Eight Key Parameters Affecting Processing in High-Speed Laser Cladding

High-speed laser cladding is a rapid laser surface treatment technology characterized by good cladding quality, high speed, and low cost, offering certain market competitive advantages. Improper selection of high-speed laser cladding process parameters can lead to issues such as poor forming quality and susceptibility to deformation.

The key parameters involved in the high-speed laser cladding process, known as processing parameters, directly affect the effectiveness and forming quality of laser cladding. For example, laser power, spot shape, spot size, and processing distance all influence the morphology and quality of the cladding layer. Below, the eight major processing parameters involved in the high-speed laser cladding process are explained.

1. Laser Power: The energy output by the laser per unit of time. High-speed laser cladding typically uses kW-level lasers, such as LT-3KW and LT-4KW, which are widely applied in the market and can meet the needs of most fields.

2. Spot Shape: Spot shape is an important factor affecting cladding quality and is determined by the laser's optical system. After the laser beam exits the powder feeder, it passes through the scanning system and reaches the substrate, forming different spot shapes at different positions. Spot shape directly influences cladding effectiveness and forming quality. Common spot shapes are circular and rectangular, and users choose based on the characteristics of the processing object.

3. Spot Size: Spot size refers to the area of the beam scanned onto the substrate surface. During laser cladding, laser energy first concentrates at the center of the cladding layer and then radiates outward. Spot size primarily affects optical power density, i.e., the light energy per unit area. Under the same power conditions, a smaller spot size results in higher optical power density. High-power density spots are suitable for high-melting-point metal powders.

4. Processing Distance: Also known as the overlap rate, it refers to the distance required for the laser beam to absorb heat from the molten pool during laser cladding. During the process, spot distance is a critical factor affecting cladding quality. In practical processing, when the spot distance varies within the range of 3-5 mm, the cladding layer quality is good, so the spot distance is generally controlled between 3-5 mm.

5. Overlap Rate: The overlap rate refers to the degree of overlap between the cladding metal powder and the substrate. It is an important parameter affecting the surface roughness of the cladding layer. A higher overlap rate between the cladding material and the substrate makes it easier to achieve a cladding layer surface with lower roughness.

When the spot diameter increases, the energy density of the laser beam rises, the molten pool heats and widens, the melting speed accelerates, and more small holes are generated on the substrate.

An increased overlap rate reduces the surface roughness of the cladding layer. However, ensuring uniformity in the overlapping areas is challenging. The depth of the overlapping regions between each cladding pass differs from the depth at the center of each pass, which affects the entire cladding layer. The overlap rate for high-speed cladding is as high as 70%-80% (compared to 30%-50% for conventional cladding).

6. Cladding Speed: Cladding speed can be expressed as either linear cladding speed or cladding area rate. In practical measurements, the linear cladding speed for high-speed laser cladding ranges from 20 m/min to 50 m/min. When the cladding thickness is 0.2-0.6 mm, the cladding efficiency is 0.6-1.2 square meters per hour.

7. Powder Feeding Method: The powder feeder in high-speed laser cladding is crucial for ensuring cladding quality. The main powder feeding methods for high-speed laser cladding are annular powder feeding and central powder feeding. Central powder feeding offers higher powder utilization than annular powder feeding but is more challenging to design, as it requires surrounding the beam with a ring. There are many applications of circular powder feeding in the market today.

8. Shielding Gas Pressure: During high-speed laser cladding, oxidation easily occurs between the substrate and the cladding material. Oxides present in the cladding material can cause the substrate surface to blacken, darken, and harden, severely affecting the workpiece's surface quality. To prevent oxidation of the cladding material, the workpiece must be shielded. High-speed laser cladding can be performed under shielding gas, typically using nitrogen or argon as the shielding gas. This is mainly used for powder feeding, creating a protective zone around the laser cladding pool to reduce oxidation.