Seventh aiCAMstir Meeting, 26 January 2023

The Seventh aiCAM^stir Meeting was held online on 26 January 2023 with 39 attendees.

Link to the video

Recording of the Seventh aiCAMstir Meeting (Total: 1:42 h, the first presentation starts at 15:55 min)

Recording of the Seventh aiCAM^stir Meeting

Agenda

The agenda of the 90 min long on-line meeting was as follows:

• Welcome and introduction (2-3 sentences each)
• Development of a new stitch friction stir welding gun and mechanical behavior of intersecting stitch welded AA 6016-T4 sheets. Dominik Walz, MPA Stuttgart, Germany (20 min + 5 min questions)
• Effect of FSW tool geometry on the joint quality of AA2024-T3/AA7075T6 joints in butt configuration. Reza Beygi, INEGI, Porto, Portugal (20 min + 5 min questions)
• Machine investment cost and tool wear of friction stir welding of battery trays of compact crossovers. Stephan Kallee, AluStir, Germany (20 min + 5 min questions)
• Collaborative projects, organisational comments and date of next meeting (25 May 2023). Mike Lewis (FTS Engineering Answers Ltd)

List of Attendees

(alphabetically sorted by first name or MS-Teams name)

Attendee	Company	Status	Signed-up on
Adrian Gerlich	Waterloo University, Canada	Guest
Azman Ismail	Universiti Kuala Lumpur, Malaysia	Guest
Breno Boretti Galizoni	Sonaca, Brazil	Guest
Carlos Santos	Mazak, USA	Guest
Christian Vogrinec	Saman Ventures, Austria	Guest
Christian Barth	CERN, Genève, Switzerland	Guest
Christoph Rößler	Sampro Software, Germany	Guest
Christoph Barth	Toolcraft, Germany	Guest
Dominik Walz	MPA Stuttgart, Germany	Guest
Egoitz Aldanondo	IK4-LORTEK, Spain	Guest
Elizabeth Hoyos Pulgarín	Universidad EIA, Colombia	Guest
Fabian Vieltorf	Technical University Munich, Germany	Guest
François Nadeau	NRC Canada, Canada	Guest
Fritz Luidhardt	Harms + Wende, Germany	Guest
Henrik Blicher Schmidt	HBS Engineering, Denmark	Guest
Ingo Hahn	Hexagon, Germany	Guest
Javier Vivas Mendez	IK4-LORTEK, Spain	Guest
Jean Pierre Bergmann	Technische Universität Ilmenau	Guest
João Gandra	ESA, Netherlands	Guest
John Hunt	TWB, USA	Guest
Jürgen Silvanus	Airbus, Germany	Guest
Mario Leitner	Stirline GmbH, Austria	Industrial Company	2022-03-02
Markus Graß	Uni Kassel, Germany	Guest
Markus Weigl	Grenzebach, Germany	Guest
Martin McDonnell	U.S. Army, TARDEC, USA	Guest
Matthew Hackett	Element 6, UK	Guest
Michael Eff	EWI, USA	Guest
Michael Hasieber	Technical University Ilmenau, Germany	Guest
Michael Zäh	Technical University of Munich, Germany	Guest
Mike Lewis	FTS Engineering Answers Ltd, UK	Consultancy service provider	2021-01-14
Nguon-Nhan Bui	Harms + Wende, Germany	Guest
Niklas Harriehausen	Sampro Software, Germany	Guest
Stephan Kallee	AluStir, Germany	Consultancy service provider	2021-01-14
Patrick, Mubiayi Mukuna	University of South Africa, South Africa	Guest
Reinhard Mauermann	Fraunhofer IWU, Germany	Guest
Reza Beygi	INEGI, Porto, Portugal	Guest
Sahin Sünger	Grenzebach, Germany	Guest
Simon Smith	Transforming Stress Ltd, UK	Consultancy service provider	2021-01-14
Tim Haynie	Bond Technologies Inc., USA	Industrial Company	2022-02-09

Presentations

Development of a new stitch friction stir welding gun and mechanical behavior of intersecting stitch welded AA 6016-T4 sheets. Dominik Walz, MPA Stuttgart, Germany, start at 15:55 min

Dominik Walz, Materials Testing Institute University of Stuttgart (MPA): Development of a new stitch FSW gun and mechanical behavior of intersecting stitch welded AA 6016-T4 sheets. 7th aiCAMstir meeting, 26 Jan 2023

Agenda: Motivation, State of the art, Working principle, Design and Engineering of the „Steppwelder“, Materials and Methods, Effect of the stitch weld length on mechanical properties and microstructure, Conclusion & Outlook

Motivation: Multi-material usage in car body construction for an optimal weight to strength ratio, Big variety of joining technologies, Friction Stir Welding (FSW) not represented despite process advantages, There is a lack of flexible, automatable machines and system solutions for FSW

