Engineering Materials

Aluminum Composite to Lower Weight in Brake Rotor

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Michigan Winter
wb8nbs   2/16/2012 9:39:06 AM
Wonder how the bare Aluminum holds up to a winter of road salt?

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Re: Metal matrix composites
JimT@Future-Product-Innovations   2/16/2012 7:03:06 AM

I was wondering about the method of manufacture and secondary finishing operation.  What alloy compound elements are tolerant enough to withstand the casting process yet still be machineable-?  From the photo, I was further wondering about the dimples on the face of the rotor; their purpose and how they were formed.  Is this a powder sintered part-?

Ann R. Thryft
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Re: Metal matrix composites
Ann R. Thryft   2/15/2012 12:12:38 PM

Thanks, Dave, I was hoping you'd weigh in with some info and feedback about metal matrix composite (MMC) technology. Thanks also for the links. I'm especially interested in what you said about machinability. In fact, when I first read about this MMC I wondered how the heck the ceramic chunks would affect both flatness and flexibility of the matrix fabric. The only thing that came to mind was if they are very, very small chunks or particles.


Ann R. Thryft
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Re: UNSPRUNG Weight Reduction!
Ann R. Thryft   2/15/2012 12:11:51 PM

Thanks for the comments and feedback. Beth, I was also pleased to see an area of the vehicle besides batteries and body panels targeted for weight reduction. Al, this is still in R&D--the prototype isn't yet completed--and there was no mention yet of any industry partners. I, too, was impressed by the 3x service life improvement--I hope it turns out to be true. Stephen, thanks for the info about unsprung weight. And I agree, it's most likely that this, like many other automotive material innovations, may be aimed at higher-priced vehicles.

Dave Palmer
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Metal matrix composites
Dave Palmer   2/15/2012 11:29:24 AM
@Ann: Thanks for a good article about an issue which is very close to my heart.  I used to work for a brake manufacturer, and heavily promoted the use of metal matrix composites for both rotors and calipers.  As your article points out, this is an area where significant weight savings can be achieved.  Many companies are doing work in this area.  One which comes to mind is GS Engineering.

It may be worth noting that cast iron itself can be thought of as a composite material (with graphite as the reinforcement), and that induction hardening can provide "functionally graded" properties.  In that sense, functionally graded metal matrix composites are not really such an exotic departure from what brake manufacturers have been doing for years -- we just never called it that.  But aluminum MMC technology gives us an even greater ability to tailor material properties, at a fraction of the weight. 

It would be very interesting to know some of the details of this product.  For example, what is the reinforcement? (Silicon carbide, aluminum oxide, both, or neither?) Is the composite made by stir casting or infiltration? How is the distribution of the reinforcing particles/fibers achieved? Of course, REL might be understandably reticent about revealing all of these details.

A major issue with MMCs, not mentioned in the article, is machinability.  Putting hard ceramic particles or fibers in a material is a great way to improve its mechanical properties.  But how do you machine something which is full of chunks of hard ceramic without destroying your tooling? You either have to use expensive diamond tooling, or you have to find an ingenious way to keep ceramic out of the areas you want to machine.

One interesting approach for brake calipers, which Allied Signal took out a patent on back in the '90s, is to cast an aluminum MMC with unreinforced aluminum inserts.  The inserts go in the areas which are going to be machined later.

I could go on and on about this.  Thanks for an article on such an important topic!

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UNSPRUNG Weight Reduction!
Stephen   2/15/2012 9:55:11 AM
The best part is the weight reduction is unsprung weight, so has the potential to improve handling and ride quality as well as improve fuel economy and hard braking performance.

Logical place to start would be w/ performance/luxury brands/models, where the higher initial cost is better tolerated, then move down into lower priced/featured vehicle lines as high volume real world experience accumulates, much as (long long ago now) front disc brakes, then, more recently, rear, have replaced drums. 

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3X Life
apresher   2/15/2012 9:16:11 AM
Ann,  Great story.  The possibility of a 3x service life is obviously a huge advantage and balances off against the higher initial cost and makes determining the value more interesting. Any specific interest among industry partners for this technology? Manufacturability and ability to scale to achieve target costs have to be a major objectives.

Beth Stackpole
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Yet another strategy for weight reduction
Beth Stackpole   2/15/2012 7:32:01 AM
Cool development and yet another tool for auto makers to take weight out of their vehicles, aiding in energy efficiency and potentially, reducing costs. With all the focus on EV battery weight and other aspects of the next-generation of more fuel efficient cars, it's great to get a handle on some of the other developments and research around materials that can also aid in promoting more efficient vehicles.

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