Abstract
Wall slip in the flow of powder injection molding (PIM) compounds can be the cause of unrealistically low viscosity values, and can lead to a failure of flow simulation approaches. Regardless of its importance, it has been considered only scarcely in the rheological models applied to PIM materials. In this paper, an online extrusion rheometer equipped with rectangular slit dies was used to evaluate the slip velocity of commercial as well as in-house-prepared PIM feedstocks based on metallic and ceramic powders at close-to-processing conditions. The tested slit dies varied in their dimensions and surface roughness. The wall-slip effect was quantified using the Mooney analysis of slip velocities. The smaller gap height (1 mm) supported the wall-slip effect. It was shown that both the binder composition and the powder characteristic affect slip velocity. Slip velocity can be reduced by tailoring a powder particle size distribution towards smaller particle fractions. The thickness of the polymer layer formed at the channel wall is higher for water-soluble feedstocks, while in the case of the catalytic polyacetal feedstocks the effect of surface roughness was manifested through lower viscosity at smooth surfaces.
Highlights
Powder injection molding (PIM) currently gains enhanced attention due to its merging with additive manufacturing
This means that the thickness of the polymer layer formed at the channel wall was higher than the surface irregularities [12,20] of the tested slit dies
Al2 O3 feedstock to wall slip as a function of the die geometry and surface roughness is generally less pronounced than for ZrO2 compound, as we showed recently [31], their surface characteristics were fairly similar—44 and 47 J/m2 for ZrO2 and Al2 O3, respectively
Summary
Powder injection molding (PIM) currently gains enhanced attention due to its merging with additive manufacturing. The PIM process consists of four steps whose accomplishment allows for the production of small and complex-shaped metal or ceramic parts that is often hardly achievable with traditional metallurgical methods [1,2]. Homogeneous highly filled polymer melt (feedstock) is prepared by compounding metal/ceramic powder into a polymer binder. The binder is an at least three-component system ensuring processability of feedstocks by injection molding, which is followed by its removal from injected parts. This step is called debinding, and can be thermal, solvent, or thermal/solvent combined. A porous powder structure is sintered to its final density
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
