Influence of Process Parameters on Forming Quality

1. Laser Power: The power directly affects the amount of powder that can be melted per unit time, influencing the cladding efficiency. When other working parameters are fixed, insufficient power may result in incomplete powder melting, pitting after polishing, inadequate bonding strength, and low coating hardness. Excessive power may cause overmelting of the melt track, leading to the appearance of oblique wrinkles on the surface.

2. Powder Feed Rate: After the powder stream interacts with the laser, it absorbs laser energy. A higher powder feed rate results in more absorbed laser energy. If the powder feed rate is too high, it may lead to insufficient laser energy, resulting in an unmelted coating, pitting after polishing, and failure to melt the substrate, preventing metallurgical bonding between the coating and substrate and causing coating peeling. A high powder feed rate leads to low powder utilization, while a low powder feed rate results in high powder utilization.

3. Scanning Speed: A higher scanning speed results in a thinner cladding layer, while a lower scanning speed results in a thicker cladding layer. Excessive scanning speed may prevent the formation of a molten pool on the substrate, leading to poor metallurgical bonding between the coating and substrate, slow cooling of the melt track, an excessively long red tail, and peeling. A lower scanning speed can improve coating hardness and powder utilization.

4. Step Over: A smaller step over results in a higher overlap rate and a smoother coating surface, while a larger step over results in a lower overlap rate and more pronounced coating streaks. The step over affects the dilution rate. A smaller step over results in less laser energy reaching the substrate, leading to a lower dilution rate. A larger step over results in more laser energy reaching the substrate, leading to a higher dilution rate.

5. Gas Flow Rate: The gas serves two purposes: transporting the powder and protecting the high-temperature coating from oxidation. Insufficient gas flow may cause powder clogging, while excessive gas flow may result in high powder velocity, significant bouncing, and low powder utilization. Generally, argon provides better protection for the coating than nitrogen, resulting in higher coating quality.

6. Nozzle Height: If the nozzle is too high, the powder dispersion increases, leading to low powder utilization. If it is too low, the nozzle is prone to powder adhesion during the cladding process.