What is a rocker?
An aluminum extrusion within an automotive rocker serves crucial functions related to structural integrity and energy absorption. Primarily, it helps in reinforcing the rocker panel, providing significant resistance to rupture during side impacts. The Verband der Automobilindustrie (VDA) bend test is an essential metric in this context, accurately measuring the material's ability to absorb energy and resist damage (Light Metal Age). Voice of customer (VOC) feedback highlights the need for consistent wall thickness, straightness, and robust integration within the vehicle.
Data from extruded aluminum research suggests that achieving optimal mechanical properties and managing grain structure are pivotal for high performance (ET paper).
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.” Jalopnik.
Rocker Structure
Extrusions are a good fit for rockers due to the low weight and ability of extruders to accommodate the desire of multiple hollows and desired geometry within the available package space. The rocker here is used on a delivery van.
Extrusions within rockers
The extrusion is a work-horse in the rocker by providing structure to the chassis, and crash energy absorption. However, it is never visible to the consumer, rather its hidden behind the Class A painted surface.
The Cadillac CT6 image highlights a number of materials that are integrated to build the body – castings, sheet metal and the extrusion. For extrusions to succeed in the automotive market, there needs to be continuous innovation and application development on integration to other materials, including aluminum to steel.
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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