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Cadillac's ATS Cuts Mass 1 Gram at a Time
1/24/2012

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The ATS body structure employs a combination of aluminum, magnesium, 
high-strength steel, and ultra-high-strength steel. 
(Source: Design News)
The ATS body structure employs a combination of aluminum, magnesium,
high-strength steel, and ultra-high-strength steel.
(Source: Design News)

Image 1 of 2      Next >

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Mike C
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Iron
Weight and Design
Mike C   1/25/2012 11:17:56 AM
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There was some discussion in posts on the weight of the ATS projected, vs the weight of a 200 dodge interpid. Being a past owner of a 2000 Dodge interpid I would state if tat weight 3200 lbs it was due to serious fibbing by Dodge. mineweighted a lot closer to 3600 lbs. I have an ide of the weight because when I JUNKED it I drove it to the JUNKYADwere it was weighed for value.

Competitive vehicle weight to the ATS today...2012 Honda CRV 3300 to 3490 lbs depending on model.  Toyota Rav 4 3300 lbs (appox). Bmw x3 2.5 (could be 2.8 BMW no longer tacks models to displacement...hanging around the old Detriot too much). 4112 lbs.

If Honda is hinring and employing a good number of aerospcae engineers, i would like to know from where. The Japanese Aerospace business is very small and people do not move much in the Japanese engineerring world do to the nature of employment. Hoonda itself is a renegade firm in that regaurd it is well know, and Honda is build ing a light jet, but it is Honda first light jet, and past smilar home grown products have been remarkable unsuccessfull.

I think it is time to parise Detroit for doing well. In the past they were darn good. Detroit did show engineering excellence for a very long time esp with keeping with the cost of the products. One can argue BMWs or MBZ prowess, however for the most part once you remove the marketing discussion...German cars cost 20 to 30 % more than equivalent American and Japanese makes.

The use of advaced CFD and CAD  techniquies is NOT the same as using the latest version of say Unigraphics. There is a lot ot getting these packages to perform to thier highest potential and developing anaysis code to be integrated ocvver the std package it a good way to do this. Being critcal of a press release is a good idea. However a better way to analyze the SOA of a firm is to read the technical papers presented at the various conferances on the specific topics.

 

While I am a critic of detriot they have come a very long way up the content, value and quality ladder. I think it is time to evaluate fairly and not with the sweeping hand of ignorance based on times past.

Dave Palmer
User Rank
Platinum
Re: Weight Wins
Dave Palmer   1/25/2012 11:03:40 AM
NO RATINGS
@windy9: As a rule of thumb, I've found that it's not a good idea to use powder metal in any application which sees significant tensile loads (like a connecting rod).  That being said, powder forged connecting rods are widely used in the automotive industry.  According to this article, more than 500 million powder forged connecting rods were produced between 1986 and 2005.  So it's not exactly like this is something new which Cadillac came up with for the ATS.

The powder forging process produces a significantly denser part than conventional powder metallurgy (nearly 100% dense), so the mechanical properties are much closer to a wrought material.

As far as aerodynamics, you have a valid point, but I'm not sure that people who buy luxury cars necessarily want something that looks like a 2000 Dodge Intrepid.

windy9
User Rank
Iron
Re: Weight Wins
windy9   1/25/2012 10:32:10 AM
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Ladies & Gents,

Your comments all seem to applaud Cadillac's design efforts.  And, for the redesign points noted, they all may be justified.  However, at 3400 pounds for a 'compact' SUV, that seems a little heavy for the mission of fuel efficiency for the next 5 years US standards.  For all of the money spent for this redesign, it appears that the computational dynamics forgot to include the aerodynamics of the vehicle.  And, when cars are so expensive, is there really that much usable space in this vehicle? In my 25+ years in commercial aviation, we always always had to consider the aerodynamic loads as the key to fuel efficiency.  Apparently, Cadillac did not based on the shape of this vehicle, and it was not mentioned in the article or any of the comments I read.  Engineering wisdom is based on past successes and failures.  The Dodge Intrepid of 2000 has more space, one of the lowest coefficient of drag at 0.42, and a weight of only 3200 pounds with the highest level of torsional ridigity of any passenger car since then, and at a much lower price while easily achieving 28 to 32 MPG at 70 MPH.

