Processes for additive manufacture and surface cladding
The use of twin supplementary feedstock wires in WAAM processes addresses deposition rate and thermal control issues, enabling higher build rates and uniform microstructure in large-scale articles.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- WAAM3D LTD
- Filing Date
- 2025-12-23
- Publication Date
- 2026-07-02
Smart Images
Figure EP2025088948_02072026_PF_FP_ABST
Abstract
Description
[0001] 008888216
[0002] 1
[0003] PROCESSES FOR ADDITIVE MANUFACTURE AND SURFACE CLADDING
[0004] Field of the disclosure
[0005] The present disclosure relates to a process for producing a 3D article by additive manufacture and a related process for surface cladding an article.
[0006] Background
[0007] Additive Manufacture (AM) is a technology that enables the creation of near net-shape 3D articles, typically based on a computer aided design (CAD) software model of the article. AM involves the deposition and fusing of multiple successive layers of one or more materials, such as metals, to build up the article. Significant advantages of AM, when compared to conventional methods of manufacturing 3D articles, such as casting or machining, include a reduction in production time and a reduction in the “buy-to-fly ratio”, i.e. the weight of material that needs to be purchased relative to the weight of that material in final manufactured part. The reduced material consumption, in particular, helps to reduce overall production costs.
[0008] In AM, the material from which the 3D article is to be made, i.e. the feedstock, is supplied to a specified location where it enters a meltpool formed on a substrate. The location of the meltpool is continuously moved around on the substrate. The melted feedstock layer fuses to the substrate, and further successive layers of material are then deposited in a similar manner on the previously deposited layers, to build up the 3D article. The substrate can be an already-existing component, onto which new features are added by AM.
[0009] Generally, an energy source such as a plasma arc, an electron beam or a laser is used to form the meltpool. This energy source can also be used to provide the energy to melt the feedstock as it enters the meltpool and to govern the overall temperature of the process (and therefore govern the cooling conditions and the microstructure and mechanical properties of the 3D article).
[0010] Wire + arc additive manufacture (WAAM) may be used for producing large-scale articles. For example, titanium aerospace parts with masses of tens of kg have conventionally been formed by machining from forgings. However, by adopting a WAAM approach, material consumption, costs and lead times can all be reduced relative to this conventional approach.008888216
[0011] 2
[0012] Such WAAM typically utilises a Plasma Transferred Arc (PT A) process, having a nonconsumable electrode with addition of material by a separate feed wire. In PTA the rate of energy input (power) and material feed rate are independently controllable, allowing high control of deposition conditions, which in turn leads to accurate deposition with a high level of thermal control.
[0013] This thermal control is important for building high quality parts, as keeping the temperature and size of the meltpool relatively constant, generally helps to reduce: changes in the deposited geometry, layer height errors, variation in mechanical properties, and defects. Departures from constant meltpool conditions mainly occur for two reasons: 1) a general increase in temperature of the part; 2) changes in thermal mass. Thermal mass variations arise from changes in part geometry, e.g. building away from the substrate, varying wall widths, wall intersections and crossovers.
[0014] More particularly, even at a fixed material deposition rate per unit length the deposited geometry (layer height, layer width and contact angle) depends on the local thermal conditions. It is generally important to maintain a constant layer height in AM as the component is typically made of hundreds or thousands of layers. If there is an error in the actual layer height compared to the planned one then there will be geometric errors in the component, or worse the deposition process may fail so that the part cannot be built. In addition, layers are generally deposited next to each other to enable wider component geometries than a single bead. The spacing between adjacent beads is set based on the expected deposited bead width. If this changes it can generate lack of fusion defects (if the width decreases) or geometry errors (if the width increases).
[0015] The deposited material microstructure, and therefore physical properties, also depends on the local thermal conditions during the freezing and cooling stages. It is generally desirable to have homogenous properties throughout a component to ensure uniform mechanical performance.
[0016] Thus, whether the local thermal conditions vary due to e.g. a change in local geometry of the underlying materials, or whether the overall temperature of the component increases due to the absorbed energy, it can be beneficial to be able to compensate for these changes by varying the energy input per unit length of the process. However, preferably this should be done without changing the material feed rate per unit length as this can otherwise change the deposited material geometry.008888216
[0017] 3
[0018] A limitation of PTA-based WAAM is its relatively low deposition rate, typically 1 kg / hr for titanium and 2-3 kg / hr for denser metals. This limit is due to the effects of arc pressure. If the electrode current is increased so does arc pressure, forming a depression in the meltpool which can lead to instabilities and defects.
[0019] The low deposition rate may not be such a problem for aerospace applications, but in nonaerospace industry sectors, such as energy, mining and construction, manufactured parts can be significantly more massive than in the aerospace sector, with articles being formed of low cost materials such as steel and having weights of 100s to 1000s of kg. Thus, while it would be desirable to be able to make such articles using WAAM in order to enjoy benefits such as: reductions in manual processes, improved performance, greater design freedom and increased customisability, a step change in WAAM build rate is desirable in order to provide realistic build times.
[0020] Higher build rates are possible by basing WAAM on a Gas Metal Arc (GMA) process, as this has significantly lower arc pressures due to its use of a consumable electrode and absence of a plasma gas constriction. GMA processes include MIG (metal inert gas), and MAG (metal active gas) processes. In the latter, active gases such as CO2 / O2 / H2are added for e.g. for control of oxidation or arc stability.
