WO2025172686A1

WO2025172686A1 - Method and apparatus for manufacturing metal and metallic products by direct deposition of molten metal

Info

Publication number: WO2025172686A1
Application number: PCT/GB2025/050212
Authority: WO
Inventors: Yan Huang
Original assignee: Brunel University London
Current assignee: Brunel University London
Priority date: 2024-02-16
Filing date: 2025-02-04
Publication date: 2025-08-21
Anticipated expiration: 2026-08-16
Also published as: GB2638247A

Abstract

Apparatus for, and methods of, manufacturing a metal or metallic product. The apparatus (10) includes a furnace (110), a heated delivery vessel (120), a support substrate (230), a moving mechanism (250), and a cooling mechanism (232, 240, 241). Metal is heated to a molten state using the furnace (110) and held and maintained in the molten state by the delivery vessel (120). The delivery vessel (120) has a delivery vessel outlet (130) which is configured to feed the molten metal in a continuous stream from the delivery vessel (120) onto the support substrate (230). Relative movement between the delivery vessel outlet (130) and the support substrate (230) is provided by the moving mechanism (250), whereby the molten metal can be deposited onto the support substrate (230) in a plurality of overlying layers. The cooling mechanism (232, 240, 241) is operable to provide for the deposited molten metal to cool so as to solidify and thereby form a metal product. By providing a continuous stream of molten metal, large metal and metallic products can be made while practically overcoming existing limitations to scale and material selection in additive and deformation manufacturing methods.

Description

METHOD AND APPARATUS FOR MANUFACTURING METAL AND METALLIC PRODUCTS

Field of the Invention

The present invention relates to a method and apparatus for manufacturing metal and metallic products, in the preferred embodiments to a direct liquid metal additive manufacturing process and apparatus. The method and apparatus taught herein are able to create 3D objects of metals and alloys, and of metal matrix composites for structural, electronic and biomedical applications. The preferred process and apparatus take advantage of additive manufacturing technology although offering extra and critical benefits to existing additive manufacturing processes by directly using liquid metal as the feedstock. The preferred embodiments could be described as providing deformation assisted direct chill liquid metal deposition.

Background of the Invention

Metal products have traditionally been made by shape casting, using casting alloys, or ingot casting, for wrought alloys, followed by a metal forming process such as rolling and extrusion. In most cases, the rolled and extruded products require further fabrication steps such as bending, drawing and stamping, or machining to obtain their final form. These conventional processes are largely developed for standard mass production and are poorly suited to the formation of small numbers or batches of products.

More recently, metal products have been formed by additive manufacturing (AM) techniques, often referred to as liquid metal 3D printing. Methods of additive manufacture for metal products include, for example, selective laser melting (SLM), in which a laser is used to selectively melt and fuse a fine layer of metal powder to form a product; and direct energy deposition (DED), in which metal feedstock in the form of powder or wire is melted and jetted as droplets onto a worksurface. These methods have significantly reduced costs and lead-times incurred in tooling conventional machining production, and have materially facilitated making of prototypes and small-batch production of components. A bespoke component can now be made almost directly from a computational modelling (CAD) file with low up-front cost.

Liquid metal additive manufacturing can also utilise printing technologies to fabricate near-net shape or fully free-standing metal objects. Various printing modes and droplet generation techniques as applied to liquid metals are in development, particularly by a continuous metal drop printing mode and by a drop-on-demand (DOD) printing mode, based on commercial inkjet printing technology.

However, such methods are limited in scale, in terms of both the size of items which may be manufactured and in the rate of production achievable. Furthermore, known additive manufacturing methods can be used with only a small number of metals and alloys, and the strength of the manufactured metal products is often limited when compared to products made by conventional methods. For example, the vast majority of the more than 5,500 alloys currently in use are not able to be used with existing additive manufacturing processes.

Product-to-product variation is also a concern with many existing additive manufacturing technologies. There are several issues that lead to microstructural defects and poor mechanical properties, including high porosity and low density, residual stresses, stair-stepping and lack of consistency. Powders are particularly associated with the formation of pores, leading to low product density and higher likelihood of cracking and failing under load. Residual stresses occur during a heating-cooling process. Extreme heating and cooling cycles in the high energy resource additive manufacturing processes can generate high levels of residual stresses, which can distort or crack components or de-bond the interface between the product and the substrate to which it adheres. Stair-stepping, or layering errors, cause the finish of a product to look similar to a staircase. This unintended surface incline requires post-processing to be rectified. Lack of consistency in quality exists in all existing additive manufacturing processes due to the variation of too many controlling factors, including for example material selection, material protection during processing, to processing parameters and post-processing operations, and so on.

These limitations have hampered the adoption of additive manufacturing methods for metals in many industries, particularly in mass production applications.

Summary of the Invention

The present invention seeks to provide an improved method of and apparatus for manufacturing metal and metallic products.

According to an aspect of the present invention, there is provided a method of manufacturing a metal product, the method including the steps of: bringing a metal material to a molten state; maintaining the metal in the molten state in a delivery vessel; feeding the molten metal through an outlet of the delivery vessel in a continuous stream from the delivery vessel to a support substrate so as to deposit molten metal on the support substrate; wherein deposition of the molten metal onto the support substrate comprises depositing molten metal in a plurality of overlying layers; and providing for the deposited molten metal to cool so as to solidify and thereby form a metal product.

The method can manufacture a metal product by deposition in quantity of a continuous stream of readily available material, and in quantities and at speeds materially greater than with prior art methods, particularly liquid metal 3D printing methods. This can greatly reduce limitations on speed of production and product size experienced with additive manufacturing methods known in the art.

Preferably, the method includes at least partially cooling a deposited layer of molten metal prior to deposition of another layer of molten metal thereover. Cooling may be sufficient to solidify a prior deposited layer prior to deposition of another layer of molten metal thereover. The method may include cooling a deposited layer of molten metal sufficiently fully to solidify that layer prior to deposition of another layer of molten metal thereover.

The method preferably includes the step of feeding molten metal through the outlet by gravity. The inventor has discovered that using a gravity feed is particularly advantageous for providing a continuous flow of molten metal to the substrate or previously deposited metal layers. The liquid metal can be fed to the delivery vessel in a controlled manner in order to ensure that the level/volume of the alloy melt in the delivery vessel remains unchanged, which can ensure in a simple manner that gravity force is maintained constant during the deposition process, thereby to allow for a uniform flow and deposition rate. In the preferred embodiments there is also provided a mechanism and control step that allows the level of liquid metal in the delivery vessel to be changed, by adjusting the amount of flow to the delivery vessel in order to alter the flow speed. This may be varied on the basis of a predetermined formula and/or on the basis of feedback from the metal deposition stage.

By using gravity to feed the molten metal, the system is made advantageously simple, reliable, and robust. These advantages are maximised when gravity alone is used to feed the molten metal through the outlet.

The method may include the step of feeding molten metal through the outlet by pressure. Introducing pressurisation of the feed can increase the range of dynamic control and/or provide a higher feed rate of the stream, and help maintain the continuity of the liquid stream, in particular when it is thin. For example, the stream of molten metal may be pressure driven by piston control, piezoelectrically, hydraulically, pneumatically, by magnetic field control, or a combination thereof. The molten metal may be fed through the outlet by a mixture of gravity and pressure to combine the advantages of both approaches.

Preferably, the method includes the step of heating the outlet while feeding molten metal therethrough. Heating the metal as it passes through the outlet helps to control the temperature of the liquid metal stream immediately prior to deposition. This can be also helpful in preventing premature solidification of the melt, and clogging of the outlet, especially when the stream is thin.

