Fused Filament Fabrication (FFF) has become one of the most commonly used additive manufacturing methods for polymeric materials. By development of highly filled feedstocks FFF can also be applied to shape metal filled filaments and obtain solid metal parts after debinding and sintering . Therefore, the shaping, debinding and sintering could present a method for low cost additive manufacturing of metal objects of complex shape .
In this work, a FFF Filament filled with 316L steel powder at 55 vol.-% was investigated and the parameters during the respective process steps were optimized. Shaping is realized using a common desktop FFF printer with a heated bed. A two-step debinding process enables successful debinding of the printed components: After chemical extraction of the main binder component (TPE) and generation of a network of interconnected pores, the remaining backbone polymer (PP) is removed by thermal debinding. The previously generated pore network serves for removing of decomposed polymer during thermal debinding. Therefore, the degradation rate of the polymer must be adjusted to the velocity of removal of degradation products. Consequently, the heating rates during thermal debinding were adjusted, to avoid an increase in internal pressure. The debinding temperatures are chosen high enough to generate pre-sintering neck growth and thereby ensure the stability of the completely debound samples. By choosing of appropriate sintering parameters, it is possible to obtain components of high density of up to 95%. Mechanical characterization shows that albeit at slightly lower strength, fracture elongations similar to rolled materials are achievable.
As the binder formulation of the filaments can be applied for a variety of metal powders, different metals can be combined in one component during the shaping step. Combined FFF of Cu and stainless steel was investigated. For the realization of successful co-sintering the difference of thermal expansion and shrinkage of the two metals was analyzed using dilatometer measurements. Adjustment of sintering parameters allows co-sintering of the two combined metals leading to solid components.