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Johnson Matthey Technol. Rev., 2015, 59, (3), 243

doi:10.1595/205651315x688686

Introduction to the Additive Manufacturing Powder Metallurgy Supply Chain

Exploring the production and supply of metal powders for AM processes

    • By Jason Dawes*, Robert Bowerman and Ross Trepleton
    • Component Technologies,
    • Manufacturing Technology Centre, Pilot Way, Ansty Business Park, Coventry, CV7 9JU, UK

*Email: jason.dawes@the-mtc.org

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Article Synopsis

The supply chain for metal powders used in additive manufacturing (AM) is currently experiencing exponential growth and with this growth come new powder suppliers, new powder manufacturing methods and increased competition. The high number of potential supply chain options provides AM service providers with a significant challenge when making decisions on powder procurement. This paper provides an overview of the metal powder supply chain for the AM market and aims to give AM service providers the information necessary to make informed decisions when procuring metal powders. The procurement options are categorised into three main groups, namely: procuring powders from AM equipment suppliers, procuring powders from third party suppliers and procuring powders directly from powder atomisers. Each of the procurement options has its own unique advantages and disadvantages. The relative importance of these will depend on what the AM equipment is being used for, for example research, rapid prototyping or productionisation. The future of the metal AM powder market is also discussed.

1. Introduction

A component fabricated using powder bed may consist of many thousands of finely spread powder layers. The uniformity of these layers can affect the properties of the final component. The way in which a powder ‘spreads’ during AM depends on the properties of the powder used. As will be discussed in this paper, even when chemically equivalent, the properties of metal powders vary widely depending on both the atomisation method used and the manufacturing process conditions. To obtain a greater degree of control over AM processes service providers must be able to control the quality of the raw powder feedstock.

The overall AM market has seen exponential growth over the last five years and during this time the sale of powder bed metal AM equipment, services and products has also followed an exponential trend (1) due to increased adoption from the aerospace, oil and gas, marine, automobile and medical sectors. As the benefits of using AM to manufacture functional metallic components start to outweigh the blockers, more component manufacturers are looking towards metal powder bed technologies to allow them to realise their next generation of innovatively and functionally designed products.

Research has shown that metal powder costs will be the biggest continuous expense through the life of an AM machine (1). The quality and consistency of the AM components depends, in part, on the characteristics of the starting powder feedstock. Hence, controlling and understanding the quality of the powder both in its as-supplied and reused condition is essential in order to achieve the desired mechanical properties of the laser melted components. Given the significance of the metal powder feedstock it is important that AM users make informed decisions when procuring the raw metal powder. The current state of the AM metal powder supply chain is that there are multiple possible methods for the manufacture of metal powders and many times as many potential suppliers. Furthermore not all metal powders are equal in terms of their fundamental properties even when manufactured via the same technique (when procured from different vendors). This presents quite a challenge to beginners in AM technology when deciding on a powder supplier. However, some AM equipment suppliers, such as EOS, sell ‘validated powder’. ‘Validated powder’ is a powder which has been identified as suitable for use in AM. Whilst validated powder can de-risk procuring powders for AM it does limit users to a single source supplier and inhibits the development of in-house expertise.

Given the complexity of the AM metal powder supply chain this review article aims to resolve some of the confusion involved and address some of the frequently asked questions by users. Additionally, the article will highlight key issues that the market needs to address, and make potential users aware of some of the key factors to consider when selecting the most appropriate powder supplier.

2. Overview of the Powder Bed AM Market

Over the last 20 year period the AM market has grown rapidly from an industry worth <US$100 million in 1993 to around US$3000 million in 2013, see Figure 1. Current predictions forecast that this rapid growth will continue and that there will be a five-fold market value increase by 2021 (1). This growth trend in AM technology is also reflected in global raw materials (powder) sales. Powder sales in the AM sector over the past decade are shown in Figure 2. After a decline in sales in 2009, due to market reaction at the beginning of the fiscal crisis, both the AM sector value and AM material sales have seen rapid growth since 2010. Specific to metal powder AM, the sale of powder for metal processes is also shown in Figure 2. It can be seen that metal sales have followed the market trend since 2010, with sales more than doubling in a three year period. However, the value of the metal powder AM market is a relatively small proportion of the whole market. This highlights the opportunity for growth for powder suppliers offering products into the metals AM market.

