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DNV GL STRATEGIC RESEARCH & INNOVATION POSITION PAPER 7-2014

ADDITIVE MANUFACTURING – A MATERIALS PERSPECTIVE SAFER, SMARTER, GREENER


2 Additive Manufacturing – A Materials Perspective

PREFACE Additive Manufacturing (AM), of which 3-D printing is but one technique, is becoming increasingly applied to many different systems. Although oil & gas and maritime industries currently constitute only about 5 % of the total AM market, it is anticipated that AM will rapidly expand its reach in these industries. AM proffers many possibilities in innovative manufacturing, but in this position paper we present our perspective on the risks associated with AM as the technologies are currently being developed. Qualification and certification may provide significant challenges in AM because of the potential for variability in specified properties. Because building up a product using AM incorporates many steps, the traditional qualification methods of repeated testing of an end product from a centralised facility will not be sufficient. The distributed nature of AM means that the product variability determined for one location may be entirely different from another; this may be due to software and hardware differences, as well as a myriad other factors. The methodology needed will relate the variability of the many

steps leading to the end product. Here we present a Bayesian network methodology that can be used to assess the risks, both to the manufacturer and the users, arising from AM. Such a framework may also assist in developing the information needed to reduce the risks from implementation of AM parts. The overall risk with AM involves many components. In this position paper, we focus on the materialsrelated risks, although some aspects of software-related risks are also mentioned.

ACKNOWLEDGEMENTS This Position paper has been co-authored by Shan Guan, Liu Cao, Francois Ayello, and Christopher Taylor, all in the Materials Program, Strategic Research & Innovation, DNVGL. The authors acknowledge the reviews and helpful comments from Thomas Mestl and Joost Vanden Berghe, DNVGL. The assessment of AM technologies was originally motivated by internal communication from Timo Kouwenhoven, DNVGL.

Contact Details: Shan Guan, Ph.D. Senior Researcher, Materials Program, Strategic Research & Innovation DNVGL: Shan.Guan@dnvgl.com Narasi Sridhar, Ph.D. Director, Materials Program, Strategic Research & Innovation DNVGL: Narasi.Sridhar@dnvgl.com


Additive Manufacturing – A Materials Perspective

CONTENT INTRODUCTION

4

AM PROCESSES

6

Important AM Processes for Maritime and Oil & Gas Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Materials and Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

WILL AM FIND APPLICATION IN THE MARITIME INDUSTRY?

16

Limiting factors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Encouraging factors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Technology Qualification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

CONCEPTUAL APPROACH TO RISK ASSESSMENT OF AM

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For OEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 For End Users. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 CASE STUDY 1: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURE ADOPTED BY OEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 CASE STUDY 2: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURED PARTS ADOPTED BY END USER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

LOOKING TO THE FUTURE

24

REFERENCES

25

IMAGES CREDIT

26

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4 Additive Manufacturing – A Materials Perspective

INTRODUCTION Additive manufacturing (AM) enables the building of three-dimensional solid objects from digital models, and thus the realisation of complex parts. This contrasts with many traditional manufacturing methods, sometimes referred to as subtractive manufacturing, in which pre-forms are made first and from these the final parts are fabricated. Near net shape manufacturing has existed for several decades through various advanced casting and powder metallurgy techniques. However, even near net shape manufacturing techniques make the whole component first and then finish it to its final dimensions. A further distinguishing feature of AM is its distributed nature. While traditional manufacturing mostly takes place at a centralised facility, with the resulting parts distributed to end users, AM has the potential for implementation at the point-of-use. This enables innovations in manufacturing value chains, many of which are still being realised. The emergence of modern AM can be traced back to the mid 1980s when Charles W. Hull was granted a patent entitled “Apparatus for Production of ThreeDimensional Objects by Stereolithography” (U.S. Patent 4,575,330). Stereolithography was described as a process of making solid objects by successively “printing” layer-by-layer of ultraviolet-curable material. Later, in 1988, 3D Systems commercialized the most popular stereolithography machine at that

time: SLA 250. Following the creation of laminated object manufacturing in 1991, the invention of selective laser sintering (SLS) machines opened the door to mass customisation of both plastic and metallic parts. For example, powder fusion bed, an AM process in which SLS technology is commonly implemented, is currently the exclusive platform for making metallic function-parts. As these machines became viable at the beginning of the 21st century, AM technologies finally indicated the possibility of a new type of industrial revolution. A survey of 105 manufacturers of 3-D printers showed that Industrial/Business Machines, Consumer Products, and Motor Vehicles were the three leading industrial sectors (Fig 1). Shipping and Oil & Gas, categorized as “others”, accounted for just 5 % of overall application areas. [1] The worldwide market for AM, consisting of all products and services, was $2.2 billion in 2012, and is expected to reach $12 billion by 2025, representing an impressive average annual growth rate of 34% (Lux Research). Although AM cannot yet manufacture large structures, it is capable of making small components that can be critical to the functioning of larger structures.


Additive Manufacturing – A Materials Perspective

Figure 1.  SLA250, Stereo lithography (left), and SLM 500 HL, SLS machine (right). (See image credit 1)

In examining the future role of AM in large-scale industrial applications, two important questions arise:

5%

17%

12% 4%

1. What is the risk associated with incorporating

AM components into systems?

5% 19%

6%

2. Which tools can be used to assess the risk

added by using these parts? Many factors could increase the risk in AM utilization, for example large variation in processing technologies and 3-D printers, lack of industrial standards and regulations, and greater variability in material properties compared with those made by traditional manufacturing processes. In this position paper, we introduce several important AM processes of interest to maritime and oil & gas applications, including their applications, technological readiness levels, and limitations. Furthermore, we examine a Bayesian network approach for assessing the risks associated with utilizing AM.

