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Comparison of various additive manufacturing technologies
CHAPTER 3
Comparison of various additive manufacturing technologies Abbreviations AM BJ CAD CT 3D DED DM DMD DMLS EBM EBAM ELI HAZ HIP LENS MDF ORNL PBF RPD SL SLM SLS UAM WAAM
Additive manufacturing Binder jetting Computer-aided design Computed tomography Three-dimensional Direct energy deposition Direct manufacturing Direct metal deposition Direct metal laser sintering Electron beam melting Electron beam additive manufacturing Extra low interstitial Heat-affected zone Hot isostatic press Laser engineered net shaping Manufacturing Demonstration Facility Oak Ridge National Laboratory Powder bed fusion Rapid plasma deposition Sheet lamination Selective laser melting Selective laser sintering Ultrasonic additive manufacturing Wire arc additive manufacturing
3.1 Technology comparison The various metal additive manufacturing (AM) technologies offer different capabilities [1]. While some of these technologies compete with one another, technologies of different categories are more complimentary. Each of these categories offers its own distinct benefits, but also has some limitations. While powder bed fusion (PBF) technologies are suitable for smaller, complex geometries, with hollow unsupported passages/structures, directed energy deposition (DED) is better suited for larger parts with coarser features, requiring higher deposition rates. The use of fine Science, Technology and Applications of Metals in Additive Manufacturing DOI: https://doi.org/10.1016/B978-0-12-816634-5.00003-0
© 2019 Elsevier Inc. All rights reserved.
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powder grains combined with smaller laser/electron beam size leads to a superior surface finish on as-built parts from PBF technologies as compared with directed energy deposition technologies. However, the majority of AM production parts need some form of finish machining for most applications. The ability of the directed energy technologies to add metal to existing parts enables them to apply surface-protective coatings, remanufacture and repair damaged parts, and reconfigure or add features to existing parts, in addition to building new parts. Binder jet technology offers low residual stress, and therefore has some distinct advantages in certain applications. Sheet lamination is good for embedded sensors, multimaterial and some special applications. PBF technologies use small layer thickness and support of the powder bed to create overhangs. However, depending on the angle of the overhang, there can be some distortion to the surface, as shown in Fig. 3.1. This test artifact was built using direct metal laser sintering (DMLS) technology and the material is stainless steel. In addition to the poorly formed surfaces, the magnified bottom picture in the figure shows the singed (blackened) and distorted upper surface of the feature intended to be square. There is similar (though less severe) distortion and singeing on the top of the 6 mm cylindrical features. The diamond features with the upper half-angle at 45 and 30 degree angles are not singed or deformed. Therefore, steeper angles produce a better surface finish and dimensional accuracy for the overhangs. Features with angles less than 45 degrees from the vertical axis, may not need support structures. The ability of the PBF
Figure 3.1 PBF (DMLS) built test artifact showing the capability to build overhangs [2,3].
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Figure 3.2 Test artifacts built using AM. (Left) Stainless steel part using DMLS technology; (right) Ti-6Al-4V part using EBM technology [2].
process to produce such closed overhangs allows these technologies to build components with passageways for cooling fluids, etc. and/or to reduce the weight of the parts by designing cavities. Various tests have been performed to estimate the degree of overhang, feature resolution, and surface finish possible using the PBF process. Fig. 3.2 shows two test artifacts produced using laser-based and electron beam-based PBF technologies. While there are subtle differences between various PBF machines [4], all in all, the feature resolution and overhang capability of PBF is greater than DED technologies. Parts built using DMLS and electron beam melting (EBM) are shown from left to right in the figure, respectively. The small laser/electron beam sizes of PBF technologies also allow them to build finer structures with small wall thicknesses. Fig. 3.3 shows a 3 3 3 3 3 octate lattice truss built using DMLS technology [5]. Fig. 3.3 also shows side and top views from computed tomography (CT) scans of the same structure showing the struts of the truss. The red lines mark the intended CAD and the solid gray color is the actual build. A maximum deviation of 100 μm from the CAD was recorded during measurements. As compared to the PBF technologies, DED technologies rely on their multiaxes deposition capability to create an overhang. However, the larger laser/electron beam/plasma/arc spot size and greater layer thickness limit this capability. Fig. 3.4 shows overhangs built using laser-based (DMD) [6] and electric arc-based (WAAM) [7] DED technologies. Due to the relatively smaller laser spot size compared to the electric arc beam size, laserbased DED offers better resolution and more complexity than arc-based systems. Fig. 3.5 shows a pictorial comparison of various metal AM technologies in terms of their size, build rate, and ability to produce complex
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Figure 3.3 (Left) DMLS-built octate truss structure. (Middle and right) Side and top views from a CT scan of the structure, respectively [5].
Figure 3.4 Overhangs built using DED technologies. (Left) DMD (laser-based DED)[6] and (right) WAAM (wire arc additive manufacturing)-built [7] structures.
geometries. PBF and BJ technologies offer the highest level of part complexity, while wire arc-based DED and sheet lamination (SL) allow the simplest capability with laser-based DED offering a medium level of complexity in the parts. However, the WAAM and EBAM process offer very high deposition rates (build rates) as compared to PBF technologies. These differences are more quantitatively demonstrated in Fig. 3.6 by plotting capabilities of specific commercially available AM technologies [15 26]. For each technology category, such as PBF or DED, several manufacturers and several machine models have been represented in the graph to show the available range of options. Note that the data are not exhaustive and there are many more DED and PBF manufacturers that are not in the list, however, the figure is representative of the capability of the respective technologies. Clearly, the build volume and deposition rates are much higher in DED technologies, while the surface finish, feature resolution, and layer thickness are all coarser. Table 3.1 summarizes the features, capabilities, benefits, and limitations of various AM technologies that are used currently for producing metal AM parts [15 26]. The layer thickness of the AM parts plays a major role in defining the surface roughness of vertical walls of the structure being
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Figure 3.5 Pictorial demonstration of part complexity and size capability of various metal AM technologies. As the size capability of the parts increases from PBF to BJ to DED, material throughput (build rate) also increases, but the ability to build complex geometries reduces. Note that the parts in the figure are not scaled to size [8 14]. DMLS (PBF) built tibial implant, photo courtesy: Lawrence Murr, University of Texas, El Paso; EBM (PBF) built hydraulic manifold, photo courtesy: Oak Ridge National Laboratory, US Department of Energy; EBM (PBF) built acetabular cup, photo courtesy: Mike Cloran, GE Additive; SLM (PBF) built pump housing, photo courtesy: Kristal Kilgore and Mark Hoefing, SLM Solutions; Binder Jet built components, photo courtesy: Mike Shepherd, ExOne; UAM (Sheet Lamination) built components, photo courtesy: Adam Hehr and Mark Norfolk, Fabrisonic; DMD (Laser DED) built diffuser case, forging tool, and repaired turbine support case, photo courtesy: DM3D Technology; WAAM (DED) built Titanium wing spar, photo courtesy: Mark Potter and Stephen Morgan, BAE Systems; EBAM (DED) built titanium propellant tank, photo courtesy: Mark Lewis, Lockheed Martin Corp.
built, while beam size (laser or electron beam) together with step over (or hatch spacing) influence the roughness of the horizontal surfaces. PBF technologies offer a better surface finish as these use a smaller beam size (for both laser and electron beam), shorter hatch spacing, and smaller layer thickness compared to DED technologies, however, as a consequence the deposition rate is also lower for these technologies. Therefore, PBF is more suitable for more accurate, complex small-sized objects, while DED is more suitable for building larger parts at a high processing rate, but with a coarser finish surface. Since DED technologies rely on deposition
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Figure 3.6 Quantitative representation of technology and machine capability of some PBF, DED, BJ, and SL manufacturers. Note that this graph is purely a representation of these capabilities and does not include all manufacturers or all systems from every manufacturer [15 26].
