An Overview of the Latest Progress in Internal Surface Finishing of the Additively Manufactured Metallic Components

Abstract

Fast progress in near-net-shape production of parts has attracted vast interest in internal surface finishing. Interest in designing a modern finishing machine to cover the different shapes of workpieces with different materials has risen recently, and the current state of technology cannot satisfy the high requirements for finishing internal channels in metal-additive-manufactured parts. Therefore, in this work, an effort has been made to close the current gaps. This literature review aims to trace the development of different non-traditional internal surface finishing methods. For this reason, attention is focused on the working principles, capabilities, and limitations of the most applicable processes, such as internal magnetic abrasive finishing, abrasive flow machining, fluidized bed machining, cavitation abrasive finishing, and electrochemical machining. Thereafter, a comparison is presented based on which models were surveyed in detail, with particular attention to their specifications and methods. The assessment is measured by seven key features, with two selected methods deciding their value for a proper hybrid machine.

Keywords: abrasive flow machining; additively manufacturing; cavitation abrasive finishing; electrochemical machining; fluidized bed machining; internal surface finishing; magnetic abrasive finishing; roughness analysis.

Figure 1

Breakdown of the active ISO/ASTM standard on AM.

Figure 2

Methodology of the literature survey.

Figure 3

Categories of different internal surface finishing methods. (AFM: abrasive flow machining; MAAFM: magnetic-assisted abrasive flow machining; MRAFF: magnetorheological abrasive flow finishing; UFP: ultrasonic flow polishing; RAFF: rotational abrasive flow finishing; UAAFM: ultrasonic-assisted abrasive flow machining; MAF: magnetic abrasive finishing; MAAJM: magnetic-assisted abrasive jet machining; HCAF: hydrodynamic cavitation abrasive finishing; UCAF: ultrasonic cavitation abrasive finishing; ECF: electrochemical finishing; FBM: fluidized bed machining; FBAJM: fluidized bed abrasive jet machining.).

Figure 4

Schematic of abrasive flow machining process [59].

Figure 5

Schematic of the material removal in AFM technique [61].

Figure 6

Optical images and height color maps of straight conformal channels in the as-built state and after the AFM process; ((a–c) refer to different types of conformal cooling) [30].

Figure 7

Schematic diagram of the additively manufactured copper and related surface roughness profiles (a) before and (b) after surface finishing in a medium consists galactomannan polymer, glycerol solution, and abrasive particles [63].

Figure 8

The surface roughness values at different temperatures with three abrasive particles [65].

Figure 9

(a) Schematic illustration of MAF process, (b) front view of finishing process on span portion, and (c) on rise portion [76].

Figure 10

Schematic of the rotating-vibrating magnetic polishing method, (a) full view, (b) cross-sectional view [29].

Figure 11

Surface roughness of internal channel in L-PBF IN718 part after different polishing methods [29].

Figure 12

Stress–strain curves of the fully heat-treated sample with homogenization process (H) and aging process (A) (without the MAF process), sample H + A + MAF (with the MAF process after the full heat treatment), and sample H + MAF + A (with the MAF process between the homogenization and aging processes) [88].

Figure 13

Schematic of (a) abrasive jet machining, (b) fluid bed abrasive jet machining [99].

Figure 14

Average surface roughness of the AFB-treated samples for different speeds of particles and various treatment times [103].

Figure 15

SEM photographs of the top surfaces of 316L stainless steel (a) before and (b) after MJP polishing. Composition analysis (c) before and (d) after MJP polishing [105].

Figure 16

(a) Details of the HCAF chamber, (b) SEM image of the SiC abrasive used in the finishing operation, (c) Single abrasive with sharp edges [28].

Figure 17

SEM micrograph from the surface of the (a) as-built internal channel and (b) after internal surface finishing using the HCAF process [28].

Figure 18

(a–c) L-PBF rocket injector prototype, (d) internal channels for surface finishing; (1) linear, (2) stepped, and (3) non-linear channels [27].

Figure 19

Details of MJ-HCAF process used for the surface finishing of Inconel 625 internal channels [28].

Figure 20

Influence of micro-abrasives in the surface finishing of the AM channels, (a–c) steps of materials removal, (d) as-built surface, (e) hydrodynamic abrasive finished surface, (f) hydrodynamic cavitation abrasive finished surface showing abrasive micro cuts, (g) as-built surface morphology with irregularities, and (h) smooth and uniform texture after surface finishing [28].

Figure 21

(a,b) Surface roughness parameters, (c) surface hardness and (d) residual surface stress of EB-PBF Ti-6Al-4V parts before and after surface finishing [114].

Figure 22

Schematic diagram of electrochemical machining [139].

Figure 23

Schematic of the UAECDG machine [149].

Figure 24

The inner wall of a hole before and after UAECDG treatment [148].

Figure 25

(a) SEM image of the 5 min electropolished Hastelloy X; (b) higher magnification SEM image of the cellular structure, with the yellow line corresponding to the start and the end position for the EDS analysis; (c) EDS analysis showing the wt% variation of the Cr, Fe, Ni, and Mo along the scanning direction [150].

Figure 26

(a) Surface finish of Ti60 alloy after ECM at different current densities [151], (b) surface morphologies of the Inconel 718 superalloys with a sequence of H (homogenization) + MAF + A (aging) [88], (c) cylindrical aluminum workpiece before and after AFM [152], and (d) surface finished AA 2024 O alloy after FBM [97].