GB2532024A

GB2532024A - Substrate cooling device

Info

Publication number: GB2532024A
Application number: GB1419688.5A
Authority: GB
Inventors: Harold Boswell John; Clark Daniel
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2014-11-05
Filing date: 2014-11-05
Publication date: 2016-05-11
Also published as: GB201419688D0

Abstract

Additive manufacturing apparatus 1 comprises a substrate heating device 2 configured to heat a sub-region of a substrate 12 and a substrate cooling device 3 having a nozzle 4 configured to direct a cooling fluid 6 onto the substrate sub-region 12 wherein an exhaust passage 5 to remove spent cooling fluid is coaxial with the nozzle 4. The nozzle may further comprise a plurality of flow channels 8 wherein the nozzle is maintained at a distance from the substrate up to twenty times the diameter of said flow channels and the channels are configured such that the flow rate of the cooling fluid varies between the flow channels 8. Also included is a method of post weld cooling using the apparatus 1.

Description

Substrate Cooling Device

Field of the Disclosure

The present disclosure relates to an apparatus and method for the reduction of residual stress in a deposited layer of a weld. In particular, though not exclusively, it relates to an apparatus and method for the cooling of said deposited layer to reduce residual stress in a given weld line or layer.

Background of the Disclosure

The process of welding is a commonly used method of fabrication used to join two similar or dissimilar materials and/ or components using coalescence. Most typically, the welding process includes a localised melting of adjoining components whilst adding a filler material.

The addition of the filler material to the melted region forms a pool of molten material termed the weld pool. Upon cooling, the weld pool solidifies to form a strong joint between the two components.

There are many welding methods known in the art, including, for example, Shielded Metal Arc Welding, Fluid Tungsten Arc Welding, Tungsten Inert Fluid (TIG) and Metallic Inert Fluid (MIG) welding. Furthermore, there are many heat sources available for heating the filler material and adjoining components, including, for example, fluid flame, electric arc, laser, electron beam, friction, and ultrasound methods. It will be appreciated that each substrate heating device may additionally comprise measures to reduce the degree of contamination during the welding process.

Of particular interest in welding operations is the area immediately surrounding the weld pool known as the Heat Affected Zone (HAZ). This area represents a region of the substrate which is not melted, but is heated to the extent that the microstructure and/ or properties of the substrate are altered or modified. In particular, the size of the HAZ may be particularly influential in deciding the properties and/ or quality of the weld following welding, such properties including the levels of residual stress and/ or distortion, and the degree of microstructural modification associated with localised heating characteristics. Such welding defects arising from poor quality welds may include, for example, cracks, distortion, fluid inclusions (porosity), non-metallic inclusions, lack of fusion, incomplete penetration, lamellar tearing, and undercutting.

Accordingly, the degree of the alteration/ modification of material properties, and in turn the quality of the weld, may depend on several factors including, for example, the substrate material, the filler material and the concentration of the heat source about a localised area.

When utilising laser welding processes for example, one method of feeding a filler material into the weld pool is by using a process known in the art as Laser Metal Deposition (LMD), also known as laser engineered net shaping or laser powder forming. LMD is an additive layer process, and may be particularly suitable for forming metal parts or weld geometries from computer-aided design (CAD) models. Using LMD, a part may be welded or a profile built by metal powder being blown or injected into a weld pool created by a focussed, high-energy laser beam, however, deleterious metallurgical features resulting from an enlarged HAZ may remain.

In particular, heating and cooling during processes such as fusion welding or additive processes such as LMD, lead to high residual stresses, along with the possibility of residual gasses within the shielding environment interacting with, and deleteriously affecting the deposited layer of the weld One commonly utilised solution is to apply cooling to the weld. This can be done using a number of methods including, for example, liquid or blown cooling on the underside of the weld. However, cooling is most effective if directed in the localised region as close to the substrate heating device as practically possible.

