD work?
A rotating tool is pressed onto a carrier material with enormous pressure. The friction creates heat, which plasticizes the metal (it becomes doughy and soft, but does not melt). New metal (as powder, rod or wire) is continuously fed through a hole in the rotating tool. This material is stirred into the base material by rotation (joined by kneading).
2. The biggest advantages of solid-state AM
The absence of a melt pool eliminates almost all of the problems that classic laser or arc processes (WAAM) struggle with.
- No distortion and no internal stresses: Since the metal is never liquefied and the temperatures remain well below the melting point, there is no shrinkage and no significant distortion after cooling.
- No porosity or cracking: Hot cracking, as occurs with many aluminum alloys when solidifying from the melt, is physically impossible. The structure is extremely dense (100% density) and very fine-grained and firm due to the constant kneading.
- No protective gas chamber required: Without a melt pool, there is no need for an expensive argon atmosphere for many metals (such as aluminum). MELD can be operated in the open air.
3. Printing “unweldable” metals
Some of the world's highest performing alloys are considered "non-weldable", making them unsuitable for laser or arc 3D printing (e.g. high-strength 7000 series aluminum alloys such as 7075). In the PBF process they would tear immediately.
With MELD technology, these high-end alloys can easily be additively processed. This opens the door to lightweight construction in aerospace, where 7000-grade aluminum is the standard for aircraft structures.
4. Scalability and applications
The process is extremely fast (build-up rates in the kilogram range per hour) and the component size is only limited by the travel path of the robot or CNC machine.
- Huge cylinders and rings: The production of meter-sized rocket tanks, pipes or structural rings for space travel is a flagship discipline of Friction Stir Additive Manufacturing.
- Repairs in use: The process can be used excellently for repairing thick metal structures (e.g. on tanks or ships), as the repaired area fuses metallurgically homogeneously with the base material.
5. Challenges and Conclusion
The MELD technology has one crucial disadvantage: geometric limitations. Since the rotating tool exerts massive forces (several tons of contact pressure), the component requires massive support. Filigree cavities, lattice structures or overhangs cannot be printed with this process.
However, for massive-walled, huge components, extremely crack-prone alloys and large-scale repairs, Friction Stir Additive Manufacturing (MELD) is an industrial game changer that often overshadows thermal processes in terms of strength and dimensional accuracy.