PSI - Issue 49

Federico Fazzini et al. / Procedia Structural Integrity 49 (2023) 59–66 / Structural Integrity Procedia 00 (2023) 000 – 000

62

4

conducted in a furnace under an atmosphere consisting of 100% clean and dry hydrogen or argon. The sintering cycle comprised two distinct phases. The first phase involved thermal debinding, where the temperature was increased at a rate of 5 K/min until reaching 600°C and maintained at that temperature for 1 hour. The second phase encompassed the actual sintering process, commencing from 600°C and gradually ramping up to 1300°C at a heating rate of 5 K/min. The sintering temperature of 1300°C was sustained for 3 hours, followed by furnace cooling, BASF Process Guidelines Ultrafure 17-4 PH (2023). Table 1 presents the typical mechanical properties of 17-4 PH for Metal Injection Molded Parts, as specified in the MPIF 35 standard (2020), along with the properties guaranteed by BASF, BASF Technical Data Sheet Ultrafuse 17-4 PH (2023). Table 1. Mechanical properties of 17-4 PH. Mechanical properties Standard MPIF 35 (as sintered) BASF Ultrafuse (as sintered) Density [kg/m 3 ] 7500 7600 Ultimate Tensile Strength [MPa] 900 990 Yield Strength [MPa] 730 765 Elongation at Break [%] 6 4 Young´s Modulus [GPa] 190 191 Printing parameters A full factorial manufacturing campaign was employed based on the principles of Design of Experiments (DoE), Montgomery (2019), during the shaping phase to investigate the effect of varying FFF process parameters on the sintered product mechanical properties and dimensional tolerances. Preliminary trials were conducted to determine the suitable parameter range for processing the material using FFF. The first investigated parameter was the deposition speed, which refers to the rate at which the nozzle deposits the material. It plays a significant role in determining the fabrication time of the manufactured part, along with the layer thickness. The second parameter is the extrusion temperature, which has influence on the material viscosity and rheological behaviour, which significantly differ from conventional polymer materials used in FFF. Additionally, the combination of deposition speed and extrusion temperature affects the onset of internal residual stresses, which can potentially lead to part failure, Wang et al. (2006). The third parameter considered was the raster angle, which represents the infill line strategy. Despite being relatively understudied, it exerts a notable influence on the properties and anisotropy of the manufactured object. Table 2 lists the parameter values. For each of the 12 parameter combinations, a code consisting of a triplet of numbers was assigned (Table 2), with the first number indicating the deposition speed, the second one representing the extrusion temperature, and the third one denoting the raster angle. For convenience, these combinations were also associated with corresponding letters, which were marked on the surface of the sample. This facilitated the identification of the parameter combinations even after the debinding and sintering processes. Table 2. Printing parameters combination – factorial design parameters. Name Deposition speed (mm/min) Extrusion Temperature (°C) Raster angle (°) 111 - A 15 230 0 112 - B 15 230 0-90 113 - C 15 230 0-45-90-135 121 - E 15 250 0 122 - I 15 250 0-90 123 - N 15 250 0-45-90-135 211 - O 30 230 0 212 - P 30 230 0-90 213 - S 30 230 0-45-90-135 221 -V 30 250 0 222 - X 30 250 0-90 223 - Z 30 250 0-45-90-135 2.2.