PSI - Issue 53

Mariana Cunha et al. / Procedia Structural Integrity 53 (2024) 386–396 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

388

3

Initially, for each procedure, the metal chips were submitted to an initial milling of 5 minutes to flatten them. The milling of procedure number 1 for disc milling (PND 1) was performed with two separate batches of 60 grams each for 30 minutes. Subsequently, both batches were combined, resulting in a total of 120 grams, and they were milled again for 10 minutes. Procedure number 2 for disc milling (PND 2) was a continuation of PND 1, the final batch of 120 grams was milled further for another 60 minutes. Procedure number 3 for disc milling (PND 3) consists of 80 minutes milling of a single batch of 120 grams. (Castanheira 2022) conducted a study on the production of sustainable powders from stainless steels, successfully producing powders for L-DED. The procedure PND 1 in this work is adopted from the optimized milling procedure developed by (Castanheira 2022). The sieving of the powder particles was carried out using in accordance with ASTM B214 standard (ASTM 2022). The method involved the use of three standard sieves from Retsch with apertures of 212 ,150 and 38 μm for further insights into the productivity of the powder particle size (PPS) for each milling procedure. Loose and tap density was determined following ASTM B212 (ASTM 2020) and ASTM B527 standard (ASTM 2022), respectively . The flowability of the powder was assessed as per ASTM B213 standard (ASTM 2020). 2.4 Powder Deposition For the deposition process, a COAX12V6 nozzle head manufactured by Fraunhofer IWS, Germany, was used. Additionally, it was connected to a Fraunhofer IWS powder splitter, enabling the separation of the powder material into four distinct channels. To supply the necessary powder, the equipment featured two independent Medicoat AG Disk powder feeders from Mägenwil, Switzerland. These feeders operated smoothly within a range of 0.5 g/min to 100 g/min, ensuring a pulsation-free powder flow. Furthermore, the carrying gas could be modified as required. Both the carrying and shielding gases were provided by an inert gas supply regulated at 6 bar. For the depositions conducted in this project, argon (Ar) Grade 3 was used as the inert gas. The energy source employed was FL3000, a fiber laser manufactured by Coherent, USA. This laser emitted a Gaussian distribution with a wavelength of 1070 ± 10 nm. It operated in continuous wave (CW) mode, providing a maximum power output of 3000 W. The employed parameters for producing depositions are presented in Table 2. Utilizing these parameters, design of experiments (DOE) Taguchi L9 method was implemented to generate eleven distinct combinations of parameters that will be further discussed. The process parameters used for laser processing are given in Table 2. 2.3 Powder Characterization

Table 2 - Parameters for the AISI P20+Ni printing

Parameter type

Parameters

Laser Power Scanning Speed Powder Feed Rate

500, 900, 1800 W

Variable

120, 360, 450, 480, 852 mm.min -1

3, 4, 6, 8 g.min -1 Argon, Grade 3

shield ing gas/carrying gas carrying gas flow rate shield ing gas flow rate

4 liters.sec -1 5 liters.sec -1

Fixed

stand - off distance inclination angle laser spot size

13 mm

5 º

2.1 mm

For each combination of parameters (laser power, scanning speed, and powder feed rate), single line printings were performed and evaluated. Through careful visual analysis of the lines' top and cross-sectional views, the line exhibiting good adhesion, least defects, and optimal linearity were chosen to proceed with printing, using the same parameters. This way, after determining the optimized parameters, the printing of a multi-layered bulk was initiated.