Process

What is Laser Metal Deposition?

Laser metal Deposition refers to a welding process where a material is introduced into a meltpool, created by a high power laser. LMD falls into the range of Directed Energy Deposition (DED) processes. Typically the filler material introduced is a powder, injected through a conical ring nozzle around the laser beam. The added material creates a weld bead, which then coats the underlying metal. The process is used in cladding applications, where the wear resistance of components is increased, in repair applications where material is added to worn components, or in freeform manufacturing of complicated geometries (3D Printing). Compared to other types of welding LMD results in a smaller heat affected zone, low dilution and low residual stresses in the components.

Additec’s Wire LMD process works in much the same way, however instead of having one laser beam that enters through the center of the deposition head, we use multiple fiber coupled diode laser sources that are distributed evenly around central axis of the head. This frees up the central path for solid filler material, and allows for the unidirectional processing of common mig welding wires. Around the wire orifice our deposition head also features a conical powder nozzle. This way, no functionality is lost compared to conventional laser cladding heads.

CAD File

Deposition Process

Finished Part

When using wire is better:

In todays industry, powder LMD is much more common than wire deposition, because it is easier to implement with a single high power laser source. However there are many downsides to processing powder:

Powder is significantly more expensive than wire. This is problematic, because LMD is typically used to manufacture medium to large components, where large quantities of material are used.

Not all powder that is ejected through the nozzle actually gets captured in the meltpool. Common real life powder efficiency figures are in the region of 20-80% for free form manufacturing and heavily depend on part finesse and process parameters. This is not only a problem form a material cost perspective, but also from an engineering perspective. Refitting a powder deposition head to any machined not specifically designed for it will result in significant wear. Further the unused powder needs to be handled, and may pose a health risk depending on material and particle size. In Contrast, using wire the material efficiency is 100% and wire feedstock does not pose any danger.

Lastly the capture efficiency variability creates annother problem. It significantly reduces process reliability with increasing number of layers, and with varying layer cross sections because the meltpool dimension changes depending on the heat of the substrate. Starting on a cold base plate, using set laser parameters results in a smaller melt pool than further up the part where the layers below it are still warm from the previous pass. This needs to be counteracted either by an expensive thermal imaging system or temperature compensated parameters in the g-code, for which there is currently no simple solution. In contrast, with wire, because the capture efficiency is 100% we always know exactly how much material goes into the bead at any point. Coupling that with our inline control process the result is a significantly more dependabe machine. In addition, detecting interruptions automatically and safely pausing the process is also much easier with wire, and implemented as a standard feature in all Additec systems.

When using powder is better:

While we strongly favor running wire prints, powder is still be more suiteable for some applications:

When adding material to a highly irregular surface, where a precise nozzle to part distance is not available as can happen when coating or repairing certain parts, powder will be a better choice.

Also while many alloys are available as wire, some of the more exotic materials may only be available in powdered form.

Annother reason for keeping and supporting powder deposition functionality on our deposition head digital alloying, where two or more materials are mixed in different ratios throughout the deposition process. An interesting middle ground is also the digital alloying of powder and wire at the same time, which is at this point only possible on our deposition system.

Wire Print Resolution:

The Print resolution of the Additec deposition system is excellent, even with wire. In fact, depending on the process parameters, it is possible to match even the best powder print quality with wire. The track width is about 1.5x wire diameter when printing in high resolution, or up to about 2.5x wire diameter when printing fast. Layer height can be set between 0.3x and 0.5x wire diameter. We support wire diameters between 0.6 and 1mm by default. Different size nozzles available on request. It is also possible to print very high aspect ration components even with small cross sections. See rodlet sample below (width 12mm height 450mm).

High resolution wire print, open atmosphere

High resolution wire print, inert atmosphere

More is Less:

Splitting up the laser sources and optics into multiple discrete units reduces the stress on the optical system to a minimum and results in long lifetimes of the optical components. The clean process also contributes to that. All optics are shielded with positive pressure argon and replacements are easy to aquire either through Additec or common optical vendors. Supply information is included in the product manual.

Material Range:

The Additec deposition system can process a vast variety materials, typically any weldable metal can be used. However, some restrictions apply when the process chamber is not inerted. For instance aluminium and titanium favor an inert processing chamber. Nevertheless, through the use of wire feed-stock using highly reactive materials in open atmoshpere conditions is significantly less dangerous than using powders, and successful results can be achieved by utilizing a large shield gas diffuser.