Ultrasonic Additive Manufacturing (UAM) has been subject to research and investigation at Loughborough University since 2001. In recent years, three particular areas of significant focus have been: • The influence of pre-process material texture on interlaminar bonding. • Secure fibre positioning through laser machined channels. • Freeform electrical circuitry integration. This paper details the key findings and a number of conclusions from these work areas. The results of this work have led to the further research and developmental applications for the UAM technology

Ross Friel (1248393)

Russell Harris (1250157)

English

Loughborough University Institutional Repository

   This item was submitted to Loughborough’s Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.      For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/  ULTRASONIC ADDITIVE MANUFACTURING RESEARCH AT LOUGHBOROUGH UNIVERSITY R. J. Friel* and R. A. Harris* * The Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, UK, LE11 3TU Abstract Ultrasonic Additive Manufacturing (UAM) has been subject to research and investigation at Loughborough University since 2001. In recent years, three particular areas of significant focus have been:  • The influence of pre-process material texture on interlaminar bonding.  • Secure fibre positioning through laser machined channels.  • Freeform electrical circuitry integration.  This paper details the key findings and a number of conclusions from these work areas. The results of this work have led to the further research and developmental applications for the UAM technology.  Introduction  Ultrasonic Additive Manufacturing (UAM) is a solid state additive manufacturing process that sequentially bonds metal foils together using ultrasonic metal welding (USW), layer by layer, and then uses Computer Numerical Control (CNC) machining to remove material to create the desired geometry (see Figure 1). UAM is therefore a hybrid of additive and subtractive manufacturing.    Figure 1 - Schematic of the UAM Process (1) 354UAM has been researched at Loughborough University since 2001. Past research has involved: Initial Characterisation Using the Alpha UAM platform (Figure 2) work was carried out to identify the process parameter settings (i.e. weld speed (mm/s), weld pressure (KPa), and sonotrode oscillation amplitude (µm)) that resulted in the successful bonding of multi- layered aluminium alloy structures (2).  Figure 2 - The Alpha Ultrasonic Additive Manufacturing System Interlaminar Bond Interface Quantification  A method of quantifying the bond between foil layers during the UAM process was devised and termed the Linear Weld Density (LWD) (3). This method of analysis involved cross-sectioning UAM samples, mounting, polishing and then microscopically analysing the samples to measure the level of porosity within the bond interface. This porosity was calculated via the LWD equation (Lb is the bonded length of the sample and Lc is the total bond interface length). 𝐿𝑊𝐷 (%) =  �𝐿𝑏𝐿𝑐� × 100 355This quantification of the bond interface was also evaluated via the use of mechanical peel testing that was performed via the use of tensile testing equipment. Object Embedding into Metal Matrices By exploiting the ‘acoustic softening’ that occurs during ultrasonic processing of metal materials (4) it was found that objects could be embedded between the foil layers during the UAM process (5). This work led to the embedding of active elements such as Shape Memory Alloys (SMA) for actuation and optical fibres for data transfer as well as passive elements, such as Silicon Carbide (SiC) fibres for structural reinforcement (6) (7).   Figure 3 - Example of an Embedded Shape Memory Alloy Fibre in an Aluminium Alloy Matrix (8)  By embedding these objects it was demonstrated that due to the matrix compliance and relatively low processing temperature (typically <50% of the metal melt temperature (9) (10)) the UAM process was suited to the manufacture of metal matrix composites in the solid state. Sonotrode Texture Importance  The sonotrode of the UAM equipment has an Electro Discharge Machined (EDM) surface that is used to ensure coupling between the metal foil surface and the tool (sonotrode) during the material processing. The importance of this texture was demonstrated via the use a smoother sonotrode surface that had occurred due to wear. It was found that this wear resulted in a reduced bond interface strength (evaluated via peel testing) and a reduced LWD (11). Plastic Flow and Work Hardening during UAM  Investigation into the flow of the matrix material around embedded SiC fibres and the hardening of the matrix material (Figure 4) was performed using polarised light optical microscopy and micro-indentation equipment. This work highlighted the grain structure deformation caused by the fibre embedding and the resultant work hardening that was caused by the embedding process (12). 356 Figure 4 - Microscopy Highlighting Matrix Plastic Flow (A) and Microhardness Testing of Matrix Post-UAM (B) (12) Interlaminar Sub-Grain Refinement  Using Dual Beam Focussed Ion Beam (DBFIB) analysis of the foil to foil interface, post UAM (Figure 5), it was identified that the sonotrode was causing sub-grain refinement in a highly localised area at the foil to foil interface and that this mechanism was resulting in a complex residual microstructure within the matrix (13) (14).  