Preferably the method includes constraining molten material deposited on the support substrate from the continuous stream in at least two peripheral extents. This provides increased control over the shape of the product. It is particularly beneficial in the manufacture of larger items for which the volume of metal deposited on the substrate is larger and therefore more prone to flowing on the surface of the substrate after being deposited. For example, the continuous stream of molten metal may have a dimension (width) in the range 1 to 20 mm and/or the outlet of the delivery vessel may have a dimension (width) in the range 1 to 20 mm, in which case the step of containing molten material is particularly beneficial due to the large size of the liquid metal stream.

The step of constraining molten material deposited on the support substrate or on a previously deposited metal layer may comprise adjusting a distance between first and second constraining elements to a desired width of the product to be manufactured. The width of each deposited layer can be controlled in this way shape the formed product.

The method may include the step of dynamically adjusting the distance between the first and second constraining elements during deposition of molten material onto the support substrate. In this way, products can be made with contoured shapes.

In a preferred embodiment, the first and second constraining elements are facing blades, preferably substantially parallel, a spacing between which is adjustable to a desired width of the product to be manufactured. This is an advantageously simple mechanism for controlling precisely the shape of each deposited layer and thereby the shape of the product.

The method may include the step of adjusting or setting a size of the outlet to a desired width of the product to be manufactured. The outlet can be used in this way as a simple mechanism for controlling the shape of the final product.

The method may include dynamically adjusting the size of the outlet during deposition of molten material onto the support substrate or a previously deposited metal layer. In this way, products can be made with contoured shapes.

Preferably the method includes the step of controlling the temperature of the support substrate so as to help control the cooling rate of molten metal deposited thereon.

Preferably the step of providing for the deposited molten metal to cool includes directly cooling the deposited metal in solidification by introducing a cooling agent in proximity to the metal (in the solidification zone) or in contact with the metal on either side of the solidification zone along the substrate travel direction. In this way, the deposited metal can be rapidly cooled and solidified. Direct cooling can also be provided through the constraining blades.

The method may include the step of moving the support substrate in at least one direction during deposition of molten metal. Scanning motion - that is, relative movement between the outlet and the substrate in order to deposit layers of material in various shapes and over the course of consecutive passes - can be provided by motion of one or both of the outlet and the substrate. Preferably, the method includes using a moving mechanism which is configured to move the support substrate while the delivery vessel and outlet (and connected components) remain static. This arrangement is advantageously simple and provides that the movement does not interfere with the flow of the liquid metal into and out of the delivery vessel.

Preferably, the method includes the step of deforming the product on the support substrate during deposition. Metal products are often required to undergo further post-processing to achieve mechanical properties sufficient for their intended use (especially if the product is intended to be load-bearing). This is true of metal products produced by any method, and in particular for methods involving a molten metal stage such as casting and additive manufacturing. Particularly beneficial post-processing for such products includes working, that is plastic deformation, in which dislocations are introduced into the material and thereby modify and improve the microstructure and mechanical properties of the product. Incorporating a plastic deformation step in the process of deposition aims to destruct casting structures, heal or harness casting defects and promote recrystallization by introducing stored energies during deformation, thus enabling an advantageously streamlined process for manufacturing a product which can meet the strength requirements of its intended use immediately, that is with limited or without further processing.

The deformation step may be carried out immediately after solidification of the deposited molten metal. The metal is deformed in this way once the metal is solidified but advantageously remains workable, e.g. malleable, due to heat retained from the molten phase. In the preferred embodiments, the deformation stage is carried out when the deposited metal is at a temperature in the range of 0.5-0.9 T_m, (T_m is the melting temperature of the metal on the Kelvin scale).

In prior art methods a formed metal product to be worked undergoes a separate heating stage (such as annealing) in order to prepare the material before it can be worked to improve its mechanical properties, which adds time and cost to the manufacturing process. The deformation stage of the method taught herein can avoid any pre-heating and conditioning, and streamlines the overall process.

The deformation should be performed in such a manner that it produces a sufficient amount of strain required for microstructure modification, with limited or minimised impact on the product shape, most preferably with no impact on the product shape. By performing the deformation stage in the process of deposition, the deformation is applied to a layer of metal that has just been deposited (prior to the deposition of a subsequent overlying layer of metal), thus the strain involved in the deformation stage is small and can be easily reversed. Accordingly, layer by layer, the whole body of the deposited product can be plastically deformed without changing the shape of the product.

The deformation step can involve one or more of rolling, hammering and pinching of the deposited metal. Preferably, a hammer with a roller head is used to apply both forging and rolling deformation. The use of a roller hammer head is particularly advantageous in avoiding high friction between the hammer head and the product, which moves constantly during the process as the roller hammer head rotates with and remains in contact with the product. More specifically, the deformation step may comprise applying a vibrational hammering operation, using a roller hammer head, to plastically deform the deposited metal. The hammering load may substantially align with the product building direction or the deposition layer thickness direction, perpendicular to the deposition plane. The hammering strike frequency and magnitude may be chosen so that the deformation penetrates through the thickness of the layer that has just been deposited and the shape change in one hammering strike is substantially reversed in the next strike, ensuring that the top surface of the product in building retains certain flatness after deformation and is ready for further deposition. The deformation step may comprise selectively deforming a portion of the product. The deformation applied need not be homogenous across the product. For example, a point of stress concentration of a product, such as a corner or transition in thickness, can be strengthened by selective deformation of that or those products

The skilled person will appreciate that the method and apparatus disclosed herein can be considered as being an additive manufacturing method, in which the product is built up, typically by deposition of successive layers of molten metal, rather than being a subtractive method, in which material is removed, such as by machining, for example.

According to another aspect of the present invention, there is provided apparatus for manufacturing a metal product, the apparatus including: a furnace configured to heat a metal material to a molten state; a heated delivery vessel configured to maintain the metal in the molten state; a delivery vessel outlet coupled to the heated delivery vessel and configured to feed the molten metal in a continuous stream from the delivery vessel; a support substrate aligned with the delivery vessel outlet such that molten metal fed from the outlet is deposited on the support substrate; a moving mechanism configured to provide relative movement between the delivery vessel outlet and the support substrate, whereby molten metal can be deposited onto the support substrate in a plurality of overlying layers; and a cooling mechanism operable to provide for the deposited molten metal to cool so as to solidify and thereby form a metal product.

Advantageously, the apparatus is configured such that metal that is molten in the furnace remains in a molten state throughout the process, until deposition on the support.

The cooling mechanism is preferably operable to provide for at least partial cooling of a deposited layer of molten metal prior to deposition of another layer of molten metal thereover. The cooling mechanism may be operable to cool a deposited layer of molten metal sufficiently to solidify that layer prior to deposition of another layer of molten metal thereover. In the preferred embodiments, the deposited metal is allowed to cool to a temperature in the range of 0.5-0.9 T_m, (T_m being the melting temperature of the metal on the Kelvin scale), prior to deformation. At this temperature the deposited metal is still readily deformable.

Preferably, the delivery vessel is configured to allow for gravity driven feeding of molten metal through the outlet. As described with reference to the associated method, initiating and controlling the feed is made simple and accurate by a configuration which takes advantage of gravity.

The apparatus preferably includes a molten metal feed control unit coupled to an outlet of the furnace, and a sensor unit configured to determine a volume of molten metal in the heated delivery vessel, whereby the molten metal feed control unit is configurable to maintain a constant volume of liquid metal in the delivery vessel and thereby a constant liquid metal flow velocity from the outlet. The size and shape of the outlet is selected in line with the desired wall thickness of the product being formed by deposition, as is the deposition speed.