An issue with cooling the area in immediate vicinity of a typical LMD weld pool is that the blown powder feed may be disrupted during deposition, or the weld pool influenced such that sub-optimal microstructures and/ or welding characteristics are observed. Furthermore, interaction of cooling fluid with the blown powder feed may increase the chance of impurities and/ or foreign matter entering the weld pool, thus reducing weld quality. However, if the cooling is not applied in close enough vicinity of the weld pool, larger HAZs will be observed, leading to sub-optimal microstructural characteristics, and a corresponding reduction in mechanical properties of the weld.

Accordingly, it would be advantageous to provide an apparatus and method for the combined deposition and cooling of said deposited layer without the aforementioned disadvantages.

Summary of the Disclosure

According to a first aspect of the present disclosure, there is provided a melt deposition additive manufacturing apparatus, the apparatus comprising a substrate heating device configured to heat a sub-region of a substrate and a substrate cooling device, the cooling device comprising a nozzle configured to direct a cooling fluid onto the substrate sub-region and an exhaust passage configured to remove spent cooling fluid, wherein the exhaust passage is coaxial with the nozzle.

Thus, the present disclosure provides an apparatus in which heat removal may be targeted at a sub-region of a substrate, as opposed to a general cooling of an enlarged area which is otherwise unheated by the additive manufacturing process. Meanwhile, the coaxial exhaust ensures that the spent cooling fluid does not interact with other parts of the substrate, which could otherwise lead to undesirable gas flows and / or heating around other parts of the substrate. Thus, in this way, cooling fluid exiting the nozzle is at least substantially held within and collected from a void created between the nozzle, the substrate sub-region and/ or deposited material, and the internal walls of the exhaust passage. Alternatively, should the exhaust passage be coaxially arranged within the nozzle, the void may be envisioned to exist between the primary nozzle, the surface of the substrate and/ or deposited material, and the internal walls of the exhaust passage.

Optionally, the apparatus may comprise a material deposition device. The sub-region may comprise a region containing material deposited by the material deposition device after heating by the heating device. Optionally, the sub-region may essentially consist of the region containing material deposited by the material deposition device after heating by the heating device.

Optionally, the exhaust passage may be configured to direct spent cooling fluid away from the substrate sub-region.

Thus, in this way, interaction of the spent cooling fluid with the material deposited by the material deposition device prior to heating may be at least substantially reduced.

Optionally, the exhaust passage may be configured to direct spent fluid in a direction away from a deposition path of the deposition device.

Thus, in this way, it will be appreciated that the nozzle may be positioned relative to the material deposition device and/ or substrate heating device such that it is maintained as closely as possible to the material deposited by the material deposition device without affecting the flow of either a shielding fluid or material during deposition.

Optionally, the nozzle and/ or exhaust passage may be positioned within around 200mm or less from the substrate heating device and/ or material deposition device.

Preferably, the nozzle and/ or exhaust passage may be spaced from the substrate heating device and/ or material deposition device by up to 100mm.

Most preferably, the nozzle and/ or exhaust passage may be spaced from the substrate heating device and/ or material deposition device by up to 50mm.

It will however be appreciated that spacings of greater than or less than the described figures may be envisaged depending on separable process parameters. For example, the nozzle and/ or exhaust passage may be spaced from the substrate heating device and/ or material deposition device by up to 300mm.

Optionally, the substrate heating device may be arranged to direct heat into the deposition path of the deposition device.

Optionally, the deposition device may be arranged to direct a deposition material into a heat path provided by the substrate heating device.

Thus, in this way, the material deposition device may be arranged to direct a deposition material into a heated sub-region created by interaction of the heat path with the substrate and/ or deposited material. Alternatively, the material deposition device may be arranged to direct a deposition material directly in to the heat path such that the deposition material is heated prior to interaction with the substrate.

Optionally, the nozzle and / or exhaust passage may be spaced from the substrate, and the apparatus may additionally comprise an actuation system to monitor and/ or alter the spacing. The nozzle may comprise a plurality of flow channels.

Thus, in this way, the positioning of the nozzle relative to the substrate may be altered depending on, for example, the size of the flow channels or the speed of the fluid exiting the nozzle.

Optionally, the nozzle may be maintained at a distance from the substrate of up to twenty times the diameter of the flow channels.

