GB2628393A

GB2628393A - A welding sensing system

Info

Publication number: GB2628393A
Application number: GB2304204.7A
Authority: GB
Inventors: Hodgkinson Jane
Original assignee: Cranfield University
Current assignee: Cranfield University
Priority date: 2023-03-22
Filing date: 2023-03-22
Publication date: 2024-09-25
Also published as: WO2024194409A1

Abstract

When welding using a welding torch 112 and/or laser on a holder, the intensity of constituents in the plasma plume generated at a weld substrate can be determined, using a light sensing system 150. A spectrometer 156 can be used to detect the intensity of light at oxygen’s wavelength in the plume. During welding, if oxygen is detected within the plasma plume; a controller can adjust welding parameters (e.g. argon shield gas flow rate, plasma forming gas flow rate, weld wire feed rate, weld current, welding torch 112 movement speed). Optical filters and detectors or imaging devices may be used. Welding may include wire arc additive manufacturing (WAAM) or laser welding. The controller 130 may determine the concentrations of other contaminants in the plasma gas, shield gas or environment around the melt pool (e.g. tungsten weld torch electrode material).

Description

A Welding Sensing System

Technical Field

The present disclosure relates to a welding sensing system and method.

Background

Wire Arc Additive Manufacturing (WAAM) is a 3D manufacturing process in which multiple layers of a weld material, e.g. metal, such as steel, nickel, aluminium, titanium or alloys thereof, are built up on top of each other, for example, using a welding process, to form a desired 3D shape. The development of WAAM has improved the ease of production of complex parts due to the freedom of motion available to the welding torch. This has assisted in the transfer of complex 3D computer-aided designs to physical components. Additionally, component manufacture through WAAM can be more cost-effective than traditional manufacturing techniques, as material waste can be reduced.

In a WAAM process, a plasma welding process may be used, in which a jet of a plasma forming gas, such as argon gas, is ejected through a nozzle in a weld torch and an electric arc is formed between the weld torch and a weld substrate via a plasma formed by ionising the plasma forming gas. The electric arc causes a melt pool to form in the weld substrate and a wire formed from the weld material, is fed into the melt pool to deposit additional weld material onto the bead which is formed as the torch is in motion. In order to reduce the presence of unwanted gases within the plasma and/or at the melt pool, a shield gas, such as argon or a mixture of argon and hydrogen, is emitted from the torch surrounding the jet of plasma forming gas. The weld torch is translated over the weld substrate to deposit layers of the weld material over the substrate, in order to build up the 3D shape.

Additionally or alternatively, a manufacturing process may involve a laser welding process, in which a high power laser is used to provide a concentrated heat source to produce the melt pool into which weld material is fed. During laser welding, a metal vapour may be produced from the weld substrate, which may become ionised to form a plasma. In some cases, the WAAM process may include both a laser and a weld torch for forming the plasma.

Although WAAM is a promising production method, there are multiple operating parameters that could be measured and monitored during the manufacturing process to provide improved process control. Measuring and monitoring such parameters can enable the production of components with improved quality and/or reduce the requirement for post manufacture quality inspections such as non-destructive testing.

Statements of Invention

According to an aspect of the present disclosure, there is provided a welding sensing system comprising: a welding system comprising: a weld torch supported by a holder, the weld torch configured to: generate a plasma between the torch and a weld substrate, in order to create a weld pool on a surface of the substrate; and emit a shield gas around the plasma, wherein the system further comprises: a spectroscopy system arranged to receive light emitted by the plasma and]of the emitted light; and one or more controllers configured to determine a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a first spectral line in the frequency spectrum corresponding to oxygen.

According to another aspect of the present disclosure, there is provided a welding sensing system comprising: a welding system comprising: a weld torch and/or laser supported by a holder, the weld torch and/or laser configured to generate a plasma at a weld substrate and create a melt pool on a surface of the substrate, wherein the welding system is configured to provide a shield gas is around the plasma and/or melt pool, wherein the system further comprises: a light sensing system configured to determine a first intensity of light at a wavelength corresponding to an emission from oxygen within the plasma; and one or more controllers configured to determine a concentration of oxygen present at the plasma, at the melt pool and/or within the shield gas based on the first intensity.

The welding system may comprise a shield gas emitter configured to emit the shield gas around the plasma and/or the melt pool. For example, the weld torch may comprise an opening configured to emit shield gas around the plasma and/or melt pool.

The light sensing system may be configured to determine a second intensity of light at a wavelength corresponding to an emission by a constituent of the shield gas. The one or more controllers may be configured to determine a concentration of oxygen present at the plasma, at the melt pool and/or within the shield gas based on the first intensity relative to the second intensity.

The light sensing system may comprise a spectroscopy system, such as an atomic emissions spectroscopy system, configured to receive light emitted by the plasma and generate a frequency spectrum of the emitted light. The light sensing system may comprise one or more filters, configured to filter predetermined wavelengths of light from the light emitted by the plasma. The light sensing system may further comprise one or more optical detectors configured to determine intensities of the light filtered by the one or more filters respectively. The light sensing system may comprise an imaging device configured to receive light emitted by the plasma. The intensities of light at different respective frequencies may be determined based on images captured by the imaging device.

