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Friction Welding Processes for Floating Solar Application

TWI assisted Sunlit Sea AS with the development of friction stir welding and friction stir spot welding for floating solar power installations.

Introduction

Sunlit Sea AS (Sunlit Sea), a technology provider to the floating solar industry, have developed a new type of technology for floating solar power installations. The solution is based on the prefabrication of serially connected solar panels, whose back plates are made from an intrinsically robust and heat conductive aluminium structure, facilitated for and integrated with a new and effective solution for logistics.

The back plates of Sunlit Sea’s floating solar application consists of two AA5083-H111 aluminium pressings with dimples in a honeycomb structure. The final float assembly, which measures 1880x1880x80mm, is shown in Figure 1. The floats are arranged in a tightly packed matrix, permitting a much more efficient production when compared with the other methods. This solution has excellent hydrodynamic and aerodynamic properties, which can handle rough sea service conditions. The combination of a solid floater and cooling results in lower degradation of the panels, lower operation and maintenance costs, and better health and safety conditions.

TWI was approached by Sunlit Sea to discuss potential joining solutions and manufacturing routes to fabricate the float assemblies. The joining methods for this product needed to be able to:

  • Weld the outer perimeter of the pressings to create a leak-tight edge
  • Weld the flat section of the dimples to increase the stiffness of the assembly
  • Create leak-tight holes in the float assembly for attachments

Considering the material chosen for this application and the service conditions during operation, TWI suggested friction stir welding (FSW) as the most suitable method for joining this assembly. FSW has been used extensively, among other applications, to weld AA5xxx series aluminium products for marine applications. TWI also suggested that friction stir spot welding (FSSW) could be used to weld the dimples and create leak-tight holes in the same fixture used for FSW to increase productivity.

Objectives

The main objectives for this project were:

  • Establish FSW and conventional FSSW parameters for AA5083-H111 that provided suitable weld integrity and static strength
  • Design suitable fixtures to enable the fabrication of floating assemblies
  • Validate the proposed manufacturing route by fabricating one demonstrator float assembly
  • Fabricate a small batch of float assemblies
Figure 1. Sunlit Sea’s float assembly
Figure 1. Sunlit Sea’s float assembly
Figure 2. Floating assembly prototype fabricated with FSW and FSSW
Figure 2. Floating assembly prototype fabricated with FSW and FSSW
Figure 3. Detail view of sealed hole for attachments using FSSW
Figure 3. Detail view of sealed hole for attachments using FSSW
Figure 4. Detail view of two intersection welds around the perimeter of the floating assembly
Figure 4. Detail view of two intersection welds around the perimeter of the floating assembly

Approach and Main Deliverables

Initially process parameters were developed on sheet for both the FSW and FSSW techniques that produced a smooth surface finish with submillimetre flash height, fully consolidated weld cross-sections and suitable static strength.

Following this first stage, TWI designed and manufactured dedicated FSW and FSSW fixtures to fabricate the float assembly prototypes. The manufacturing route for this product consisted of:

  • Welding the outer perimeter of the assembly using FSW
  • Welding the flat section of the dimples using FSSW
  • Creating leak-tight hole locations on outer perimeter of the assembly using FSSW
  • Machining of outer perimeter of float assembly to final dimensions

The proposed manufacturing route and developed fixtures were validated with the fabrication of one demonstrator float assembly. The quality and conformity of the float assembly was assessed and approved by Sunlit Sea before a small batch of floating assemblies were fabricated

Conclusions and Future Developments

TWI developed and validated FSW and FSSW manufacturing solutions for the fabrication of float assemblies in accordance with Sunlit Sea’s design. Sunlit Sea are now working on the implementation of FSW and FSSW in the future design for their fully automated assembly line.

Based on the experience and the data acquired by TWI during this project, Sunlit Sea’s engineering team is already advancing on the integration of this modern welding technique in the design of their future production line through a 3-axis gantry type machine, similar to that used by TWI.

FSW and FSSW are particularly interesting welding technologies, compatible with automated production. Operation time, simplicity, control, repeatability and finish aspect will be the key performance indicators for this implementation.

The small batch of panels produced by TWI have now been deployed in front of the town hall in Oslo city centre and Sunlit Sea are now looking forward to investigating further FSW and FSSW projects with TWI.

Figure 5. Detail view of dimple section of floating assembly, welded using FSSW
Figure 5. Detail view of dimple section of floating assembly, welded using FSSW
Figure 6. Serially connected floating solar panels
Figure 6. Serially connected floating solar panels
Figure 7. Sunlit Sea team
Figure 7. Sunlit Sea team
Avatar Dr Pedro Santos IEng Pedro Santos - Senior Project Leader

Pedro received his MSc Degree in Mechanical Engineering from NOVA School of Science and Technology in Portugal. As part of his industrial placement at The Welding Institute (TWI, Ltd), his MSc thesis focused on the optimisation of Friction Stir Welding process parameters and industrialization to produce tailor welded blanks for lightweight transport application, a project sponsored by Innovate UK (LightBlank).

His PhD research, co-funded by the Industrial Members of TWI as part of the Core Research Programme and Coventry University, focused on the development of the Refill Friction Stir Spot Welding (Refill FSSW) process for lightweight aerospace applications.

Pedro is currently working as a senior project leader in TWI’s Friction and Forge Processes section, managing client relationships and the delivery of projects involving friction welding technologies, predominantly for the aerospace and space sectors. Due to his experience in engineering projects, Pedro is affiliated with the Engineering council and The Welding Institute. As an active STEM ambassador, he frequently presents and supports workshops on engineering related topics to audiences ranging from Year 1 to sixth form students.

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