Author:

Abstract:

Additive manufactured surfaces, specifically metal powder bed fusion (PBF) surfaces, present unique challenges for measurement due to their complex topographic nature [1]. One of the challenges is to properly separate local surface texture from the form deviations of the specimen. Especially since AM enables manufacturing of intricate forms, it may be hard to distinguish the texture from the intended form. Also the surface signature changes: AM surfaces often have significant figures compared to traditional manufacturing methods. In this study a semi-sinusoidal shaped specimen including flat and inclined areas is used. The effect of two phenomena on the surface roughness was considered: the local gradient of the form and remelting. In order to define and remove the form, a filtering method based on Legendre polynomials was developed, using lower order polynomials to a certain degree while the higher order polynomials are filtered in a way that maintains a Gaussian filter characteristics, as it is normally used in roughness analysis [2]. In this way, the form, wavinness and roughness can be separated in a single filtering operation, where the removal of the significant form is independent of the roughness filtering. Therefore, there is no interaction and ‘double filter’ effects are avoided as well. This is illustrated by analysis of the sine-shaped specimen where the surface topography was modified in several stages of AM-production and remelting. It is shown that the form, waviness and roughness can be attributed to separate and independent regions in the polynomial order spectrum. A rational choice can thus be made regarding the polynomial degree that is still considered as part of the form and from which subsequently a useful roughness/wavinness distinction can be made. The presentation will explain these procedures and make a comparison with more traditional form and roughness filter methods. [1] Leach R. K., Bourell D., Carmignato S., Donmez A., Senin N., Dewulf W. Geometrical metrology for metal additive manufacturing. CIRP Annals. 68, 2, 2019. [2] Haitjema H, Surface profile and topography filtering by Legendre polynomials. Surface Topography: metrology and Properties 9(1) 015017, 2021