[0021] However, there are problems associated with using GMA in high build rate applications. Firstly, in GMA power input and material feed rate are strongly linked, so that independent thermal control of the process is limited. For example, the heat or energy input per unit length (El) is the power supplied by the GMA device divided by the travel speed (TS) of the meltpool, and thus to change the El in WAAM based on conventional GMA (or indeed based on any similar AM process) requires changing either the power input or TS. The GMA power input can be adjusted in small amounts by adjusting the “trim”, which has the effect of lengthening the arc, and thereby increasing the arc voltage and the power input. Another possibility is to change to gas mixes containing He, but this expensive and not suitable for adjustments in real time. Thus the only practical option for changing the GMA power input significantly is changing the electrode current (power input and electrode current being linearly dependent on each other). However, varying the electrode current requires changing the wire feed speed (WFS) of the consumable electrode for stable metal transfer. This is discussed for example in Lee, H.K. et al., Int. J. Nav. Archit. Ocean Eng. (2015) 7:770-783 (incorporated herein by reference). Moreover, in WAAM the rate of material deposition per unit length, defined by the WFS / TS ratio, has to be kept constant in order to008888216
[0022] 4
[0023] maintain a constant deposition geometry. Therefore, if the WFS or the TS is changed the other one needs to change in the same sense to provide a constant deposition geometry, leading to no change in El and thus no thermal control.
[0024] WO 2022 / 122922 A1 provides an enhanced-GMA WAAM approach which addresses these issues. In particular, it discloses simultaneously feeding into the moving meltpool (i) a consumable electrode (’’hot wire”) of a gas metal arc welding device to provide a first material feed rate into the meltpool, and (ii) a non-electrode, supplementary feedstock (“cold wire”) to provide a second material feed rate into the meltpool, the ratio of the first material feed rate to the second material feed rate being varied in performance of the feeding step. In this way, higher overall build rates can be achieved for a given power input compared to conventional GMA processes without the supplementary feedstock. For example, one option is to vary the cold wire feed rate for a given hot wire feed rate (and therefore given supplied power), while simultaneously varying the TS so that the ratio of the total material feed rate to the TS is kept constant. The variation in TS leads to a variation in the El, and this option therefore allows the feed rate to be maximised whilst changing the El, thereby enabling maximisation of productivity. A constant hot wire feed rate also helps to produce stable metal transfer into the meltpool.
[0025] When introducing the cold wire into the meltpool, it is important that it should avoid interfering significantly with the stream of hot melt emanating from the hot wire, as this can introduce instabilities into the process. Also, in general, it is helpful if the cold wire melts in the arc above the meltpool, rather than arriving in the meltpool while still solid. These limitations can place an upper limit on the feed rate of the cold wire.
[0026] Summary
[0027] It would be desirable to provide an enhanced-GMA WAAM process which addresses these issues.
[0028] An option for introducing a cold wire into a meltpool in a way which avoids interference with the hot wire and helps to avoid instabilities is to position the cold wire so that it is laterally offset from the hot wire with respect to the direction of travel of the deposition. This single cold wire option can help to reduce interaction of the cold wire with the hot wire, while still passing the cold wire through the arc above the meltpool. However, a drawback of this option as that it results in an asymmetrical deposit.008888216
[0029] 5
[0030] Accordingly, in a first aspect there is provided a process for producing a 3D article by additive manufacture, wherein the method includes the steps of:
[0031] forming a meltpool on an already-existing part of the article using heat supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, and moving the meltpool relative thereto;
[0032] simultaneously feeding into the moving meltpool: (i) the consumable electrode of the gas metal arc welding device to provide a first material feed rate into the meltpool, and (ii) molten material from respective ends of twin, non-electrode, supplementary feedstock wires to provide a second material feed rate into the meltpool, whereby a layer of material is deposited and fused on the already-existing part; and
[0033] repeating the forming and moving, and the feeding steps to build up successive layers of material, and thereby produce the 3D article;
[0034] wherein the twin supplementary feedstock wires extend from the arc, with one on either side of a plane containing the consumable electrode and the direction of movement of the consumable electrode relative to the already-existing part.
[0035] In this way, higher overall build rates can be achieved, while forming a symmetrical deposit by reducing meltpool instabilities. In particular, the second material feed rate can be increased significantly relative to the single cold wire option referred to above, e.g. by passing the supplementary feedstock wires through the arc above the meltpool, while preventing the supplementary feedstock wires interfering with the molten stream emanating from the consumable electrode.
[0036] A related process can be used for surface cladding an article. Accordingly, in a second aspect there is provided a process for surface cladding an article, wherein the method includes the steps of:
[0037] forming a meltpool on the surface of the article using heat supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, and moving the meltpool relative thereto; and
[0038] simultaneously feeding into the moving meltpool: (i) the consumable electrode of the gas metal arc welding device to provide a first material feed rate into the meltpool, and (ii) molten material from respective ends of twin, non-electrode, supplementary feedstock wires to provide a second material feed rate into the meltpool, whereby a cladding layer of material is deposited and fused on the surface of the article;
[0039] wherein the twin supplementary feedstock wires extend from the arc, with one on008888216
[0040] 6
[0041] either side of a plane containing the consumable electrode and the direction of movement of the consumable electrode relative to the already-existing part.