Preferably, the nozzle may be maintained at a distance from the substrate of up to ten times the diameter of the flow channels.

Most preferably, the nozzle may be maintained at a distance from the substrate of up to six times the diameter of the flow channels.

It will however be appreciated that distances of greater than or less than the described figures may be envisaged depending on separable process parameters. For example, the nozzle may be maintained at a distance from the substrate of up to around thirty times the diameter of the cooling holes.

Optionally, an outlet of the nozzle and an inlet of the exhaust passage may be differently spaced from the substrate. The coaxially outer one of the nozzle outlet and the exhaust inlet may be more closely spaced from the substrate than the other one of the nozzle outlet and the exhaust inlet.

Optionally, the coaxially outer one of the nozzle and the exhaust may be more closely spaced from the substrate than the other one of the nozzle and the exhaust.

Thus, in this way, the coaxially outer one of the nozzle or exhaust passage may be spaced from the sub-region of the substrate such that fluid surrounding the outer walls of the exhaust passage may be drawn into the void under reduced pressure.

Optionally, the flow channels may be configured such that mass flow rate of cooling fluid may vary between the flow channels.

Optionally, the nozzle is configured such that the velocity of cooling fluid leaving the nozzle is at or about the speed of sound of the cooling fluid.

Optionally, the one or more of the mass flow rate and the pressure ratio of the fluid supplied to the nozzle or flow channels is such that the cooling fluid leaving the nozzle or flow channels is at or about the speed of sound of the cooling fluid.

Optionally, the flow channels may be shaped, angled or positioned relative to one another to preferentially direct cooling fluid through a subset of flow channels to preferentially direct cooling to a predetermined location.

Thus, in this way, it is possible to preferentially direct cooling fluid through certain flow channels to promote cooling in a desired location, area or pattern. In particular, the arrangement of flow channels may give rise to tailored heat gradients to minimise metallurgical implications and potentially deleterious effects arising from rapid cooling.

Optionally, the flow channels may be arranged as an array of holes, such as a grid pattern, a series of slots, a circular pattern or a teardrop pattern.

Optionally, the flow channels may be arranged as multiple clusters of holes in accordance with the aforementioned arrangements.

Thus, in this way, the flow of cooling fluid exiting the one or more cooling passages may be configured such that at least a substantial portion of the cooling fluid may exit the nozzle at a predetermined position or region within the substrate cooling device.

Optionally, the flow channels may be arranged such that at least a substantial portion of the cooling fluid leaving the nozzle is directed away from a heat affected zone.

Alternatively, cooing fluid leaving the nozzle may be directed towards the substrate subregion in a direction substantially perpendicular to the surface. Additionally or alternatively, cooling fluid may be directed towards the exhaust passage to at least substantially prevent cooling fluid from mixing with the shielding gas.

Optionally, the substrate heating device may comprise a weld head configured to melt the sub-region of the substrate to provide a melt pool. Alternatively, pre-heating of the subregion may be provided by either a laser or an induction device.

Optionally, the substrate heating device may comprise a post weld heat treatment device.

According to a second aspect of the present disclosure, there is provided a method of post-weld cooling utilising an apparatus in accordance with the first aspect of the present

disclosure.

According to a third aspect of the present disclosure, there is provided an article formed by the method in accordance with the second aspect of the disclosure.

Brief Description of the Drawings

A preferred embodiment of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a cross-section of a first additive manufacturing apparatus in accordance with

the present disclosure;

Figure 2 shows a cross sectional view of the part of figure 2 along the line A-A; Figure 3 shows a cross sectional view of part of the apparatus of figure 1; Figure 4 shows an end view of the part of the apparatus of figure 3; Figure 5 shows a cross section of a part of a second apparatus in accordance with the present disclosure; an, Figure 6 shows part of a third apparatus in accordance with the present disclosure.

