Green Machining of Gelcast Ceramic Materlals

Abstract

Ceramic green bodies prepared by gelcasting were shown to be readily machinable using WC cutting tools. Samples of alumina and silicon nitride were examined. It was found that a gelcasting formulation which uses a high molecular weight crosslinking agent produces a green body having superior machining characteristics. Samples fabricated with a lower molecular weight cross-linker exhibited a poor machined surface finish due to chipping. Machining tests showed that using a 3.2 m (0.125 in.) diameter cutting tool at a cutting speed of 162.5 c d s e c (64 ft./sec.) to machine a flat-bottomed groove 3.2 mm wide and 9.5 mm deep (0.125 x 0.375 in.) using three passes, feed rates ranging from 0.85 to 6.35 c d s e c (0.33 to 2.50 in./sec.) could be used without damaging the sample.

Development of Low‐Toxicity Gelcasting Systems

“…However, there was not any cloudy layer above the sediment, which indicated that none of the finest particles were still in suspension. In contrast, dispersants 1, [8][9][10][11]16, and 17 exhibited cloudy layers that were higher than the control (dispersant 7), which indicated that they were holding the finest particles in suspension quite well, even after 3 weeks. These dispersants were selected for additional study.…”

Machining and Ceramic/Ceramic Joining to Form Internal Mesoscale Channels

“…However, dried gelcast parts are readily machined by metalworking tools. Nunn and Kirby machined 55‐mm‐diameter gelcast alumina and silicon nitride discs using a lathe, drill press, surface grinder, and a computer‐numerically‐controlled (CNC) 3‐axis milling machine 44 . The CNC mill with tungsten‐carbide bits was used to machine channels with rectangular cross section (3.2 mm across and 9.5 mm deep) using three passes at feed rates from 0.85 cm/sec to 6.35 cm/sec and a plunge depth of approximately 3.2 mm per pass 44 .…”

“…Nunn and Kirby machined 55‐mm‐diameter gelcast alumina and silicon nitride discs using a lathe, drill press, surface grinder, and a computer‐numerically‐controlled (CNC) 3‐axis milling machine 44 . The CNC mill with tungsten‐carbide bits was used to machine channels with rectangular cross section (3.2 mm across and 9.5 mm deep) using three passes at feed rates from 0.85 cm/sec to 6.35 cm/sec and a plunge depth of approximately 3.2 mm per pass 44 . Although Nunn and Kirby 44 noted that “early machining experiments showed that tool steel wore rapidly when used for cutting gelcast ceramics,” they did not supply further data on the wear rate of the tool steel bits or the tungsten‐carbide bits they used subsequently, except to state wear rate of the tungsten‐carbide bits was much lower than the rate for the tool steel bits 44 .…”

Green ceramic machining: A top-down approach for the rapid fabrication of complex-shaped ceramics

“…10-30 MPa) than that from conventionally pressed or cast ceramic green bodies. 21 However, gelcasting has not been widely accepted by industry due to the toxic monomers used in the processing. Cold isostatic pressing (CIP) with the addition of polymer binders has also been reported to make strong green ceramics for green machining.…”