Use of 450-808 nm diode lasers for efficient energy absorption during powder bed fusion of Ti6Al4V

Abstract

The additive manufacturing process selective laser melting (SLM) uses a powder bed fusion approach to fully melt layers of powdered metal and create 3D components. Current SLM systems are equipped with either single or multiple (up to four) high-power galvo-scanning infrared fibre laser sources operating at a fixed wavelength of 1064 nm. At this wavelength, a limited laser energy absorption takes place for most metals (e.g. alloys of aluminium have less than 10% absorption and titanium 50-60% absorption). The lower absorption of 1064-nm laser sources requires higher laser powers to compensate for the loss of energy due to reflectivity and fully melt the feedstock material. This makes the use of 1064-nm lasers within current powder bed fusion SLM systems energy inefficient. Further to this, there is limited potential for scale-up of these laser sources within an SLM system architecture due to physical space requirements and high economic cost, placing further limitations on current state-of-the-art SLM productivity. This research investigates the use of low power, highly scalable fibre coupled diode laser sources and the influence of shorter laser wavelengths (450–808 nm) on material absorption and processing efficiency using a diode area melting (DAM) approach. It was found that when processing Ti6Al4V, absorption was 11% higher using 450-nm lasers when compared to using 808-nm lasers and 14% higher than 1064-nm lasers. The maximum powder bed temperature for irradiation at 450 nm and 808 nm was 1920 0C and 1760 0C respectively when using only 3.5 W of laser power. Due to the speed at which the DAM process scans the powder bed, the melt pool cooling rate was much slower (750–1400 0C/s) than traditional SLM (105–106 0C/s). This encouraged the development of β phases within the formed Ti6Al4V component. The low power, low cost, highly compact short wavelength diode laser is viable energy source for future powder bed fusion additive manufacturing systems, with potential for productivity scale-up using a DAM methodology.

Laser Emission Spectroscopy of Graphene Oxide Deposited on 316 Steel and Ti6Al4V Titanium Alloy Suitable for Orthopedics

“…This is due to the lower heat conductivity of titanium compared with steel (~6 W/m∙K for Ti6Al4V [ 17 ] vs. ~18–24 for 316 steel [ 18 ]). On the other hand, it has a higher absorption coefficient for 1064 nm with respect to steel (~65% for Ti vs. 30% for iron [ 19 , 20 ]).…”

In situ melt pool measurements for laser powder bed fusion using multi sensing and correlation analysis

“…The initial heating interval typically takes 0.2 ms. The occurrence of this interval is owing to the power rise time (0.05 ms, measured by the laser manufacturer) of the laser and the possible thin layer of oxidization on the substrate surface, knowing that the absorptivity of the 1064 nm laser of Titanium Oxide is less than 0.1 while the Ti–6Al–4V is over 60% 73 , 74 .

Figure 3 ( a – l ) The selected high-speed X-ray images of the melt pool of Trial #20.

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“…5 , 410 SS is harder to melt by the 1070 nm laser. This is because Ti–6Al–4V has a higher absorptivity at 1070 nm (60%) compared with steel (30%) 74 , 81 . Specifically, Trial #5 (410 SS, 130 W, 2 ms) has the same laser power as Trial #17 (Ti–6Al–4V, 130 W, 0.6 ms).…”

Exploring the Effects of Laser Surface Modification on AISI 301LN Steel: A Micro-Mechanical Study

“…The results showed that due to the shorter wavelength of the diode laser (~808 nm) compared to Nd:YAG (~1064 nm), which leads to more absorption of laser energy, the diode laser produces a higher surface hardness, and also bigger depth and width of hardened zone than the Nd: YAG laser. Moreover, it creates more MHD depth and width than Nd: YAG laser [18]. However, scarce information related to this topic is available in the literature regarding metastable austenitic stainless steel (MASS) and, in particular, by using the Nd:YLF laser to conduct superficial texture and/or patterns at the superficial level [19].…”