Hey All,

I am just going into my rear end to PM it over the winter... I was expecting to put in reinforcement plates, considering I was on the 'threshold' as to when they started putting them in. One way or another, I have them... I am just curious if anyone thinks it would be better to leave the existing spot welds, or if I should go in and place a solid bead around the plate completely??

Is it *Always* a good idea to weld up a solid bead whenever possible??

http://www.warhof.com/warp/mod/diff/04.jpg

'tanks,
Chris

All M3's had the reinforcement plates on the chassis for the subframe.

The few bead welds on it right now are stronger, than a continuious bead.

ryanjames

The few bead welds on it right now are stronger, than a continuious bead.

I'm no structural expert, but this doesn't make sense to me.

I'm no structural expert, but this doesn't make sense to me.

Why would factory just not weld it up then... Are they structural experts, maybe - maybe not???

My fabricator advised against fully welding the plates for the reason I had mentioned above.

Kinda like when you seam weld a chassis - it's not one continuious bead, at least the chassis(s) I've seen.

ryanjames

All M3's had the reinforcement plates on the chassis for the subframe.

The few bead welds on it right now are stronger, than a continuious bead.

ryanjames

Then why do the Rear Trailing Arm mounting inserts pull out with the 2-3 bead welds, but the fix is a continous weld??

Then why do the Rear Trailing Arm mounting inserts pull out with the 2-3 bead welds, but the fix is a continous weld??

I thought the subject area was the subframe plates???

Am I wrong or confused:rolleyes ?

ryanjames

There are all sorts of other factors that weigh into what the factory does. The same question could be asked as for why the plates weren't on all E36's from the factory. Or why they didn't just make the chassis out of 1/4 steel to eliminate any chance of the mounts pulling out (and make the car bulletproof). Obviously weight, manufacturing time, cost, etc all weigh into the equation.

As for seem welding a chassis...it has been explained to me that it's a matter of decreasing effectiveness for added weight. i.e. the added increase in weight and time needed to fully weld the seam isn't worth the limited increase in strenght of the joint.

I thought the subject area was the subframe plates???

Am I wrong or confused:rolleyes ?

ryanjames

Easy Ryan;

It was just a reference why a few bead welds would be better than a continueous weld. :D

Ryan, you are incorrect. Sorry, but your information is wrong.

There are more accountants and financial analysis employees than structural/manufacturing engineers. If they can achieve a level of safety/structure for thier use for a much lower price, they will.

If you were to fully weld a chassis, opposed to "seam welding" it will be stronger, however it'll be heavier. The extra rigidity/strength from the additional welds would not be worth it, and its a case of weight vs. additional useless extra strength...nothing to do with it being less strong.

Technically if you "seam weld" a chassis, it will be continuous full beads. However, the traditional way to perform this is to "stitch weld," because it saves weight and adds the required additional strength.

As for seem welding a chassis...it has been explained to me that it's a matter of decreasing effectiveness for added weight. i.e. the added increase in weight and time needed to fully weld the seam isn't worth the limited increase in strenght of the joint.

Are the load-paths put on the joints&welds of the chassis shear or direct... or both?

Where I am going with this is in the instance of the Subframe Reinforcement Plate, the load path is predominantly vertical, or in the same direction of the pressure provided from the reinforcement plate, whereas the welds put on the RTAB bushing carrier are to prevent shear b/w the two pieces of the carrier, reducing pressure on the surrounding welds thus achieving better load distribution.

Any structure that encounters loads is only as strong as its weakest point. If you reinforce one place, you should be reinforcing everything within that system to properly "fix" any existing/planned problems.

Any structure that encounters loads is only as strong as its weakest point. If you reinforce one place, you should be reinforcing everything within that system to properly "fix" any existing/planned problems.

Steve-

This area (the subframe) is already equally reinforced.

I will still stand by what I have advised - as would my cage builder.

Things sure to turn into " well then why this " or "you are wrong that" real quick here..

There are areas where the heat effect has no issue at all, based on load..



ryanjames

Can you explain why you advise or believe this, "The few bead welds on it right now are stronger, than a continuious bead."

