Additive manufacturing of metal-polymer hybrid parts: the influence of as-printed LPBF surface roughness on the joint strength

Abstract

As-printed Laser-Powder Bed Fusion (LPBF) surfaces can provide anchoring spots for the infiltration of polymer printed by Fused Filament Fabrication (FFF), enhancing metal-polymer joint strength. This work evaluates the influence of the as-printed LPBF surface roughness and FFF parameters on the strength of Ti-6Al-4V/PA-CF joints produced by this process combination. A three-point bending testing method based on ISO 14679:1997 was deployed, whereby the energy dissipated by the joint interface was measured. Roughness was varied by 3D-printing the substrate with different inclination angles; Height and printing speed of the coating layer (the polymer layer in direct contact with the metal) were also varied. Data was interpreted using a combination between Decision Tree and Gradient Boosting Regression, ultimately suggesting that printing speed is the prominent parameter followed by inclination angle for joint strength. Additionally, the combined effect of low printing speed and inclination angle resulted in the highest energy absorption at the interface (>200 J).

Manufacturing of Metal–Polymer Hybrid Parts Using a Desktop 3-Axis Fused Filament Fabrication 3D-Printer

“…The present publication can be considered a direct continuation of the work reported in [3,12], both dealing with the optimization of AddJoining parameters for the said material combination (using rolled and 3D-printed substrates, respectively). Therefore, details concerning parameter selection, joint microstructure, mechanical properties and micromechanical fracture mechanisms will be mostly omitted.…”

“…Specific geometry details and dimensions for each demonstrator are presented in the following sub-sections. The "direct assembly" strategy implemented for Demonstrator 1 used the same approach as reported by most AddJoining studies [2][3][4][5][6][7][8][9][10][11][12], whereby the ensuing joint strength was strictly a function of the bond strength of both the metal/coating layer and coating layer/subsequent layer interfaces. Demonstrator 2, however, applied a different approach, whereby (1) a portion of the polymer/composite is 3D-printed by FFF, (2) the The "direct assembly" strategy implemented for Demonstrator 1 used the same approach as reported by most AddJoining studies [2][3][4][5][6][7][8][9][10][11][12], whereby the ensuing joint strength was strictly a function of the bond strength of both the metal/coating layer and coating layer/subsequent layer interfaces.…”

“…At the coupon level, dimensions are relatively small, which may cause a heat build-up effect that, together with heated bed and/or heated chamber, increases substrate temperature even further. In fact, this additional heat build-up provided by the hot end itself can be considered relevant for the temperature profile and even beneficial for the joint strength, as observed before [3,12]. However, whether such an effect can be carried over to the manufacturing of larger parts is still unknown.…”

“…The schematics of the AddJoining approach is presented in Figure 1. To date, the AddJoining technique (whether named as such or not) has been studied at the coupon level with several material combinations and from different perspectives [2][3][4][5][6][7][8][9][10][11][12]. While several different approaches have been utilized to improve metal-polymer joint strength, little to no attention has been devoted to the manufacturing of larger and more complex parts using the proposed technique.…”

“…While more-recent 5-axis setups can be considered more advanced technologically and therefore more capable of addressing the aforementioned challenges, they are also considerably more expensive and much less user-friendly, both in terms of slicing algorithms, toolpath generation and machine tailoring/modification. Therefore, to preserve aspects that have made desktop 3D-printers extremely popular while still being able to manufacture 3D models over large and/or complex (i.e., nonflat) substrate geometries, it is necessary to introduce printing strategies that can work To date, the AddJoining technique (whether named as such or not) has been studied at the coupon level with several material combinations and from different perspectives [2][3][4][5][6][7][8][9][10][11][12]. While several different approaches have been utilized to improve metal-polymer joint strength, little to no attention has been devoted to the manufacturing of larger and more complex parts using the proposed technique.…”