Laser cutting has become an increasingly popular method of working a piece of material especially when precise tolerances are necessary. Currently, many laser processing heads incorporate features and devices that help ensure optimal and consistent processing results. A laser processing head typically includes a focusing optic to concentrate the laser beam and a nozzle, usually made of copper, having a conical inner surface tapering toward an outlet aperture for directing a stream of gas such as nitrogen, oxygen, or air coaxial with the focused laser beam.
The inner surface of the nozzle serves as the boundary between the flowing gas at high pressures and the outside world. The roughness of the surface directly influences the turbulence of the flow. Additionally, any discontinuities from machining processes produce friction and turbulence. The laser usually consists of a YAG or CO2 lasing medium, at wavelengths between 1 and 11 microns. Normally the laser is aligned so as to travel through the nozzle without striking it. However, a misaligned laser beam will reflect or glance off of the inner surface of the nozzle. If the reflective properties of the surface are not sufficient the beam will be absorbed resulting in heat that can destroy or deform the contours of the nozzle. In addition, laser reflections off a work-piece during a laser operation may reflect back at the nozzle. This may cause damage to the nozzle if the inner and outer surfaces of the nozzle do not have adequate reflective properties.
The current state-of-the-art uses nozzles that are machined on various high-speed lathes utilizing free machining copper alloys such as tellurium copper. The resulting nozzles while of high quality have a surface roughness inside or 15-20 micro inches RMS and can have burrs and chips left over from the material removal required. A new method of shaping the interior for cold forming a nozzle for a laser includes placing a slug of oxygen-free copper into a die. A mandrel is forced into this slug with a high compressive force causing the copper to cold flow around the mandrel. The inner surface of the slug is an exact replica in reverse of the mandrel and the outside of the slug assumes the shape of the outer retention die.
Further areas of the applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.