Fig. 1.

AM market growth 1991–2013 (1)

AM market growth 1991–2013 (1)

Fig. 2.

History of materials sales for AM systems worldwide: () all AM materials, () metallic AM materials only (metallic powder sale data not available prior to 2009) (1)

History of materials sales for AM systems worldwide: (– ) all AM materials, (– ) metallic AM materials only (metallic powder sale data not available prior to 2009) (1)

Based on data from 2013 there are 855 powder manufacturers worldwide (425 located in North America, 205 in Europe and 225 in the Asia-Pacific region) capable of producing an estimated 1.12 million metric tonnes, to a value of approximately US$6.9 billion (2). The top six powder manufacturers have a combined market share of 44% and generally serve the press and sinter market. The remaining market share is made up of small businesses, likely producing powder for a specific purpose or application. When the metal powder market is evaluated, only US$32.6 million was sold for AM usage (0.0047%). This shows that despite the enormous anticipation of the impact of AM, traditional powder processes such as press and sinter and metal injection moulding (MIM) still dominate the marketplace. However, as AM processes become more established as component manufacturing routes, rather than rapid prototyping technologies, the potential for growth in the metal AM powder supply is considerable.

3. Selection of AM Powder

3.1 The Importance of Powder

The AM process uses powder as its raw material feedstock, as such the consistency of the powders used to build AM components will have a critical influence on the final component properties. During the build sequence of an AM component, the raw powder feedstock is stored in a hopper, the design of the hopper and the method by which powder is introduced into the build chamber depends entirely on the equipment manufacturer. A discrete amount of powder from the hopper is spread (either using a rake or roller system) across the build chamber to form a thin (no more than one to two particle diameters) continuous layer of powder. After spreading it is critical that the layer is homogenous over the entire area of the build chamber, any degree of inhomogeneity may result in porosity (in the absence of powder) or incomplete through-thickness melting (too much powder pooled up in one area). The spread layer is selectively fused using either a laser source or an electron beam based on an input sliced three-dimensional (3D) computer aided design (CAD) model. Following selective sintering another layer of powder is spread over the first. This iterative process of powder spreading followed by selective melting is continued until the build is complete. The total number of powder layers spread will of course depend on the size of component being built but the number could be in the region of 7000 layers. Furthermore it is common to build multiple components during one build event.

The layer spreading, hopper dosing and bulk packing performance of the AM powder will depend entirely on the properties of the powder being used. Further complicating the use of AM powder is that the volume of the actual component built can be significantly less than the total volume of powder that has been spread. As a consequence there is a large amount of unused powder left over in the build chamber, given the high cost of metal powders it is essential that the unused powder is effectively recovered and reused in future builds. However, the effect of continued recycling of the unused powder on the actual powder properties and hence subsequent component properties has not been the subject of intensive scientific study. In the few scientific journals published in the field of metal powder recycling in AM, it has been observed that recycling powders in powder bed AM processes results in an increase in powder particle size distribution (PSD) (2, 3). The thermal effects that result from the process, such as chamber temperature and the radiation energy in selective laser melting (SLM) of metal powders, may cause physical as well as chemical changes to the recycled powder. Furthermore contamination, either through impurities, foreign bodies or interstitial elements may be introduced to the powder as a result of handling during pre-processing or post-processing stages.

The first step in understanding powder requirements for AM processes is to assess the types of metallic powder that are available. The following sections provide an overview of the methods of metal powder production routes.

3.2 Routes of Powder Production

The production of AM metal powder generally consists of three major stages as outlined in the flow diagram shown in Figure 3. Briefly, the first stage involves the mining and extracting of ore to form a pure or alloyed metal product (ingot, billet and wire) appropriate for powder production; the second stage is powder production and the final stage is classification and validation.

Fig. 3.

From ore to validated AM powder – powder production steps flow chart

From ore to validated AM powder – powder production steps flow chart

The supply chain of taking ore and extracting a metal is well established and supplies a vast range of pure metals and specific alloys to global markets. Once an ingot of the metal or alloy has been formed a number of additional processing steps may be required to make the feedstock suitable for the chosen atomisation process. For example, plasma atomisation requires the feedstock material to be either in wire form or powder form, thus adding additional rolling and drawing work or a first step powder production route.

