Mark Norfolk - Paper

8/6/2019 Mark Norfolk - Paper

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A VERY HIGH-POWER ULTRASONICADDITIVE MANUFACTURING

SYSTEM FOR ADVANCEDMATERIALS

Mark Norfolk, Matt Short, Karl GraffEdison Welding Institute

Columbus, Ohio


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ABSTRACT

Ultrasonic additive manufacturing (UAM) has found several applications in the fieldof metal-based additive manufacturing, such as injection molding dies and sensors.In order to expand the range of uses, it is important to increase the range of

materials, part volumes, and production speeds that can be dealt with by thetechnology. EWI, cooperating with Solidica, several industry, agency, and academicpartners, and with the support of the State of Ohios Wright Program, is developing aVery High-Power Ultrasonic Additive Manufacturing System (VHP UAM) intendedto address certain limits of the present technology. A key part of the development isthe design of a 9.0-kW Push-Pull ultrasonic system able to produce sound welds inadvanced materials. This aspect has already been demonstrated on a VHP TestBed, where welding of materials such as Ti 6-4, 316SS, 1100 Cu, and Al7075 hasbeen demonstrated. The higher ultrasonic power levels are expected to permitwelding thicker, wider metal tapes at higher production speeds and for larger parts.The VHP system that is being installed will be capable of fabricating metal parts

having lineal dimensions of up to 1.5 1.5 0.6 m, and will be described.Accompanying process and software developments enable the new system to dealwith contoured surfaces. Several applications of the current technology will bereviewed including solid metal parts with embedded channels for thermalmanagement, metal matrix composites (MMC) for structural materials, embeddedshape memory alloys (SMA) for active stiffness control, composite-to-metal transitionparts, and solid-state cladding for petro-chemical applications.

Acknowledgements: The support of Ohios Third Frontier Wright Project and teampartners Boeing, General Electric, Lockheed-Martin, Army Research Laboratory,Solidica, and The Ohio State University in carrying out this development isacknowledged.


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1 INTRODUCTION

Ultrasonic additive manufacturing (UAM) has found several applications in the fieldof metal-based additive manufacturing, such as injection molding dies and sensors(Gibson, 2010). In order to expand the range of uses, it is important to increase the

range of materials, part volumes, and production speeds that can be dealt with bythe technology. EWI, cooperating with Solidica, several industry, agency, andacademic partners, and with the support of the State of Ohios Wright Program, isdeveloping a Very High-Power Ultrasonic Additive Manufacturing System (VHPUAM) intended to address limitations of the present technology (Graff, 2008).

The key features of the VHP UAM system will be described, including a 9.0-kWPush-Pull ultrasonic system, a VHP Test Bed that has demonstrated systemfeasibility and the full-scale VHP system that will have been recently installed. Anumber of applications, demonstrated on both UAM and VHP UAM systems will bereviewed, including those involving bonding of advanced materials.

2 UAM TECHNOLOGY

The UAM process consists of building up solid metal objects through ultrasonicallywelding successive layers of metal tape into a three-dimensional shape, withperiodic machining operations to create the detailed features of the resultant object(White, 2002). The key features of the process are shown in Figure 1. Thus, Figure1(a) shows a rolling ultrasonic welding system, consisting of an ultrasonictransducer, a booster, the (welding) horn, and a second dummy booster. Thevibrations of the transducer are transmitted to the disk-shaped welding horn (which isalso referred to as the sonotrode, a term used in ultrasonic metal welding) rolling inthe x-direction, and from there to the tape-metal base, which creates an ultrasonicsolid-state weld between the thin metal tape (shown as Al in the figure) and a baseplate. The continuous rolling of the horn over the tape welds the entire tape to theplate.

By welding a succession of tapes, first side by side, then one on top of the other (butstaggered so that seams do not overlap), it becomes possible to build a solid metalpart, as shown in Figure 1(b). Through the course of the build, there will be periodicmachining operations, using an integrated CNC system, to add features to the part,

as suggested by the slot in Figure 1(b), to remove excess tape material and to trueup the topmost surface of the part. Thus, the process also involves subtractive aswell as additive steps.

