Direct metal deposition of functional graded material

Functional graded materials (FGMs) are a class of composite materials that have a continuous variation of properties from one point to another. FGMs are not new but they could be an approach for eliminating the sharp interface between clad and substrate in the laser cladding process. It is possible to relieve stress concentration appearing in these laminated materials because the gradation may reduce both thermal and residual stresses. Coating techniques using powder as added material can be adapted for the manufacture of composition gradients if a mixing unit is included in the powder feed system. The powder feed is the basis of laser cladding technology for the production of layers with composition closer to the fed material. FGM is obtained if mixing parameters are changed along the process. But mixing parameters are not the only ones to be changed. New problems appear when dealing with these FGMs. Due to the change in composition, optimal process parameters could vary from one layer to the other and even from one track to the closest one. Changing the composition during the process requires the use of a delay time between tracks due to the distance between the feeder and the laser head. Overall heating of the processed part produces increase in temperature, if temperature is wanted constant it has to be measured and controlled during the process. This measurement depends on the emissivity which, at the same time, depends on the composition. In this work the performance of a software tool capable of modifying the process parameters at any point of the produced part is presented. Process parameters are: laser power, scan speed, feed rate and relative composition of the deposited layer. This change can be established initially or modified according to any external measurement, normally temperature signal in a photodetector that will have a different reference value depending on the current composition.