The shield gas may comprise argon. The second intensity may relate to argon.

The welding sensing system may comprise a Wre Arc Additive Manufacturing (WAAM) system. The weld torch may be a weld torch of the WAAM system. Additionally or alternatively, the welding sensing system may comprise comprises a laser welding system. The laser may be a laser of the laser welding system.

The one or more controllers may be configured to modify an operating parameter of the welding system, or halt operation of the welding system, based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas. The operating parameter of the welding system may comprise a flow rate of shield gas, a flow rate of plasma forming gas, a feed rate of weld wire, a weld current, and/or a speed at which the weld torch is moved relative to the substrate.

The light sensing system may comprise an optical fibre for receiving the light emitted by the plasma. An end of the optical fibre may be mounted on the holder for movement together the weld torch and/or laser.

The first intensity may be less that an intensity of light at another wavelength corresponding to an emission from oxygen within the plasma. In other words, an amplitude of the first spectral line may be less than an amplitude of another spectral line corresponding to oxygen. Hence, an optical sensor of the light sensing system may not be saturated at the wavelength corresponding to the first intensity. A sampling frequency of the spectroscopy system may be between 500Hz and 0.1Hz.

The controller may be configured to determine a presence of a contaminant at the plasma, at the weld pool and/or within the shield gas based on an intensity of light emitted by the plasma at a contaminant wavelength corresponding to light emitted by the contaminant. The contaminant wavelength may be spaced apart from emission wavelengths corresponding to the material of a weld wire, the weld substrate and/or constituents of the shield gas.

For example, the controller may be configured to determine a presence of a contaminant at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a contaminant spectral line in the spectrum corresponding to the contaminant. The contaminant spectral line may be spaced apart from spectral lines corresponding to the material of a weld wire, the weld substrate and/or constituents of the shield gas.

According to another aspect of the present disclosure, there is provided a welding sensing system comprising: a welding system comprising: a weld torch supported by a holder, the weld torch configured to: generate a plasma between the torch and a weld substrate, in order to create a weld pool on a surface of the substrate; and emit a shield gas around the plasma, wherein the system further comprises: a spectroscopy system arranged to receive light emitted by the plasma and generate a frequency spectrum of the emitted light; and one or more controllers configured to determine a presence of a contaminant material at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a contaminant spectral line in the spectrum corresponding to the contaminant material. The contaminant spectral line may be spaced apart from spectral lines corresponding to a material of a weld wire, a material the weld substrate and/or a constituent of the shield gas.

According to another aspect of the present disclosure, there is provided a welding sensing system comprising: a welding system comprising: a weld torch and/or laser supported by a holder, the weld torch configured to generate a plasma at a weld substrate, and create a melt pool on a surface of the substrate, wherein the welding system is configured to provide a shield gas around the plasma and/or melt pool, wherein the system further comprises: a light sensing system configured to determine a contaminant intensity of light at a wavelength corresponding to an emission from a contaminant material within the plasma; and one or more controllers configured to determine a presence of a contaminant material at the plasma, at the weld pool and/or within the shield gas based on the contaminant intensity. The contaminant may comprise tungsten or another undesirable material. The wavelength corresponding to an emission from a contaminant material may be between 250nm and 430nm, such as between 280nm and 305nm. The contaminant spectral line may be at a wavelength of between 250nm and 430nm, such as between 280nm and 305nm.

According to another aspect of the present disclosure, there is provided a welding sensing method, the method comprising: generating a plasma between a weld torch of a welding system and a substrate, in order to create a weld pool at weld site on a surface of the substrate; providing a shield gas around the plasma and/or the melt pool; receiving, by a spectroscopy system, light emitted by the plasma; generating, by the spectroscopy system, a frequency spectrum of the emitted light and determining a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a first spectral line in the frequency spectrum corresponding to oxygen.

According to another aspect of the present disclosure, there is provided a welding sensing method, the method comprising: generating a plasma at a weld substrate, and creating a melt pool on a surface of the substrate; providing a shield gas around the plasma and/or the melt pool; receiving, by a light sensing system, light emitted by the plasma; determining, by the light sensing system, a first intensity of light at a wavelength corresponding to an emission from oxygen within the plasma; and determining a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on the first intensity.

The method may further comprise: determine a second intensity of light at a wavelength corresponding to an emission by a constituent of the shield gas within the plasma, wherein the concentration of oxygen is determined based the first intensity and the second intensity.

The method may further comprise: modifying an operating parameter of the welding system based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas.

The method may further comprise: determining a presence of a contaminant material at the plasma, at the weld pool and/or within the shield gas based on an intensity of light emitted by the plasma at a contaminant wavelength corresponding to an emission by the contaminant material.

The method may further comprise: determining a presence of a contaminant material at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a contaminant spectral line in the spectrum corresponding to the contaminant, wherein the contaminant spectral line is spaced apart from spectral lines corresponding to a material of a weld wire, a material the weld substrate and/or a constituent of the shield gas.

The method may comprise: introducing a predetermined concentration of oxygen into the shield gas emitted by the weld torch. The method may further comprise determining a relationship between a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas and a ratio of the first and second intensities. For example, a relationship between a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas and a ratio of an amplitude of a first spectral line in the spectrum corresponding to oxygen relative to an amplitude of a second spectral line in the spectrum corresponding to a constituent of the shield gas.