Once the first processing form has been obtained there are a number of methods available to produce metal powders including, but not limited to: solid-state reduction, electrolysis, various chemical processes, atomisation and milling. Historically, for reasons that will be discussed, atomisation has been identified as the best way to form metal powders for AM due to the geometrical properties of the powder it yields.

None of the powder production routes actually produce a 100% powder yield in the required size fractions. Some post processing is therefore necessary. As a minimum, the as-produced metal powder must be classified into a well-defined particle size distribution suitable for the required process: typically 15–45 μm for SLM and 45–106 μm for electron beam melting (EBM).

3.2.1 Water Atomisation

All atomisation processes begin with melting the feedstock alloy. The melting process has a number of variations, but generally when atomising using water, the feedstock is first melted in a furnace before being transferred to a tundish (a crucible that regulates the flow rate of the melt into the atomiser). The liquid alloy enters the atomisation chamber from above; here it is free to fall through the chamber. Water jets are symmetrically positioned around the stream of liquid metal, atomising and solidifying the particles. The final powder exits at the bottom of the chamber, where it is collected. Additional processing steps are then required to dry the powder. Metal powder produced in this way is typically highly irregular in morphology which reduces both packing properties and flow properties. Water atomisation is the main method of producing iron and steel powders and typically feeds into the press-and-sintered industries rather than the specialised AM industry.

3.2.2 Gas Atomisation

The gas atomisation process mimics water atomisation, with the differentiator being the use of gas instead of water during processing. Air can be used as the atomising media, but it's more likely that an inert gas (nitrogen or argon) will be used to reduce the risk of oxidation and contamination of the metal. The process of melting the metal ingots can be the same as described for water atomisation, however for powders produced for high end applications such as aerospace, the need to control interstitial elements has led to increased use of vacuum induction melting (VIM) furnaces. A VIM furnace is typically installed directly above the atomisation chamber such that the molten stream of liquid metal enters the atomisation chamber directly from the furnace rather than through a tundish, similar to the set-up shown in Figure 4. The stream of liquid metal is atomised by high pressure jets of gas. Due to the lower heat capacity of the gas (compared to water) the metal droplets have an increased solidification time which results in comparatively more spherical powder particles (i.e. droplet spheroidisation time is shorter than the solidification time). Whilst it is not possible to have complete control over the particle size of as-atomised powder, the distribution can be influenced by varying the ratio of the gas to melt flow rate. Research in the field of gas atomisation has shown that even finer particle size distributions can be achieved through the use of hot gas atomisation (4).

Fig. 4.

Schematic of the gas atomisation process for production of AM powders (Courtesy of LPW Technology, UK)

Schematic of the gas atomisation process for production of AM powders (Courtesy of LPW Technology, UK)

Although interstitial elements can be well controlled in gas atomised powders, there are still potential contamination risks. Contamination most pertinent to non-static critical components, such as aero-engine parts, include refractory materials which can originate from the ceramic crucibles and atomising nozzles used. One solution to this is to use electrode induction melting gas atomisation (EIGA). EIGA is a variation of gas atomisation where the metal is fed into the atomiser in the form of a rod that is melted by an induction coil just before entering the atomisation chamber, as shown in Figure 5. This application is used when processing reactive alloys, such as Ti-6Al-4V, minimising the risk of contamination from exposure of the molten titanium to the crucible and the atmosphere (5).

Fig. 5.

Schematic of the EIGA process for production of AM powders (Courtesy of LPW Technology, UK)

Schematic of the EIGA process for production of AM powders (Courtesy of LPW Technology, UK)

3.2.3 Plasma Atomisation

Plasma atomisation is a method of producing highly spherical particles. The feedstock used in the process can either be in wire form such as the method used by AP&C Advanced Powders and Coatings Inc, Canada, or in powder form such as the method used by Tekna Plasma Systems Inc, Canada. The spool of wire or powder feedstock is fed into the atomisation chamber, where it is simultaneously melted and atomised by co-axial plasma torches and gas jets, such as that shown in Figure 6.

Fig. 6.

Schematic of the plasma atomisation process for production of AM powders (Courtesy of LPW Technology, UK)

Schematic of the plasma atomisation process for production of AM powders (Courtesy of LPW Technology, UK)

Plasma rotating electrode process (PREP) is a variation of plasma atomisation whereby a bar of rotating feedstock is used instead of a wire feed. As the rotating bar enters the atomisation chamber plasma torches melt the end of the bar, ejecting material from its surface. The melt solidifies before hitting the walls of the chamber.

