Variation of texture anisotropy and hardness with build parameters and wall height in directed-energy-deposited 316L steel

Calibrated Closed-Loop Control to Reduce the Effect of Geometry on Mechanical Behaviour in Directed Energy Deposition

“…Earlier work by Bi (2006a), had reported a similar effect on single-walled 316 L steel samples, and also showed corresponding trends in microstructure and hardness. A further development by Chechik et al (2020) used side-view imaging to monitor DED of thin walled samples (6 hatches, 2.7 mm thickness), and found cooling rate to be higher close to the baseplate, as expected from a smaller melt pool. This raises the possibility that different machine set-ups and clamping strategies could change the strength of this heat sink and cause differences in the manufactured product.…”

Multi-Faceted Monitoring of Powder Flow Rate Variability in Directed Energy Deposition

“…The hopper was loaded with approximately 3 kg of GA316 powder and > 200 g of powder was run through the pipework to allow the system to stabilise before collecting data. The maximum hopper rotation speed is 10 rpm, and data was collected at 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 rpm, covering the standard range of powder flow rates found in literature [14][15][16] . The data was collected as a single run, with 5 min at each turntable speed stepping up from 0.5 rpm to 3.0 rpm.…”

“…From literature, powder flow rate is generally between 5 g/min and 20 g/min in DED, although some use flow rates outside this range [14][15][16] . As the hoppers are volumetrically controlled, the material density and packing density have an influence on the volume of powder required to achieve a target mass flow rate.…”

“…To understand how this can impact the process, it is necessary to consider the distance that a DED nozzle moves relative to any variation in powder flow rate. At a nozzle speed of 2000 mm/min, if mass flow drops for just 1 second it affects 30 mm of melt track, and at higher speeds the affected region will be even longer [15] .…”

Controlling grain structure in metallic additive manufacturing using a simple, inexpensive process control system

“…The mechanical properties of a metal are dependent on the scale of the microstructure (including grain size, dendrite arm spacing and precipitate dispersion) and the heat treatments experienced 8 . The scale of the microstructure is dependent on the cooling rate during solidi cation, which can be correlated with the melt pool size 9,10 . This leaves many values which could be controlled to improve component homogeneity.…”