Examples of UAM fabricated parts and some of the unusual capabilities of theprocess are shown in Figure 2, with Figure 2(a) showing the mold (or cavity)component of an injection molding die, made from 3003 Al, and approximately 100-mm W 150-mm L 20-mm T the associated plastic part is also shown. Figures2(b,c) show another UAM capability, that of creating embedded channels. As a partbuild progresses, open channels are machined at one stage and then covered by thenext welding stage(s). The apparently solid Al block (100-mm W 100-mm L 13-

mm T) of Figure 2(b) is shown by X-ray in Figure 2(c) to consist of a complex,


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multilevel, interconnected network of channels. Channel sizes can range from 2

mm, down to 10-20 m.

Yet another UAM capability is that of embedding materials within a metal matrix.This can take the form of tapes, wires, meshes or fibers, and is illustrated for

embedded Mo tapes in Figure 2(d). The approach is to build the part to a desiredheight, then lay down individual or multiple wires or tapes and then weld the nexttape layer which covers and embeds the underlying wires/tapes.

3 VHP UAM SYSTEM

UAM systems typically operate at 1.5-3.0 kW and encounter some issues in seekingto bond advanced materials, such as Ti alloys, stainless steels, Cu alloys, advancedAl, and Ni-based alloys. Limits are also encountered in bonding thicker tapes and inincreasing production speeds, which also tends to place limits on overall part sizes

that can be considered.

To a significant extent, all of these issues can be related to the need to apply greaterultrasonic power to the bonding process. Since making the ultrasonic bond dependson being able to shear and plastically deform opposing asperities at the tapeinterfaces, with increasing alloy strengths greater interface shearing forces arerequired to bring about the necessary interface deformations which directly requireincreased ultrasonic power (de Vries, 2004). Likewise, the mass associated withincreased tape thicknesses and/or widths requires increased power to be able todrive it in ultrasonic vibrations.

3.1 Approach for VHPThe technique for achieving higher levels of ultrasonic power is shown in Figure 3.Current UAM technology, shown in Figure 3(a), is powered by a single ultrasonictransducer of 1.5 to 2.0 kW, resulting in sharp limitations in materials and parts thatcan be fabricated. It was determined that it would be possible to make a significantjump in ultrasonic power by combining two transducers, each of 4.5-kW power, in aso-called push-pull configuration to arrive at 9.0-kW capacity as shown in Figure 3(b)(Short, 2008). Subsequent development of yet higher power transducers, configuredfor the UAM system, will permit yet higher powers, and hence greater performance,to be achieved.

3.2 VHP module and test bedIt was felt critical, before proceeding to design/construction of the full VHP UAMsystem to prove out the operation of the push-pull ultrasonic system. This was doneby designing the 9.0-kW module and incorporating it into a test bed to test its weldingcapabilities. These developments are shown in Figures 4 and 5.

Thus, a drawing of the 9.0-kW push-pull module is shown in Figure 4(a), andconsists of the two high-power ultrasonic transducers and the welding sonotrode.Referring to the previous Figure 3(b), it is seen that the transmission componentslocated between the transducer and the sonotrode (typically known as a boosters)

have been eliminated in this design, greatly reducing the length of the push-pull


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system. A complete module assembly is shown in Figure 4(b) in the invertedposition.

In order to prove out the basic performance of the 9.0-kW welding system, it wasimportant to construct a simplified test bed to evaluate the high power and welding

characteristics of the 9.0-kW design, with this being shown in Figure 5 with thelocation of the VHP module highlighted. This unit has only limited functionality, beingable to lay down single tapes on flat plates, and does not have tape feed ormachining capability.

3.3 VHP UAM systemThere was a two-fold purpose in going to the VHP system, the first of which wasbonding advanced materials. The second purpose was increased productivity,meaning the ability to produce parts more rapidly, and in so doing, to make theproduction of larger parts feasible, both from a size and production time standpoint(thus, higher ultrasonic power permits better bonding of materials, but also faster

speed of travel, and welding of thicker tapes). The initial concept for the systemhaving these features is shown in the upper left corner of Figure 6.

Once the sponsorship of the Wright Project was obtained, a detailed set ofperformance specifications were set and the design finalized, as shown in the lowerleft of Figure 6. At the time of submission of this paper, the machine was in the finalconstruction phase at the machine builder, as shown in the right of Figure 6. Keyperformance features:

Materials to be used for Ti, Cu, advanced Al alloys, stainless steels, and Ni-based alloysFeed Stock 0.15-mm up to 0.5-mm thick, depending on material; 25-mmwide up to 250-mm wide tape (or sheet)Part Size working envelope of 1.8 m 1.8 m 0.9 m

Speed welding speeds up to 900 cm/minute with integrated CNC machining

It is anticipated that at the time of the conference, the machine will be installed andoperational at EWI.