3.2.4 Hydride-Dehydride Process

The hydride-dehydride (HDH) method (6) of powder production differs from the atomisation processes described above due to the fact that it does not involve melting of the metal feedstock. Instead, it involves crushing, milling and screening to resize larger lumps of metal feedstock into finer powder particles. The HDH process relies on the brittle nature of certain metals, such as titanium, when exposed to hydrogen. In the case of titanium, titanium hydrides are formed in a hydride unit by introducing hydrogen and heat. The brittle lumps can then be crushed and screened into the required PSD. The powder is then returned to the hydride unit to remove the excess hydrogen from the metal powder particles. Powder particles produced using HDH are typically highly irregular. HDH powders are typically used either in their as-made condition or used as the powder feedstock for plasma atomisation.

3.2.5 TiROTM Process

The TiROTM process (7, 8) is a relatively new method for the production of pure titanium powder developed by CSIRO, Australia. The TiROTM process is a two stage continuous production method in which titanium tetrachloride (TiCl4) is first thermally reduced to an MgCl2/Ti composite under the presence of magnesium in a fluidised bed reactor. The MgCl2/Ti composite is then separated using vacuum distillation to produce high purity Ti powder. The as-processed Ti powder is unsuitable for AM processes due to the particle size range primarily being 150–600 μm. As such it is necessary that the powder is modified using a high shear milling process in a controlled environment to resize the powder to a range suitable for AM.

3.2.6 Summary of Powder Production Routes

Each of these processes yields powder with varying characteristics, a summary of which can be seen in Table I. A series of micrographs highlighting the various particle morphologies obtained from each manufacturing route is shown in Figure 7.

Table I

Summary of Powder Characteristics by Manufacturing Process

Manufacturing ProcessParticle size, μmAdvantagesDisadvantagesCommon uses
Water atomisation 0–500

High throughput

Range of particle sizes

Only requires feedstock in ingot form

Post processing required to remove water

Irregular particle morphology

Satellites present

Wide PSD

Low yield of powder between 20–150 μm

Non-reactive
Gas atomisation (inc. EIGA) 0–500

Wide range of alloys available

Suitable for reactive alloys

Only requires feedstock in ingot form

High throughput

Range of particle sizes

Use of EIGA allows for reactive powders to be processed

Spherical particles

Satellites present

Wide PSD

Low yield of powder between 20–150 μm

Ni, Co, Fe, Ti (EIGA), Al
Plasma atomisation 0–200 Extremely spherical particles

Requires feedstock to either be in wire form or powder form

High cost

Ti (Ti64 most common)
Plasma rotating electrode process 0–100

High purity powders

Highly spherical powder

Low productivity

High cost

Ti

Exotics

Centrifugal atomisation 0–600 Wide range of particle sizes with very narrow PSD Difficult to make extremely fine powder unless very high speed can be achieved Solder pastes, Zinc of alkaline batteries, Ti and steel shot
Hydride–dehydride process 45–500 Low cost option

Irregular particle morphology

High interstitial content (H, O)

Ti6/4

Limited to metals which form a brittle hydride

Fig. 7.

Example SEM micrographs of typical particle morphologies obtained using: (a) HDH process; (b) gas atomisation; (c) plasma atomisation; and (d) plasma rotating electrode process. In all micrographs the powder shown is Ti-6Al-4V and images were taken using a Hitachi TM3000 SEM

Example SEM micrographs of typical particle morphologies obtained using: (a) HDH process; (b) gas atomisation; (c) plasma atomisation; and (d) plasma rotating electrode process. In all micrographs the powder shown is Ti-6Al-4V and images were taken using a Hitachi TM3000 SEM

3.3 Powder Key Process Variables

The quality of a component built in an SLM process is assessed based on part density, dimensional accuracy, surface finish, build rate and mechanical properties. In order to achieve predictable and consistent component qualities it is desirable that the characteristics of the powder bed and the parameters of the machine are maintained at a constant level since the powder bed and machine parameters are closely correlated. In order to maintain a constant powder bed during each SLM build process it is important to understand and control characteristics such as powder bed temperature and density. These characteristics are governed by the KPVs of the starting powder. Due to the complex nature of powders, characterising their performance is not a trivial task. A list of variables (and analysis techniques) that may be considered to have an impact on performance is provided in Table II.

