Control Arm Question....
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,118
Likes: 2
Control Arm Question....
I recently changed the shape of the rear control arms. I machinned away an area needed to clear my 12" HRE 547s. To compensate for this I tig welded in a support plate of 6061-t6 aluminum that more than doubles the cross section of the arm. The tig process was done under water by a certified aircraft welder......the question is: are the control arms heat treated to a specific strength spec? The arms never got above 250 degrees F, so would that change the overall temper of the casting?
Melting Slicks
Joined: May 2000
Posts: 2,974
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From: CenTex Texas
Sorry I can't anwser your question. But what I was wondering is why did you modify your control arms? I know you said you did it to clear the 12" rims but there are alternatives (and probably cheaper too).
Thread Starter
Melting Slicks
Joined: Dec 2000
Posts: 2,118
Likes: 2
There are no alternatives if you want 12"x18" wheels inside the wells. I do not like the look of wheels sticking out 1/2" or more. With a 72mm offset and a 1 1/2" tub, the HREs are even with the body, but with the ride height where I want it, there was rubbing when the car lifted hard over a rise. My new arms have eliminated this problem....I just want to be sure that the original temper has not been compromised.
Melting Slicks
Joined: May 2000
Posts: 2,974
Likes: 5
From: CenTex Texas
LPE's Shock-Travel-Limter/Shock-Relocation Kit should work for 18x12 rims. If not then have your shocks modified to shorten the expaned travel length, that's what I did. I'm running 82mm offset, albeit on a 19x12 rim, but nonetheless modifying the shocks should still work. And it only cost me $130 (I'm using Bilstiens Sport Shocks, and I had them do the modifications). If you decided later to go this route shoot me an email and we can discuss it in futher detail. 
Burning Brakes
Joined: Oct 2002
Posts: 797
Likes: 1
From: Sunny Earthquake Country, USA On the Left Coast (which is becoming more Right!)
HIGHRPM
Any time you weld on most any metal you are melting metal and it's cooling. That's the same as "casting" with the same resultant strength in the weld area as a casting would have (even though done under water). So if you have a forging with 75,000 psi tensile after heat treat, the weld area (where it melted) will have the strength of a casting, say 15,000 to 25,000 PSI, and could act as a stress riser depending on its shape and location relative to the loads on the member.
A thing to know about Aluminum is that it does not have a fatigue limit like steel, so you have to be carefull about alternating tensile stresses in the most highly stressed areas.
However you have probably increased the section modulus and perhaps reduced the stress in that area by reinforcing it.
I would take some photos of the arm with your changes and try and find an engineering stress analyst who could venture a guess.
Perhaps someone here on CF!
I know this does not really answer your question specifically, but it's something to give direction towards finding the answer.
Roy
Any time you weld on most any metal you are melting metal and it's cooling. That's the same as "casting" with the same resultant strength in the weld area as a casting would have (even though done under water). So if you have a forging with 75,000 psi tensile after heat treat, the weld area (where it melted) will have the strength of a casting, say 15,000 to 25,000 PSI, and could act as a stress riser depending on its shape and location relative to the loads on the member.
A thing to know about Aluminum is that it does not have a fatigue limit like steel, so you have to be carefull about alternating tensile stresses in the most highly stressed areas.
However you have probably increased the section modulus and perhaps reduced the stress in that area by reinforcing it.
I would take some photos of the arm with your changes and try and find an engineering stress analyst who could venture a guess.
Perhaps someone here on CF!
I know this does not really answer your question specifically, but it's something to give direction towards finding the answer.
Roy
Last edited by 7.0sc SuperVette; Aug 12, 2004 at 02:30 AM.
Team Owner
Joined: Mar 1999
Posts: 28,753
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From: San Jose/Bear Valley CA
CA Events Coordinator
The only downside to beefing up the A-arms is in the event of impacting something to the point of frame damage. From what I can tell, these a-arms were meant to break at a certain point of stress so the main frame could survive. Vipers have such strong a-arms that it is a common problem to break the frame of the car on a side impact instead of the a-arms snapping like ours do.
VR
VR
