R. Ghosh, Air Products & Chemicals, Inc., Allentown, PA; J. Knopf, D. Gibson, T. Mebrahtu, Air Products and Chemicals, Allentown, PA; G. Currie, TEKIA, Inc., Irvine, CA
Machining intraocular lenses is an acceptable industry practice, especially with rigid hydrophilic polymer materials. For softer hydrophobic materials, however, with glass transition temperatures (Tg) at or below room temperature, traditional machining is a challenging proposition due to the flexibility of the workpiece at room temperature and smearing of the soft material due to cutting. Cooling approaches involving cold air guns and ice-blocking have been unsuccessful, since they do not lower the temperature below the glass transition temperature of the material. In the present work, a new cooling approach involving liquid nitrogen is discussed that allows generation of machined surfaces comparable to rigid hydrophilic material. The new cryogenic machining technology also allows the part to be held at a constant temperature during machining, resulting in a predictable machining process and avoidance of cracking and other surface defects at extremely cold temperatures.
Machining intraocular lenses is an acceptable industry practice, especially with rigid hydrophilic polymer materials. For softer hydrophobic materials, however, with glass transition temperatures (Tg) at or below room temperature, traditional machining is a challenging proposition due to the flexibility of the workpiece at room temperature and smearing of the soft material due to cutting. Cooling approaches involving cold air guns and ice-blocking have been unsuccessful, since they do not lower the temperature below the glass transition temperature of the material. In the present work, a new cooling approach involving liquid nitrogen is discussed that allows generation of machined surfaces comparable to rigid hydrophilic material. The new cryogenic machining technology also allows the part to be held at a constant temperature during machining, resulting in a predictable machining process and avoidance of cracking and other surface defects at extremely cold temperatures.
Summary: Machining intraocular lenses is an acceptable industry practice, especially with rigid hydrophilic polymer materials. For softer hydrophobic materials, however, with glass transition temperatures (Tg) at or below room temperature, traditional machining is a challenging proposition due to the flexibility of the workpiece at room temperature and smearing of the soft material due to cutting. Cooling approaches involving cold air guns and ice-blocking have been unsuccessful, since they do not lower the temperature below the glass transition temperature of the material. In the present work, a new cooling approach involving liquid nitrogen is discussed that allows generation of machined surfaces comparable to rigid hydrophilic material. The new cryogenic machining technology also allows the part to be held at a constant temperature during machining, resulting in a predictable machining process and avoidance of cracking and other surface defects at extremely cold temperatures.
