QMT Features: April 2013
Quality debate heats up
As  Boeing’s Dreamliner get  ready to resume flights after the grounding of the planes earlier this year, 3DX-Ray’s Vince Deery, discusses the need for stringent quality control of lithium-ion batteries

In January this year regulators grounded Boeing’s Dreamliner planes on safety grounds surrounding the use of lithium-ion (Li-ion) batteries. The decision came after the batteries overheated on two separate airplanes. Although no crew or passengers were hurt the safety of everyone on board was paramount and all of the new 787 planes were stopped from taking to the skies.

It’s not the first time Li-ion batteries have caused a safety scare. The batteries became somewhat infamous due to heat problems, with previous concerns around laptops, electric cars and smartphones catching fire.

In 2006 ago a number of laptop companies recalled batteries manufactured by Sony because they were overheating and in some cases exploding or causing fires.
Although there are many advantages to using these types of batteries, particularly their ability to hold more power for longer, the problems arise from the unique design of the batteries that enables these benefits.

Inside lithium-Ion batteries you’ll find pressurized containers that house tiny pieces of metal and a flammable, lithium liquid. The batteries also contain separators that keep the anodes and cathodes apart. Through the manufacturing process tiny pieces of metal float in the liquid, but if the battery gets too hot through recharging or use, these metals move around. If they puncture the separator it can cause a short circuit.

Although good manufacturing techniques can limit the incidence of these floating metal pieces, the reduction in size of Li-ion batteries can increase the likelihood of problems occurring.

Importance of testing

Only last month a South Korean man suffered burns when his smartphone battery exploded in his trousers even though the battery itself was not even in the phone at the time. These fires are for the most part very rare, and in portable devices the number of incidents has certainly declined in recent years. Nonetheless a risk remains and an exploding battery on a plane has the potential to be far more catastrophic.

As a result this latest case with Boeing emphasizes the need for more stringent quality control regimes for batteries, especially in relation to the anode and cathode inside the battery.

Whether a device works from a purely functional point of view can be easily tested at the end of the production line. On the other hand, checking whether batteries will remain functional for the whole period of their designed life is a far greater challenge.

In particular being able to see latent faults inside the battery, where elements may only be slightly misaligned, could easily go undetected by simple electrical tests. These latent faults that may cause complications long after the batteries have left the factory - potentially a huge problem and can be very dangerous for users as these faults are exacerbated by real world use as we have seen.

In order to guarantee the absolute safety and reliability of Li-Ion batteries manufacturers must provide 100% in-line inspection to check the manufacturing integrity of each and every product on the production line.

X-rays for100% inspection
X-rays uniquely enable you to see inside components, objects or systems that are opaque, or to examine products internally in a way that would be impossible with the naked eye or other vision inspection systems. X-ray scanning is the best way to see inside the batteries to check on the internal structure and to ensure that there are no problems with each battery. There are potentially over 40 features within the electrical assembly of a Li-ion battery that need to be checked in order ensure the absolute safety of each product.

Using modern x-ray systems manufacturers can perform rapid checks on all of these features on the production line. For example x-rays can check for tab clearance between cell walls and the anode and cathode over lap, checking tolerances in millimetres. They can accurately measure linear distances and alignments as well as checking for short circuits and misaligned components that may be present in the electrical assembly.

By introducing these sorts of checks manufacturers can reduce their reliance on limited destructive testing at the end of the line for only a small sample of each batch.

Enhancing manufacturing integrity
Manufacturing integrity is crucial because controlling the quality of batteries can save costs, reducing or even eliminating, faults and product recalls.
The Boeing Dreamliner is perhaps the most ambitious application of Li-ion batteries to date and the company continues to conduct ground and flight tests to check the battery system on board its new plane as it awaits Federal Aviation Administration approval.

However, lessons must be learnt from previous problems. In the end the only way manufacturers were able to restore confidence in the Li-ion batteries for portable products was by stiffening production line inspection regimes. This is a lesson that Boeing and its suppliers are now learning the hard way.l
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Rob Tremain Photographer
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