Table II

Powder KPVs and Techniques that Could be Used for their Measurement

Particulate propertiesBulk properties
Powder propertyAssessment techniquePowder propertyAssessment technique
Particle shape (morphology)

SEM

Optical microscopy

Apparent density

Hall flow

Freeman FT4

Tap density Tapped density tester
Particle size and particle size distribution

Sieve Laser diffraction

Optical microscopy

Flowability

Hall flow

Dynamic flow testing (e.g. revolution, Freeman FT4)

Shear cell

Angle of repose

Cohesiveness Freeman FT4
Particle Porosity Particle polishing and optical microscope Surface Area BET surface area analysis
Chemical composition

ICP-OES

XRD

Inert gas fusion

Combustion infrared detection

3.3.1 Particle Morphology

Particle morphology will have a significant impact on the bulk packing and flow properties of a powder batch. Spherical or regular, equiaxed particles are likely to arrange and pack more efficiently than irregular particles (9). Research into the effect of particle morphology on the AM process has shown that morphology can have a significant influence on the powder bed packing density and consequently on the final component density (1012), where the more irregular the particle morphology the lower the final density. As a consequence of this highly spherical particles tend to be favoured in the AM process. This limits the use of potentially cheaper powder production routes such as water atomisation and HDH. Furthermore as can be observed in Figure 7(b) gas atomised powders are only nominally spherical. In the case of the titanium alloy Ti-6Al-4V, this has led to widespread adoption of plasma atomised powder. Plasma atomised powder is typically highly spherical, but is currently produced by a single source – AP&C, Canada.

3.3.2 Particle Size Distribution

Characterisation of PSD in a batch of powder ensures that the optimum range of particles, by size, are used in each process. In general, EBM uses a nominal PSD between 45–106 μm, whilst SLM uses a finer PSD between 15–45 μm. PSD will have an obvious impact on both the minimum layer thickness and the resolution of the finest detail in the component. An inappropriate combination of PSD and layer thickness can potentially lead to in situ segregation due to the mechanical re-coater pushing coarser particles away from the bed (13), segregation in this sense could lead to variation in build quality in the vertical direction. It is generally well reported that using powders with a wide PSD and a high fine content produce components with a higher fractional density (13, 14). However, the use of fine materials increases the risk of health and safety issues. This is particularly true when processing reactive materials such as titanium where finer particulates are likely to be more flammable and explosive.

3.3.3 Bulk Packing and Flow Properties

Powder flowability is one of the most important technological requirements for powders used in AM. The density homogeneity of the final part depends on the layer-by-layer melting being performed on thin and uniform layers that are accurately deposited by the feeding device. Cohesive powders which exhibit poor flow properties are likely to be more problematic in terms of obtaining homogenous density layers throughout the build than powders which are comparatively more free flowing. Powder flow is difficult to relate to any one given parameter of a powder but there are some general rules which can typically be applied (15, 16):

  1. Spherical particles are generally more free flowing than irregular or angular particles

  2. Particle size has a significant influence on flow – larger particles are generally more free flowing than smaller particles

  3. Moisture content in powders can reduce flow due to capillary forces acting between particles

  4. Flow properties often show a dependency on the packing density at the time of measurement – powders with a higher packing density are less free flowing than powders with a lower packing density

  5. Short range attractive forces such as van der Waals forces and electrostatic forces can adversely affect powder flow and may cause particle agglomeration (short range forces have a bigger impact on finer particles).

3.3.4 Chemical Composition

The laser sintering behaviour of a metal powder will not only depend on the physical properties, it will of course also depend on the chemical properties. Powder chemical composition for AM should ideally be optimised for the machine or application. Validating chemical composition helps to ensure that the manufactured component has homogenous material properties.

As well as the bulk alloying chemistry, it is important to understand the effect of interstitial elements, such as O and N, since component properties will depend on the amount of interstitial elements present. For example, it is well known that the tensile strength and ductility properties of Ti-6Al-4V are influenced by O content whereby an increase in O results in an increase in tensile strength and a subsequent decrease in elongation (17). Research has also shown that interstitial elements can influence the melting kinetics of the powder by interfering with the surface tension of the melt pool resulting in Marangoni flow (18). Marangoni flow can have a negative influence on the porosity of the final component (11, 19).

