Investigation of laser polishing of part surfaces produced by additive manufacturing

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Thesis Type: Doctorate

Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2022

Thesis Language: Turkish

Student: ŞAFAK NESLİ

Supervisor: Oğuzhan Yılmaz

Abstract:

Additive manufacturing (AM) is one of the advanced manufacturing methods that enables the production of highly complex parts, which cannot be produced with traditional production methods, with less material expense. However, the high roughness values of the surfaces, especially of the samples produced by powder bed AM methods, is one of the biggest obstacles to the direct use of these samples after production. Laser polishing (LP) is a potential finishing technique used to reduce the surface roughness of parts produced using different manufacturing methods, including additive manufacturing. In this thesis, LP process was applied onto the surfaces of Inconel 718 samples produced by selective laser melting (SLM) and Ti-6Al-4V produced by electron beam melting (EBM ), which are one of the AM methods, and it was aimed to investigate the concept of surface integrity by analyzing the surface morphology, microstructure, microhardness properties and performing numerical modeling. According to the morphological analysis results, the surface roughness improved by 90% for the Inconel 718 sample and 94% for the Ti-6Al-4V sample, respectively. The dendritic and columnar microstructures of the SLE-Inconel 718 sample were removed by the LP process, and the (α+β) microstructure of the EIE-Ti-6Al-4V sample transformed into a needle-like (α) structure with the LP process. In addition, the LP process increased the microhardness values of Inconel 718 and Ti-6Al-4V sample surfaces by approximately 18% and 12.5%, respectively. Numerical modeling was carried out in order to examine the thermal behavior between the laser beam and the material surface during the LP process. With the thermal model, the remelted and heat-affected zone formed by the effect of the LP process was determined and these zones were compared with optical analyses. As a result, the experimental studies were confirmed 95% for the remelted zone and 90% for the heat-affected zone. 

Key Words : Additive manufacturing, laser polishing, surface integrity, microstructure, microhardness, numerical modeling