GB2636111A

GB2636111A - A temperature measurement assembly and pyrometer assembly

Info

Publication number: GB2636111A
Application number: GB2318208.2A
Authority: GB
Inventors: Peter Tatam Ralph; Mullaney Kevin
Original assignee: Cranfield University
Current assignee: Cranfield University
Priority date: 2023-11-29
Filing date: 2023-11-29
Publication date: 2025-06-11
Also published as: WO2025114235A1; GB202318208D0

Abstract

Pyrometer assembly 150 comprises objective lens 152, camera 154 (e.g. visible or short-wave infrared), bandpass filter 158 which passes a wavelength band of thermally emitted light and filters out light emitted by a source of light interference, and an assembly to optically couple the objective lens to the camera, perhaps a borescope tube or flexible fibre bundle with a diameter of 10 mm or less. A field of view of 10-45° and working distance of 40-300 mm from the objective lens may be achieved. The filter wavelength band may be a portion of the range 425-2000 nm, with 40% transmission of a central wavelength of 1015 nm. In a wire-arc additive manufacturing (WAAM) assembly, the source of light interference may be weld torch or laser 112 that generates plasma at the surface of weld substrate 118 to create a melt pool. Controller 130 may control a WAAM operating parameter based on the temperature of the melt pool, its surrounding or an adjacent area.

Description

A Temperature Measurement Assembly and Pyrometer Assembly

Technical Field

The present disclosure relates to a temperature measurement assembly and a pyrometer assembly, and is particularly, although not exclusively, concerned with a pyrometer assembly which is adapted for use in a WAAM assembly.

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 sequentially deposited 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. The weld torch is translated over the underlying substrate to deposit layers of the weld material over the substrate, in order to build up the desired 3D shape.

Additionally or alternatively, the 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. In particular, it may be desirable to measure the temperature of the melt pool, the deposited metal bead and/or the area of the substrate adjacent to the melt pool.

Previously proposed temperature measurements systems, which have been applied to measure the temperature of the melt pool in a welding process, have experienced inaccuracies due to the high temperature environment in which the system is operating; the presence of the plasma line spectrum and other background radiation sources.

Additionally, when the weld torch and/or laser of the WAAM system is mounted on a movable end effector where space is physically limited, movement of the melt pool in x & y directions has increased the difficulty of temperature measurement due to space constraints.

Statements of Invention

According to an aspect of the present disclosure, there is provided a temperature measurement assembly for measuring a temperature of a surface in the presence of light interference, wherein the assembly comprises: a source of light interference; and a pyrometer assembly, wherein the pyrometer assembly comprises: an objective lens; a camera, e.g. a visible or short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermally emitted light and filter out at least a portion of light emitted by the source of light interference; and an optical assembly configured to optically couple the objective lens to the camera.

The source of light interference may generate light, e.g. visible and/or non-visible light, for example, in a wavelength range of 425nm to 2000nm. The temperature measurement assembly may comprise an assembly for performing a laser-based additive manufacturing processes, a fusion and/or gas welding processes, or may comprise an assembly including, or operating at least partially within, a plasma environment, an internal combustion engine and/or a gas-turbine engine.

The assembly may be a Wire Arc Additive Manufacturing (WAAM) assembly. The source of light interference may comprise a weld torch and/or laser configured to generate a melt pool in a weld substrate. The pyrometer assembly may be configured to determine a temperature of the surface of the weld substrate at the melt pool and/or in an area surrounding, e.g. within a predetermined threshold distance of, and/or adjacent the melt pool.

The bandpass filter may be configured to pass a band of wavelengths including at least a portion of the wavelength range 425 nm to 2000 nm. The bandpass filter may be arranged between the optical assembly and the camera, which may improve ease of access to the bandpass filter. Alternatively, the bandpass filter may be arranged on an opposite side of the objective lens from the optical assembly or within the borescope tube.