Table 3.1 Comparison of various technologies [15 27]. Powder bed fusion (PBF)
Directed energy deposition (DED)
Binder jetting (BJ)
Sheet lamination (SL)
Ultrasonic energy
UAM
Large, up to 1524 3 1524 3 914
Energy source
Laser (Single, dual or quad laser up to 1 kW)
Electron beam (up to 6 kW)
Laser (up to 8 kW)
Electron beam (up to 42 kW)
Gas tungsten arc or plasma
Technologies
EBM
DMD, LENS, LDT, DED
EBAM
RPD/WAAM
Build envelope (mm)
DMLS, SLM, laser cusing, LM, LBM, DMP Limited, up to 800 3 400 3 500
Binder for powder adhesion, followed by sintering in furnace BJ
Large and flexible, 1425 3 1020 3 1020
Very large, 5791 3 1219 3 1219
Large and flexible, 900 3 600 3 300
Medium, up to 800 3 500 3 400
Beam/bead size
Small, 0.1 0.5 mm
Limited, 250 diameter 3 430 height Small, 0.2 1 mm
Not available
1 12 mm
Wall thickness Layer thickness Build rate
0.15 0.3 mm Small, 25 100 μm Low, 6 171 cc/h
0.25 mm Small, 50 100 μm Low, 55 80 cc/h
Large, can vary from 2 to 4 mm 1 4 mm Large, 500 1000 μm Medium, 16 320 cc/h
N/A 150 μm NA
Very good, Ra 9 12 μm, Rz 35/40 μm
Good, Ra 25/ 35 μm
1 12 mm 1 4 mm Very high 1128 2257 cc/h Coarse, Ra 200 μm
.1.5 mm 150 μm High 900 1350 cc/h
Surface finish
2.5 6.25 mm NA Very high 717 2050 cc/h Very coarse
Very good, Ra 15 μm
N/A
Relative density Residual stress
High .99% High
High .99% Minimal
High .99% Very high
98% after sintering Very low
High .99% Low
Heat treatment
Stress relief preferred, HIP’ing preferred
Stress relief not required, HIP’ing may/ may not be performed
High .99% High in substrate, low in deposit Stress relief required, HIP’ing may/may not be performed
Stress relief preferred, HIP’ing preferred
Mandatory for sintering, densification and strength
May be required for interdiffusion between layers
Medium, Ra 20 50 μm, Rt 150 300 μm, depends on beam size High .99% High Stress relief preferred, HIP’ing preferred
N/A
(Continued)
Table 3.1 (Continued) Powder bed fusion (PBF)
Chemistry
Negligible loss of elements
Build capability
Complex geometry possible with very high resolution. Capable of building internal features and channels
Repair/ remanufacture
Possible only in limited applications (requires horizontal plane to begin remanufacturing)
Feature/metal addition on existing parts
Possible only in limited applications (requires horizontal surface for starting point) Not possible
Not possible
Multimaterial build or hard coating Machining in the build chamber
Loss of elements (such as Al) needs to be compensated in powder Complex geometry possible with good resolution. Capable of building internal features and channels Not possible
Directed energy deposition (DED)
Binder jetting (BJ)
Sheet lamination (SL)
Negligible loss of elements
Loss of elements (such as Al) needs to be compensated in powder
Negligible loss of elements
Negligible loss of elements
No loss of elements
Relatively simpler geometry with less resolution. Limited capability for internal features and channels, etc.
Simple geometry with low resolution. No internal features and channels
Simple geometry with low resolution. No internal features and channels
Simple geometry with low resolution. Limited capability in internal features and channels
Limited
Possible
Not possible
Limited capability
Possible
Not possible
Not possible
Not possible
Possible (capable of adding metal on 3D surfaces under 5 1 1-axis configuration making repair solutions attractive) Possible. Depending on dimensions ID cladding is also possible Possible
Complex geometry possible with good resolution. Capable of building internal features and channels Not possible
Not possible
Possible
Not possible
Possible
Not possible
Possible
Not possible
Possible
Possible
Possible (part of the process)
Not possible
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processes, they are able to add metal onto an existing part. This critical capability of DED allows it to repair and remanufacture damaged parts. This also gives DED technologies the ability to add multiple metals in a single build leading to its multimaterial processing capability. BJ technologies have the benefit of very low residual stress and are useful for many applications, while SL is good for special applications involving embedded components, e.x. sensors. The following section describes different application capabilities of metal AM technologies.
3.2 Free form capability Small beam size and layer thickness, along with the support of the powder bed, allow PBF technologies, such as EBM, DMLS, or SLS, to produce complex geometries with high precision and unsupported structures. Fig. 3.7 shows one such example of a hydraulic manifold mount for an underwater manipulator built using EBM technology. Building the integrated mount and manifold with internal passageways in a single operation eliminates multiple part fabrication and results in significant cost savings. The good surface finish of the part eliminated finish machining needs on all surfaces, except seal surfaces and threading of screw holes. Generally the PBF technique gives a better surface finish than the DED approach,
Figure 3.7 Hydraulic manifold built using EBM technology. The part was built at the Manufacturing Demonstration Facility (MDF) at the Oak Rridge National Laboratory (ORNL). Courtesy: Oak Ridge National Laboratory, Department of Energy.
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Figure 3.8 Injection mold core using DMLS technology. (Left) CAD design showing internal cooling channels. (Right) DMLS-built actual core using 300 Maraging steel [29]. Courtesy: EOS North America, Adam J. Penna.
however for demanding applications (such as in aerospace) finish machining and/or other surface finishing operations are still required [28]. Fig. 3.8 shows an injection molding core built using DMLS technology [29]. This tool represents one core in a 16-core production tool for injection molding plastic parts. The left side shows a CAD model of the tool with internal cooling channels and the right side shows the actual tool built using 300 Maraging steel. The ability of PBF technologies to produce three-dimensional cooling passages following the part contours allows such tool building. One benefit of this is the placement of cooling channels closer to the part surface, leading to faster and uniform plastic cooling, which results in a shorter cycle time and better part quality. These capabilities are unique to PBF processes and/or BJ (binder jetting). Fig. 3.9 shows a Grid Fin part made using In718 alloy with laser DED process (LMD) [30]. Even though all three parts are identical, different process parameters have been used to build these parts. The part on the left used only 1070 W laser power, 17 cc/h deposition rate resulting in 30.5 h deposition time. The part in the middle used 1700 W laser power, 33 cc/h deposition rate resulting in 17 h deposition time, but a rougher surface finish. In contrast, the part on the right used 2620 W laser power, 66 cc/h deposition rate, and resulted in fastest processing for 8.5 h. However, the surface finish was the coarsest of all. This clearly illustrates that in AM there are various ways to build a part and a careful consideration of the build strategy and process optimization is essential depending on part geometry, material, and commercial requirements.
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Figure 3.9 In718 grid fins built using LMD (laser-based DED) technology with variable deposition rates [30]. The part on the left was built using lowest laser power (1070 W) and deposition rate (17 cc/h). The part in the middle used higher laser power (1700 W) and deposition rate (33 cc/h), while the part on the right used highest laser power (2620 W) and highest deposition rate (66 c/h). Courtesy: RPM Innovations, Tyler Blumenthal, and Nick Wald.
Figure 3.10 Binder jet (BJ) built stator part. The material is S4 stainless steel and bronze [31]. Photo courtesy: ExOne, Mike Shepherd.