The apparatus may include a pressurization unit coupled to the delivery vessel and configured to provide for pressure driven feeding of molten metal through the outlet. The pressurization unit can be configured to provide for a mixture of gravity and pressure driven feeding of molten metal through the outlet. As described with reference to the disclosed method, pressurisation of the feed can increase the feed rate and the range of control over the stream.

The apparatus preferably comprises a heating element configured to heat the delivery vessel outlet. Heating the outlet can facilitate the control of the temperature of the liquid metal stream immediately before deposition, and improve the fluidity of the metal stream, helping to prevent premature solidification and clogging of the outlet.

Preferably, the apparatus includes a constraining mechanism configured to constrain molten material deposited on the support substrate from the continuous stream in at least two peripheral extents. The constraining mechanism can provide control over the shape of the liquid metal as it solidifies. It is particularly beneficial for producing larger items for which the volume of metal deposited on the substrate is larger and therefore more prone to flowing on the surface of the substrate after being deposited. In the preferred embodiments, the constraining mechanism comprises first and second constraining elements in the form ef facing blades, preferably parallel to one another, and an adjustment device configured to adjust a spacing between the blades to a desired width of the product to be manufactured. The width of each deposited layer can be controlled in this way to shape the product.

The adjustment device may be configured to provide dynamic adjustment of the distance between the first and second constraining elements during deposition of molten material onto the support substrate. This allows products to be made with more complicated shapes.

Preferably, the delivery vessel outlet is adjustable or settable in size and/or shape. The outlet is preferably dynamically adjustable during deposition of molten material onto the support substrate. This helps in producing products with more complicated shapes, for example with varying thickness. Additionally, or alternatively, the apparatus may comprise a plurality of delivery vessel outlets, selectable for coupling to the delivery vessel. The apparatus may comprise outlets of different shapes and sizes.

The apparatus may comprise an outlet of hollow frame form. In this way, the stream of material flowing from the outlet is made hollow. This is particularly advantageous for depositing larger diameter flows of material, and therefore for making larger products. In cross-section, the frame form outlet may be curved or straight sided.

Preferably, the cooling mechanism is operable to control a rate of cooling of molten metal deposited on the support element. As described with reference to the disclosed method, controlling the temperature of the substrate allows for greater control of the solidification and crystallisation of the metal and, therefore, the material properties of the resulting product.

The cooling mechanism is preferably operable to cool directly the deposited metal over substantially the entirety of an external surface of the deposited metal by introducing a cooling agent in proximity to the metal or in contact with the metal. In this way, the deposited metal can be rapidly and evenly cooled all over to control solidification. The apparatus preferably includes a deformation mechanism configured to deform the product on the support substrate. More particularly, the apparatus preferably includes a deformation mechanism configured to plastically deform the product in the process of deposition. It is preferred that the deformation mechanism comprises at least one of a roller element, a hammering element, and a pinching element. By incorporating a deformation mechanism, the apparatus is able to perform a streamlined and integrated process in which a product is formed and effectively post-processed in a single compound operation.

In some embodiments, the deformation mechanism may be a part of the constraining mechanism, for example a rigid component of the constraining mechanism.

The cooling mechanism may be advantageously configured to cool a surface of the deformation mechanism which in use contacts the deposited metal.

The delivery vessel preferably comprises a heated nozzle section in communication with the outlet. By use of a heated nozzle section, the apparatus provides for concentrated heating of the liquid metal flow as it is shaped for deposition onto the substrate.

The apparatus may comprise a plurality of delivery vessels disposable over the support substrate. The plurality of vessels provides for the same or different molten materials to be held and deposited, alternately or simultaneously.

Other aspects and features of the present invention are described below and shown in the accompanying drawings.

Brief Description of the Drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of apparatus for manufacturing a metal product;

Figure 2 is an extract of the schematic diagram of Figure 1 , showing an enlarged view of an outlet of the apparatus; Figure 3 shows, in cross-section, various shapes of aperture for use in the outlet of the apparatus of Figure 1 .

Figure 4 is an illustration in a plan view of a constraining mechanism of the apparatus of Figure 1 ;

Figures 5 and 6 are, respectively, front elevational and plan views in schematic form of a metal component in the process of being manufactured and depicting the constraining blades of the apparatus;

Figures 7 and 8 show a preferred embodiment of hammer and roller hammering head for the deformation stage of the apparatus;

Figure 9 is a flow-chart representing the steps of a method of manufacturing a metal product according to the teachings herein.

Description of Preferred Embodiments

Described below are apparatus for and a method of manufacturing a metal product. The term “metal” is used herein to denote any metal or metallic product, including alloys and metal matrix composites.

The method of the preferred embodiment could be described as a direct liquid metal additive manufacturing process, which is able to manufacture 3D objects. The process takes advantage of additive manufacturing technology and introduces further benefits by directly using liquid metal as the feedstock. This is described in detail below, beginning with a description of specialised apparatus which has been developed for putting the process into practice.

The apparatus 10 includes generally a first hot section 100 for producing and supplying liquid metal M, and a cool section 200 for receiving and solidifying the liquid metal M into a product.

The upper section 100 includes principally a furnace 110 and a delivery vessel 120 which is connected to the furnace 110 and has an outlet 130. The lower section 200 includes a chamber 210 for maintaining an inert atmosphere for deposition, to protect the liquid metal stream and the deposited layer from being oxidised. The chamber 210 is filled with an inert gas (for instance argon or nitrogen) provides the atmosphere required used and can also provide cooling. The cool section 200 includes principally a bed 220 which is positioned beneath the vessel 120, and a cooling mechanism, described in further detail below. The bed 220 has an upper surface having a support substrate 230, which is aligned with the outlet 130 to receive liquid metal delivered from the delivery vessel 120. The cooling mechanism is configured to cool the liquid metal which is deposited onto the substrate 230. Figure 1 is a schematic diagram of the apparatus, showing a side elevational cross-sectional view of the primary components of the apparatus.

The furnace 110 is configured to heat a supply of metal in bulk to a molten state to be fed through a delivery coupling 122 to the delivery vessel 120. The furnace 110 can be used to produce a constant supply of liquid metal M throughout the manufacturing process. The furnace type, melting procedure, and liquid metal protection measures can be substantially similar to those used in conventional casting, in particular permanent mould casting or direct chill casting for any particular metal or alloy. The furnace 110 is preferably suitable to melt high melting point metals for engineering applications, such as aluminium (which has a melting point in the region of 660 degrees Celsius) and steels (which have a melting point in the region of about 1 ,350-1 ,550 degrees Celsius). Agents can be added to the melt in the furnace for alloying, degassing or to improve the microstructure and solidification performance of the metal (for example by promoting equiaxed growth and grain refinement behaviour). Using the furnace 110 in this way, the operator is able to integrate processes of preparing the metal stock into the manufacturing stage for increased efficiency.

The delivery vessel 120 is a reservoir for the liquid metal received from the furnace 110 through the inlet conduit 122. The inlet 122 is positioned at the top of the delivery vessel 120 and to a suitable exit point of the adjacent furnace 110. The walls 125 of the vessel 120 form an internal chamber for holding the liquid metal and are preferably made of insulating material to as to retain the heat in the molten metal. The delivery vessel 120 advantageously includes heating elements 140 disposed around a perimeter of the internal vessel chamber and operable to maintain the metal in the molten state ready for delivery. The heating elements 140 heat the vessel walls 125 conductively, thereby maintaining a supply of heat to the metal within the chamber. The apparatus preferably comprises a control unit configured to control the heating elements 140 to maintain a temperature inside the vessel 120 suitable to the metal or metal alloy held in the vessel 120. Typically, the control unit is operable to control the heating elements 140 to maintain the molten metal M in the delivery vessel 120 at a predetermined temperature at or above the melting point (liquidus temperature) of the metal in the vessel 120. Occasionally, the molten metal M may be maintained at a temperature slightly below its liquidus temperature.

