Reflectance and transmittance of TrueForm^TM powder and its composites to CO₂ laser

Purpose: The purpose of this paper is to report on a study of the effect of glass microsphere (GMS) and potassium bromide (KBr) powder as an additive on the reflectance and transmittance of TrueForm^TM acrylic-styrene co-polymer (TF) powder to CO₂ laser during selective laser sintering (SLS).

Design/methodology/approach: GMSs and KBr powder were chosen because glass is opaque to CO₂ laser while KBr is transparent. The GMSs were treated with silane coupling agent and hydrofluoric acid to study the surface effect on the optical properties of TF/GMS blends. KBr powder was blend with TF powder in an attempt to modify the penetration depth of the laser in the powder bed. An integrating sphere was used to measure the reflectance of the powder bed. In the measurement of transmittance, a power meter was placed below the powder layer, which was supported by a KCl disc, to register the transmitted laser energy through the powder layer.

Findings: For the TF/GMS blends, smaller GMSs gave a higher reflectance while the surface treatments had little effect. The transmittance of both the polymer and the blends were very low. Although bulk KBr is highly transparent to CO₂ laser, adding 30 vol% of KBr powder to TF hardly increased the transmittance of the powder bed.

Research limitations/implications: Experiments were carried out on a modified laser engraving machine rather than a commercial SLS machine. The laser energy density used was lower than that for normal SLS processes and no significant changes of physical condition of the powder bed were inflicted. The results only indicate the optical properties in the initial state.

Practical implications: The effects of transparent and non-transparent fillers on the optical properties of the powder bed are presented. Originality/value: This work furthers the understanding of heat absorption behavior of the powder bed during SLS.