BJ technologies also allow fine-featured part build up with internal geometries. However, during the subsequent furnace sintering process to enhance the strength, part distortion will occur and must be accounted during design and processing. Fig. 3.10 shows a stator part made of S4 stainless steel and bronze [31]. The part replaced a traditionally manufactured 4140 steel stator that would usually be machined out of a solid
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Figure 3.11 Ti-6Al-4 V wing spar built using a WAAM system; top view and side view [32]. Photo courtesy: BAE Systems, Mark Potter and Stephen Morgan.
blank, resulting in significant cost saving. In addition, S4 stainless steel provides better abrasion resistance and longer life for the component. Some DED technologies, such as EBAM, WAAM, and rapid plasma deposition (RPD), are particularly suited for processing very large components with simple geometries due to their very high deposition rate and the large spot size of the energy source (electron beam, electric arc, plasma, respectively). Fig. 3.11 shows a 1.2 m Ti-6Al-4V wing spar, which was deposited in a flexible enclosure using plasma arc welding with a seven-axis robotic system [32]. The part features straight and curved features, all printed perpendicular to the substrate. Two parts were built simultaneously by alternating deposition on either side of a sacrificial substrate in order to balance and minimize distortion stresses on the substrate plate. The deposition rate was 0.8 kg/h with a buy-to-fly ratio of 1.2.
3.3 Repair and remanufacturing Repair and remanufacturing of worn out and damaged components is an important application area for AM. Fig. 3.12 shows a tool insert with one of the fingers on the top broken during service [33]. Once the tool was scanned and a CAD geometry regenerated, the tool was rebuilt using DMLS technology. Instead of replacing the damaged tool with a new tool, repair of the damaged tool can make significant savings. One of the best application areas suited for DED techniques is repair and remanufacturing. Due to their ability to add metal on selected locations on 3D surfaces, these technologies can be used to rebuild lost material on various components [34 36]. Closed loop technologies, such as
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Figure 3.12 (Left) Damaged tool; (middle) scanned image of the damaged tool; (right) rebuilt tool [33]. Courtesy: EOS North America, Adam J. Penna.
Figure 3.13 DMD repair of turbine components; (left) repaired vane, (middle) macrocross-section, and (right) microstructures (top to bottom show the clad, interface, and base material). Courtesy: DM3D Technology.
DMD, offer the particular benefit of minimum heat-affected zone (HAZ) in the repaired part and help to retain the integrity of the part. The close loop control allows DMD to repair parts with a short HAZ and produce a high-quality repaired part. Fig. 3.13 shows the cross-section microstructures of the DMD area of a remanufactured turbine blade. The excellent process control during DMD leads to a fully dense microstructure as observed in the vertical cross-section. A layer thickness of about 0.1 0.2 mm has been applied in this case and a minimal HAZ is observed in the as-deposited blade. The DMD vision system plays a significant role in this type of remanufacturing. A calibrated vision system integrated with the machine allows automatic identification of part location in the machine coordinate system and provides precision processing. Similar repairs have been demonstrated in rotor drums containing Ti6242 alloy
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Figure 3.14 Die-casting tool repair. (Left) CAD showing the tool and part assembly; (middle) damaged and cracked tool from service; (right) DMD rebuilt tool ready for machining and return to service [38].
blisks (bladed disks) [37]. Other components that can be repaired include housings, bearings, casing flanges, seals, landing gears, etc. Fig. 3.14 shows a DMD-repaired die-casting tool [38]. This H13 tool was extensively worn and the core cracked during an aluminum diecasting process. The tool was premachined to remove damaged material and then rebuilt with 300 Maraging steel using the DMD process. In some cases, AM repair may not be cost effective, however, it offers a significant reduction in lead time and may be critical for defense applications. An example of such a benefit is depicted in Fig. 3.15 [39]. An F/A18 rudder antirotation bracket has been repaired using a laser-based DED process. The original bracket material was 17-4 PH stainless steel with a hardness of HRC 35 38. In order to match this hardness, a mixture of gas-atomized stainless steel SS316 and SS420 powders was used to form deposited layers over the grind out area using a high-power laser and a six-axis robotic equipment with a deposition head. Even though the replacement part cost for this application was not high, the lead time was very long (18 months) and AM repair can be achieved in weeks, making it a useful tool for the end user.
3.4 Hybrid manufacturing for large-part additive manufacturing Directed energy deposition technologies, such as DMD, have the ability to add metal onto 3D surfaces and thus allow the addition of features to existing parts and/or blanks. Even though this capability has been demonstrated on horizontal surfaces with the PBF technology it remains very
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Figure 3.15 Images of the FA-18 rudder antirotation bracket LC repair: (A) pin area damage before repair, (B) after depositing over the grind out area, and (C) after machining [39].
Figure 3.16 Diffuser case produced by adding features with AM on a roll formed Inconel cylinder [40]. Courtesy: DM3D Technology.
limited for now. Adding features to a forged or cast preform as opposed to machining of such features can provide the most cost-effective manufacturing option, where a significant reduction of the preform size and weight can be effected through the elimination of the need for a machining allowance. Examples include various casings and housings in jet engines where flanges, bosses, etc. can be added onto cast or forged cylindrical performs. This is demonstrated for a diffuser case in an aero engine (Fig. 3.16) [40] using a combined hybrid process. First, Inconel sheet metal was roll formed and then laser seam welded to create a cylindrical shape. This was followed by building of bosses and flanges using DMD.
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Figure 3.17 (A) Ti-6Al-4V scaffold [44] and (B) porous Ti-6Al-4V [45] for medical implant applications fabricated using PBF technology.
3.5 Porous structural concepts One of the distinct advantages of AM over conventional manufacturing techniques is its control and ability to build each layer from a predetermined design. This has allowed the use of AM in the medical implant industry to control porosity which facilitates bone growth onto the implant [42,43]. Because of their smaller beam size and ability to build unsupported structures, PBF systems are more suitable to fabricate components with the engineered and/or graded porosity required by applications. Scaffolds with a porosity content up to about 80% and pore size of about 700 μm [44,45] and random porous structures [45] with porosity content up to about 70% and pore size 300 500 μm have been reported using EBM, SLM, and DMLS technologies from Ti-6Al-4V (Fig. 3.17). LENS technology (DED) has been reported to be used to fabricate titanium structures with graded porosity (23% 32%) and corresponding tailored elastic modulus (7 60 GPa) to match that of human cortical bone [46].
3.6 Multimaterial manufacturing using additive manufacturing One unique attribute of AM technologies is their ability to fabricate single components with different materials to perform various functions as required by the application. Since AM involves depositing materials one layer at a time, it allows the introduction of multiple materials at different
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Figure 3.18 (A) As-deposited and finish-machined bimetallic core with H13 steel on a copper base. (B) Microstructure from the bimetallic core showing H13 steel, buffer material, and base copper material [9]. Courtesy: DM3D Technology and David Schwam, Case Western Reserve University.
layers or in the same layer at different locations. This gives AM a clear advantage over all other conventional manufacturing processes and provides superiority to AM components. Fig. 3.18A shows images of a core from an aluminum die-casting tool [9]. The tool has been manufactured using laser-based DMD where H13 tool steel is cladded on a copper base with the application of an intermediate buffer material (Fig. 3.18B). The higher thermal conductivity of copper (almost 6X. that of tool steels) allows the copper base to work as a heat sink and provides faster cooling of cast parts leading to a reduction in cycle times. As a result of cooler core temperatures, dissolution of the core material (commonly called soldering in the die-casting industry) in liquid aluminum is also reduced. Development of such applications is only possible using AM technologies that allow application of multiple materials in a single build to control heat inputs and minimize dilution of layers. The application of multiple metals is not restricted to occur across multiple layers, but can be achieved through dynamic adjustment of the process within a layer. Fig. 3.19 shows a hybrid demonstration part where In718 and a Co Cr alloy have been applied in the same part to create a hybrid structure [47]. The figure on the right shows a CT scan with light areas indicating Co Cr alloy and darker gray indicating In718 alloy. Such capabilities open up the possibility of generating a completely new type of application with high-performance targets. DED technologies are best suited for fabricating multimaterial components, although other AM technologies, such as ultrasonic AM, can also be used. Laser-based AM has been used to create functionally graded coatings of Rene88DT (Ni-base superalloy) on Ti-6Al-4V alloy [48].
