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PROJECT DELIVERABLE REPORT

Grant Agreement Number: 260153

Project Acronym: QCOALA

Project Title: Quality Control of Aluminium Laser-welded Assemblies

Funding Scheme: FoF.ICT.2010.10-1 Seventh Framework Programme

Date of latest version of Annex I against which the assessment will be made:

23 November 2013

Deliverable Number and Title: D6.3 Evaluation

Name, title and organisation of the scientific representative of the project's coordinator

1:

Paola De Bono Senior Project Leader Specialist Materials and Joining Sector Advanced Materials and Processes Group TWI Ltd Granta Park, Great Abington, Cambridge CB21 6AL United Kingdom F: +44 (0)1223 892588 W: www.twi.co.uk

Tel: +44 (0)1223 899530 Direct

E-mail: Paola.debono@twi.co.uk

Project website2 address: www.qcoala.eu

QCOALA Project Document Reference: PDB.DR.148.fs.14

Author(s): Paola De Bono, Dieter Paethe, David Bremaud, Ralf Nett

1 Usually the contact person of the coordinator as specified in Art.1 of the grant agreement.

2 The home page of the website should contain the generic European flag and the FP7 logo which are available

in electronic format at the Europa website (logo of the European flag:

http://europa.eu/abc/symbols/emblem/index_en.htm ;

logo of the 7th FP: http://ec.europa.eu/research/fp7/index_en.cfm?pg=logos). The area of activity of the project

should also be mentioned.

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Table of Contents

1 Introduction ........................................................................................................................................ 3

2 Demonstrator 1 – PV Cell Interconnections (based on data provided by Flisom) ............................. 4

2.1 Introduction .............................................................................................................................. 4 2.2 Assumptions for cost comparison ........................................................................................... 4 2.3 Techno-economic observations .............................................................................................. 5 2.4 Conclusion ............................................................................................................................... 7

3 Demonstrator 2 – Battery Interconnections (based on data provided by Volkswagen) ..................... 8

3.1 Introduction .............................................................................................................................. 8 3.2 Assumptions for cost comparison ........................................................................................... 8 3.3 Techno-economic observations ............................................................................................ 10 3.4 Conclusions ........................................................................................................................... 12

4 Recommendations ............................................................................. Error! Bookmark not defined.

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1 Introduction

QCOALA, Quality Control of Aluminium and copper Laser-welded Assemblies, is a collaborative project based around the development of new dual-wavelength laser processing systems for welding thin-gauge aluminium (Al) and copper (Cu), 0.1mm to 1.5mm in thickness, with integrated process monitoring and in-line non-destructive inspection, to provide a reliable, high-speed, low-cost and high-quality joining solution for electric car battery and thin-film photovoltaic (PV) cell interconnections. The main technologies developed include:

A dual wavelength (‘GreenMix’) laser system, which has been developed and already commercialised.

A dual-wavelength laser platform for welding Cu and Al for electrical connections in solar cell and battery applications, using fixed and scanning optics.

A weld process monitoring system.

An in-line, post-weld, eddy current and digital radiograghy defect inspection systems. Two different laser platforms were produced for the PV and battery interconnections:

Pulsed laser platform for the PV cell interconnections The Lasag GreenMix dual wavelength system (WP2) integrated with the weld monitoring system (WMS) (WP4) and the digital radiography (DR) NDT system (WP5).

Hybrid continuous wave and pulsed platform for the battery interconnections (CW) infrared (IR) fibre laser and pulsed green laser sources delivered through the same dual wavelength processing head for the battery interconnections. The laser sources and process head were integrated with the WMS system (WP4), the eddy current (EC) and DR NDT systems (WP5).

The QCOALA project focused on the following three main objectives:

Quality - Aimed to achieve a reliable in-line quality assurance system for the QCOALA applications, by monitoring the processing input parameters and by direct measurement of quantifiable parameters (such as physical and geometrical information) to provide feedback information into the production line. Major defects under inspection included surface cracks, internal porosity, and no fusion between the busbar and the battery terminal. The quality of welds was benchmarked against the EN ISO standard 13919-2:2001, ‘Welding – Electron and laser beam welded joints – Guidance on quality levels for imperfections, Part 2’.

Productivity - By using the new laser platform, with its dual wavelength capability, and tailored

welding strategies developed for both thin-gauge Al and Cu (in the thickness range from 100μm to 1.5mm), welding speeds up to 6m/min were achieved for the battery application and this is in line with volume productions speeds defined by the automotive industry.