Detailed Description of the Preferred Embodiments

Figures 1 to 4 show a first embodiment of an additive manufacturing process. Fig. 1 shows a cross-section of the additive manufacturing apparatus 1. The additive manufacturing apparatus includes a material deposition device and/ or substrate heating device 2 and a substrate cooling device 3 which includes cooling channels and/ or flow holes 8. The substrate cooling device 3, as shown in figure 1, is comprised of a nozzle 4 coaxially aligned within an exhaust passage 5, the nozzle being configured to direct a cooling fluid 6 onto a substrate sub-region 12 via at least one cooling passage in the form of flow channels 8,4. The exhaust passage 5 is configured to vent spent fluid to atmosphere. Optionally, the exhaust passage 5 may extend into an exhaust passage extension flue 9 as shown in Figure 1. In particular, the exhaust passage 5 is configured to remove spent cooling fluid and direct spent cooling fluid away from the substrate sub-region 12.

As shown in Figure 1, the material deposition device and/ or substrate heating device 2 may also comprise an application head 13 which may further comprise, for example, a weld head 17 which provides heat to form a weld pool 18 to bond powder provided by the deposition head 2 to the substrate 11. In a further embodiment, a post weld heat treatment device such as for example, a laser 19 may also be provided, which provides further heat to areas heated by the weld head to avoid developing a HAZ.

It will be appreciated that the additive manufacturing apparatus 1 of figure 1 may be particularly suitable for, although not limited to use with Laser Metal Deposition (LMD) processes. In particular, filler material 34 in the form of a powder may be delivered through an application head 13 or weld head 17 directly into the weld pool 18 and/ or laser beam 19 in order to form a deposited layer of material 7,10, the deposited layer 7,10 forming a further layer atop a pre-existing substrate 11. Powder may be delivered, for example, by use of gravity or a pressurised carrier fluid. During the welding process, inert shroud fluids such as, for example, argon or nitrogen may be used to shield or aid in preventing elements such as oxygen from interacting with or being absorbed into the melt pool, thus reducing the integrity and/ or mechanical properties of the final weld.

LMD is commonly associated with a number of advantages over some of the more commonly used welding methods. In particular, LMD has the added advantage that the process may produce parts in a wide range of alloys, including titanium, stainless steel, aluminium, or other specialty/ specially formulated materials such as nickel-based superalloys; as well as composite and functionally graded materials. As such applications may typically include, for example, repair and overhaul, rapid prototyping, rapid manufacturing and limited-run manufacturing for aerospace, defence, and medical markets.

In particular, LMD may also be suitable for producing "near" net shape parts in instances where it might not possible to make an item to exact specifications. In these cases, and due to, for example, blown powder inconsistencies or irregularities, post production light machining, surface finishing, or heat treatment may be applied to achieve final compliance with a given specification or surface finish characteristic.

Referring again to Figure 1, Figure 1 shows the arrangement of the substrate cooling device 3 relative to the substrate heating and/ or material deposition device 2, along with the movement in use of the cooling fluid 6 during operation.

In particular, Figure 1 shows cooling fluid 6 being directed through the nozzle 4 onto the substrate sub-region 12. Upon contact of the cooling fluid 6 with the surface of the substrate 12, the fluid 6 is heated and spent cooling fluid is subsequently removed via the exhaust passage 5, thus removing thermal energy from the substrate 12. In this way, thermal energy is removed from the surface of the metallic structure by heating the fluid 6 and continually replacing spent fluid 15 with fresh cooling fluid 6 such that spent fluid 15 is directed towards and into the exhaust passage 5. Alternatively, it may be envisioned that the spent cooling fluid 15 be recirculated, for example, within a closed, or semi-closed system to collect and/ or cool the fluid 6 once spent fluid 15 has interacted with the substrate 12. In particular, it may be envisioned that the exhaust 9 be connected to a recirculating pump that that recirculates the gas via a heat exchanger to cool the spent fluid 15 before being supplied once again to cool the substrate surface 12, but it will be appreciated that any such method may alternatively be used. Additionally, the system may include a separate control system to monitor the condition or quantity of the fluid within the system, so replenishing any lost fluid, replacing the fluid, or providing an indication when the fluid may require replacement. It will be appreciated that any such process parameter may be similarly monitored and/ or controlled by any such similar means of feedback and/ or process control.

