Automotive Flexplate material

[christianroth]

I'm looking for some input on material selection for a automotive flex plate. The material needs to have at least 40,000 psi yield strength, 60,000 tensile strength and 10% elongation.

I've been discussing it with a number of people and their is a debate going on. Some feel the higher the % elongation the better, along with the highest possible yield strenght. Any comments.

I have see some flexplates made from 4130 steel.

 

[Metalguy]

You probably don't require something as good as 4130 for such low properties. Does your company make them now, and if so what is your experience w/them.

Or, are you a student?

 

[GregLocock]

I'd have thought fatigue life was more important than elongation or yield strength.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[tbuelna]

christianroth,

You may also want something easily weldable. Most commercial flex plates have the starter ring gear welded to the OD of the flex plate, for cost reasons.

4130, even in a normalized condition, has TS and elongation characteristics that far exceed your requirements. There are also many commercial grades of high strength, low alloy steels (HSLA) that will meet your requirements, but at lower cost than 4130.

 

[patprimmer]

All flex plate failures I have seen are the results of cracks after extended use, hence I agree with Greg.

Using thicker material will improve stiffness, and thereby reduce fatigue on the part.

My experience tells me that stiffness is the major quality required to keep the ring gear in good mesh when starting.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[christianroth]

I'm more concerned with your guys opinions on the important material characteristics. I've heard some negative aspect as well regarding the 4130 as it tends not to flex very well in a high strength or heat treated state.

We currently use a low carbon steel, low alloy steel right now with propertes around 80k psi ts, 70k psi ys and about 21% elogation.

I would like to reduce the thickness of this material as we are at 3/16" thick.

 

[Metalguy]

4130 was/is widely used as structural members, including engine mounts, on light aircraft. *IF* it is welded correctly it is very good stuff. *IF* it is HT correctly, it is also. But it is not as "foolproof" as low carbon steel.

 

[christianroth]

I had no idea that 4130 had to be so critically handled when wleding or HT.

 

[Metalguy]

Any time you use a "high strength" material you should be aware that you give up some of the very forgiving nature of good old low carbon steel or cast iron. You need to be aware of how scratches, sharp radii and the metallurgical condition you have.

Usually you have pearlite with low carbon steel, but you may have martensite with 4130. While tempered mart. can be great stuff, untempered mart. is a crack waiting to happen--even with no applied load.

Suggest you take a basic metallurgy course or two--the subject is fascinating!

 

[tbuelna]

christianroth,

Like metalguy says, producing a suitable welded structure in 4130 is not as straightforward as low carbon steel.

For a flexplate of 4130 material that is welded, you should assume the finished part material properties will be in a normalized condition. After welding 4130, it is good practice to stress relieve and normalize the weldment. While it is also possible to put the part through a quench and temper to increase the TS, the quench will likely cause unacceptable distortion of your flexplate.

 

[Tmoose]

"All flex plate failures I have seen are the results of cracks after extended use...........
Using thicker material will improve stiffness, and thereby reduce fatigue on the part."

If the flex is due to the un-meshed starter bendix pusing the ring gear axially (equal force) then the stress would generally be lower with the thicker plate.

But If the flex is due to engined/transmission misalignment then I think the stresses might be higher with the thicker part.

If thin-ness is sought for weight reduction then some expensive creative forming or sculpting or even big holes based on FEA and known failures could achieve it.

If the thin-ness is sought to directly whack down material cost then I'd kind of expect a careful analysis might be able to determine the balance point.

 

[christianroth]

The majority of the application failures are from an over torque stand point.