[0042] Like the process of the first aspect for producing a 3D article, the cladding process of the second aspect enables higher cladding rates to be achieved while still forming a symmetrical deposit. In particular, the feedstock wires can be arranged so that they pass through the arc above the meltpool, but do not interfere with the molten stream emanating from the consumable electrode.
[0043] The following discussion of optional features pertains to the method of the first or second aspect.
[0044] Preferably, the twin supplementary feedstock wires are in a mirror image relationship to each other across said plane. This can help to produce a symmetrical deposit.
[0045] Preferably, the twin supplementary feedstock wires extend from the arc along directions which form a first angle to each other of less than 30° and preferably of less than 20°.
[0046] Indeed, the wires may extend from the arc along the directions which are parallel to and spaced from each other. With such an arrangement the dwell time of the wires in the arc can be increased, improving the efficiency of heating of the wires, and helping to ensure that the wires are fully melted in the arc before arriving in the meltpool. Conveniently, the feeding of the twin supplementary feedstock wires may include receiving the twin supplementary feedstock wires from initial directions which are at a relatively large second angle to each other and turning the wires such that the second angle reduces to the first angle when they reach the arc.
[0047] The spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode may be greater than the diameter of the consumable electrode. In this way, the wires can be prevented from interacting with the consumable electrode and the molten stream emanating therefrom. On the other hand, the spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode is typically limited by the need for these wires to melt in the arc, and thus is dependent on the arc energy profile.008888216
[0048] 7
[0049] The energy distribution of the arc can typically be considered to be a normal (i.e. Gaussian) distribution, having a maximum of the energy distribution at the centre. An envelope of the arc may be considered to be defined by a notional boundary located at 1 / e2times the maximum of the energy distribution of the arc. In some embodiments, the spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode is such that the twin supplementary feedstock wires are located inside the envelope of the arc. This is considered to have benefits in terms of ensuring separation of the twin supplementary feedstock wires, to avoid interference with droplets formed from the consumable electrode, while still ensuring that the twin supplementary feedstock wires melt appropriately and feed the meltpool. This can have particular advantages at high supplementary feedstock wire feed speeds.
[0050] In some circumstances, the spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode may for example be no more than four or five times the diameter of the consumable electrode. Such an upper limit on the spacing helps to ensure that the wires are well-exposed to the energy of the arc, for a typical arc, to encourage melting of their respective ends. Typically, the consumable electrode extends in a vertical direction.
[0051] The twin supplementary feedstock wires may extend from the arc along directions which are at an angle of at least 60° and / or at most 75° from the vertical direction. Bringing the wires into the arc along directions which are at a relatively high angle from the vertical direction and a relatively shallow angle to the horizontal plane helps to increase the exposure of the wires to the arc while avoiding the consumable electrode and any obstacles at the level of the meltpool. Increasing the wires’ exposure to the arc is particularly beneficial as their melting efficiency in the arc is significantly greater than their melting efficiency in the meltpool. A further benefit of the shallow angle to the horizontal plane is that it facilitates the maintenance of an optimum height range above the meltpool at which droplets detach from the ends of the supplementary feedstock wires: if the droplets detach significantly above such an optimum height range they can produce unwanted spatter, and if they detach significantly below the optimum height range the risk of the wires entering the meltpool in an incompletely melted state is increased.
[0052] The twin supplementary feedstock wires may extend from the arc to the front or the rear of the consumable electrode relative to said direction of movement, but preferably extend to the008888216
[0053] 8
[0054] front as this tends to enhance wire melting and process stability, and avoids clashes with previously deposited material.
[0055] The ratio of the first material feed rate to the second material feed rate can be varied in performance of the feeding step. Conveniently, the ratio of the first material feed rate to the second material feed rate can be varied to vary the power supplied by the gas metal arc welding device for a given combined sum of the first and second material feed rates.
[0056] Advantageously, thermal control of the process can thereby be achieved by, for example, simultaneously varying the first material feed rate and the second material feed rate, such that the ratio of the total material feed rate (i.e. the first feed rate + the second feed rate) to the TS is kept constant for a given TS. Another option to varying the ratio of the first material feed rate to the second material feed rate is to vary the second material feed rate for a given first material feed rate (and therefore given supplied power), while simultaneously varying the TS so that the ratio of the total material feed rate to the TS is kept constant. However, the variation in TS will lead to a variation in the El. This option therefore can allow the feed rate to be maximised whilst changing the El, which can advantageously enable maximisation of productivity.
[0057] Preferably, the process may further include measuring a local temperature of the article, the measurement typically being made ahead of the meltpool. The ratio of the first material feed rate to the second material feed rate can then be varied based on the measured local temperature. In this way, closed loop control of the process can be achieved.
[0058] During the moving of the meltpool, cooling fluid may be applied to the article to improve thermal control of the process. The cooling fluid can conveniently be a cryogenic liquid or chilled gas, such as Ar, N2or CO2. The amount and timing of application of the cooling fluid can be based on the local geometry of the article and / or a measured local temperature of the article ahead of the meltpool.