In the preferred embodiments, the heating elements 140 are advantageously embedded in the walls 125 of the vessel 120 and distributed over substantially the internal height of the chamber, surrounding the chamber. The selection of materials for the vessel walls 125 depends on the range of working temperatures, possible chemical reactions involved, the volume capacity requirement of the process, and structural requirements for the vessel 120. In this embodiment the vessel 120 and internal chamber therein are generally cylindrical in shape, but in other embodiments can take any practical shape.

The outlet 130 of the vessel 120 has an open configuration and a closed configuration, selectable so that flow of liquid metal M out of the vessel 120 is selectively allowed or prevented.

With reference also to the enlarged section of Figure 2, the outlet 130 includes an aperture 132 through which, when the adjustable outlet 130 is in the open configuration, the molten metal can flow from the vessel 120 in a continuous, that is unbroken, stream. In contrast to a droplet-based jetted printing system, the outlet 130 is configured to allow an uninterrupted, unbroken flow of liquid metal from the delivery vessel 120 to the substrate 230 of the bed 220 beneath, as can be seen in Figure 1 . This allows for the swift deposition of the liquid metal in quantity for the production of large items.

In this embodiment, the outlet 130 is positioned at the bottom of the vessel 120 so that the liquid metal is driven most effectively by gravity (acting against the body of liquid metal in the vessel 120) through the aperture 132 when the outlet 130 is in the open configuration. The liquid level in the delivery vessel 120 can be maintained or adjusted by the continuous supply from the furnace to control the gravity force and, thereby, control the feed of metal through the outlet 130.

The outlet 130 can be operated by being moved laterally across the opening of nozzle 150, so as to align the aperture 132 with the nozzle to allow flow, or to block the opening of nozzle 150 when the aperture 132 is not aligned with the opening of the nozzle, thereby to prevent flow. In other embodiments, the outlet 130 could comprise a selectively openable and closable aperture, such as an iris aperture.

Referring again to Figure 1 , the bed 220 and the outlet 130 are spaced from one another such that there is a gap between the substrate 230 of the bed 220 and the outlet 130. When liquid metal leaves the outlet 130, it flows in a free stream across the gap. The apparatus 10 is configured so that the stream is unconstrained and unbroken as it flows across the gap from leaving the outlet 130 to being deposited on the substrate 230. Various parameters of the apparatus are controlled to control the flow of liquid metal, which is determinative of the deposition of material onto the substrate 230. In particular, it is desired that the flow of liquid metal between the outlet 130 and substrate 230 is continuous and uniform to provide consistent and predictable build-up of material layers. In general, it is preferred that flow is of sufficient rate to reduce processing time and prevent premature cooling of the liquid metal, while ensuring previously deposited layers have time to solidify sufficiently prior to being overlaid with further liquid metal. The liquid metal feeding rate and the solidification time are determined by the deposition speed. Described below are means by which an optimised liquid metal supply can be provided for deposition, particularly so as to match the cooling capacity for solidification of the material and for maintaining a constant deposition speed.

Parameters of the apparatus which can be adjusted to control the flow include: the liquid level and volume of liquid metal M in the delivery vessel 120 (and therefore, the gravity force driving the flow); the size and shape of the outlet 130; and, the temperature (and thereby viscosity) of the liquid metal M leaving the vessel 120. The preferred embodiment of the apparatus includes an additional flow rate control mechanism working in conjunction with the outlet. In particular, with reference to Figure 2, the hot section 100 of the apparatus 10 includes a nozzle section 150 disposed between the vessel chamber of the delivery vessel 120 and the outlet 130, which helps to condition the flow of liquid metal leaving the delivery vessel 120. The nozzle section 150 has an internal lumen for liquid metal to flow through from the delivery vessel 120 and includes first and second portions 151 ,152 (through which the flow passes before exiting the outlet 130).

The first, upper portion 151 of the nozzle section 150 is adjacent to and in fluid communication with the internal chamber of the delivery vessel 120 and has a tapered cross-section which provides a constricted passage for flow of liquid metal therethrough, the passage having a taper from a first diameter at the upper end to a second smaller diameter at the lower end. In this embodiment, the first portion 151 has a frustoconical shape.

An elongate second portion 152 of the nozzle section 150 is positioned between (and is in fluid communication with) the first portion 151 and the outlet 130. In the preferred embodiment shown, the second nozzle section 152 extends from the first portion 151 to the outlet 130. The second portion 152 has a cylindrical shape. The internal cross-sectional diameter of the second nozzle portion 152 is substantially uniform.

Heating elements 145 of the apparatus 10 are also disposed along the nozzle section 150 (substantially along the length of the second portion 152) to heat the flow of liquid metal as it passes through to the outlet 130. In the preferred embodiment, the heating elements 145 are arranged as a coil which is coiled around (and thereby surrounds) the second portion 152 of the nozzle section to supply even heating to a maximal area of the second portion 152. The heated nozzle section is particularly beneficial for keeping the liquid metal at either the same temperature as in the vessel or at least in the molten state.

Such temperature control is relevant for controlling and maintaining the temperature of the liquid metal prior to the deposition, thereby to ensure that the thermal state of the molten pool is substantially known. The shape of the liquid metal stream can be controlled with the cross-sectional geometry of the outlet 130, and particularly the aperture 132. In the embodiment shown, the aperture 132 of the outlet 130 is a fenestration in a rigid plate which is positioned at a bottommost end (that is, the terminus) of the outlet 130 and coupled to the delivery vessel 120. Figure 3 shows a selection of shapes of apertures 132 for the outlet 130, including circular (at Figure 3i), elliptical (at Figure 3ii), and rectangular (at Figures 3iii and 3iv). Each aperture 132 has an internal height a, and an internal width b. By selecting a shape and manipulating (that is, setting) the height, width, and aspect ratio (which is the height divided by the width) of the aperture 132, the size and shape of the stream can be controlled. In this way, the aperture 132 functions like a die for the liquid metal which is passed through the outlet 130. Within reason, any conceivable shape of aperture 132 may be employed. The shapes of apertures 132 shown in Figure 3 are particularly convenient and practical examples. In this embodiment, the opening of the aperture 132 of the outlet 130 is smaller than the diameter of the internal lumen or passage of the second portion 152.

Further compound aperture shapes can be used to create a shape of stream with more complexity. An example is shown at Figure 3iv which includes an internal blank 135 whereby the aperture 132 (that is, the fenestration for flow to pass through at the terminus of the outlet 130) is a frame shape formed between a pair of nested (concentric) rectangles. The internal blank 135 selectively obstructs the flow, in this case preventing the liquid from occupying the middle of the outer rectangle and thereby creating a hollow stream around the inner rectangle. When using an aperture or opening 132 with a hollow frame form such as this, the stream can have a tendency to rejoin and refill the hollow space. The distance between the outlet 130 and substrate 230 should therefore be configured to maintain the hollow characteristic of the stream over the freestream distance x. An outlet 130 which provides a hollow metal stream (using a valve-like mechanism as described above) is particularly beneficial for depositing metal in a large track width. This is because a full (that is, non-hollow) liquid stream may supply an excessive amount of liquid metal for deposition when the track width is large, whereas the cooling capacity can be insufficient to complete solidification within the time defined by the deposition speed. Using a hollow stream, the amount of liquid metal supply can be largely reduced to match the solidification speed while maintaining the required track width.

