Laser Welding Equipment

Abstract

A laser welding apparatus (10) is provided that includes an evacuable chamber (12) incorporating a transparent region (16) through which laser radiation (14) can pass to heat a weld region (32) on a workpiece (26), and a gas knife (46) configured to generate a gas flow (48), the primary chamber (40) and the secondary chamber (42) being connected to one another by a permeable passage (44) to allow the laser radiation (14) to reach the workpiece (26), and a pumping system (30) is connected to the secondary chamber (42) and configured to draw the gas flow (48) from the secondary chamber (42). One end of the permeable passage (44) is located between the gas knife (46) and the pumping system (30). The pumping system (30) includes an inlet (50) substantially axially aligned with the direction of travel of the gas flow (48). The inner surface of the sub-chamber (42) has a smoothness value in the range of 0.8 to 1.6 μmRa, and the sub-chamber (42) is maintained at a lower vacuum than the main chamber (40).

Description

[Technical field]

[0001] The present invention relates to laser welding apparatus, and more particularly to such apparatus which performs welding in a vacuum. [Background technology]

[0002] Laser welding of metal parts using high power disk and fiber lasers has become common in the automotive and aerospace manufacturing industries because laser welding imparts very low heat input to the part compared to some other welding techniques, which results in better weld quality and less distortion of the manufactured part.

[0003] Typically, a laser is coupled into a transmission fiber to deliver laser energy to the welding tool, and the laser radiation is focused to a fine spot through a convex optical lens, resulting in an intense spot of heat that vaporizes material to form the keyhole weld. A flat cover glass, acting as a protective window, is generally placed between the optical lens and the parts to be welded to protect the lens from welding vapors and spatter generated by the welding.

[0004] Because protective windows are relatively expensive to replace, shielding gases are often used to help keep them clean and to interrupt the creation of a plasma plume above the keyhole weld. The plasma plume is created by the intense heat of the welding laser, which vaporizes the material and the local atmosphere; once the plume is established, it can scatter a significant portion of the laser beam, subsequently requiring the laser to input more power to achieve the same weld penetration. However, using more input power widens the weld profile, allowing more heat into the parts being welded, resulting in poorer weld quality and increased distortion.

[0005] Shielding gases are only partially effective in reducing harmful plasma plumes, and to improve laser welding, welding is often performed in a vacuum chamber, because the reduced atmosphere prevents the plasma plume from establishing outside the weld keyhole. The vacuum also reduces the boiling point of the material being welded, so the amount of power required to create the keyhole weld is reduced, and the lack of air particles results in reduced weld porosity. In vacuum laser welding, an additional vacuum laser-transmitting window is disposed in the path between the focusing lens and the protective window to maintain the vacuum chamber seal.

[0006] During vacuum laser welding, when the protective window is contaminated by welding vapor, the transmittance of the window begins to decrease, and the decrease in transmittance means the decrease in weld strength. When more vapor accumulates and solidifies on the window, it absorbs the laser energy and heats up rapidly, causing deformation and failure of the weld. To prevent contamination of the protective window, gas such as argon is often introduced into the vacuum chamber adjacent to the protective window to try and prevent the vapor particles from reaching the protective window. Summary of the Invention [Problem to be solved by the invention]

[0007] The introduction of gases into vacuum chamber welding creates problems that are detrimental to some of the benefits gained by welding in a vacuum chamber. The introduction of gases requires a more powerful set of pumps to maintain a high vacuum in the chamber, making it uneconomical and in some cases impossible to reach high vacuum levels. As gas particles are scattered upon entering the chamber, some interact with and combine with the welding vapors to form soot, resulting in an undesirable weld finish when welding materials that is unacceptable in some industries. [Means for solving the problem]

[0008] According to the invention, there is provided a laser welding apparatus comprising an evacuable chamber incorporating a transparent area or window through which the laser radiation can pass to heat a weld area on a workpiece, and a gas knife configured to generate a flow of gas, the evacuable chamber comprising a main chamber in which the welding takes place and at least one sub-chamber in which the gas knife is located, the main chamber and the at least one sub-chamber being connected to each other by a transparent passage to allow the laser radiation to reach the workpiece, and a pumping means or system comprising a vacuum pump is connected to the sub-chamber and configured to draw a flow of gas from the sub-chamber. Thus, in use, the flow of gas is prevented from entering the main chamber and interacting with the weld area, and weld vapors and spatter are diverted from depositing on the transparent area and are instead removed as the flow of gas is pumped out of the sub-chamber.