State of the art – robot guided friction stir welding

Design & Optimization: Working principle, Design and Engineering of the Steppwelders

Working principle of the „Steppwelder“

Working principle of the „Steppwelder“: Angled plate with short 10 mm stitch welds, Angled plate with 45 mm stitch welds, Curved weld consisting of intersecting stitch welds

Working principle of the „Steppwelder“: Motor cooling circuit, Main bearing (tapered roller bearings), Caseless motor, Internal water cooling, Motor feedback, Tool holder (Collet ER32)

Feasibility of cycle time reduction: Parameter set, Plunge speed [mm/s], Holding time [s], Feed speed [m/min], Retract speed [mm/s]

Agenda: Materials and Methods, Effect of the stitch weld length on mechanical properties and microstructure

Characterizing of friction stitch welds: Welding, Test program ( Temperature measurements, Macroscopic intersections, Hardness measurements, Tensile tests, Fatigue tests) Conclusions

Characterizing of friction stitch welds: Hypothesis: Through repeated plunging, the material does not have sufficient time to cool down, it assumes a state similar to the artificially aged state in the area of re-plunging, Repeated annealing ( following stitching joints) causes (over-) aging, The mechanical properties are affected by those temperature cycles

Characterizing of friction stitch welds - Temperature measurements Coarsening of precipitates at temperatures >175 °C after FSW [Sat02, Rod09]. Big precipitates grow at the expense of smaller precipitates and block them. Coarse precipitation pattern leads to a decrease in hardness. The higher the heat input, the wider the area of lower hardness in the weld [Sat02]

Characterizing of friction stitch welds – Microstructure and hardness

Characterizing of friction stitch welds – Tensile tests: Substitute proof strength R_p0,2 constant, Tensile strength R_m scalable with stitch weld length, A_g scalable with stitch weld length

Characterizing of friction stitch welds – Fatigue tests / Wöhler curve

Characterizing of friction stitch welds – Fatigue tests: Influence / Scaling effect of the stitch length on the stress amplitude, Tunnel defects occuring with this parameter set on conventional FSW welds and long stitch welds have an impact on the results

Conclusion & Outlook:
❖ A functioning welding gun was developed and tested.
❖ It is possible to perform intersecting stitch welds with excellent strength properties.
❖ The tensile strength, ultimate plastic elongation and fatigue strength can be scaled with the stitch weld length.
❖ The temperature cycles in intersecting stitched welds have a significant effect on the microstructure and hardness distribution of the welds.
➢ Further mechanical improvment of the design of the welding gun
➢ Installation and start-up of a robotic manufacturing cell
➢ Further investigation of the mechanical properties of the joints
➢ Overlap joints, variation of materials (5xxx, 7xxx alloy)
➢ Further improvment/ reduction of the weld cycle time
➢ Practical demonstrators (3-sheet connection, influence of adhesive,...)

Presentation data published at: https://www.mdpi.com/2052690

Literature (please click here or scroll down)

Effect of FSW tool geometry on the joint quality of AA2024-T3/AA7075T6 joints in butt configuration. Reza Beygi, INEGI, Porto, Portugal, start at 39:50 min

R. Beygia (Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), Rua Dr. Roberto Frias, 4200-465 Porto, Portugal) and LFM da Silva (Department of Mechanical Engineering, Faculty of Engineering of the University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal): Effect of FSW Tool Geometry on the Joint Quality of AA2024-T3/AA7075-T6 Joints in Butt Configuration. Seventh aiCAM^stir meeting, 26 January 2023

Content. Introduction, Method, Results and discussion, Conclusion

Introduction: Applications AA2024 and AA7075 alloys: Aerospace industry (wing, fuselage, outer panel structure), Advantages of these alloys, Weight reduction, High fatigue strength, Challenges of joining of these alloys by fusion welding processes, Solidification cracking, Distortion

Introduction: Friction stir welding (FSW), No melting and solidification, Lower heat, Issues during FSW, Defects formation, Softening, Lack of consolidation, Kissing bond, Dissolution of the precipitates, Coarsening of the precipitates

Introduction: Aims of the present study, Obtaining the highest UTS of joints between AA2024T3-AA7075T6, The effect of tool geometry on UTS of the joints

Experimental procedure: Materials, Sheets with 3 mm thicknesses, Process (DOE based on central composite design)

Experimental procedure: Tool geometries

Experimental procedure: Characterization of the joints: Tensile testing: ASTM E8-M, Optical microscopy, Scanning electron microscopy (SEM), Fractography

Experimental procedure: Artificial Neural Network (ANN)

