Welding system for X-ray monitoring of electron beam welds.

Abstract

A welding system (16) is provided, the welding system (16) comprising an evacuable welding chamber (26), an electron beam gun (20) connected to the welding chamber (26), a control system (44) for redirecting an electron beam (22) generated by the electron beam gun (20), and a detector (40) for acquiring X-ray images, wherein the first and second X-ray sources (14, 14') are positioned proximate a weld site (24) within the welding chamber (26). The control system (44) is configured to synchronize the acquisition of X-ray images of the weld site (24) by the detector (40) with the periodic generation of X-rays by the X-ray sources (14, 14') in response to the incident electron beam.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a welding system for monitoring electron beam welds using X-rays. [Background technology]

[0002] Background of the Invention During electron beam welding, defects in the weld can occur due to, for example, incorrect weld penetration depth and weld porosity. X-rays have been used in other types of welding (see, for example, CN213302040) to detect defects in aluminum tubes during welding, where the defective area is marked using an extendable rod. However, problems often arise with targeting the X-rays at the weld site with the necessary components to ensure that the X-ray beam is suitable for use in detecting defects. Summary of the Invention [Means for solving the problem]

[0003] Summary of the Invention According to the present invention, there is provided a welding system comprising: an evacuable welding chamber; an electron beam gun connected to the welding chamber; a control system for redirecting an electron beam generated by the electron beam gun; and a detector for acquiring X-ray images, wherein a first X-ray source and a second X-ray source are positioned proximate to a weld site within the welding chamber, the first X-ray source emitting X-rays in a first direction through the weld site and the second X-ray source emitting X-rays in a second direction through the weld site, the first direction and the second direction being substantially perpendicular to each other, thereby ensuring that the X-ray beam generated by the source can be directed through the weld site without the need for beam collimation.

[0004] The second X-ray source is preferably positioned orthogonal to the first X-ray source. Preferably, the control system is configured to synchronize the acquisition of X-ray images of the weld site by the detector with the periodic generation of X-rays by the first X-ray source and the second X-ray source.

[0005] The first and second X-ray sources preferably produce X-rays in response to the incident electron beam and may be formed from a high atomic number metal such as tungsten or tantalum.

[0006] The first and second X-ray sources are preferably positioned 1-5 mm from the weld site and may include at least one angled surface to direct X-rays through the weld site. Typically, the first and second X-ray sources are in the form of elongated blocks having at least one angled upper surface.

[0007] Preferably, the detector comprises at least one input, such as a pinhole optical fiber, located within the welding chamber, typically 10-200 mm from the weld site, and at least one detector element, such as a photodiode or camera, located outside the welding chamber or within an X-ray shielding box within the chamber.

[0008] The detector may have one input associated with a first X-ray source and another input associated with a second X-ray source.

[0009] An aperture shim may be positioned between the or each input and the weld site to reduce weld debris impinging on the input and to provide filtering of low energy x-rays.

[0010] The welding system is particularly useful for welding areas that include materials that are penetrable by low energy x-rays, such as copper and aluminum.

[0011] Preferably, the weld has a thickness in the range of 1 to 3 mm to allow x-rays to penetrate the area of ​​the weld.

[0012] The invention will now be described, by way of example only, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a plan view of a workpiece prepared for welding. [Figure 2] 1 is a schematic diagram of a welding system used to obtain an X-ray image of a workpiece from a single side view. [Figure 3] FIG. 1 is a schematic diagram of a welding system. DETAILED DESCRIPTION OF THE INVENTION

[0014] explanation FIG. 1 shows a stationary workpiece 10 including a plurality of copper or aluminum hairpins 12, typically about 1-3 mm thick, configured as four pillars and requiring spot welding with an electron beam. A first X-ray source in the form of an elongated tungsten block 14 is secured between each pair of adjacent rows of hairpins 12 using small bolts (not shown), extending along the channel between adjacent rows of hairpins and proximal to each hairpin in the row. A second X-ray source is provided by an additional tungsten block 14' positioned orthogonally to the block 14 and positioned between each adjacent row of hairpins, such that two orthogonally positioned tungsten blocks 14, 14' are proximal to each hairpin. For clarity, only a selected number of blocks 14' are shown. The multiple tungsten blocks 14, 14' positioned around the workpiece 10 allow X-rays to be generated proximal to each individual hairpin, thus enabling monitoring of weld quality as each hairpin is welded.

[0015] A schematic diagram of a welding system 16 with a workpiece 10 is shown in FIG. 2, in which an electron beam gun 20 generates an electron beam 22 having a beam diameter typically in the range of 80 μm to 200 μm. A tungsten block 14' and a portion of one of the tungsten blocks 14 are shown positioned within a vacuum chamber 26 proximate a weld site 24. Each block 14, 14' is substantially rectangular with a triangular profile in the upper region 30 so as to present two sloping upper surfaces 32, 34. Typical dimensions of block 14 are 30 mm long, 10 mm high, and 5 mm wide. Block 14' is shorter, typically having a length of about 5 to 10 mm.

[0016] In response to the incident high-energy beam 22', 22", the tungsten block 14, 14' produces an X-ray beam of a diameter similar to the electron beam diameter; thus, typically, the X-ray beam is about 100 μm in diameter. The triangular profile of the tungsten block 14, 14' ensures that the weld site 24 proximal to the sloped upper surface 32 emits X-rays at a different angle relative to the angle of incidence of the impinging electron beam 22', 22", thus ensuring that the X-ray beam 36, 36' passes through the weld site 24. Depending on the configuration of the articles being welded, tungsten X-ray sources can be formed into a variety of different shapes.

