No porosity. No sintering. No shrinkage.
Melting metal causes problems. Since there is no melting in MELD, we’re able to avoid these issues and create better, stronger parts. MELDed products are already fully dense, meaning there are no voids in the deposited material. With melt-based processes, the additively-manufactured part contains small pockets without material, similar to a sponge. These “green” parts must then go through a second process during which they are compressed. Finally, they are ready for the last processing steps before they are considered ready. MELD, on the other hand, requires no additional steps and skips these costly and time-consuming procedures.
Additionally, residual stress is a concern for all processes – additive and subtractive. Material can collect stress from initial production methods and processes, like finish machining. Residual stress often shows itself as distortion in a part. Heat is a major contributor to this issue. Comparing stresses in additive manufacturing steps, MELD has an advantage because it is a low-heat process. We’ve seen quarter inch thick plates of steel bend into a U shape with laser deposition.
The MELD process “stirs” plastically-deformed, or softened, metal together or into the layer below. This stirring action breaks up the individual grains that make up metal. Because of that, MELDed products have “refined” or smaller grain size than the parent material used. In metal, you can generally expect greater strength, greater corrosion resistance, and greater wear resistance as grain size gets smaller. Reduced grain size is one reason we see better mechanical properties from MELDed products.
Here’s an example: Inconel 625 is a nickel-based super alloy. The image below shows the material before and after the MELD process under a microscope at xxxx magnification. Before MELD, the average grain size is 12 microns. After MELD, the average grain size is 5 microns. Testing done at the University of Alabama shows that Inconel 625 is stronger after the MELD process. Further, grains have orientation. Depending on how individual grains are oriented to each other, the whole part may be stronger in one direction or another. Differing strength to stand up to stress can sometimes be desirable. Most of the time, parts work best when their strength is equal in all directions. MELD creates equiaxed grain structure, meaning the grains are oriented to each other in a similar way in all axes. It also means that MELDed parts have similar strengths in all directions.
Here’s another example: Inconel 625, when melted and applied using Pulsed Plasma Arc Deposition, shows “columns” of grains. MELDed Inconel 625 shows a grain pattern that is consistent.
MELD-deposited materials don’t just look great, they also exhibit exceptional mechanical properties that meet or exceed material specification. This means that your MELDed material will behave as expected, allowing your designs to be limited only by your imagination and not by your additvely-manufactured material. Whether you need to MELD aluminum, titanium, or nickel-based super alloys, our MELD machines will deposit high-quality material in a single step.
MELDed Inconel 625 was seen to have upwards of 4x the cycles to failure compared to the as-received Inconel 625 bar stock. The increase in fatigue life is contributed to the dense, refined granular microstructure observed within the MELD process.