The method may comprise: operating the welding system in a controlled atmosphere whilst the predetermined concentration of oxygen is being introduced into the shield gas.

To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention. For example, features described in relation to the first mentioned aspect may be combined with the features of the second mentioned aspect.

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic view of a welding sensing system according to arrangements of

the present disclosure;

Figure 2 is a graph showing an atomic emission spectrum relating to plasma produced by a weld torch of the welding sensing system depicted in Figure 1; Figure 3 is an enlarged view of a portion of the atomic emission spectrum shown in Figure 2, including spectrums measured with varying concentrations of oxygen present at the plasma.

Figure 4 is a graph illustrating a relationship between oxygen concentration and a ratio of amplitudes of spectral lines in the spectrum, shown in Figures 2 and 3, corresponding to oxygen and a constituent of the shield gas; Figure 5 is a graph showing an atomic emission spectrum relating to plasma produced by the weld torch of the welding sensing system shown in Figure 1 in the presence of a contaminant; and Figure 6 is a flow chart illustrating a welding sensing method according to arrangements of the present disclosure.

Detailed Description

With reference to Figure 1, a welding sensing system 100 according to arrangements of the present disclosure comprises a welding system 110 and a light sensing system 150.. The welding system 110 may be a Wire Arc Additive Manufacturing (WAAM) system.

In the arrangement depicted in Figure 1, the welding system 110 comprises a weld torch 112 supported on a weld torch holder 114 and may comprise a bed 116, for supporting a weld substrate 118. The welding system 110 further comprises a power supply 120, a gas source 122, configured to supply plasma forming gas and/or shield gas to the weld torch, and a source of weld wire 124, e.g. a metal weld wire, such as weld wire formed of steel, nickel, aluminium, titanium or alloys thereof. When the shield gas comprises a different gas or mixture of gases from the plasma forming gas, the welding system 110 may comprise a further gas source for providing the shield gas or additional component of the shield gas.

In use of the welding sensing system 100, a jet of the plasma forming gas is emitted from the weld torch 112 towards the substrate 118 supported on the bed 116. A potential difference between an electrode of the weld torch 112 and the bed 116, e.g. generated by the power supply 120, causes the plasma forming gas to become ionised as a plasma and an electrical current to pass between the weld torch and the substrate via the plasma. The electric current causes a melt pool to form on the substrate. In alternative welding system, the current might pass into the torch instead. Weld wire is fed, through or adjacent to the weld torch, to the melt pool (or fed directly at an angle) and material from the weld wire is deposited onto the substrate at the melt pool.

The welding system 110 may further comprises a shield gas emitter 113 configured to emit a shield gas around the melt pool produced by the welding system 110 and/or around the plasma. In the arrangement shown in Figure 1, the shield gas emitter 113 comprises a portion of the weld torch. For example, the weld torch may comprise a nozzle for emitting the plasma forming gas and an opening arranged about the nozzle for emitting the shield gas, so that the shield gas surrounds the plasma. In other arrangements, the weld substrate 118 may be arranged within an enclosure 140. The shield gas may be provided within the enclosure, such that the shield gas is around the plasma and/or melt pool.

In use of the welding system 110, a flow of the shield gas is emitted from the shield gas emitter 113, e.g. the weld torch 112, surrounding the jet of plasma forming gas, in order to prevent undesired gases, such as oxygen, e.g. atmospheric oxygen, from reaching the plasma and/or the melt pool.

In other arrangements, the welding system 110 may comprise a laser configured to act as a heat source for producing a melt pool on a surface of the weld substrate 118. The laser may be mounted on the weld torch holder. Heating of the substrate by the laser may lead to the metal of the substrate being vapourised and ionised to form a plasma.

The laser may be provided in addition, or as an alternative, to the weld torch 112.

When the weld torch 112 is not provided, the shield gas may be emitted by a separate shield gas emitter, e.g. comprising a nozzle or opening for emitting the shield gas around the plasma and/or melt pool.

The welding system 110 further comprises a holder actuator 126 for moving and/or rotating the weld torch holder 114 in one or more axes relative to the bed 116. For example, the holder actuator 126 may comprise a robot arm configured to move and or rotate the weld torch holder in 3 or more, such as 4, 5, 6, 7 or 8, axes. In some arrangements, the welding system 110 may further comprise a bed actuator 128 for moving and/or rotating the bed 116 in one or more axis relative to the weld torch holder 114. The holder actuator and bed actuator may be together configured such that the weld torch can be moved and/or rotated relative to a weld substrate supported on the bed in more than 3 movement axes, such as 4, 5, 6, 7 or 8 axes. Movement of the weld torch holder 114 and bed 116 may be controlled, e.g. based on Computer Numerical Control (CNC), in order to produce a component through the WAAM process. For example, the welding system 110 may comprise a CNC controller for controlling the holder actuator 126 to move the weld torch holder 114 and the bed actuator 128 to move the bed 116 in order to produce a component.