Autonomous operation - All system components were integrated through robust ICT protocols to ensure that product quality could be assured and maintained (QA/QM), as well as full autonomy of the processing system. The introduction of 100% inspection through integrated process monitoring and in-line weld inspection reduced scrap rate and repair costs of the high-volume automotive and PV applications under investigation.

The content of this deliverable report is based on data provided by the end-users Flisom and Volkswagen. The document forms the basis for evaluating the newly developed fully integrated QCOALA laser platforms. Recommendations were derived for further developments and improvements, with regards to the short and medium-term implementation of the systems into the planned production lines.

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Techno-economic comparisons were carried out to demonstrate the performance of the fully integrated QCOALA laser platforms, compared with conventional manufacturing techniques employed for the thin-film PV and electric battery interconnections. An initial laser system technology review was carried out as part of Task 2.1 and it is reported in D2.1 Laser technology assessment report.

2 Demonstrator 1 – PV Cell Interconnections (based on data provided by

Flisom)

2.1 Introduction

The final user in the PV industry is interested in how much electricity it is possible to generate and at what cost. Therefore, it is common practise to calculate the costs for solar modules per Watt and not per square meter or similar. The most important aspect is the efficiency of the solar modules which describe how much of the incoming energy from the light is converted into current. Since the sun can have different intensities depending on the location or season, standard test conditions (STC) typically carried out at 1.5 air mass (AM1.5) have been internationally defined to make all results comparable and consistent with the used guidelines. The costs per Watt are therefore not only taking into account the production costs but also the quality of a solar module. In this report we are comparing the advantage of the laser busbar welding technology, developed in the QCOALA project, with the commonly used technology at the moment, so-called adhesive tapes, which use busbars with conductive glue. All cost estimations and calculations are done for a yearly production of solar modules with a nominal power of total 100 MW. This mass-production is needed to bring down the costs to competitive values and is representative of current practice. Solar modules may be used for various applications. They can be integrated in vehicles (like trucks, buses, ships, etc.), in rooftops or facades (so-called Building Integrated Photovoltaic, BIPV) or used for harvesting electricity in solar farms. Depending on their application different sizes of solar modules are required with different power and designs. The length of busbar needed for each type of module varies therefore accordingly. The costs are calculated for 3 different solar modules. Their main properties can be seen in Table 1. Table 1: Properties of the 3 solar modules for cost calculation

Solar module Size [m

2] Power [W] Busbar length [m]

L 8 980 18.2

M 1 120 3.1

S 0.5 60 2.6

2.2 Assumptions for cost comparison

For production cost comparisons between busbar welding and adhesive tapes, several assumptions have been made on material, personnel and equipment costs:

Material costs Adhesive tapes are more expensive than classical busbar due to additional conductive glue. Concrete numbers are available from suppliers of busbars, but cannot be disclosed in this report due to confidentiality reasons.

Personnel cost We assume that personnel effort and costs are the same for application of adhesive tapes and laser busbar welding.

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Equipment For the mechanical application of the busbar (eg clamping system for busbar welding, tape application system for adhesive tapes) we have also estimated nominally identical costs. Exact numbers are not available since automatised systems for large production are customised products and not available off the shelf, but preliminary feedback shows similar values, since mechanical application is also similar.

2.3 Techno-economic observations

It should be clarified that there is no inspection system for the busbar when using the current adhesive tapes technique. If a problem occurs, it would be detected at the final stage, where the power of solar modules is measured. On the other hand, an inspection unit is required in the case of laser busbar welding. Based on these considerations, additional costs need to be considered in the case of laser busbar welding, compared to the adhesive tapes technique, and this is associated to the use of the laser and the monitoring systems. In Table 2 the costs of the different components of a complete QCOALA platform (for the PV application) are shown as they were given by the respective project partner. For each equipment mentioned in Table 2, a depreciation time of 10 years and annual maintenance costs of 10% were assumed, if nothing else was specified. Table 2: Cost for laser and monitoring system developed within the QCOALA project. (WMS: Welding Monitoring System, DR: Digital Radiography, Laser: GreenMix Laser)

WMS DR Laser Total

Costs [EUR cents/W]

