GB2612361A

GB2612361A - Laser welding apparatus

Info

Publication number: GB2612361A
Application number: GB2115646.8A
Authority: GB
Inventors: Plumb Paul; Ince Harrison; Nentwich Max
Original assignee: Aquasium Technology Ltd
Current assignee: Aquasium Technology Ltd
Priority date: 2021-11-01
Filing date: 2021-11-01
Publication date: 2023-05-03
Also published as: GB202115646D0; WO2023073349A1

Abstract

A laser welding apparatus comprising an evacuatable chamber 12 with a region 16 through which laser radiation 14 is transmissible to weld a workpiece 32, 26, and a gas knife 46 to generate a stream of gas 48, wherein the main (welding) 40 and (at least one) subsidiary (gas knife) chambers 42 are connected by a transmission passage 44 to enable laser radiation 14 to reach the workpiece 26. A pump 30 is connected to the subsidiary chamber 42 to draw the stream of gas 48 from the chamber, and the pump inlet 50 may be substantially axially aligned with the direction of travel of the gas 48. The subsidiary chamber 42 may have a smoothness value in range 0.8-1.6μm Ra for an inner surface and may be maintained at a lower vacuum than the main chamber 40.

Description

Title: Laser Welding Apparatus

Field of the Invention

This invention relates to laser welding apparatus, and in particular such apparatus undertaking welds in a vacuum

Background to the Invention

Laser welding of metallic components using high powered disc and fibre lasers has become common place in automotive and aerospace manufacturing industries because in laser welding gives very low heat input into a part compared with some other welding techniques This leads to a higher weld quality and less distortion of a manufactured part Typically a laser is coupled into a transmission fibre for delivery of laser energy to the welding tooling, with the laser radiation focused to a fine spot through a convex optical lens so that an intense spot of heat is generated which vaporises material to create a keyhole weld. A flat cover glass acting as a protective window is generally positioned between the optical lens and the part being welded to protect the lens from weld vapour and spatters generated by the weld.

The protective window is relatively expensive to replace and so shielding gases are often used to assist in keeping the protective window clean and also to interrupt the generation of a plasma plume above the keyhole weld. The plasma plume is generated by the intense heat of the weld laser vaporising the material and the local atmosphere and once the plume is established, it can cause a significant portion of the laser beam to be scattered which then requires the laser to input more power to achieve the same weld penetration. However using more input power widens the weld profile and puts more heat into the part being welded, so reducing weld quality and increasing distortion.

Shielding gas is only partially effective at reducing the detrimental plasma plume and to improve laser welding often welding takes place within a vacuum chamber because the reduced atmosphere prevents the plasma plume from being able to establish outside of the weld keyhole. The vacuum also decreases the boiling point of the material being welded so reducing the amount of power required to create a keyhole weld, and the lack of air particles creates a reduction in weld porosity. In vacuum laser welding an extra vacuum laser transmission window is disposed in the path between the focal lens and the protective window, so maintaining the seal for the vacuum chamber.

During vacuum laser welding if the protective window becomes contaminated by weld vapour, the transmissivity of the window will start to drop and any reduction in in transmission will mean a reduction in weld intensity. As more vapour deposits and solidifies on the window, it will absorb the laser energy and will rapidly heat up causing deformation and failure of the weld. To prevent contamination of the protective window, a gas such as argon is often introduced into the vacuum chamber adjacent to the protective window to try and prevent the vapour particles from reaching the protective window.

Introducing gas into a vacuum chamber weld creates problems that are detrimental to some of the advantages gained by welding in a vacuum chamber. The introduction of the gas requires a more powerful pump set to maintain a high vacuum in the chamber making it uneconomical and, in some cases, impossible to reach high vacuum levels.

Due to the scattering of gas particles upon entering the chamber, some will interact and combine with the weld vapour to create a soot that leads to an undesirable weld finish that is unacceptable when welding materials in some industries.