The weld torch and/or laser may be configured to generate a plasma. The plasma may emit light at one or more plasma wavelengths. The bandpass filter may be configured to filter out light at the one or more (e.g. predetermined) plasma wavelengths and/or laser wavelengths. The filter may be configured to filter out a wavelength of light emitted by a gas species within the plasma, such as argon. The filter may have a transmission characteristic of 40% or greater at a central wavelength of the passband of the filter. The filter may have a 3dB bandwidth of between 5 nm and 20 nm. A passband of the filter may have a central wavelength of 1015 nm. Alternatively, the filter may have a central wavelength at a longer or shorter wavelength, such as 1100, 1150, or 895 nm for example, providing that the filter transmission bandwidth does not also transmit a plasma/laser emission line. The choice of filter wavelength may also influence the allowable operating temperature range, accuracy of the instrument and camera selection.

The objective lens and/or optical assembly may be configured to achieve a field of view of 10 -45 degrees and/or a working distance of 40-300 mm from the objective lens. One or more lenses of the optical assembly and/or the camera may be configured such that a circular field of view of the optical assembly is aligned, e.g. completely aligned, with a sensor chip of the camera.

The weld torch and/or laser may be supported by an end effector, e.g. of the WAAM assembly. The objective lens may be movable together with the end effector. The optical assembly may comprise a borescope tube, e.g. a small diameter (< 10mm), rigid borescope tube. Additionally or alternatively, the optical assembly may comprise a fibre bundle, e.g. a flexible imaging fibre bundle. The optical assembly, e.g. the borescope tube or fibre bundle, may have a diameter of approximately 10 mm or less. The camera has a sensor array size equal to or greater than 320 x 256 pixels with a pixel pitch of 15 pm. Alternatively, the sensor may have an array size less than 320 x 256 pixels. In either case, the pixel pitch may be less than 15 pm. The camera may be an InGaAs or silicon based camera (e.g. comprising a semiconductor formed from InGaAs and/or silicon), or any other camera which has a spectral response within the filter spectral passband of the bandpass filter.

The assembly may further comprise a controller. The controller may be configured to: determine a temperature of the melt pool, and/or an area surrounding (e.g. within a predetermined threshold distance of) and/or adjacent the melt pool based on measurements by the camera. The controller may be configured to control an operating parameter of the WAAM assembly based on the temperature of the melt pool, and/or an area surrounding and/or adjacent the melt pool. For example, the controller may control a wire feed speed or travel speed for example, based on the temperature of the melt pool, in order to maintain the temperature of the melt pool within a predetermine temperature range.

According to another aspect of the present disclosure, there is provided a pyrometer assembly for the temperature measurement assembly of any of the preceding claims, the pyrometer assembly comprising: an objective lens; an camera, e.g. a short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermally emitted light; and an optical assembly configured to carry light from the objective lens to camera.

According to another aspect of the present disclosure, there is provided a temperature measurement method, the method for measuring the temperature of a surface in the presence of light interference from a light interference source, the method comprising: providing the above-mentioned pyrometer assembly, wherein the bandpass filter is configured to filter out at least a portion of the light interference; arranging the objective lens to receive thermally emitted light from the surface; and determining a temperature of the surface based on measurements by the camera.

According to another aspect of the present disclosure, there is provided a method for a Wire Arc Additive Manufacturing (WAAM) assembly comprising: a weld torch and/or laser; and a pyrometer assembly, wherein the pyrometer assembly comprises: an objective lens; a camera, e.g. a short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermal emission light; and an optical assembly configured to carry light from the objective lens to the infra-red camera, wherein the method comprises: generating a melt pool in a weld substrate using the weld torch and/or laser; determining a temperature of the melt pool based on measurements by the camera; and controlling an operating parameter of the WAAM assembly based on the temperature of the melt pool.

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 subsequently 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 assembly according to arrangements of the

present disclosure;

Figure 2 is a schematic view of a pyrometer assembly for the welding assembly illustrated in Figure 1, according to arrangements of the present disclosure; Figure 3 is a schematic view of a pyrometer assembly for the welding assembly illustrated in Figure 1, according to another arrangement of the present disclosure; Figure 4 is a graph showing a typical short-wave infra-red spectrum measured during a plasma arc deposition process; Figure 5 is a graph showing a typical transmission characteristic of a band pass filter for the pyrometer shown in Figure 2 or 3; Figure 6 is a flow chart illustrating a temperature measurement method according to arrangements of the present disclosure; and Figure 7 is a flow chart illustrating a method for a welding assembly according to arrangements of the present disclosure.

