Christian Kukla

Additive Manufacturing of Metallic and Ceramic Components by the Material Extrusion of Highly-Filled Polymers: A Review and Future Perspectives

Additive manufacturing (AM) is the fabrication of real three-dimensional objects from metals, ceramics, or plastics by adding material, usually as layers. There are several variants of AM; among them material extrusion (ME) is one of the most versatile and widely used. In MEAM, molten or viscous materials are pushed through an orifice and are selectively deposited as strands to form stacked layers and subsequently a three-dimensional object. The commonly used materials for MEAM are thermoplastic polymers and particulate composites; however, recently innovative formulations of highly-filled polymers (HP) with metals or ceramics have also been made available. MEAM with HP is an indirect process, which uses sacrificial polymeric binders to shape metallic and ceramic components. After removing the binder, the powder particles are fused together in a conventional sintering step. In this review the different types of MEAM techniques and relevant industrial approaches for the fabrication of metallic and ceramic components are described. The composition of certain HP binder systems and powders are presented; the methods of compounding and filament making HP are explained; the stages of shaping, debinding, and sintering are discussed; and finally a comparison of the parts produced via MEAM-HP with those produced via other manufacturing techniques is presented.

Effect of Particle Size on the Properties of Highly-Filled Polymers for Fused Filament Fabrication

Fused Filament Fabrication (FFF) could replace injection molding as the shaping step in a process similar to powder injection molding (PIM). Herein after shaping by using a highly-filled polymer the part is debound and sintered to obtain a solid part of metal or ceramic. New feedstock materials have been developed that can be printed using conventional FFF equipment. And after debinding and sintering stainless steel parts can be obtained. However, there are many parameters that can affect the performance of the FFF feedstock materials. One important parameter is the particle size distribution of the filler particles. In this paper, feedstocks containing 316L steel powder with different particle size distributions were characterized in terms of viscosity and mechanical properties, and tested regarding the printability using a conventional FFF machine. It has been observed that the particle size significantly affects the properties of feedstock materials and thus their ability to be printed.Fused Filament Fabrication (FFF) could replace injection molding as the shaping step in a process similar to powder injection molding (PIM). Herein after shaping by using a highly-filled polymer the part is debound and sintered to obtain a solid part of metal or ceramic. New feedstock materials have been developed that can be printed using conventional FFF equipment. And after debinding and sintering stainless steel parts can be obtained. However, there are many parameters that can affect the performance of the FFF feedstock materials. One important parameter is the particle size distribution of the filler particles. In this paper, feedstocks containing 316L steel powder with different particle size distributions were characterized in terms of viscosity and mechanical properties, and tested regarding the printability using a conventional FFF machine. It has been observed that the particle size significantly affects the properties of feedstock materials and thus their ability to be printed.

Controlled shear stress method to measure yield stress of highly filled polymer melts

Powder injection moulding (PIM) is a multi-stage process to manufacture metallic or ceramic complex, functional parts in large quantities and with high material requirements. The flow in PIM filling process is a complicated non-isothermal problem with viscoelasticity effects and instabilities. The exact description of the whole process of the flow is very difficult. The existence of a yield stress on PIM-feedstock depends on particle interactions within the polymer matrix. Further factors, like powder loading and dispersion during the measurements, are influencing the rheological characterisation of PIM-feedstocks. Additionally, inertial and gravitational effects can have an influence for systems with a very low viscous matrix. Quantifying yield stress, however, must be done carefully because the value obtained depends on the analytical technique used. Knowing the flow behaviour of PIM-feedstock is necessary for successful filling simulation of PIM. In this context, the yield behaviour of a stainless stee...