Results and discussion: Results of the tensile test

Results and discussion: Results of the tensile test

Results and discussion: Neural network results

Results and discussion: Interaction plot

Results and discussion: Welds cross sections

Results and discussion: Interaction plot

Results and discussion: Interaction plot

Results and discussion: Interaction plot

Results and discussion: Interaction plot

Conclusions: Main results

Conclusions: Main results:
- ANN was successfully used to understand the effect of welding parameters and tool geometry on the ultimate tensile strengths of the welds. The optimum condition was obtained by the SA method which corresponded to the experimental result successfully.
- All the joints possessed a root defect at a low rotation speed of the joint due to a lack of material flow under the pin.
- The joints made by the pyramidal pin possessed the lowest joint strengths due to the various welding defects at different tool rotation speeds: At 1200 rpm the lack of plastic flow, at 1000 rpm the banding structure, and 800 rpm the root defect.
- The joints made by the conical pin were free of defects at higher rotation speeds but still had a low tensile strength. This was attributed to the softening caused by the precipitates coarsening in the stir zone due to a high temperature during welding.
- The UTS of the welded specimens had little sensitivity to the welding speed.
- The optimum joint strength was obtained using the cylindrical tool at high rotation speed where the root defect disappeared due to enough material flow. This tool having a low volume did not cause a high temperature during welding and therefore softening was minimized.

Any question? Thank you for your attention

Machine investment cost and tool wear of friction stir welding of battery trays of compact crossovers. Stephan Kallee, AluStir, Germany, start at 1:04:38 h

Stephan Kallee, AluStir: Machine investment cost and tool wear of friction stir welding of battery trays of compact crossovers

VW and Ford: Compact Crossovers, Sandy Munro: „Some really fancy extrusions with some fancy welding and some fancy machining“, „Integrate the battery structure into the vehicle, having the battery and body work together“, Modular approach, Cost optimized materials, joining processes and interfaces

Alu^Stir Battery Tray, 1.3 x 1.7 m floor plate, Made from hollow aluminium extrusions, 14 parallel friction stir welds: 22 m weld length Cut off the start and stop or park the end hole in a suitable place, Benchmarking study is based on producing trays for 200,000 cars per year in Europe, 100 sec per car

Quality and Cost: aiCAM^stir Software, The vision is to develop a software-package that adjusts the parameters automatically based on CFD, analytical modelling, parameter monitoring, image analysis and non-destructive testing, aiCAM^stir Ontology, To predict the quality and cost of FSW based on parameters, variables and boundary values

Flow Drilling

VW ID.4: Munro and Sabic, Necked 8.8 bolts, stretched by a torque wrench („it would take an act of congress, to change that”), Flow Drill fasteners, Anaerobic serpentine seals, Interlayers against galvanic corrosion

Flow Drilling: Weber, System 46,000-48,000 € + 350 kg payload robot, Spare parts, IP 12 „bit“ at 17-20 € for 200,000-300,000 parts Brackets for 500,000-800,000 parts, Fasteners, 2×18 + 2×23 = 82 per car, 0.03, 0.10 or 0.15 €

Flow Drilling: Weber and OTC etc

FSW (friction stir welding)

FSW: Ideal for Aluminium, Low distortion, Very reliable process, Use high quality extrusions with good tolerances, Use rigid machines with sophisticated force and position control, Good clamping required, To be welded from one side using a mechanical interlock or from both sides simultaneously, Run-on and run-off tabs are possible

Gantry, CNC-Cell or Robot? Welding speed > 3m/min (up to 5 m/min) depends on rigidity and pin length. Bespoke FSW machine or converted milling machine? FSW and CNC milling in the same fixture? High performance gantry machines for EV battery trays

FSW Tools: Wear Mechanisms, Adhesion (tribological reactions): pits and notches (scoring), Diffusion (embrittlement and fatigue): shearing off the pin. Recommendations, Avoid notch between pin and shoulder, Use Triflat instead of Triflute, Reduce the rotation speed, Increase pin diameter, Keep shoulder diameter as small as possible, Use harder materials, Use coatings

Three cells with a total of six FSW machines are required for 200,448 cars/year

MIG Welding (metal inert gas welding)

Ford Mach-E: Munro: MIG welding, Variation LHS-RHS: robotic and manual or differently programmed, End-crater parked away from the highly stressed zone, Burn-in at the weld start, Consistency and accuracy are required, MIG welding of aluminium is more difficult than MAG welding steel, because you cant see the temperature, Production ramp-up is complicated and expensive

Ford Mach-E: Nemak, 2 Fanuc robots, 2 MIG welding kits, 1 positioner, Simple automated hydraulic fixtures

