High-speed laser cladding process has been highly recognized by the market, and high-speed laser cladding instead of ordinary laser cladding will become an inevitable trend in the development of industry technology. However, laser cladding is a complicated process. Based on years of experience, Guosheng Laser summarizes the knowledge points of high-speed laser cladding process and the reasons for various process problems as follows, hoping to help the majority of industry peers.
How high-speed laser cladding works
High-speed laser cladding uses a high-energy laser beam to melt metal powder flow in the air, and also melts the matrix to form a molten pool.After the molten powder is combined with the molten matrix, it is rapidly cooled to form a metallurgically bonded coating.
Key parameters of high-speed laser cladding process and their influence on cladding effect
1. Laser power
The power directly affects the amount of powder that can be melted per unit time and affects the cladding efficiency. When other working parameters are determined, the power is too small, which may lead to incomplete melting of the powder, pitting after grinding, insufficient binding force, and low coating hardness. The power is too large, it is possible to melt the fuse, resulting in oblique wrinkles on the surface.
2. Powder feeding amount
After the powder flow meets the laser, it absorbs the laser energy.The larger the amount of powder, the more laser energy is absorbed.When the amount of powder is too large, the laser energy will be insufficient, the coating will not melt through, and pitting will appear after grinding and polishing. The matrix will not melt, and the coating and the matrix will not be metallurgically bonded, leading to coating peeling problems.The amount of powder is large and the powder utilization rate is low.The powder volume is small and the powder utilization rate is high.
3. Line speed
The greater the linear speed, the thinner the cladding, and the smaller the linear speed, the thicker the cladding.If the linear speed is too high, the substrate cannot form a molten pool, the coating and the substrate cannot be well metallurgically bonded, the melt channel cools slowly, the red tail is too long, and peeling occurs. Small linear speed can improve coating hardness and powder utilization.
4. Step by step
The smaller the step, the greater the overlap rate and the finer the coating surface.The larger the step, the smaller the overlap ratio and the more obvious the coating stripes. The step affects the dilution rate. When the step is small, the laser energy irradiated on the substrate is small and the dilution rate is low. When the step is large, more laser energy is irradiated on the substrate and the dilution rate is high.
5. Air supply volume
The gas has two functions, one is to transport the powder, and the other is to protect the high-temperature coating and prevent oxidation.If the amount of powder feeding air is too small, it is easy to block the powder.The powder supply air volume is too large, the powder speed is too fast, the ejection is large, and the powder utilization rate is low.In general, argon protects coatings better than nitrogen and results in higher coating quality.
6. Nozzle height
If the nozzle is too high, the powder will spread out and the powder utilization rate will be low.If it is too low, powder will easily stick to the nozzle during the cladding process.
Analysis of common problems and causes during high-speed laser cladding process
1. Peeling
This is because the matrix does not form a molten pool and there is no metallurgical bond between the powder and the matrix.Possible reasons include: too low power, too large amount of powder, too fast linear speed, oil stain or electroplating layer on the surface of the workpiece, etc.
2. Crack
The reasons for cracks in the coating include: the hardness of the substrate is too high (quenching, carburizing/nitrogen); the substrate has a fatigue layer; the hardness of the powder is too high, etc.Nickel-based powders are prone to cracks; cracks may also occur during multi-layer cladding of powders with high hardness.
3. Pore
The reasons for the occurrence of pores in the coating include: rust and oil stains on the substrate, impurities in the powder, unstable powder flow, excessive powder volume, insufficient power, or excessive linear speed, etc.
4. There is a lot of floating powder and the coating has no metallic luster.
Possible reasons include: too much powder; too little power; too fast linear speed; too high nozzle height; too small laser spot; lens contamination, etc.
5. Pits appear after grinding and polishing
Possible reasons include: insufficient power; too much powder; too fast linear speed, etc.
6. Oblique wrinkles appear in the coating
Possible reasons include: excessive power; excessive molten pool temperature; excessive liquefaction of the powder.
7. Nozzle sticky powder
Possible reasons are: the powder ejection is too high; the copper head temperature is too high; the nozzle working distance is too low, and the nozzle surface is too rough or contaminated (polishing is recommended).The cladding head is placed off-center to help reduce powder sticking.
8. Blocking powder
Possible reasons include: the sticky powder is not removed in time; the powder has poor fluidity; the powder has impurities or the powder is damp (it needs to be baked), etc.When feeding powder from multiple channels, uneven powder feeding from each channel is an important cause of powder blockage.
9. There is a sizzling sound during cladding
Possible reasons include: the powder is contaminated; the powder is damp; the matrix is not clean, etc.Excessive power density will also cause the molten pool metal to vaporize and produce cladding noise.These problems will affect the corrosion resistance of the coating.
10. Cladding sparks flying
Possible reasons include: excessive linear speed; excessive power density; mismatch between power and powder volume; excessive air flow, etc.
11. Unstable powder flow, resulting in uneven coating
The reasons for unstable powder flow include: large scraper wear; blocked powder feeding channel; too small air flow; poor sealing of the powder feeder sealing ring or damaged powder feeding pipe, etc., resulting in air leakage.
12. Decreased cladding efficiency (thinner coating thickness)
Possible reasons: contamination of the protective mirror; wear of the scraper; inappropriate working distance; grinding of the powder outlet hole and thickening of the powder flow; reduction of laser power, etc.