I will still stand by what I have advised - as would my cage builder.

That's fair, I'm just simply asking for an explanation as to why your advice is true besides your answer of "BMW did it." I've already explained why I don't think that makes sense as an explanation. Your advice goes against everything I've learned to this point from the advice of engineers/structural folks and my own study, but I'm open to learning more.

I've always been told and believe, when welding a thicker plate to thin sheet metal - it's better to stitch weld it - which keeps the specific area stronger. We all know how thin this specific area is. More so, why heat fatigue an area which is a known problem - (this all being based on the area being welded and the constant load it absorbs)


I'm not saying in all circumstances or areas a full weld is not desired, but we all know that.



ryanjames

That's fair, I'm just simply asking for an explanation as to why your advice is true besides your answer of "BMW did it." I've already explained why I don't think that makes sense as an explanation. Your advice goes against everything I've learned to this point from the advice of engineers/structural folks and my own study, but I'm open to learning more.

We also know the factory does not get all right - that's the reason these plates are on our chassis(s) - though the correction is accurate.

I've not done any studies, though I'm also going off what I've learned and been advised - and have done on my car.

The main point being - these plates need no further reinforcement.

I didn't on my car -

Watt's did Barry and the guys weld yours up???

ryanjames

Watt's did Barry and the guys weld yours up???

Nope. We tied all 4 subframe mounts directly into the cage, so there's really no need.

http://www.bryanwatts.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=810&g2_serialNumber=2

Nope. We tied all 4 subframe mounts directly into the cage, so there's really no need.

http://www.bryanwatts.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=810&g2_serialNumber=2


As did I -



B.Watts That's fair, I'm just simply asking for an explanation as to why your advice is true besides your answer of "BMW did it." I've already explained why I don't think that makes sense as an explanation. Your advice goes against everything I've learned to this point from the advice of engineers/structural folks and my own study, but I'm open to learning more.


Steve J. Can you explain why you advise or believe this, "The few bead welds on it right now are stronger, than a continuious bead."

I've explained my thought on the subject - people(s) can argue the fact of which is right or better , bluh , bluh, bluh... I chose a fabricator that has been building pro cages before I was born, I trust his opinion and quality.

Chris was asking for an opinion, I gave it.

Chris - what it all boils down to is, asking your fab / cage guy - they'll know. They may or may not agree with what I said -

How much chassis reinforcement has/will be done - via cage / welds, etc,...?

ryanjames

A continuous weld on thin metal puts too much heat into it. Which results in too much distortion of the sheet metal. Not totaly a strength issue since the stitched weld results in a whole bunch of stress risers at the ends on the stitches.

If I remember my British Standard Weld guide correctly, the allowable stress at the nose of a weld is about 3,000 psi. In the middle of a continuous weld it's about 4,300-5,000 psi (its been 12 years - gimme a break if I'm wrong :) )

The whole point of backing plates, doublers, or reinforcement plates is to spread out the applied load to a longer linear distance of welds. Long weld lines that have been stiched will be better then shorter weld lines that are continuous since there will be less distortion due to less heat.

I just gave the engineering answer to a question that long time fabricators know by experience. Take your pick, the answer will be the same. :)

All of which doesn't mean much if you tie the subframe pickups directly to the cage. :)

All of which doesn't mean much if you tie the subframe pickups directly to the cage. :)


Giddyup. Do it right the first time ;)

Where are you out of osborni?

Im up in Dubuque...

From the looks of those pics I dont know if I would call those beads... they look more like tacks to me...

And Id have to agree with both sides, there is really going to be a difference on what is stronger depending on what is getting welded, more often than not stiching is used for time savings as well, welding an entire body with continous beads would be a nightmare... And as stated the time required, and the weight that is obtained far out weigh the actual addition of strength.

Curious if you guys stich welded in your roll cage mounting points? Im not familiar with CCA rules but SCCA and Midwest Council only allow a plate that has an overall area of 144sq inches or 100dq inches, it slips my mind currently. I think our plates on the main hoop measured something like 6x8... And are fully welded... I dont think I would feel safe not fully welding a small plate like this?

thoughts?