Equipment costs 5'000 55'500 95'000 155'500 0.016

Electricity costs /a

2'460 2'460 0.002

Maintenance costs /a 500 5'550 9'836 15'886 0.016

Total 0.034

A key value to final costs would be the throughput of a laser busbar welding system. The throughput is not only limited by the laser welding speed itself but can also be mainly determined by the mechanical clamping system itself. Since this was not the goal of the QCOALA project, a significant statement cannot be given. If the throughput of one system is too low, it would mean that several laser and monitoring systems are needed. If everything (i.e. the whole 100 MW) can be done with only one system, the savings would be 0.22, 0.31 and 0.55 EUR cent/W for modules of size L, M and S respectively. The required throughput would then be 69, 94 and 159 mm busbar/s respectively. In Figure 1 the percentage of laser busbar application costs in relation to the total costs of a module per W is given (assuming only 1 system). If more than one system is needed the saving of using laser busbar welding would be reduced. In Figure 2 the yearly savings are given in relation to the number of needed systems. As can be seen the laser busbar welding technique can generate substantial savings if small number of systems are required or if small size modules are produced. However with increasing number of systems and size of modules, the savings are reduced or.

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a)

b)

c)

Figure 1 Percentage of busbar costs (in red) compared to total costs for different module sizes and busbar application. a) Module size L; b) Module size M; c) Module size S.

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Figure 2 Yearly cost savings, for different solar module sizes in dependence of number of laser systems, for a 100 MW production line if busbar welding is used instead of adhesive tapes. 2.4 Conclusion

The laser busbar welding technique definitely shows strong potential to reduce production costs of solar modules. However, this strongly depends on balancing the material costs of the busbar (adhesive tapes and raw busbar) with the exact number of welding systems needed. This is determined by the throughput and processing speed of the welding system, not only the laser part, but also the busbar mechanical application part.

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3 Demonstrator 2 – Battery Interconnections (based on data provided by Volkswagen)

3.1 Introduction

Laser welding is an advanced technology that has already been proven to be capable of providing advanced automation into the mainstream manufacturing of car bodies, as a replacement of conventional resistance spot welding. For electric car batteries, there is the same aim of replacing more conventional techniques (in this case mechanical screwing) with laser welding. This is due to the advantages of the laser technology in terms of high-speed, low heat input and low-distortion. Also less raw material is needed for connecting individual cells (eg screw nuts and bolts are not required). In addition, the implementation of in-line-monitoring and inspection offers the capability to feed-back into the production line, offering continuous quality improvement and reduction of waste. It should be noted that the laser technology is a new approach for welding Cu and Al for electrical connections in battery terminals and therefore yet to be implemented for high volume production environments. The techno-economic analysis, carried out for the battery application, compared the QCOALA combined laser system (green q-switch and fiber laser) with a IR fibre laser as well as the more conventional mechanical screwing technique. Important factors that were considered for the techno-economic analysis were:

Investment costs for the manufacturing concept.

Space requirements for the manufacturing concept.

Weight reduction of battery module when using the laser welding technology. 3.2 Assumptions for cost comparison

Similarly as the case for the PV application, some assumptions needed to be made for the battery application, in order to be able to carry out a cost comparison between laser busbar welding (combined green and IR wavelengths and just IR wavelength) and the more conventional screwing technique. The analysis focused on a system composed of 12 individual battery cells, connected together through the use of Cu busbars. The 12 individual battery cells formed a module unit. Images of a battery module unit, busbar interconnection configuration and dimensions are reported in Figure 3.

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a)

b)

c) Figure 3 Top-view images of a battery module unit and Cu busbar interconnection configuration: a) and b) c) Dimensions of Cu busbars.

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The cost analysis was based on the following further assumptions:

One manufacturing shift with 450 module units.

Automated module unit assembly.

For the laser welding technique - Two seams for each terminal-busbar interconnection at a welding speed of 100mm/sec (6m/min) were set as target. Figure 4 shows the laser welding path to produce two seams for each busbar-terminal interconnection and connect 12 battery cells.

In the case of the QCOALA platform, a total equipment cost of €200,000 was estimated and this included the laser system and process diagnostics (weld monitoring, DR and EC systems). Also in this case a depreciation time of 10 years and annual maintenance costs of 10% were assumed, if nothing else was specified.

For the conventional screwing technique - One interconnection on each busbar-terminal was the target. The screwing tool is currently equipped with process diagnostics.