Detailed Description

With reference to Figure 1, a temperature measurement assembly, e.g. a welding assembly, such as a Wire Arc Additive Manufacturing (WAAM) assembly 100 according to arrangements of the present disclosure will now be described.

The temperature measurement assembly comprises a source of light interference. In the arrangement depicted in Figure 1, the welding assembly 100 comprises a weld torch 112 supported on a holder 114, e.g. a weld torch holder, and may comprise fixture tooling 116, for locating a weld substrate 118. The welding assembly 100 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 assembly 100 may comprise a further gas source for providing the shield gas or additional component of the shield gas.

In use of the welding assembly 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 assemblies, the current may 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 assembly 100 may further comprises a shield gas emitter 113 configured to emit a shield gas around the melt pool produced by the welding assembly 100 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 other arrangements, the welding assembly 100 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 114. 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 source of light interference may comprise the weld torch and/or laser.

The welding assembly 100 may 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 an end effector of 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 assembly 100 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 assembly 100 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 assembly 100 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, 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 temperature of the melt pool and surrounding areas, e.g. an area within a threshold distance of a centre of the melt pool, and/or an area adjacent the melt pool, e.g. within a predetermined distance behind the melt pool relative to the weld torch. The melt pool and area surrounding and/or adjacent the melt pool may be referred to as a melt pool region. In particular, it may be desirable for the temperature of the melt pool region to be maintained within a predetermined threshold range, such as between about 2500°C and 500°C, e.g. when the weld material comprises a titanium alloy. The temperature of the melt pool and/or the melt pool region during the WAAM process may affect the material properties of a layer of weld material deposited. Controlling the temperature of the melt pool and/or the region behind the melt pool, is therefore desirable in order to achieve the desired material properties of the deposited material. Further, if the melt pool temperature varies during deposition of a layer of weld material and/or between layers, the material properties of the weld material may vary between different parts of the manufactured component, which may be undesirable.

The temperature of the melt pool region may be affected by the weld current.

Additionally or alternatively, the temperature of the melt pool may be affected by the number of layers previously deposited, inter-pass temperature, feed rate of the weld wire, flow rates of the plasma forming gas and/or shield gas, and/or movement and/or rotation speed of the weld torch and/or work piece travel speed.

In order to provide an improved determination of the temperature at and/or around the melt pool, the welding assembly 100 according to the present disclosure comprises the pyrometer assembly 150, which is configured to determine the temperature at and/or around the melt pool, e.g. within a predetermined distance of the melt pool.

As depicted in Figure 1, the pyrometer assembly 150 comprises an objective lens 152, configured to receive radiation, e.g. thermally emitted light, from the melt pool and/or the melt pool region, a camera 154, such as a visible light and/or infrared camera, and an optical assembly 156 configured to carry light from the objective lens 152 to the camera 154. The objective lens 152 and the optical assembly 156 may together form a borescope assembly 151. As depicted, the objective lens 152 may be coupled to, e.g. mounted on or supported by, the holder 114, so that the objective lens 152 moves together with the weld torch and/or laser during a WAAM process. In some arrangements, the camera 154 may also be coupled to, e.g. mounted on or supported by, the holder 114, so that the camera 154 moved together with the weld torch and/or laser during a WAAM process.

As described in greater detail below, the pyrometer assembly 150 further comprises a filter, e.g. a band pass filter 158, configured to pass wavelengths of radiation within a desirable band of wavelength. For example, the band pass filter may be configured to pass wavelengths corresponding to a desired band of visible and/or infrared, such as short wavelength infra-red light (e.g. up to 1.7 microns or up to 2 microns). The pyrometer assembly 150 is configured such that light carried by the optical assembly is filtered by the bandpass filter 158 prior to reaching the camera 154.

