Field of the Invention

This invention relates to a welding assembly used in electron beam and laser welding, and in particular a welding assembly for welding of large items such as large tubular steel sections used for wind turbines and oil pipelines.

Background to the Invention

When welding large structures such as oil pipes or wind turbine structures, external welding of joints conventionally takes place using arc welding which is a slow and laborious process requiring multiple passes of a welding head and non-instructive testing between each weld operation.

Electron beam welding or laser welding can achieve more rapid, higher quality welds but for large structures, the weld quality can be compromised unless a vacuum is provided on both sides of the weld joint. This is difficult to achieve for very large structures of many metres in length. Sometimes a structure to be welded has its internal volume subdivided by welding internal plates in position so that only a reduced volume needs to be evacuated behind the weld joint. However for large objects, particularly those with very large diameters, it is still difficult to pump out the region and requires very expensive vacuum pumps which take a long time to achieve the necessary vacuum.

Summary of the Invention

In accordance with the present invention, there is provided a welding assembly comprising front and rear plates disposable to the front and rear of a joint to be welded, wherein each plate comprises an array of spaced apart evacuatable chambers, one of the chambers being adapted to receive a welding gun, such as an electron-beam gun or laser welding gun. This arrangement allows a pressure profile to be created along the array with a fine vacuum achievable at the chamber adapted to receive the welding gun to allow high quality welding to achieved using and electron beam or laser. By having front and rear plates each with the same array of chambers, matching vacuums can be achieved to the front and rear of a weld joint in a workpiece, and in particular in relation to weld joints on industrial scale workpieces.

Preferably the array is a linear array, being particularly suitable for spacing the evacuatable chambers along a linear weld j oint.

The evacuatable chambers are preferably arranged so as to produce a pressure profile having a minimum pressure at the chamber adapted to receive a welding gun. Typically a pressure of around 10 ² mBar will be achieved at the location of the chamber adapted to receive a welding gun so that electron beam or laser welding can take place.

The chamber adapted to receive a welding gun may be located centrally within the array with at least two subsidiary chambers disposed either side of the central chamber. Additional subsidiary chambers may be provided and in a particularly preferred embodiment, two pairs of subsidiary chambers are disposed either side of the central chamber, producing a total of five chambers.

Preferably each chamber is connectable to a vacuum pump. Opposing chambers of the front and rear plates, i.e. those at the same position within the array, may be connected to common vacuum pumps. The chambers are preferably adapted to be connected to different types of vacuum pumps depending on their position along the array. At positions of the array furthest from a weld joint, a vacuum pump suitable for achieving a rough vacuum is attached, with the vacuum pump associated with the central chamber being capable of achieving a fine vacuum of around 10 ² mBar. By having a linear array of spaced apart evacuation chambers a pressure profile can be achieved reducing in pressure from the end to the centre of the array, with a minimum pressure achieved at the centre of the array. The front and rear plates are preferably substantially identically configured so as to have substantially identical configurations and spacings of chambers. The chambers are preferably circular in cross-section. The main chamber adapted to receive the welding gun is preferably approximately 1.5 times the width, or diameter, of the other chambers within the array, with the other chambers in the array having a common width.

Desirably the central chamber has a first width or diameter and the subsidiary chambers within the array have a second width or diameter with the distance between the edge of one chamber and the edge of the adjoining chamber matching the width or diameter of the subsidiary chambers.

The front and rear plates desirably occupy the same footprint so as to overlay each other such that in use the workpiece and thus weld joint are positioned between the front and rear plates.

A resilient sealing means may be located on an internal face of each plate and disposed around each chamber so as to be proximal to a workpiece to be welded. The resilient sealing means may be in the form of a sheet formed with apertures matching the array of chambers so that an evacuatable channel extends from each plate through the resilient sheet towards the weld joint. Alternatively individual seals may be located around the chambers, on the internal face. Preferably the resilient sealing means is made of a self lubricating material so as to improve movement of the plates relative to a workpiece as a weld progresses, and in particular the resilient material may be made from silicone rubber with a Shore value of 30. The welding assembly may further comprise movement means, such as one or motors, to produce relative movement of the plates with respect to the workpiece, and may further comprise a detector to provide information about weld beam characteristics.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure l is a view from the front of a welding assembly;

Figure 2 is a side perspective view of the welding assembly;

Figure 3 is an exploded view of the welding assembly; Figure 4 is a horizontal section through the welding assembly;

Figure 5 is a view of a sealing sheet used in the welding assembly;

Figure 6 is a vertical section through the welding assembly to illustrate passage of an electron beam to a weld joint; and

Figure 7 is a graph illustrating pressure variation across the welding assembly. Description

Figures 1 and 2 show a welding assembly 10 suitable for electron beam welding or laser welding comprising front and rear welding plates 12, 14 disposed either side of a workpiece 16 which is typically an industrial scale workpiece such as a large tubular section having a wall thickness of between 40 to lOOmm and a diameter of typically 0.5 to 5m. Front and rear silicone rubber seals 20, 20’ are attached to an internal face of each plate 12, 14, see Figure 3, such that seals 20, 20’ intimately adjoin workpiece 16.

