Powder Catchment Research Articles

Laser attenuation of the focused powder streams in coaxial laser cladding

The optical attenuation of a laser beam passing through a powder stream during coaxial laser cladding has an important effect on the powder catchment efficiency for this new process. This attenuation for variations in the powder stream focus was studied both experimentally and theoretically in this article. Measurement of the laser attenuation caused by the streams was made to compare with the theoretical results. It shows that more than 50% of the laser energy could be lost in the powder stream and the focused stream gives less powder catchment than the nonfocused stream in coaxial laser cladding for 304 L stainless steel powder on mild steel with 1 kW CO2 laser radiation.

Coaxial laser cladding on an inclined substrate

This paper describes an experimental and theoretical study of the cladding mode of coaxial laser cladding on an inclined substrate. Based on the image analysis of the powder stream and clad profile measurements in coaxial laser cladding, it was found that irregular clad profiles always formed on an inclined surface and the location of the peak profile shifted away from the clad center. This phenomenon is caused by uneven distributions of powder concentration and laser beam intensity. A modified Gaussian mode for powder stream and laser beam was proposed to estimate the clad profiles on an inclined plane under laser beam irradiation. The effects of the inclined steel substrate on the CO 2 laser beam absorption and stainless-steel powder catchment were examined experimentally. The results show that both the laser absorption and the powder catchment on the mild steel decrease with increasing the cladding angle. From the analysis of laser beam mode, the clad width is equivalent to the beam spot size on the inclined substrate. However, the clad height correlates well with the distribution of the powder concentration. The results show that the Gaussian cladding mode could be adopted in various laser cladding applications such as rapid prototyping and butt welding to predict the clad profiles precisely.

A simple model of powder catchment in coaxial laser cladding

High efficiency of the powder deposition in coaxial laser cladding is a key subject for this new technique adopted to the industry. A catchment model was proposed in this study to characterise the particle bonding under laser heating in the cladding process. The phenomena of the particle rebound and adhesion on substrate were discussed and the catchment efficiency was mathematically modelled based on the beam spot and the stream cross-section area. The theoretical catchment efficiency was further verified with the experiments and the results give an insight of the powder stream characteristics of the coaxial nozzle.

An in-process method for the inverse estimation of the powder catchment efficiency during laser cladding

An estimation of the heat loss by conduction can be obtained from measurements of the surface temperature and an overall heat balance at the clad laser interaction zone. Through an inverse calculation of the boundary temperature from observed surface temperatures the powder catchment efficiency can be estimated along with the variation in the clad height expected during laser cladding. This method shows a possible way to monitor and control the clad height and profile as required by near net shape manufacturing methods based on laser cladding.