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Figure 3.19 Hybrid structure built using DMD technology at the MDF of Oak Rridge National Laboratory [47]. (Left) As-built structure; (right) CT scan showing light gray Co Cr alloy and dark gray Inconel 718.
A controlled experiment produced a continuous gradation of Rene88DT from 0 to 38% Rene88DT alloying over a distance of about 40 mm. This raised the hardness from 450HV to 750HV and transformed the microstructure from columnar α(Ti) 1 β(Ti) to α(Ti) 1 β(Ti) 1 Ti2Ni to equiaxed β(Ti) 1 Ti2Ni (Fig. 3.20). Such precise engineering of microstructures and properties can enhance the performance of components manyfold. Similarly, graded alloying has been performed with Ti Mo alloys and Ti V alloys using other DED technologies [49]. Multilayered hybrid metal laminates have been studied widely for armor applications as gradients of different metals can be used to design highly customized through- thickness mechanical properties. Throughthickness properties such as strength, toughness and stiffness can be varied to produce a system with the highest performance at the lowest weight. Ultrasonic additive manufacturing (sheet lamination) has been used to produce armor panels with a combination of aluminum and titanium alloys (Fig. 3.21) [50]. Typically, layers are in the range of 150 microns and alternated with each layer to build the gradient through-thickness structure.
3.7 Special applications AM allows many special applications that are not possible using conventional manufacturing technologies. Embedding sensors using UAM is one such special application. Since UAM does not involve heat energy during processing, it is possible to embed or encapsulate sensors in metal casings without any damage to the sensors. The solid-state nature of UAM bonds
100
Composition (wt.%)
(A)
0
10
20
30
40
50
60 40
80
30 Ti Ni Co Cr
60 40
20 10
20 0
(C)
0
10 20 30 40 50 Distance from the substrate (mm)
0 60
(D)
Composition (wt.%)
(B) 10
0.1
(E)
Al Mo Nb V
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Figure 3.20 Functionally graded coating of Rene88DT alloy on Ti-6Al-4V using laserbased AM (DED). (A, B) Composition gradients of various elements along the depth from the top surface. The corresponding microstructures are shown in (C) Ti-6Al-4V0%Rene88DT, (D) Ti-6Al-4V-19%Rene88DT, and (E) Ti-6Al-4V-38%Rene88DT [48].
Figure 3.21 Laminated armor after ballistic testing. The part was built using ultrasonic additive manufacturing (UAM) [50]. Courtesy: Adam Hehr and Mark Norfolk, Fabrisonic LLC.
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Figure 3.22 Embedded noninvasive fiberoptic strain sensors into the brackets and struts for drones to measure load. The assembly was manufactured using UAM technology [51]. Photo courtesy: Fabrisonic, Adam Hehr and Mark Norfolk.
allows for encapsulation of wires, fibers, and sensors into metallic substrates for lasting security and reliability, preventing wear and/or impact damages during service of the components. Fig. 3.22 shows an embedded sensor application in aerospace health monitoring [51]. UAM was used to embed noninvasive fiberoptic strain sensors into the brackets and struts for existing drones. The instrumented components were then used in controlled laboratory tests to directly correlate external loads to internal strain at specific locations. Applications like these allow scientists to study failure behaviors and re-engineer components for increased performance in service.
References [1] B. Dutta, F.H. (Sam) Froes, Additive manufacturing of titanium alloys, Adv., Mater. Proc. (2014) 18 23. [2] S. Moylan, J. Slotwinski, A. Cooke, K. Jurrens, M.A. Donmez, An additive manufacturing test artifact, J. Res. Natl. Inst. Standards Technol. 119 (2014) 429 459. Available from: https://doi.org/10.6028/jres.119.017. [3] S. Moylan, J. Slotwinski, A. Cooke, K. Jurrens, M.A. Donmez, NIST Technical Note 1801, Lessons Learned in Establishing the NIST Metal Additive Manufacturing Laboratory, June 2013, pp. 1 37. ,https://doi.org/10.6028/NIST.TN.1801.. [4] E. Yasa, F. Demir, G. Akbulut, N. Cızıo˘glu, S. Pilatin, Benchmarking of different powder-bed metal fusion processes for machine selection in additive manufacturing, Proc. Solid Freeform Fabrication Symp., University of Texas, 2014, pp. 390 403.
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[5] M.B. Bauza, S. P. Moylan, R.M. Panas, S.C. Burke, H.E. Martz, J.S. Taylor, P. Alexander, Study of accuracy of parts produced using additive manufacturing, american Soc. For Prec. Eng., in: 2014 Spring Topical Meeting, vol. 57, pp. 86 91. [6] B. Dutta, S. Palaniswamy, J. Choi, L.J. Song, J. Mazumder, Additive manufacturing by direct metal deposition, Adv. Mater. Processes (May 2011) 33 36. [7] P. Kazanas, P. Deherkar, P. Almeida, H. Lockett, S. Williams, Fabrication of geometrical features using wire and arc additive manufacture, Proc. Inst. MechE Pt. B J. Eng. Manuf. 226 (6) (2012) 1042 1051. Available from: https://doi.org/10.1177/ 0954405412437126. [8] K. Kilgore, M. Hoefing, Private Communication. SLM Solutions, 2019. [9] Private Communication. DM3D Technology, 2016. [10] Mike Cloran, Private Communication. GE Additive, 2019. [11] L.E. Murr, S.M. Gaytan, E. Martinez, F. Medina, R.B. Wicker, Next generation orthopaedic implants by additive manufacturing using electron beam melting, Int. J. Biomater. (2012). 1 Article ID 245727, 14 pages. [12] ,https://www.exone.com/Portals/0/ResourceCenter/Materials/PSC_X1_ MaterialData_17-4_SS_US_012018.pdf. (accessed 31.12.18). [13] ,https://3dprint.com/142052/lockheed-martin-sciaky-ebam/. (accessed 31.12.18). [14] ,https://fabrisonic.com/creating-complex-internal-geometry/. (accessed 31.12.18). [15] ,https://www.eos.info/systems_solutions/metal. (accessed 31.12.18). [16] ,https://slm-solutions.com/. (accessed 31.12.18). [17] ,https://www.concept-laser.de/en/technology.html. (accessed 31.12.18). [18] ,https://www.renishaw.com/en/additive-manufacturing-products--17475. (accessed 31.12.18). [19] M. Koike, P. Greer, K. Owen, G. Lilly, L.E. Murr, S.M. Gaytan, et al., Evaluation of titanium alloys fabricated using rapid prototyping technologies—electron beam melting and laser beam melting, Materials 2011, 4, 1776 1792; ,https://doi.org/ 10.3390/ma4101776.. [20] ,http://dm3dtech.com/index.php?option 5 com_content&view 5 article&id 5 218& Itemid 5 917. (accessed 31.12.18). [21] ,http://www.optomec.com/3d-printed-metals/lens-printers/. (accessed 31.12.18). [22] ,http://www.rpm-innovations.com/index.php?page 5 news-article&id 5 5. (accessed 31.12.18). [23] M.F. Zah, S. Lutzmann, Modelling and simulation of electron beam melting, Prod. Eng. Res. Dev 4 (2010) 15 23. Available from: https://doi.org/10.1007/s11740-009-0197-6. [24] ,http://www.norsktitanium.com/technology. (accessed 31.12.18). [25] ,https://www.aerospacemanufacturinganddesign.com/article/ultrasonic-additivemanufacturing/. (accessed 31.12.18). [26] ,https://www.exone.com/Systems. (accessed 31.12.18). [27] S. Stecker, K.W. Lachenberg, H. Wang, R.C. Salo, Advanced Electron Beam Free Form Fabrication Methods & Technology, AWS Conference, 2006, pp. 35 46. [28] D. Ryan, D. Chad, P. William, Y. Yukinori, C. Wei, B. Craig, et al., Case study: additive manufacturing of aerospace brackets, Adv. Mater. Processes 171 (3) (2013) 19 22. [29] ,https://www.eos.info/press/customer_case_studies/fwb. (accessed 27.12.18). [30] T. Blumenthal, N. Wald, Private communication. RPM Innovations. 2019. [31] ,https://www.exone.com/Portals/0/ResourceCenter/CaseStudies/ X1_CaseStudies_All%209.Pdf. (accessed 01.01.19). [32] S.W. Williams, F. Martina, A.C. Addison, J. Ding, G. Pardal, P. Colegrove, Wire 1 arc additive manufacturing, Mater. Sci. Technol. 32 (7) (2016) 641 647. [33] ,https://www.eos.info/industries_markets/tooling/tool_repair. (accessed 01.01.19). [34] A. Harooni, B. Dutta, The Use of Direct Metal Deposition (DMD) Additive Manufacturing on Forging Dies, Forge Magazine, Feb 2019, vol 11, No 1, 22 25.