During manufacture of a component using a WAAM process, the weld torch 112 is moved and/or rotated relative to the substrate in order to deposit layers of weld material over the substrate to build up the three-dimensional shape of the component. During manufacture of the component, a number of parameters of the welding system 110 may be adjusted in order to affect, e.g. improve, a quality of the weld. In particular, the feed rate of the weld wire, flow rates of the plasma forming gas and/or shield gas, the welding current passed through the torch, the temperature of the deposited layers, and/or movement and/or rotation speed of the weld torch and/or bed may be adjusted in order to affect weld quality. One operating parameter that affects the quality of the manufactured part is the presence of oxygen, e.g. atmospheric oxygen, at the plasma, e.g. in the plasma forming gas, in the shield gas or in the environment around the melt pool. In particular, oxidation of the weld material can lead to a layer or volume of lower strength material being present in the manufactured part. Additionally or alternatively, the oxidised layer or volume can be hard and difficult to machine.

The concentration of oxygen present at/within the plasma, shield gas and/or melt pool may be affected by, for example, air currents around the welding system 110 leading to disturbances in the shield gas, which expose the plasma to the atmosphere around the weld torch 112. Additionally or alternatively, operating parameters of the welding system 110, such as the feed rate of the weld wire, the flow rates of the plasma forming gas and/or shield gas, and/or the movement and/or rotation speed of the weld torch and/or bed, may affect the concentration of oxygen present at/within the plasma, within the shield gas and/or melt pool, and/or may otherwise affect the quality of a layer or volume of weld material being deposited. Additionally or alternatively again, a specific geometry of the component being produced may affect the concentration of oxygen present at/within the plasma, shield gas and/or melt pool. For example, enclosed geometries, e.g. corners, in the component may trap pockets of atmospheric gases, which may be released into the shield gas or plasma as the weld torch and/or bed moves/rotates.

A preferred oxygen concentration range for titanium alloy, e.g. Ti64V, welding may be between 100ppm and 4000ppm in a WAAM process. In particular, a concentration of less than 800ppm may be desirable when depositing weld material. Previously, oxygen concentrations may be measured using a commercial oxygen probe 102, which obtains a sample of gases around the welding system in order to infer a concentration of oxygen at/within the plasma, shield gas and/or melt pool. As depicted, the oxygen probe 102 is positioned at a distance away from the plasma and the melt pool due to material constraints of the probe. Hence, previously, determinations of the concentration of oxygen at the plasma and/or melt pool have been estimated based on the concentration of oxygen at the location of the probe tip.

In order to provide an improved determination of oxygen concentration at/within the plasma, shield gas and/or melt pool, the welding sensing system 100 according to the present disclosure comprises the light sensing system 150, which is configured to determine the concentration of oxygen using, for example, spectroscopic techniques.

As depicted in Figure 1, the light sensing system 150 may comprise a spectroscopy system, such as an atomic emissions spectroscopy system. In the arrangement shown, the light sensing system comprises an optical fibre or optical fibre cable 152, such as a single mode fibre optic cable. A first end 152a of the optical fibre may be mounted on the weld torch holder 114, and may be oriented to receive light from the plasma generated by the welding system. The light sensing system 150 may further comprise a lens 154, such as a collimating lens, mounted on the weld torch holder. The lens 154 may be configured to focus light from the plasma to the first end 152a of the optical fibre.

In the arrangement depicted, the light sensing system 150 further comprises a spectrometer 156. A second end 152b of the optical fibre is coupled to the spectrometer 156. The spectrometer 156 comprises optical and electrical components configured to receive the light from the optical fibre 152 and generate a frequency spectrum of the light. For example, the spectrometer 156 may comprise one or more optical components, such as optical gratings, to separate the light from the optical fibre 152 into spectral components, one or more photo detectors, configured to generate one or more electrical signals based on the intensities of the spectral components of light, and a spectrometer controller configured to receive the electrical signals and generate the frequency spectrum.

The spectrometer controller may be configured to capture intensity measurements from the one or more photo detectors at one or more sensing frequencies. Due to the high intensity of light received from the plasma, the spectrometer controller may be configured to capture the intensity measurement from the one or more photo detectors at a high sensing frequencyin order to reduce the likelihood of the one or more photo detectors becoming saturated. The spectrometer controller may be configured to capture the intensity measurement from the one or more photo detectors at frequencies of between 500Hz and 0.1Hz.

In other arrangements, as an alternative to the spectrometer, the light sensing system 150 may comprise one or more optical filters arranged to receive the light from the plasma, e.g. via the optical fibre cable 152, and pass light of different respective predetermined wavelengths or bands of wavelengths. The light sensing system 150 may further comprise one or more optical detectors configured to detect the light passed by the respective optical filters.

When the light sensing system 150 comprises one or more optical filters rather than the spectrometer, the light sensing system 150 may comprise a light sensing controller, configured to determine intensity measurements of the light passed by the one or more optical filters from the one or more optical detectors respectively.

The light sensing system 150 may further comprise an imaging device configured to receive light emitted by the plasma. For example, the light sensing system may be a Hyperspectral imaging system. When the light sensing system comprises the one or more optical filters, the imaging device may be configured to receive the light passed by the one or more optical filters.

