PSI - Issue 54

570 Daniel F.O. Braga et al. / Procedia Structural Integrity 54 (2024) 568–574 Daniel F.O. Braga et al. / Structural Integrity Procedia 00 (2023) 000–000 3 hot forming tools with geometrically complex cooling channels while simultaneously assuring the necessary strength, surface hardness and high temperature strength in the tool contact area.

2. Materials and methods Hybrid SLM-LMD specimens were manufactured out of DIN 1.2709 tool steel (SLM) and TS700 tool steel (LMD). TS700 is a 5 % Chromium tool steel with high hardness and high work temperature, suitable for hot working tools. The SLM section was manufactured on a Trumpf TruPrint 3000 and the LMD on a Trumpf TruLaser Cell 3000, equiped with a 3 kW maximum power laser. SLM process parameters were kept constant and based on previous experience, while LMD depositions were made following the DoE. Table 1 lists the SLM manufacutring parameters for the DIN 1.2709 tool steel with 60 µ m layer.

Table 1. SLM process parameters

Core/Infill

Down-skin

Up-skin

Laser pattern

Chess 5 mm 216W

Chess 5 mm 100W

Stripes 10 mm 240W

Width

Laser power Laser speed Hatch distance Hatch offset

810 mm/s 0.125 mm 0.11 mm

1000 mm/s 0.10 mm 0.10 mm

810 mm/s 0.048 mm 0.10 mm

Down-skin thickness Up-skin thickness

N.A. N.A.

2 layers

N.A.

N.A.

3 layers

For DoE a Central Composite Design (CCD) with a distance of each axial point ( α ) of 1.7 was used, varying laser power, scan speed and powder flow, with the remaining process parameters kept constant. The process parameters are listed in Table 2. The build directions used to manufacture the hybrid SLM-LMD specimens is shown in Fig. 1, as well as the resulting material block prior to machining to final dimensions.

Table 2. LMD process parameters

Level -1

Level 0

Level 1

Laser power Scan speed Powder flow Track width Inert gas flow Track overlap Transport gas flow

1000W

1300W

1600W

700 mm/min 7.5 g/min

900 mm/min

1100 mm/min 12.5 g/min

10 g/min 3 mm 5 l/min 12 l/min

50 %

As per DoE, 20 Run Orders were manufactured and 3 specimens of each were tensile tested at constant cross head speed of 1 mm/min. Strain was measured through digital image correlation (DIC). Specimens were painted with a white base-coat and random speckle pattern of black dots to enable full-field 2D strain measurement in the specimen. Beyond mechanical testing the region of the interface of SLM-LMD was observed with optical microscope. The cross-section was sanded, polished and etched in Nital etchant with 5% concentration in nitric acid for 60 seconds and then analyzed in a ZEISS AxioVert A1 Mat optical microscope.