GB2580723A

GB2580723A - Powder handling apparatus

Info

Publication number: GB2580723A
Application number: GB1906179.5A
Authority: GB
Inventors: Edward Beeby David; Stephen James Forman Mark
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2019-05-02
Filing date: 2019-05-02
Publication date: 2020-07-29
Also published as: GB201906179D0

Abstract

A powder handling apparatus comprising a powder conduit to direct a flow of powder along a powder flow path; and a sampler 160 having a sample inlet 162 with an elongate sample accumulator for receiving powder from the flow path. A seperator, e.g. with sieve (134, fig 2a) and/or cyclonic separator (132, fig 2a), may remove oversized particles, and may supply powder to a hopper 150, (140, fig 2a). The accumulator is designed for monitoring powder in an additive manufacturing system and the flow path may possess an outlet 168 to the system to form a recirculation loop (120, fig 2a), which may recirculate powder from a previous manufacturing process. An inert gas may maintain the powder under an inert atmosphere.

Description

POWDER HANDLING APPARATUS

Field of Invention

The present invention relates to powder handling apparatus and particularly, but not exclusively, to powder handling apparatus for powder based additive manufacture.

Background

Additive manufacturing methods (which in some cases may be referred to as "3D printing") typically form three-dimensional articles by building up material in a layer-by-layer manner. Additive manufacture has several benefits over traditional manufacturing techniques, for example: additive manufacture has very few limitations on component geometry; additive manufacturing may reduce material waste (as even complex geometries can be produced at or near to their final net-shape); and additive manufacture does not require dedicated tooling so can enable flexible manufacture of small batches or individually tailored products.

One type of additive manufacture is powder bed fusion, which is particularly applicable to high strength materials such as metal alloys (but may also be used for ceramic or polymer based materials). In powder bed fusion a thin layer of powder is provided on a base and is selectively exposed to an energy source to fuse sections of the layer. A further layer of powder is provided over the solidified layer, generally by lowering a platform supporting the powder, and the subsequent layer is selectively fused. This fuses the powder both within the new layer and to the fused regions of the previous layer. The process is repeated to build the full component on a layer-by-layer basis. Powder bed fusion includes, for example, Selective Laser Melting (in which the energy source is a Laser) and Electron Beam Melting (in which the energy source is an Electron Beam).

In order to gain the full benefits of the additive manufacture process, the powder used in additive manufacture must be extremely fine and of high quality (both chemically and physically). Characteristics of the powder such as the particle size, particle shape and particle shape distribution can, for example, directly impact powder flow and layer build up such that they may have a direct impact upon the final component quality and consistency. Metallic powder particles for use in powder bed additive manufacture may, for example, have a particle size in the range of 15 to 45 tam (fer Selective Laser Melting).

For both process and safety reasons the powders used in additive manufacture must be handled with caution. For example, fine metal powders are a health risk to humans through skin contact or inhalation and are a fire or explosion risk. Further, exposure of metal powders to moisture and/or oxygen can cause powder degradation. For example, some materials such as titanium alloys are particularly reactive and prone to absorption of atmospheric impurities such as oxygen and nitrogen. It is therefore, best practice to keep powders for additive manufacture in an inert atmosphere for example by using sealed powder flasks and powder loading arrangements.

The amount of unfused powder in a typical layer-by-layer build may be relatively high such that much of the powder in the powder bed is available for re-use. In order to maintain process quality and consistency, any recycled unfused powder will typically require some degree of processing before being re-introduced to the additive manufacture process to ensure that the recycled powder is chemically and/or physically consistent with virgin powder to provide consistent results. For example, the recycled powder may pass through a sieve or filter to remove oversized particles (which can be formed by the heating of the additive process -for example particles that have become sintered together or have formed irregular shaped agglomerates).

Commercially available additive manufacturing systems, for example the Applicant's Renishaw AM systems, are available with powder recirculation arrangements. Such systems allow powder to be sieved and recirculated through the additive manufacture system without the need to remove powder from the system. Such arrangements provide clear benefits in reducing handling of powder and can enable the powder to be held within an inert system loop once loaded into the system.