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[35] B. Dutta, S. Palaniswami, J. Choi, J. Mazumder, Rapid manufacturing and remanufacturing of DoD components using direct metal deposition, AMMTIAC Q. 6 (2) (2012) 5 9. [36] B. Dutta, H. Natu, J. Mazumder, Near net shape repair and remanufacturing of high value components using DMD, in: TMS Proceedings, vol. 1: Fabrication, Materials, Processing and Properties, 2009, pp. 131 138. [37] K.H. Richter, S. Orban, S. Nowotny, Proceedings of the 23rd International Congress on Applications of Lasers and Electro-Optics 2004. [38] D. Schwam, M. Kottman, B. Dutta, Repair of die casting inserts by laser direct metal deposition, NADCA Congress Proceedings, March 2014, pp. 1 7. [39] Q. Liu, R. Djugum, S. Sun, K. Walker, J. Choi, M. Brandt, Repair and manufacturing of military aircraftcomponents by additive manufacturing technology, 17th Australian Aerospace Congress, 26 28 February 2017, Melbourne, pp. 363 368. [40] F.H. (Sam) Froes, R. Boyer, B. Dutta, Additive manufacturing for aerospaceapplications—PART II, Adv. Mater. Processes 175 (2) (2017) 18 22. [41] A.T. Sidambe, Biocompatibility of advanced manufactured titanium implants—A Review, Materials 7 (2014) 8168 8188. Available from: https://doi.org/10.3390/ ma7128168. [42] Z.J. Wally, W. van Grunsven, F. Claeyssens, R. Goodall, G.C. Reilly, Porous titanium for dental implant applications, Metals 5 (2015) 1902 1920. Available from: https://doi.org/10.3390/met5041902. [43] J. Wieding, A. Jonitz, R. Bader, The effect of structural design on mechanical properties and cellular response of additive manufactured titanium scaffolds, Materials 5 (2012) 1336 1347. Available from: https://doi.org/10.3390/ma5081336. [44] A. Jonitz-Heincke, J. Wieding, C. Schulze, D. Hansmann, R. Bader, Comparative analysis of the oxygen supply and viability of human osteoblasts in three-dimensional titanium scaffolds produced by laser-beam or electron-beam melting, Materials 6 (2013) 5398 5409. Available from: https://doi.org/10.3390/ma6115398. [45] T.B. Kim, S. Yue, Z. Zhang, E. Jones, J.R. Jones, P.D. Lee, Additive manufactured porous titanium structures: Through-process quantification of pore and strut networks, J. Mater. Process. Technol. 214 (2014) 2706 2715. [46] A. Bandyopadhyay, F. Espana, V.K. Balla, S. Bose, Y. Ohgami, N.M. Davies, Influence of porosity on mechanical properties and in vivo response of Ti6Al4V implants, Acta Biomater. 6 (2010) 1640 1648. [47] E. Cakman, N. Sridharan, S.V. Venkatakrishnan, H.Z. Bilheux, L.J. Santodonato, A. Shyam, et al., Feasibility study of making metallic hybrid materials using additive manufacturing, Metall. Mater. Trans. A 49A (2018) 5035 5041. [48] X. Lin, T.M. Yue, H.O. Yang, W.D. Huang, Solidification behavior and the evolution of phase in laser rapid forming of graded ti6al4v-rene88dt alloy, Metal. Mater. Trans. A 38A (2007) 127 137. Available from: https://doi.org/10.1007/s11661006-9021-5. [49] P.C. Collins, R. Banerjee, S. Banerjee, H.L. Fraser, Laser deposition of compositionally graded titanium vanadium and titanium molybdenum alloys, Mater. Sci. Eng. A352 (2003) 118 128. Available from: https://doi.org/10.1016/S0921-5093(02) 00909-7. [50] M. Norfolk, Private Communication, Fabrisonic LLC, Received on Dec 30, 2015. [51] ,https://fabrisonic.com/embedded-electronics-sensors/. (accessed 01.01.19).
Comparison of various additive manufacturing technologies Abbreviations AM BJ CAD CT 3D DED DM DMD DMLS EBM EBAM ELI HAZ HIP LENS MDF ORNL PBF RPD SL SLM SLS UAM WAAM
Additive manufacturing Binder jetting Computer-aided design Computed tomography Three-dimensional Direct energy deposition Direct manufacturing Direct metal deposition Direct metal laser sintering Electron beam melting Electron beam additive manufacturing Extra low interstitial Heat-affected zone Hot isostatic press Laser engineered net shaping Manufacturing Demonstration Facility Oak Ridge National Laboratory Powder bed fusion Rapid plasma deposition Sheet lamination Selective laser melting Selective laser sintering Ultrasonic additive manufacturing Wire arc additive manufacturing
3.1 Technology comparison The various metal additive manufacturing (AM) technologies offer different capabilities [1]. While some of these technologies compete with one another, technologies of different categories are more complimentary. Each of these categories offers its own distinct benefits, but also has some limitations. While powder bed fusion (PBF) technologies are suitable for smaller, complex geometries, with hollow unsupported passages/structures, directed energy deposition (DED) is better suited for larger parts with coarser features, requiring higher deposition rates. The use of fine Science, Technology and Applications of Metals in Additive Manufacturing DOI: https://doi.org/10.1016/B978-0-12-816634-5.00003-0
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powder grains combined with smaller laser/electron beam size leads to a superior surface finish on as-built parts from PBF technologies as compared with directed energy deposition technologies. However, the majority of AM production parts need some form of finish machining for most applications. The ability of the directed energy technologies to add metal to existing parts enables them to apply surface-protective coatings, remanufacture and repair damaged parts, and reconfigure or add features to existing parts, in addition to building new parts. Binder jet technology offers low residual stress, and therefore has some distinct advantages in certain applications. Sheet lamination is good for embedded sensors, multimaterial and some special applications. PBF technologies use small layer thickness and support of the powder bed to create overhangs. However, depending on the angle of the overhang, there can be some distortion to the surface, as shown in Fig. 3.1. This test artifact was built using direct metal laser sintering (DMLS) technology and the material is stainless steel. In addition to the poorly formed surfaces, the magnified bottom picture in the figure shows the singed (blackened) and distorted upper surface of the feature intended to be square. There is similar (though less severe) distortion and singeing on the top of the 6 mm cylindrical features. The diamond features with the upper half-angle at 45 and 30 degree angles are not singed or deformed. Therefore, steeper angles produce a better surface finish and dimensional accuracy for the overhangs. Features with angles less than 45 degrees from the vertical axis, may not need support structures. The ability of the PBF
Figure 3.1 PBF (DMLS) built test artifact showing the capability to build overhangs [2,3].
