This invention relates to a powder splitter, and in particular, but without limitation to, a low velocity powder splitter suitable for use, for example, in a powder additive manufacturing process.

Powders, such as metal powders, are commonly used in additive manufacturing processes. In certain types of additive manufacturing, a stream of powder can be melted in-situ, for example, using a laser beam. In other additive manufacturing processes, a plurality of convergent power streams is used, and a laser, or other heat source, is applied at the "focus" or intersection of the converging powder streams. Heating of the powder causes it to fuse and/or melt, so as to form a solid/fused layer, which can, in certain cases, be built-up to form a 3D part; or in other cases, to provide an adhered surface coating on a substrate.

In additive manufacturing processes, and especially those which use convergent powder streams, it is often desirable for each of the streams to have, or to have as close as possible, the same flow characteristics, for example, to have the same or similar mass-flow rates, powder density, powder velocity, etc.. however, this is not a readily attainable goal because powder fed through separate tubes/nozzles inevitably emerges with different flow parameters.

This invention seeks to provide a solution to the problem of differing powder flows, and/or to provide an alternative means, method and/or apparatus for achieving the same or similar.

Aspects of the invention are set forth in the appended independent claim(s). Preferred or optional features of embodiments of the invention are set forth in the appended dependent claims.

According to the invention, there is provided a powder splitter comprising an inlet and a plurality of outlets, a homogeniser interposed between the inlet and the outlet, and a splitter interposed between the homogeniser and each of the outlets.

The powder splitter of the invention has an inlet, through which a gas-powder mix or mixture enters it. The gas-powder mixture can be, for example, a fine metal powder entrained in an air stream. However, any powder (metal or non-metal) may be used, and any gas (inert or reactive) may be used. In certain cases, the gas-powder mixture is substituted for a liquid-powder mix, in which the liquid may be a conventional liquid, but it could, for example, equally be a super-critical fluid, or a condensed gas in other cases. Regardless, it will be appreciated that in a poly-phase, pseudo-liquid, flow characteristics are rarely in equilibrium for extended periods, and so maintaining flow characteristics within certain parameter windows needed for an additive manufacturing process can, therefore, be difficult to achieve.

The gas-powder mix that enters the inlet is typically in a laminar flow regime. Due to boundary and/or surface interaction effects that occur in laminar flow situations (e.g. along a feed pipe) the properties of the gas-powder mix are unlikely to be uniform across any given cross-section of the flow. Typically, the powder : gas ratio will vary across the cross-section (often approximating a Gaussian distribution), or the flow rate may be higher towards the centre of the stream, compared to nearer the boundaries. These differences lead to heterogeneity in the air-powder stream, which in turn, can lead to subsequent anisotropy in parts or coatings made by additive manufacturing processes.

The present invention proposes to interpose a homogeniser between the inlet and the splitter, which helps to ensure better uniformity in the powder prior to splitting, and thus better homogeneity between the air-powder streams post-splitting.

The greater the homogeneity of the gas-powder stream prior to splitting, the better will be the homogeneity between the separate streams post splitting. Thus, certain embodiments of the invention propose using a multi-stage homogeniser. The multi-stage homogeniser, in certain embodiments, may comprise any one or more of the group comprising:

A restrictor part, comprising a relatively narrow part forming a restriction, which may be of approximately half of the inlet flow port diameter. This can cause a corresponding increase in fluid flow velocity to turbulent flow and thus bring any off-axis mass flow of powder into this turbulent flow area;

An exit part, through which the turbulent flow gas-powder mix exits the restrictor part; and A first expansion chamber in which the fluid flow type suitably reverts to a laminar flow regime comprising a diverging gas-powder mix with the highest area of mass flow in the centre of the gas- powder stream. Ideally, there is an approximately Gaussian distribution of powder particles within the gas stream.

Suitably, there are a series of restrictor parts, exit parts and expansion chambers such that the constriction and expansion process can repeated, thereby better homogenising the flow.

A final constriction part and a subsequent expansion part, are suitably provided, which lead to the splitter.

