Method for Efficient Laser Cutting Based on Surface Darkening

Abstract

A method of laser cutting with improved efficiency for reflective and transparent materials is described. The method improves the absorption of the laser beam in the material being cut. Laser cutting is typically performed with a flow of a high pressure gas, termed assist gas, directed at the cutting point. Per this invention, a gaseous additive is added into the flow of the assist gas. The additive decomposes or reacts when it comes into contact with the hot laser-irradiated surface of the material and leaves a residue of elemental carbon (such as soot) on the surface. The residue of elemental carbon has excellent beam absorption characteristics and serves to efficiently transfer the energy from the laser beam to the material, thus enabling higher cutting speeds and greater maximum material thicknesses for the same laser optical power.

Claims

1. A method of laser cutting comprising: directing a laser beam onto a material being cut, thereby producing a heated zone on said material being cut; directing a flow of gas onto said heated zone, wherein said flow of gas contains a chemical additive which produces a form of elemental carbon when in contact with said heated zone.

2. The method according to claim 1 wherein said form of elemental carbon is soot.

3. The method according to claim 1 wherein said chemical additive is selected from the group consisting of hydrocarbons and halogenated hydrocarbons.

4. The method according to claim 1 wherein said chemical additive is selected from the group consisting of benzene, toluene, acetylene, ethylene, propene, propane, butane, and dichloromethane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 shows diagrammatically the gas handling system of the preferred embodiment.

[0023] FIG. 2 shows diagrammatically the gas handling system of an alternative embodiment where the additive is a liquid.

DETAILED DESCRIPTION OF THE DRAWINGS

[0024] The gas handling system of the preferred embodiment is shown schematically in FIG. 1. The gas system serves to deliver the assist gas with the admixed additive to the cutting head. An inert gas 1 such as nitrogen is sourced from a liquid storage tank, usually at a pressure below that required for the cutting process. A flow regulator 2 determines the flow rate of the inert gas. Gaseous additive 3 is sourced, for instance, from a compressed gas cylinder. Another flow regulator 4 controls the flow rate of the additive. If the additive is not gaseous at room temperature, its vapor in an inert carrier gas can be used instead. The additive flow and the inert gas flow are mixed in a gas mixer 5. The mixer outputs the resulting flow to a compressor 6 that increases the gas pressure to that required in the cutting process. The assist gas containing the additive is then directed to the cutting head 7.

[0025] In an alternative embodiment, the chemical additive is a liquid at ambient conditions (for example benzene, C.sub.6H.sub.6), and the gas handling system is modified accordingly, as shown in FIG. 2. The inert gas 1 from the liquid storage tank is directed through a flow regulator 2 to an evaporator 5 (which may be heated) rather than a gas mixer. The liquid additive 3 is fed into a liquid flow regulator and injector 4, which in turn feeds it into the evaporator 5. After the liquid is vaporized into the inert gas in the evaporator 5, the vapor-containing assist gas proceeds to the compressor 6 and the cutting head 7, as in the preferred embodiment. Care must be taken to ensure that the condensation of the additive does not occur anywhere along the path of the modified assist gas.

CITATIONS

[0026] 1. U.S. Pat. No. 5,380,976. Process for high quality plasma arc and laser cutting of stainless steel and aluminum. [0027] 2. U.S. Pat. No. 6,521,864. Method and apparatus for the laser cutting of mild steel or structural steel with a multifocus optical component. [0028] 3. U.S. Pat. No. 6,891,126. High-speed laser cutting method with adapted gas.