In operation, due to the large temperature difference between the cooling fluid and the heated substrate, and in accordance with Fourier's equation for heat transfer heat flux, flow of cooled fluid onto the surface of the deposited layer or weld, in sufficient quantities or at a sufficient flow rate results in rapid cooling of the localised region. This is due to the large temperature difference (AT) between the substrate 12 and the fluid 6, along with high heat transfer coefficients of the fluid resulting in a large heat flux from the surface of the work piece. Of note, the rate and quantity of heat removal will depend on, for example, the specific heat capacity of the fluid 6, plus the mass and temperature of the substrate 12 itself. As such, it is preferable to use a highly pure fluid 6 with a high specific heat capacity and inert properties in order to optimise the rate of thermal energy removal and prevent elements contained within the fluid from reacting with, or diffusing into the surface of the substrate 12, particularly at elevated temperatures. Such a fluid 6 may include, for example, argon or nitrogen.

Referring again to Figure 1, the exhaust passage 5 shown is configured around the nozzle 4 such that the nozzle 4 is coaxially aligned within the exhaust passage 5. During use, the exhaust passage 5 is configured to remove spent exhaust fluid 15 once the fluid 6 has interacted with the substrate 12. As such, it can be seen that the cooling fluid 6 exiting the nozzle 4 and interacting with the substrate 12 is at least substantially held within and collected from a void 14 within the nozzle 4 and exhaust passage 15 arrangement.

In particular, a portion of the exhaust passage 5 may extend radially outwardly from the substrate cooling device 3 via an exhaust extension passage 9, i.e. generally normally to the nozzle 4 such that exhaust fluids 15 are released a sufficient distance and in a direction away from the material deposition device 2 and/ or process. Releasing spent fluids 15 at a safe distance from the area adjacent the deposition process ensures that interaction of the exhaust fluids 15 with the material deposition device 2 and associated processes is at least substantially reduced. In particular, the exhaust passage 5 is intended to aid in reducing the quantity of exhaust fluid disturbing powder flow, or interacting with the newly despotised material 7,10 during additive manufacture.

Figure 2 shows a frontal view of the substrate cooling device 3 along the direction of travel. In particular, figure 2 shows the outermost region of the exhaust passage 15 along with the arrangement of the exhaust extension flue 9 relative to the exhaust passage 5.

In particular, it will be appreciated that many discrete factors may influence the quality of a weld and/ or the material immediately surrounding the weld pool 12. Focusing on the HAZ, depending on the characteristics of the weld, the HAZ can be of varying size and geometry depending, for example, on the material being used (inclusive of the thermal diffusivity), the method of welding and the heating input and/ or output. Accordingly, the amount of heat input provided by the welding process has a direct effect on the size of the HAZ. As a result, processes having smaller or increasingly focussed heat inputs are advantageous due to a reduction in the size of the HAZ. As such, processes such as, for example, electron beam or laser beam welding techniques that provide a highly focused heat input and a reduced amount of heat spread typically result in a smaller HAZ and a corresponding increase in weld quality.

Figure 3 shows a cross-section of the substrate cooling device 3 along line A-A', as shown in Figure 2, including cooling channels and/ or flow holes 8.

Figure 4 shows an end view from the direction B of figure 3 of the substrate cooling nozzle 4 and exhaust passage 5, the view showing internal features of the cooling device 3 inclusive of cooling channels and/ or flow holes 8 configured to direct cooling fluid 6 to one or more locations upon the substrate sub-region 12. In particular, Figure 4 shows an arrangement of cooling channels and/ or flow holes 8 suitable for the flow of individual jets of fluid 6 onto the substrate sub-region 12.

