Machinability of IFS Empress (R) 2 framework ceramic: Potential for ceramic dentures

Using ceramic materials for an automatic production of ceramic dentures by CAD/CAM is a challenge, because many technological, medical, and optical de mands must be considered. The IPS Empress(R) 2 framework ceramic meets most of them. This study shows the possibilities for machining this ceramic wit h economical parameters. The long life-time requirement for ceramic denture s requires a ductile machined surface to avoid the well-known subsurface da mages of brittle materials caused by machining. Slow and rapid damage propa gation begins at break outs and cracks, and limits life-time significantly. Therefore, ductile machined surfaces are an important demand for machine d ental ceramics. The machining tests were performed with various parameters such as tool grain size and feed speed. Denture ceramics were machined by j ig grinding on a 5-axis CNC milling machine (Maho HGF 500) with a high-spee d spindle up to 120,000 rpm. The results of the wear test indicate low tool wear. With one tool, you can machine eight occlusal surfaces including rou ghing and finishing. One occlusal surface takes about 60 min machining time . Recommended parameters for roughing are middle diamond grain size (D107), cutting speed nu(c) = 4.7 m/s, feed speed nu(ft) = 1000 mm/min, depth of c ut a(e) = 0.06 mm, width of contact a(p) = 0.8 mm, and for finishing ultra fine diamond grain size (D46), cutting speed nu(c) = 4.7 m/s, feed speed nu (ft) = 100 mm/min, depth of cut a(e) = 0.02 mm, width of contact a(p) = 0.8 mm. The results of the machining tests give a reference for using IPS Empr ess(R) 2 framework ceramic in CAD/CAM systems, (C) 2000 John Wiley & Sons, Inc.