Despite the advantages of powder recirculation arrangements they are not universally adopted. In some applications of additive manufacture stringent performance or regulatory requirements may, for example, currently limit the use of recirculation. Such restrictions may require the use of virgin powder or may require unfused powder to be tested and certified prior to reuse. Thus, there is a desire to provide additive manufacturing methods and apparatus which enable the increased use of recirculation.

Summary of Invention

According to a first aspect of the invention, there is provided a handling apparatus compri sing: a powder conduit to direct a flow of powder along a powder flow path; and the powder handling apparatus further comprising a sampler having a sample inlet positioned within the powder flow path and disposed such that a sample of the powder travelling along the powder flow path is captured by the sampler; and an elongate sample accumulator for receiving powder from the sample inlet.

The conduit may be any suitable part of the handling apparatus in which the powder to be sampled flows through in use. For example, the conduit may include a pipe, duct, cooling tower and/or hopper.

The powder handler may be specifically adapted for use in an additive manufacturing process. The sampler may, for example, be positioned in the powder flow path of a powder supply. Embodiments of the invention may be particularly useful in powder bed additive manufacturing in enabling powder sampling and/or tracking of powder history whilst keeping the powder in an inert atmosphere. Thus, a further aspect of the invention may provide an additive manufacturing system powder handling apparatus comprising: a powder recirculation loop having an inlet for receiving powder, such as from the additive manufacture system or a powder supply; an outlet for supplying powder to the additive manufacture system; and a powder flow path extending between the inlet and the outlet; the powder handling apparatus further comprising a sampler having a sample inlet positioned within the powder flow path and disposed such that a sample of the powder travelling along the powder flow path is captured by the sampler; and an elongate sample accumulator for receiving powder from the sample inlet.

The provision of an elongate sample accumulator enables the sampler to accumulate an incremental build-up of powder passing through the powder handling system. This advantageously enables the system to be both used for spot testing of sampled powder and to test the powder quality over an extended time period.

The sample inlet may extend transversely across the powder flow path and may extend perpendicular to the local powder flow path.

The sampler may, for example, comprises a tube. At least a portion of the tube may be aligned substantially parallel to the portion of the powder flow path local to the sample inlet. The tube may have a first linear portion parallel to the portion of the powder flow path and a second portion which is not parallel to the first portion (and may be linear or non-linear as required, for example depending upon the layout of the powder handling apparatus). The provision of at least a first portion which is parallel to the powder flow path may help to ensure that a sample of the powder is captured and accumulated without unwanted mixing or blockages The powder conduit, such as the recirculation loop, may typically include a separator disposed within the powder flow path for removing oversized powder particles from the powder flow path/recirculation loop. The separator may for example be a sieve (such as an ultrasonic sieve). The separator may additionally or alternatively comprise an inertial separator, for example a cyclonic separator.

Accordingly, the separator may comprise a multi stage separator.

The sample inlet may be positioned downstream of the separator. This ensures that the sampler is obtaining a sample of the powder after it has been processed and is ready to be returned to the additive manufacture process.

The sampler may be positioned vertically below the separator. Thus, the sampler may receive powder that is falling under gravity from the separator. In such an arrangement the initial portion of the tube may be vertically aligned.

The powder recirculation loop may comprise a hopper for storing powder. The hopper may typically be positioned after the separator and ahead of the outlet. Thus, the hopper may hold powder which has been processed and is ready for reuse in the additive manufacturing process. The sampler may be positioned within the hopper. The sampler may for example comprise a vertical tube extending through the hopper.

The elongate sample accumulator may extend from a first end proximal to the sample inlet to a distal end. The distal end may be provided with an outlet through which a powder sample may be selectively drawn in use. The outlet may for example have a manually operated valve.

The powder handling apparatus may comprise a module which is adapted for removable attachment to an additive manufacturing system. Such a modular system is advantages in enabling the powder system to be removed from the machine and substituted for a new module when a powder change is required (such that only the process chamber parts of the additive manufacture system require cleaning).

The powder handling apparatus may further comprise a supply of inert gas for maintaining the powder within the powder conduit/recirculation loop under an inert atmosphere. The inert gas supply may for example comprise a supply of nitrogen or argon. The inert gas may additionally serve as a motive flow for carrying powder along the powder conduit/around the recirculation loop. Accordingly, the powder handling apparatus may further comprise a pump for supplying inert gas from the supply to the powder flow path as a motive flow for powder in the powder conduit/recirculation loop. The powder conduit/powder recirculation loop may comprise at least one gas inlet.

