Micro extrusion of high aspect ratio bi-lumen tubes using 17-4PH stainless steel feedstock

The manufacturing of metallic micro multi-lumen tubes of high length to diametrical aspect ratio for biomedical and multi-fluidic applications is still a challenge for the current manufacturing methods. The recent research advancements suggested metal particles loaded feedstock extrusion processing as a highly promising method for manufacturing metallic micro multi-lumen tubes where conventional metal extrusion and other feedstock processing technologies are constrained. Feedstock extrusion of micro multi-lumen tubes was inhibited by the absence of understanding on extrusion behavior of feedstocks for attaining high aspect ratio parts. The feedstock micro extrusion processing also experienced difficulties in maintaining the geometrical accuracy and surface finish due to lack of knowledge on influence of extrusion parameters on the properties of the extruded parts and absence of a quality control strategy during extrusion. In this research work, the effect of feedstock extrusion parameters on the dimensional variation as well as surface finish of the extruded multi-lumen tubes are studied by extruding high aspect ratio micro bi-lumen tubes using biocompatible grade 17-4PH stainless steel feedstock. A methodology called ‘product fingerprint’ combined with multi-objective optimization on the basis of ratio analysis (MOORA) method has been studied to assure the quality of the tubes in-line by identifying and monitoring very specific features of the tubes at optimum process conditions. The study showed that extrusion parameters such as extrusion temperature and screw speed have significant influence on diameters, roundness of the tube as well as lumens and the surface roughness. High aspect ratio bi-lumen tubes of optimum dimensional quality with an average green state areal surface roughness value of 1.97 μm were achieved at optimum process parameters levels. This research demonstrated how to manufacture micro bi-lumen tubes made of 17-4PH stainless steel with unrestricted length and even more, control their quality by monitoring couple of identified product fingerprint features of bi-lumen tube, such as external diameter of tube as well as its roundness and varying the process parameters.