With reference to Figure 2, a pyrometer assembly 200 for the welding assembly 100, according to arrangements of the present disclosure, will now be described. The pyrometer assembly 200 may be provided in place of the pyrometer assembly 150 described above. The pyrometer assembly 200 is similar to the pyrometer assembly 150 and features described above in relation to the pyrometer assembly 150 may apply equally to the pyrometer assembly 200. In particular, the pyrometer assembly 200 comprises an objective lens 202, a band pass filter 204, a camera 206 and an optical assembly 208 configured to carry light from the objective lens 202 to the camera.

In the arrangement depicted in Figure 2, the band pass filter 204 is arranged between the optical assembly 208 and the camera 206 and so filters the light being transmitted by the optical assembly prior to the light reaching the infra-red camera. However, in other arrangements, the band pass filter 204 may be provided in any other location in the pyrometer assembly 200. Depending on the position of the band pass filter, the band pass filter 204 may be arranged such that a cone-angle of the light incident on the band pass filter does not compromise the optical function and efficiency of the filter. For example, the band pass filter can be provided on an opposite side of the objective lens 202 from the camera 206 or optical assembly 208. Accordingly, light passes through the band pass filter 204 to arrive at the objective lens 202.

As illustrated, in the arrangement of Figure 2, the optical assembly 208 comprises a borescope tube 212, e.g. a rigid borescope tube. More particularly, the optical assembly 208 may comprise a borescope tube 212 having a diameter, e.g. an internal or external diameter, of approximately 6 mm, or less than or equal to 6 mm. The borescope tube 212 may be a metal tube, such as a steel or stainless steel tube. The objective lens 202 may be provided at a first end 212a the borescope tube and the infra-red camera may be arranged at or spaced apart from a second end 212b of the borescope tube opposite the first end. In some arrangements, the objective lens 202 may be a forward viewing objective lens. Alternatively, the objective lens 202 may be a side viewing objective lens.

The optical assembly 208 may further comprise one or more lenses 214, 216 for focusing the light onto a sensor 206a of the infrared camera 206. In the arrangement illustrated, the optical assembly comprises two or more lenses. For example, one or more, such as two, eyepiece lenses 214 may be provided at the second end of the borescope tube. The optical assembly 208 may comprise an eyepiece housing 218 and the eyepiece lenses 214 may be mounted in the eye piece housing. As depicted, the borescope tube 212 may extend at least partially into the eyepiece housing. The eye piece lenses 214 may be supported in the eyepiece housing so that the eye piece lens 214 is spaced apart from the second end 212b of the borescope tube.

A camera adaptor lens 216 may be provided between the eyepiece lens 214, or the second end of the borescope tube, and the camera 206, e.g. the sensor 206a. In some arrangements, the camera adaptor lens 216 may be provided as part of the camera 204, or, as illustrated, may be part of a cameral adaptor 220 of the optical assembly 208. The cameral adaptor may comprise an adaptor housing 222 for coupling between the borescope and the camera, e.g. between the eyepiece housing 218 and the infra-red camera 206. The camera adaptor lens may be housed inside the adaptor housing 222. The adaptor body may be configured to support the camera adaptor lens 220 between the second end 212b of the borescope tube, or the eye piece lens 214, and the camera sensor 216a, so as to focus the light from the borescope onto the camera sensor.

The pyrometer assembly 200, e.g. the objective lens 202 and/or the borescope tube 212, and/or the lenses 214, 216 (if present) may be configured to achieve a desired field of view and a desired working distance, e.g. from the objective lens. For example, the pyrometer assembly may be configured to achieve a field of view of 10-45 degrees and a working distance of 40-300 mm from the objective lens. Additionally or alternatively, the sensor 206a of the camera may be configured, e.g. dimensioned, in order to achieve a desired resolution of the image captured by the pyrometer assembly, e.g. given that the image is typically in motion along an x or a y axis. For example, the sensor 206a may be 320 x 256 pixels with a pixel pitch of 15 pm. The sensor 206a of the camera may comprise an Indium gallium arsenide (InGaAs) based semiconductor material. Additionally or alternatively, the sensor 206a of the camera may comprise a silicon based semiconductor material for higher temperature range measurements. Alternatively, the camera may be any other type of camera with any sensor which is responsive to light within the range 425-2000 nm.