[0009] Preferably, one end of the permeate passage is located between the gas knife and the pumping means and gas is drawn across the end of the passage by the pump.

[0010] The pumping means or pump may comprise an inlet substantially axially aligned with the direction of gas flow, and thus the inlet is preferably substantially perpendicular to the permeate passage.

[0011] The sub-chamber may be tapered at an end proximal to the pumping means and at least a portion of the sub-chamber proximal to the pumping means may be frusto-conical in shape.

[0012] Preferably, the inner surface of the antechamber has a smoothness value in the range of 0.8 to 1.6 μm Ra to ensure that the gas from the knife encounters as little surface friction as possible.

[0013] The pumping means is desirably configured to generate a flow rate of gas across the permeable passage in the range of 0.1 to 5 L / min. The flow rate is selected to ensure that gas is drawn across the permeable passage fast enough to divert the welding vapor from reaching the transparent region.

[0014] The antechamber is preferably maintained at a lower vacuum than the main chamber. A number of interconnected sub-chambers may be provided, with a gas knife located in one or more of the sub-chambers.

[0015] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view of a laser welding apparatus according to the present invention; [Diagram 2] FIG. 2 is a perspective view of an antechamber forming part of the laser welding apparatus; [Diagram 3] FIG. 2 is a cross-sectional view of the antechamber. [Figure 4] FIG. 4 is a schematic cross-sectional view of a second embodiment of a laser welding apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] explanation The laser welding apparatus 10, shown diagrammatically in Figure 1, comprises an evacuable welding chamber 12 in which a beam of laser radiation 14, within the dashed line in Figure 1, is directed through a protective window 16 and focused into a fine image using a convex lens (not shown) outside the chamber 12 and a proximal vacuum window 16. A wall 22 defines an opening 24 in the chamber 12 through which the beam 14 passes to reach a workpiece 26 requiring welding. One or more pumping systems or pumps 28, 30 are provided for evacuating the chamber 12 and maintaining the vacuum.

[0018] In use, the laser beam 14 is focused to a fine spot 32 on the component 26 to form a keyhole weld.

[0019] The chamber 12 includes a main welding chamber 40 and an ancillary chamber 42 connected to one another by a permeable passageway 44, through which the laser beam 14 travels to reach a workpiece 26 located within the main chamber 40. A pump 28 serves to evacuate the main chamber 12 and maintain a vacuum high enough for laser welding to occur. The ancillary chamber 42 has a separate pumping system 30 and is maintained at a lower vacuum than the main chamber 40.

[0020] Disposed within the antechamber 42 is a gas knife 46 having a thin, elongated nozzle for generating a laminar flow of gas, the knife 46 having an associated gas supply 47. The gas knife 46 is disposed on one side of the passageway 44 such that a flow of gas 48 generated by the gas knife 46 extends across and over an upper end 49 of the passageway 44 towards an inlet 50, the inlet 50 being disposed on the other side of the passageway 44. The pumping system 30 is configured to continuously operate at a speed that draws the gas jet 48 across the chamber 42 and into the pumping port 50 for extraction, substantially preventing the gas 48 from entering the passageway 44 and the main chamber 40. The port 50 is substantially axially aligned with the gas knife 46 to ensure that pumping is along the primary direction of travel of the gas 48 as it exits the knife 46. The direction of travel of the gas flow 48 is substantially parallel to the flat inner surface of the window 16 and substantially perpendicular to the vertical axis of the passageway 44. Typically, when the gas entering through gas supply 47 is at room temperature, the flow rate is 0.1-5 L / min and the velocity is up to 400 m / s.