As shown in Figure 3, it will be appreciated that cooling fluid flow rate/ velocity may vary between the flow channels 8 depending on, for example, sizing and/ or location of the flow channels 8 themselves. In particular, flow rate of the cooling fluid 6 may be varied between the flow channels 8 depending on, for example, the choking of the nozzle 4 or flow channels 8, and/ or the size of the cooling holes 8 selected for the specific application. In this instance, choking the nozzle 4 or flow channels 8 shall ensure that the pressure ration across the nozzle 4 or flow channels 8 is sufficient for the flow to be at its maximum velocity, which is the speed of sound for the cooling fluid 6 utilised to cool the substrate 12. It is known that heat transfer depends on several factors, including for example, Reynolds number and velocity of cooling fluid 6. As such, increasing the Reynolds number or velocity of cooling fluid shall intrinsically lead to an increased heat transfer coefficient. Where increased cooling fluid velocity equates to a high Reynolds number, a choked nozzle 4 shall therefore give rise to the maximum cooling fluid velocity, and the maximum cooling effect for that particular cooling fluid, nozzle and flow channel arrangement.

Thus, a flow array or nozzle 4 being either transverse or in line with the deposited layer, a square/ rectangular array, or a single tube could equally be used to alter flow characteristics of the fluid 6 exiting the nozzle 4. In this way, flow channels 8 may be shaped, angled or positioned to alter the flow characteristics to suit particular temperature profiles and/ or cooling rates. In particular, flow channels 8 may be sized, shaped, angled or positioned so as to achieve a greater mass flow rate of cooling fluid flow within the centre of any one or more of the flow channel arrangement, the substrate cooling nozzle 4 or the exhaust passage 5.

Referring once again to Figure 3, Figure 3 also demonstrates the arrangement of the nozzle 4 relative to the exhaust passage 5, wherein the nozzle 4 and/ or exhaust passage 5 may be spaced from the substrate heating device and/ or material deposition device 2 by up to 200mm. In particular, a void 14 is shown to exist within the substrate cooling device 3 itself.

This void 14 is provided since an outlet of the nozzle 4 is spaced from the substrate 12 by a greater distance than the than the inlet of the exhaust passage 5 such that the flow channels 8 are at least partially recessed within the nozzle arrangement 4. In a further embodiment, it will be appreciated that the nozzle 4 may be shorter or longer, and the flow channels 8 may alternatively project from the nozzle arrangement 4 itself. In the described embodiment shown in figure 1, the nozzle 4 is spaced up to six times the diameter of the cooling holes 8 from the substrate 12, and the entrance to the exhaust passage Sis spaced two or more times the diameter of the cooling holes 8 from the substrate 12. In other cases, the nozzle 4 could be spaced up to twenty times the diameter of the cooling holes 8 from the substrate 12. Thus, in a further embodiment, the coaxially outer one of the nozzle 4 and the exhaust passage 5 may be more closely spaced from the substrate 12 than the other one of the nozzle 4 and the exhaust passage 5.

Referring again to Figures 1 and 3, the size of the substrate cooling device 3 and the number and arrangement of the flow channels 8 within the nozzle 4 will depend on various process parameters arising from the additive manufacturing process. More specifically, important factors in determining the amount of cooling required might include, for example, the energy density (W/mm2) required for the fusion process, the thermal mass of material 12 adjacent the material deposition process, the working temperature required for deposition, the proximity of the substrate cooling device 3 relative to the material deposition device 2, the specific heat gradient or cooling pattern required and the travel rate of the material deposition device 2 and/ or substrate cooling device 3 relative to the substrate 12.

In such a way, the specific arrangement of the substrate cooling device 3 relative to the substrate 12, along with the arrangement, size and location of cooling holes 8 will directly influence the cooling process. For example, a process with a high energy density will require more heat extraction via more holes 8, more flow or a larger cooling nozzle 4. Also the amount of thermal energy removed will depend, for example, on the size of the area cooled 12 by the substrate cooling device.

During use, the nozzle 4 may be at spaced from the deposited layer, weld or substrate 12. In particular, the spacing between the cooling device 3 and the deposited layer, weld or substrate 12 may be controlled via an actuation system so as to vary the spacing so as to control the amount of adjacent fluid 16 entering the void under reduced pressure. Furthermore, a flow of fluid 16 into the void 14 and through the system under reduced pressure provides the further advantage that hot fluid 16 will be removed from the deposition atmosphere, thus reducing the temperature of the operational environment 16.

