| The research outlined in this thesis involves the development of a unique Rapid Prototyping (RP) machine with multi-material and multi-process capability. The first stage of development of this new system involves a three-dimensional translation table, two powder feeders, a custom powder delivery system and a low-power diode laser energy source and a custom designed nozzle, both with variable inclination. The RP machine has been designed, assembled, and tested as reported in this thesis. The experimental control and operation of the novel RP machine has been performed through custom software and CNC code, with material feed rate, laser power, and table translation speed, being the central control variables. Gas-based material delivery was tested ensuring sufficient powder mixing as particles are transported from storage hoppers to the melting pool. The operation of the custom RP machine has been investigated both theoretically and experimentally. Theoretical investigations have involved the development of a mathematical model to predict the temperature of particles as they are irradiated between the exit of the material delivery nozzle and the melting pool. Model assumptions of particle speed and direction were verified experimentally through the use of side-view high speed imaging and low-power laser-light sheet illumination. The analytical model has demonstrated that a more vertical position of the material delivery nozzle will lead to a more uniform temperature distribution of the particles over the melting pool. The system has been experimentally tested and samples have been generated with a single metal (Iron) and with a graded composition (Iron-Copper). The machine has proven to be capable of building components with both a single material and with functionally graded composition. The specimens have been analyzed with optical microscope and Scanning Electron Microscope (SEM) in order to assess the machine functionality. The results for the single material samples have revealed a similar microstructure and some macroscopic issues related to the adopted process parameters. The analysis of the graded samples has demonstrated that Copper content causes grain refinement in the observed microstructure. Micro hardness tests have revealed an increase in the material hardness, in particular in the region of low Copper content. |
