Direct Laser Sintering Of Metal Powder Densification Theory And Its Validation

Selective laser sintering (SLS) technology is a new rapid prototyping (RP) technology, which dates from later 1980's. It is the integration of material science, computer technology and laser science. As an important branch of SLS, the direct metal laser sintering (DMLS) technology can manufacture metal parts with any geometry shape directly. People focus more on it than before.DMLS technology has been developing for many years, but its physics process and densification mechanism still not be well understood. Developing the processing parameters for different metal powder systems and preparing the special powders for laser sintering are the future direction. For solving those problems, it is very important to research the sintering mechanism of DMLS quantitatively, to establish the math or physics model simulating the sintering process, to investigate the microstructure and densification of different metal powders.This thesis researches the physics behavior of DMLS, establishes the sintering model, puts forward the densification theory, and validates the experimental results to the theory. The work I have finished mainly includes:a. Based on the interaction mechanism between laser and metal powders, set up the "melting-balling-spreading-retracting" model of DMLS. According to the competition between metal melt spreading and retracting, put forward the densification criterion: Ca number (Ca= (v/σ)·V_r). During DMLS, the laser style, process parameters, powder characterization all influence the value of Ca harmoniously. Only the three factors satisfy the densification criterion, can get the ideal densification result. Then, get the P-V chart of DMLS.b. Token the characterization of several powder systems through some experiments. Using our densification theory, we forecast the sintering results of those powder systems. It is proved that adjusting the powder characterization can improve the quality of direct laser sintering. Investigate the influence of laser powder, laser spot diameter and powder depth to the variation of temperature field of DMLS using ANSYS. The simulation result accords with our theory prediction well.c. Do some experiments to research the DMLS densificationprocess of 316 stainless steel powder and Fe₇₀Cu₃₀ water-atomized powder according to the densification theory. The cuboid and cylinder sample have been manufactured successfully. The experiment result tallies with the theory prediction.