Based on prior calibration with analogist samples, a system, consisting of a CCD camera, a frame grabber and
a computer, is developed to in-situ measure the molten pool parameters during laser cladding. The signals captured by
CCD vary with change in substrate or clad material, so that, in order to gain the true data of the molten pool parameters,
calibration of the instrument must be performed for every set of substrate and clad materials. In this study, a new strategy
for on-line acquisition of molten pool parameters is presented. Before measurement of the objective molten pool,
cladding is performed to get some analogist samples of the same materials as those used to generate the objective molten
pool. The width of a certain segment of the clad bead on the analogist sample is gauged to calibrate the CCD
camera-grabbed image of the molten pool which has solidified to this segment of the clad bead. The pool width in the
grabbed image can be confirmed to the gauged bead width times the scaling because the width of the clad bead segment
must be equal to the width of the related pool. It is assured which type of area in the grabbed image is located on by the
pool, and the CCD is calibrated for this set of substrate and clad materials. After calibration, the CCD system is applied
to in-situ measure the molten pool parameters during laser cladding. In the presented experiments, the measured values
agree well with the actual ones.
Experiments of laser transformation hardening were performed with various process parameters on the surface of ductile
cast iron block, which is often used for vehicle body. The distribution of microhardness along the case depth direction
and the variation of microstructure of hardened track were investigated. Wear test was carried out using a
ball-on-flat-type wear-test machine. The results indicate that the hardened layers after the laser surface hardening
treatment have excellence wear resistance. It is seen that the surface hardness of ductile cast iron blocks increases greatly
at suitable values of process parameters in laser transformation hardening, which satisfies the vehicle dies.
The current state and future trend of laser bio-cladding technology are discussed. Laser bio-cladding
is used in implants including fabrication of metal scaffolds and bio-coating on the scaffolds. Scaffolds have
been fabricated from stainless steel, Co-based alloy or Ti alloy using laser cladding, and new laser-deposited Ti
alloys have been developed. Calcium phosphate bioceramic coatings have been deposited on scaffolds with
laser to improve the wear resistence and corrosion resistence of implants and to induce bone regeneration. The
types of biomaterial devices currently available in the market include replacement heart valve prosthesis, dental
implants, hip/knee implants, catheters, pacemakers, oxygenators and vascular grafts. Laser bio-cladding
process is attracting more and more attentions of people.
Laser cladding was performed on the ductile cast iron substrate with Ni-base alloy under different process conditions.
The cracks were observed. The temperature field and stress field in laser cladding under different process conditions
were simulated with ANSYS finite element software. It was found that cracks were influenced by process variables. In
certain ranges of laser power and scanning speed, while the other process parameters remain constant, the numbers of
cracks increase with laser power increasing. Similarly the number of cracks increases with scanning velocity increasing
while the other process parameters remain constant. In comparison with experimental results, the simulation with
ANSYS finite element software could help to predict, to some extent, the crack of laser cladded Ni-alloy on ductile cast
In this paper, the effects of the gas flow and defocusing distance from laser beam focus on powder-feed laser cladding
are investigated, and a quantitative expression to describe the free surface of the molten pool is derived. The effect of
transporting gas flow on the powder feed rate, and those of the transporting and shielding gas flow on the divergent angle
of the gas-powder flow and the characteristics of the formed clad bead are worked out, respectively, while the other
process variables being constant. The effect of gas-powder flow on the molten pool is presented as a boundary condition
equation for developing the numerical model of the molten pool. The experimental results obtained at variable
defocusing amount show that the negative defocusing amount rather than the positive one is suitable for laser cladding
and that the defocusing amount influences the molten height below the substrate surface.
In this paper, the temperature field of nodular cast iron in laser transformation hardening was simulated by using ANSYS
software and tested with CCD-based colorimetric temperature measurement method. Firstly, the temperature field was
calculated, and the width of the hardened track was estimated according to the calculated result. Then, the temperature
field was measured in the presented experiments. After comparison of the calculated results to the experimental ones, it
was found that the width of the hardened track can be predicted by the measured temperature field, which would help
analyse the effect of process parameters and carry out real-time control in laser transformation hardening process.
In this paper, attenuation of laser power by coaxial powder flow was studied. Given that the distribution of laser power as well as that of powder concentration was defined as a Gaussian function and no grain was shielded from laser by other grains, resolution model of laser power attenuated by coaxial powder flow was established. The attenuation of laser power by powder flow was a function of process parameters such as powder feed rate, moving velocity of grains, spraying angles and waist positions and diameters of laser beam and powder flow, grain diameter and run of laser beam through powder flow. The attenuation coefficient increased with powder feed rate or run of laser beam through powder flow and decreased with rise in grain diameter or moving velocity. The impacts of spraying angles and waist positions and diameters of laser beam and powder flow on attenuation coefficient were complicated. In practice, powder feed rate and run of laser beam through powder flow were both often adjusted, and other parameters were usually constant under certain conditions. In the presented experiment, the experimental results agreed well with the calculation results, and it was demonstrated that attenuation of laser power by coaxial powder flow rose with powder feed rate or run of laser beam through powder flow.