Figure 2 shows an example of an atomic emission spectrum 200 generated by a spectrometer, such as the spectrometer 156, based on light from the plasma generated by a WAAM weld torch, such as the weld torch 112. The atomic emission spectrum 200 comprises a plurality of spectral lines 202 present at a plurality of respective wavelengths. The spectrum 200 may be processed to correct for background light, by subtracting a background spectrum determined when no plasma was present. The spectrum 200 may further be processed by subtracting a baseline from the spectrum 200. The baseline comprises a trend line fitted to regions on either side of one or more peaks where the spectrum is relatively flat and there is no significant emission line.

Atoms of different elements have distinct spectra, e.g. a distinct combination of spectral lines within an atomic emissions spectra, corresponding to the atoms emitting light of a particular wavelength or combination of wavelengths. Amplitudes of spectral lines within an atomic emission spectrum, e.g. intensities of light, that are at a wavelength known to correspond to a particular atom can be use used to determine the presence and quantity of the particular atom. Spectral lines 202 present in the atomic mission spectrum 200 may correspond to the material of the weld wire, the material of the weld substrate, a constituent of the plasma gas, the constituents of the shield gas, and/or a contaminant such as oxygen.

As illustrated in Figure 2, despite the high sensing frequency of the spectrometer, a number of the spectral lines may be present at a maximum intensity value 204, which may indicate saturation of a photo detector of the spectrometer.

In order to determine a concentration of oxygen present in the in the plasma gas, shield gas or in the environment around the melt pool, a spectral line known to correspond to oxygen and having an amplitude less than a maximum intensity value, such as the first spectral line 202a, may be identified and an amplitude of the identified spectral line determined. The amplitude of the first spectral line 202a may be a first intensity.

When the light sensing system comprises the one or more optical filters, one of the filters may have a pass band including the wavelength of the first spectral line 202a. an intensity of light passed by the optical filter having a pass band included the wavelength of the first spectral line 202a may be the first intensity.

Returning to Figure 1, the welding sensing system 100 further comprise a controller 130. The controller 130 may receive the atomic emission spectrum from the spectrometer 206, and may determine the amplitude of the first spectral line, e.g. the first intensity. Alternatively, the controller 130 may receive the intensity measurements of the light passed by the one or more optical filters from the light sensing controller. In some arrangements, the controller 130 may be configured to perform the functions of the spectrometer controller described above, e.g. to generate the atomic emission spectrum, or the functions of the light sensing controller. The controller 130 is configured to determine a concentration of oxygen present at the plasma based on the first intensity, e.g. the amplitude of the first spectral line 202a or intensity of the light detected by an optical detector receiving light passed by the one of the optical filters having a pass band including the wavelength of the first spectral line 202a.

Figure 3 is a graph illustrating the variation in intensity of the first spectral line 202a with concentration of oxygen present at the plasma. The graph includes a first graph line 302 corresponding to a first oxygen concentration, such as 5Oppm, a second graph line 304 corresponding to a second oxygen concentration, such as 500ppm, a third graph line 306 corresponding to a third oxygen concentration, such as 1000ppm, a fourth graph line 308 corresponding to fourth oxygen concentration, such as 1500ppm, a fifth graph line 310 corresponding to fifth oxygen concentration, such as 2000ppm, a sixth graph line 312 corresponding to sixth oxygen concentration, such as 2500ppm, a seventh graph line 314 corresponding to seventh oxygen concentration, such as 3000ppm, an eighth graph line 316 corresponding to an eighth oxygen concentration, such as 4000ppm, and a ninth graph line 318 corresponding to a ninth oxygen concentration, such as 5000ppm. The graph lines illustrated in Figure 3 have been processed in similar manner to the spectrum in 200, by subtracting background and baseline values from the intensity values. As can be seen from the lines shown in Figure 3, a relationship between emission spectrum intensity and oxygen concentration may be non-linear. In addition, it will be appreciated by the skilled person, that the intensity of a particular wavelength of light within a particular emissions spectrum may be affected by parameters relating to the configuration of the welding sensing system 100, such as the position of the optical fibre 152 relative to the weld torch 112.

Figure 3 also depicts a third spectral line 202c proximate the first spectral line 202a.

The third spectral line may also correspond to oxygen. As illustrated in Figure 2, the emission spectrum 200 further comprises a second spectral line 202b, which may correspond to a constituent of the shield gas, such as argon. The emission spectrum 200 may further comprise a fourth spectral line 202d corresponding to the constituent of the shield gas. As will be appreciated by the skilled person, the emission spectrum 200 may comprise one or more further spectral lines, which may correspond to oxygen and/or a components of the shield gas. In the arrangement described herein, the amplitudes of the first and second spectral lines, first and second intensities, are used by the welding sensing system to determine a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas. However, it will be appreciated that in other arrangements, amplitudes of others of the spectral lines, such as the third and/or fourth spectral lines may be used by the welding sensing system for determining a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas e.g. instead of the amplitude of the first and/or second spectral line.

When the light sensing system comprises the one or more optical filters, one of the optical filters may have a pass band including the wavelength of the second spectral line 202b. The intensity of light passed by the optical filter having a passband including the wavelength of the second spectral line may be the second intensity. It will also be appreciated that in other arrangements, the optical filters may include filters having pass bands including different wavelengths, such as wavelengths of the third and/or fourth spectral lines, and that intensities of light passed by these optical filters may be used by the welding sensing system for determining a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas.