3.4 Powder Recycling

It has been mentioned previously that for a powder bed AM process to be economically viable it is necessary to recycle the large amount of unused powder. The effect of continuous powder reuse on the KPVs is an area that has up until recently received relatively little scientific attention. A handful of researchers have investigated the effect of continuous reuse of powders (2, 3) for example, however further study is required to fully understand the impact of recycling on process performance.

4. Procurement Options

Once a suitable atomisation route has been selected, the AM user then faces more decisions around powder supply. The market opportunity for metal AM powder supply has not gone unnoticed, and three main options for powder supply have emerged. Firstly, users can choose to procure powder directly from the AM machine provider. Secondly, users could choose to procure powder from third party companies, who offer AM machine ‘validated’ powders. Finally powder can be sourced direct from an atomisation company. Indeed several powder manufacturers are now offering AM specific powders as part of their product portfolio (the largest of these, and the alloys they provide are listed in Table III). A summary of the advantages and disadvantages of each procurement option is presented in Table IV.

Table III

Supplier List of Powders Specified for AMa

CompanySupplier typeMaterialBuilding processManufacturing processes
LocationManufacturerThird partyFe-BasedAl-BasedTi-BasedNi-BasedCo-BasedCu-BasedPrecious metalsEBMSLMWaterGasPlasmaCentrifugal
Advanced Powders and Coatings – AP&C Canada
Carpenter Technology Corp US
GKN Hoeganaes Corp US
H.C. Starck GmbH EU
Höganäs Sweden AB EU
Sandvik Materials Technology EU
TLS Technik GmbH & Co. Spezialpulver KG EU
LPW Technology Ltd UK

aInformation obtained from the supplier websites (Accessed April 2015)

Table IV

Advantages and Disadvantages of Procuring Powder from Machine Manufacturers, Third Party Suppliers and Direct from Powder Manufacturers

Supplier typeAdvantagesDisadvantages
Machine manufacturers Standard machine parameters are provided and are ready to use Potentially higher cost of materials
Powder that has been ‘tried and tested’ Material options are limited
Support from the supplier should a build have issues Experimenting with powder of a different specification is limited
Ease of sourcing Lack of traceability of material source and manufacturing process
Already established procurement routes
Validated third party suppliers Able to select powder from the entire powder metallurgy industry Lack of traceability of material source and manufacturing process
A wide range of batch sizes are offered Lack of support from the machine manufacturer should a build fail
Powder that has been ‘tried and tested’ Potentially higher cost of materials
Ease of sourcing
Direct from powder manufacturers Wide range of material choices Lack of support from the machine manufacturer should a build fail
Potentially lower cost of powder (highly dependent of material/process) No guarantee that the material will produce a successful build
Choice of manufacturing process, allowing a degree of control over powder characteristics Minimum batch orders may apply, due to minimum powder yields from a manufacturing process
Can use local manufacturers Will powders be produced to the exacting standards required for AM?
An increased level of material traceability Lack of powder specification with each order

At present the majority of powder sales are through AM machine manufacturers or third party suppliers. The powder provided by these suppliers has been optimised for each additive process, also known as being ‘validated’.

By validating a powder, the supplier is ensuring that the powder given to the customer is of suitable quality so that, when being processed, it will behave as intended, leading to a successfully built part that will adhere to the chemical composition and the mechanical properties of the given metal or alloy. Simply put, the machine will successfully build with that material, thus de-risking powder supply for the end user.

Machine suppliers can validate powder as they will develop processing parameters on their machines for each specific material. Once the machine repeatedly builds reliable, mechanically suitable parts then the parameters will be stored and sent out with batches of that material to users. The powder being used will be characterised using some of the techniques discussed in Section 3.3 and all subsequent batches will undertake the same testing to ensure that they adhere to the same specification. This ensures that the end user is receiving consistent powder across batches that has been validated for their specific process. Third party suppliers offer a similar service, refining powder size and morphology to ensure they work in process.

From this it can be seen that machine manufacturers and third party suppliers undertake a lot of work to ensure the powder they provide is suitable for their AM process. There are a number of obvious advantages from procuring powder through these routes. However, this increased level of material supply security does also draw some limitations.