To create products with complicated shapes, the apparatus 10 can include an outlet 130 having a plurality of apertures 132 and/or a delivery vessel 120 having a plurality of outlets 130 (held for example by a magazine or paternoster mechanism) which can be selectively engaged and disengaged (that is, coupled to and decoupled from the delivery vessel 120 to be placed in or removed from the flow path). In this way, the user may switch between outlet elements 130 of different shapes and sizes in creating the product. Additionally, or alternatively, the outlet 130 can include an adjustment mechanism by which the aperture 132 can be dynamically adjusted in size and shape to control the cross-section of the liquid stream so that the track width of deposition can be maintained dynamically equal to the width of the product in making. For example, the aperture adjustment mechanism can include a blade or shutter which engages with the outlet 130 to selectively obstruct the flow.

Returning to Figure 1 , the upper surface of the bed 220, provided with heating elements 222, comprises the support substrate 230 which is aligned with the outlet 130 so that the stream of material flowing from the outlet 130 is deposited onto the substrate 230. The support substrate comprises a cooling element 232. In the course of a continuous pour of liquid metal, successive layers can be deposited onto the substrate 130, whereby a subsequent layer of metal is applied onto a previous layer which has already somewhat cooled. Solidification preferably takes place substantially within the molten pool, that is in the space formed between the constraining mechanisms, the product built and the current layer that has just solidified. In this way the material is overlaid in successive strips or layers.

The substrate 230 is made of a heat-resistant (heat stable) material for contacting the deposited liquid metal, on top of which the product P is formed as the deposited metal cools and solidifies. In this embodiment, the substrate 230 is generally planar and flat. The assembly 10 also includes a cooling mechanism 241 , as does the dynamic mould 240, to provide direct cooling of the molten metal as it is deposited on the substrate 230 or on a previously deposited metal layer.

The cooling mechanism which provides for the deposited metal to cool so as to solidify and form the product. In the preferred embodiment shown, the cooling mechanism comprises multiple components 232, 240, 241 , which each serve to aid in cooling, and thereby solidifying, the deposited metal.

The direct cooling elements are configured to cool directly the exterior surface of the deposited metal. Many cooling techniques are suitable for this purpose. A particularly practical technique includes jetting a cooling agent (a cooling liquid or gas) onto the deposited material and/or the substrate 230. In this embodiment, the direct cooling element comprises a supply of argon or nitrogen gas and a plurality jetting nozzles 241 configured to dispense the inert gas as a cooling agent onto the deposited material, over exterior surface of the product P. The jetting nozzles 241 are preferably positioned between the outlet 130 and the deposited metal layer (and spaced laterally from the outlet 130 so as not to obstruct the liquid stream). Additionally or alternatively, the substrate 230 can be provided with an inbuild cooling element 232, of a type that will be familiar to the person skilled in the art of cooling. The dynamic mould 240, that is the blades, may also be provided with a cooling mechanism, which may be an in-built cooling device as for the substrate 230 or cooling jets 241 . Other embodiments may provide a bath or reservoir of a liquid cooling agent into which the deposited material can be gradually submerged layer by layer.

The substrate cooling element 232 is configured to cool the support substrate 230 specifically, thereby aiding the deposited molten metal in cooling and solidifying particularly at the bottommost layer(s) of material. In this embodiment, the substrate cooling element 232 is embedded in the support substrate 230 and comprises a circulated supply of a cooling agent (liquid or gas). The cooling agent is contained for example in a network of tubing (of the substrate cooling element 232) which includes at least a portion that passes through and is embedded in the substrate 230 (and thereby in proximity to the metal deposited thereon) for transferring heat from the deposited hot metal. The shroud 210 provides a sealed and insulating envelope around the support substrate 230 and also the outlet 130, within which the metal material is deposited. The shroud 210 provides a controlled atmosphere for the deposition and solidification process. An inert atmosphere (comprising inert gas such as argon) can be contained within the envelope of the shroud 210 to inhibit oxidation of the deposited metal. The protection of a continuous liquid stream from oxidation is much easier than for powders or liquid droplets as the latter have much higher surface area to volume ratio. The atmosphere within the shroud 210 can also be maintained in a cooled state (for example, by containing the cold gas supplied by the direct cooling element 232) to facilitate and control solidification of the deposited metal. An insulating property of the shroud 210 helps to maximise the cooling effect.

It is particularly advantageous for the apparatus 10 to include multiple cooling sources. However, in other embodiments, the apparatus may comprise one or any combination of the direct cooling elements described above.

In conjunction (and communication) with an associated processor and temperature probes (not shown) of the apparatus 10, the cooling mechanism 232, 240, 241 can provide precise programmable solidification control of the deposited metal for forming the product, and of the components of the cool section 200 of the apparatus.

The cool section 200 of the apparatus 10 further comprises a constraining mechanism 240 disposed between the outlet 130 and the substrate 230. The constraining mechanism 240 functions to hold and contain all the liquid metal deposited onto the bed 220 (and specifically the substrate 230), constraining the molten material in at least two peripheral directions (of the substrate surface) so as to ensure that each freshly deposited layer solidifies in the desired shape. In this embodiment, the constraining mechanism comprises first and second opposing constraining elements in the form of blades 242, as shown in Figure 4. Each blade 242 is substantially planar in form, preferably arranged with its longitudinal axis generally parallel to a major axis of the substrate 230 and having a generally planar surface extending orthogonally to the neighbouring major surface of the substrate 230. The blades 242 are positioned beneath the outlet 130 and at opposite sides of the outlet 130 (spaced laterally from the outlet 130 so as not to obstruct flow of liquid metal to the substrate 230). The facing blades 242 define an open channel therebetween and are preferably substantially parallel to each other. The blades 242 are set apart from each other by a distance y which corresponds to the track width of each deposited layer (and therefore the local dimension of the solidified product). The constraining mechanism 240 is configured so that the track width y can be adjusted, by setting in advance or dynamically during the process (using a programmable adjustment mechanism), to control the width of each deposited layer. In this way, the constraining mechanism 240 can function as a dynamic mould for the deposited metal. It will be appreciated that the constraining mechanism 240 can be moved or spaced vertically from the substrate 230 during operation as the lowest layers solidify. It is desired that, in operation, the constraining elements are always positioned at least level with the topmost layer of liquid metal.

The blades 242 are preferably made of heat-resistant and wetting-resistant material. The constraining mechanism 240, in the preferred embodiment, also comprises an anti-wetting mechanism (not shown) which is configured to apply vibration to the blades 242 in order to minimise wetting between the blades 242 and the solidified metal and thereby to allow the free movement of the substrate 230 for further deposition. This is particularly effective when the vibration has a low magnitude and high frequency. The vibration can also improve the product surface quality.