Figure 5 - DBFIB Image of Sub-Grain Refinement and Plastic Flow at the Bond Interface in a UAM Component (13) Imparted Topology  Further work into the effects of the sonotrode texture identified that it was not only the sonotrode texture that was important for the UAM process. Using white light interferometry, peel testing, optical microscopy and LWD measurements researchers at Loughborough were able to identify that a key factor for the UAM process was the change in Interlaminar foil surface topology that was induced by the sonotrode contact (Figure 6). This topology change was found to be dependent on the sonotrode surface texture as well as the process parameters that were used during the UAM process (15). 357 Figure 6 - White Light Interferometry and Optical Microscopy Showing the Foil Topology Change Caused by Two Different Sonotorde Textures (a = rougher, b = smoother) Sub-Grain Refinement due to Fibre Embedding  Through DBFIB analysis of the matrix around UAM embedded fibres it was uniquely identified that the embedding of objects into metal matrices via the UAM process results in sub-grain refinement that is similar to that induced by the sonotrode to foil contact (Figure 7) (16).   Figure 7 - Images Showing the Sub-Grain Refinement of the Matrix around UAM Embedded Fibres (a = DBFIB above the fibre, b = SEM above the fibre) (16) 358 Current UAM Work at Loughborough University  Current work at Loughborough University into UAM has been involved in key research focuses to maximise the potential of UAM. These are the detailed analysis of surface topography in UAM and the effects on interlaminar bonding (Figure 8) and the use of a fiber laser to create channels onto a UC sample surface for secure fibre placement and maximised matrix plastic flow (Figure 9).  Figure 8 - Microscopic Detailed Analysis of the Interlaminar UAM Surface (15)  Figure 9 - Schematic of the use of a Fiber Laser for Secure Fibre Postioning and Reduced PLastic Flow Requirements in UAM Interlaminar Bonding in UAM  By using sonotrodes of varying surface textures and by using a full range of UAM processing parameters a detailed ANOVA study was performed. The process parameters 359were related to the surface texture and the effect that this had on the resultant peel strength and LWD of the UAM samples. The surfaces of the sonotrode and samples were measured for a range of surface parameters using white light interferometry.   This detailed analysis led to new insight into the importance and effect of the sonotrode and thus foil surface topology for the UAM process. The key findings were: • The most important factors for bond strength are the Sa of the sonotrode, the sonotrode amplitude and the weld pressure (Sa is > amplitude > weld pressure) • Between the ranges measured in the study the weld speed was not found to be significant for UAM • The sonotrode weld surface texture features of amplitude (Sa), spacing (Sal) and shape (Sku) emerged as the most influential factors that appear to effect interlaminar porosity and bond strength in UC. Laser Channelling in UAM The use of a fiber laser for channelling was shown to be successful for the creation of secure placement channels and should features to aid fiber embedding in UAM (Figure 10).  Figure 10 - White Light Interferometry Image Showing Multiple Channels on a UAM Sample Surface Using optical microscopy, white light interferometry and EDAX the full effects of the laser processing on the UAM surfaces was characterised. The key findings of the work were: • That using a multi-pass lasing technique allows for a smoother channel surface that more accurately follows a Gaussian profile. • It is possible to create channels that are a diameter match to the intend fibres that will be embedded.  • That by using a carefully controlled gas flow rate during laser processing shoulder features can be created which would reduce the need for plastic flow around the fibres during UAM embedding. However this should feature is difficult to make symmetrical and usually has a bias to either side of the channel. 360• Through the use of multiple laser passes a progressive Heat Affected Zone (HAZ) is created that results in an elemental compositional change in the UAM material. Future UAM Work at Loughborough University Future work into UAM at Loughborough University has begun to focus on improving and increasing the functionality of UAM parts through the integration of functional electrical circuitry during the UAM process (Figure 11). This work is being carried out in conjunction with a UK based SME with expertise in the printing of electronics – Printed Electronics Ltd.  Figure 11 - Schematic of the Integration of Functional Electrical Circuitry into UAM Components via Inkjet Printing  By printing the electrical components and the insulating materials directly onto the UAM samples it has been possible to embed these electronics via the UAM process (Figure 12).  