Design and modeling of abrasive flow finishing of freeform surfaces of FDM printed femoral component of knee implant pattern

The design and manufacture of medical implants is a dynamic and important area of research, both from a medical and an engineering standpoint. For use in the actual fabrication of the end-use implant utilizing the investment casting method, a replica of a knee implant can be produced using the fused deposition modeling (FDM) technique. Whereas there are numerous benefits of the FDM process, the outer surface of the FDM printed parts are subjected to poor surface finishing due to the successive addition of material layers. So FDM printed details need to be post-processed using suitable surface finishing techniques, i.e., abrasive flow machining (AFM) process. This paper describes an experimental investigation on AFM of freeform surfaces of FDM printed femoral component of knee implant replica for investment casting application. The AFM media is made with a base material of corn-starch powder, a carrier medium of EDM oil, and additives of aloe barbadensis miller (aloe vera gel) and glycerin. The rheology of this newly developed AFM media has been measured and optimized for maximum material removal rate. AFM media is also characterized to check its thermal stability and functional elements using thermogravimetric analysis (TGA) and Fourier Transform Infrared (FTIR) spectroscopic method. Finally, the FDM printed pattern of the femoral component of the knee implant is finished using a one-way AFM machine using the newly prepared optimized AFM media. For an FDM printed pattern of a femoral component of a knee implant, the maximum percentage improvement in average surface roughness (Ra) that a medium based on corn-starch (50% corn-starch powder) can achieve is 83%, and the initial surface roughness was reduced by 81.58%, from 9.30 to 02.10 μm.