14% 18%

Motor Vehicles (17%) Architectural (4%) Government/Military (5%) Academic Institutions (6%) Medical (14%) Consumer Products (18%) Industrial/Business Machines (19%) Aerospace (12%) Other (5%)

Figure 2.  AM industrial applications and revenues in 2014 [1]

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6 Additive Manufacturing – A Materials Perspective

AM PROCESSES A generic AM value chain typically contains eight steps. [2] 1. Conceptualisation and Computer Aided Design

(CAD) to generate a 3-D model.

many processes sound different but basically employ similar methods and materials. In January 2012, ASTM International Committee F42 on AM Technologies recommended names and definitions for seven AM processes in the specification of ASTM F2792. [3]

2. Conversion of 3-D model to STL or newer AMF

file format, which is supported by both CAD software and AM machines. 3. 3-D file manipulation1 and transfer to AM

machine.

1. Binder Jetting: a liquid bonding agent is

selectively deposited to join powder materials. 2. Directed Energy Deposition: focused thermal

energy is used to fuse materials by melting them as they are being deposited.

4. AM machine setup, tuning, and maintenance. 3. Materials Extrusion: material is selectively 5. Building parts by joining materials deposited in

dispensed through a nozzle or orifice.

successive layers. 4. Materials Jetting: droplets of build material are 6. Removing parts and support structures, perhaps

selectively deposited.

additional cleaning. 5. Powder Bed Fusion: thermal energy selectively 7. Post-processing2 for application purposes. 8. Inspection.

fuses regions of a powder bed. 6. Sheet Lamination: sheets of material are bonded

to form an object. AM system manufacturers have created unique process names and material designations in order to differentiate themselves from their competitors. [2] This has led to confusing terminologies as

1 File manipulation includes verification of part geometry, selection of orientation and location, addition of support structure, scale and duplication, etc. 2 Post-processing may involve infiltration, hot isostatic pressing, heat treatment, surface finish, coating and assembly.

Vat Photopolymerization: liquid polymer in a vat is selectively cured by light-activated polymerization. However, some newly invented processes may not fit into this system, e.g. Electrochemical Liquid Deposition (ECLD), Laser Transfer Direct Write (LTDW), Dip-pen Nanolithography, etc. A brief summary of each category and related terminologies from manufacturers is provided in Table 1.


Additive Manufacturing – A Materials Perspective

AM PROCESSES

Directed Energy Deposition

Powder Bed Fusion

Materials

Plastic

Materials Extrusion

Metal

Ceramic

Composite

Materials Jetting

Binder Jetting

Sheet Lamination

Vat Photopolymerization √

√ √

Others

Wax, photopolymer

Sand

Paper

Resin, liquid photopolymer

Energy Source

Laser, electron beam

Laser, electron or ion beam

Heating coil

Heating coil, UV light

N/A

Laser, ultrasonic

UV light, X-ray or y-rays

Relevant Terms

LENS, DMD, LBMD, EBF3, DLF, LFF, LC, CMB, IFF

SLS, SLM, DMLS, DMP, EBM, SPS, Laser Cusing

FDM, FFF, FLM

Inkjet, PolyJet, MJM, Aerosol Jet, ThermoJet

3DP, LPS, DSPC

LOM, UC, UAM

SL, SLA, MPSL, DLP, FTI

Leading Manufacturer

Optomec, DM3D, TRUMPF, Fraunhofer

3D Systems, EOS, Concept Laser, SLM Solutions,

Stratasys, 3D Systems

3D Systems, Stratasys, Solidscape,

3D Systems, Voxeljet, ExOne

Mcor, Cubic, Fabrisonic

3D Systems, EnvisionTEC, RapidShare

High

Part Durability

Detail Precision

Durability

High

Surface Roughness

Low

Details or Precision

High

Low

Surface Roughness

Low

Build Speed

Slow

Slow

Medium

Medium

Fast

Fast

Medium

Cost3

High

High

Low

Low

Medium

Medium

Medium

Support

No

Yes

Yes

Yes

No

No

Yes

Post-process

Yes

Yes

Minimum

Minimum

Yes

Yes

No

3DP, 3-Dimensional Printing CMB, Controlled Metal Build-up DLF, Directed Light Fabrication DLP, Digital Light Processing DMD, Direct Metal Deposition DMLS, Direct Metal Laser Sintering DMP, Direct Metal Printing DSPC, Direct Shell Production Casting EBF3, Electron Beam Freeform Fabrication EBM, Electron Beam Melting

FDM, Fused Deposition Modelling FFF, Fused Filament Fabrication FLM, Fused Layer Modelling/Manufacturing FTI, Film Transfer Imaging IFF, Ion Fusion Formation LBMD, Laser-based Metal Deposition LC, Laser Consolidation LENS, Laser Engineered Net Shaping LFF, Laser Freeform Fabrication LOM, Laminated Object Manufacturing

Table 1.  Comparison of Different AM Processes.

3 Cost of AM machines, materials feedstock, and regular maintenance.

LPS, Liquid Phase Sintering MJM, Multi-Jet Modelling MPSL, Mask Projection Stereolithography SL, Stereolithography SLA, Stereolithography Apparatus SLM, Selective Laser Melting SLS, Selective Laser Sintering SPS, Spark Plasma Sintering UAM, Ultrasonic AM UC, Ultrasonic Consolidation

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8 Additive Manufacturing – A Materials Perspective