[0059] The process may further include preheating the twin supplementary feedstock wires to a predetermined temperature before their arrival at the arc (for example by electrical resistance heating, induction heating, laser heating or non-transferred plasma arc heating). Such pre-heating can also be used to improve thermal control of the process. In particular, the predetermined temperature can be varied during the moving of the meltpool to improve thermal control of the process. The amount and timing of preheating can be based on the008888216
[0060] 9
[0061] local geometry of the article and / or on a measured local temperature of the article, e.g. ahead of the meltpool.
[0062] In a third aspect, there is provided a system for producing a 3D article by additive manufacture in which a meltpool is formed on an already-existing part of the article using heat supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, the meltpool is moved relative to the already-existing part to deposit and fuse a layer of material on the already-existing part, and the forming and moving and feeding are repeated to build up successive layers of material, and thereby produce the 3D article, the system comprising:
[0063] the gas metal arc welding device having the one consumable electrode which provide a first material feed rate into the meltpool;
[0064] a feedstock directing arrangement configured to feed twin, non-electrode, supplementary feedstock wires so that molten material from respective ends of the supplementary feedstock wires is fed into the meltpool simultaneously with the consumable electrode, the supplementary feedstock wires providing a second material feed rate into the meltpool; and
[0065] a computer controller configured to control movement of the gas metal arc welding device and the feedstock directing arrangement relative to the already-existing part, and to control the first and second feed rates;
[0066] wherein the feedstock directing arrangement is further configured to feed the twin supplementary feedstock wires such they extend from the arc with one on either side of a plane containing the consumable electrode and the direction of movement of the consumable electrode relative to the already-existing part.
[0067] Thus the system of the third aspect is suitable for performing the process of the first aspect, and the feedstock wires can be arranged so that they pass through the arc above the meltpool, but do not interfere with the molten stream emanating from the consumable electrode. However, the system is also suitable for performing the process of the second aspect. Therefore, the system is also a system for surface cladding an article in which a meltpool is formed on the article using energy supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, the meltpool being moved relative to the article to deposit and fuse a cladding layer of material on the surface of the article.
[0068] Preferably, the twin supplementary feedstock wires are in a mirror image relationship to each other across said plane.008888216
[0069] 10
[0070] Preferably, the feedstock directing arrangement is configured to feed the twin supplementary feedstock wires so that they extend from the arc along directions which are at a first angle to each other of less than 30° and preferably of less than 20°. Indeed, the wires may extend from the arc along the directions are parallel to and spaced from each other. Conveniently, the feedstock directing arrangement may include a guide system which receives the twin supplementary feedstock wires from directions which are at a relatively large second angle to each other and turns the wires such that the second angle reduces to the first angle when they reach the arc.
[0071] The spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode may be greater than the diameter of the consumable electrode. On the other hand, the spacing between the twin supplementary feedstocks wire at their closest approach to the consumable electrode may be no more than four or five times the diameter of the consumable electrode.
[0072] Typically, the gas metal arc welding device is configured such that the consumable electrode extends in a vertical direction.
[0073] The feedstock directing arrangement may be further configured such that the twin supplementary feedstock wires extend from the arc along directions which are at an angle of at least 60° and / or at most 75° from the vertical direction.
[0074] The feedstock directing arrangement may be further configured such that the twin supplementary feedstock wires extend from the arc to the front or the rear of the consumable electrode relative to said direction of movement, but preferably extend to the front.
[0075] The system may further comprise a computer controller configured to control movement of the gas metal arc welding device and the feedstock directing arrangement relative to the article, and to control the first and second feed rates. The ratio of the first material feed rate to the second material feed rate can be varied by the computer controller while controlling the first and second feed rates. For example, the ratio of the first material feed rate to the second material feed rate may be varied by the computer controller to vary the power supplied by the gas metal arc welding device for a given combined sum of the first and second material feed rates. Additionally or alternatively, the ratio of the first material feed rate to the second material feed rate may be varied by varying the second material feed rate for a given first material feed rate. The computer controller may then be further configured to008888216
[0076] 11
[0077] simultaneously vary the travel speed of the meltpool so that the ratio of the sum of the first material feed rate and the second material fed rate to the travel speed is kept constant.
[0078] The system may further comprise a measuring device for measuring a local temperature of the article, e.g. ahead of the meltpool. The computer controller may then be further configured such that the ratio of the first material feed rate to the second material feed rate is variable based on the measured local temperature. Additionally or alternatively, the computer controller may be further configured such that the ratio of the first material feed rate to the second material feed rate is variable based on: a predetermined requirement for a change in overall energy input, e.g. due to local changes in geometry of the article which change the thermal mass; and / or to achieve a predetermined temperature rise or to limit an unwanted temperature rise due to energy accumulation.
[0079] The system may further comprise a cooling device for applying cooling fluid to the article, wherein the computer controller may be further configured to control the cooling device. For example, the control may be based on: the local geometry of the article; a need to achieve predetermined temperature rise or to limit an unwanted temperature rise due to energy accumulation; and / or on a measured local temperature of the article (e.g. ahead of the meltpool).
[0080] The system may further comprise a heating device for preheating the twin supplementary feedstock wires to a predetermined temperature before their arrival at the arc, wherein the computer controller may be further configured to control the heating device. For example, the control may be based on: the local geometry of the article; a need to achieve predetermined temperature rise or to limit an unwanted temperature rise due to energy accumulation; and / or on a measured local temperature of the article (e.g. ahead of the meltpool).
