Qualification, testing and inspection of laser welds

Copyright © TWI Ltd 2015

QCOALA

Quality Control Of Aluminium Laser-welded Assemblies

An idea from : A collaboration between:

LASAG, Precitec, CIT and SAFEL,

Flisom, SolarPro and VW,

Ruhr-Universität Bochum, Fraunhofer ILT and TWI


QCOALA Call & Consortium

• FoF.ICT.2010-10-1 Smart Factories: ICT for agile and environmentally friendly manufacturing

• Duration: 47months (until July 2014)

• 10 participants from 5 countries

• Industry involvement in R&D:

• 30% RTD

• 40% SMEs (laser manufacture, process monitoring, NDT, end-user)

• 30% LE (solar energy, automotive)


Our Consortium


QCOALA Outline

What? Develop a dual-wavelength laser platform for the welding of thin-gauge Al and Cu

Why? To establish capability to provide a reliable, high speed, low-cost and high-quality joining solution

• Electric car battery, and

• Thin-film PV interconnections

Courtesy of Flisom

(solar cell end-user)

Courtesy of Volkswagen

(automotive end-user)


Technical Basis

Steen, 2003


The actual solution

• Precitec dual (Red-Green) wavelength processing head

• Processing head integrated with the pulsed q-switched green laser


Project Outputs

8 Defined Exploitable Outcomes (as per final report)

~30 Events attended (10 by industrial partners)

4 IPR outputs

2 patents

1™

1 Design

Cost-Benefit

Analysis


Two seams for each terminal / busbar interconnection

(6m/min welding speed)

One manufacturing shift - 450 units

Automated unit assembly

Screwing: 3 stations

Laser-welding: 1 station

Cost-Benefit Analysis (Auto. Battery)

Investment for manufacturing concepts

Space requirements for manufacturing concepts

Product weight reduction by using laser welding

Screwing (Existing)

GreenMix Laser (QCOALA)

Fibre Laser (Red laser)


Dissemination and Promotion of the Project Results

Dissemination activities:


Dissemination and Promotion of the Project Results


LASAG

Dual Wavelength-Laser for reliable spot welding of copper

Innovation

Single laser source capable to deliver Green and IR wavelength at the same time. Proportion of Green and IR radiation is set online via pulse shaping.

Customers target

Electronics industry (Ribbon and wire bonding). Solar industry (thin film bonding).

Benefits

More reliable and reproducible copper welding process. Higher yield, less pre-processing costs.

Exploitable Result 1


Precitec TWI

Dual-wavelength laser welding head with sensor interfaces

Innovation

Using green laser radiation improves the quality of laser welding of copper because of the higher absorption of this wavelength. The dual-wavelength laser welding head provides the facility to combine the green and infrared laser wavelength for high quality laser welds even in thicker materials. Additionally all interfaces are offered to attach sensor systems for in-process quality monitoring.

Customers target

End-users (Laser welding companies) Machine integrators R&D facilities

Benefits

Quality enhanced for laser welding of copper. Reproducible results and less quality fluctuations



Safel RUB TWI

Know-how for laser welding copper and aluminium thin sheets (monometallic and dissimilar joining)

Innovation

The laser process development allowed to develop a tool or procedure for assisting in equipment and process selection for micro laser welding of copper and aluminium for electrical connections. A dual-wavelength laser welding head was used to deliver combined green and infrared laser sources, due the perceived innovative capability of this system to address the battery application, in terms of penetration and welding speed required.

Customers target The transport sector as well as other industry sectors involving electronic assemblies using

Copper and Al materials.

Benefits Quality enhanced laser welding of copper (monometallic) and copper to copper dissimilar joining. Reproducible results and less quality fluctuations. A tool procedure to guide industry on selection of the appropriate process window to laser weld

copper and aluminium thin sheets (eg reduced formation of melt ejections, blow holes).



ILT

Indirect measurement of penetration depth in continuous-wave welding of copper for quality assurance

Innovation

Indirect measurement of penetration depth is researched by analysing the relationship of penetration with measurable process quantities such as radiation in visible spectrum or dimensions of the liquid material. The investigation results are novel for this wavelength of the laser radiation and material, due to the intricate nature of laser welding.

Customers target OEM / End-users Machine integrators

Benefits

Assuming enough accuracy and precision of the measurement technique for an application, the weld can be quality assured synchronously with the processing with regard to penetration depth. After further research closed-loop controls can enable welding of new geometries requiring rapid adjustment, e.g. of laser power.

Exploitable Result 4 & 5

TWI

Eddy Current Inspection of Battery Electrode Welds

Innovation Eddy current probe design (micro sized coils), operating procedure for thin metal welds.

Customers target Users of critical laser welds on thin non-magnetic materials or coatings.

Benefits Improved inspection allowing operation for thin materials in more critical conditions.


CIT

Thin wall material NDT digital radiography inspection system

Innovation The ability to inspect laser welded thin material made of Aluminium or copper or composite material can be inspected with this technology.

Customers target Solar panel manufactures. Aircraft manufacturing companies using composite material products.

Benefits Improvement in product quality with reduced cost or ownership. Risk mitigation with evidence of product quality that reduces liability protection.



FLISOM CIT

Welding of busbars on flexible solar modules

Innovation Welding of busbars on flexible solar modules to collect and extract the current

Customers target Solar panel manufactures Aircraft manufacturing companies using composite material products

Benefits Improved and more stable contacting of the busbar with the solar modules


Courtesy of Flisom


VOLKSWAGEN

Laser welded battery terminal connection with copper materials for weight and volume optimisation

Innovation Laser welding process by using the combination of a green q-switch laser and a high power continuous infrared laser for high volumes productions with In-line weld inspection for welding quality of battery terminals

Customers target High volume battery system manufacturer

Benefits Laser welding of copper with high process stability Economical production of connected battery cells for high production rates


Courtesy of Volkswagen


Several standards exist for laser weld quality – not specifically relevant

The most relevant, EN ISO 13919-2:2001, ‘Welding – Electron and laser beam welded joints – Guidance on quality levels for imperfections, Part 2’, relates to electron and laser beam welding of aluminium alloys.

It should be noted that ISO 13919-2:2001 is non-application specific and relates to welds with penetration depths of ≥1mm.

No recognised international standards for laser weld quality QCOALA components and materials

New to industry application of laser welding to battery terminals and solar module electrical interconnections; in-house quality criteria for such joints are in the process of being developed.

For the QCOALA applications, key quality requirements identified:

Minimum spatter from the surface of the welds to maintain a clean

production environment. This requirement will be reflected in a lack of blow holes and melt ejections from the surface of the lap-welds produced.

For Cu-to-Al dissimilar welding minimised formation of cracks due

to intermetallic phase formation between the two metals.

Standards and Regulations


Constant ‘battle’ within the consortium about following DoW vs ‘Doing the relevant thing’

RTO/University [keep EC happy] vs

Industrial partners [solve their problems]

Consensual decisions were made

SolarPro left the consortium at M24 – due to external environment (rather than project progress)

Approached the EC for a single amendment (M24) – which was accepted Did ignore / not include new side-ground developments (i.e. can

use Red lasers solely)

Project Management and Governance


Thank you for your attention

Documents

Qualification, testing and inspection of laser welds