Laser powder deposition welding (LMD-p) for coatings
The scalpel of heavy industry: repairing and armoring tools with carbide.
1. Introduction: Repair instead of throwing away
When a meter-long drill bit or the multi-ton drive shaft of a ship's engine wears out on the surface in heavy industry or mining, the component often ends up in the scrapyard. Justifying a new purchase is extremely expensive with these special parts.
Rescue comes in the form of laser powder deposition welding (LMD-p / Laser Metal Deposition with Powder, also called laser cladding). In contrast to powder bed-based 3D printing, LMD-p does not build a component layer by layer in a box, but rather blows metal powder directly onto an existing component in order to coat, harden or repair it.
How does LMD-p (Laser Cladding) work?
A laser beam is directed through a nozzle onto the surface of the workpiece and creates a melt pool there. At the same time, the nozzle (often coaxial around the laser) blows fine metal powder directly into this melt pool using a carrier gas. The powder immediately fuses with the surface and creates an extremely adhesive weld bead (track).
2. Wear protection (hardfacing) par excellence
LMD-p is the undisputed supreme discipline for wear protection.
- Instead of casting an entire component from expensive hard metal, a cheaper steel core (e.g. structural steel) is used. The robot arm with the LMD head moves over the surface and coats it millimeter-thin with extremely hard, wear-resistant alloys such as Stellite (cobalt-chrome) or tungsten carbide matrices.
- The metallurgical bond (fusion) is much stronger than with thermal spraying because the build material is completely welded to the base material. The layer does not flake off even under extreme loads (no delamination).
3. Low heat input and hardly any distortion
Conventional deposition welding using TIG (tungsten inert gas) or MIG brings enormous, uncontrolled heat into the component. The risk of massive distortion (warping) or structural damage to the base material is extremely high.
The laser in the LMD-p procedure, on the other hand, is extremely focused and often pulsates at high frequencies. The Heat Affected Zone (HAZ) is tiny. The mixing (dilution) of the hard powder with the softer base material is minimal (often less than 5%). In this way, the component retains its original dimensional stability and core strength.
4. Freeform 3D printing without limits
LMD-p is not just a coating technology, but full-fledged 3D printing (Directed Energy Deposition - DED).
Since the LMD head is usually mounted on a 5-axis robot arm or in a large CNC milling center, it is not tied to any installation space (no box). You can print meter-high titanium rocket tanks in free space or build up missing teeth on huge gears layer by layer (in-situ repair).
5. Conclusion: The scalpel for heavy industry
The wire-based LMD-w is even faster, but the powder-based LMD-p offers a much finer surface quality and allows completely new alloys to be mixed directly in the nozzle (powder mixture). For repairing high-end turbine blades, coating drill heads or refining inexpensive steel tools with carbide armor, LMD-p is the most versatile and lucrative tool in modern welding technology.