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AssigneeHypertherm, Inc.
InventorsRichard W. Couch, Jr., Nicholas A. Sanders, Zhipeng Lu, Lifeng Luo, Staffan C. O. Stenfelt
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Plasma arc or laser cutting uses a mix of reactive and reducing gas flows to cut sheets of stainless steel, aluminum and other non-ferrous metals. The reducing gas flow to the cut varies as a percentage of the total gas flow to maintain a reducing atmosphere down through the cut, but to leave a predominantly oxidizing atmosphere at the intersection of the cut and the bottom surface of the sheet being cut. In plasma arc cutting these flows can also be characterized as either a plasma gas flow, one that forms the arc, or a shield gas flow that surrounds the arc. The reactive gas is preferably a flow of air, oxygen, nitrogen, carbon dioxide or a combination of these gases. The reducing gas is preferably hydrogen, hydrogen 35, methane, or a mixture of these gases. For aluminum, the reactive gas is preferably air or nitrogen and the reducing gas is preferably methane or a mixture of methane and air. In laser cutting the reducing gases such as methane can be used by mixing them with reactive assist gases.
A metal cutting process for use with a plasma arc cutting torch for producing a high quality kerf in stainless steel and non-ferrous workpieces that have an upper surface adjacent the torch and a bottom surface opposite the torch, where the torch uses a total gas flow to the kerf, comprising, forming a portion of the total gas flow from a reducing gas, and adjusting the ratio of said reducing gas flow to said total gas flow to produce a predominantly reducing atmosphere generally at the region defined by the bottom surface and the kerf, said adjusting including increasing the proportion of said reducing gas introduced into the kerf with respect to the total gas flow in coordinating with an increasing of the thickness of the workpiece.
A process for high quality cutting using a plasma arc torch to cut stainless steel and non-ferrous metal workpieces with the torch using a total gas flow through the torch that enters the kerf, comprising forming said total gas flow of at least one reactive gas and at least one reducing gas, and adjusting the relative proportions of said at least one reducing and at least one reactive gases so that said kerf is substantially sheeny and has substantially no bottom dross, said adjusting including increasing the proportion of said reducing gas introduced into the kerf with respect to the total gas flow in coordination with an increasing of the thickness of the workpiece.
A process for producing a high quality cut in sheets of stainless steel and non-ferrous metals with a plasma arc cutting torch located opposite an upper surface of the sheet and cuts a kerf that extends to a bottom surface of the sheet and where the torch uses a total gas flow from the torch to the kerf, comprising, forming said plasma gas at least in part of a reactive gas, forming said total gas flow at least in part of a reducing gas, and controlling the ratio of the reducing gas flow to the total gas flow such that the reducing gas is consumed in the kerf leaving a negligible concentration of said reducing gas at said bottom surface, said controlling including increasing the proportion of said reducing gas introduced into the kerf with respect to the total gas flow in coordination with an increasing of the thickness of the workpiece.
Dependencies are inferred from the claim text.