| Direct metal deposition (DMD) has gained increasing attention in the area of rapid manufacturing and repair. It has demonstrated the ability to produce fully dense metal parts with complex internal structures that could not be achieved by traditional manufacturing methods. However, this process involves extremely high thermal gradients and heating and cooling rates, resulting in residual stresses and distortion, which may greatly affect the product integrity. The purpose of this thesis is to study the features of thermal stress and deformation involved in the DMD process. Utilizing commercial finite element analysis (FEA) software ABAQUS, a 3-D, sequentially coupled, thermo-mechanical model was firstly developed to predict both the thermal and mechanical behavior of the DMD process of Stainless Steel 304. The simulation results show that the temperature gradient along height and length direction can reach 483 K/mm and 1416 K/mm, respectively. The cooling rate of one particular point can be as high as 3000 K/s. After the work piece is cooled down, large tensile stresses are found within the deposited materials and unrecoverable deformation exists. A set of experiments then were conducted to validate the mechanical effects using a laser displacement sensor. Comparisons between the simulated and experimental results show good agreement. The FEA code for this model can be used to predict the mechanical behavior of products fabricated by the DMD process and to help with the optimization of design and manufacturing parameters. |
