Net-Shape Forming of Sintered Microcellular Foam Parts

Abstract

The time required to saturate a polymer with gas increases with the square of the diffusion length. This has effectively limited the application of the batch process of producing microcellular foam to thin parts. Saturating powdered polymer rather than solid polymer and then sintering the particles to create a net-shape microcellular part is an alternative technique. The advantage of sintering microcellular parts from saturated polymer powder is the great reduction in the diffusion length reduces saturation time from days to minutes. Saturation time is decoupled from part thickness. A prototype has been designed and tested in which saturated polymer powder is blown into a mold under the pressure of the saturating gas. The absorbed gas plasticizes the polymer. The powder is compressed into a solid preform to remove macroscopic voids, increase the diffusion distance to slow gas desorption, and to increase thermal conductivity. The preform is then heated, the mold expanded, and microcellular part formed to net shape in a closed mold. Preliminary tests with polycarbonate, amorphous polyethylene terephtalate (PET-G), and cellulose acetate have been successful.