In order to determine a concentration of oxygen at the plasma, at the weld pool and/or within the shield gas, the controller 130 may be configured to determine a ratio of the amplitude of the first spectral line 202a corresponding to oxygen to an amplitude of a second spectral line 202b of the emission spectrum 200 (depicted in Figure 2), e.g. a ratio of the first intensity to the second intensity. The second spectral line may be a spectral line in the emission spectrum 200 identified as corresponding to a constituent of the shield gas, such as argon. In other words, the controller may be configured to determine a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on the amplitude of the first spectral line in the spectrum corresponding to oxygen relative to the amplitude of the second spectral line in the spectrum corresponding to the constituent of the shield gas, e.g. argon. Additionally, the second spectral line 202b may be a spectral line selected as having an intensity less than the maximum intensity of the emission spectrum 200.

In arrangements in which the light sensing system 150 comprises one or more filters, the welding sensing system may be configured to determine a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on the first and second intensities determined by optical sensors detecting light passed by optical filters having passbands including the wavelength of the first spectral line 202a and the second spectral line 202b respectively.

Figure 4 is a graph illustrating relationships between oxygen concentration in the plasma gas, shield gas or in the environment around the melt pool and the ratio of the amplitudes of spectral lines, e.g. the intensities of light at the particular wavelengths of the spectral lines, corresponding to oxygen and a constituent of the shield gas, e.g. argon, at a particular weld current, such as 40 Amps. In particular, the graph includes a first graph line 402 illustrating the relationship between oxygen concentration and a ratio of the amplitudes of the first spectral line 202a and the second spectral line 202b, a second graph line 404 illustrating the relationship between oxygen concentration and a ratio of the amplitudes of the first spectral line 202a and the fourth spectral line 202d, a third graph line 406 illustrating the relationship between oxygen concentration and a ratio of the amplitudes of the third spectral line 202c and the second spectral line 202b and a fourth graph line 408 illustrating the relationship between oxygen concentration and a ratio of the amplitudes of the third spectral line 202c and the fourth spectral line 202d.

Returning briefly to Figure 1, in order to determine the relationship between oxygen concentration at the plasma, at the weld pool and/or within the shield gas and the ratio of the amplitudes of the first spectral line 202a and the second spectral line 202b, the welding system 110 may initially be operated within the enclosure 140. A controlled atmosphere may be provided within the enclosure 140, for example, the enclosure may be filled with an inert gas, such as argon gas. The welding sensing system 100 may then be operated whilst a predetermined concentration of oxygen is introduced into the shield gas supplied by the shield gas emitter. The welding sensing system 100 may further comprise a source of oxygen 123. The source of oxygen may be configured to enable oxygen to be introduced into the shield gas supplied by the shield gas emitter, e.g. the weld torch, around the plasma and/or the melt pool. The ratio of the amplitudes of the first spectral line and the second spectral line, e.g. the ratio of the first and second intensities, may then be determined whilst the known concentration of oxygen is being introduced into the shield gas. The process of operating the welding sensing system 100 whilst the predetermined concentration oxygen is introduced into the shield gas may be repeated with one or more other predetermined concentrations of oxygen being introduced into the shield gas in order to determine the relationship between oxygen concentration at the plasma, at the weld pool and/or within the shield gas and the ratio of the amplitudes of the first spectral line and the second spectral line. During the process of determining the relationship between oxygen concentration at the plasma, at the weld pool and/or within the shield gas and the ratio of the amplitudes of the first spectral line and the second spectral line, the welding system 110 may be operated without a feed of weld wire. The process of determining the relationship between oxygen concentration at the plasma, at the weld pool and/or within the shield gas and the ratio of the amplitudes of the first spectral line and the second spectral line may be repeated for one or more different weld current values.

As depicted in Figure 4, there may be a substantially linear relationship between oxygen concentration at the plasma, in the shield gas or in the environment around the melt pool and the ratio of the amplitude of a spectral line corresponding to oxygen, such as the first spectral line or third spectral line, and the amplitude of a spectral line corresponding to a constituent of the shield gas, e.g. argon, such as the second spectral line 202b or the fourth spectral line 202d, at a particular weld current. Furthermore, the relationship may be independent of a number of parameters of the configuration of the welding sensing system, such as the position of the optical fibre 152 and the weld torch 112.

The controller 130 may be configured to modify an operating parameter of the welding system 110 based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas. For example, the controller may be configured to modify a feed rate of the weld wire, flow rates of the plasma and/or shield gas, a welding current passed through the torch, and/or a movement and/or rotation speed of the weld torch and/or bed based on the concentration of oxygen present at the plasma. In some arrangements, the controller 130 may be configured to modify the operating parameters of the welding system 110 in order to maintain the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas between predetermined upper and lower threshold values. Further, if the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas exceeds a predetermined maximum threshold level, the controller 130 may be configured to alert a user to the high concentration of oxygen present during the WAAM process. In some arrangements, the controller may be configured to alert the user if the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas exceeds the predetermined threshold level or another threshold level for a predetermined period of time.

In addition or as an alternative to determining the concentration of oxygen, the controller 130 may be configured to determine the presence of one or more (further) contaminants in the plasma gas, shield gas or in the environment around the melt pool. In particular, the controller 130 may be configured to determine the presence of a material originating from the weld torch 112, such as the electrode of the weld torch. For example, the controller 130 may be configured to determine the presence of tungsten at the plasma, shield gas or in the environment around the melt pool.