Summary of the Invention

In accordance with the invention, there is provided laser welding apparatus comprising an evacuatable chamber incorporating a transparent region or window through which laser radiation is transmissible to heat a weld region on a workpiece and a gas knife configured to generate a stream of gas, wherein the evacuatable chamber comprises a main chamber in which welding takes place and at least one subsidiary chamber in which the gas knife is located, the main chamber and the at least one subsidiary chamber connected together by a transmission passage to enable laser radiation to reach the workpiece, and a pumping means or pumping system comprising a vacuum pump is connected to the subsidiary chamber and is configured to draw the stream of gas out of the subsidiary chamber. Thus in use the stream of gas is prevented from entering the main chamber and interacting with the weld region, and weld vapour and sputter is diverted from depositing on the transparent region and is instead removed as the stream of gas is pumped out of the subsidiary chamber.

Preferably one end of the transmission passage is situated between the gas knife and pumping means, with gas being drawn across the end of the passage by the pump in The pumping means or pump may comprise an inlet substantially axially aligned with a direction of travel of the stream of gas, and thus the inlet is preferably substantially perpendicular to the transmission passage The subsidiary chamber may be tapered at one end proximal the pumping means, and at least part of the subsidiary chamber proximal the pumping means may be fmstro-conical in shape Preferably an inner surface of the subsidiary chamber has a smoothness value in range Ra so as to ensure gas from the knife encounters as little surface friction as possible.

The pumping means is desirably configured to generate a flow rate of the stream of gas across the transmission passage in the range in the range 0.1-5L/min. The flow rate is selected to ensure the gas is drawn across the transmission passage fast enough to divert the weld vapour from reaching the transparent region.

The subsidiary chamber is preferably maintained at a lower vacuum than the main chamber.

A plurality of interconnected subsidiary chambers may be provided, with a gas knife located in one or more of the subsidiary chambers The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a schematic cross-section through laser welding apparatus in accordance with the invention; Figure 2 shows a perspective view of a subsidiary chamber forming part of the laser welding apparatus; Figure 3 shows a cross-sectional view of the subsidiary chamber; and Figure 4 shows a schematic cross-section through a second embodiment of laser welding apparatus.

Description

Laser welding apparatus 10 as shown schematically in Figure 1 comprises an evacuatable welding chamber 12 into which a beam of laser radiation 14 within the dashed lines of Figure 1 is directed through protective window 16 and focussed to a fine image using a convex lens (not shown) outside chamber 12 and proximal vacuum window 16 Wall 22 defines an aperture 24 within chamber 12 through which beam 14 passes to reach workpiece 26 requiring welding. One or more pumping systems or pumps 28, 30 are provided to evacuate chamber 12 and to maintain a vacuum.

In use, laser beam 14 is focussed to a fine spot 32 on part 26 so as to create a keyhole weld.

Chamber 12 comprises main welding chamber 40 and subsidiary chamber 42 connected together by transmission passage 44, with laser beam 14 travelling through subsidiary chamber 42 and passage 44 to reach workpiece 26 located in main chamber 40. Pump 28 acts to evacuate main chamber 12 and maintain a sufficiently high vacuum for laser welding to take place. Subsidiary chamber 42 has a separate pumping system 30 and is maintained at a lower vacuum than main chamber 40 Within subsidiary chamber 42, there is disposed a gas knife 46 with a thin elongate nozzle to generate a laminar flow of gas, knife 46 having an associated gas feed 47 Gas knife 46 is positioned to one side of passage 44 with inlet 50 positioned the other side of passage 44 such that the stream of gas 48 generated by gas knife 46 extends towards inlet 50, across and over an upper end 49 of passage 44. Pumping system 30 is arranged to operate continuously at a rate that draws gas jet 48 across chamber 42 to pumping port 50 for extraction, and substantially prevents gas 48 from entering passage 44 and main chamber 40. Port 50 is substantially axially aligned with gas knife 46 to ensure pumping is along the dominant direction of travel of gas 48 as it is ejected from knife 46. The direction of travel of gas stream 48 is substantially parallel to the planar internal face of window 16 and substantially perpendicular to a vertical axis of passage 44. Typically the flow rate will be between 0.1 to 5L/min with a velocity of up to 400m/s when gas entering through gas feed 47 is at room in temperature.

