The main process parameters affecting laser cladding quality include laser power, cladding speed, lens focal length, focusing position, and shielding gas. Laser power and cladding speed are the primary parameters affecting cladding quality. The cladding thickness depends on the laser power, approximately 0.7 times the power (kW).
Generally, increasing the power increases the cladding depth; increasing the speed results in a shallower cladding depth, narrower weld seam and heat-affected zone, and increased productivity. However, excessively high cladding speed and laser power will increase the tendency for porosity and voids. The focal length of the laser cladding lens is determined by the diameter of the output laser spot, and there is an optimal matching value between the two. Generally speaking, the deeper the required cladding depth, the longer the lens focal length. Short focal length lenses have higher focusing requirements, and there is more spatter during powder metallurgy cladding, leading to severe lens contamination. Lenses with excessively long focal lengths diffract, causing the focal point to become larger, and the energy density at the focal point cannot reach its maximum value. In China, lens focusing optical systems are generally used. These systems can only be used in situations with lower laser power; higher laser power will cause lens focal point drift, resulting in poor weld formation and quality. In high-power applications abroad, reflective focusing optical systems are mostly used because of their superior cooling conditions, thermal stability, uniform and beautiful weld formation, and reliable cladding quality. Laser cladding achieves a large cladding depth (approximately 1/3 of the plate thickness) by focusing the laser at a specific location below the workpiece; the horizontal focus location depends on the specific situation. The shielding gas protects the focusing lens and prevents weld oxidation; an inert gas, such as helium, is preferred. In my country, due to the high cost of helium, argon is generally used. The gas flow rate must be carefully controlled; too low a flow rate will be ineffective, while too high a flow rate will waste gas and cause the weld pool to churn, resulting in undulating ridges on the weld surface. Laser cladding can be broadly classified into two categories based on the method of supplying the cladding material: pre-positioned laser cladding and synchronous laser cladding. The main process flow of pre-positioned laser cladding is: substrate material cladding surface pretreatment – pre-positioning of cladding material – preheating – laser melting – post-heat treatment. The primary process flow of synchronous laser cladding is as follows: substrate material surface pretreatment – laser melting – post-heat treatment. Laser cladding uses a high-energy laser beam (10⁴–10⁶ W/cm²) to irradiate the surface of a metal substrate, causing the thin layer on the substrate surface and the cladding material to interact. Through rapid melting and solidification, a coating layer with special physicochemical properties such as high hardness, good wear resistance, and corrosion resistance is formed. This is a novel composite material that can supplement the excellent properties lacking in the substrate, more fully utilizing the advantages of both and overcoming their respective shortcomings, thereby significantly improving the wear resistance, corrosion resistance, heat resistance, oxidation resistance, and other physicochemical properties of the substrate surface.
Since the 1980s, laser cladding technology has developed rapidly and has become a hot topic in laser surface modification research both domestically and internationally. Laser cladding technology has significant technical and economic benefits and is widely used in machinery manufacturing and repair, automobile manufacturing, textile machinery, marine and aerospace, and petrochemical fields.
Laser cladding technology has achieved certain results and is in the initial stage of gradually moving towards industrial application. Future development prospects mainly include the following aspects:
(1) Basic theoretical research on laser cladding.
(2) Design and development of cladding materials.
(3) Improvement and development of laser cladding equipment.
(4) Establishment of theoretical models.
(5) Rapid prototyping technology for laser cladding.
(6) Automation of cladding process control.