Alternatively, it is possible to procure powder directly from the powder manufacturer. There are a range of benefits from purchasing powder directly from the manufacturer; however, there are some underlying risks that a customer must also be aware of. The most pertinent of these risks was alluded to in Section 2. The current state of the metallic AM powder market is that it contributes an almost insignificant proportion of the income generated by powder producers (i.e. 0.0047% of the income generated from metal powders was due to sales into the AM market). Since the AM powder market is not currently a major source of income for powder producers it is likely that powders will not be produced to the strict requirements of AM. A further risk with this procurement method is losing the support of the AM machine manufacturer. This can be slightly de-risked by purchasing material from one of the small number of powder manufacturers who are starting validate their own powder for AM processes.

The major advantage of procuring powder from this route is the increased choice of materials and cheaper procurement costs. To ensure that the specification of the powder is met, a customer may need to undertake their own characterisation analysis. Further to this a manufacturer may only supply the powder in a wider PSD than the customer wants, therefore additional sieving may be required. Both of these add complexity to the powder supply.

5. Customer Considerations

When deciding where to purchase powder from, a customer has a number of considerations to make. Most importantly:

  • Can they supply me with the material I require?

  • Is the price of the powder competitive?

  • Can they provide the batch size I require?

  • Is there traceability of the material source? Do I require traceability?

  • Do I require knowledge over the powder specification? Do I require control over the powder specification?

Additionally, the customer should always consider the use of the machine and powder. For instance: is the machine being used in production or research? What is the use of the end component? A machine used purely for production purposes will be required to make parts of the highest quality, therefore powder from the AM machine supplier or third party supplier is likely to be the best procurement route. The added benefit of this is that the machine manufacturer will support the customer if there are any build issues. However, if complete control and traceability of the powder used for the build is required, then there may be a lack of transparency from the AM machine supplier as to the complete history of their powder.

Research-based machines have a different range of considerations to make. If the primary use of the machine is to prototype or develop the technology, then the customer will likely want the additional control over the powder that they are using. The customer will also likely want to attempt building with new materials or experiment with machine parameters. Therefore sourcing material directly from the powder manufacturer may be best suited here.

There is no right answer for the procurement route that customer takes. However, careful consideration needs to be given to the application and desired end results of the AM system.

6. Future of Powder Supply Chain

There are a number of theories of how this growing material market will develop over the next five to ten years. Here, some ideas are explored.

  1. Increased production and industrialisation of AM drive the price of powder down: all market predictions show the continued growth of metal AM over the coming years. Naturally, as the technology becomes widely used, the supply chain of materials will also grow. Factors such as increasing competition and larger production runs should see the cost of powder per kilogram be driven down. As the powder metallurgy supply chain infrastructure is already well established, the increase in suppliers of specific AM powders is likely to happen rapidly. This theory also applies to processes that are currently expensive to run, for example plasma atomisation. If, as the market develops, this is seen as the best atomisation route then the amount of powder produced by it will significantly increase. Feedstock for the process will become cheaper and it is likely that the range of materials available will increase.

  2. Game changing powder production techniques emerge: throughout this article only atomisation as a way of producing powders for AM has been discussed. However, in the near future, there is the likelihood that an altogether new manufacturing method will eclipse atomisation, providing suitable powder for a fraction of the production cost. Companies such as Metalysis, UK, are developing new ways in which powder can be made at a significantly reduced price.

  3. Introduction of third party suppliers increases competition: the emergence of third party suppliers could see the price of powder driven down further. Purely through competition, suppliers will be able to procure large batches of powder and pass the savings onto the end user.

  4. Will machine and powder supply lock down or open up? This will be an extremely important moment for metal AM. Other industries, namely polymer-based AM, have seen companies use bar-coded systems on their machines, such that a system will not physically build unless a bar code of a material that they supply is scanned. If this is the case with metal AM machines then it could cause a severe tightening on the research capabilities of these machines. However, this is only likely to happen on the highest value, production use systems. Again, as seen with polymer-based machines, competitors with machines of more open architecture are likely to enter the market. It is highly likely that a lot of machines of this nature will emerge as patents from the major machine manufacturers start to expire.

7. Conclusions

The three main options available for the procurement of AM powders include AM equipment providers, third party suppliers and directly from powder atomisers.

There is some degree of security in purchasing powder directly from AM equipment suppliers. This is because the powder batch they supply will be at least nominally the same grade as the powder batch used to develop melt theme parameters. However, the AM equipment supplier has ownership over the powder source thus limiting the powder supply chain competiveness. This results in powder costs which remain the highest of all procurement options.

