Laser Powder Deposition Process Research Articles

Application of vibration in the laser powder deposition process

Laser powder deposition (LPD) has been used for a few decades as a technique that is unique in the application of complex geometry part manufacturing, high-value parts repairing, and surface modification. However, improving the buildup quality of LPD process is still a challenge because of the presence of defects. In this paper, the effect of in-process vibration frequency on the buildup properties of LPD is studied. Experimental results show that the vibratory energy has a significant effect on reducing porosity. Up to an 80% reduction in the porosity and the maximum defect size can be obtained by choosing the appropriate vibration parameters. In addition, a more homogeneous microstructure is achieved that results in less deviation in hardness throughout the buildup.

Characterization of laser powder deposited Ti–TiC composites and functional gradient materials

Laser powder deposition (LPD) is an important process for the preparation of functional gradient materials due to its unique layer-by-layer additive manufacturing character. In this paper, based on preliminary experiments and analysis of LPD Ti–TiC composites with different premixed ratios of Ti to TiC, two thin walls of functional gradient material of Ti to Ti–40vol.%TiC were successfully deposited by adjustment of processing parameters and real-time variation of the feeding ratio of Ti to TiC during LPD process. The tensile strength of LPD deposited Ti–TiC composites changed marginally with TiC content, while the ductility displays a sharp reduction with increase in TiC addition. The wear resistance under dry sliding wear test can be improved with addition of TiC. Microstructure observation and hardness testing performed along the composition gradient direction indicated that functional gradient materials of Ti to Ti–40vol.%TiC without a discrete interface could be easily obtained through this process.

Adaptive Modeling of Laser Powder Deposition Process for Control and Monitoring Application

The laser powder deposition (LPD) process is an advanced material processing technique with many applications. Despite this fact, reliable and accurate control schemes have not yet been fully developed for the process. In this paper, identification of the LPD process is examined to find a more accurate model to predict and control the height of clad in real time. The model is adaptive single input—single output (SISO) and its structure is very similar to the Hammerstein model when the effective power (a function of laser power and velocity) is selected as the input and the clad height as the output. Weighted extended recursive least square (WERLS) is adopted to simultaneously estimate the model parameters using experimental data. Comparison of the results shows that this method can be used very efficiently in control of laser powder deposition process.

A mechatronics approach to laser powder deposition process

This paper introduces a mechatronics approach for the development of a closed-loop control system utilized in laser powder deposition. The laser powder deposition process, as a manufacturing technique, is combined with a feedback control system to increase the quality of the final formed parts. The interconnections between the technologies involved in this complex mechatronics system along with the development of a CCD-based optical detector are explained. The optical CCD-based detector monitors the process zone to provide a series of single pass band images of the near-locus region. A pattern recognition algorithm is incorporated into the feedback device to obtain the clad’s height and angle of solid/liquid interface in real-time. This feedback device is blended in a PID-based controller, which is designed using a knowledge-based model, to adjust the laser pulse energy for enhancing the output of the process. The experimental assessments of the developed system are also presented at different process conditions and disturbances when Fe–20%Al was deposited on mild steel. It is shown that the PID-based controller can effectively improve the geometrical characteristics of the clad around the operating point by overcoming the effects of various disturbances.

Prediction of melt pool depth and dilution in laser powder deposition

This paper presents a mathematical model of laser powder deposition (LPD) to predict temperature field, melt pool depth and dilution. The model validated by experiments is developed using the moving heat source method. In this method, the temperature distribution inside the clad and the substrate is obtained using the superposition principle and the solution of the heat diffusion due to a point heat source. The model, which can be used in real-time applications, predicts the melt pool depth and dilution as a function of clad height and clad width, which in practice can be measured by a vision system. Numerical and experimental analyses show a non-linear behaviour of the melt pool depth as a function of process speed. This indicates that the melt pool depth has a maximum at a certain process speed. The comparisons between the numerical and experimental results show that this model is capable of predicting the characteristics of the LPD process accurately. Using the model, some general curves that show the behaviours of the melt pool depth and dilution as a function of clad height, scanning speed and laser power are illustrated.