Honeycomb Structure is the Bee’s-Knees for Automotive Lightweighting

The honeycomb design found in the insect world is making its way into the auto industry, beating out man-made blow molded polypropylene in terms of strength and weight.

Used within a variety of automotive components, the honeycomb structure consists of corrugated paper that is made to resemble a honeycomb. It is surrounded on either side by fiber glass sheets and a layer of polyurethane is sprayed on the top and bottom.

“The reason this technology is gaining prominence is that it’s extremely high strength, but also extremely low weight,” said Jeff Hagar, market segment manager for automotive interiors with BASF’s Performance Materials Division. “It’s been on the marketplace for nearly 15 years, but as pressure to lightweight increases, this low risk application will continue to be used to pull weight out of the vehicle.”

Automakers have been making lightweighting strides using this technology in interior applications such as trunk load floors, hatchbacks and sun shades. The European market jumped on the trend first, followed by North America as the Environmental Protection Agency regulations and carbon footprint usage requirements continued to tighten. The honeycomb design is especially popular as it allows automakers to easily reduce weight within non-safety critical applications as opposed to the vehicle’s chassis applications. There is less risk of it negatively impacting its ability to absorb the impact of a crash, in addition to fewer safety restrictions.

BASF has seen a direct correlation between the greater pressure to lightweight and the amount of honeycomb load floors in the marketplace. But BASF’s customer, automaker Daimler AG, was determined to take it a step further, having already used a polyurethane honeycomb system in some of its semi-structural interior vehicle parts.

The request from Daimler to its supplier partners, BASF and Fehrer Composite Components, was to create a lighter weight roof for the new smart fortwo small city cars using the existing honeycomb technology and same Class A foil from previous roof models.

BASF and Fehrer Composite Components rose to the challenge, creating the first exterior car part featuring honeycomb sandwich structure with a class-A film, resulting in 30 percent weight savings compared to the previous roof. To meet the demand, BASF used its Elastoflex® technology, which has multiple benefits including:

  • The cycle time of its chemistry. You can build the part in as quick as 40 seconds. The leading competitor’s product currently takes 90 seconds.
  • The chemistry increases the amount of builds possible before the need to clean the mold. The mold-in release of the chemistry enables the customer to build up to 800 parts without having to clean the mold. This is compared to 100 to 200 parts with other systems.
  • An efficient amount of material is used in its construction. BASF’s polyurethane chemistry is engineered to ensure that it sticks to the surfaces without dripping into the composite or onto the floor. You’ll use less material per part, saving you weight and money.

Some modifications were required to ensure that this part could meet Daimler’s needs of an exterior application, including adjusting the viscosity and reactivity of Elastoflex. The solution can be optimally processed in each manufacturing step and shows good adhesion properties, guaranteeing uniform, thin wetting of the fiber glass mats.

The industry-leading properties of BASF’s polyurethane chemistry continue to make it a top choice for Tier I suppliers and automakers when constructing honeycomb structures and the company looks forward to keeping the industry buzzing about its latest offerings.