Advanced Computing in the Age of AI | Friday, March 29, 2024

BMW Sheds Weight for the New i3 

<img style="float: left;" src="http://media2.hpcwire.com/dmr/BMW_i3.jpg" alt="" width="95" height="64" border="0" />As BMW starts to make plans for their i3 electric city car, the word on every designer's mind is “efficiency.” While an electric car is already much more efficient than most vehicles on the road, BMW hopes take it one step further, and have turned to lightweight metals to get the job done.

As BMW starts to make plans for their i3 electric city car, the word on every designer's mind is “efficiency.”  While an electric car is already much more efficient than most vehicles on the road, BMW hopes take it one step further, and have turned to lightweight metals to get the job done.

To do this, the company has developed an ultra-lightweight platform, called LifeDrive, that combines a passenger cell made of carbon fiber reinforced plastic with an aluminum Drive module, which holds the battery, powertrain, and structural crash protection.  Through this, BMW has already managed to sheer a tremendous amount of weight from the car.  But going even further, the automaker has implemented magnesium, an incredibly light material, in the instrument panel supports.

According to BMW, “Every step in the development of the i3 has been shaped by the demands of weight optimization.”

However, weight optimization is not as easy as one might think.  Problems do arise and one in particular is that many of the lightweight materials that are being used are not compatible with one another.  For example, attaching a lightweight aluminum roof panel to a steel body presents significant problems when it comes to welding. 

In 2012, Gizmag reported, “Although some engineers have had success in spot welding steel and aluminum together, it has largely been considered impossible to achieve reliable, continuous welds directly between the two dissimilar metals.” 

While this could pose a serious problem for BMW’s i3, researchers from Brigham Young University and Oak Ridge National Laboratory (ORNL) have come up with a solution.  Known as friction bit joining, the solution allows for the metals to work together. 

According to Zhili Fenger, a group leader in the materials joining group at ORNL, temperature is the key.  “Welding steel to steel is not a problem because the two pieces being joined have the same melting temperature,” he says. “But carbon steel liquefies at a much higher temperature [2,600-2,800 degrees Fahrenheit] than aluminum [1,220 degrees F], so the two don’t connect well. The quality of the weld is not good—cracking is a big problem, for instance. That’s why we needed a way of putting them together without melting.”

The friction bit joining approach not only works, but also provides a very strong connection between the metals.  By inserting a thin layer of steel between the two different metals being joined, “A consumable bit cuts through the upper layer of metal to be joined, then friction welds to the lower layer. The bit then snaps off, leaving a flange,” explains a BYU paper.

Michael Miles, a professor of manufacturing engineering technology at BYU says, “Friction bit joining is good for bonding anything very hard [like that steel] to something very soft [like aluminum].”  He also comments that there are other benefits to using the friction bit joining technique, “It’s not just about joining the two metals together, it’s about doing it faster and cheaper.”

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