Seventh aiCAMstir Meeting, 26 January 2023

The Seventh aiCAM^stir Meeting was held online on 26 January 2023 with 32 attendees.

Recording of the Sixth 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)

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

Kevin Colligan (CTC, Concurrent Technologies Corporation): Analysis of Torque Data from Friction Stir Welds in Aluminum

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

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.

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

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

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

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Next meeting

We want to invite you to attend the Eight 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.