Abstract
Despite numerous applications of Fused Filament Fabrication (FFF), the poor surface finish, being an inherent defect, is major obstruction against utilization of prototypes for rapid casting applications. The conventional finishing methods are effective, however, the dimensional stability is compromised which is completely unacceptable in case of biomedical implants as minute dimension variations may lead to post-operative complications. The paper explores possibilities to produce chemically finished plastic replicas of hip implant through FFF which can be further used as patterns for investment casting. An advanced post-processing technique i.e. Chemical Vapor Smoothing (CVS) is tested to improve surface characteristics and dimensional accuracy of ABS replicas. The repeatability and consistency of coupled CVS and FFF processes is tested through experimentation and statistical analysis in order to endorse an alternative process for mass production of biomedical implants. The Taguchi L18 DOE was used to perform experiments which measures impact of two input parameters of FFF i.e. orientation angle and density, and four parameters of Chemical Vapor Smoothing i.e. pre-cooling time, smoothing time, smoothing time and number of cycles. The multi response optimization technique was employed to acquire optimum set of parameters yielding best surface finish, dimensional accuracy and surface hardness and hence, the overall desirability of 0.7891 was achieved. The process capability and reliability was tested at optimum settings by manufacturing twenty replicas by measuring surface roughness, hardness and dimensional accuracy at different locations of parts. It was observed that values of Cp for all the response parameters was greater than 1.33 while Cpk was greater than 1. The analysis of histograms and capability indices reveal that the FFF-CVS process carried out at optimized conditions can be defined as “statistically controlled” for fabrication of ABS replicas for biomedical applications.