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Figure 3.2 Test artifacts built using AM. (Left) Stainless steel part using DMLS technology; (right) Ti-6Al-4V part using EBM technology [2].
process to produce such closed overhangs allows these technologies to build components with passageways for cooling fluids, etc. and/or to reduce the weight of the parts by designing cavities. Various tests have been performed to estimate the degree of overhang, feature resolution, and surface finish possible using the PBF process. Fig. 3.2 shows two test artifacts produced using laser-based and electron beam-based PBF technologies. While there are subtle differences between various PBF machines [4], all in all, the feature resolution and overhang capability of PBF is greater than DED technologies. Parts built using DMLS and electron beam melting (EBM) are shown from left to right in the figure, respectively. The small laser/electron beam sizes of PBF technologies also allow them to build finer structures with small wall thicknesses. Fig. 3.3 shows a 3 3 3 3 3 octate lattice truss built using DMLS technology [5]. Fig. 3.3 also shows side and top views from computed tomography (CT) scans of the same structure showing the struts of the truss. The red lines mark the intended CAD and the solid gray color is the actual build. A maximum deviation of 100 μm from the CAD was recorded during measurements. As compared to the PBF technologies, DED technologies rely on their multiaxes deposition capability to create an overhang. However, the larger laser/electron beam/plasma/arc spot size and greater layer thickness limit this capability. Fig. 3.4 shows overhangs built using laser-based (DMD) [6] and electric arc-based (WAAM) [7] DED technologies. Due to the relatively smaller laser spot size compared to the electric arc beam size, laserbased DED offers better resolution and more complexity than arc-based systems. Fig. 3.5 shows a pictorial comparison of various metal AM technologies in terms of their size, build rate, and ability to produce complex
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Figure 3.3 (Left) DMLS-built octate truss structure. (Middle and right) Side and top views from a CT scan of the structure, respectively [5].
Figure 3.4 Overhangs built using DED technologies. (Left) DMD (laser-based DED)[6] and (right) WAAM (wire arc additive manufacturing)-built [7] structures.
geometries. PBF and BJ technologies offer the highest level of part complexity, while wire arc-based DED and sheet lamination (SL) allow the simplest capability with laser-based DED offering a medium level of complexity in the parts. However, the WAAM and EBAM process offer very high deposition rates (build rates) as compared to PBF technologies. These differences are more quantitatively demonstrated in Fig. 3.6 by plotting capabilities of specific commercially available AM technologies [15 26]. For each technology category, such as PBF or DED, several manufacturers and several machine models have been represented in the graph to show the available range of options. Note that the data are not exhaustive and there are many more DED and PBF manufacturers that are not in the list, however, the figure is representative of the capability of the respective technologies. Clearly, the build volume and deposition rates are much higher in DED technologies, while the surface finish, feature resolution, and layer thickness are all coarser. Table 3.1 summarizes the features, capabilities, benefits, and limitations of various AM technologies that are used currently for producing metal AM parts [15 26]. The layer thickness of the AM parts plays a major role in defining the surface roughness of vertical walls of the structure being
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Figure 3.5 Pictorial demonstration of part complexity and size capability of various metal AM technologies. As the size capability of the parts increases from PBF to BJ to DED, material throughput (build rate) also increases, but the ability to build complex geometries reduces. Note that the parts in the figure are not scaled to size [8 14]. DMLS (PBF) built tibial implant, photo courtesy: Lawrence Murr, University of Texas, El Paso; EBM (PBF) built hydraulic manifold, photo courtesy: Oak Ridge National Laboratory, US Department of Energy; EBM (PBF) built acetabular cup, photo courtesy: Mike Cloran, GE Additive; SLM (PBF) built pump housing, photo courtesy: Kristal Kilgore and Mark Hoefing, SLM Solutions; Binder Jet built components, photo courtesy: Mike Shepherd, ExOne; UAM (Sheet Lamination) built components, photo courtesy: Adam Hehr and Mark Norfolk, Fabrisonic; DMD (Laser DED) built diffuser case, forging tool, and repaired turbine support case, photo courtesy: DM3D Technology; WAAM (DED) built Titanium wing spar, photo courtesy: Mark Potter and Stephen Morgan, BAE Systems; EBAM (DED) built titanium propellant tank, photo courtesy: Mark Lewis, Lockheed Martin Corp.
built, while beam size (laser or electron beam) together with step over (or hatch spacing) influence the roughness of the horizontal surfaces. PBF technologies offer a better surface finish as these use a smaller beam size (for both laser and electron beam), shorter hatch spacing, and smaller layer thickness compared to DED technologies, however, as a consequence the deposition rate is also lower for these technologies. Therefore, PBF is more suitable for more accurate, complex small-sized objects, while DED is more suitable for building larger parts at a high processing rate, but with a coarser finish surface. Since DED technologies rely on deposition
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Figure 3.6 Quantitative representation of technology and machine capability of some PBF, DED, BJ, and SL manufacturers. Note that this graph is purely a representation of these capabilities and does not include all manufacturers or all systems from every manufacturer [15 26].
Table 3.1 Comparison of various technologies [15 27]. Powder bed fusion (PBF)
Directed energy deposition (DED)
Binder jetting (BJ)
Sheet lamination (SL)
Ultrasonic energy
UAM
Large, up to 1524 3 1524 3 914
Energy source
Laser (Single, dual or quad laser up to 1 kW)
Electron beam (up to 6 kW)
Laser (up to 8 kW)
Electron beam (up to 42 kW)
Gas tungsten arc or plasma
Technologies
EBM
DMD, LENS, LDT, DED
EBAM
RPD/WAAM
Build envelope (mm)
DMLS, SLM, laser cusing, LM, LBM, DMP Limited, up to 800 3 400 3 500
Binder for powder adhesion, followed by sintering in furnace BJ
Large and flexible, 1425 3 1020 3 1020
Very large, 5791 3 1219 3 1219
Large and flexible, 900 3 600 3 300
Medium, up to 800 3 500 3 400
Beam/bead size
Small, 0.1 0.5 mm
Limited, 250 diameter 3 430 height Small, 0.2 1 mm
Not available
1 12 mm
Wall thickness Layer thickness Build rate
0.15 0.3 mm Small, 25 100 μm Low, 6 171 cc/h
0.25 mm Small, 50 100 μm Low, 55 80 cc/h
Large, can vary from 2 to 4 mm 1 4 mm Large, 500 1000 μm Medium, 16 320 cc/h
N/A 150 μm NA
Very good, Ra 9 12 μm, Rz 35/40 μm
Good, Ra 25/ 35 μm
1 12 mm 1 4 mm Very high 1128 2257 cc/h Coarse, Ra 200 μm
.1.5 mm 150 μm High 900 1350 cc/h
Surface finish
2.5 6.25 mm NA Very high 717 2050 cc/h Very coarse
Very good, Ra 15 μm
N/A
Relative density Residual stress
High .99% High
High .99% Minimal
High .99% Very high
98% after sintering Very low
High .99% Low
Heat treatment
Stress relief preferred, HIP’ing preferred
Stress relief not required, HIP’ing may/ may not be performed
High .99% High in substrate, low in deposit Stress relief required, HIP’ing may/may not be performed
Stress relief preferred, HIP’ing preferred
Mandatory for sintering, densification and strength
May be required for interdiffusion between layers
Medium, Ra 20 50 μm, Rt 150 300 μm, depends on beam size High .99% High Stress relief preferred, HIP’ing preferred
N/A
(Continued)
Table 3.1 (Continued) Powder bed fusion (PBF)
Chemistry
Negligible loss of elements
Build capability
Complex geometry possible with very high resolution. Capable of building internal features and channels
Repair/ remanufacture
Possible only in limited applications (requires horizontal plane to begin remanufacturing)
Feature/metal addition on existing parts
Possible only in limited applications (requires horizontal surface for starting point) Not possible
Not possible
Multimaterial build or hard coating Machining in the build chamber
Loss of elements (such as Al) needs to be compensated in powder Complex geometry possible with good resolution. Capable of building internal features and channels Not possible
Directed energy deposition (DED)
Binder jetting (BJ)
Sheet lamination (SL)
Negligible loss of elements
Loss of elements (such as Al) needs to be compensated in powder
Negligible loss of elements
Negligible loss of elements
No loss of elements
Relatively simpler geometry with less resolution. Limited capability for internal features and channels, etc.