4. VHP UAM PERFORMANCE AND APPLICATIONS

Two areas are fundamental to future uses of UAM technology, (1) the range ofmaterials that can be joined by the process, and (2) the scope of potentialapplications and parts. Each will be addressed in the following.

4.1 VHP bonding of advanced materialsThe VHP test bed is being used to test the weldability of a number of advancedmaterials. Some of the results to date are highlighted in Figure 7.

Referring to the numbered cross sections and welds of the figure:

(1) shows the bonding of five layers of 0.10-mm Ti CP-2 foil to a Ti base plate,while (2) shows the welded samples before testing


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(3) shows Al 6061-H18, 0.15-mm foil bonded with low-power UAM

(4) shows the bonding of 12 layers of Al 6061-H18 0.18-mm foil, while (6) isthe cross section of that sample

(5) shows the bonding of 12 layers of Cu 1100, 0.18-mm foil, while (5a) showsthe cross section of the bonded Cu. The horizontal white arrows indicate theinterface locations between Cu layers

(7) shows the top view of three, 2-layer bonds of 0.13-mm 316L stainlesssteel, as well as the metallurgical section of one of the bonds

Special reference is made to comparing, in Figure 7, the appearance of the 6061bonding achieved with low-power UAM, (3) with the results from the VHP test bed,(6). The key feature is the great reduction in voids along the bond interface in theVHP results. Likewise, the Cu bonding of (5a) shows a near absence of interfacevoids. Tests are continuing on additional alloys, and in further improvement in bondquality of the resulting VHP welds.

Extensive work has been done, and is ongoing, on characterizing the metallurgicaland mechanical properties of materials bonded by the UAM and VHP UAM systems(Janaki Ram, 2006; Schick, 2010; Johnson, 2008; Dehoff, 2010; Ramanujam, 2010).

4.2 Application spaceApplied usage of the UAM technology is in its infancy. However, a number of

concept demonstrations have been created that show the potential of thetechnology. Additionally, many prototype products have been built for particularsponsors that go beyond concept to functional testing. Due to confidentiality thefollowing describes the application space based on general categories of capabilityat a high level without divulging business-sensitive works:

4.2.1 Thermal management and heat transferThe ability of UAM to create conformal channels within a part has been noted inSection 2 and Figure 2. These channels may be curvilinear, multi-tiered, andinterconnected, thus having forms extremely difficult to achieve by conventionalmachining processes. Because of the layered nature of the UAM process, it is

possible to add features within the channels that will enhance the overall heattransfer process. This is brought out in Figure 8(a) which shows a cross sectionthrough a part, cutting across two channels. A close up of the channels, Figure 8(b),shows the fin details that are possible with the UAM process.

The most common use of conformal channels is to provide controlled cooling (orheating) of a part. By strategically placing the channels one can design for acontrolled heat flux, of importance in plastic injection molding where rapid cooling ofan injected part can be greatly increased, thus increasing machine throughput. Thepotential of using the VHP UAM process for fabricating hot stamping dies, whichhave similar issues, is under review.


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One interesting application is in the area of high-power laser optics, where new fiberlaser technologies have increased power densities. These high power levels taxtraditionally cooled Cu optics to the point where they distort, causing focusing issues.Using UAM conformal channels can be built in Cu alloys that are within millimeters ofthe focusing surface to quickly wick away heat. A final application example is the

creation of micro channel devices. By using very small channels in a solid, thesurface area available for heat transfer is greatly increased. However, traditionalmachining methods are costly for drilling very small diameter holes to any usefuldepth. By creating the part one layer at a time, the micro channels can be machinedin during manufacturing at lower costs. Micro channels are finding use in aerospacecooling applications as well as high-efficiency bioreactors for making fuels from bio-mass.

4.2.2 Metal matrix composites (MMC)The capability of UAM to embed materials has also been noted in Section 2 andFigure 2. It is found that ultrasonic vibratory energy will sufficiently soften and

plasticize the matrix tape material such that it will flow around and embed wires andtapes. This allows two dissimilar metals to be applied in making a composite withoutthe creation of brittle intermetallic compounds that would normally occur in a fusionoperation. This has obvious structural implications such as embedding high strengthwires and tapes in an Al matrix to increase strength for lightweight structural parts.