As mentioned above, the filter 204 depicted in Figure 2 is arranged between the optical assembly 208 and the camera. However it may be also be arranged on an opposite side of the objective lens 202 from the optical assembly 208.

With reference to Figure 3, a pyrometer assembly 300 for the welding assembly 100, according to another arrangement of the present disclosure will now be described. The pyrometer assembly 300 may be similar to the pyrometer assembly 200 described above, and features described in relation to the pyrometer assembly 200 may apply equally to the pyrometer assembly 300. In particular, the pyrometer assembly 300 may comprise a borescope assembly comprising an objective lens 302, a bandpass filter 304, an optical assembly 310, and a camera 306.

The pyrometer assembly 300 differs from the pyrometer assembly 200 in that the optical assembly 310 comprises an imaging optical fibre bundle 312, e.g. in place of the rigid borescope tube 212. The imaging fibre bundle may have a total number of individual fibres ranging from 6,000 -100,000. The imaging optical fibre bundle 312 may be flexible so that the position of the camera may vary relative to the position of the objective lens 302. For example, when the pyrometer assembly 300 is proved as part of the WAAM assembly 100, the objective lens and a first end 312a of the optical fibre bundle may be arranged to move together with the holder 114 and the camera 206 may not be coupled to the holder 114 and/or may not move together with the weld torch and/or laser during a WAAM process. This is especially advantageous when there is limited space and/or when it is not possible to arrange the optical axis of the assembly in a straight line.

As depicted, the pyrometer assembly 300 may further comprise one or more eye piece lenses 314 and one or more camera adaptor lenses 316, which may be similar to the eye piece lenses 214 and camera adaptor lenses 216 described above. The pyrometer assembly may further comprise one or more imaging lenses 317 provided between the imaging optical fibre bundle 312 and the one or more eye piece lenses 314, e.g. in order to couple the light from the imaging fibre bundle and the camera.

Figure 4 illustrates an example emission spectrum 400 of light that may be sensed from the melt pool of a WAAM assembly, such as the WAAM assembly 100. As shown, the emission spectrum may comprise one or more plasma spectrum lines 402 corresponding to the emission of components of the plasma, such as argon and/or other gases. In order to improve the accuracy of temperature measurements made by the camera, it may be desirable that light interference, e.g. light corresponding to the plasma spectral lines, is not received by the camera. Further, only the thermally emitted radiation from the metal surface may be useful for temperature measurement.

Additionally or alternatively, the emission spectrum may include further spectral lines or emission bands corresponding to other background sources of radiation (e.g. local industrial lighting) that are desirably filtered out of the thermally emitted light arriving at the camera, e.g. in order to improve the accuracy of the temperature measurements made by the camera. Accordingly, a transmission characteristic for the band pass filter 204, 304 may be selected such that light corresponding to the light interference, e.g. plasma spectral lines or further spectral lines are not passed by the band pass filter.

Figure 5 illustrates an example transmission characteristic 500 of a band pass filter, such as the band pass filter 204. As depicted, a passband of the filter may have a central wavelength of 1015 nm. The filter may have a transmission characteristic of 40% or greater at a central wavelength (CWL) of the passband of the filter. The filter may have a 3dB bandwidth of between 5 nm and 20 nm. In the spectral regions where the filter is not transmitting, the filter light attenuation may be greater than an optical density of 4. In other arrangements, the passband of the filter may have a different central wavelength, such as 1100, or 1150 nm (or shorter/ longer wavelengths). The central wavelength and/or 3dB bandwidth may be selected such that the filter transmission bandwidth does not coincide with a plasma spectral line and/or a further spectral line. Additionally, the central wavelength may be selected based on a desired pyrometer operating temperature range and/or desired pyrometer accuracy, and/or dependant on the metal the temperature of which is being measured.

Returning to Figure 1, the WAAM assembly 100 may further comprise a WAAM controller 130. The WAAM controller may be configured to control the operation of the WAAM assembly. In particular, the WAAM controller 130 may be configured to control the operation of the weld torch and/or laser and the pyrometer assembly.