Referring now to Figure 5, this shows a front elevational view in schematic form of a product P being formed between two constraining blades 242 of the apparatus. As can be seen in the drawing, the deposited metal is in three states. Below the level of the blades 242 the product P is already formed and solidified. At zone P1 , having a height or depth H, molten metal is in the process of being solidified from the liquid stream; whereas above that there is a liquid stream Mi of molten metal coming from the vessel 150. The constraining blades 242 are located at the solidification zone. The constraining blades 242 are, in this example, disposed within a frame formed by a support mechanism 243, which includes an internal channel or chamber for cooling through fluid 245 which exits the chamber as jets to cool the deposited matter as product P is being formed. It will be appreciated that as successive layers of molten metal are deposited onto the substrate and onto previous layers, the substrate 230 will be moved downwardly with respect to the blades 242, so that the blades 242 and the associated cooling mechanism 243/245 remain within the solidification zone Pi, so in effect the constraining blades 242 can be said to move relatively upwards of the product being formed. The liquid stream of molten metal Mi will generally have a smaller width compared to the width of the product being formed, caused by narrowing of the liquid stream in the gap between the outlet 130 and the top of the product P being formed due to the effect of gravitational forces on the stream Mi. This ensures that the liquid stream remains within the bounds of the constraining blades 242 during manufacture of the product.

Referring now to Figure 6, this shows a plan view similar to Figure 5 and in which product P being formed is in various states, with only metal just deposited being in liquid (L) state, while sections of the product either side of that having already cooled and solidified. Figure 6 also shows the preferred location of the deformation zone 251 at which the formed product P is deformed as described herein. It will be appreciated that the substrate will be moved not only in the direction of travel shown in Figure 6 but also backwards and forwards as the product P is successfully formed by subsequent layers of molten metal, as well as downwardly to accommodate new layers formed over previous layers.

The apparatus includes a moving mechanism to effect scanning motion (that is, relative movement between the outlet and the substrate in order for layers of material to be deposited over the course of consecutive passes). The moving mechanism is programmable by communication with the processor of the apparatus so that the deposition follows a predetermined pattern to build the product layer by layer. The moving mechanism can be configured to move one or both of the outlet 130 and the substrate 230. In this embodiment, the moving mechanism is configured to move the support substrate 230 while the delivery vessel 120 and outlet 130 (and connected components) remain static. In particular, the bed 220 includes a motion stage, which is an underlying table including a moving mechanism 250 which is driven by a motor 260 and configured to move the substrate 230 relative to the outlet 130. In this preferred embodiment, the moving mechanism 250 is configured to provide for motion of the substrate 230 in three dimensions (that is, with at least three translational degrees of freedom relative to the outlet 130). The moving mechanism 250 can be further configured to provide for (and control) additional rotational movement of the substrate 230 (that is, to provide rotational as well as translational degrees of freedom).

Complicated structures (for example, a cylindrical structure with changing wall thickness) can be made by programming changes of the constraining element separation with the constraining mechanism 240 and the size and shape of the stream with the outlet 130 to produce the desired width (or widths) of the product layers in co-ordination with the scanning motion provided by the motion mechanism 250. The separation of the constraining elements (and thereby the track width of deposition) and the aperture diameter should be maintained equal to each other and to the desired width of the product.

The cool section 200 of the apparatus 10 also includes a deformation mechanism 270 for deforming the metal product. It is desirable to deform the deposited material because casted metals are not as strong or tough as formed metals, and because, in some instances, feeding alone may not avoid voids, cracks or porosity forming in the material. Deformation is applied substantially for improving the quality of the product by: breaking the as-cast dendritic (possible coarse columnar) structure; releasing possible residual stresses to prevent cracking; healing possible solidification defects such as hot tears, cracks, and pores; enhancing diffusion of solute atoms and consequently chemical homogenisation; promoting recrystallisation to form a refined and equiaxed grain structure and significantly accelerating the chemical homogenisation process through dislocation reorganisation, grain boundary migration and grain boundary diffusion; and, healing possible unbonded areas between layers.

Referring now to Figures 7 and 8, there is shown an embodiment of deformation mechanism 270, which in this embodiment includes a hammer 280 with a roller hammering head 282. The hammer 280 applies force to the product 282, while the roller reduces friction between the hammer 280 and the product P being deformed. As will be apparent in Figure 8, the roller hammering head 280- 282 has a width that is preferably at least as wide as the product being formed so that the entirety of the lateral extent of the product P can be deformed in one pass.

The material has to be allowed to solidify before it can be deformed plastically. However, there is a significant advantage in the described method which uses heat released during solidification in the material to keep it soft and malleable to deform it more easily (compared, for example, with a sheet layer that might be formed otherwise and then have to be reheated before being worked separately). In particular, deformation is substantially performed at a temperature in the range of 0.6-0.9T_m (where Tm is the melting temperature of the metal in the kelvin scale). Applying deformation when the component's temperature is very high means it is easier and more effective than if done when it is colder. The deformation mechanism 270 of the apparatus enables the operator to take advantage of this by deforming the deposited metal in-situ immediately after solidification.

In this embodiment, the deformation mechanism includes a hammer 270 positioned above the substrate 230 which is operable to impact (and thereby deform) the deposited metal in-situ on the substrate.

The deformation mechanism can therefore include one or more of the constraining elements, in this case both of the blades 242. The constraining elements can be used in this way in conjunction with another component of the deformation mechanism (such as the hammer) as in this case, or as a stand-alone deformation mechanism 270 for deforming the metal product. In other embodiments, the deformation mechanism 270 can include any other form of roller or hammer element, a pinching element or any other such practical mechanism for deforming the deposited material.

The deforming step need not be applied uniformly across the product, and therefore the deformation need not be homogenous across the product. Plastic strain generated by deformation may change from location to location to optimise the overall performance of the structure. In particular, the amount of strain produced in the product may be varied at different locations for structural design to give priority to relatively weaker locations or to particularly strengthen areas which will be regions of stress concentration in use.

It will be appreciated that the cooling mechanism 232, 240, 241 is advantageously configured also to cool working surfaces of the deformation mechanism. In particular, in this embodiment, the direct cooling element 241 is configured to apply cooling agent (in this case, an inert gas such as argon or nitrogen) directly to the constraining elements 242 as well as the deposited metal. In other embodiments, the apparatus can include separate cooling elements integrated into the constraining elements of the constraining mechanism 240 or as stand-alone components.

The cool section 200 of the apparatus 10 preferably comprises a heating mechanism to remove possible moisture from the substrate and dry surfaces which will contact the liquid metal in operation prior to deposition and to set up a temperature that facilitates wetting and solidification in the initial stages of deposition.

It will be appreciated that various modifications can be made to the specific embodiment of the apparatus described without prejudice to the functionality described. For example, the furnace 110 and inlet 122 are positioned at the top of the vessel 120, whereas they could be placed elsewhere. A pressurisation unit can be included to drive the feed of liquid metal (in addition to, or alternatively, to gravity). Further or alternative flow control mechanisms can be included in the apparatus 10 to work in conjunction with the outlet 130. For example, the liquid metal stream flowing through the outlet may be manipulated to facilitate deposition by the application of an electromagnetic field to alter the trajectory of the stream before it reaches the substrate 230. The apparatus 10 can include multiple vessels 120 and/or multiple outlets 130 to be used for distributed deposition with the same material, or for producing structures of different metals by simultaneous or alternate operation.

An example method of manufacturing a metal product is set out below, the steps of which are represented in the flow chart of Figure 9 by numerals 301-309. The example method includes the following steps. Prior to the manufacture/formation of the metal part, the system preferably provides for (i) the selection of a product to be manufactured, (ii) the generation of a digital model of the product to be manufactured, and (iii) programming of the apparatus to move and thereby deposit metal to form the desired product, as well as selection of the appropriate aperture element. Following this the method proceed as follows.

Step 1 (shown as 301): setting the separation distance (y) between the blades 242 of the constraining mechanism 240 to a desired width of the product to be manufactured.