IMPORTANT AM PROCESSES FOR MARITIME AND OIL & GAS APPLICATIONS Most AM processes have been pioneered for a couple of decades by manufacturers listed in Table 1, and who still possess the key technologies and their improvements in the industry-level AM machines. These machines are capable of managing minimum feature size at micron scale and finishing single part sizes as large as 4m x 2m x 1m (Voxeljet VX4000). In general, AM machines have to address the compromise between build speed and accuracy, which has been improved by successfully employing technologies such as different scan strategies, multiple nozzles, and print heads, hybrid process, etc. Recent releases of earlier AM patents enable production of low budget, consumer-level, desktop 3-D printers for prototyping. However, industries are more interested in AM processes that enable direct part production, with advantages in complexity for free and quick 3 F’s – Form, Fit and Function.[2] Applications of metal or plastic functional parts made by AM processes have to tackle the potential impact on performance and integrity compared with counterparts made by traditional methods; adverse consequences are unacceptable for many industries, such as Aerospace, Automotive, Maritime, Energy, Oil & Gas, and Medical. Three categories of AM processes with high potential for implementation in part production for Maritime and Oil & Gas applications have been selected and are described in greater detail in the following sections. Materials Extrusion Material contained in a reservoir is forced through a nozzle and bonded with adjacent material when it is in a semi-solid or liquid state, while the extrusion head or the build platform moves in the x-y plane. The material solidifies fully afterwards. After a layer is completed, the build platform moves down, or the extrusion head moves up, for the next layer to be extruded. The raw material is typically a filament of thermoplastic coiled onto a spool, but plastic pellets or granules are also used. Support structures are required for bottom surfaces and overhanging features. The first material extrusion system, Fused Deposition Modelling (FDM), was introduced in 1991 by Stratasys. For the ease of support structure removal, FDM machines use two spools of material in printing, build material and support material. The latter either has a lower melting point, or weaker mechanical properties, or can be dissolved in a specific solvent. In comparison with other AM processes, FDM

systems and materials are relatively inexpensive and therefore dominate the budget 3-D printer market ($500~$5000). A particular scan strategy is employed to balance the build speed and precision in an FDM system: an outline of the 3-D model is first plotted at low speed using a small size nozzle and material is filled inside later at high speed using a larger nozzle size. Material flow rate must be accurately controlled to match the changes in speed and direction of the extrusion head. Alternate scan pattern of adjacent layers, sufficient residual heat of extruded filament, and minimum overlap with previously laid material are also required to ensure minimal gaps between extruded route and effective bonding to form a coherent solid structure. However, the properties of the final parts are not as uniform as for their injectionmoulded counterparts. The properties along the z-direction and at places where the extrusion nozzle changes direction are usually the weaker points. Powder Bed Fusion Thermal energy is used to fuse selected regions of a thin layer of powder that has been spread across a build platform by a scraping blade or counter-rotating levelling roller. The source of the thermal energy could be a laser, electron beam, or focused ion beam. On completion of a layer, the build platform is lowered by one layer thickness and the powder compartment is raised by one layer thickness to feed the next layer. The entire process takes place in a closed chamber filled with inert gas to minimize oxidation of the powder materials. Both polymer and metallic materials are available in powder bed fusion processes, and are described by “sintering” and “melting” respectively. For polymers, the unfused loose powder around selected regions serves as support structure, so no additional supports are usually needed. For metals, anchors are typically required to attach a part to the build platform and support overhanging features, since high thermal gradients in the build chamber can lead to thermal stresses and warping. In order to prevent non-uniform thermal expansion and contraction, the build platform is usually maintained at an elevated temperature to preheat the powder material. Powder bed fusion systems usually cost more than other AM processes to own and operate. The thermal process has the potential to cause warping, residual stresses and heat-induced distortion for all materials


Additive Manufacturing – A Materials Perspective

Support material filament Build material filament Extrusion head Drive wheels Liquifiers Extrusion nozzles

Part Foam base

Part supports

Build platform

Support material spool

Build material spool

Injection mould

Tool and fixtures

Functional prototype

ULTEM® Air duct

Figure 3.  An illustration of a Fused Deposition Modelling (FDM) process and some plastic parts fabricated by FDM. (See image credit 2)

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10 Additive Manufacturing – A Materials Perspective

Directed Energy Deposition Focused thermal energy is used to melt materials in a narrow region as the material is being deposited from powder or wire feedstock. Each pass of the deposition head creates a track of solidified material, and adjacent overlapping tracks of material make up layers. Manufacturing of complex 3-D geometry may require a support structure or multi-axis deposition head. In most cases, the metal powders are injected into a pool of molten metal created by a focused laser beam, similar to laser cladding.

fabricated by powder bed fusion. Loose powders are easily affected by heat surrounding the building part, and grow a “skin” of porous attachment on the desired part. The fine powder materials used for this process degrade slightly each time they are exposed to the elevated temperature; therefore proper powder handling and recycling procedures are required. The final part made from powder bed fusion process also suffers from porosity, which adversely impacts part performance and needs to be minimized.

Lenses

X-Y scanning mirror Laser

Laser beam Sintered paint

Leveling roller Powder bed

Powder feed supply

Powder feed piston Powder feed piston Build chamber

Powder feed supply Build piston

Micro-metal gear

Co-Cr dental building platform

Titanium hinge bracket

Aluminium automotive heat exchanger

Figure 4.  An illustration of Selective Laser Sintering (SLS) process and some metal parts fabricated by SLS. (See image credit 3)

Co-Cr Fuel injector and swirler


Additive Manufacturing – A Materials Perspective

Directed energy deposition systems are not as popular as other AM systems on the market, but they enable deposition of multi-component or functionally graded materials. Many directed energy deposition systems use a 4-axis or 5-axis motion system to position the deposition head, which provides extra flexibility to the building process instead of being limited to successive horizontal layers. This capability makes directed energy deposition suitable for adding material onto an existing part, such as a component repair.

