The high-speed laser cladding process has been highly recognized by the market. The replacement of ordinary laser cladding by high-speed laser cladding will become an inevitable trend in the development of industry technology.However, laser cladding is a relatively complex process. In order to help the majority of high-speed laser cladding users master the process quickly, based on many years of experience, Guosheng Laser has summarized the key points of knowledge and various process issues of the high-speed laser cladding process. The reasons are summarized as follows. I hope it can be helpful to the majority of colleagues in the industry.
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 melted powder and the melted matrix are combined, they are 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.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
When the powder meets the laser, it absorbs the laser energy. The greater the amount of powder, the more laser energy is absorbed. When the amount of powder is too large, it will lead to insufficient laser energy, the coating will not melt through, and the pitting will appear after grinding and polishing. The substrate can not be melted, the coating and the substrate can not achieve metallurgical bonding, resulting in coating peeling problems. If the powder quantity is large, the powder utilization rate is low. If the powder quantity is small, the powder utilization rate is high.
3. Line speed
The higher the linear velocity, the thinner the cladding, and the lower the linear velocity, the thicker the cladding. Excessive linear speed will prevent from forming a molten pool on the matrix, and the coating and the matrix can not be well combined in metallurgy. If the fuse cooling is slow, the red tail is too long, and the peeling phenomenon occurs. Low linear speed can improve coating hardness and powder utilization.
4. Stepping
The smaller the stepping, the larger the lap rate and the finer the coating surface; The larger the stepping, the smaller the lap rate and the more obvious the coating streaks. The stepping affects the dilution rate. When the stepping is small, the laser energy irradiated on the matrix is small and the dilution rate is low. When the stepping is large, more laser energy is irradiated to the matrix, 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 to prevent oxidation. If the powder delivery gas amount is too small, it's easy to plug the powder. If the powder delivery gas amount is too large, the powder speed is too fast, the ejection is large, and the powder utilization rate is low. In general, argon coating protection is better than nitrogen, and the coating quality is higher.
6. Nozzle height
If the nozzle is too high, the powder divergence is large, and the powder utilization is low. If too low, the coating nozzle is easy to stick powder.
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 the powder is not metallurgically combined with the matrix. Possible causes are: the power is too low; Too much powder; Too fast line speed; There is oil or electroplating on the surface of the workpiece.
2. Cracks
The causes of coating cracks are: The matrix hardness is too high (quenching, carburizing/nitrogen); The matrix has fatigue layer; Powder hardness is too high. Nickel-based powder is prone to crack. When the powder with high hardness is coated in multiple layers, cracks will also appear.
3. Pores
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. Too much floating powder, coating without 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. Pitting appears after polishing
Possible reasons include: Insufficient power; Too much powder; Too fast linear speed, etc.
6. Oblique wrinkles appear on the coating
Possible reasons include: Excessive power; Excessive molten pool temperature; Excessive liquefaction of the powder.
7. Nozzle sticks powder
The possible causes are: The powder ejection is too high; The copper head temperature is too high; The nozzle working distance is too low; The nozzle surface is too rough or polluted (polishing treatment is recommended). The off-center placement of the cladding head is conducive to reducing the sticky powder phenomenon.
8. Blocking powder
The possible reasons are: Sticky powder is not removed in time; Powder fluidity is not good; Powder impurities or powder damp (to dry), etc. During multi-route feeding of powder, the unequal feeding of each route is an important cause of powder blocking.
9. There is a sizzling sound during cladding
The possible causes are: powder contamination; The powder is damp; The matrix is not clean, etc. Excessive power density can also lead to metal gasification in the molten pool, resulting in cladding noise. These problems will affect the corrosion resistance of the coating.
10. The cladding sparks splash
The possible reasons are: Excessive linear velocity; Power density is too large; Power and powder quantity do not match; Air flow is too large.
11. Unstable powder flow, resulting in uneven coating
The reasons for the unstable powder flow are: The scraper wear; Powder delivery channel is blocked; The airflow is too small; The sealing ring of the powder feeder is not well sealed or the powder pipe is damaged, leading to air leakage.
12. Decreased cladding efficiency (thinner coating thickness)
Possible causes: Contamination of the protective mirror; Scraper wear; The working distance is not suitable; The powder hole is ground big; The powder flow is coarse; Laser power drop, etc.
Xi'an Guosheng Laser Technology Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing and sales of automatic laser cladding machine, high-speed laser cladding machine, laser quenching machine, laser welding machine and laser 3D printing equipment. Our products are cost-effective and sold domestically and abroad. If you're interested in our products, please contact us at bob@gshenglaser.com.