When the powder handling system is connected to an additive manufacturing apparatus the outlet (and, in the case of a powder recirculation loop, the inlet) will each be in communication with the process chamber of the additive manufacture apparatus. The inlet for receiving powder and outlet for supplying powder may be configured for connection to a process chamber of an additive manufacturing system to form a closed loop. The inlet and outlet may be sealing engaged with corresponding ports on the additive manufacturing apparatus. As such, in use, the powder recirculation loop and the process chamber will form a closed loop system. This ensures that the powder is held under an inert atmosphere both within the additive manufacturing apparatus and in the powder handling apparatus and does not need to be removed from the inert atmosphere at any point in normal use. Advantageously, embodiments of the invention may enable samples of powder to be taken from a closed loop without interruption to the flow.

According to another aspect of the invention there is provided an additive manufacturing system comprising an additive manufacturing apparatus and at 20 least one powder handling apparatus in accordance with an embodiment. The additive manufacturing apparatus may be a powder bed fusion apparatus.

According to a further aspect of the invention, there is provided a method of monitoring powder in a powder handling system, comprising: directing a powder flow powder through a powder conduit; capturing a portion of the powder flow within a sampler; accumulating powder captured in the sampler to provide an incremental build up of powder passing through the powder conduit.

According to a further aspect of the invention, there is provided a method of monitoring powder in an additive manufacturing system, comprising: passing unused powder through a powder recirculation system; capturing a portion of the powder flow within the recirculation system in a sampler; accumulating powder captured in the sampler to provide an incremental build-up of powder passing through the recirculation system.

Another aspect of the invention comprises a method of powder handling in additive manufacture, comprising recycling unused powder from the additive manufacture system; passing unused powder through a powder recirculation system; capturing a portion of the powder flow within the recirculation system in a sampler; accumulating powder captured in the sampler to provide an incremental build-up of powder passing through the recirculation system; and returning powder from the powder recirculation system to the additive manufacturing system.

The method of powder handling may further comprise passing the powder through at least one separator within the powder recirculation system. The method may further comprise maintaining an inert atmosphere over the powder.

Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description or drawings.

Description of the Drawings

Embodiments of the invention may be performed in various ways, and embodiments thereof will now be described by way of example only, reference 30 being made to the accompanying drawings, in which: Figure 1 shows an existing commercially available additive manufacturing system; Figures 2a and 2b are schematic representations of an additive manufacture powder handling apparatus; Figure 3 is an isolated three-dimensional view of the hopper from the powder handling apparatus of Figure 2; and Figure 4 is a cross sectional view of the hopper of Figure 3.

Detail Description of Embodiments

It may be appreciated that references herein to vertical or horizontal are with reference to the axis of the additive manufacture process. In particular, as powder bed fusion is a layer by layer process the horizontal axis corresponds to the plane of the layers (which is in turn defined by the powder bed and support) and the vertical axis is perpendicular to the powder bed.

A commercially available additive manufacturing system 100, the Applicant's RenANT 500 Series, is shown in Figure 1. The additive manufacturing system 100 includes both an additive manufacture apparatus 30 and an integrated powder handling apparatus 1. The additive manufacturing apparatus includes a process chamber 2, accessible via a chamber door 3, in which a laser is used to melt selective regions of a bed of powder on a layer-by-layer process. The additive manufacture process is generally controlled by a computer and may have a touchscreen interface 4 for operator interaction. The powder handling apparatus 1 is provided in an integrated cabinet 6 and accessible through a service door. The powder handling apparatus includes a hopper 12 for storing powder for use by the additive manufacturing apparatus 30. The hopper 12 may be filled with powder via a filling point 15 which is provided with an isolation valve 14. The powder handling apparatus includes an inlet in the form of a return pipe 13 for returning unused powder from the process chamber 2 to the hopper 12. Below the hopper 12 there is provided a powder metering screw 10 which feeds, via isolation valves 8 and 9, an ultrasonic sieve 7. The ultrasonic sieve is used to remove oversized particles from the powder so that they can be collected and removed from the machine via a metal flask, such as flask 18. Different size sieve meshes may be use for different materials. The powder handling apparatus maintains the powder loaded into the hopper and passing through the recycling system under an inert atmosphere. The powder handling apparatus may also include filtering for the inert gas used in the process chamber and/or powder handling apparatus (although the skilled person will also appreciate that such filtering may alternatively be provided in the additive manufacturing apparatus 30). The example system of Figure 1 includes both first and second filters 17 capture process emissions from the inert gas atmosphere.