From the stuff i've seen in the past year...i'm more worried about the quality of the weld, regardless of anything else, i've seen some horrendous welds that are barely penetrating and are almost all exterior. Quality still supercedes quantity :)

Definatly agree there... Its sad to see people that have actually sought out the help from a 'qualified' shop as well and then see the poor welds and distorted bends...

At least road racing seems to be a little more tuned in with safety when it comes to cage construction...

Go to a local stock car race sometime, local guys around here I swear are going to Meinekee, and using their bender... Ive seen main hopes with the kinks common to production exhaust benders... incomplete welds, and many times not even the inclusion of a base plate, just the tube welded directly to the floor :eyecrazy

Its odd that these guys can even get an insurance to cover these weirdos...


And since I never truthfully voiced my oppion, I would just weld that puppy all the way around

Snowman...unfortunately, i've seen those crazy things at BMW and other track events :(

And since I never truthfully voiced my oppion, I would just weld that puppy all the way around

Taking quality of the weld into consideration as a new variable to this whole process:

I spoke to my machinist at work here, he said that one advantage to stitch welding it is that if there is a crack in the weld from a bad weld, at least it won't spread all the way around making the whole thing weaker than where I started at...

Taking quality of the weld into consideration as a new variable to this whole process:

I spoke to my machinist at work here, he said that one advantage to stitch welding it is that if there is a crack in the weld from a bad weld, at least it won't spread all the way around making the whole thing weaker than where I started at...

Eh, thats not a valid counter-excuse (or whatever) because if one stitch weld failed, then the remaining welds are taking more stress, and more likely to fail soon as well...so it really does not benefit.

What kind of company are you at Warptkid?

On many of my weld designs where thin material is used, I weld one quadrant then go 180 dgrees and weld another quadrant and then continue. Other time I use tack welds at circumferential intervals to minimize distortions and keep the parts concentric, then come back and weld the entire joint for strength. You keep a good geometry, minimize stress concentrations (if its a thru weld), and get a hermetic seal (neccesary in my industry).

BMW is far from a good example to look at for structural integrity. My roadster is in the dealership getting fixed on BMW NA dime for a piss poor rear diff mount and trunk floor design. E36, E46, and Z3 all have a problem. The Z8 is even having frame and strut tower problems that are pretty pathetic.

In the motorsport welding course I took, our instructor welded an Aluminum can without distortion and a PERFECT bead, thats approx .006" thick.

This course concentrated in welding VERY thin chromoly, mild steel, and aluminum to other thickness's.

As long as you take your time, and move around all over the place, and don't concentrate in one place, you can full weld pretty much anything without distorting. There are key benefits to using tig, and this is one of them. As long as your components are properly fabricated to keep gaps to a minimum, it should be pretty straight forward to get anything done with Tig.

If you lookat Aluminum weldments on containers, obviously they have to be welded all around and leakproof (pressure as well obviously) so you are going from a solid part to thin sheet. This can be applied to the steel examples as well.

Steve -

uh, I'm a little surprised it took this many posts for you to talk about tigin'.;)

steve has mentioned an obvious benefit if tig welding.

However, this does not answer Chris(s) question

ryanjames

I just assumed, other then filling in major gaps from "quick" cage fabrication (not necassarily bad, but some builds are rushed) MIG comes in veru handy, especially if you cna make MIG's look beautiful, its a great skill. I like TIG because you have much more control...but with more control you also have more things to make sure you are doing properly. I wish I can just tig all day everyda and become a master welder, but i'm far from it haha. Someday...

Steve-

OT: which motorsport course did you take???

Aside from the local welding courses available, I'd love to take a more advanced course.

ryanjames

It was actual a custom course we had for us in NY for our Fsae team. We had this crazy welder teach us for 9 hours a day for 2 days straight. It was a lot to take in but it was worth it...just to see him weld coke cans together!

Lincoln electric offers motorsports welding courses. Expensive though...but welding is probably one of the top two manufacturing skills to have, no doubt.

Here ya go Ryan http://www.lincolnelectric.com/focus/motorsports/school/school.asp