Safety Q&A: Airbag Containers
The airbag system in your car is a safety-critical application, working to save lives during a car crash. Jos Bellemakers, Application Development Engineer responsible for DSM's polymer supply for airbag containers, talks about safety and DSM's involvement in this application.
Q: What makes airbag systems so challenging?
A: Airbag systems protect drivers and passengers in the case of an accident. When the system deploys, it inflates the airbag – which can be 30 to 70 litres on the driver’s side, and 60 to 170 litres on the passenger side – within 45-60 milliseconds. This induces a high explosive load on the container, and very high stresses on the plastics used to make it.
''The polymer supplier needs to deliver the material within a very narrow specification.''
The polymer supplier needs to deliver the material within a very narrow specification, so that the customer can design a container that fits the space provided by the OEM, that will work as expected, and that ensures up to 30-year longevity required for the part.
Q: Which material characteristics are critical to the success of airbag containers?
A: The material needs to withstand a high impact load from -40°C to 85°C, with an equal property level and consistent performance across the entire temperature range.
''The material needs to withstand a high impact load from -40°C to 85°C.''
At -40°C, plastics become brittle and can break. Any piece that breaks off the container can become a projectile moving at the speed of the unfolding bag, with speeds up to 300km/h, so there can be no breakage during deployment – it must stay intact. At 85°C, the PA6- based plastic will be less strong and more flexible. Finding the right balance between the flexibility required at low temperatures and the rigidity needed at high temperatures is critical to the success of the system.
Q: What has DSM’s involvement been in the production of airbag containers?
A: We have been producing the polymer for airbag containers commercially for more than 14 years. These containers are used in more than 120 million vehicles, and 200 different vehicle types – without a single failure.
''These containers are used in more than 120 million vehicles, and 200 different vehicle types – without a single failure.''
We produce the material in four different compounding facilities – in Europe, the US, China and India – and we have a guaranteed supply of all our source materials so that we can ensure our product is always within the specifications needed by our customers. We offer two main Akulon polyamide 6 polymers – one that is 30% glass fibre by weight, and one that is 40% glass fibre. Both of these have a balanced impact modifier package.
''Molding these parts out of plastic instead of metal provides the opportunity to integrate many features.''
Molding these parts out of plastic instead of metal provides the opportunity to integrate many features, and saves a lot of weight. A metal airbag container from 10 years ago contained 20 working parts, weighing 3.2 kilograms, with 12 separate manufacturing processes. Today, with Akulon, we can make a container with five working parts, weighing as little as 1.0 kilograms (on the passenger side), and with only six process steps. As the industry continues to find ways to make vehicles lighter and more fuel efficient, a 2 kilogram reduction on one part is significant.
Q: What steps does DSM take to ensure a consistent supply of the polymer?
A: There are four main ingredients in the polymer: the base PA6 polymer, glass fibres (for stiffness), impact modifier (for flexibility), and colourant. We have assured supply of all four materials from multiple high-quality sources, so that we can always meet production levels without the need for additional validations.
In addition to testing each material before compounding, we test each batch produced at three different temperatures (-40°C, 23°C and 85°C) on a variety of mechanical properties: tensile strength, stress at break, elongation at break, modulus, impact, relative viscosity, water content, and glass fibre content.
''We supply our customers with limit polymers, so that they can test the extreme limits of the part.''
Finally, we supply our customers with limit polymers, so that they can test the extreme limits of the part in their last verification stage before production.
For high temperatures, the material is the most flexible polymer they could ever possibly receive from us – with the lowest limit of glass fibre and the highest limit of impact modifier in the mix. For low temperatures, the material is the most brittle, with the lowest limit of glass fibre and the lowest limit of impact modifier. They can then use these polymers to test the part with all elements of the airbag system at the extreme edge – with the highest gas generation, the biggest airbag, etc. If these parts do not fail, they can be assured the component is ready for production.
''We deliver the most consistent material possible with every single batch.''
It’s important to note that the customer would never receive these limit polymers during normal production. We set our variation tolerance much closer so we can be sure we deliver the most consistent material possible with every single batch.