The WAAM controller 130 may be configured to determine a temperature at or around the melt pool, e.g. in the melt pool region, based on a signal received from the camera 206, 306 of the pyrometer assembly, for example, the WAAM controller 130 may be configured to process the signal received from the camera, e.g. using temperature measurement software to determine the temperature in the melt pool region. In some arrangements, the WAAM controller may be configured to control the operation of the WAAM assembly based on the temperature. For example, the WAAM controller 130 may be configured to control an operating parameter of the WAAM assembly 100, such as 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, laser power, inter-pass temperature and/or movement and/or travel speed of the weld torch and/or bed, based on the temperature. The WAAM controller 130 may control the operating parameter in order to maintain the temperature within a predetermined threshold range of temperatures, e.g. using a feed-back loop.

In the arrangements described above, the pyrometer assembly is provided as part of a WAAM assembly for measuring a temperature of a surface of a weld substrate in the melt pool region in the presence of light interference from the weld torch and/or laser, which generates plasma during operation of the WAAM assembly. However, in other arrangements, the pyrometer assembly may be provided as part of any other temperature measurement assembly within which it is desirable to determine the temperature of a surface in the presence of light interference, e.g. originating from a light interference source included in the temperature measurement assembly. For example, the temperature measurement assembly may comprise a laser-based additive manufacturing processes, a fusion and/or gas welding processes, an assembly including a plasma environment, an internal combustion engine and/or a gas-turbine engine. Features described above in relation to the WAAM assembly may equally apply to such a temperature measurement assembly.

With reference to Figure 6, a temperature measurement method 600 according to the present disclosure, will now be described. The method may be for measuring the temperature of a surface, e.g. of a weld substrate, in the presence of light interference from a light interference source, such as light from plasma generated by a weld torch or laser. The method 600 may be performed by a temperature measurement assembly, such as the welding assembly described above.

The method may comprise a first step 602, in which light interference is generated by a component of the temperature measurement assembly. For example, when the temperature measurement assembly comprises the welding assembly, the first step 602 may comprise generating a plasma using the weld torch and/or laser. Additionally or alternatively, light interference may be generated by a source that is not part of the temperature measurement assembly.

The method comprises a second step 604, in which a pyrometer assembly, such as the pyrometer assembly 150 is provided. In a third step 606, the pyrometer assembly, e.g. the objective lens of the pyrometer assembly, is arranged to receive thermally emitted light from the surface.

The method further comprises a fourth step 608, in which a temperature of the surface is determined based on measurements by the camera. For example, the temperature may be determined in the fourth step 608 in the manner described above with reference to the operation of the temperature measurement assembly, e.g. the welding assembly.

With reference to Figure 7, a method 700 for a welding assembly, e.g. a WAAM assembly, such as the WAAM assembly 100 shown in Figure 1 will now be described.

The WAAM controller 130 may be configured to control the operation of the WAAM assembly 100 to carry out the method. The method 700 comprises a first step 702, in which a melt pool is generated in a weld substrate using a weld torch and/or laser; The method may further comprise a second step 704, in which a temperature of the melt pool and/or melt pool region is determined based on the signal output from the pyrometer assembly, e.g. the camera. The method 700 may further comprise a third step 706, in which an operating parameter of the WAAM assembly is controlled based on the temperature of the melt pool and/or the melt pool region.

