Page 11 - 3DMP Summer 2022

customizable LPBF test platform, it provides complete access to the hardware, optics and software overlays. As a result, the OAS offers unparalleled control of the path-planning variables, optical hardware, motion-control digital input for triggering and integration, on-and-off axis ports for sensor integration, and multiple sensor-mounting ports within the process cham- ber. Using the OAS, EWI has executed numerous government and commercially funded programs to correlate in-situ process-monitoring data with known quality metrics, and in this program, to demonstrate closed-loop process control.
Process Parameters for Trials
We employed a circular stirring pattern along with the laser parameters for the coupon trials (Fig. 3), which show, for Type 316L stainless steel, the typical as-built microstructure for lin- ear hatching and variations in microstructure possible with stirred hatching. The stirred hatching builds to display larger grains, columnar grains, less-elongated grains and/or combi- nations of large and small grains, depending on the stirring parameters employed.
AM Insights 3D SS316L STIRRED BUILD PARAMETERS
Build ID
SS-1 SS-2 SS-3 SS-4 SS-5 SS-6
Speed, mm/s
1450 1650 1650 1100 1450 1250
Power, W
275 175 325 225 175 125
Hatch Spacing, mm
0.18 0.10 0.18 0.18 0.14 0.10
Hatch Spacing, mm
0.11 0.11 0.15 0.15 0.15 0.19 0.19 0.23 0.23
NI718 STIRRED BUILD PARAMETERS
Build ID
Speed, mm/s Power, W
960 285 1120 250 1120 250 1120 285 960 250 1120 215
TI-6AL-4V STIRRED BUILD PARAMETERS
Ni-1
Ni-2
Ni-3
Ni-4
Ni-5
Ni-6
Ni-7 1280 250 Ni-8 1120 285 Ni-9 960 285
SYSTEM HARDWARE
Laser
IPG Photonics YLR -700
Galvo-scanner
Scanlabs Hurryscan 20
Motion controller
Aerotech A3200
Recirculating filter system
EOS M280; argon/nitrogen
Build-plate temperature capacity
500 C
Build envelope
125 by 125 by 50 mm
PROCESS-MONITORING SENSORS
Recoater-axis-mounted laser profilometer
Keyence LJV-7060
Recoater-drive sensor
Hall-effect Sensor
Two-color pyrometer (on-axis)
Stratonics ThermaViz
Infrared imager
Micro-Epsilon TIM 640
Photodiode
Thorlabs PDA36A
Build ID Speed, mm/s
Ti-1 1950
Ti-2 1700
Ti-3 1700
Ti-4 1950
Ti-5 2450
Ti-6 1700
Ti-7 1950
Ti-8 3000 335 Ti-9 1950 225 Ti-10 1450 180
Fig. 2
Power, W
Hatch Spacing. mm
0.14 0.22 0.14 0.18 0.14 0.22 0.18 0.22 0.18 0.18
130 180 130 180 180 130 130
Fig. 4 shows the typical as-built microstructure for linear hatching and variations in microstructure possible with stirred hatching for Inconel 718. Grain refinement and the formation of necklace microstructure, containing both large and small grains, are apparent in the stirred hatching builds.
Fig. 5 shows the typical as-built microstructure for linear
hatching and variations in microstructure possible with stirred hatching for Ti-6Al-4V.
Summary and Takeaways
As seen in the material studies, LPBF microstructures (the columnar microstructure visible in the linear hatched builds) can be coarsened or refined to various levels through the application of stirred hatch parameters. These positive results for three popular LPBF alloys show that laser-stirred hatching effectively can be used to tailor microstructure in 3D builds. Grain refinement, reduction of anisotropy and texture alteration are accomplished by laser stirring through balancing heat input, oscillation travel speed, linear travel speed and thermal-response time of the material being processed, to ensure that grains are broken up after partial processing solidification. The same factors
3DMPmag.com
SUMMER 2022 • 3D METAL PRINTING | 9