Rocker Role

The rocker located is just below the door and plays a critical structural role in the body stiffness and in side impact protection. One way to understand the point of impact protection is to look at all of the EV battery boxes that contain multi-hollow extrusions along the sides to protect the batteries.

  • Tight tolerances
  • Multi-hollow
  • Extrusion achieved in long length

Rockers Success Stories 

Engineering Design

Engineers today have the generative design tools to optimize the shape to meet the design goals within the allowable package. With the critical need of energy absorption, multiple hollows are better than one. The rocker extrusions shown here demonstrate these points well—intentional shapes, multiple hollows, and available in long lengths in mass production.

Cross Sections of Extruded Rockers

  • Multi Hollow
  • Structural Extrusions
  • Efficient Product Performance

The Porsche Taycan EV body is made of predominately steel, yet when it comes to side crash protection, the best choice was extruded aluminum. The reviewer here quotes:

“One of the most obvious crash mitigation components are the 0.6-inch extruded aluminum honeycomb structures running the length of the rocker panels (shown in blue below), which help protect the battery and occupant in side crashes.”


Rocker Structure

Another steel-intensive car with an extruded rocker structure is the Tesla Model 3. The extruded structure consists of a simple row of boxes neatly placed within the sheet metal pocket, delivering on economics, weight, and safety.

Extrusions within rockers

Extrusions are used within the rockers to provide structure and energy absorption, so as you can see here with the Cadillac CT6, the surrounding sheet metal provides the Class A surfaces.

Note, on the Cadillac CT6, the vacuum high pressure die castings, sheet metal, and the extrusion underneath. For application success, your extrusion partner needs to know how you intend to join the extrusion to adjacent materials. The typical options range from flow drill screws or self-piercing rivets to fusion welding and structural adhesives.

Fastening & Joining

The materials for rockers varies within the range of the 6000-series alloys; easy-to-extrude 6005A may be the most common, yet stronger alloys like 6063 are heat treated and quenched to deliver better ductility and energy absorption in a crash. The stronger alloys can be produced with thinner walls for reduced weight.

For best results, begin the conversation early with your extrusion partner to discuss your needs on topics such as strength, ductility, geometry, economics, heat treat, and extrusion speed.

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