Materials costs - The screwing technique requires the use of additional material (screw nuts and bolts) compared to laser busbar welding, detailed figures cannot be disclosed in this report due to confidentiality reasons but information on saving costs are captured (in terms of %) in paragraph 3.3 of this document.

Personnel cost - Similarly as the PV application, it is assumed that personnel effort and costs are the same for both mechanical screwing and busbar laser welding.

Figure 4 Laser welding path to produce two seams for each busbar-terminal interconnection. 3.3 Techno-economic observations

As already mentioned in the introduction paragraph of this document, the laser platform produced for the battery interconnections was composed of two laser systems (a hybrid CW IR fibre laser and a pulsed green laser sources) delivered through the same dual wavelength processing head. Figure 5 shows a graph which compares investment costs for the welding platform (with weld monitoring, EC and DR diagnostic systems) and the screwing technique (with incorporated diagnostic system). It was estimated that the QCOALA integrated dual-wavelength platform is just under 40% less expensive than the screwing technique, while it is just above 10% more expensive than a welding platform using just an IR fibre laser equipment (due to the use of just one laser source instead of two). It was estimated by the end-user Volkswagen that the use of the laser technology is able to reduce the number of working stations from three to one (for producing 450 module units) compared with the screwing technique.

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The additional working stations present in the conventional technique are associated with the need to use equipment for accurately positioning screws and bolts in the right locations. This determines the additional costs.

Figure 5 Investment cost (%) on equipment for producing battery module units. Comparison between the laser welding technique and the conventional screwing technique.

A reduction of working stations produces great benefits also in terms of space requirements (Figure 6), which decreases by 70% in the case of the laser welding technology (compared to the screwing technology).

Figure 6 Space requirements for producing battery module units. Comparison between the laser welding technique and the conventional screwing technique.

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Volkswagen also performed calculations to estimate the weight reduction of each module unit when using the laser welding technique. The bolt-free and screw-free joints allowed a 10% weight reduction when producing battery units, compared to the conventional screwing process Figure 7). This factor is extremely important for contributing to an improvement of fuel economy of vehicles.

Figure 7 Weight reduction of battery module units. Comparison between the laser welding technique and the conventional screwing technique.

3.4 Conclusions

The QCOALA project showed the viability of using the laser welding technology in manufacturing, for welding Cu and Al car battery interconnections. This is a very important step forward for the automotive industry, which has used mechanical screwing so far for producing such electrical connections. The following conclusions can be made to outline some key advantages for using the laser welding technology, compared to the more conventional screwing technique.

Construction aspects: No additional parts are required, such as screws and bolts. Weight reduction of battery module units by 10%.

Manufacturing concept: Welding speed of 6m/min results in reduction of necessary manufacturing stations and space

requirement. Reduced investment for realisation.

General advantages: Low heat input during welding process. Good long term stability. High conductivity. High flexibilty concerning the seam geometry.

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4 Recommendations

For both the PV and battery interconnections applications, the techno-economic comparisons (between the fully integrated QCOALA laser platforms and the respective conventional manufacturing techniques) showed strong potential to reduce manufacturing cost and improving in-line quality control. Both end users of the QCOALA project, Flisom and Volkswagen, provided encouraging data, which outlined the advantages of implementing the QCOALA laser platforms into the planned production lines. Although the general architecture of the QCOALA laser platforms was found fit for production environments, some key points still require validations. Therefore, it is recommended that some key areas are fully assessed prior to implementation of the QCOALA platforms in line production; specifically: For the PV application:

The material cost of the busbar (adhesive tapes versus raw busbar) has a strong impact on the final manufacturing costs. Definitive ways to manage material costs still needs to be fully assessed.

There is potential of reducing manufacturing costs by further optimising welding parameters (such as process speed) as well as by optimising the technique used for positioning the busbar onto the flexible PV module prior to welding. These aspects require further assessment.

For the battery application:

The QCOALA laser platform has mainly focused on meeting high speed processing requirements (of the order of 6m/min) in line with the automotive industry. Also the quality control technologies focused on defect monitoring and weld profile validation. The QCOALA project did not investigate in depth the aspects of thermal management to enhance safety levels during manufacturing in line production since it was not the main objective of the project (eg for safely handling the chemistry inside the battery cells during welding of the electrical connections). Although it is expected that the laser technology is compatible with effective thermal management in production (very localised heat input at high processing speeds), it is important that this aspect (and therefore costs associated with effective thermal management) is fully assessed prior to any implementation in line production.