[0081] Brief description of the drawings
[0082] Embodiments will now be described by way of example only, with reference to the Figures, in which:
[0083] Figure 1 shows schematically a system for producing a 3D article by additive manufacture;008888216
[0084] 12
[0085] Figure 2A is a perspective view from the front of a guide system of a feedstock directing arrangement of the system of Figure 1 , and Figure 2B is a perspective view from the rear of the guide system;
[0086] Figure 3 shows a longitudinal cross-sectional view through the guide system of Figures 2A and 2B;
[0087] Figure 4 shows schematically a longitudinal cross-sectional view through a variant of the guide system of Figures 2A, 2B and 3;
[0088] Figure 5 is a perspective close-up view from the side of the working zone of an example system for producing a 3D article by additive manufacture; and
[0089] Figure 6 is a still from a video sequence showing the system of Figure 5 successfully depositing a track of material on a substrate.
[0090] Figure 7 shows a modified and enlarged version of parts of Figure 3, showing a cross-sectional view of the positions of the cold wires relative to the hot wire and arc, but omitting the guide system shown in Figure 3.
[0091] Detailed description
[0092] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.
[0093] Figure 1 shows schematically a system for producing a 3D article by additive manufacture. The system includes a GMA torch 1 having a contact tip 2 and a gas shroud 3. A hot wire 4 emerges from the contact tip to form a vertically extending consumable electrode, an arc 5 being formed between the hot wire and the growing article 6 formed on a substrate 7.
[0094] Alternatively the system can be used for surface cladding an existing article.
[0095] The arc 5 forms a meltpool on the article 6 into which the hot wire 4 is fed. In addition, however, a feedstock directing arrangement 8 is attached by a clamp assembly 9 to the GMA torch 1, and twin, supplementary feedstock, non-electrode cold wires 10 are fed from a guide system 14 of the feedstock directing arrangement, simultaneously with the hot wire, so that respective ends of the cold wires are melted in the arc 5 and droplets enter into the advancing meltpool. The terms “hot” and “cold” are used to distinguish respectively the008888216
[0096] 13
[0097] consumable electrode and the non-electrode feedstocks, although of course the materials of all the wires 4, 10 ultimately mix in and attain the temperature of the meltpool. The cold wires are shown entering the meltpool from the front, which is preferred as regards process stability and to avoid clashes with previously deposited material, but they can alternatively enter from the rear.
[0098] Figure 2A is a perspective view from the front of the guide system 14 of the feedstock directing arrangement 8, the twin cold wires 10 leaving the guide system through respective outlet holes 16; Figure 2B is a perspective view from the rear of the guide system 14, the twin cold wires 10 entering the guide system 14 at respective inlet holes 17; and Figure 3 shows schematically a longitudinal cross-sectional view through the guide system 14. The twin cold wires 10 arrive at the guide system 14 from respective spools having passed through a heating device 13 (discussed further below). Mounting holes 18 allow the guide system 14 to be mounted to the feedstock directing arrangement 8 at the heating device 13.
[0099] The guide system 14 locates the cold wires on either side of a plane A-A containing the hot wire 4 and the direction of movement of the consumable electrode relative to the already-existing part. More particularly, a pair of channels 15 on opposite sides of the plane A-A connects each inlet hole 17 to one of the outlet holes 16. These channels turn the wires from a relatively large angle relative to each other as they pass through the heating device 13, to run parallel to but spaced from each other as they enter the arc 5. The channels are arranged so that the cold wires are in a mirror image relationship to each other across the plane A-A, and thus contribute to the production of a symmetrical deposit by the advancing meltpool. The spacing between the parallel cold wires imposed by the channels 15 is greater than the diameter of the hot wire 4 so that the wires have little direct impact on the stream of hot metal emanating from the hot wire when they enter the arc. On the other hand, to ensure that the cold wires penetrate into central parts of the arc and are fully melted before arriving in the meltpool, generally the spacing is no more than four or five times the diameter of the hot wire. Further considerations of this issue are set out below.
[0100] The cold wires 10 are typically identical to each other. However, the cross-sectional areas of the hot wire 4 and each cold wire can be the same, or one of the hot wire and each cold wire can have a larger area than the other. The hot wire and each cold wire can also have the same or different cross-sectional shapes, e.g. round, profiled, strip etc.008888216
[0101] 14
[0102] As indicated in Figure 1, the cold wires 10 extend from the arc 5 at an angle a to the vertical direction. Typically this angle is at least 60° and / or at most 75°, and thus the cold wires are at a relatively high angle from the vertical direction and a relatively shallow angle to the horizontal plane. This increases the exposure of the cold wires to the arc while avoiding the hot wire 4 and any obstacles at the level of the meltpool.
[0103] The feed rate of the hot wire 4 into the meltpool provides a first material feed rate, and the combined feed rates of the cold wires 10 into the meltpool provides a second material feed rate. These feed rates are controlled by a computer controller 11 , which also controls movement of the GMA torch 1 relative to the substrate 7 and GMA power input. A further benefit of the shallow angle to the horizontal plane is that it helps the controller 11 to maintain the ends of the cold wires within an optimum height range above the meltpool. If the height range is exceeded, droplets detaching from the ends of the cold wires 10 can produce unwanted spatter, whereas if it is undershot there is an increased risk of the wires entering the meltpool in an incompletely melted state.