Step 2 (shown as 302): selecting an outlet 130 with a size of aperture 132 corresponding to the desired width of the product to be manufactured and coupling the outlet 130 to the delivery vessel 120.

Step 3 (shown as 303): bringing a metal material to a molten state using the furnace 110.

Step 4 (shown as 304): supplying the molten metal from the furnace 110 to the delivery vessel 120 and maintaining the metal in the molten state in the delivery vessel 120, and repeating step 3.

Step 5 (shown as 305): heating the bed 220 to a given temperature to remove moisture and set up the initial temperature for the substrate 230; followed by switching the outlet 130 from a closed configuration to an open configuration, thereby allowing the molten metal to be fed through the outlet 130 of the delivery vessel 120 by gravity in a continuous stream from the delivery vessel 120 to the support substrate 230 beneath.

Step 6 (shown as 306): constraining molten material deposited on the support substrate 230 from the continuous stream in two peripheral extents using the blades 242 of the constraining mechanism 240.

Step 7 (shown as 307): simultaneously with step 6, moving the support substrate 230 relative to the outlet 130 with the movement mechanism 250 so that the molten metal is deposited in a plurality of overlying layers on the support substrate 230.

Step 8 (shown as 308): simultaneously with steps 6 and 7, jetting cold inert gas using the cooling mechanism 210 onto the deposited metal thereby providing for the deposited molten metal to cool so as to solidify and thereby form a metal product, whereby each deposited layer of molten metal is cooled sufficiently to solidify that layer prior to deposition of another layer of molten metal thereover.

Step 9 (shown as 309): deforming the product in-situ on the support substrate 230 immediately after solidification of the deposited molten metal by side-pinching the material with the blades 242 of the constraining mechanism 240.

The resulting product is essentially in a deformed and annealed state, requiring little further processing for many applications. Further processing steps can include hardening treatment and/or treatment for improving surface quality of the product, or limited machining if necessary.

It will be appreciated that steps 1-4 of the example method could be performed in any order.

The direct liquid metal additive manufacturing process and the apparatus described have potential applications in various areas, including structural, electronic, and biomedical fields.

The inventors foresee that an application of particular technical value is in the production of aluminium products, prevalent for example in the field of ground and space transportation. Aluminium has a high specific heat capacity and latent heat, high reflectivity, and a high tendency of surface oxidation. This makes it more difficult than nearly all other metals to be instantly melted by direct energy sources, which are utilized in existing additive manufacturing methods. In fact, the vast majority of the more than 600 aluminium alloys in use today are not attainable by any existing additive manufacturing processes. The apparatus and process described, however, are not so limited and may be particularly suited for the production of aluminium products.

Advanced aerospace 2000 and 7000 series aluminium alloys are commonly used for aircraft fuselage parts with specific and complicated geometries. They are wrought alloys and cannot be cast into shapes. The products are largely machined with a material waste ratio of up to 90%. There is therefore great potential for the technology described to be employed in the manufacturing of these structures with significant cost and material savings, and without compromise in performance. 5000 and 6000 series aluminium alloys have better formability than the aerospace aluminium alloys referenced above, and their sheet products and extrusions are widely used in the automotive industry. However, extensive further processing such as forming, joining, and welding is required to make components suitable for vehicle manufacture. The method and apparatus described also have the ability to produce consolidated structures of 5000 and 6000 series aluminium alloys, potentially with improved performance.

Additive manufacturing technologies, in general, offer benefits including access to complex geometries and design freedom, reduced material waste, rapid prototyping and iteration, ease of customisation, weight reduction and material optimisation, consolidation of products and improved performance efficiency, and on-demand production leading to lesser lead-times and cost savings.

The process described, while enjoying the above benefits, has significant advantages over many additive manufacturing processes of the art for the production of metal products, such as direct energy deposition and powder-bed fusion. These include: i. Shortened manufacturing route, reduced cost and energy consumption

Direct energy deposition and powder-bed fusion techniques use expensive powder or wire as feedstock material, both of which require preparatory melting and casting and forming (by atomisation for powders and through extrusion and drawing for wire). Further, these techniques require high intensity energy sources such as lasers and electron beams for melting and deposition, and yet require extensive post-processing. The process described directly uses liquid metal as the build material, eliminating the use of high energy resources, steps of powder making and wire production, and extensive manual post-processing. ii. High productivity and high scalability

AM processes are known for comparatively slow manufacturing speeds, largely preventing the technology from being suitable for high-scale production applications. The complicated solidification dynamics due to the use of high energy sources and the consequent successive re-melting and solidification thermal cycles involved in the deposition process are part of the reason for their typically slow speed. By such a regime, any speed increase may lead to a compromise in the quality of the product. By contrast, the process described can perform at a significantly higher deposition rate without sacrificing quality as it does not involve local heating, melting, and remelting of the solidified material. The deposition speed is simply determined by the cooling rate for a given product height and track width. High cooling rates normally result in a higher nucleation rate for solidification and equiaxed growth, giving rise to enhanced product quality. Yet, the liquid metal thermal field is well defined and the temperature gradient can be substantially lower than that in a conventional AM process using high energy sources. Specifically, the process is designed to supply a continuous liquid stream with a track width equal to the width of the product. These dimensions (and the corresponding dimension of the outlet) can be varied practically without scale limit. Technically, the scalability of the process described is only limited by the cooling ability of the substrate and the structure of the product being made. iii. High product quality

The product-to- product variation is a concern for many existing additive manufacturing methods. There are several issues that lead to microstructural defects and poor mechanical properties. These include high porosity and low density, residual stresses, stair-stepping and lack of consistency. Powders are particularly associated with the formation of pores, leading to low product density and higher likelihood of cracking and failing under load. Residual stresses occur during a heating-cooling process. Extreme heating and cooling cycles in the high energy resource additive manufacturing processes can generate high levels of residual stresses, which can distort or crack components or de-bond the interface between the product and the substrate to which it adheres. “Stair-stepping” is the nickname given to a layering error that causes a product’s finish to look similar to a staircase. This unintended surface incline requires post-processing to be rectified. Lack of quality and consistency is a challenge in all existing additive manufacturing processes due to the variation of too many controlling factors, from material selection, material protection during processing to processing parameters and post-processing operations. The process can easily mitigate or avoid these problems and produce a high-quality product. Firstly, the use of a continuous liquid stream makes it easier to protect the material from being oxidized or contaminated. Secondly, there are no heating-melting-remelting cycles in the deposition of a continuous liquid stream and solidification is controlled by cooling rate, under a well define thermal field and low temperature gradient. Thus, residual stresses are low or negligible. Thirdly, the application of in-situ deformation can substantially improve the microstructure and chemical homogeneity, giving rise to enhanced mechanical properties. Finally, the use of a constraining mechanism during deposition (and also during deformation by side pinching for example) helps to maintain the product dimension accuracy and can produce a desirable surface finish. In-situ deformation can also help destruct possible coarse columnar dendritic structures through recrystallization, further improving the quality of the product. iv. Wide material selection and application

Fusion-based additive manufacturing methods using high energy sources can only work reliably with a limited range of metals and alloys, the most relevant being Ti6AI4V, Inconel 718, and AISi Mg. In these processes, the rastering of the direct energy source (laser or electron beam or arc) generates certain overlapping lines in a back-and-forth pattern in order to continuously fuse successive layers of powder or wire. This is analogous to welding processes and the suite of printable metal alloys are limited to those known to be easily weldable. The vast majority of the more than 5,500 alloys available cannot be directly processed because of the melting and solidification dynamics during additive manufacturing, which lead to undesirable microstructures with a variety of defects as described above. Such alloys are often termed as “unweldable” or “AM unattainable” alloys. The process described herein eliminates boundaries between weldable and unweldable alloys, and even the boundaries between classical casting and wrought alloys. The process manufactures a product through layer-by-layer continuous deposition of a continuous liquid metal stream along the scanning direction, under a well-defined thermal field, low temperature gradients and cooling rote driven dynamics. Therefore, there is no requirement of weldability. The solidification takes place effectively in an open space, which facilitates uniform material shrinking during solidification, and thus there is no requirement of fluidity either to allow the liquid metal flow into the cavities to form a shape as in conventional casting processes. All the existing alloys can be used in the process described. The applicability of existing alloys to the process is extremely promising for solving the currently difficult situation within the additive manufacturing industry that there are deficiencies in material information with the lack of a comprehensive material database with established printing parameters and clearly defined specifications.

