The laser micro-spot welding process was studied to implement a sheet lamination process-based methodology for the fabrication of austenitic stainless steel scaffolds. AISI 302 sheets with a thickness of 254 μm were laser cut and laser welded. Experimental tests were carried out with different values of average laser power (i.e., 180, 200, and 220 W) and different exposure times (25, 50, 75, 100, 125 ms). The micro-spot welds were visually inspected according to the ISO 13919-1 Class B requirements. Spot welds were qualitatively characterized, and weld dimensions were measured (i.e., penetration depth, top, middle, and bottom width and the heat-affected zone (HAZ)) to identify the cross-sectional shape. Furthermore, process efficiencies (i.e., coupling, melting, and process) were studied. A seam welding model was adapted to calculate the required exposure time and was used to obtain a micro-spot weld to accomplish the quality requirements of the scaffold. A scaffold prototype was designed and manufactured using the selected parameters by experimental trials and using the mathematical model (i.e., a laser power of 220 W and an exposure time of 45 ms).
A novel manufacturing approach was used to fabricate metallic scaffolds. A calibration of the laser cutting process was performed using the kerf width compensation in the calculations of the tool trajectory. Welding defects were studied through X-ray microtomography. Penetration depth and width resulted in relative errors of 9.4%, 1.0%, respectively. Microhardness was also measured, and the microstructure was studied in the base material. The microhardness values obtained were 400 HV, 237 HV, and 215 HV for the base material, HAZ, and fusion zone, respectively. No significant difference was found between the microhardness measurement along with different height positions of the scaffold. The scaffolds’ dimensions and porosity were measured, their internal architecture was observed with micro-computed tomography. The results indicated that geometries with dimensions under 500 µm with different shapes resulted in relative errors of ~2.7%. The fabricated scaffolds presented an average compressive modulus ~13.15 GPa, which is close to cortical bone properties. The proposed methodology showed a promising future in bone tissue engineering applications.
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