Since all three types of processes involve deposition, melting, and solidification of material powder on a substrate surface, they result in a high density of parts. The typical small size molten pool and relatively rapid travel speed combine to produce very high cooling rates and large thermal gradients, which produce non-equilibrium solidification microstructure and a finer grain structure than traditional castings. On the other hand, residual stresses as a result of fast solidification can lead to cracking during or after part construction. The scan

Lens Repairing Titanium Vane Edge

Figure 5.  An illustration of the laser metal deposition process to build and repair metal parts. (See image credit 4)

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12 Additive Manufacturing – A Materials Perspective

pattern is important for part quality and has to be changed from layer to layer to minimize residual stress built-up. AM generally does not have any advantage for large volume production of parts with regular geometries. Nevertheless, AM technologies for production offer several beneficial features for the maritime and oil & gas industries: a. “Complexity for free” enables complex

geometries to be manufactured. Examples include cellular/lattice internal structures for a better strength to weight ratio, high efficiency fuel injector with fine flow channels, and conformal internal cooling channels in heat exchangers or drill heads that can lower operational temperature and prolong lifetime. b. Flexible manufacturing operation allows highly

customizable components in low volume and fast production cycles to save lead time and cost. c. Additive process and minimum need of tooling

are appealing for making components involving expensive and hard materials. d. Decentralised production using AM technologies

simplifies the supply chain and reduces inventory required.

(a)

MATERIALS AND PERFORMANCE The materials available for AM processes are summarised in Table 2. A variety of plastic materials with a diverse range of properties are commercially available for AM machines. Nevertheless, plastics are mainly used for prototyping and considered as consumable components with a short lifetime. Even as end-use parts, long-term performance is not a critical concern for the application of plastics. Plastic parts are cheaper and faster to fabricate using AM technologies, and any damaged parts are routinely replaced without severe consequences. Powder bed fusion and directed energy deposition processes are typically capable of producing metal parts. Metallic components used in maritime or oil & gas industries often operate under demanding loads and environments, and are expected to last a long period in service without compromise in performance. Because of the critical nature of such applications, several factors inherent in the production of AM parts must be addressed: Porosity In most AM systems, metal parts are built by solidification from metal powder-melt to obtain nearly 100 % density. However, less than fully dense parts often result in inferior properties and performance than the cast or wrought counterparts. Porosity could act as crack initiation sites and lead to premature failure, especially under cyclic stress conditions. [1] Powder compaction methods, such as hot isostatic pressing (HIP) used in powder metallurgy, are transferred to AM as a postprocessing method to reduce parts’ porosity.

(b)

Figure 6.  Typical porosity of AM metal part: (a) Scanning Electron Microscopy image shows open pores on the surface of SLM-processed Inconel 718 and (b) optical microscope image shows pores in the bulk of DMLS-processed commercial Al-Si-Mg alloy. (See image credit 5)


Additive Manufacturing – A Materials Perspective

Figure 7.  Optical microscope images of Al-Si-Mg alloy sample fabricated by DMLS after etching with Weck’s reagent: (a) a section along the build direction (z-axis) shows layer-wise structure consisting of individual scan paths; (b) a section parallel to the powder deposition plane (xy-plane) displays overlaid multiple scan paths. (See image credit 6)

Layered Structure Building a 3-D object, layer-by-layer, may unavoidably break the uniformity along the z-direction perpendicular to the layers, leading to as much as a 50 % loss of properties in the z-direction.[2] Improvement of properties in the z-direction relies on the materials bonding between the adjacent layers, which requires accurate control of sufficient energy injection and residual heat energy to form coherent solid structure across layer interfaces, and alternate scan patterns of adjacent layers to minimize gaps between them. Quality and Reliability AM parts are being increasingly used as final products. The requirement for rigorous and repeatable production quality is a considerable challenge to the application of AM in several industries that have minimum risk tolerance. AM is capable of creating high quality parts, but the consistency of their quality and long-term performance have not been sufficiently investigated. To be accepted, AM parts must comply with the same international or company standards used for conventional parts. ASTM International Committee F42 formed in 2009 to address the lack of AM standards in an attempt to control part-to-part consistency.

Safety and Sustainability Industries are also seeking safe and sustainable development, while materials and technologies advance. AM may be inherently more sustainable than conventional manufacturing as it produces less waste and transportation supply chains are reduced significantly because of point-of-use production capabilities. However, several safety and sustainability issues need to be evaluated. Manufacturing of metal powders can be an energyintensive and wasteful process compared with conventional ingot and cast metallurgy. Powders of raw material may also result in various health and safety concerns if proper handling and recycling of fine powders is not followed. A number of photopolymers have been invented for lithographic techniques, but they degrade slowly on exposure to UV, resulting in the need for replacement. Specific disposal procedures are required for those new plastics and many other one-time used prototyping parts. In evaluating AM, all these issues need to be considered for a sustainable process.

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14 Additive Manufacturing – A Materials Perspective

AM Materials

AM Processes

Major Manufacturer and Supplier

Applications

PLA, ABS, PC, PC/ ABS blend, PP, TPE, PMMA, wax

FDM, SLS, Materials Jetting, Binder Jetting

Stratasys, 3D Systems, Solidscape, Voxeljet

Automotive, aerospace, medical devices, electronics housing, packaging, seals, precision casting patterns, kitchen tools, HVAC, art & fashion.

Nylon, ULTEM, PPSF/PPSU, PS, PET, PVA

FDM

Stratasys

PA, PAEK, PS, TPU

SLS

EOS, 3D Systems, CRP Technology, Materialise

Acrylics, acrylates, epoxy, resin, rubberlike, ABS-like

SLA, DLP, PolyJet, MJM

3D Systems, Stratasys, Solidscape, DSM Somos, EnvisionTEC

Medical & dental, packaging, seals, investment casting patterns, demonstration.

tool steel, SS 316L & SS, Ti-6Al-4V & Ti alloy, Co-Cr, Ni-Cr, Ni alloy, Al-Mg-Sc, AA 4047, Cu alloy

SLS, SLM, DMLS, EBM, LENS, DMD, Aerosol Jet

EOS, Optomec, Arcam, ATI Powder Metals, Carpenter, LPW, GE Aviation, Airbus

SS, tool steel, bronze, Fe, W, w/bronze infiltrant

Binder Jetting

ExOne

Automotive, aerospace, maritime, energy, oil & gas, mining, tooling, cladding, metal component repair, functionally graded laminates, electronics, injection/die casting mould, medical/biomedical implant, art & jewellery.