Referring to figure 1, the substrate cooling device 3 will be mounted in close proximity to the material deposition device 2 and will substantially follow the path of the material deposited during material addition, such that the substrate 12 will be cooled in use by the substrate cooling device 3 following deposition and heating by the material deposition and/ or substrate heating device 2. Figure 1 shows one particular arrangement, wherein the substrate cooling device 3 is angled away from the material deposition device 2 so as to direct flow from the nozzle 4 away from one or more of the shielding fluid flow during welding and the material being deposited during the deposition process.

Figure 5 shows a second embodiment of an additive manufacture apparatus inclusive of an array cooling 20. In particular, Figure 5 shows an array comprising two or more linearly aligned channels or nozzles 21, which may be particularly suitable for the build of a thin lattice structure by material deposition and/ or additive manufacture wherein multiple substrate cooling devices or flow channels are required.

In use, and as shown by the arrangement of figure 5, one or more inlet nozzles 22 direct fluid into a plenum-type chamber 23, which splits inlet flow into two or more linearly aligned channels 21. In this way, cooling fluid passing through the channels 21 may then be directed onto the deposited layer, weld or substrate 12. Upon contact of the cooling fluid 6 with the surface of the deposited layer, weld or substrate 12, the fluid is heated and subsequently removed by the spent cooling fluid 15 passing into the exhaust passage 5. As such, thermal energy is removed from the surface of the metallic structure by heating the fluid 6 and continually replacing spent fluid 15 with fresh cooling fluid 6 such that spent fluid 15 is directed towards and into the exhaust passage 9. Alternatively, it will be appreciated that fluid may be recycled by collecting, cooling and recirculating spent fluid 15.

In use, it may be that a stepped or graduated cooling effect is required, which may be achieved, for example, by altering the flow characteristics of the device and/ or the mass flow rates or velocity of fluid 6 exiting the separate nozzles, for example, by changing the size of, or choking certain holes and/ or flow channels 21, or altering the flow characteristics of the fluid entering the device 20.

It will be appreciated that a variety of arrangements may also be made possible through the use of multiple heads. Such arrangements may include, for example, two or more heating 2 or cooling 3,20 devices -one or more devices heating an area ahead of a deposition/material deposition device 2, and one or more cooling devices 3,20 trailing the deposition/material deposition device 2.

Figure 6 shows an alternative embodiment inclusive of a square or rectangular cooling array, or heating device 30 with extended channels 31, the device being particularly suitable for a large substrate, or the requirement for a large cooling effect and/ or area. In particular, Figure 6 shows an array of channels 31 extending from a plenum chamber 33, which is itself fed by one or more inlet nozzles 32.

In use, an inlet nozzle 32 directs fluid into a plenum-type chamber 33, which splits inlet flow into two or more linearly aligned flow channels 31. In this way, cooling fluid passing through the channels 31 may then be directed onto the deposited layer, weld or substrate 12. Upon contact of the cooling fluid 6 with the surface of the deposited layer, weld or substrate 12, the fluid is heated and subsequently removed by the cooling fluid 15 passing into the exhaust passage 5. Of note, and to aid in preventing the inlet fluid 6 from being over-heated, figure 6 also shows the exhaust passage 9 to be positioned adjacent the outlet of the flow nozzles 31. As such, thermal energy is removed from the surface of the metallic structure 12 by heating the fluid 6 and continually replacing spent fluid 15 with fresh cooling fluid 6 such that spent fluid 15 is directed towards and into the exhaust passage 9. Alternatively, it will be appreciated that fluid 6 may be recycled by collecting, cooling and recirculating spent fluid 15.

Referring again to figure 6, the extended channels 31 reduce pressure losses from the nozzle due to an increased length to diameter ratio (for example, around 2:1). Figure 6 also shows the substrate cooling device 30 and/ or flow channels 31 to be angled away from the direction of travel of the material deposition device 2 to avoid interaction of the fluid flow with either the weld or the powder flow between the material deposition device 2 and/ or the substrate 12.

The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the disclosure as defined by the accompanying claims.