OTC MIG Welding, 2 OTC FD-B6L, 1 OTC FD-V166

2 MIG welding robots

Aluminium vs. Plastics

Market Segments: Battery enclosure mate-rials of current vehicles, The majority of long range BEVs in current production worldwide use aluminum as the main material for the battery enclosure, However, dissimilar material combinations are getting increasingly attractive

Benchmarking: Munro and Sabic, Expensive tooling for die casting of aluminium, Most OEMs have excellent foundries and want to keep their staff employed, Tray and Total Assembly made from Plastics, Battery Tray: 72 kg vs. 43 kg: Δ 29 kg (weight saving by using plastic), Total Assembly 489 kg vs. 427 kg: Δ 62 kg (cost saving by using plastic)

LME (London Metal Exchange): Premiums and Discounts, According to a rule of thumb, the cost of FSW-specific aluminium 6000 series extrusions is about LME + Premium + 1.0-1.2€/kg

Cost Comparison: Not included, Labour, maintenance and training, Factory building, Sawing and collating of extrusions, Pressure testing, Adhesives and paints, Material storage and handling, Development, crash and fire testing

Benchmarking: Conclusions, An empty battery tray costs approx. 480 €, FSW is very cost effective: 0.69 €/m, The material costs for the aluminium extrusions are the main cost factor, Dissimilar material combinations are often beneficial.
The cost calculation procedure and more details on purchasing aluminium extrusions and selecting the joining processes as well as four Munro Live videos can be found in the following article: Stephan Kallee: Cost of FSW of Battery Trays — Benchmarking of Friction Stir Welding and Other Processes for Battery Trays of Compact Crossovers.

A video recording of this online meeting is available via the following link:

Recording of the Seventh aiCAMstir Meeting (Total: 1:45 h, the first presentation starts at 0:10:16 h)

Literature

• [WAL23] Dominik Walz, Robin Göbel, Martin Werz and Stefan Weihe: Effect of Weld Length on Strength, Fatigue Behaviour and Microstructure of Intersecting Stitch Friction Stir Welded AA 6016-T4 Sheets. https://doi.org/10.3390/ma16020533.

• [BYO11] Badarinarayan, H.; YANG, Q.; Okamoto, K. Effect of weld orientation on static strength and failure mode of friction stir stitch welds in lap-shear specimens of aluminium 6022-T4 sheets. Fatigue & Fracture of Engineering Materials & Structures 2011, 34, 908– 920. https://doi.org/10.1111/j.1460-2695.2011.01584.x

• [OHH05] Okamoto, K.; Hunt, F.; Hirano, S. Development of Friction Stir Welding Technique and Machine for Aluminum Sheet Metal 261 Assembly- Friction Stir Welding of Aluminum for Automotive Applications (2) -. In Proceedings of the SAE Technical 262 Paper Series. SAE International400 Commonwealth Drive, Warrendale, PA, United States, 2005, SAE Technical Paper Series. 263 https://doi.org/10.4271/2005-01-1254

• [HBO06] Hunt, F.; Badarinarayan, H.; Okamoto, K. Design of Experiments for Friction Stir Stitch Welding of Aluminum Alloy 6022- 265 T4 - Friction Stir Welding of Aluminum for Automotive Applications (3) -. In Proceedings of the SAE Technical Paper 266 Series. SAE International400 Commonwealth Drive, Warrendale, PA, United States, 2006, SAE Technical Paper Series. https: 267//doi.org/10.4271/2006-01-0970.

• [SVN19] Suresh, S.; Venkatesan, K.; Natarajan, E.; Rajesh, S.; Lim, W.H. Evaluating weld properties of conventional and swept friction stir 272 spot welded 6061-T6 aluminium alloy. Materials Express 2019, 9, 851–860. https://doi.org/10.1166/mex.2019.1584.

• [Sat02] Sato, Y.S.; Urata, M.; Kokawa, H. Parameters controlling microstructure and hardness during friction-stir welding of precipitation- 297 hardenable aluminum alloy 6063. Metallurgical and Materials Transactions A 2002, 33, 625–635. https://doi.org/10.1007/s11661-0 29 02-0124-3.

• [Rod09] Rodrigues, D.M.; Loureiro, A.; Leitao, C.; Leal, R.M.; Chaparro, B.M.; Vilaça, P. Influence of friction stir welding parameters 300 on the microstructural and mechanical properties of AA 6016-T4 thin welds. Materials & Design 2009, 30, 1913–1921. https://doi.org/10.1016/j.matdes.2008.09.016.

Next meeting

We want to invite you to attend the Eighth online aiCAM^stir Meeting on using artificial intelligence in Computer Aided Manufacture of friction stir welds. The meeting will be held on Thursday, 25 May 2023, 16:00 - 17:30 (London), as shown on upcoming events.

Please contact stephan.kallee@alustir.com, if you want to attend the meeting and/or if you want to participate in the project.