Simple geometry with low resolution. No internal features and channels
Simple geometry with low resolution. No internal features and channels
Simple geometry with low resolution. Limited capability in internal features and channels
Limited
Possible
Not possible
Limited capability
Possible
Not possible
Not possible
Not possible
Possible (capable of adding metal on 3D surfaces under 5 1 1-axis configuration making repair solutions attractive) Possible. Depending on dimensions ID cladding is also possible Possible
Complex geometry possible with good resolution. Capable of building internal features and channels Not possible
Not possible
Possible
Not possible
Possible
Not possible
Possible
Not possible
Possible
Possible
Possible (part of the process)
Not possible
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processes, they are able to add metal onto an existing part. This critical capability of DED allows it to repair and remanufacture damaged parts. This also gives DED technologies the ability to add multiple metals in a single build leading to its multimaterial processing capability. BJ technologies have the benefit of very low residual stress and are useful for many applications, while SL is good for special applications involving embedded components, e.x. sensors. The following section describes different application capabilities of metal AM technologies.
3.2 Free form capability Small beam size and layer thickness, along with the support of the powder bed, allow PBF technologies, such as EBM, DMLS, or SLS, to produce complex geometries with high precision and unsupported structures. Fig. 3.7 shows one such example of a hydraulic manifold mount for an underwater manipulator built using EBM technology. Building the integrated mount and manifold with internal passageways in a single operation eliminates multiple part fabrication and results in significant cost savings. The good surface finish of the part eliminated finish machining needs on all surfaces, except seal surfaces and threading of screw holes. Generally the PBF technique gives a better surface finish than the DED approach,
Figure 3.7 Hydraulic manifold built using EBM technology. The part was built at the Manufacturing Demonstration Facility (MDF) at the Oak Rridge National Laboratory (ORNL). Courtesy: Oak Ridge National Laboratory, Department of Energy.
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Figure 3.8 Injection mold core using DMLS technology. (Left) CAD design showing internal cooling channels. (Right) DMLS-built actual core using 300 Maraging steel [29]. Courtesy: EOS North America, Adam J. Penna.
however for demanding applications (such as in aerospace) finish machining and/or other surface finishing operations are still required [28]. Fig. 3.8 shows an injection molding core built using DMLS technology [29]. This tool represents one core in a 16-core production tool for injection molding plastic parts. The left side shows a CAD model of the tool with internal cooling channels and the right side shows the actual tool built using 300 Maraging steel. The ability of PBF technologies to produce three-dimensional cooling passages following the part contours allows such tool building. One benefit of this is the placement of cooling channels closer to the part surface, leading to faster and uniform plastic cooling, which results in a shorter cycle time and better part quality. These capabilities are unique to PBF processes and/or BJ (binder jetting). Fig. 3.9 shows a Grid Fin part made using In718 alloy with laser DED process (LMD) [30]. Even though all three parts are identical, different process parameters have been used to build these parts. The part on the left used only 1070 W laser power, 17 cc/h deposition rate resulting in 30.5 h deposition time. The part in the middle used 1700 W laser power, 33 cc/h deposition rate resulting in 17 h deposition time, but a rougher surface finish. In contrast, the part on the right used 2620 W laser power, 66 cc/h deposition rate, and resulted in fastest processing for 8.5 h. However, the surface finish was the coarsest of all. This clearly illustrates that in AM there are various ways to build a part and a careful consideration of the build strategy and process optimization is essential depending on part geometry, material, and commercial requirements.
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Figure 3.9 In718 grid fins built using LMD (laser-based DED) technology with variable deposition rates [30]. The part on the left was built using lowest laser power (1070 W) and deposition rate (17 cc/h). The part in the middle used higher laser power (1700 W) and deposition rate (33 cc/h), while the part on the right used highest laser power (2620 W) and highest deposition rate (66 c/h). Courtesy: RPM Innovations, Tyler Blumenthal, and Nick Wald.
Figure 3.10 Binder jet (BJ) built stator part. The material is S4 stainless steel and bronze [31]. Photo courtesy: ExOne, Mike Shepherd.
BJ technologies also allow fine-featured part build up with internal geometries. However, during the subsequent furnace sintering process to enhance the strength, part distortion will occur and must be accounted during design and processing. Fig. 3.10 shows a stator part made of S4 stainless steel and bronze [31]. The part replaced a traditionally manufactured 4140 steel stator that would usually be machined out of a solid
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Figure 3.11 Ti-6Al-4 V wing spar built using a WAAM system; top view and side view [32]. Photo courtesy: BAE Systems, Mark Potter and Stephen Morgan.
blank, resulting in significant cost saving. In addition, S4 stainless steel provides better abrasion resistance and longer life for the component. Some DED technologies, such as EBAM, WAAM, and rapid plasma deposition (RPD), are particularly suited for processing very large components with simple geometries due to their very high deposition rate and the large spot size of the energy source (electron beam, electric arc, plasma, respectively). Fig. 3.11 shows a 1.2 m Ti-6Al-4V wing spar, which was deposited in a flexible enclosure using plasma arc welding with a seven-axis robotic system [32]. The part features straight and curved features, all printed perpendicular to the substrate. Two parts were built simultaneously by alternating deposition on either side of a sacrificial substrate in order to balance and minimize distortion stresses on the substrate plate. The deposition rate was 0.8 kg/h with a buy-to-fly ratio of 1.2.
3.3 Repair and remanufacturing Repair and remanufacturing of worn out and damaged components is an important application area for AM. Fig. 3.12 shows a tool insert with one of the fingers on the top broken during service [33]. Once the tool was scanned and a CAD geometry regenerated, the tool was rebuilt using DMLS technology. Instead of replacing the damaged tool with a new tool, repair of the damaged tool can make significant savings. One of the best application areas suited for DED techniques is repair and remanufacturing. Due to their ability to add metal on selected locations on 3D surfaces, these technologies can be used to rebuild lost material on various components [34 36]. Closed loop technologies, such as
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Figure 3.12 (Left) Damaged tool; (middle) scanned image of the damaged tool; (right) rebuilt tool [33]. Courtesy: EOS North America, Adam J. Penna.
Figure 3.13 DMD repair of turbine components; (left) repaired vane, (middle) macrocross-section, and (right) microstructures (top to bottom show the clad, interface, and base material). Courtesy: DM3D Technology.
DMD, offer the particular benefit of minimum heat-affected zone (HAZ) in the repaired part and help to retain the integrity of the part. The close loop control allows DMD to repair parts with a short HAZ and produce a high-quality repaired part. Fig. 3.13 shows the cross-section microstructures of the DMD area of a remanufactured turbine blade. The excellent process control during DMD leads to a fully dense microstructure as observed in the vertical cross-section. A layer thickness of about 0.1 0.2 mm has been applied in this case and a minimal HAZ is observed in the as-deposited blade. The DMD vision system plays a significant role in this type of remanufacturing. A calibrated vision system integrated with the machine allows automatic identification of part location in the machine coordinate system and provides precision processing. Similar repairs have been demonstrated in rotor drums containing Ti6242 alloy
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Figure 3.14 Die-casting tool repair. (Left) CAD showing the tool and part assembly; (middle) damaged and cracked tool from service; (right) DMD rebuilt tool ready for machining and return to service [38].
blisks (bladed disks) [37]. Other components that can be repaired include housings, bearings, casing flanges, seals, landing gears, etc. Fig. 3.14 shows a DMD-repaired die-casting tool [38]. This H13 tool was extensively worn and the core cracked during an aluminum diecasting process. The tool was premachined to remove damaged material and then rebuilt with 300 Maraging steel using the DMD process. In some cases, AM repair may not be cost effective, however, it offers a significant reduction in lead time and may be critical for defense applications. An example of such a benefit is depicted in Fig. 3.15 [39]. An F/A18 rudder antirotation bracket has been repaired using a laser-based DED process. The original bracket material was 17-4 PH stainless steel with a hardness of HRC 35 38. In order to match this hardness, a mixture of gas-atomized stainless steel SS316 and SS420 powders was used to form deposited layers over the grind out area using a high-power laser and a six-axis robotic equipment with a deposition head. Even though the replacement part cost for this application was not high, the lead time was very long (18 months) and AM repair can be achieved in weeks, making it a useful tool for the end user.
