Study On Influence Factors And Control Methods Of Laser Cladding Cracks

Laser cladding technology is a new advanced manufacturing and repairing technology.It sprang up abroad in 1990 s.As a branch of intelligent manufacturing,laser cladding technology has been widely used in China at the beginning of the 21 st century.The basic principle of laser cladding is that high-energy laser beam melts the cladding powder.The addition of cladding powder is through gas feeding or pre-positioning,and through laser beam.Irradiation makes the powder and matrix material form a good metallurgical bond.Laser cladding technology has the characteristics of rapid melting of the local surface of the substrate and small heat-affected zone of the matrix.It can realize the automation of laser processing or cladding repair parts by reasonable multi-channel overlapping technology.There are many problems in laser cladding technology.Among them,the main problems in laser cladding technology are the planning of cladding trajectory,the selection of cladding layer quality and parameters.The most important quality problem is crack and pore.Cracks in cladding layer will seriously affect the mechanical properties of cladding layer,resulting in defects in processing quality.At the same time,they also affect the basic properties of the whole cladding layer,such as wear resistance,corrosion resistance and oxidation resistance.Cracks in laser cladding technology are caused by complex factors such as melting and solidification of metals,residual stress and so on.Among these factors,the thermal stress of cladding powder produced by rapid solidification and cooling after laser beam irradiation,the internal stress caused by the difference of physical properties between matrix material and powder,and the brittleness of cladding substrate itself lead to lower tensile stress.Ability is an important factor affecting crack generation.At the same time,in the laser cladding technology,the generation of gas holes in the cladding layer is also a defect that can’t be ignored,which affects the overall performance of the cladding layer.Due to the different temperature distribution at the bottom,middle and top of the cladding layer during laser cladding,the stress and structure of each part are different due to the influence of heat flow.At the same time,laser cladding technology is involved in the complex process of metal or ceramic powder solidification,which makes the cracks in the cladding layer may appear at any stage of the cladding process,which to a certain extent makes the cladding technology as an important link affecting the quality of the cladding layer,and puts forward more stringent requirements.By analyzing the heat absorbed by the cladding layer,the trend of cracks and holes in the cladding layer is produced.The laser energy density absorbed by the cladding layer during cladding process is the main factor affecting the generation of cracks and holes.The parameters such as laser power,scanning rate,defocusing amount and powder feeding amount determine the energy density.In order to obtain a good quality cladding layer,laser cladding is made possible.The matching and optimization of coating parameters play an important role in laser cladding technology.At the same time,the numerical simulation method lays a foundation for the in-depth study of the cracks in the cladding layer by the preheating of the matrix,which provides a certain reference value for the actual processing and production to a certain extent.Considering that optimizing process parameters can’t completely eliminate cracks and pore formation in the cladding layer,ultrasonic vibration-assisted laser cladding technology was used to clad nickel-based cladding layer on 45 steel surface.The basic properties of the cladding layer,such as microstructure and microhardness,were analyzed by metallographic microscope,scanning electron microscope and microhardness tester.At the same time,through the interference of ultrasonic vibration in the laser cladding process,it is concluded that ultrasonic vibration can eliminate the cracks in the cladding layer to a certain extent and restrain the pore in the cladding layer to a certain extent.Furthermore,ultrasonic vibration can also make the cladding layer grain refinement,uniform distribution of microstructure and wear resistance significantly improved.