Figure 5 illustrates an example emission spectrum 500 determine based on light from the plasma of a weld torch in which a further contaminant, e.g. tungsten, is present. As depicted, the emissions spectrum comprises a plurality of spectral lines which may correspond to either the material of the weld wire/substrate of the contaminant. For example, uncertain spectral lines 502, 504 may correspond to either or both of titanium or tungsten. As depicted, the emission spectrum 500 further comprises a contaminant spectral line 506 at a wavelength corresponding to the contaminant, e.g. tungsten, which is spaced apart in wavelength from spectral lines corresponding to the weld wire/substrate. Additionally, the contaminant spectral line 506 may be spaced apart in wavelength from spectral lines corresponding to the shield gas and oxygen. As depicted, the contaminant spectral line may be at a wavelength of between 250nm and 430nm, such as between 280nm and 305nm, or between 275nm and 310nm.

The controller 130 may be configured to determine the presence of the contaminant, e.g. tungsten, at the plasma, shield gas or in the environment around the melt pool based on a contaminant intensity of light from the plasma at the wavelength of the contaminant spectral line, e.g. an amplitude of the contaminant spectral line. For example, the controller 130 may compare the amplitude of the contaminant spectral line relative to a predetermined threshold value and it may be determined whether the contaminant is present based on the comparison. When the light sensing system 150 comprises one or more optical filters, the optical filters may include a filter with a pass band including the wavelength of the contaminant spectral line, e.g. a wavelength associated with light emitted by the contaminant, and an associated optical detector for determining a contaminant intensity of light filtered by the filter with a pass band including the wavelength of the contaminant spectral line.

With reference to Figure 6, a welding sensing method 600, according to arrangements of the present disclosure, comprises a first step 602, at which a plasma is generated, e.g. between a weld torch of a welding system, such as the welding system 110, and a substrate, and a melt pool is created at a location on a surface of the substrate. The welding sensing method 600 further comprises a second step 604, in which a shield gas is emitted by a shield gas emitter, e.g. an opening of the weld torch, around the plasma. The welding sensing method 600 further comprises a third step 606 in which light emitted by the plasma is received by a light sensing system, e.g. a spectroscopy system. The method further comprises a fourth step 608, in which intensities of the emitted light at one or more predetermined wavelengths are determined. For example, a frequency spectrum of the emitted light may be generated by the spectroscopy system. Alternatively, light within bands including the predetermined wavelengths may be filtered and the intensities of the filtered light within the bands determined. The method 600 further comprises a fifth step 610, at which a concentration of oxygen present at the weld site is determined based on intensities of the light at the one or more predetermined wavelengths. For example, the concentration of oxygen present at the weld site may be determined based on an amplitude of a first spectral line in the spectrum corresponding to oxygen. The concentration of oxygen present at the weld site may be determined based on an amplitude of a first spectral line in the spectrum corresponding to oxygen relative to an amplitude of a second spectral line in the spectrum corresponding to a constituent of the shield gas, such as argon. It will be appreciated that a plurality of the steps of the method may be performed substantially simultaneously. Further, the steps of the method 600 may be repeated during operation of the welding system.

The method 600 may further comprise modifying an operating parameter of the welding system based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas. For example, a feed rate of the weld wire, flow rates of the plasma and/or shield gas, welding current passed through the torch, and/or a movement and/or rotation speed of the weld torch and/or bed may be modified based on the concentration of oxygen present at the plasma. If the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas exceeds a predetermined threshold level, the method 600 may comprise alerting a user to the high concentration of oxygen present. The method 600 may comprise modifying the operating parameters of the welding system 110 in order to maintain the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas between predetermined upper and lower threshold values. Additionally or alternatively, in some arrangements, if the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas exceeds the predetermined threshold level or another threshold level for a predetermined period of time, the method 600 may comprise alerting a user to the high concentration of oxygen present.

Additionally or alternatively to the fifth step 610, the method may comprise determining a presence of a contaminant at the plasma, at the weld pool and/or within the shield gas based on an amplitude of a contaminant spectral line in the frequency spectrum, the contaminant spectral line corresponding to the contaminant, or an intensity of light passed by an optical filter having a pass band including a corresponding wavelength. As described above, the contaminant spectral line may be spaced apart in wavelength from spectral lines corresponding to the weld wire/substrate. Additionally, the contaminant spectral line may be spaced apart in wavelength from spectral lines corresponding to the shield gas and/or oxygen. For example, the contaminant spectral line may by at a wavelength of between 275nm and 310nm.

The method 600 may comprise a first relationship determination step, in which a predetermined concentration of oxygen is introduced into the shield gas emitted by the weld torch. The method 600 may further comprise a second relationship determination step, in which a relationship between a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas, and a ratio of an amplitude of a first spectral line in the spectrum corresponding to oxygen to an amplitude of a second spectral line in the spectrum corresponding to a constituent of the shield gas, such as argon, is determined. The method 600 may comprise operating the welding system in a controlled atmosphere whilst the predetermined concentration of oxygen is being introduced into the shield gas.

