National Aeronautics and Space Administration

Compact Additively Manufactured Innovative

Michael C. Halbig NASA Glenn Research Center, Cleveland, OH

EnergyTech 2017, Cleveland, Ohio, October 31 to November 2, 2017.

www.nasa.gov www.nasa.gov National Aeronautics and Space Administration Outline • NASA Aeronautics Strategic Thrusts and Goals • CAMIEM intro: the objectives and approach • Limitations of conventional manufacturing • Benefits from additive manufacturing • New component designs for integration into the motor • Fabrication and evaluation of a baseline motor • Summary and next steps

2 www.nasa.gov National Aeronautics and Space Administration NASA Aeronautics Research Six Strategic Thrusts

Achieve and exceed N+2 and N+3 goals for increased efficiencies and reduced emissions. 3 www.nasa.gov National Aeronautics and Space Administration Stakeholders and Applications

NASA projects: STARC-ABL Hybrid Electric Sugar VoltVertical Lift • STARC-ABL • AATT • RVLT • SCEPTOR

Distributed X-57 (Technology demonstration aircraft for reductions in fuel use, Propulsion emissions, and noise) • Benefits: no in-flight emissions, low noise operation, and ~ 30% reduced operating costs. Cruising efficiency expected to increase 3.5-5-fold. • 14 Electric Motors: • 12 low speed take-off propellers, ~14 kW electric motor for each • 2 larger wingtip propellers for cruise, ~50 kW electric motor for each CAMIEM is currently an independent feasibility study.

However, the motor class is very compatible to that of X-57. 4 www.nasa.gov National Aeronautics and Space Administration CAMIEM - Compact Additively Manufactured

Innovative Electric Motor LP Baseline Motor

Objective: Utilize additive manufacturing methods to achieve new motor designs that have significantly higher power densities and/or efficiency. Methods: • New topologies with compact designs, lightweight structures, innovative cooling, high copper fill, and multi-material systems/components. • Compare new components/new motor against a baseline motor. Projected Performance Specs: Benefits: Eliminates extensive machining, expensive tooling and design •6 kW at 7500 rpm, 95% efficient, changes, and high labor of conventional manufacturing. 3.3 kW/kg power density (@ well below max. allowable temp.) •10 kW at 7500 rpm, 5.5 kW/kg Team members: NASA GRC, NASA LaRC, NASA AFRC, LaunchPoint power density (@ max. allowable 5 Technologies, and the University of Texas - El Paso temp.) www.nasa.gov National Aeronautics and Space Administration Conventional Manufacturing of Electric Motors

Radial Flux Motor

Axial Flux Motor w/PCB

LP Conventional Axial Flux Stator www.youtube.com/watch?v=sMtQ10J1agk&nohtml5 w/Litz Copper Wire Windings 6 www.nasa.gov National Aeronautics and Space Administration Motor Performance Metrics • Motor specific power is approximately a product of several factors

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𝑇𝑇𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑚𝑚𝑚𝑚−𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 – = 𝑚𝑚 𝑠𝑠�𝑠𝑠𝑠𝑠𝑠𝑠 𝑘𝑘 ∗ 𝑅𝑅𝑡𝑡푡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 ∗𝜔𝜔 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 � • The𝑃𝑃 CAMIEM sub-project will seek to make 𝑚𝑚𝑚𝑚improvements𝑚𝑚𝑚𝑚 to many factors:

Km – motor constant Stator Temperature Rise • Km represents the electromagnetic • Net thermal resistance from the • _ 𝑹𝑹𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕 efficiency of the motor at converting stator to the ambient • Represents the ability of the environment – the ultimate sink current into torque 𝑇𝑇𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑚𝑚𝑚𝑚 − 𝑇𝑇𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 stator to resist heating caused by for waste heat from the motor • Units of torque per sqrt(power) the electric current in the motor • Comprised of conductive and • Making Km bigger also make the • Increasing the max. allowable convective terms – for the motor larger and heavier, so to stator temp. allows higher baseline motor convection is improve performance we want to currents and more torque from much better than conduction make Km larger without increasing the motor and dominates this term mass too much 7 Mass: lighter weight materials, less volume. www.nasa.gov National Aeronautics and Space Administration Overview of Additive Manufacturing Technologies

Wire Embedding Copper wire is fed through a Direct Write Printing heated ultrasonic nozzle. Controlled dispensing of inks, pastes, and slurries.

Fused Deposition Modeling Plastic or metal is heated and supplied through an extrusion nozzle and deposited.