Another configuration for an additive manufacturing system has been proposed in US Patent Application US2019/0001413. The system described in this patent application has a powder supply apparatus and a powder recovery apparatus which are combined to form a subassembly that is designed as an interchangeable module.

An additive manufacturing powder handling apparatus 1 in accordance with an embodiment of the invention is shown in figures 2a and 2b (which are alternate views of the same apparatus). The embodiment shown in figure 2 is adapted to be a self-contained powder handling module and it may be noted that it is mounted on a frame 101 with casters to enable ease of removal to and from the associated additive manufacturing apparatus. It will be appreciated that powder handling apparatus 100 in accordance with embodiments of the invention may be utilised in systems having either an integrated or an interchangeable powder handling apparatus and are not limited accordingly.

It may be noted that, for clarity purposes, some parts of the powder handling apparatus 100 are omitted in figure 2. Such features, for example ducting sections would be considered standard by those skilled in the art. Additionally, the skilled person would understand that the invention is not limited to any specific additive manufacturing apparatus, or particularly any specific build chamber thereof, for example the additive manufacturing apparatus may be substantially similar to the RenAM 500 Series described above (and shown in figure 1) with only routine modification required to operate with the powder handling apparatus of figure 2.

The powder handling apparatus 100, comprises a powder silo 110 which may receive powder from either a fresh powder inlet 112 and/or from the process chamber (not shown) of the additive manufacturing system via powder inlets 114.

The silo 110 has a powder feed 114 at its lowermost end and tapers towards the powder feed to direct powder contained therein. The powder silo is located on the supporting frame 101 at a level below the position of the process chamber (which would be in the space immediately above the inlets 114) such that it may be gravity fed when receiving powder. The powder feed 114 is arranged to pass powder through a valve into a recirculation loop 120.

The recirculation loop 120 circulates inert gas around the powder system. The recirculation loop also takes output gas, including emissions from the process, from the process chamber to a filter system before returning inert gas to the process chamber. The skilled person may appreciate that there may be multiple flow routes for gas through the chamber to optimise emissions removal and maintain a clean and optically clear process chamber. For example, the RenAM 500 series includes both a high volume and flow horizontally across the powder bed and a cascading flow of gas from a showerhead type arrangement in the ceiling of the process chamber The inert gas flow in the recirculation loop 120 provides a motive flow for carrying powder. The powder is fed into the loop 120 by the powder feed 114 and is entrained in the inert gas such that it is carried from the lower most portion of the powder handling apparatus 1 to the upper most portion. Advantageously, once at the upper part of the powder handling apparatus 1, the powder can move under gravity. At the top of the frame 101 is positioned a separator 130 comprising both a cyclonic separator 132 and an ultrasonic sieve 134. The skilled person will appreciate that both the cyclonic separator 132 and ultrasonic sieve 135 may be of any convenient design and of a type well known in the art. Further it will be appreciated that other separator arrangements are also possible and may be used with embodiments of the invention. The separator of the illustrated embodiment includes an inlet port 131 through which inert gas and powder is introduced and an outlet port 133 through which gas leaves the cyclonic separator 132. It will be appreciated that the ducting to/from the ports 131 and 133 has been omitted from Figure 2 for clarity but that in practice, for example, a simple duct would continue the recirculation loop 120 by extending from the coupling 121 to the inlet port 131.

Gas separated from the powder in the cyclone may be directed from the outlet port 133 to at least one filter for further removal of emissions or contaminants before being returned for use in the process chamber. The powder is separated from the gas by the cyclonic separator 132 and falls under gravity through to the next stage of the separator 130. For example, the powder may pass through an ultrasonic sieve 134 to remove oversize particles from the powder.

