Fusion zone purification by controlled laser welding

Claim 1

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least two kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least one but less than one hundred megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification; maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and aspirating the weld to remove impurities from the melted metal by establishing a flowing inert gas environment above the melted metal which excludes atmospheric gases from the melted metal and simultaneously prevents plasma formation in the region of the focus laser beam.

Claim 2

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least two kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least one but less than one hundred megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification; maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and aspirating the weld to remove impurities from the melted metal by establishing a flowing inert gas environment above the melted metal which excludes atmospheric gases from the melted metal and simultaneously prevents plasma formation in the region of the focus laser beam.

Claim 6

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in cross section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion of the weld joint during welding; providing a stable beam of radiation from a carbon dioxide laser in a fundamental transverse electromagnetic mode containing at least two kilowatts of power to initiate melting at the surface of the metal; focusing the beam to a spot having a power density of at least one but less than one hundred megawatts per square inch to produce a keyhole cavity in the base metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities from the molten metal escape from the melt before solidification; providing a heat sink at the base of the weld to promote progressive solidification of the metal in the weld zone from the point of deepest penetration in the metal to the surface at which metal melting is initiated; introducing a relative motion of at least 20 inches per minute between the metal and the focused spot to maintain a dynamic equilibrium between the vaporized metal in the keyhole and the adjacent molten metal and to prevent collapse of the keyhole cavity thereby allowing vaporized impurities to escape from the melt prior to solidification; maintaining a layer of argon gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and aspirating the weld to remove impurities from the melted metal by establishing a flowing inert gas environment above the melted metal which excludes atmospheric gases from the melted metal and simultaneously prevents plasma formation in the region of the focus laser beam.

Claim 7

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in cross section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion of the weld joint during welding; providing a stable beam of radiation from a carbon dioxide laser in a fundamental transverse electromagnetic mode containing at least two kilowatts of power to initiate melting at the surface of the metal; focusing the beam to a spot having a power density of at least one but less than one hundred megawatts per square inch to produce a keyhole cavity in the base metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities from the molten metal escape from the melt before solidification; providing a heat sink at the base of the weld to promote progressive solidification of the metal in the weld zone from the point of deepest penetration in the metal to the surface at which metal melting is initiated; introducing a relative motion of at least 20 inches per minute between the metal and the focused spot to maintain a dynamic equilibrium between the vaporized metal in the keyhole and the adjacent molten metal and to prevent collapse of the keyhole cavity thereby allowing vaporized impurities to escape from the melt prior to solidification; maintaining a layer of argon gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and aspirating the weld to remove impurities from the melted metal by establishing a flowing inert gas environment above the melted metal which excludes atmospheric gases from the melted metal and simultaneously prevents plasma formation in the region of the focus laser beam.

Claim 9

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least 2 kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least 1 but less than 100 megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification; maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and isolating the melted metal from atmospheric gases with an environment of inert gas which is flowed above the melted metal.

Claim 10

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of: shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least 2 kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least 1 but less than 100 megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification; maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and isolating the melted metal from atmospheric gases with an environment of inert gas which is flowed above the melted metal.

Claim 11

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of; shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing, the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least 2 kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least one but less than 100 megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification. maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and establishing a flow of inert gas adjacent to the melted metal in order to aspirate the weld and remove impurities from the melted metal while excluding atmospheric gases from the melted metal, and to prevent plasma formation in the region immediately adjacent to the metal.

Claim 12

The method of providing a purified fusion zone through the controlled welding of a metal having an impurity content including in combination the steps of; shaping the metal to eliminate any significant gap between the pieces to be joined to avoid a reduction in the section thickness at the weld joint; cleaning the surfaces of the metal to be joined in the immediate vicinity of the weld zone to remove surface contamination prior to the fusion of the metal in this zone; juxtaposing, the metal in the immediate vicinity of the weld zone to describe a weld joint; clamping the metal to be joined to assure good alignment and to eliminate relative motion at the weld joint during welding; providing a stable beam of laser radiation in a fundamental, transverse electric mode containing at least 2 kilowatts of power to initiate melting at the surface of the metal; focusing the laser beam to a spot having a power density of at least one but less than 100 megawatts per square inch to produce a keyhole cavity in the melted metal in which a column of vaporized metal is formed adjacent to the molten metal and vaporized impurities escape from the melted metal before solidification. maintaining a layer of shield gas adjacent to the weld to avoid chemical reaction between the heated metal and the atmosphere; and establishing a flow of inert gas adjacent to the melted metal in order to aspirate the weld and remove impurities from the melted metal while excluding atmospheric gases from the melted metal, and to prevent plasma formation in the region immediately adjacent to the metal.