[0104] Just as the two cold wires are typically identical to each other, their respective feed rates are both controlled so that they typically experience the same WFS.
[0105] With this system, thermal control can be achieved by varying the WFS of the hot wire 4 and the WFS of each cold wire 10 simultaneously, such that the total WFS (defined as the sum of the WFSs of the three wires) and therefore total WFS / TS ratio is kept constant.
[0106] Alternatively, the WFS of each cold wire 10 can be varied (the same variation being applied identically to both cold wires) whilst maintaining a constant WFS for the hot wire 4 (and therefore maintaining a constant power input) but simultaneously varying the TS so that the total WFS / TS ratio is kept constant but the El is varied.
[0107] In general, the compositions of the hot wire and the cold wire are the same so that the composition of the built up material does not vary with changes to the ratio of the cold wire WFS to the hot wire WFS. However, this does not exclude that in some special applications wires of different composition could be used, e.g. two different low carbon steels or two different aluminium alloys. Accordingly, notwithstanding that having the same WFS is the norm, it is possible for the WFSs of the cold wires to be different, e.g. if their compositions and / or cross-sectional areas are different.008888216
[0108] 15
[0109] The cold wires 10 may be pre-heated to a predetermined temperature under the control of the computer controller 11 to increase the power input. Thus, such pre-heating can be used as a further means of thermal control. For example, the predetermined temperature can be increased for parts of the article where thermal losses are higher and reduced where they are lower. Additionally, or alternatively, the predetermined temperature can be varied based on a local temperature of the part, typically measured ahead of the meltpool (discussed in more detail below). The pre-heating can be achieved in various ways, such as electrical resistance heating, induction heating, laser heating, and non-transferred plasma arc heating.
[0110] Changing the El by independently varying the WFS of the hot wire 4 and the WFS of the cold wires 10 allows:
[0111] 1. The deposited bead shape and the material microstructure (and consequent mechanical properties) to be kept constant even as thermal losses change due to the thermal mass changing with changes to the local geometry of the part.
[0112] 2. The deposited bead shape and the material microstructure (and consequent mechanical properties) to be kept constant even as the overall part temperature changes (typically increases) due to the deposition process. Control of the El can thus be linked to a process in which the temperature of the part is measured just before deposition, e.g. using a pyrometer or other temperature sensing device 12 which moves with the GMA torch 1 to measure a local temperature of the part ahead of the meltpool and provides the temperature measurement to the computer controller 11.
[0113] 3. The deposited bead shape to be changed, e.g. to accommodate different geometries and desired finishes of the growing part.
[0114] 4. Further control over the deposition process can be exercised by providing the heating device 13 which, under the control of the computer controller 11 , preheats the cold wires 10 to a predetermined temperature before feeding into the arc 5. For example, the heating device can conveniently comprise an RF induction coil through which the cold wires are fed before conveyance through the guide system 14 to the arc.
[0115] A problem that can be encountered when using WAAM to manufacture parts at high build rates is overall temperature control. For example, build rates of > 10kg / hr require many kW of input power, which can lead to overheating of the part. One option is to introduce cooling008888216
[0116] 16
[0117] times between added layers, but this significantly reduces productivity. Thus to ensure high productivity, in-process active cooling systems can be applied. For example, cryogenic liquid or chilled gas (e.g. Ar, N2or CO2) cooling can be used in the system of Figure 1 by directing the cryogenic liquid or chilled gas onto the growing part with suitable a nozzle(s). Control of such cooling can be performed by the computer controller 11 , so that it is a fully integrated part of the process. The computer controller 11 can determine the amount of cooling on the basis of temperature measurements on the article.
[0118] In Figures 2 and 3 above, the channels 15 of the guide system 14 turn the cold wires 10 so that they enter the arc 5 parallel to but spaced from each other. In this way, the wires can pass through and be melted by the arc above the meltpool, but do not interfere with the molten stream emanating from the hot wire 4. It is also possible, however, for the guide system 14 to be configured so that the cold wires 10 extend from the arc on either side of the plane A-A along directions which are at an angle to each other. Figure 4 shows schematically a longitudinal cross-sectional view through a variant of the guide system 14’ which has such a configuration. In order that the cold wires still pass through the arc 5 above the meltpool, but do not interfere with the molten stream emanating from the hot wire 4, in general the wires extend out of the arc along directions which are at an angle p to each other of less than 30° and preferably of less than 20°. Despite the angle between the cold wires, at their closest approach to the hot wire 4, the spacing between the cold wires is still greater than the diameter of the hot wire to avoid interfering with its molten stream.
[0119] Figure 5 is a perspective close-up view from the side of the working zone (i.e. gas shroud 3, hot wire 4, cold wires 10 and guide system 14’) of an example system in readiness to deposit on a substrate 7, and Figure 6 is a still from a video sequence showing this system successfully depositing a track of material on the substrate. Visible in Figure 6 are the arc 5, the meltpool 20 at the head of a deposited track, the molten stream 21 descending from the hot wire and droplets 22 falling from the ends of the cold wires 10 into the meltpool. The feed rate from the 1.2 mm diameter hot wire was 4.8 kg / hr and the combined feed rate from the two identical 0.8 mm diameter cold wires was 6.2 kg / hr, giving a total build rate of 11 kg / hr. In operation, even at this high build rate, the system produced a stable meltpool with no spatter and with full melting of the cold wires being in the arc.
