Processing and characterizations of 2%PF/silica sand core–shell composite powders by selective laser sintering with a higher transmittance fiber laser

Previous investigations on selective laser sintering were focused on opaque powders from the primary outer surface absorption of the powder bed. In the paper, the sintering behavior of “transparent” materials with a higher transmittance over 90% is demonstrated. Phenol–formaldehyde resin- (PF-) coated silica sand composite powders were sintered by a fiber laser considering their high transmittance at 1064 nm wavelength. The affluences of process parameters on the dimension, shrinkage depth and porosity of the sintered sample were studied, and microstructures by optical microscopy (OM) and scanning electron microscopy (SEM) were observed. Furthermore, the absorption and transmission of laser beam within the powder bed were investigated based on a developed analytical model and the Zemax optical design program. Experimental results showed that composite powders could be successfully sintered by the fiber laser. That was because poor absorption of laser energy could still raise the temperature of the PF shell over its glass transition point. However, the heat absorbed within the powder bed was not uniform by the action of the convergence of the micro spherical lens from the “transparent” composite powder. Finally, some components were manufactured and the feasibility of using this process to build casting molds was verified.

► Selective laser sintering of the “transparent” powders first studied.
► The “transparent” materials with a higher transmittance over 90% at 1064 nm wavelength are sintered by a fiber laser.
► The sintering characteristics of the transparent powders are demonstrated.
► For laser sintering the “transparent material”, both the surface and inside absorptions are performed in SLS.