Wire stripping of metal sheathed thermocouples using lasers.
Probe thermocouples consist of a number of thin delicate wires embedded in a densified ceramic powder inside an ultra-high temperature metal sheath of around 1.5-2mm diameter. The traditional method of exposing the wires is to use a modified lathe to ‘turn’ the metal sheath away without breaking the wires inside. The metal sheath is tough so the cutting forces are high but the wall thickness of the tube is very thin, so the turning process distorts the tube and bends it away from the cutting tool. Also the spiral of swarf produced by the cut must be controlled to prevent it wrapping around the now exposed delicate wires and the lathe tool extrudes the metal creating an inward facing burr on the cut edge which can make an electrical connection to the wires.
DeBe Lasers have developed a laser cutting process which resolves all the traditional failure issues, greatly reducing the reject rate of the process. Laser cutting is a contactless process so there are no forces on the sheath to distort it. The accuracy and repeatability of the laser allows it to completely penetrate the metal sheath but not cut through the ceramic insulator to embedded the wires.
The cut is done in multiple stages creating a final cut edge that is dross free and is radiused, removing any possibility burrs or sharp edges. Finally a cleaning pass is made to remove any loose debris, ceramic or redeposited metal vapour to provide a ready to use product.
To further simplify the customer’s production process instead of rotating the thermocouple the beam delivery system can rotate around the stationary thermocouple assembly.