[0021] In use, welding vapor or splatter 52 from the welding area 32 along the passageway 44 passing through the opening 24 is diverted from reaching the window 16 by the constant flow of gas 48 across the chamber 42 towards the inlet port 50. By locating the gas knife 46 within the antechamber 42, the area surrounding the workpiece 26 is not subject to the gas flow, thereby preventing the generation of soot at the workpiece 26. The antechamber 42 is typically about 10 -3 It operates at a moderate vacuum of mbar, and since a higher vacuum is required for laser welding at the workpiece 26 , a higher vacuum is maintained in the chamber 40 proximate the welding area 32 .

[0022] The secondary chamber 42 is shown in more detail in Figures 2 and 3 and comprises a substantially rectangular housing 60 in which the gas knife 46 is located, and a tapered neck portion 62 connected between the housing 60 and the pumping port 50. Other configurations for the chamber 42 are possible, such as a frusto-conical shape having sufficient internal volume to accommodate the gas knife 46.

[0023] Opposing openings 66, 68 are disposed in an outer wall 70 of the housing 60 to allow a laser beam to transmit through the chamber 42 and through the passageway 44. The window 16 is secured over the opening 68 with a connector portion 72 defining a passageway 44 secured about the opening 66 and used to connect the secondary chamber 42 to the main welding chamber 40.

[0024] Within the chamber 42, all surfaces are constructed to be as smooth and non-abrupt as possible, and whenever possible corners are smoothed into arcs rather than maintained as vertical mating surfaces (see corner 74). All internal surfaces of the chamber 42 are typically ground during manufacture to give a smoothness in the range of 0.8-1.6 μm Ra, where Ra is the roughness average value. This ensures that the gas 48 encounters as little surface friction as possible. Any interaction with a vertically sloped surface would introduce turbulence into the gas 48, potentially causing a flow of gas 48 away from the port 50 and down the passageway 44 into the main welding chamber 40. Thus, smoothing the internal surfaces of the chamber 42 ensures that a thin jet of gas 48 flows smoothly into the pumping port 50 without interacting with any vertically sloped surfaces. This ensures that the working chamber 40 is free of soot and maintained at the vacuum level desired by the operator, while maintaining the transmittance of the optics 16. This arrangement protects the window 16 from deposition of welding vapors and prevents the gas 48 from reaching the main chamber 40 .

[0025] Multiple sub-chambers can be used, and referring to Figure 4, two sub-chambers are used as an example, each with a gas knife 46, 46' and a pumping port 30, 30'. These stacked chambers can have a number of different configurations, for example no gas knife in the sub-chamber closest to the main chamber 40 to allow more effective pumping, multiple sub-chambers of the same size to allow better window protection with multiple gas flows, or multiple sub-chambers with various no gas knife / with gas knife configurations.

Claims

1. A laser welding apparatus comprising an evacuable chamber incorporating a transparent region through which laser radiation can pass to heat a welding region on a workpiece, and a gas knife configured to generate a gas flow, wherein the evacuable chamber comprises a main chamber in which welding is performed and at least one sub-chamber in which the gas knife is located, the main chamber and the at least one sub-chamber are connected to each other by a transmission passage to enable laser radiation to reach the workpiece, and pumping means is connected to the sub-chamber and configured to draw out the gas flow from the sub-chamber.

2. The laser welding apparatus according to claim 1, wherein one end of the transmission passage is located between the gas knife and the pumping means.

3. The laser welding apparatus according to claim 1, wherein the pumping means comprises an inlet substantially axially aligned with the direction of travel of the gas flow.

4. The laser welding apparatus according to claim 1, wherein the sub-chamber tapers at one end proximal to the pumping means.

5. The laser welding apparatus according to claim 1, wherein at least a part of the sub-chamber proximal to the pumping means is frustoconical in shape.

6. The laser welding apparatus according to claim 1, wherein the inner surface of the sub-chamber has a smoothness value in the range of 0.8 to 1.6 μm Ra.

7. The laser welding apparatus according to claim 1, wherein the pumping means is configured to generate a gas flow rate across the transmission passage in the range of 0.1 to 5 L / min.

8. The laser welding apparatus according to claim 1, wherein the sub-chamber is maintained at a lower vacuum than the main chamber.

9. The laser welding apparatus according to any one of claims 1 to 8, wherein a plurality of interconnected sub-chambers are provided and a gas knife is provided in one or more of the sub-chambers.

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