(1) Skinning
This is because the matrix does not form a molten pool and there is no metallurgical bond between the powder and the matrix. Possible causes are: low power; Too much powder; The linear speed is too fast; There is oil stain or electroplated coating on the surface of the workpiece.
(2) Cracks
The reasons for cracks in the coating are: the hardness of the substrate is too high (quenching, carburizing/nitriding); The matrix has a fatigue layer; The hardness of the powder is too high. Nickel based powder is easy to crack; Cracks may also occur during multi-layer cladding of high hardness powder.
(3) Blowhole
The causes of pores in the coating are: rust and oil stain on the substrate; There are impurities in the powder; The powder flow is unstable; Too much powder; Insufficient power; Or the linear speed is too high.
(4) There are many floating powders, and the coating has no metallic luster
Possible reasons are: too much powder; Power is too low; The linear speed is too fast; The nozzle height is too high; The laser spot is too small; Lens pollution, etc.
(5) Pits appear after polishing
Possible causes are: insufficient power; Too much powder; Too fast linear speed, etc.
(6) Inclined wrinkles in the coating
Possible reasons are: too much power; The temperature of molten pool is too high; Excessive liquefaction of powder.
(7) Affix powder to the nozzle
Possible causes are: too high powder spraying amount; Copper head temperature is too high; The working distance of the nozzle is too low, and the nozzle surface is too rough or polluted (polishing is recommended). The eccentric placement of the covering head is conducive to reducing the powder sticking phenomenon.
(8) Clog powder
Possible reasons include: the sticky powder is not removed in time; Poor powder fluidity; There are impurities in the powder or the powder is wet (to be dried). When powder is fed in various ways, uneven feeding is an important reason for powder plugging.
(9) There is a hissing sound when covering
Possible causes are: powder is polluted; Wet powder; The substrate is not clean. Excessive power will also lead to metal gasification in the molten pool and cladding noise. These problems will affect the corrosion resistance of the coating.
(10) Coating spark splash
Possible causes are: excessive linear speed; Excessive power density; Power and powder quantity do not match; Excessive gas flow, etc.
(11) Unstable powder flow, resulting in uneven coating
The reasons for unstable powder flow are: the scraper is worn seriously; The powder feeding channel is blocked; The airflow is too small; The sealing ring of the powder feeder is poorly sealed or the powder feeding pipe is damaged, causing air leakage.
(12) Reduced coating efficiency (thinner coating thickness)
Possible causes: contaminated goggles; Scraper wear; Improper working distance; The powder outlet hole is big and the powder rheology is rough; Laser power drop, etc.
Source: Guosheng Laser