Binder Jet 3D Printing Selective Laser Sintering An inkjet-like printing head moves High powered laser fuses plastic, across a bed of powder and deposits a liquid binding material. 8 metal, or ceramic powders. www.nasa.gov National Aeronautics and Space Administration Additive Manufacturing Processes Being Applied to Motor Fabrication

Direct Write Printing (GRC) Wire Embedding (UTEP)

Binder Jet 3D Printing (GRC) 9 Selective Laser Sintering (LaRC) www.nasa.gov National Aeronautics and Space Administration LaRC: Structural Components Objective: Investigate the feasibility of attaining 1.56x improved power density over current motor design. Kevlar Approach Prototype of the reinforcement • Identify parts with potential for significant mass reduction. baseline motor • Model the baseline design and re-designed parts to determine their potential to concept redesigned with continuous achieve performance improvements. Kevlar-reinforced • Use 3D printing for rapid prototyping and screening of design modifications. structure. PA-6, Nylon • Verify contribution of modifications to improved power density goal. Plate Advanced Design Performance Prediction with FEM

Form Fitted Printed Model/Prototype

Advanced Design (Housing) Component by Component mass = 65 g, Aluminum 6061 63% mass savings 10 Mass Evaluation www.nasa.gov National Aeronautics and Space Administration UTEP: Stator with Wire Embedding CNC router capable of: Objectives: Investigate the feasibility for wire embedding in parts • Machining FDM Machine 1 • Direct-write produced with material extrusion AM to yield new stator designs • Wire embedding • Robotic component that have higher wire density and passive thermal management placement strategies. Sub- Stator: 2 layers of 6 Kapton coated wire coils to be embedded Six-axis robot Workpiece Element Approach demonstrations with embedding and cavity forming arm (Yaskawa Motoman Design • Embedded bondable Litz wire with material extruded above FDM Machine 2 MH50) Approach • Specimen with preformed cavities for manual introduction of final 1.52 mm (0.06”) diameter Kapton coated wire Multi3D System Final Kapton coated wire Bondable Litz wire

Brass roller Tilt Platform s Motor

Wire spool Stator design: LaunchPoint & UTEP 3 coils embedded Quarter stator with cavities placing and printed over 0.06” Kapton coated Litz wire. 11 Wire embedder www.nasa.gov National Aeronautics and Space Administration GRC: Direct Printed Stator Objective: Investigate the feasibility for direct printing to allow for innovative stator designs that are compact and lightweight with multiple coils and iron improving magnetic flux. Approach • Additively manufacture a stator with 3-phase coils by printing the constituent materials: conductor, dielectric, and iron. Printed 4-Pt • Evaluate silver inks, sintering methods, and carbon nanostructures Probe Winding. additions.

NScrypt SmartPump and Direct Write Printer Silver Conductor and Dielectric Print Layers 12 www.nasa.gov National Aeronautics and Space Administration GRC Stator Effort - Conductive Inks

Direct printed conductors for circuits and coils CB028, Conductive Silver – Evaluating baseline silver inks/pastes Paste - DuPont • Planning for inks with 250°C use temperatures • Thermogarvimetric analysis (TGA) and differential scanning calorimetry (DSC) being conducted • Different diameter dispensing tips, oven curing, and resulting electrical conductivity and microstructures TGA Ag ink L16016 air being evaluated 100.5 Conductive Silver 100 Ink L16016 - • Different curing/sintering methods 99.5 Fraunhofer 99 98.5 < 3 wt.% loss

– Resistivity Measurements Weight % 98 97.5 • Printing winding patterns and conducting 4-point 0 200 400 600 probe measurements Temperature (°C) – Plan to investigate additions to inks for higher conductivity • Want electrical conductivities as good as or better than copper wire – Also, printing relevant dielectric patterns Additions of graphene and carbon nanotubes 13 www.nasa.gov National Aeronautics and Space Administration Paste Comparison of Different Vendors

PLAIN PASTE Paste Composition Lowest Resistivity Obtained [Ωm] Conductivity [Ωm]^-1 Max Temp (*C) Vendor Resistivity CB028 (DuPont) 2.82 x 10-8 3.54 x 107 175 7 – 10 (mΩ/sq/mil) CL20-11127 (Heraeus) 4.37 x 10-8 2.29 x 107 300 N/A CB100 (DuPont) 5.23 x 10-8 1.91 x 107 175 >7.5 x 10-8 Ωm