Al, Cu, Ti, SS

UC, UAM

Fabrisonic

Silica sand, alumina/ silica

Binder Jetting, SLS

Voxeljet, ExOne, EOS, Viridis3D

Sand cores/moulds for casting, art design

PA filled w/ glass, carbon fibre, aluminium, WC

SLS

3D Systems, EOS

Automotive, aerospace, defence.

Al, Cu, SS foils w/ TiNi fiber

UC, UAM

Fabrisonic

Superstructure, reinforced low-cost matrix.

AA, Aluminium Alloy ABS, Acrylonitrile Butadiene Styrene HVAC, Heating, Ventilation & Air Conditioning PA, polyamide PAEK, Polyaryletherketone PC, Polycarbonate

PET, Polyethylene Terephthalate PLA, Polylactic Acid PMMA, Polymethyl Methacrylate PP, Polypropylene PPSF/PPSU, Polyphenylsulfone PS, Polystyrene PVA, Polyvinyl Alcohol

Table 2.  Types of materials used in AM and according AM processes.

SS, Stainless Steel TPE, Thermoplastic Elastomer TPU, Thermoplastic Polyurethane ULTEM®, amorphous thermoplastic polyetherimide


Additive Manufacturing – A Materials Perspective

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16 Additive Manufacturing – A Materials Perspective

WILL AM FIND APPLICATION IN THE MARITIME INDUSTRY? AM technologies generate enthusiasm and bold manufacturing ideas, from 3-D printing of an entire house to an entire aeroplane. [6, 7] What about an entire ship? Will AM processes be used to build large ships, for example? To answer this question we must take into account both the requirements of future ships and the prospective improvements in AM technologies; and then we must attempt to predict where the two technologies meet.

LIMITING FACTORS Building time: Current AM processes are quite slow. Only 4 litres of steel per hour can be deposited, an equivalent of 0.75 tons of steel per day. The speed is limited by the laser melting steel powder and cooling time before the next pass of the laser in order to deposit the next layer. We can expect deposition speed to increase slightly, but because of the physical constraints of the process this will not be by orders of magnitude. Building costs: The present high price of starting material is the main factor in determining the high price of 3-D printed parts. Human labour and CAPEX are dwarfed in comparison with the high price of starting materials (e.g. $180/kg for stainless steel powder vs. $6/kg for stainless steel bar). In order to be competitive, the price of raw material will have to decrease by two orders of magnitude.

Depending on the AM process to be used and any customization of AM equipment, capital costs can also be high. Uniformity of properties: Directionality and variability of properties can be significant for AM parts and may limit the type of parts made by AM. The metallurgical quality of large parts made using powder metallurgical techniques as implemented in AM has not been clearly established nor have the techniques been optimized. The fatigue and fracture strengths of large-scale objects made by such methods need further assessment.

ENCOURAGING FACTORS On the other hand, AM is capable of providing new manufacturing solutions. For example: ¾¾ Lighter and stronger structures (see Figure 8; aeroplane structure mimicking bone structure) ¾¾ More efficient designs (see Figure 9; ship construction mimicking ‘organic’ shape could save significantly on fuel consumption). If large-scale AM proves to be economically and technical viable in the future, we can predict that the freedom from conventional manufacturing processes will allow ‘strange’ ships to roam the sea.


Additive Manufacturing – A Materials Perspective

Figure 8.  Left, picture of bone structure. Right, Boeing new concept for commercial aeroplanes; AM processes would allow nature to be copied, thereby making lighter and more efficient planes. (See image credit 7)

TECHNOLOGY READINESS LEVELS IDENTIFIED FOR AM PROCESSES BASED ON NASA AND ISO DEFINITIONS

Figure 9.  The irregular shape of the whale fins provide reduced drag (current manufacturing processes for ships have difficulties imitating such structures). (See image credit 8)

TECHNOLOGY QUALIFICATION Many approaches have been considered by the engineering community in evaluating new technologies and the pathways for inserting them effectively into a system. In the 1980s, NASA developed Technology Readiness Level (TRL) as a way to define the position of a specific technology with respect to its maturity and plan for its further development. More recently, ISO has developed

TRL 1

Basic principles observed and reported

TRL 2

Technology concept and application formulated

TRL 3

Analytical or experimental proof-of-concept

TRL 4

Technology validation in laboratory environment

TRL 5

Technology validation in relevant environment

TRL 6

Prototype demonstration in a laboratory environment

TRL 7

Prototype demonstration in a relevant environment

TRL 8

Technology integrated in relevant environment.

TRL 9

Proven technology through years of successful testing in relevant environment (i.e. Marine environment)

a revised TRL definition, essentially mirroring the original NASA definitions. These definitions can be tailored to AM processes. An initial assessment of AM technologies for small and large components shows that AM is at a TRL 3 level for large components (see inset for definitions). DNVGL Technology qualification standard RP-A203 classifies technology maturity levels in terms of a matrix. It further identifies methods to assess the reliability and risk of new technology through a variety of methods, depending on the history of the system examined. The end result, in addition to detailed risk assessment, could be a qualitative risk ranking.

