Mohsin, I. U. (2011). Modeling of thermal de-binding and sintering processes in metal injection molding [Dissertation, Technische Universität Wien]. reposiTUm. http://hdl.handle.net/20.500.12708/160232
The metal injection molding (MIM) process is an efficient method for the high volume production of complex shaped components from powders for high performance applications. In the present thesis, kinetic analysis and modeling were used as model approach to simulate the thermal de-binding and sintering processes of MIM parts. The advantage of kinetic modeling is that all parameters for the simulation are obtained directly from the measurement of the real material with low experimental effort. Three systems, pure copper, Fe-12wt%Cu and heavy alloy parts from W-8%Ni-2%Cu powder mix were fabricated by metal injection molding using a feedstock with 50 vol% binder. Dilatometer specimens with the dimension of 12 x 6 x 4 mm³ and thermo-gravimetric specimens with dimension of 3.5 x 3.5 x 6.0 mm³ were used. The soluble part of the binder was removed by organic solvent debinding in n-heptane. The solvent de-waxed specimens were used to study thermal de-binding of each system using evolved gas analysis technique. The thermo-gravimetric technique coupled with infrared and mass spectrometry provides sufficient knowledge to understand the degradation and reaction mechanisms during thermal de-binding of the backbone binder of metal injection molded compacts. This information is helpful in formal kinetics modeling of selected materials fabricated through the metal injection molding technique. Dilatometer was used to measure the shrinkage kinetics of brown (=thermally debinded) specimens, and a kinetic model was established by importing data into the Netzsch software package. Rate controlled debinding and sintering steps were employed to validate kinetic models, and good agreement between simulation and experimental results showed the validity of the models and the method. Thermo-physical data, on which temperature field calculation is strongly dependent, were also measured with best of available resources in AIT (Austrian Institute of Technology) laboratory using DSC, TGA-FTIR-MS, DIL and LFA instruments. Then finite element models were formulated by embedded kinetics model and thermo-physical data of the system. The formulated FE model described the binder behavior during the thermal de-binding and sintering. The model helps to calculate the binder contents at different positions and temperatures during the backbone burnout process and the shrinkage during subsequent sintering. The results from finite element models were compared with those from an experimental production furnace, and satisfactory agreement was found. However, the simplified temperature field calculation in the FE (no heat transfer by convection or radiation) and unknown conditions during the experiment in the laboratory furnace (inhomogeneous temperature field, actual gas conditions) make comparison between experiments and simulation difficult. For more accurate results, temperature field calculation can be improved by applying real furnace conditions (gas flow, temperature gradient inside the furnace, heat loss etc.).