The embodiment of Figure 2 includes two hoppers 140 and 150 to which powder exiting the separator 130 may be selectively directed and accumulated. The first hopper 140 is a "total loss" hopper which is arranged to collect powder which is not being recycled by the powder handling apparatus. The total loss hopper is, therefore, used to accumulate unused powder so that it may be removed from the system via an outlet valve 142 provided at the bottom of the total loss hopper. As such, it will be understood that the total loss hopper 140 is not normally part of the recirculation loop. Whilst not being immediately recycled it is still desirable that the powder held in the total loss hopper 140 is under an inert gas. This ensures that the powder can be removed subsequently used, for example after testing or processing or for later use by the additive manufacturing system, for example for a component having less restrictive material requirements. In this regard it may be noted that the outlet 142 is positioned relatively close to, and above, an inlet 112 in an upper sidewall of the silo 110. This enables powder from the total loss I 5 hopper to be reintroduced into the powder recirculation loop if required (by simply attaching a suitable hose line) without being removed from the powder handling apparatus or leaving the inert atmosphere therein.

The second hopper 150 is a powder dispensing hopper and is part of the powder recirculation loop. The powder dispensing hopper has an inlet 152 at its upper end which receives powder from the sieve 134 of the separator 130. The lower end of the powder dispensing hopper 150 tapers towards an outlet 154 for providing powder to the additive manufacturing apparatus. The outlet 154 may be an interface for connecting to the build chamber of the additive manufacturing apparatus and may include or connect to a powder dispensing arrangement. For example, the additive manufacturing system may have a drawer type powder dispensing arrangement similar to the type shown, for example, in published Patent Application W02010/007396.

As the powder in the dispensing hopper 150 is being recycled on a rolling basis (substantially continuously when the additive manufacturing system is in use) conventionally it is difficult to monitor or measure the quality of the powder. This may be at least one of the reasons that when manufacturing some parts, for example safety critical parts or parts subject to strict regulations, by additive manufacture it is preferred to use only virgin or pre-tested powder and to direct any unused powder to the total loss hipper 140. Further, testing of the powder within the recirculation loop (including the dispensing hopper 150) may require interruption of the powder flow (and therefore the additive manufacture process) and/or opening of the recirculation loop which will release inert gas and allow the entry of oxygen and moisture from the air.

Accordingly, as shown in Figure 4 and 5, the dispensing hopper 150 of embodiments of the invention is provided with a sampler 160. The sampler 160 comprises a pipe extending through the dispensing hopper 150 from an inlet 162 internally located within the hopper and to an outlet 168 external to the hopper 150. The sampler 160 is positioned to capture a small proportion, for example less than 5%, of the powder flowing through the recirculation loop in the region of the sampler 160. The outlet 168 includes a valve, which is user operated, for removing powder from the sampler 160. Thus, the sampler 160 can be used to capture and then remove a sample of the powder flowing through the powder handling apparatus to allow the powder to be tested without interrupting the operation of the apparatus.

The sampler inlet 162 is positioned below the outlet of the separator 130 proximal to the inlet 152 of the powder dispensing hopper 150. The inlet 162 of the sampler is positioned to be aligned horizontally so that it extends transversely across the powder dispensing hopper 150. By being positioned with the inlet across the hopper 150, the axis of at least the initial portion 161 of the sampler pipe 160 is aligned with the local flow direction of the powder recirculation (which is vertical since the powder in this portion of the powder handling apparatus is flowing under gravity).

In the illustrated embodiment it may be noted the outlet end 163 of the sample pipe 160 is not co-axial with the inlet end 161; rather the two portions are arranged at an obtuse angle. This configuration allows the outlet to be conveniently positioned whilst allowing the inlet 162 to be positioned in a generally central location of the hopper 150 (to ensure it receives a representative sample of powder). The transition between the outlet end 163 and the inlet end 161 is generally radiused to avoid powder catching on the sides of the pipe which could lead to the sampler becoming blocked or powder in the sampler mixing.

A particular advantage of embodiments of the invention is provided by the elongate nature of the pipe used to form the sampler 160. The elongate shape enables a sample of powder to be accumulated over a period of time in which the powder handling apparatus is running and to form an incremental build-up of "stacked" powder. Accordingly, the sampler 160 can build up a history of the powder passing through the recirculation system and enable testing and/or monitoring of powder as it is recycled through the system.