[0120] The present inventors have carried out further work to consider the effects of the spacing of the cold wires and their feed speed. In the experiments reported below, the conditions were the same as reported with respect to Figure 6, unless stated otherwise. The arc voltage was008888216
[0121] 17
[0122] 34 V, arc current 330 A. The torch shielding gas was 2.5% CO2in argon with a torch shielding gas flow rate of 15 L / min. The hot wire feed speed was kept constant at 10 m / min. The CTWD (contact tip to work distance) was 18 mm.
[0123] The spacing between the twin cold wires at the arc was held at 1 mm in one set of experiments and at 3 mm in another set of experiments. The effect of this, for the same arc properties, is that the cold wires penetrate to different extents into the arc envelope. Then, for each spacing, different cold wire feed speeds were used (but identical for each of the two cold wires), varying between 4 m / min and 16 m / min.
[0124] High speed video analysis of the process shows that, for cold wire spacing of 1 mm, there is a risk that metal droplets generated from the hotwire may interfere with the ends of the cold wires. The result of this can be unwanted spatter of droplets. This issue becomes more prominent with increasing cold wire feed speeds.
[0125] Accordingly, in the experiments conducted, it was found that the maximum cold wire feed speed before unacceptable spatter was 12 m / min for the 1 mm cold wire gap arrangements in a twin wire embodiment of the present invention (CW-MIG twin wire). It was found that this was the same maximum cold wire feed speed as for single wire CW-MIG before unacceptable spatter. However, the maximum cold wire feed speed before unacceptable spatter was 16 m / min for the 3 mm cold wire gap arrangements in a twin wire embodiment of the present invention (CW-MIG twin wire).
[0126] Figure 7 shows a modified and enlarged version of parts of Figure 3, showing a cross-sectional view of the positions of the cold wires relative to the hot wire and arc, but omitting the guide system shown in Figure 3. The twin cold wires 10 are guided as described with respect to Figure 3 to be located on either side of a plane A-A containing the hot wire 4 and the direction of movement of the consumable electrode relative to the already-existing part. In this embodiment, the cold wires 10 are arranged to be substantially parallel at their position of closest approach, but it will be understood that similar considerations will apply to a modification of the arrangement of Figure 4, for example.
[0127] The arc is shown generally by reference number 5. It will be understood that the arc is in effect an energy distribution. This can typically be defined as a normal (Gaussian) distribution. The maximum of the energy distribution is at the centre. Indicated008888216
[0128] 18
[0129] schematically at reference number 5E in Figure 7 is a notional boundary of the arc envelope, located at 1 / e2times (i.e. about 0.14 times) the maximum of the energy distribution.
[0130] Accordingly, it is advantageous for the cold wires to be spaced apart but still inside the envelope of the arc, the envelope of the arc conveniently be considered to be located at 1 / e2times the maximum of the energy distribution of the arc.
[0131] ***
[0132] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.
[0133] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.
[0134] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.
[0135] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
Claims
00888821619CLAIMS1. A process for producing a 3D article (6) by additive manufacture, wherein the method includes the steps of:forming a meltpool on an already-existing part of the article (6) using heat supplied to the already-existing part by an arc (5) of a gas metal arc welding device (1) having a consumable electrode (4), and moving the meltpool relative thereto;simultaneously feeding into the moving meltpool: (i) the consumable electrode (4) of the gas metal arc welding device (1) to provide a first material feed rate into the meltpool, and (ii) molten material from respective ends of twin, non-electrode, supplementary feedstock wires (10) to provide a second material feed rate into the meltpool, whereby a layer of material is deposited and fused on the already-existing part; andrepeating the forming and moving, and the feeding steps to build up successive layers of material, and thereby produce the 3D article (6);wherein the twin supplementary feedstock wires (10) extend from the arc (5) with one on either side of a plane (A-A) containing the consumable electrode (4) and the direction of movement of the consumable electrode relative to the already-existing part.
2. A process for surface cladding an article, wherein the method includes the steps of:forming a meltpool on a surface of the article using heat supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, and moving the meltpool relative thereto; andsimultaneously feeding into the moving meltpool: (i) the consumable electrode of the gas metal arc welding device to provide a first material feed rate into the meltpool, and (ii) molten material from respective ends of twin, non-electrode, supplementary feedstocks to provide a second material feed rate into the meltpool, whereby a cladding layer of material is deposited and fused on the surface of the article;wherein the twin supplementary feedstock wires extend from the arc with one on either side of a plane containing the consumable electrode and the direction of movement of the consumable electrode relative to the article.
3. The process of claim 1 or 2, wherein the twin supplementary feedstock wires (10) are in a mirror image relationship to each other across said plane (A-A).008888216204. The process of any one of the previous claims, wherein the twin supplementary feedstock wires (10) extend from the arc (5) along directions which form a first angle to each other of less than 30°.
5. The process of claim 4, wherein feeding the twin supplementary feedstock wires (10) includes receiving the twin supplementary feedstock wires from initial directions which are at a relatively large second angle to each other and turning the wires such that the second angle reduces to the first angle when they reach the arc.
6. The process of any one of the previous claims, wherein the spacing between the twin supplementary feedstock wires (10) at their closest approach to the consumable electrode (4) is greater than the diameter of the consumable electrode (4).
