Laser cladding, an emerging surface treatment technology, has been widely popularized and applied in metal surface modification and metal spare parts repair in large area.
As for cladding materials, there is a wide range of varieties, such as nickel-, iron-, cobalt-base alloy and ceramic phase materials, of which composition is free from metallurgical thermodynamics. Using laser cladding, high-melting materials can be cladded on the surface of low-melting substrate. When cladding layer binds up with substrate to form a metallurgical bonded coating after solidification, the substrate materials will be much higher in resistance to wear and corrosion.
When using preset powder feeding, it means that alloy powder will be covered on substrate surface in advance, then, laser beam scans across pre-cladding layer. After taking in laser energy, the above layer rises in temperature and begins to melt. Meanwhile, the surface heat is passed inwards through heat conduction. As a result, a metallurgical bonded coating is about to take its shape after laser beam leaves and the molten metal quickly solidifies on substrate surface. Its advantages are high efficiency, uniform coating layer and firm binding with substrate. But, it also has the disadvantages of inflexibility and failure of cladding some special-shaped and small workpieces. This technically mature craft is now applied in the strengthening of axle parts of coal mine machinery, steelworks, petroleum drilling and so on.
In regard to synchronized powder feeding, special powder feeder, together with powder feeding pipe and airflow, is usually used to feed alloy materials to the waiting area. Now, the mainstream type lies in coaxial feeding, that is, powder and laser arrive at substrate surface simultaneously. In this way, the substrate receives less heat input, better quality of cladding layer and lower degree of surface roughness. At this moment, only simple work is needed to make cladding layer much smoother. Hence, this mode is fitted for cladding the special-shaped workpieces. Working with a manipulator, complex stereo workpiece is also easy to be cladded without any disassembly. As thus, this laser cladding will be high in speed when coaxial powder feeding is put into use. In spite of its maturity, it is highly demanding on powder feeding devices, shielding gas, cladding units, etc.