Preferably, the splitter comprises a blade or knife-edge type device, which parts the stream of homogenised gas-powder into a desired number of separate streams. A single, straight knife-edge, for example, could split the stream into two separate streams, or a star-shaped arrangement of knife- edges could split the stream into a corresponding (i.e. any desired) number of streams.

In a preferred embodiment of the invention, the splitter comprises a quad splitter, which effectively divides the homogenised gas-powder stream into four separate streams. The separate streams, downstream of the splitter, can be fed, for example via a manifold, tubing, etc. to a respective number (in this case, four) of separate powder delivery nozzles.

The divergent powder-gas stream produced by the preceding stages is suitably divided into N (e.g. four) equal parts (where N = the number of outlets) by a blade device. Suitably, the splitter divides the homogenised gas-powder stream equally: for example into two halves, three thirds, four quarters, etc. Such a configuration means that the same amount of powder can be delivered to each of the gas-powder outlets/nozzles, which can be advantageous in certain situations.

Where a quad (four-way) splitter is provided, there can be four outlets.

Where the splitter comprises a quad-splitter, the blade can comprise a crossed (e.g. cruciform) blade, such that each quadrant thus produced can be fed to a separate chamber, which in turn may lead to one of N (e.g. four) outlet ports.

Advantages of the invention include, but are not limited to: A means of accurately splitting a single input, laminar flow gas-fluidised powder stream into N (e.g. four) output gas-fluidised powder streams. This may be suitable for the purpose of blown- powder additive manufacture, wherein the input powder particle mass flow rate of the single gas fluidised powder stream is divided equally between each of the N (e.g. four) output gas-fluidised powder streams.

On existing the device, unequal spatial distribution of the inlet particle mass flow within a feeder pipe or tube often results in unequal splitting of the gas-powder stream. This device first corrects this uneven spatial distribution of powder particles and then divides the resultant gas powder stream by, for example, a crossed-blade method, and directs it to four output ports.

Exemplary embodiments of the invention are shown in the accompanying drawings, in which:

Figure 1 is a schematic cross-sectional view of a first embodiment of a powder splitter in accordance with the invention; and

Figure 2 is a schematic cross-sectional view of a second embodiment of a powder splitter in accordance with the invention.

Referring to Figure 1 of the drawings, a powder splitter 10 comprises a main body 12 formed from a stack of generally cylindrical main body components 14, which are held together by axial through-bolts (not shown). By forming the powder splitter 10 from a "stack of discs" disassembly and reassembly for cleaning, maintenance, repair, purposes etc. is greatly facilitated. Each main body component 14 is typically formed from milled stainless steel, or tool steel, for durability and other reasons which will be readily apparent to the skilled reader.

The main body 12 comprises an upper part 16, which houses an inlet tube 18 that forms an inlet port 20 for the powder splitter 10. The inlet port 20 is where a supply of laminar flow, gas-powder mixture is fed into the device 10.

The inlet port 20 narrows at its lower end (as shown in the drawings) to a restriction 22, which is of approximately half of the inlet flow port 20 diameter. He restriction 22 causes a corresponding increase in fluid flow velocity, which breaks-down the laminar flow into turbulent flow, which in-turn brings any off-axis mass flow of powder into a turbulent flow area 24 within and/or downstream of the restriction 22.

The turbulent flow gas-powder mix then exits the restrictor 22 and enters a first expansion chamber 26, in which the fluid flow type reverts back to being a laminar flow regime. The fluid flow within the expansion chamber 26 comprises a diverging gas-powder mix with the highest area of mass flow in the centre of the gas-powder stream (i.e. an approximate Gaussian distribution of powder particles within the gas stream).

This constriction 22 and expansion 26 process is repeated in a series of further, in-line restrictions 28 and expansion chamber 30. In the illustrated embodiment, there is one further restriction 28 and expansion chamber 30, but there may be more in other embodiments.

Finally, the gas-powder enters a final constriction 32 and a subsequent expansion chamber 34. It will be noted that the final expansion chamber 34 has a much greater cross-sectional area than the preceding expansion chambers, and this effectively creates a divergent, slowed-down stream of power-gas mix down immediately before it meets the splitter 40.