Ag-PM100 (Applied Nanotech) 9.13 x 10-8 1.10 x 107 300 >5 x 10-8 Ωm Kapton (DuPont) 2.11 x 10-7 4.74 x 106 225 <5 (mΩ/sq/mil)

Conductivity of bulk metals [Ωm]^-1: 7 -Silver: 6.3 x 10 Width ~1125 µm (0.04”) -Copper: 6.0 x 107 Height ~171 µm (0.007”) Cross-Section 123671 µm2 ± 2213 µm2 Area (1.9 x 10-4 in2) Printed silver has lower conductivity, Resistivity 2.36x 10-7 Ωm however the conductor packing is Nozzle 0.013” Resistance: 1.203 Ω, 160ºC heat treat higher than for Litz copper wire. Sample 072817C: CB028 (0.2 wt% CNS) 14 www.nasa.gov National Aeronautics and Space Administration Sample 032917-6: DuPont Silver CB028 High Conductivity Silver Ink • Nozzle 0.013”, 4 mm/s • Resistance: 0.7 Ω after 24h, 150ºC heat treat Width 969 µm ± 6.7 µm (0.04”) Height 39 µm ± 3.1 µm (0.002”) Cross- 25422 µm2 ± 1844 µm2 Section 100 µm (3.9 x 10-5 in2) 969μm ~ 0.04” Area Resistivity 2.8 x 10-8 Ωm

Sample 71017G: Heraeus CL20-11127

16 www.nasa.gov National Aeronautics and Space Administration Sintering Processes Photonic Sintering Investigating the use for photonic sintering for printed silver inks. • Rapid post processing of conductive patterns • Few second to minute processing times without damaging/heating the substrate

Thermal/Oven Photonic Sintering Curing for high through-put

Electrical Resistance (Ohmic) Sintering

Sebastian Wünscher et all, 2014

15 Andreas Albrecht et all, 2016 www.nasa.gov National Aeronautics and Space Administration LaunchPoint and AFRC: Baseline Motor Fabrication and Testing Objective: Evaluate the full performance of a state-of-the-art axial flux Approach motor to establish baseline electric motor performance. • LaunchPoint will fabricate 3 baseline motors and 2 controllers and conduct performance test before delivery. • AFRC will evaluate the full performance spectrum of the baseline motor in the Airvolt. Leverage X-57 cruise motor testing. Motor Motor Airvolt Adapter

Baseline motor with a propeller. Torque / Thrust Sensor Propeller * Bringing experience from X-57 Cruise Motor/Airvolt assembly and testing.

Schematic of the Airvolt Motor being tested on test stand at AFRC. 17 LaunchPoint dynamometer. www.nasa.gov National Aeronautics and Space Administration

Summary Summary and Next Steps • Additive manufacturing technologies were demonstrated to be capable of enabling new innovative motor designs. • New component designs are being pursued for the rotor, housing, wire embedded stator, and coil printed stator. • New designs will offer performance gains through such improvements as lighter weights, higher coil packing, higher coil electrically conductive, higher temperature operation, and higher magnetic flux.

Next Steps • Establish the baseline motor’s performance. • Additively manufacture innovative components. • Evaluate new component performance against the baseline performance. • Determine performance and manufacturing benefits. 18 www.nasa.gov National Aeronautics and Space Administration Acknowledgements

Support provided by the Convergent Aeronautics Solutions Project within the ARMD Transformative Aeronautics Concepts Program.

Organization Name Role Organization Name Role Michael Halbig (POC) PI and GRC POC Kurt Papathakis (POC) AFRC POC and ground testing Mrityunjay "Jay" Singh Armstrong Ethan Niemen Additive manufacturing Valerie Wiesner Flight Research Kristen Fogg Electric propulsion ground Daniel Gorican AM Processes/Direct Center Matthew Walderson testing Glenn Greg Piper printing Patricia Martinez Research Steven Geng Motors and Samuel Hocker Center Additive manufacturing Peter Kascak Electric motors Langley Christopher Stelter Chun-Hua "Cathy" Chuang Insulator materials Research Russell “Buzz” Wincheski NDE David Ashpis CFD and thermal analysis Center Stephen Hales Materials evaluation Jeff Chin System benefits John Newman Computational materials Michael Ricci (POC) Jose Coronel LaunchPoint Baseline & innovative University of Stator winding and cooling Jon Sugar David Espalin (POC) Technologies motor designs Texas El Paso efficiency Dave Paden Ryan Wicker GRC 2017 Summer Students: Anton Salem (Washington University in St. Louis) 19 and Jessica Zhou (Case Western Reserve University). www.nasa.gov