During use, weld vapours or splatter 52 from weld region 32 passing through aperture 24 and along passage 44 are diverted from reaching window 16 by the constant flow of gas 48 across chamber 42 towards inlet port 50. By positioning gas knife 46 in subsidiary chamber 42 the area surrounding workpiece 26 is unaffected by the gas flow which prevents sooting taking place at workpiece 26 Subsidiary chamber 42 operates at a medium vacuum of typically around lembar, with a higher vacuum being maintained in chamber 40 proximal weld region 32 as a high vacuum is required for laser welding at workpiece 26.

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

Opposing apertures 66, 68 are positioned in outer wall 70 of housing 60 to allow transmission of laser beam through chamber 42 and into passage 44. Window 16 is secured over aperture 66 with connector portion 72 defining passage 44 secured around aperture 68 and used to connect secondary chamber 42 to main welding chamber 40 Within chamber 42 all surfaces are configured to be as smooth and non-abrupt as possible, with wherever possible corners smoothed to an arc rather than being maintained as perpendicular joining faces, see corner 74. All inner surfaces of chamber 42 are typically ground during manufacture so as to give a smoothness in the range 0.8-1.6pm Ra where Ra is the roughness average value. This ensures gas 48 encounters as little surface skin friction as possible. Any interaction with perpendicularly angled surfaces would introduce turbulence into gas 48 and potentially cause flow of gas 48 away from port 50 and down passage 44 into main welding chamber 40. Thus smoothing the internal surface of chamber 42 ensures the in thin jet of gas 48 flows smoothly into pumping port 50 without interaction with perpendicularly angled surfaces. This ensures working chamber 40 remains free of soot and at a vacuum level that the operator desires while also maintaining the transmissivity of the optical component 16. This arrangement protects window 16 from deposition of weld vapour and prevents gas 48 from reaching the main chamber 40.

A plurality of subsidiary chambers can be used, see Figure 4 where by way of example two subsidiary chambers are used, each subsidiary chamber having a gas knife 46, 46' and a pumping port 30, 30'. These stacked chambers can have multiple different setups, for example no gas knife in the subsidiary chamber closest to main chamber 40 so as to allow for more effective pumping, multiple subsidiary chambers of the same size to allow for better window protection with multiple gas flows, or multiple subsidiary chambers with varied no-gas-knife/with-gas-knife configurations.

Claims

Claims 1. Laser welding apparatus comprising an evacuatable chamber incorporating a transparent region through which laser radiation is transmissible to heat a weld region on a workpiece and a gas knife configured to generate a stream of gas, wherein the evacuatable chamber comprises a main chamber in which welding takes place and at least one subsidiary chamber in which the gas knife is located, the main chamber and the at least one subsidiary chamber connected together by a transmission passage to enable laser radiation to reach the workpiece, and a pumping means is connected to the subsidiary chamber and is configured to draw the stream of gas out of the in subsidiary chamber.
2. Laser welding apparatus according to claim 1, wherein one end of the transmission passage is situated between the gas knife and pumping means.
3. Laser welding apparatus according to claim 1 or claim 2, wherein the pumping means comprises an inlet substantially axially aligned with a direction of travel of the stream of gas.
4. Laser welding apparatus according to any of the preceding claims, wherein the subsidiary chamber is tapered at one end proximal the pumping means
5. Laser welding apparatus according to any of the preceding claims, wherein at least part of the subsidiary chamber proximal the pumping means is frustro-conical in shape.
6. Laser welding apparatus according to any of the preceding claims, wherein an inner surface of the subsidiary chamber has a smoothness value in range 0.8-1.6pm Ra.
7. Laser welding apparatus according to any of the preceding claims, wherein the pumping means is configured to generate a flow rate of the stream of gas across the transmission passage in the range 0. 1-5L/min.
8. Laser welding apparatus according to any of the preceding claims, wherein the subsidiary chamber is maintained at a lower vacuum than the main chamber.
9 Laser welding apparatus according to any of the preceding claims, wherein a plurality of interconnected subsidiary chambers are provided, a gas knife located in one or more of the subsidiary chambers.