In the illustrated embodiment, the splitter 40 is a quad splitter, which splits the gas-powder stream into four, equal portions, which are directed to separate outlets 42 and thence to separate nozzles (not shown).

The quad splitter 40, has a pair of orthogonal blades 46, which divide the gas-powder stream into four equal parts. The "crossed blade" configuration of the splitter 40 means that each quadrant captures a quarter of the gas-powder flow and directs it to its respective outlet 42 and/or nozzle.

Referring now to Figure 2 of the drawings, a second, but somewhat simpler version of a powder splitter 10 in accordance with the invention is shown. The main body 12 of the powder splitter 10 is, as before, formed from a stack of components 14 that are held together by axial through bolts (not shown). A mounting flange 50 projects radially outwardly from one of the components 14, which enables the powder splitter 10 to be more easily mounted in, for example, an additive manufacturing machine. The upper component 14 (in the drawing) has a rebated 21 inlet port 20 that connects to a power-gas supply (not shown). The inlet port 20 is formed as a generally conical through hole 23, which narrows down to a parallel-sided restriction 24.

Downstream of the restriction 24, there is an outwardly-flaring, rounded edge at the lower surface of the upper component 14, which forms an expansion chamber 26 immediately downstream of the restriction 24.

The next component 15 of the stack has an axial through hole in it, which has a generally conical lead-in 22 to a parallel sided restriction 28, which then diverges into a secondary expansion part 30, which causes the gas-powder mix to diverge and decelerate as it enters a chamber 54 immediately upstream of a splitter 40.

Again, the splitter 40 is a quad-splitter and thus has two orthogonal blades 46 that divide the gas-powder stream into four equal parts. The quad-splitter is generally crown-shaped - having curved surfaces 56 that flow from each side of each blade 46 and smoothly guide the gas-powder mix towards, and into the corresponding outlets 42.

This device differs from other methods of splitting powder streams for blown powder additive manufacture by the use of, for example, a crossed blade quadrant splitter device which, when coupled with the use of restrictors and expansion chambers to produce a divergent laminar flow powder-gas stream with an approximate Gaussian distribution of powder particles within it, allows more accurate division of this stream into four equal parts. Though it is possible to approximate this result with a single constriction-expansion cycle, experiment has shown that repeating this process results in more accurate division of the gas-powder stream.

The following statements are not the claims (which define the scope of the invention), but instead relate to features of possible embodiments of the invention.

Statement 1. An improved powder splitter, described as a device for dividing an incoming mixture of powder particles and carrier gas (a "powder stream") into two or more outflows which are substantially equal to each other in terms of mass flow of the mixture of powder particles and gas and the velocity thereof.

Statement 2. One embodiment of such a powder splitter comprises:

In inlet port or ports to convey the incoming mixture of powder and carrier gas into the device.

A restrictor orifice to accelerate the powder stream mix.

An enclosed expansion chamber to allow the powder stream to expand and allow further homogenisation of the distribution of powder particles, including by elastic collision with each other and the chamber walls

A further restriction orifice to again accelerate the powder stream mix.

A further enclosed expansion chamber to allow the powder stream to expand and allow further homogenisation of the distribution of powder particles and containing a powder stream divider or splitter in the form of a set of blades or walls with radial symmetry arranged around a centre point such that the powder stream incident upon it is divided into two or more substantially equal streams, each conveyed to a separate outlet port.

Outlet ports conveying the divided powder streams.

Statement 3. An improved powder splitter according to statement 1 or 2, which is connected to or forms part of a powder feeder device such as a hopper system.

Statement 4. An improved powder splitter according to any preceding statement, which is connected to or forms part of a powder delivery system such as a nozzle system used for the deposition of powder.

The invention is not restricted to the details of the foregoing embodiment, which is merely exemplary of one possible embodiment of the invention. In particular, the number of constriction/expansion stages can be reduced ort increased; the number of inlets and outlets can be increased or decreased to suit different applications; and the type of splitter can be changed - all without departing from scope of the invention/this disclosure.