Procuring powder directly from the atomisers may be a cheaper alternative. However, despite the recent exponential growth, the AM market is currently a relatively small source of revenue for most powder atomisers. Furthermore, because of the specific particle size fractions used in AM, powder atomisers may not produce powder specifically for AM. Instead atomisers may obtain the required size fractions from an atomised powder batch intended for use in other industries such as powder hot isostatic pressing (PHIP) or press and sinter. The originally intended process for these powder batches may not require the same high quality as powders used in AM and as such their performance in an AM process may not be adequate or as expected.

This risk of going direct to atomisers can be limited by using a third party powder supplier. In this case the third party supplier takes on the associated risks of procuring powder batches in much higher quantities than would be needed by any one AM service provider. This then allows the AM service provider to procure only the amount they need. The higher powder quantities procured by a third party supplier potentially provides them with the necessary influence to demand higher quality powder batches that are atomised specifically with AM as the intended end use. The level of pre-sale powder qualification is also much more detailed from third party suppliers than from the atomisers themselves. Even with this option the procurement costs can be higher than going directly to the atomisers and less support will be made available from equipment suppliers should the procured powder be considered a potential factor for build failures.

What increases the complexity, and indeed uncertainty, of procuring powders for AM is the lack of AM specific powder specifications. It is commonplace to make decisions to accept or reject powder batches based on specifications used for press and sinter applications. These specifications would at best include chemical composition, sizing by sieve analysis and flow assessment by Hall flow. Such specifications can be inadequate to use as a benchmark for AM powder quality. As discussed throughout this article predicting powder performance is highly complex and can be difficult to characterise using simple techniques. Future work needs to be aimed at systematically identifying the properties of metal powders that have the biggest influence on the powder performance in terms of hopper discharge and powder spreading and also how the powder responds to the AM melting process. Work in this field will allow the development of specifications which adequately define and control the key process variables of powders used in AM.

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References

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Supplementary Information

LPW Technology. Powder Production - LPW Technology. lpwtechnology.com. [Online] 04 2015.

Advanced Powders and Coatings. Our Technology - AP&C. advancedpowders.com. [Online] 2015. http://advancedpowders.com/plasma-atomization-technology/our-technology/.

Carpenter. Products from Carpenter. Cartech.com. [Online] 2015. https://www.cartech.com/ssalloys.aspx?taxid=90.

GKN Hoeganaes. Home. gkn.com. [Online] http://www.gkn.com/hoeganaes/Pages/default.aspx.

H.C. Starck. AMPERSINT Atomized Metal Powders and Alloys. hcstarck.com. [Online]

Hoganas. Hoganas products. hoganas.com. [Online] https://www.hoganas.com/en/products/.

Sandvik. Metal powder for additive manufacturing. smt.sandvik.com. [Online] http://www.smt.sandvik.com/en-gb/products/metal-powder/additive-manufacturing/.

TLS Technik. TLS - The Products. tls-technik.de. [Online] http://www.tls-technik.de/e_3.html.

The Authors

Jason Dawes is a Senior Research Engineer at the Manufacturing Technology Centre (MTC) where he leads the Particulate Engineering research group. His role is in the technical management of highly innovative research projects involving powder based manufacturing technologies such as additive manufacturing, laser cladding and hot isostatic pressing. He was awarded EngD from University of Birmingham, UK, in 2014 in the field of Chemical Engineering.

Robert Bowerman is a Research Engineer at MTC where he leads projects within the field of additive manufacturing. He has experience in the following technologies: electron beam melting (EBM), selective laser melting (SLM), stereolithography (SLA), digital light processing (DLP) and fused deposition melting (FDM). His projects focus on innovative research and development work primarily on the Manufacturing Capability Readiness Levels (MCRLs) 4 to 6. Work carried out covers all areas of additive manufacturing, including development and productionisation of technology and designing for AM. He is presently working towards Chartered Engineer status.

Ross Trepleton is the Component Technologies Group Technology Manager at the MTC. He is responsible for the coordination and management of the MTC Research Programme, in the area of Component Technology to meet the needs of clients and stakeholders. The aim of this area of research is to develop new technologies that enable improved component manufacturing. He was awarded a PhD from University of Birmingham in the field of Metallurgy and Materials.

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