7. The process of claim 6, wherein the spacing between the twin supplementary feedstock wires (10) at their closest approach to the consumable electrode (4) is no more than five times the diameter of the consumable electrode (4).
8. The process according to any one of claims 1 to 7, wherein an energy distribution of the arc has a maximum of the energy distribution at the centre of the arc and an envelope of the arc is defined by a notional boundary located at 1 / e2times the maximum of the energy distribution of the arc, and wherein the spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode is such that the twin supplementary feedstock wires are located inside the envelope of the arc.
9. The process of any one of the previous claims, wherein the twin supplementary feedstock wires (10) extend from the arc (5) along directions which are at an angle of at least 60° from the vertical direction.
10. The process of any one of the previous claims, wherein the twin supplementary feedstock wires (10) extend from the arc (5) along directions which are at an angle of at most 75° from the vertical direction.
11. The process of any one of the previous claims, wherein the twin supplementary feedstock wires (10) extend from the arc (5) to the front of the consumable electrode (4) relative to said direction of movement.
12. A system for producing a 3D article (6) by additive manufacture in which a meltpool is formed on an already-existing part of the article using heat supplied to the already-existing00888821621part by an arc (5) of a gas metal arc welding device (1) having a consumable electrode (4), the meltpool is moved relative to the already-existing part while feeding the consumable electrode thereinto to deposit and fuse a layer of material on the already-existing part, and the forming and moving and feeding are repeated to build up successive layers of material, and thereby produce the 3D article, the system comprising:the gas metal arc welding device (1) having the consumable electrode (4) which provides a first material feed rate into the meltpool; anda feedstock directing arrangement (8) configured to feed twin, non-electrode, supplementary feedstock wires (10) so that molten material from respective ends of the supplementary feedstock wires is fed into the meltpool simultaneously with the consumable electrode (4), the supplementary feedstock wires providing a second material feed rate into the meltpool;wherein the feedstock directing arrangement (8) is further configured to feed the twin supplementary feedstock wires (10) such they extend from the arc (5) with one on either side of a plane (A-A) containing the consumable electrode (4) and the direction of movement of the consumable electrode relative to the already-existing part.
13. A system for cladding an article in which a meltpool is formed on a surface of the article using heat supplied to the article by an arc of a gas metal arc welding device having a consumable electrode, and the meltpool is moved relative to the article while feeding the consumable electrode thereinto to deposit and fuse a cladding layer of material on the article, the system comprising:the gas metal arc welding device having the consumable electrode which provides a first material feed rate into the meltpool; anda feedstock directing arrangement configured to feed twin, non-electrode, supplementary feedstock wires so that molten material from respective ends of the supplementary feedstock wires is fed into the meltpool simultaneously with the consumable electrode, the supplementary feedstock wires providing a second material feed rate into the meltpool;wherein the feedstock directing arrangement is further configured to feed the twin supplementary feedstock wires such that they extend from the arc with one on either side of a plane containing the consumable electrode and the direction of movement of the consumable electrode relative to the article.0088882162214. The system of claim 12 or 13, wherein the twin supplementary feedstock wires (10) are in a mirror image relationship to each other across said plane (A-A).
15. The system of any one of claims 12 to 14, wherein the feedstock directing arrangement is configured to feed the twin supplementary feedstock wires (10) so that they extend from the arc (5) along directions which are at a first angle to each other of less than 30°.
16. The system of claim 15, wherein the feedstock directing arrangement (8) includes a guide system (14) which receives the twin supplementary feedstock wires (10) from directions which are at a relatively large second angle to each other and turns the wires such that the second angle reduces to the first angle when they reach the arc.
17. The system of any one of claims 12 to 16, wherein the feedstock directing arrangement (8) is further configured such that the spacing between the twin supplementary feedstock wires (10) at their closest approach to the consumable electrode (4) is greater than the diameter of the consumable electrode (4).
18. The system of claim 17, wherein the feedstock directing arrangement (8) is further configured such that the spacing between the twin supplementary feedstock wires (10) at their closest approach to the consumable electrode (4) is no more than five times the diameter of the consumable electrode (4).
19. The system according to any one of claims 12 to 18, wherein the gas metal arc welding device (1) is configured so that an energy distribution of the arc has a maximum of the energy distribution at the centre of the arc and an envelope of the arc is defined by a notional boundary located at 1 / e2times the maximum of the energy distribution of the arc, and wherein the feedstock directing arrangement (8) is configured so that the spacing between the twin supplementary feedstock wires at their closest approach to the consumable electrode is such that the twin supplementary feedstock wires are located inside the envelope of the arc.
20. The system of any one of claims 12 to 19, wherein the feedstock directing arrangement (8) is further configured such that the twin supplementary feedstock wires (10) extend from the arc (5) along directions which are at an angle of at least 60° from the vertical direction.0088882762321. The system of any one of claims 12 to 20 wherein the feedstock directing arrangement (8) is further configured such that the twin supplementary feedstock wires (10) extend from the arc (5) along directions which are at an angle of at most 75° from the vertical direction.
22. The system of any one of claims 12 to 21 , wherein the feedstock directing arrangement (8) is further configured such that the twin supplementary feedstock wires (10) extend from the arc (5) to the front of the consumable electrode (4) relative to said direction of movement.