[0017] The tungsten blocks 14, 14' are positioned as close as possible to each hairpin weld site 24, typically 1-5 mm from the weld site, to ensure that the x-ray beams 36, 36' pass through the weld site 24 without requiring collimation of the x-ray beams 36, 36'.

[0018] Located within the vacuum chamber 26 near the weld site 24, detectors in the form of pinhole fiber optic inputs 37, 37' positioned orthogonally to one another are used to detect x-rays 36, 36' transmitted through the weld site 24 (see FIG. 3). The use of fiber optic or other small pinhole-like inputs allows the inputs 37, 37' to be positioned very close to the weld site 24, and multiple switchable inputs can be used as needed to ensure speed and ease of image acquisition at multiple consecutive weld sites, such as a row of individual hairpins.

[0019] Each input 37, 37' is connected to an image detector 40, 40', such as a single photodiode, an array of sensing elements, or an X-ray camera, located outside the vacuum chamber 26. The pinhole diameter of the inputs 37, 37' is desirably equal to or less than the beam diameter to ensure a good signal-to-noise ratio. Optionally, an aperture shim 38, 38' can be positioned in front of each input 37, 37' to provide protection from weld debris and ensure that only X-rays transmitted through the weld site 24 reach the input 37, 37'.

[0020] X-ray camera 40 includes a high-speed scintillator and image acquisition electronics. X-ray images detected by camera 40 generate image data that are processed in processor 42. The processed data from processor 42 is passed to deflection control system 44, which changes the direction and focus of electron beam 22, moves beam 22 from weld site 24 to blocks 14, 14', and controls the time of image acquisition by camera 40.

[0021] This configuration of blocks 14, 14' as two separated x-ray sources generating x-rays in substantially orthogonal directions to impinge on weld site 24 allows for the generation of 3D images in real time as the weld is being performed, and is particularly suitable for workpieces having multiple weld sites in staggered positions relative to one another.

[0022] During welding, which is typically performed at a voltage of about 40-170 kV, the electron beam 22 is controlled by system 44 to move between the weld site 24 as beam 22, the tungsten block 14 as beam 22', and the tungsten block 14' as beam 22". The electron beam movement is typically in a raster pattern, with each traverse from the blocks 14, 14' back to the weld site 24 taking about 250 μs. The acquisition of X-ray images by camera 40 is periodic and synchronized with the electron beam striking the tungsten blocks 14, 14' and producing X-rays. Thus, images are acquired simultaneously with the production of X-rays from the tungsten blocks 14, 14'.

[0023] The resolution of the x-ray image is limited by the response time of the scintillator in camera 40, with fast scintillators typically having a response time of less than 100 μs, thus allowing a resolution of greater than 50×50 pixels. FPGA closed-loop image processing can be used to control the duration of the welding process, monitor the images acquired to determine when the weld is complete, and allow monitoring of beam penetration at the weld site so that the welding beam power can be increased to achieve the required melting.

[0024] After the weld is made, the electron beam can, if desired, be subjected to a high resolution scan, typically a raster scan, with x-ray images taken at different depths through the weld site 24 to produce x-ray slices through the weld that can be used to create a 3D x-ray image of each weld.

Claims

1. 1. A welding system comprising: a welding chamber capable of being evacuated; an electron beam gun connected to the welding chamber; a control system for changing the direction of an electron beam generated by the electron beam gun; and a detector for acquiring X-ray images, wherein a first X-ray source and a second X-ray source are positioned within the welding chamber proximate a weld site, the first X-ray source emitting X-rays in a first direction through the weld site and the second X-ray source emitting X-rays in a second direction through the weld site, the first direction and the second direction being substantially perpendicular to each other.

2. The welding system of claim 1 , wherein the second x-ray source is positioned orthogonal to the first x-ray source.

3. 3. The welding system of claim 1, wherein the control system is configured to synchronize acquisition of X-ray images of the weld site by the detector with periodic generation of X-rays by the first X-ray source and the second X-ray source.

4. 10. The welding system of claim 1, wherein the first X-ray source and the second X-ray source generate X-rays in response to an incident electron beam.

5. 10. The welding system of claim 1, wherein the first X-ray source and the second X-ray source are formed from tungsten.

6. 10. The welding system of any preceding claim, wherein the first X-ray source and the second X-ray source are positioned 1 to 5 mm from the weld site.

7. 10. The welding system of any preceding claim, wherein the first x-ray source and the second x-ray source include at least one angled surface to direct x-rays through the weld site.

8. 10. The welding system of any preceding claim, wherein the detector comprises at least one input located within the welding chamber and at least one detector element located outside the welding chamber.

9. 9. The welding system of claim 8, wherein the detector comprises one input associated with the first x-ray source and another input associated with the second x-ray source.

10. The welding system of claim 8 or 9, wherein an aperture shim is positioned between the input and the weld site.

11. 10. The welding system of any preceding claim, wherein the weld site comprises a material that is penetrable by low energy x-rays.

12. 10. A welding system according to any preceding claim, wherein the weld area has a thickness in the range of 1 to 3 mm.

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