Abstract
As is widely known, additive manufacturing (AM) allows very complex parts to be manufactured with porous structures at a relatively low cost and in relatively low manufacturing times. However, it is necessary to determine in a precise way the input values that allow better results to be obtained in terms of microgeometry, form errors, and dimensional error. In an earlier work, the influence of the process parameters on surface roughness obtained in fused filament fabrication (FFF) processes was analyzed. This present study focuses on form errors as well as on dimensional error of hemispherical cups, with a similar shape to that of the acetabular cup of hip prostheses. The specimens were 3D printed in polylactic acid (PLA). Process variables are nozzle diameter, temperature, layer height, print speed, and extrusion multiplier. Their influence on roundness, concentricity, and dimensional error is considered. To do this, adaptive neuro-fuzzy inference systems (ANFIS) models were used. It was observed that dimensional error, roundness, and concentricity depend mainly on the nozzle diameter and on layer height. Moreover, high nozzle diameter of 0.6 mm and high layer height of 0.3 mm are not recommended. A desirability function was employed along with the ANFIS models in order to determine the optimal manufacturing conditions. The main aim of the multi-objective optimization study was to minimize average surface roughness (Ra) and roundness, while dimensional error was kept within the interval . When the simultaneous optimization of both the internal and the external surface of the parts is performed, it is recommended that a nozzle diameter of 0.4 mm be used, to have a temperature of 197 °C, a layer height of 0.1 mm, a print speed of 42 mm/s, and extrusion multiplier of 94.8%. This study will help to determine the influence of the process parameters on the quality of the manufactured parts.
Highlights
Extrusion printing processes such as fused filament fabrication (FFF) allow printing parts with complex shapes without high costs if low-cost machines are employed
The samples have the shape of hemispherical cups, which are similar to the prostheses that are used to replace the acetabula in hip prostheses
The form errors of the manufactured parts were measured inside and outside of the hemispherical cups made of polylactic acid (PLA) material that were printed using FFF technology
Summary
Extrusion printing processes such as fused filament fabrication (FFF) allow printing parts with complex shapes without high costs if low-cost machines are employed. Surface finish, form error, and dimensional quality of the printed parts are not excellent [1,2]. Additive manufacturing (AM) processes have been widely used in different sectors such as the automotive, electronics, and medical sectors. In the latter case, AM has been used to manufacture, among others, surgical guides, phantoms, implants, etc. Prostheses require a smooth surface in those areas which will be in contact with sliding elements. They require low form errors, so that they are as similar as possible to the original bone. It is important to have a low concentricity error in order to ensure a good fit between the different elements and good operation of the prosthesis
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