Fused deposition modelling (FDM), one of the most commonly used additive manufacturing techniques in the industry, involves layer-by-layer deposition of melted material to create a 3D structure. The staircase and beading effect caused by the printing process and temperature variation cause delamination and poor surface finish in FDM-printed parts. This hinders the use of these specimens in various applications, which are then usually resolved using pre-processing and post-processing techniques. Higher surface finish in pre-processing is achieved by increasing the resolution, changing layer thickness and optimizing build orientation. However, this increases the processing time considerably. On the other hand, post-processing techniques involve different processes such as mechanical, chemical, thermal and hybrid methods but can affect the mechanical and structural properties of the printed components. This review paper analyses three different aspects in the area of improving the surface finish of FDM-printed parts. First, this article reviews the state-of-the-art attempts made to improve the surface finish of FDM-printed parts concentrated mainly on different vapour polishing techniques and their respective merits and demerits. Second, it focuses on the changes in mechanical properties before and after polishing. Finally, the paper explores the development in the 3D printing of thermosets and composite materials and their post-processing processes and process parameters.

Fused deposition modelling (FDM) is a process of layer-by-layer material deposition using a heated extruder. FDM printed parts have stair-stepped effect and ridge patterns that diminish surface quality. This research intends to develop a low-cost, high-efficiency experimental system for polishing a variety of materials using various chemicals, with a chemical vapour smoothening process. For evaluating the created set-up, tetrahydrofuran (THF) is used and acetone as solvents to polish polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). Taguchi multiparameter optimization was used to optimize the input parameters (reagent volume, temperature, concentration, and time) in the vapour smoothening process. With the ideal input parameters, the roughness of the FDM printed parts was reduced by over 95%. The effectiveness of a vapour smoothening system is better when the system temperature is maintained at the boiling point of the reagent, the reagent is of its highest concentration, and when the specimens placed are placed directly over the ultrasonic mist-maker. The system discussed works best with FDM printed parts having minimum porosity and better quality. The hot chemical vapour smoothing approach reduced specimen flexural strength and increased top layer wear. The findings of this study will help develop a large-scale polishing system for FDM printed thermoplastics and enhance the use of FDM components in sectors that need highly polished parts.