It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more exemplary examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1. A welding sensing system comprising: a welding system comprising: a weld torch and/or laser supported by a holder, the weld torch and/or laser configured to generate a plasma at a weld substrate and create a melt pool on a surface of the substrate, wherein the welding system is configured to provide a shield gas around the plasma and/or melt pool, wherein the system further comprises: a light sensing system configured to determine a first intensity of light at a wavelength corresponding to an emission from oxygen within the plasma; and one or more controllers configured to determine a concentration of oxygen present at the plasma, at the melt pool and/or within the shield gas based on the first intensity.
2. The welding sensing system of claim 1, wherein the welding system comprises a shield gas emitter configured to emit the shield gas around the plasma and/or the melt pool.
3. The welding sensing system of claim 1 or 2, wherein the light sensing system is configured to determine a second intensity of light at a wavelength corresponding to an emission by a constituent of the shield gas, wherein the one or more controllers are configured to determine a concentration of oxygen present at the plasma, at the melt pool and/or within the shield gas based on the first intensity relative to the second intensity.
4. The welding sensing system of any of the preceding claims, wherein the light sensing system comprises a spectroscopy system, such as an atomic emissions spectroscopy system, configured to receive light emitted by the plasma and generate a frequency spectrum of the emitted light.
5. The welding sensing system of any of claims 1 to 3, wherein the light sensing system comprises one or more filters, configured to filter predetermined wavelengths of light from the light emitted by the plasma; and one or more optical detectors configured to determine intensities of the light filtered by the one or more filters respectively.
6. The welding sensing system of any of the preceding claims, wherein the light sensing system comprises an imaging device configured to receive light emitted by the plasma, wherein the intensities of light at different respective frequencies is determined based on images captured by the imaging device.
7. The welding sensing system of claim 3 or any of claims 4 to 6 when depending on claim 3, wherein the shield gas comprises argon, wherein the second intensity relates to argon.
8. The welding sensing system of any of the preceding claims, wherein the welding sensing system comprises a Wire Arc Additive Manufacturing (WAAM) system, wherein the weld torch is a weld torch of the WAAM system.
9. The welding sensing system of any of the preceding claims, wherein the welding sensing system comprises a laser welding system, wherein the laser is a laser of the laser welding system.
10. The welding sensing system of any of the preceding claims, wherein the one or more controllers are configured to modify an operating parameter of the welding system, or halt operation of the welding system, based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas.
11. The welding sensing system of claim 10, wherein the operating parameter of the welding system comprises a flow rate of shield gas, a flow rate of plasma forming gas, a feed rate of weld wire, a weld current, and/or a speed at which the weld torch is moved relative to the substrate.
12. The welding sensing system of any of the preceding claims, wherein the light sensing system comprises an optical fibre for receiving the light emitted by the plasma, wherein an end of the optical fibre is mounted on the holder for movement together the weld torch and/or laser.
13. The welding sensing system of any of the preceding claims, wherein the first intensity is less that an intensity of light at another wavelength corresponding to an emission from oxygen within the plasma.
14. The welding sensing system of any of the preceding claims, wherein a sampling frequency of the spectroscopy system is between 500Hz and 0.1Hz.
15. The welding sensing system of any of the preceding claims, wherein the controller is configure to determine a presence of a contaminant at the plasma, at the weld pool and/or within the shield gas based on an intensity of light emitted by the plasma at a contaminant wavelength corresponding to light emitted by the contaminant, wherein the contaminant wavelength is spaced apart from emission wavelengths corresponding to the material of a weld wire, the weld substrate and/or constituents of the shield gas.
16. The welding sensing system of claim 15, wherein the contaminant comprises tungsten or another undesirable material.
17. The welding sensing system of claim 15 or 16, wherein the contaminant spectral line is at a wavelength of between 250nm and 430nm, such as between 280nm and 305nm.
18. A welding sensing method, the method comprising: generating a plasma at a weld substrate, and creating a melt pool on a surface of the substrate; providing a shield gas around the plasma and/or the melt pool; receiving, by a light sensing system, light emitted by the plasma; determining, by the light sensing system, a first intensity of light at a wavelength corresponding to an emission from oxygen within the plasma; and determining a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas based on the first intensity.
19. The method of claim 18, wherein the method further comprises: determine a second intensity of light at a wavelength corresponding to an emission by a constituent of the shield gas within the plasma, wherein the concentration of oxygen is determined based the first intensity and the second intensity.
20. The method of claim 17 or 18, wherein the method further comprises: modifying an operating parameter of the welding system based on the concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas.
21. The method of any of claims 18 to 20, wherein the method further comprises: determining a presence of a contaminant material at the plasma, at the weld pool and/or within the shield gas based on an intensity of light emitted by the plasma at a contaminant wavelength corresponding to an emission by the contaminant material.
22. The method of any of claims 18 to 21, wherein the method comprises: introducing a predetermined concentration of oxygen into the shield gas emitted by the weld torch; determining a relationship between a concentration of oxygen present at the plasma, at the weld pool and/or within the shield gas and a ratio of the first and second intensities.
23. The method of claim 22, wherein the method comprises: operating the welding system in a controlled atmosphere whilst the predetermined concentration of oxygen is being introduced into the shield gas.