Advantages and disadvantages of lateral and coaxial powder feeding in laser cladding

Disadvantages of side axis powder feeding technology
1. The selection of metal powder is limited
Due to the lack of protective gas, the laser melt pool can only rely on the self-protection of the molten slag during the melting of the overlay powder. Therefore, in current industrial production, self melting alloy powder is often used in the side axis powder feeding system. The melted powder relies on the slagging effect of elements such as B and Si to generate self-protection on the surface of the melt pool.

2. The surface of the cladding layer has significant undulations
The side axis powder feeding adopts a preset powder feeding method, and after melting, the surface of the melting layer has a very obvious melt path, with large and uneven grooves. After melting is completed, corresponding turning, throwing, and grinding are required, resulting in high processing costs.

3. Processing surface is restricted
Side axis powder feeding is not suitable for use on inclined workpieces or inner hole cladding due to gravity feeding, and its application range is limited.

Advantages of Side Axis Powder Feeding Technology
1. High utilization rate of metal powder
Compared to coaxial powder feeding, the material utilization rate of off-axis powder feeding laser cladding technology can reach over 95%. The powder of coaxial powder feeding laser cladding technology is blown towards the laser melt pool by inert gas. During this process, due to collisions between powders, splashing of the melt pool, and the accuracy of the powder feeding channel, a considerable proportion of metal powder cannot form a cladding layer and is wasted, resulting in a material utilization rate of only about 50% -80% (the smaller the light spot, the lower the material utilization rate). And the side axis powder feeding laser cladding can achieve a very high material utilization rate and save a lot of material costs by pre setting the powder on the surface of the workpiece and scanning and irradiating it with a laser beam to melt it.

2. The fusion efficiency is relatively high
The side axis powder feeding laser cladding technology adopts a rectangular spot scheme, which can significantly improve the cladding efficiency by increasing the laser power and spot width while ensuring the energy density of the cladding direction spot remains unchanged. At present, in actual production, the width of a single pass cladding can reach over 30mm, and the cladding line speed can reach 1.0m/h.

3. No inert gas consumption, low cost
On the one hand, the side axis powder feeding laser cladding technology generally adopts gravity powder feeding method, which does not require the consumption of inert gas; On the other hand, due to the use of pre-set powder feeding, the airflow will affect the pre-set and stacking of the powder, so the fusion head does not have a dedicated inert gas protection function. Therefore, the side axis powder feeding laser cladding technology does not require the consumption of any other gas besides compressed air. From a cost perspective, it saves a significant amount of inert gas costs; In terms of technology, this technology has certain requirements for the oxidation resistance of powder materials, which limits its application fields.

4. Scope of application
Side axis powder feeding laser cladding technology is generally used for surface cladding and additive remanufacturing of large and simple shaped parts such as hydraulic cylinders and rollers due to its high efficiency and low cost.

Disadvantages of coaxial powder feeding technology
1. Low utilization rate of metal powder
Coaxial powder feeding laser cladding technology adopts pneumatic powder feeding, where inert gas is blown towards the laser melt pool while assisting in the output of metal powder. Under the action of gas, metal powder collides with each other, splashes occur in the melt pool, and a considerable proportion of metal powder cannot absorb laser melting and is wasted. Therefore, in practical applications, the powder utilization rate is only about 50% -70%, and the faster the powder output speed, the lower the powder utilization rate.

2. Easy to block powder, high maintenance costs
In the circular powder feeding or multi beam powder feeding scheme, the powder feeding channel is relatively narrow and needs to achieve equal powder distribution. Due to the influence of gravity or air flow fluctuations, uneven powder distribution may occur, which easily leads to blockage of the powder outlet channel and affects the continuity of production operations. In severe cases, the nozzle needs to be replaced, and maintenance costs are high.

3. Poor safety and stability
The coaxial powder feeding melting head adopts a central output laser, and the surrounding powder path, gas path, and water path structures are complex. The cooling effect of the melting head is poor, and the temperature of the melting head will be too high when working for a long time, which will cause the adhesion of splashing powder.

Advantages of coaxial powder feeding technology
1. The fusion surface is relatively flat
Compared to side axis powder feeding, coaxial powder feeding has a smoother surface, simpler post-processing steps, and smaller processing volume.

2. Integrated design of powder feeding and laser, high degree of freedom and easy automation integration
Coaxial powder feeding is a pneumatic powder feeding method that can obtain cladding layers of the same quality at different angles and in any direction. Due to its ability to move towards any direction during cladding, it can obtain cladding layers with consistent morphology and quality. Therefore, there are no restrictions on its cladding direction, and it can be used in conjunction with industrial robots or multi axis motion machine tools to perform surface cladding on parts of any path or shape. It can also be used for laser coaxial powder feeding 3D printing.

3. The inert gas protection effect of the molten pool is good
Coaxial powder feeding adopts an airborne powder feeding method, with a dedicated inert gas flow channel set on the melting head. During the melting process, the molten pool is always in a good inert gas atmosphere, greatly reducing the oxidation of the molten pool and the melting layer. There are fewer oxide inclusions in the melting layer, resulting in a small molten pool, uniform heating of the powder, and good crack resistance of the melting layer.

4. Small melt pool, uniform heating of powder, and good crack resistance of the cladding layer
The spot size of coaxial powder feeding laser cladding is generally between Φ 1 and Φ 5mm. The powder is in uniform contact with the beam, and the heat transfer during the cladding process is more uniform. Therefore, the cladding layer has good crack resistance. Especially for the melting of ceramic particles containing tungsten carbide and other materials, it is suitable for preparing crack free and uniformly distributed tungsten carbide coatings.

5. Low melting depth and low heat input
Coaxial powder feeding laser cladding has a smaller spot diameter and higher cladding line velocity. Compared with wide spot lateral powder feeding laser cladding and arc welding, it has lower cladding heat input, moderate dilution rate, and smaller heat affected zone depth. It has excellent cladding performance and has less impact on the properties of the base material.

6. Scope of application
Due to the aforementioned characteristics of coaxial powder feeding laser cladding technology, it is commonly used for surface cladding modification and additive remanufacturing of high-precision and complex shaped parts such as spindles, gears, and casings. Meanwhile, metal 3D printing based on coaxial powder feeding laser cladding technology is mainly applied in the net forming of large parts and the preparation of gradient materials.