Multi-material 3D printing in metal
Combination of different alloys (e.g. copper and steel) in one component.
1. Introduction: The next evolutionary stage of 3D printing
Classic metallic 3D printing processes usually process a single, homogeneous powder or wire. Multi-material 3D printing breaks down this barrier and enables the seamless combination of multiple metals in a single component. This means that the specific advantages of different materials can be used exactly where they are needed in the component.
This white paper highlights the technologies, challenges and immense potential of multi-material printing for the industry.
Why print multi-material?
A typical example is the combination of copper and steel in tools or engines. Copper offers excellent thermal conductivity but is soft. Tool steel, on the other hand, offers wear resistance but conducts heat poorly. Multi-material printing, for example, allows injection molding tools with a hard steel jacket and a heat-conducting copper core to be produced in one operation.
2. The technologies at a glance
Not every 3D printing process is suitable for multi-material use. The most common approaches are:
- Directed Energy Deposition (DED): During laser deposition welding with powder (LMD-P), different powder conveyors can be controlled simultaneously or alternately. This allows graded transitions (Functionally Graded Materials) between two alloys, without hard edges.
- Wire Arc Additive Manufacturing (WAAM): Here different welding wires can be fed simultaneously or alternately. Here too, alloy adjustments are possible “on the fly” (in-situ alloying).
- Powder Bed Fusion (PBF-LB): Multi-material printing in a powder bed is extremely complex because the powder cannot simply be applied mixed after the layer. However, special coating systems (e.g. with ultrasonic dosing) enable different powders to be deposited precisely within one layer.
3. The challenge: Thermal stresses and intermetallic phases
The biggest problem when fusing two different metals is their different thermal expansion coefficients and melting points.
- Cracking: If one material contracts more strongly than the other when cooling, enormous internal stresses arise, which often lead to tearing (delamination) at the interface.
- Intermetallic phases: At the interface between two metals, brittle chemical compounds can form that weaken the structure. “Soft”, graded transition layers (e.g. via intermediate alloys) provide a remedy here.
4. Applications in practice
Multi-material printing opens the door to completely new component concepts:
- Rocket engines: Combination of high-temperature-resistant Inconel on the outside and heat-conducting copper coating on the inside of the combustion chamber.
- Electric motors: Direct printing of rotors with embedded copper interconnects to increase efficiency and power density.
5. Conclusion: complexity that pays off
Multi-material printing is still in its infancy in some areas (such as PBF), while it is already being used industrially in the DED area. Mastering the metallurgy at the interfaces is key. However, for high-performance components, the combination of multiple metals is the ultimate lever for greater performance and efficiency.