One application of UAM embedding is the development of sensors and actuators. Amethod that has been demonstrated for building a sensor/actuator that involvesembedding a shape memory alloy (SMA) such as nitinol, into an Al matrix. ThisSMA exhibits up to 8% no-load strain recovery when heated through its martensite-austenite transition temperature. The phase change can also be induced usingoutside strain, causing a change in electrical resistivity of about 16%, thus permittingits use as both a sensor and an actuator. By heating the nitinol one can cause achange in the bulk stiffness of the material. Conversely, by straining the materialone can measure the change of resistivity of the nitinol and relate it to strain. Figure9 shows nitinol wires embedded in an Al matrix (Hahnlen, 2010).

Taking this particular alloy system further, it is possible to design a MMC with acustomized coefficient of thermal expansion (CTE). Upon heating past the phasetransformation temperature, the nitinol contracts, straining against the bulk Al matrix,which is thermally expanding. By tailoring the relative mixture of nitinol and Al, a

material with a custom CTE over a specific temperature range can be designed.Figure 10(a) shows instrumented samples that have strain gages on Al/nitinol MMCtest specimens. The graph in Figure 10(b) shows the measured strain on heatingversus the expected strain from the base Al substrate (Hahnlen, 2010).

As a final example, the embedding of wires, meshes and tapes in a metal matrix canbe used to create composites having tailored, anisotropic mechanical properties.Figure 11 shows a stainless steel mesh that has been embedded in an Al 3003substrate. Such a MMC can be used to produce high strength, light-weight materialstructural parts.


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4.2.3 Dissimilar materialsIt has been noted that the UAM process is fundamentally one of solid-state welding,and thus based on the mechanisms of the ultrasonic metal welding process, which iswell known to be capable of bonding a range of dissimilar materials (de Vries, 2004).

As also noted, the solid-state nature of the bond avoids issues of intermetallics thatarise in fusion joining of dissimilar materials, and thus opens a large range ofapplications. The simplest application is that of cladding. Structures such aspipelines and pressure vessels are typically clad with a high value metal, such asstainless steel, in order to achieve specific properties such as corrosion resistance.By cladding a low-cost base with a layer of a high value metal the bulk structure orpart can be constructed for less cost. The most prevalent cladding methods involvethe use of an arc welding process to deposit the clad layer. Due to mixing betweenthe clad material and bulk material a significant amount of the cladding material mustbe deposited to assure needed properties at the surface (typically exceeding 6-7mm). When a clad deposit is laid down with UAM, however, there is no metallurgical

mixing. Thus, a much thinner clad layer can be deposited, resulting in significantcost savings of high-value material.

A similar application involves the creation of transition joints. Again, in thepetrochemical industry there is often a need to transition in a pipeline from onematerial to another. This is typically accomplished with complicated seals andgaskets that are prone to leakage. With UAM a transition flange could be madewhere the transition from one material to another over 10-15 cm would be possible.The resulting transition joint would then be arc welded into the pipe. As an exampleof the concept, Figure 12(a) shows a transition from an Al base to a Cu upperstructure.

A final application of dissimilar materials involves the creation of a functionallygraded MMC. Figure 12(b) shows a composite that is made from alternating layersof Al and Ti. As demonstrated by the changing color of the material through thethickness, the ratio of Al to Ti is graded. This allows for the top surface of thematerial to have different mechanical properties than the bottom surface. This givesengineers the ability to design structural materials with engineered compliance andstrength through a part.

5 SUMMARY

The development of a Very High-Power Ultrasonic Additive Manufacturing System(VHP UAM), operating at up to 9.0 kW of ultrasonic power, has been described. Thepurpose of the development has been to expand the range of uses, in terms ofmaterials, part sizes and rates of production and, ultimately, the total range ofapplications, of the basic ultrasonic additive manufacturing process. The technicalaspects of the unique Push-Pull ultrasonic system were noted, including its firstimplementation in a very high power Test Bed. Using the test bed, welding ofmaterials such as Ti 6-4, 316SS, 1100 Cu, and Al7075 has been demonstrated, withtrials on other advanced materials in progress. The current status of the VHP UAM,

recently installed at EWI was also described, noting that it will be capable offabricating metal parts having lineal dimensions of up to 1.5 m 1.5 m 0.6 m. A


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number of part and material applications of this new system were reviewed, includingsolid metal parts with embedded channels for thermal management, metal matrixcomposites (MMC) for structural materials, embedded shape memory alloys (SMA)for active stiffness control, composite-to-metal transition parts, and solid-statecladding for petro-chemical applications.