For example, the nozzle could be located coaxially outwardly of the exhaust passage. In such a case, the nozzle could be more closely spaced from the substrate than the exhaust passage. While the melt deposition additive manufacturing apparatus of the described embodiment comprises a blown power laser melt deposition apparatus, other forms of melt deposition additive manufacturing apparatus could be used with the disclosure. For example, the blown powder could be replaced by metal wire, and the laser heating could be replaced by electron beam heating.

Claims

CLAIMS1. A melt deposition additive manufacturing apparatus, the apparatus comprising: a substrate heating device configured to heat a sub-region of a substrate and a substrate cooling device, the cooling device comprising: a nozzle configured to direct a cooling fluid onto the substrate subregion; and an exhaust passage configured to remove spent cooling fluid, wherein the exhaust passage is coaxial with the nozzle.
2. An apparatus according to claim 1, wherein the apparatus comprises a material deposition device.
3. An apparatus according to any of claims 1 or 2, wherein the exhaust passage is configured to direct spent cooling fluid away from the substrate sub-region.
4. An apparatus according to any of claims 2 to 3, wherein the exhaust passage is configured to direct spent fluid in a direction away from a deposition path of the deposition device.
5. An apparatus according to any of claims 2 to 4, wherein the nozzle and/ or exhaust passage may be spaced from the substrate heating device and/ or material deposition device up to 200mm.
6. An apparatus according to any of claims 2 to 5, wherein the substrate heating device is arranged to direct heat into the deposition path of the deposition device.
7. An apparatus according to any of claims 2 to 6, wherein the deposition device is arranged to direct a deposition material into a heat path provided by the substrate heating device.
8. An apparatus according to any preceding claim, wherein the nozzle and/ or exhaust passage is spaced from the substrate, and the apparatus additionally comprises an actuation system to monitor and/ or alter the spacing.
9. An apparatus according to any of the preceding claims, wherein the nozzle comprises a plurality of flow channels.
10. An apparatus according to claim 9, wherein the nozzle is maintained at a distance from the substrate up to twenty times the diameter of the flow channels.
11. An apparatus according to any preceding claim, wherein the coaxially outer one of the nozzle and the exhaust passage is more closely spaced from the substrate than the other one of the nozzle and the exhaust passage.
12. An apparatus according to claim 9 or any claim dependent thereon, wherein the flow channels are configured such that mass flow rate of cooling fluid varies between the flow channels.
13. An apparatus according to any of the preceding claims, wherein the nozzle is configured such that the velocity of cooling fluid leaving the nozzle is at or about the speed of sound of the cooling fluid.
14. An apparatus according to claim9 or any claim dependent thereon, wherein the flow channels are shaped, angled or positioned relative to one another to preferentially direct cooling fluid through a subset of flow channels to preferentially direct cooling to a predetermined location.
15. An apparatus according to claim 14, wherein the flow channels are arranged as an array of holes such as a grid pattern, a series of slots, a circular pattern or a teardrop pattern.
16. An apparatus according to claim 15, wherein the flow channels are arranged as multiple clusters of holes.
17. An apparatus according to claim 9 or any claim dependent thereon, wherein the flow channels are arranged such that at least a substantial portion of the cooling fluid is directed away from a heat affected zone.
18. An apparatus according to any of the preceding claims, wherein the substrate heating device comprises a weld head configured to melt the sub-region of the substrate to provide a melt pool.
19. An apparatus according to any of the preceding claims, wherein the substrate heating device comprises a post weld heat treatment device.
20. A method of post-weld cooling using the apparatus described in claims 1 to 19, the method comprising the steps of: directing heat towards a sub-region of a substrate; depositing a deposition material onto the sub-region of the substrate; and locally applying a cooling fluid to at least a part of the substrate and/ or deposited material, the application of fluid including the steps of: directing the cooling fluid onto the sub-region; and, removing spent fluid.
21. An article formed by the method of claim 20.
22. An apparatus as hereinbefore described by reference to the accompanying drawings. 15
23. An article as hereinbefore described by reference to the accompanying drawings.