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18 Additive Manufacturing – A Materials Perspective

CONCEPTUAL APPROACH TO RISK ASSESSMENT OF AM Although it may be said that AM provides “complexity for free”, there is no such thing as a “free lunch.” With this caveat in mind, the decision to adopt AM technology – either as an end user or as an original equipment manufacturer (OEM) - should be made with a keen awareness of the risks that would be introduced throughout the lifetime of a given part produced by this method. A generic lifecycle is presented in Figure 10. Risks that emerge during Phase I include the lack of design principles for efficient design of the AM process, reliability of models such as finite element simulation to optimize part geometry, and research and development costs associated with optimizing the process and post-process parameters (such as print orientation, materials selection and heat-treatment) as well as developing testing and characterization protocols for parts produced according to this manufacturing method. [8-12] Regulation and qualification may also prove challenging, given rapid advances in the manufacturing process compared with the relatively slower pace of standard development. [1, 3] Risks that emerge in Phase II may arise from variations in material quality and availability, changes in production units/upgrades, and “user-dependent” factors. Post-processing steps may also introduce additional risks of non-conformance. Finally, parts must pass quality control standards.

During Phase III, the end-user will encounter risks that predominantly arise due to the relative novelty of the technology and lack of extended lifetime data for parts produced by AM. The exact magnitude of risk will depend upon the expected longevity of the part and the consequences of materials failure. A layer-by-layer manufacturing technique introduces isotropic and anisotropic heterogeneities (such as voids and internal interfaces) in the material, potentially creating new failure modes that may be reduced through post-processing treatments.[13, 14] Accordingly, new materials inspection procedures and decision-making criteria may need to be developed, tested, and employed. Underappreciated risks could emerge if failure criteria developed for conventionally machined parts are applied to their AM counterparts. The end user will also encounter risks due to increase in part cost due to the AM procedure (as materials costs, for example, are higher for metallic powders). [15, 16] Risks can also emerge when parts need to be replaced, and these will be a function of the supply chain and the availability of in-house AM units that could be used for replacement and repair options. Finally, the decision made by an end user to employ a part produced by AM process will be largely motivated by the degree to which a technology is enabled by (that is, contingently dependent upon) the AM component (for example, the production of highly efficient heat exchangers where AM provides unique design and manufacturing options [17]).


Additive Manufacturing – A Materials Perspective

PHASE I

PHASE II

Installation and Deployment

Design specification

CAD Design

Additive Manufacture

In silco Manufacture/ FEM Optimization

Post-Processing

Prototype Print, Post Process, Determination, Testing

PHASE III

Validation

Inspection Maintenance Corrosion Mitigation

Exceeds Lifetime

Failure

Dispose and Recycle

Regulation and Qualification

Figure 10.  The three phases of the lifecycle of a part produced by AM. Phase I: Design and qualification; Phase II: Additive manufacture; Phase III: Deployment and use until failure.

FOR OEM Risks from Phases I, II and II have been combined to provide a generic and comprehensive model for risk assessment using the method of Bayesian inference and Bayesian networks. Bayesian networks provide the opportunity to investigate the cause-effect relationships between sources of risk and so can be used to isolate the key contributors to any risksensitive decision making; in this case, the decision to employ AM or not. [18, 19] Generic risk networks have been created for two classes of user: the OEM and the End User of the part. A risk analysis for OEMs can be divided into three key categories: Design risk, Production risk, and Qualification requirements. Design risk can be reduced by the presence of design principles, including FEM optimisation of part geometries and rules for adjusting designs to accommodate part-shrinkage and minimize the use of supports. Design risk will also be a function of the overall part complexity, including the materials composition and number of components such as overhangs and struts. The production risk has similar contributors, such as the composition of the material used (which will influence availability and variability), the material quantity (small components

are more cost-effective to produce using AM than large components), and the level of post-processing required. Finally, qualification requirements will be related to the application: more demanding applications require stricter tolerances. Ultimately the decision to apply AM to a component will require a comparison between the risks associated with using AM technology and the risks from producing the material via a conventional route. In some cases AM may be the only option, such as when it is an enabling technology, yet this does not obviate the fact that risks may still be incurred during service or sourcing the part from an OEM.

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20 Additive Manufacturing – A Materials Perspective

FOR END USERS The risk analysis for the end user follows a similar decomposition. Risks are sub-divided into Acquisition risk, Service risk, and Supply risk. Acquisition risk will be based upon the cost of the component compared with conventional manufacture, system qualification requirements, and whether or not AM is required as an enabling technology. The Service risk will entail the risk of failure, which must be considered based on technology maturity, intended lifetime and the service environmental conditions, as well as the option that AM provides for facile component repair. Supply risks may be reduced due to the ability of AM to produce highly reproducible parts, given the design algorithms, process and powder (i.e. raw material) stability and control over supply sensitivity.

LIKELIHOOD

Additive Manufacture

Impact

Low

Minimal

Costly

Design challenges

Supply chain

Medium

Production process acquisition costs

High

Qualification and testing

Conventional Manufacture

Catastrophic

Unforeseen failures

Impact Minimal

LIKELIHOOD

Furthermore, networking provides the ability for distribution and control over designs from the central design office to remote locations. The option of a user having an on-site AM machine can also decrease supply risk, but at the cost of increasing the acquisition risk due to the necessity of owning or leasing the machine, as well as obtaining the in-house expertise. A cost-benefit analysis would be required to evaluate the relative advantages, and could particularly favour a distributed approach for off-shore and remote applications.

Costly

Catastrophic

Low

Qualification and testing

Unforeseen failures

Medium

Supply C chain acquisition costs

High

Design challenges production process

Table 3.  General comparison of risks encountered in AM as compared with conventional manufacture


Additive Manufacturing – A Materials Perspective

CASE STUDY 1: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURE ADOPTED BY OEM The power of Bayesian networks for assisting in making a risk analysis can best be demonstrated by concocting some simple examples. For an original equipment manufacturer we consider the primary sources of risk as emerging from design, production and qualification. In the case of a metallic component, with pre-existing design principles, stringent qualification requirements and a high-level of post-processing, a generic Bayesian network analysis can be performed.