3.4 Hybrid manufacturing for large-part additive manufacturing Directed energy deposition technologies, such as DMD, have the ability to add metal onto 3D surfaces and thus allow the addition of features to existing parts and/or blanks. Even though this capability has been demonstrated on horizontal surfaces with the PBF technology it remains very
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Figure 3.15 Images of the FA-18 rudder antirotation bracket LC repair: (A) pin area damage before repair, (B) after depositing over the grind out area, and (C) after machining [39].
Figure 3.16 Diffuser case produced by adding features with AM on a roll formed Inconel cylinder [40]. Courtesy: DM3D Technology.
limited for now. Adding features to a forged or cast preform as opposed to machining of such features can provide the most cost-effective manufacturing option, where a significant reduction of the preform size and weight can be effected through the elimination of the need for a machining allowance. Examples include various casings and housings in jet engines where flanges, bosses, etc. can be added onto cast or forged cylindrical performs. This is demonstrated for a diffuser case in an aero engine (Fig. 3.16) [40] using a combined hybrid process. First, Inconel sheet metal was roll formed and then laser seam welded to create a cylindrical shape. This was followed by building of bosses and flanges using DMD.
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Figure 3.17 (A) Ti-6Al-4V scaffold [44] and (B) porous Ti-6Al-4V [45] for medical implant applications fabricated using PBF technology.
3.5 Porous structural concepts One of the distinct advantages of AM over conventional manufacturing techniques is its control and ability to build each layer from a predetermined design. This has allowed the use of AM in the medical implant industry to control porosity which facilitates bone growth onto the implant [42,43]. Because of their smaller beam size and ability to build unsupported structures, PBF systems are more suitable to fabricate components with the engineered and/or graded porosity required by applications. Scaffolds with a porosity content up to about 80% and pore size of about 700 μm [44,45] and random porous structures [45] with porosity content up to about 70% and pore size 300 500 μm have been reported using EBM, SLM, and DMLS technologies from Ti-6Al-4V (Fig. 3.17). LENS technology (DED) has been reported to be used to fabricate titanium structures with graded porosity (23% 32%) and corresponding tailored elastic modulus (7 60 GPa) to match that of human cortical bone [46].
3.6 Multimaterial manufacturing using additive manufacturing One unique attribute of AM technologies is their ability to fabricate single components with different materials to perform various functions as required by the application. Since AM involves depositing materials one layer at a time, it allows the introduction of multiple materials at different
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Figure 3.18 (A) As-deposited and finish-machined bimetallic core with H13 steel on a copper base. (B) Microstructure from the bimetallic core showing H13 steel, buffer material, and base copper material [9]. Courtesy: DM3D Technology and David Schwam, Case Western Reserve University.
layers or in the same layer at different locations. This gives AM a clear advantage over all other conventional manufacturing processes and provides superiority to AM components. Fig. 3.18A shows images of a core from an aluminum die-casting tool [9]. The tool has been manufactured using laser-based DMD where H13 tool steel is cladded on a copper base with the application of an intermediate buffer material (Fig. 3.18B). The higher thermal conductivity of copper (almost 6X. that of tool steels) allows the copper base to work as a heat sink and provides faster cooling of cast parts leading to a reduction in cycle times. As a result of cooler core temperatures, dissolution of the core material (commonly called soldering in the die-casting industry) in liquid aluminum is also reduced. Development of such applications is only possible using AM technologies that allow application of multiple materials in a single build to control heat inputs and minimize dilution of layers. The application of multiple metals is not restricted to occur across multiple layers, but can be achieved through dynamic adjustment of the process within a layer. Fig. 3.19 shows a hybrid demonstration part where In718 and a Co Cr alloy have been applied in the same part to create a hybrid structure [47]. The figure on the right shows a CT scan with light areas indicating Co Cr alloy and darker gray indicating In718 alloy. Such capabilities open up the possibility of generating a completely new type of application with high-performance targets. DED technologies are best suited for fabricating multimaterial components, although other AM technologies, such as ultrasonic AM, can also be used. Laser-based AM has been used to create functionally graded coatings of Rene88DT (Ni-base superalloy) on Ti-6Al-4V alloy [48].
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Figure 3.19 Hybrid structure built using DMD technology at the MDF of Oak Rridge National Laboratory [47]. (Left) As-built structure; (right) CT scan showing light gray Co Cr alloy and dark gray Inconel 718.
A controlled experiment produced a continuous gradation of Rene88DT from 0 to 38% Rene88DT alloying over a distance of about 40 mm. This raised the hardness from 450HV to 750HV and transformed the microstructure from columnar α(Ti) 1 β(Ti) to α(Ti) 1 β(Ti) 1 Ti2Ni to equiaxed β(Ti) 1 Ti2Ni (Fig. 3.20). Such precise engineering of microstructures and properties can enhance the performance of components manyfold. Similarly, graded alloying has been performed with Ti Mo alloys and Ti V alloys using other DED technologies [49]. Multilayered hybrid metal laminates have been studied widely for armor applications as gradients of different metals can be used to design highly customized through- thickness mechanical properties. Throughthickness properties such as strength, toughness and stiffness can be varied to produce a system with the highest performance at the lowest weight. Ultrasonic additive manufacturing (sheet lamination) has been used to produce armor panels with a combination of aluminum and titanium alloys (Fig. 3.21) [50]. Typically, layers are in the range of 150 microns and alternated with each layer to build the gradient through-thickness structure.
3.7 Special applications AM allows many special applications that are not possible using conventional manufacturing technologies. Embedding sensors using UAM is one such special application. Since UAM does not involve heat energy during processing, it is possible to embed or encapsulate sensors in metal casings without any damage to the sensors. The solid-state nature of UAM bonds
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Figure 3.20 Functionally graded coating of Rene88DT alloy on Ti-6Al-4V using laserbased AM (DED). (A, B) Composition gradients of various elements along the depth from the top surface. The corresponding microstructures are shown in (C) Ti-6Al-4V0%Rene88DT, (D) Ti-6Al-4V-19%Rene88DT, and (E) Ti-6Al-4V-38%Rene88DT [48].
Figure 3.21 Laminated armor after ballistic testing. The part was built using ultrasonic additive manufacturing (UAM) [50]. Courtesy: Adam Hehr and Mark Norfolk, Fabrisonic LLC.
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Figure 3.22 Embedded noninvasive fiberoptic strain sensors into the brackets and struts for drones to measure load. The assembly was manufactured using UAM technology [51]. Photo courtesy: Fabrisonic, Adam Hehr and Mark Norfolk.
allows for encapsulation of wires, fibers, and sensors into metallic substrates for lasting security and reliability, preventing wear and/or impact damages during service of the components. Fig. 3.22 shows an embedded sensor application in aerospace health monitoring [51]. UAM was used to embed noninvasive fiberoptic strain sensors into the brackets and struts for existing drones. The instrumented components were then used in controlled laboratory tests to directly correlate external loads to internal strain at specific locations. Applications like these allow scientists to study failure behaviors and re-engineer components for increased performance in service.
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