Front and rear plates 12, 14 substantially match in configuration, each having a plurality of spaced apart cylindrical ports 24, 24’, 26, 26’, 28, 28’, 30, 30’ and 32, 32’ arranged in a regular array. Thus each plate is provided with a linear array of five cylindrical ports providing channels extending towards workpiece 16. Central port 32, 32’ is associated with an electron beam 34, with typically an electron beam gun being attached to electron beam port 32 so as to generate an electron beam for use in welding joint 40. Plates 12, 14 are disposed in an overlying relationship either side of workpiece 16, occupying the same footprint. Front and rear plates 12, 14 are substantially rectangular in shape with their respective ports arranged in a line to overlie a joint 40 to be welded, see Figure 3. Different shapes of plate and arrangements of port arrays can be used depending on the path of the joint to be welded. The arrangement shown in Figure 1 is suitable for a linear weld joint.

All ports are vacuum ports connectable to vacuum pumps via conduits, see for example ports 24, 26 and conduits 41, 4G in Figure 1, so that in use a vacuum suitable for electron beam or laser welding can be generated at central ports 32, 32’ with typically a vacuum of around 10 ² mBar being required. Subsidiary ports 24, 24’ 26, 26’ 28, 28’ 30 and 30’ have a common diameter with central or main port 32, 32’ being larger at around one and a half times the diameter of the subsidiary ports. The ports are typically spaced apart by a distance equivalent to the diameter of the subsidiary ports, the spacing of the edge of each port from the next adjoining port being the same distance as the diameter of the subsidiary ports. The precise configuration of the port sizes and spacing depends on the vacuum pumps used to generate the vacuum. Opposing ports in the respective plates, and thus ports at identical positions within the array, are pumped to the same level of vacuum and if desired, opposing pairs of ports, for example ports 24, 24’, can be connected to a common vacuum pump.

As shown in Figure 5, seals 20, 20’ are substantially rectangular so as to match the configuration of plates 12, 14 and are formed with apertures 42, 42’ to match the positioning and size of the evacuatable ports shown in Figure 4. This ensures that the channel through each plate provided by each port extends to the face of workpiece 16.

Figure 6 shows a vertical cross section through ports 32, 32’ showing the alignment of central apertures 42, 42’ with electron beam ports 32, 32’ so that electron beam 34 is able to travel unimpeded to reach weld joint 40. Weld joint 40 occurs at the gap between two adjacent parts of the workpiece, the gap typically being 0.25mm to l.OOmm. Typically some of the electron beam travels beyond the region of the joint with this excess beam energy stopped by electron beam blocker 46 positioned behind plate 14, with beam blocker 46 typically made from 50 to lOOmm thick carbon steel.

Whilst the embodiment includes sealing sheets 20, 20’, these can be omitted and plates 12, 14 placed within close relationship to the workpiece. Typically the thickness of silicone sheets 20, 20’ will be 20mm and the thickness of plates 12, 14 around 45mm. However use of a resilient sheet, particularly a silicone rubber sealing sheet being self lubricating and having a Shore value of 30, improves glide of the welding assembly with respect to the workpiece surface. Sheets 20, 20’ can be replaced with elliptical or circular seals located around the ports if required.

Plates 12, 14, together with sealing sheets 20, 20’ if used, are able to move relative to the workpiece so as to perform a weld easily, with either the welding assembly moving or the workpiece moving, typically using an arrangement of one or more motors. Due to the size of the workpiece, which may be several metres in diameter or length, the plates of the welding assembly will generally move in preference. In use, outer subsidiary vacuum ports 24, 24’, 26, 26’ are attached to pumps designed to achieve a rough vacuum of around 0.1 to lOmBar, inner subsidiary ports 28, 28’, 30 and 30’ are attached to vacuum pumps capable of further reducing a rough vacuum, with electron beam ports 32, 32’ attached to pumps capable of achieving a fine or high vacuum of around 10 ² mBar suitable for electron beam or laser welding, and typically having a value of 2xl0 ² mBar. Pumps with different vacuum capabilities are thus used in conjunction to achieve a pressure profile across plates 12, 14 so that a suitable vacuum for electron beam welding or laser welding is achieved at the weld site, with a substantially matching pressure profile achieved at the front face of the workpiece where the beam impinges and the rear face of the workpiece where the beam exits the weld.

By having a spaced apart array of evacuatable chambers, a pressure reduction can be obtained from the chambers at the outer end of the array to central chamber 32, 32’, see for example Figure 7 where the pressure profile over plate 12 along the array of ports 24, 26, 28, 30, 32 is shown for welding of two adjacent regions of a lOOmm thick workpiece, with the profile shown for differing size weld gaps of 0.2mm, 0.5mm and 0.7mm. A pressure of 1 atmosphere at the edge of the plate reduces over the plate so as to reach a minimum fine vacuum of at least 1 O ² mBar at the centre of the plate where chamber 32 is located and where electron beam 34 impinges on the weld region. Higher vacuums are possible for smaller weld gaps. Plate 14 will exhibit a substantially identical profile across its array of ports. By evacuating at multiple points across the plates disposed on the front and rear faces of a workpiece, a vacuum adequate for welding can be created without the need to restrict the volume pumped in any way, as for example in the prior art where temporary internal structures are used to subdivide internal regions for ease of pumping.

By having multiple evacuatable chambers, a pressure drop from the edges of the plates to the centre can be provided such that a fine vacuum is easy achievable in the weld region. Progress of the weld can take place either horizontally or vertically or circumferentially. The configuration of substantially matching front and rear plates with multiple evacuatable chambers ensures that substantially the same pressure profile is achieved for both plates and that the same degree of vacuum is maintained at the front and rear of the weld which is important for weld quality and ensures the amount of air passing through the weld joint can be controlled.