Under the assumptions made in our approximate model, the combined probabilities for this feature set led to a 16:84 ratio of go: no-go, i.e. leaning towards a risk that weighs against the selection of additive manufacturing for this technology. (See Network A) Note: this analysis uses only a crude approximation, and so a more sophisticated analysis would need to be constructed for practical implementation of this model, since, for instance, within the composition category of “metal” many sub-selections exist, and similarly for all other variables in the Bayesian network.

Material Quantity Post Processing

0,00 Low 100,00 High

74,26 High 25,74 Low

Part Complexity

Composition 100,00 Metal 0,00 Ceramic 0,00 Polymer

50,00 High 50,00 Low

Design Principles

Production 10,00 Low 90,00 High

100,00 Yes 0,00 No

Design 27,50 High 25,00 Medium 47,50 Low

Qualification Requirements 100,00 Stringent 0,00 Relaxed

Network A A second case could be made for a polymer component with high production, low postprocessing, with design-principles in place and a relaxed qualification requirement. In this case, the opposite analysis results: 80:30 go: no-go ratio, indicating that the technology is mature enough to lead to the selection of additive manufacturing with a high confidence of success.

Manufacturer 15,22 Go 84,78 NoGo

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22 Additive Manufacturing – A Materials Perspective

CASE STUDY 2: BAYESIAN NETWORK ANALYSIS OF RISKS FROM ADDITIVE MANUFACTURED PARTS ADOPTED BY END USER Additive manufacturing may pose unique risks not only to original equipment manufacturers, but also the users of parts produced by additive manufacturing technologies. As in the case of OEMs, some generic probability matrices can be populated to gauge the sensitivity of successful adoption of additive manufactured parts to these control variables.

For instance, in Network B a part with low technological maturity but relatively high intended lifetime, in which additive manufacturing has a key role as an enabling technology, with low costs and distributed manufacture results in a 50:50 don’t adopt:adopt probability ratio. The key reason for the risk assessment of this nature comes down to the fact that the new level of technological maturity does not provide much historical evidence to build confidence against the risk of service failure.

Powder Stability 100,00 Stable 0,00 Unstable

Process Stability 50,00 Stable 50,00 Unstable

Intended Lifetime 17,80 Short 29,84 Medium 52,36 Indefinite

Environmental Conditions

Technology Maturity

Reproducibility

Repair

100,00 New 0,00 Early 0,00 Later

67,57 Yes 32,43 No

Supply 18,13 Unreliable 81,87 Reliable

Failure

Acquisition

Service

55,00 Yes 45,00 No

51,13 Performs 48,87 Fails

Network B In contrast, when the technological maturity is at a later stage the weighting in favor of adoption of the technology is increased to 60:40 for adopt:don’t adopt. The network analysis provides the ability to “slide the scales” of risk or selection factors throughout the connected diagram, as well as the opportunity to add further factors as the particular technology is framed in greater detail.

User 46,59 Don't Adopt 53,41 Adopt


Additive Manufacturing – A Materials Perspective

The risk analysis framework provided in these two cases can be adapted to any particular industrial component. Based on the information available today, comparative risk matrices can be assembled for complex parts manufactured using AM compared with conventional manufacture (Table 3). The first risk matrix shows that AM provides a lower risk for design of parts with high complexity, a reduced probability of costly supply chain risks compared with conventional manufacturing, a medium probability for high costs associated with production and acquisition, and a high probability for costs associated with qualification and testing, mainly due to the relative novelty of the technology.

Supply Sensitivity 50,00 High 50,00 Low

Materials Cost 0,00 High 100,00 Low

Centralized vs Distributed 0,00 Centralized 100,00 Distributed

Process Costs 0,00 High 100,00 Low

Cost vs Conventional System Qualification 33,33 Unprepared 33,33 Stringent 33,33 Relaxed

Enabling Technology 100,00 Yes 0,00 No

There is a medium probability assigned to unforeseen failures, with potentially catastrophic consequences, due to the lack of long-term historical service data and testing, especially if the parts are to be used as functional parts in maritime or oil & gas industries. This should be compared with the risk matrix for conventional manufacture. In this case, for complex parts, the design challenges and production process have a high probability of incurring a high cost, and supply chain risks also become more likely. We expect acquisition costs to be quite similar at present, as additive manufacture tooling is still quite high. On the other hand, qualification and testing become less likely barriers to incurring a financial risk, due to the maturity of these methods. For similar reasons, unforeseen failures also become less probable.

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24 Additive Manufacturing – A Materials Perspective

LOOKING TO THE FUTURE AM technologies have the potential to revolutionise the manufacture of equipment in the maritime and oil & gas industries. Efforts are already underway to manufacture small parts using AM techniques and the scope of these will broaden. Examples for the oil & gas industry could include pumps, valves, drill bits, and sensors. Examples for maritime applications could include pumps, valves, sensors, and special segments of ship structures, although building an entire ship is perhaps for the future. The promise of AM is that it will free designers from traditional manufacturing constraints and free users from traditional supply chain constraints.

Nevertheless, the risks of AM to both manufacturers and users need to be carefully evaluated. Traditional reliability assessment techniques, using repeated testing of finished parts, are insufficient to address AM. Reliability and risk assessment using a Bayesian network is a promising approach to managing the risks associated with introducing such exciting technologies.


Additive Manufacturing – A Materials Perspective

REFERENCES 1. Wohler’s Report 2014, 3D Printing and Additive Manufacturing State of the Industry Annual Worldwide Progress Report, Wohler’s Associates Inc., 2014.

11. G. Bi, C. N. Sun, and A. Gasser. “Study on influential factors for process monitoring and control in laser aided additive manufacturing.” J. Mater. Proc. Tech. 213 (2013) 463-468.

2. I. Gibson, D. W. Rosen and B. Stucker, ed., Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing, Springer, 2010.

12. K. Zhang, S. Wang, W. Liu, and X. Shang. “Characterization of stainless steel parts by laser metal deposition shaping”, Mater. Des. 55 (2014) 104-119.