Although the invention has been described above with reference to preferred embodiments, it will be appreciated that various changes or modification may be made without departing from the scope of the invention as defined in the appended claims. For example, whilst the provision of the sampler within the powder delivery hopper is particularly useful as it is the final powder location prior to use in the additive manufacture system (and is convenient as it may be gravity fed) the invention is not limited to such a location. In some systems it may be desirable to accumulate samples in other locations or multiple locations within the powder handling apparatus. Provided the sampler is suitably aligned with the local flow of powder in any desired location the sampler will be able to trap and accumulate powder in use.

Further, it will be readily appreciated that the geometry and size can be easily tailored depending upon the powder sampling required. for example, the inlet size may be altered (and could even have funnel shape) to adjust the proportion of powder flow which enters the sampler. Further, by altering the relative proportions of the collecting part of the sampler it is possible to adjust the effective resolution over time for which the powder history can be determined.

Whilst the embodiment described above is with reference to the particular application of a powder handling apparatus for additive manufacture systems, it will be appreciated that that embodiments of the invention may be useful in other powder handling systems. In particular, embodiments of the invention may be useful in any powder systems where it is desirable to sample the history of the powder passing through the system.

Claims

Claims 1. A powder handling apparatus comprising: a powder conduit to direct a flow of powder along a powder flow path; and the powder handling apparatus further comprising a sampler having a sample inlet positioned within the powder flow path and disposed such that a sample of the powder travelling along the powder flow path is captured by the sampler; and an elongate sample accumulator for receiving powder from the sample inlet.
2. A powder handling apparatus as claimed in claim 1, wherein the sample inlet extends perpendicular to the local powder flow path.
3. A powder handling apparatus as claimed in claim 1 or 2, wherein the sampler comprises a tube aligned substantially parallel to the portion of the powder flow path local to the sample inlet.
4. An additive manufacture powder handling apparatus comprising a powder handling apparatus as claimed in any of claims 1 to 3 and further comprising: a powder recirculation loop having an inlet for receiving powder from an additive manufacture system; an outlet for supplying powder to the additive manufacture system; and wherein the powder flow path is between the inlet and the outlet.
5 A powder handling apparatus as claimed in any preceding claim, wherein the powder conduit further comprises a separator disposed within the powder flow path for removing oversized powder particles from the powder flow path; and the sample inlet is downstream of the separator.
6. A powder handling apparatus as claimed in claim 5, wherein the separator comprises a sieve, and the sampler is positioned vertically below the sieve.
7 A powder handling apparatus as claimed in claim 5 or 6, wherein the powder conduit further comprises a hopper for receiving powder from the separator and wherein the sampler is positioned within the hopper.
8. A powder handling apparatus as claimed in claim 7, wherein the sampler comprises a vertical tube extending through the hopper.
9. A powder handling apparatus as claimed in any preceding claim wherein the elongate sample accumulator comprises from a first end proximal to the sample inlet to a distal end, the distal end being provided with an outlet through which a powder sample may be selectively drawn in use.
10. A powder handling apparatus as claimed in any preceding claim, wherein the apparatus comprises a module for removable attachment to an additive manufacturing system.
11 A powder handling apparatus as claimed in any preceding claim, further comprising a supply of inert gas for maintaining the powder within the apparatus under an inert atmosphere.
12. A powder handling apparatus as claimed in claim 10, wherein the powder handling apparatus further comprises a pump for supplying inert gas from the supply to the powder flow path as a motive flow for powder in the powder flow path.
13. A method of monitoring powder in an additive manufacturing system, comprising: passing unused powder through a powder conduit; capturing a portion of the powder flow within a sampler; accumulating powder captured in the sampler to provide an incremental build up of powder passing through the powder conduit.
14. A method of powder handling in additive manufacture, comprising recycling unused powder from the additive manufacture system; monitoring powder as claimed in claim 13; and returning powder from the powder conduit to the additive manufacturing system.
15. The method of powder handling as claimed in claim 14, further comprising: passing the powder through at least one separator within the powder conduit and maintaining an inert atmosphere over the powder.