The use of a continuous liquid metal stream allows better control of solidification during deposition than existing droplet-based liquid metal printing techniques, in which the use of droplets tends to result in the formation of microstructural defects, such as porosity, cracks, and residual stresses.

In embodiments using multiple outlets, the process described may also be fit for manufacturing laminated or hybrid structures of different materials or metal matrix composite materials. v. Eco-friendly system

The current additive manufacturing ecosystem seems to be fragmented; there are a lot of little solutions and companies that one has to cobble together to create a workflow and end-to-end solution. The technology described herein is more consolidated as everything can be done in one process (under the same roof). This also contributes to the minimisation of carbon footprint. The technology is also highly accessible to existing manufacturing industries as it has a seamless connection to conventional metallurgical procedures.

All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Further, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments, are combinable and interchangeable with one another.

Claims

1 . A method of manufacturing a metal product, the method including the steps of: bringing a metal material to a molten state; maintaining the metal in the molten state in a delivery vessel; feeding the molten metal through an outlet of the delivery vessel in a continuous stream from the delivery vessel to a support substrate, thereby depositing molten metal on the support substrate; wherein deposition of the molten metal onto the support substrate comprises depositing molten metal in a plurality of overlying layers; and providing for the deposited molten metal to cool so as to solidify and thereby form a metal product.

2. A method according to claim 1 , including constraining molten material deposited on the support substrate from the continuous stream in at least two peripheral extents.

3. A method according to claim 2, wherein the step of constraining molten material deposited on the support substrate comprises adjusting a distance between first and second constraining elements to a desired width of the product to be manufactured, optionally dynamically adjusting the distance between the first and second constraining elements during deposition of molten material onto the support substrate.

4. A method according to claim 3, wherein the first and second constraining elements are facing blades, preferably substantially parallel to one another, a spacing between which is adjustable to a desired width of the product to be manufactured.

5. A method according to any preceding claim, including the step of cooling a deposited layer of molten metal prior to deposition of another layer of molten metal thereover.

6. A method according to claim 5, including the step of cooling a deposited layer of molten metal sufficiently to solidify that layer prior to deposition of another layer of molten metal thereover.

7. A method according to any preceding claim, including the step of feeding molten metal through the outlet by gravity.

8. A method according to any preceding claim, including the step of feeding molten metal through the outlet by pressure.

9. A method according to any preceding claim, including maintaining a constant level of molten metal in the delivery vessel.

10. A method according to any preceding claim, including the step of controlling the temperature of the support substrate so as to assist a rate of cooling of molten metal deposited thereon.

11. A method according to any preceding claim, wherein the step of providing for the deposited molten metal to cool includes directly cooling the deposited metal over substantially the entirety of an external surface of the deposited metal by introducing a cooling agent in proximity to the metal or in contact with the metal.

12. A method according to any preceding claim, including the step of heating the outlet while feeding molten metal therethrough.

13. A method according to any preceding claim, including the step of adjusting or setting a size of the outlet to a desired width of the product to be manufactured, optionally dynamically adjusting the size of the outlet during deposition of molten material onto the support substrate.

14. A method according to any preceding claim, including the step of moving the support substrate in at least one direction during deposition of molten metal.

15. A method according to any preceding claim, including the step of deforming the product on the support substrate, optionally comprising one or more of rolling, hammering and pinching of the deposited metal.

16. A method according to claim 15, wherein the deformation step is carried out immediately after solidification of the deposited molten metal.

17. A method according to claim 15 or 16, wherein the deformation step comprises selectively deforming a portion of the product.

18. A method according to any preceding claim, wherein the method is an additive manufacturing method.

19. Apparatus for manufacturing a metal product, the apparatus including: a furnace configured to heat a metal material to a molten state; a heated delivery vessel configured to maintain the metal in the molten state; a delivery vessel outlet configured to feed the molten metal in a continuous stream from the delivery vessel; a support substrate aligned with the delivery vessel outlet such that molten metal fed from the outlet is deposited on the support substrate; a moving mechanism configured to provide relative movement between the delivery vessel outlet and the support substrate, whereby molten metal can be deposited onto the support substrate in a plurality of overlying layers; and a cooling mechanism operable to provide for the deposited molten metal to cool so as to solidify and thereby form a metal product.

20. Apparatus according to claim 19, including a constraining mechanism configured to constrain molten material deposited on the support substrate from the continuous stream in at least two peripheral extents.

21 . Apparatus according to claim 20, wherein the constraining mechanism comprises first and second constraining elements in the form ef facing blades, optionally substantially parallel to one another, and an adjustment device configured to adjust a spacing between the blades to a desired width of the product to be manufactured.

22. Apparatus according to claim 21 , wherein the adjustment device is configured to provide dynamic adjustment of the distance between the first and second constraining elements during deposition of molten material onto the support substrate.

23. Apparatus according to any one of claims 19 to 22, wherein the cooling mechanism is operable to provide for cooling a deposited layer of molten metal prior to deposition of another layer of molten metal thereover.

24. Apparatus according to claim 23, wherein the cooling mechanism is operable to cool a deposited layer of molten metal sufficiently to solidify that layer prior to deposition of another layer of molten metal thereover.

25. Apparatus according to any one of claims 19 to 24, wherein the delivery vessel is configured to allow for gravity driven feeding of molten metal through the outlet.

26 Apparatus according to any one of claims 19 to 25, including a pressurization unit coupled to the delivery vessel and configured to provide for pressure driven feeding of molten metal through the outlet.

27. Apparatus according to any one of claims 19 to 26 , including a feed control mechanism to maintain a constant level of molten metal in the delivery vessel.

28. Apparatus according to any one of claims 19 to 27, wherein the cooling mechanism is operable to control a rate of cooling of molten metal deposited on the support substrate.

29. Apparatus according to any one of claims 19 to 28, wherein the cooling mechanism is operable to directly cool the deposited metal over substantially the entirety of an external surface of the deposited metal by introducing a cooling agent in proximity to the metal or in contact with the metal.

30. Apparatus according to any one of claims 19 to 29, comprising a heating element configured to heat the delivery vessel outlet.

31 . Apparatus according to any one of claims 19 to 30, wherein the delivery vessel outlet is adjustable or settable in size, optionally dynamically adjustable during deposition of molten material onto the support substrate.

32. Apparatus according to claim 31 , comprising a plurality of delivery vessel outlets of different shapes and sizes, selectable for coupling to the delivery vessel.

33. Apparatus according to any one of claims 19 to 32, including a deformation mechanism configured to deform the product on the support substrate, optionally comprising at least one of a roller element, a hammering element and a pinching element.

34. Apparatus according to claim 33, wherein the cooling mechanism is configured to cool a surface of the deformation mechanism which in use contacts the deposited metal.