Honda sells more cars than Cadillac.  Maybe the reason for that success is that Honda started and still employs design engineers from the aviation industry.  And, 'powdered metal connecting rods' - that is a recall just waiting to happen.

Alexander Wolfe
User Rank
Blogger
Re: Slow and steady wins the race
Alexander Wolfe   1/24/2012 4:04:25 PM
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Great point about computational analysis, which ties in with the recent crop of stories Beth Stackpole has done about CFD and FEA (computational fluid dynamics and finite element analysis) seeing broader usage. Of course, the automakers have long performed such analyses.

Rob Spiegel
User Rank
Blogger
Re: Slow and steady wins the race
Rob Spiegel   1/24/2012 2:41:45 PM
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Great article, Chuck. With all of the strong metals, I can't help but think one of the objectives is to protect the driver and passengers in the case of a collision. I know one of the fears involved in small-car purchases is the problem that comes when a small vehicle hits a giant SUV. Perhaps these metals answer that fear.

Charles Murray
User Rank
Blogger
Re: Slow and steady wins the race
Charles Murray   1/24/2012 12:54:53 PM
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Beth, here's an addendum to my earlier response: Cadillac's official press info says, "Advanced computational development helped determine the most efficient design." The press info also makes special note of the fact that a team of mathematicians was involved in the design.  

Charles Murray
User Rank
Blogger
Re: Weight Wins
Charles Murray   1/24/2012 12:51:49 PM
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Good points, David, especially regarding the use of steel. As for composites, Cadillac said they employed a composite intake manifold, but, as you point out, they did not use it in the body structure.

Charles Murray
User Rank
Blogger
Re: Slow and steady wins the race
Charles Murray   1/24/2012 12:45:25 PM
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Beth: I didn't ask David Masch about CAE and FEA at the auto show, but I'm sure that played a big role. These days, it's almost unheard-of to do a structural design like this one without the aid of FEA. The beauty of FEA is that it enables engineers to manage stresses and strains in a way that allows them to optimize the cross-sectional area of members, and therefore optimize the weight.

Dave Palmer
User Rank
Platinum
Re: Weight Wins
Dave Palmer   1/24/2012 11:17:02 AM
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Chuck, thanks for a great article on an important topic.  This is a good lesson about how to do lightweighting the right way.  Although the headline of the article says that they cut mass one gram at a time, it's important to note that Cadillac has a well thought-out overall approach, rather than just blindling chunking mass out of components.

I've worked on projects where design groups working on each subsystem were each mandated to reduce weight by 10%.  There was no "big picture" view.  Designers frantically scrambled to take weight out of components wherever possible, reducing wall thicknesses, adding holes and pockets, etc.  In many cases, this resulted in poor decisions, many of which had to be reversed later at significant cost.  

In contrast, Cadillac started out with load path optimization.  Then they built the vehicle around the optimized load path.  This is a much smarter approach, which focuses around making sure that mass is utilized efficiently.

It's also noteworthy that Cadillac's lightweighting strategy made extensive use of steel.  The idea that lightweighting always consists of replacing steel with aluminum is simply wrong.  In some cases, steel is the best way to get the strength and stiffness you need with a minimum of material.

Another thing worth noting is that plastics and composites apparently were not a major part of this lightweighting effort.  I'm sure that Cadillac probably looked at the possibility of using plastics or composites for some of these parts.  It would be interesting to hear their reasons for staying away from these materials.

Alexander Wolfe
User Rank
Blogger
Weight Wins
Alexander Wolfe   1/24/2012 9:43:37 AM
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This story is a significant look at incremental engineering to achieve a goal. The "big" weight-reduction wins aren't there anymore, but there's still gas mileage savings to be achieved with every -- as you say -- gram you can shave off the weight of a car. Cadillac focused its engineering team on this task and achieved it. There's an important lesson here about the team engineering process which extends beyond the car. It applies to the entire auto industry, as well as to smaller-scale product design such as in medical miniaturization.

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