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 temperature measurement assembly for measuring a temperature of a surface in the presence of light interference, wherein the assembly comprises: a source of light interference; and a pyrometer assembly, wherein the pyrometer assembly comprises: an objective lens; a camera, e.g. a visible or short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermally emitted light and filter out at least a portion of light emitted by the source of light interference; and an optical assembly configured to optically couple the objective lens to the camera.
2. The temperature measurement assembly of claim 1, wherein the assembly is a Wire Arc Additive Manufacturing (WAAM) assembly; wherein the source of light interference comprises a weld torch and/or laser configured to generate a melt pool in a weld substrate; and wherein the pyrometer assembly is configured to determine a temperature of the surface of the weld substrate at the melt pool and/or in an area surrounding and/or adjacent the melt pool.
3. The temperature measurement assembly of claim 1 or 2, wherein the bandpass filter is configured to pass a band of wavelengths including at least a portion of the wavelength range 425 nm to 2000 nm.
4. The temperature measurement assembly of any of claims 1 to 3, wherein the bandpass filter is arranged between the optical assembly and the camera.
5. The WAAM assembly of claim 2, or any of the preceding claims when depending on claim 2, wherein the weld torch and/or laser is configured to generate a plasma, wherein the plasma emits light at one or more plasma wavelengths, and wherein the bandpass filter is configured to filter out light at the one or more plasma wavelengths and/or laser wavelengths.
6. The WAAM assembly of claim 5, wherein the filter is configured to filter out a wavelength of light emitted by a gas species within the plasma, such as argon.
7. The temperature measurement assembly of any of the preceding claims, wherein the filter has a transmission characteristic of 40% or greater at a central wavelength of the passband of the filter.
8. The temperature measurement assembly of any of the preceding claims, wherein the filter has a 3dB bandwidth of between 5 nm and 20 nm.
9. The temperature measurement assembly of any of the preceding claims, wherein a passband of the filter has a central wavelength 1015 nm.
10. The temperature measurement assembly of any of the preceding claims, wherein the objective lens and/or optical assembly are configured to achieve a field of view of 10 -45 degrees and/or a working distance of 40-300 mm from the objective lens.
11. The temperature measurement assembly of any of the preceding claims, wherein one or more lenses of the optical assembly and/or the camera are configured such that a circular field of view of the optical assembly is aligned, e.g. completely aligned, with a sensor chip of the camera.
12. The WAAM assembly of claim 2, or any of the preceding claims when depending on claim 2, wherein the weld torch and/or laser is supported by an end effector, wherein the objective lens is movable together with the end effector.
13. The temperature measurement assembly of any of the preceding claims, wherein the optical assembly comprises a borescope tube, e.g. a small diameter (< 10mm), rigid borescope tube.
14. The temperature measurement assembly of any of claims 1 to 12, wherein the optical assembly comprises a fibre bundle, e.g. a flexible imaging fibre bundle.
15. The temperature measurement assembly of any of the preceding claims, wherein the optical assembly, e.g. the borescope tube or fibre bundle, has a diameter of approximately 10 mm or less.
16. The temperature measurement assembly of any of the preceding claims, wherein the camera has a sensor array size equal to or greater than 320 x 256 pixels with a pixel pitch of 15 pm.
17. The temperature measurement assembly of any of the preceding claims, wherein the camera is an InGaAs camera.
18. The WAAM assembly of claim 2, or any of the preceding claims when depending on claim 2, wherein the assembly further comprises a controller, wherein the controller is configured to: determine a temperature of the melt pool, and/or an area surrounding and/or adjacent the melt pool based on measurements by the camera.
19. The WAAM assembly of claim 18, wherein the controller is configured to control 15 an operating parameter of the WAAM assembly based on the temperature of the melt pool, and/or an area surrounding and/or adjacent the melt pool.
20. A pyrometer assembly for the temperature measurement assembly of any of the preceding claims, the pyrometer assembly comprising: an objective lens; an camera, e.g. a short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermally emitted light; and an optical assembly configured to carry light from the objective lens to camera.
21. A temperature measurement method, the method for measuring the temperature of a surface in the presence of light interference from a light interference source, the method comprising: providing the pyrometer assembly of claim 20, wherein the bandpass filter is configured to filter out at least a portion of the light interference; arranging the objective lens to receive thermally emitted light from the surface; and determining a temperature of the surface based on measurements by the camera.
22. A method for a Wire Arc Additive Manufacturing (WAAM) assembly comprising: a weld torch and/or laser; and a pyrometer assembly, wherein the pyrometer assembly comprises: an objective lens; a camera, e.g. a short wave infra-red camera; a bandpass filter configured to pass a band of wavelengths comprising thermal emission light; and an optical assembly configured to carry light from the objective lens to the infra-red camera, wherein the method comprises: generating a melt pool in a weld substrate using the weld torch and/or laser; determining a temperature of the melt pool based on measurements by the camera; and controlling an operating parameter of the WAAM assembly based on the temperature of the melt pool.