Figure 12 - UAM Sample with Embedded Functional Printed Electrical Circuitry  Further work will investigate the optimisation of the embedding process via the use of mechanical and microscopic analysis. The use of the components for further electrical testing will also be performed. The second major stage of the project will involve investigating the integration of the electrical circuitry in a 3D manner (i.e. in the z axis, perpendicular to the layup process). Summary Since 2001 multiple research projects into UAM have been performed by Loughborough University. This research has led to many important findings and essential work to helping maximise the potential of the UAM process.  361The key areas of research have been:  • Process fundamentals for ensuring quality of bonding is maximised and that this is monitored through suitable techniques such as peel testing and LWD. • Fibre embedding of multiple different types. • Fibre-Matrix investigations into the micro and nano structural effects of the ultrasonic processing on interlaminar bonding and object embedding during UAM using analysis techniques such as SEM and DBFIB. • Topology effects both in terms of the sonotrode and process parameters have been studied via the use of white light interferometry and ANOVA studies. • Improving the application and functionality of UAM has and is continuing to be researched through the integration of functional, printed, electrical circuitry.  Research into UAM at Loughborough University is continuing and expansion for the future is now happening. Acknowledgments  The authors would like to thank the EPSRC for their generous support of the UAM research at Loughborough University. References 1. Field Repair and Replacement Part Fabrication of Military Components using Ultrasonic Consolidation Cold Metal Deposition. Schwope, L-A. Friel, R.J. Harris, R.A., Bonn : NATO, 2009, October 19-22. NATO RTO-MP-AVT-163 Additive Technology for the Repair of Military Hardware. p. Paper 22.  2. Optimum process parameters for ultrasonic consolidation of 3003 aluminium. Kong, C.Y., Soar, R.C. and Dickens, P.M., Loughborough : Elsevier, 28 February 2004, Journal of Materials Processing Technology, Vol. 146, pp. 181-187. 3. A model for weld strength in ultrasonically consolidated components. Kong, C.Y., Soar, R.C. and Dickens, P.M., Loughborough : Professional Engineering Publishing, January 2005, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, Vol. 219, pp. 83-91. 4. Effects of ultrasound on deformation characteristics of metals. Langenecker, B. : IEEE, 1966, IEEE Transactions on Sonics and Ultrasonics, Vol. 13. ISSN: 0018-9537. 5. Fabrication of metal-matrix composites and adaptive composites using ultrasonic consolidation process. Kong, C.Y. and Soar, R.C., Elsevier, 2005, Materials Science and Engineering: A, Vol. 412, pp. 12-18. 6. Kong, C.Y. Investigation of ultrasonic consolidation for embedding active/passive fibres in aluminium matrices. Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, UK. 2005. PhD Thesis. 3627. Characterization of Process for Embedding SiC Fibers in Al 6061 O Matrix Through Ultrasonic Consolidation. Li, D., Soar, R.C., 2009, Journal of Engineering Materials and Technology, Vol. 131, p. 021016. ISSN: 0094-4289. 8. Friel, R.J. Investigating the Effect of Ultrasonic Consolidation on Shape Memory Alloy Fibres. Wolfson School of Mechanical and Manufacturing Engineering, Loughbrough University, UK. 2011. PhD Thesis. 9. Ultrasonic Welding. Jones, J.B. and Powers Jr., J.J.: American Welding Society, 1956, The Welding Journal, Vol. 35, pp. 761-766. ISSN: 0043-2296. 10. de Vries, E. Mechanics and Mechanisms of Ultrasonic Metal Welding. Ohio : Ohio State University, 2004. PhD Thesis. 11. Influence of sonotrode texture on the performance of an ultrasonic consolidation machine and the interfacial bond strength. Li, D. and Soar, R.C.,: Elsevier Inc., 2009, Journal of Materials Processing Technology, Vol. 209, pp. 1627-1634. ISSN: 0924-0136. 12. Plastic flow and work hardening of Al alloy matrices during ultrasonic consolidation fibre embedding process. Li, D. and Soar, R.C.,: Elsevier Inc., 2008, Materials Science and Engineering: A, Vol. 498, pp. 421-429. ISSN: 0921-5093. 13. Johnson, K. Interlaminar subgrain refinement in ultrasonic consolidation. Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, UK. 2008. PhD Thesis. 14. New discoveries in ultrasonic consolidation nano-structures using emerging analysis techniques. Johnson, K. Edmonds, H.C. Higginson, R.L. Harris, R.A., : SAGE Publications, 2011, Proc. Inst. Mech. Eng. L J. Mater. Des. Appl., Vol. 225, pp. 277-287. ISSN: 2041-3076. 15. The effect of interface topography for ultrasonic consolidation of aluminium. Friel, R.J. Johnson, K. Dickens, P. Harris, R.A.,  Elsevier Inc., 2010, Materials Science and Engineering: A, Vol. 527, pp. 4474-4483. ISSN: 0921-5093. 16. A nanometre-scale fibre-to-matrix interface characterization of an ultrasonically consolidated metal matrix composite. Friel, R.J. and Harris, R.A.: Sage Publications, 2010, Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, Vol. 224, pp. 31-40. ISSN: 2041-3076.  363

Ultrasonic additive manufacturing research at Loughborough University

https://repository.lboro.ac.uk/articles/Ultrasonic_additive_manufacturing_research_at_Loughborough_University/9555791/files/17187674.pdf

Ultrasonic additive manufacturing research at Loughborough University

Abstract

Similar works

Full text

Available Versions

Loughborough University Institutional Repository