3. ASTM F2792, Standard Terminology for Additive Manufacturing Technologies, ASTM International, West Conshohocken, PA, 19428-2959, USA.

13. Y. N. Zhang, X. Cao, P. Wanjara, and M. Medraj. “Oxide films in laser additive manufactured Inconel 718”, Acta Mater., 61 (2013) 6562-6576.

4. Q.B. Jia, and D.D. Gu, “Selective laser melting additive manufacturing of Inconel 718 superalloy parts: Densification, microstructure and properties”, Journal of Alloys and Compounds, 585 (2014) 713–721.

14. S. Leuders, M. Thone, A. Riemer, T. Niendorf, and T. Troster, H. A. Richard and H. J. Maier, “On the mechanical behaviour of titanium alloy TiAl6V4 manufactured by selected laser melting: Fatigue resistance and crack growth performance”, Int. J. Fatigue, 48 (2013) 300-307.

5. D. Manfredi, F. Calignano, M. Krishnan, R. Canali, E. P. Ambrosio, and E. Atzeni, “From powders to dense metal parts: characterization of a commercial AlSiMg alloy processed through direct metal laser sintering”, Materials, 6 (2013) 856-869.

15. C. Lindemann, U. Jahnke, M. Moi and R. Koch, “Impact and influence factors of additive manufacturing on product lifecycle costs”, in Proc. Solid Free Form Fabrication Symposium, 2013, 998-1009.

6. http://www.theguardian.com/artanddesign/architecturedesign-blog/2014/mar/28/work-begins-on-the-worlds-first3d-printed-house. accessed June, 2014

16. S. H. Khajavi, J. Partanen, and J. Holmstrom, “Additive manufacturing in the spare parts supply chain”, Computers in Industry, 65 (2014) 50-63.

7. http://www.forbes.com/sites/parmyolson/2012/07/11/ airbus-explores-a-future-where-planes-are-built-with-giant3d-printers/. accessed June, 2014

17. L. Li, M. Hong, M. Schmidt, M. Zhong, A. Malshe, B. H. Veld, and V. Kovalenko, “Laser nano-manufacturing- state of the art and challenges”, CIRP Annals – Manuf. Tech., 60 (2011) 735-755.

8. G. A. O. Adam, and D. Zimmer, “Design for additive manufacturing-element transitions and aggregated structures”, J. Manuf. Sci.Tech., 7 (2014) 20-28. 9. M. Sugavaneswaran, and G. Arumaikkannu, “Modelling for randomly oriented multi material additive manufacturing component and its fabrication”, Mater. Des., 54 (2014) 779785. 10. T. A. Krol, C. Seidel, and M. F. Zaeh, “Prioritization of process parameters for an efficient optimization of additive manufacturing by means of a finite element method”, Procedia CIRP, 12(2013) 169-174.

18. T. M. Mitchell, “Machine Learning”, McGraw-Hill, Boston, 1997. 19. D. Koller and N. Friedman, “Probabilistic Graphical Models. Principles and Techniques.” MIT Press, Cambridge, 2009.

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26 Additive Manufacturing – A Materials Perspective

IMAGES CREDIT Figure 1. SLA250, Stereolithography (left): http:// www.3dsystems.ru/products/slaseries/sla250/index.asp. htm, and SLM 500 HL, SLS machine (right): http://www. rapidreadytech.com/2012/12/slm-solutions-releases-slm-500hl/. Figure 3. An illustration of Fused Deposition Modeling (FDM) process and some plastic parts fabricated by FDM. (Image courtesy of CustomPartNet, Copyright © 2008 and Stratsys), for the plastic parts, image link: http://www.tritech3d.co.uk/ stratasys-printer-family/dimension.php, and http://www. tritech3d.co.uk/stratasys-printer-family/fortus.php Figure 4. An illustration of Selective Laser Sintering (SLS) process and some metal parts fabricated by SLS. (Image courtesy of CustomPartNet, Copyright © 2008 and EOS GmbH). Figure 5. An illustration of laser metal deposition process to build and repair metal parts. (Image courtesy of LPW Technologies, TRUMPF Laser, and Optomec). Figure 6. Typical porosity of AM metal part: (a) SEM image shows open pores on the surface of SLM-processed Inconel 718 (Image courtesy sees reference 4), and (b) optical microscope image shows pores in the bulk of DMLS-processed commercial Al-Si-Mg alloy (image courtesy sees reference 5).

Figure 7. Optical microscope images of Al-Si-Mg alloy sample fabricated by DMLS after etching with Weck’s reagent: (a) a section along the build direction (z axis) shows layer-wise structure consisting of individual scan paths; (b) a section parallel to the powder deposition plane (xy-plane) displays overlaid multiple scan paths. (Image courtesy sees reference 5). Figure 8. Left, picture of bone structure. Right, Boeing new concept of for commercial airplanes, additive manufacturing process would allow to copy nature and make lighter and more efficient planes. Image courtesy left: http://www.brsoc.org. uk/gallery/images/19lg.jpg, and right www.industrytap.com/ airbus-planning-to-3d-print-planes-vital-components/8694. Figure 9. The irregular shape of the whales fins, provide reduced drag (current manufacturing processes for ships have difficulties imitating such structures). Image courtesy: http://4.bp.blogspot.com/-8DTmoSkSVpc/UMH9ieZq2LI/ AAAAAAAADKU/MAfrpsDB77M/s1600/animal+attacks +news++dangerous+animal+attacks+fromthe+deep+ sea+whale+ocean++blue+fin+whale+endangered+animals+ from+the+deep+sea+animal+migration+picture.jpg


28 Additive Manufacturing – A Materials Perspective

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Additive Manufacturing - A materials perspective  

DNV GL strategic research & innovation position paper 7-2014

Additive Manufacturing - A materials perspective  

DNV GL strategic research & innovation position paper 7-2014

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