6 REFERENCES

Dehoff, R., Babu, S.S. (2010, in press) Characterization of InterfacialMicrostructures in 3003 Aluminum Alloy Blocks Fabricated by UltrasonicAdditive Manufacturing, Acta Materialia.

De Vries, E. (2004) Mechanics and Mechanisms of Ultrasonic Metal Welding,Ph.D. Dissertation, The Ohio State University.

Gibson, I., Rosen, D.W., Stucker, B. (2010) Additive Manufacturing Technologies,Springer.

Graff, K. (2008) Development of a Very High Power Ultrasonic AdditiveManufacturing System for Advanced Materials, Proposal to The State of OhioWright Projects Program.

Hahnlen, R., Dapino, M. (2010) UAM Fabrication of Metal-Matrix Smart MaterialsComposites. Proceedings of 39thAnnual UIA Symposium.

Janaki Ram, J.D., Yang, Y., Stucker, B.E. (2006) Effect of Process Parameters onBond Formation during Ultrasonic Consolidation of Aluminum Alloy 3003. Journalof Manufacturing Systems, 25:221238..Johnson, K. (2008) Interlaminar Subgrain Refinement in UltrasonicConsolidation, Ph.D. Dissertation, Loughborough University, Loughborough, U.K.

Ramanujam, S.M., Babu, S.S., Short, M. (2010) Bonding Characteristics DuringVery High Power Ultrasonic Additive Manufacturing of Copper. ScriptaMaterialia, 62, 560-563.

Schick, D.E., Hahnlen, R.M., Dehoff, R., Collins, P., Babu, S., Dapino, M.J., Lippold,J.C. (2010) Microstructural Characterization of Binding Interfaces in Aluminum3003 Blicks Fabricated by Ultrasonic Additive Manufacturing. Welding Journal,89(5), 105s-115s.

Short, M., Zhang, P.H., Graff, K. (2008) Development of a VHP UAM System, TheUltrasonics Industry Association.

White, D.R. (2002) Object Consolidation Employing Friction Joining, U.S. Patent6,4457,629, October 1, 2002.


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(a) UAM welding system (b) Machining operation

Figure 1. The UAM process

(a) IJAMdie and part

(b) Plate withembedded channels

(c) X-ray ofchannel

network of (b)

(d) Embedded MoTape, 2.5-mm W

0.1-mmT

Figure 2. Applications of UAM

(a) Current UAM (b) VHP UAM push-pull setup

Figure 3. UAM, VHP UAM systems

RotatingTransducer,Booster, HornSystem

Transducer Booster HornDummyBooster

Al Base Plate

Anvil

Al Tape

Y

XZ


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(a) SolidWorks model of 9.0-kWmodule

(b) 9.0-kW push-pull module

Figure 4. VHP UAM 9.0-kW module

Figure 5. VHP UAM test bed

Sonotrode

Transducers


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Figure 6. VHP UAM system from concept to (near) final system

Figure 7. VHP welding tests on several advanced materials

606

(6

300

(1) (2

(3

(4

(5

(7

Color difference resultof su erim osin two

(5a


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(a) Cooling channelswithin part

approximately 2.7-mmsquare

(b) Close up of channelcross section showing

internal fins

Figure 8. Cooling channels with internal fins (courtesy of Solidica)

Figure 9. NiTi (nitinol) wires, 100-m diameter in Al matrix (Hahnlen, 2010)

(a) Instrumentedsamples

(b) Thermal strain in test samples

Figure 10. Nitinol/Al MMC having a designed CTE (Hahnlen, 2010)


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Figure 11. Stainless steel mesh in Al matrix (courtesy of Solidica)

(a) Al to Cu transition (b) Al-Ti layered transitioncomposite (courtesy of Solidica)

Figure 12. UAM dissimilar material transitions

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Mark Norfolk - Paper