*Article* **A Comparative Analysis of Chemical, Thermal, and Mechanical Post-Process of Fused Filament Fabricated Polyetherimide Parts for Surface Quality Enhancement**

**Ariadna Chueca de Bruijn, Giovanni Gómez-Gras \* and Marco A. Pérez**

IQS School of Engineering, Universitat Ramon Llull, Via Augusta 390, 08017 Barcelona, Spain;

ariadnachuecad@iqs.url.edu (A.C.d.B.); marcoantonio.perez@iqs.url.edu (M.A.P.)

**\*** Correspondence: giovanni.gomez@iqs.url.edu

**Abstract:** Additive manufacturing technologies are increasingly being used in production systems because they shorten product development time and production cost, but surface integrity remains a limitation to meet the standards set by conventional manufacturing. In this research article, two chemical, one thermal, and three mechanical finishing operations are proposed to post-process fused filament fabricated Ultem 9085 parts. Their effects on the parts' surface quality and dimensional accuracy (changes in their width, height, length, and mass) are examined through optical and electron scanning microscopy, and the advantages and disadvantages of each method are discussed. Microscope evaluation has proven to be a powerful tool to observe apparent differences and understand the nature of different morphological changes. Results indicate that chemical and thermal treatments and ball burnishing are good candidates to significantly enhance the finish of the parts, despite requiring the use of solvents or provoking dimensional changes to the parts. The effects of abrasive mechanical treatments are more moderate at a macroscopic scale, but the surface of the filaments suffers the most remarkable changes.

**Keywords:** additive manufacturing; fused filament fabrication; PEI Ultem 9085; postprocessing; finishing operations; surface enhancement; vapor smoothing; thermal annealing; abrasive shot blasting; shot peening
