Bolted joints and how they're designed
- Thread starter Mike_H
- Start date
Be pretty hard for it to be there since the arm they are using as an example has a slot for the bolt at one end.
Vtx531
TJ Addict
I can say that my rear arm slot wallowed out up and down to the point that my control arm bushing steel inner sleeve imbeds itself into the slot and I can't get proper tension. I suppose the same could happen to a trackbar or any similar connection.
My plan is to pull the axle and weld in a new piece of steel to replace the slot with a hole that is not wallowed out.
My plan is to pull the axle and weld in a new piece of steel to replace the slot with a hole that is not wallowed out.
In my last mechanical engineering gig, I was the bolted joint SME (Subject Matter Expert) for the division that made a certain class of vehicle. We had one particular joint in a suspension that was the most difficult bolted joint issue I've ever solved. There was one particular geographic area where failures occurred and nowhere else so testing solutions was not quick or simple. Through testing, the solution was to go to a different material and torque-to-yield like a head bolt. We did the exact same testing described in that article using torque drivers to figure out the torque spec for the service manual (on the production line, the torque drivers could be set to individually adjust torque to just over the yield point). That was a fun problem to solve!
OP
I've done more torque studies than I care to remember. Self threading screws into plastic though...so a bit different. All tension type fasteners, but they were for OSRVM and that particular component is an inverted delta in a FMEA...thanks FMVSS. I loved the DC drivers we used though. Spendy buggers but the level of control we had on each individual screw was amazing (and necessary).
Let me take a stab at translating. He was involved in quality control for side view mirror assembly and/or installation on cars, and the federal government requires that the manufacturing process include monitoring process variables (screw torque, in this case) to ensure safety. It’s your basic nanny-state intrusion into our lives that few people know even happens. How’d I do Mike_H?OK, now I understand...
OP
Pretty good!
OSRVM - Outside Rear View Mirror. I was a manufacturing engineer (designed assembly lines and worked with product design to make sure what they were thinking was actually possible to manufacture) for a company that designed and built those things. FMVSS (federal motor vehicle safety standards) is a government spec that tells automakers and suppliers what quality standards and design criteria they need to meet regarding safety. FMEA is failure modes and effects analysis...and when you violate the FMVSS, its a 10 severity (the highest/worst severity)...and would get the "inverted delta" as a special note that the design and process guys absolutely, positively need to make sure that whatever component or feature had the ranking wouldn't fail. FWIW, the other things that got 10s in the FMEA were things that would cause death without warning. Yeah...Violating a government standard was the same as something atrocious (like the exploding Pinto fuel tank) that would (not could) cause someone to die.OK, now I understand...
I had manufacturing/assembly responsible for a whole customer's product lineup at our plant (5 programs for a certain company with a blue oval). I worked on the programs from cradle to grave. I used to do torque studies to attach different pieces and parts to a mirror assembly. They are mostly plastic. So, studs into a plastic base that will then be bolted to a car door (if a driver's mirror assm falls off the door, its a violation of FMVSS). I would also do torque studies on the actuator assm to the bracket...because if the glass falls off, its the same violation. There is a HUGE amount of engineering that goes into such a "simple" product.
I was explaining to one of the engineers who worked at Eaton on the OEM supply side about my TJ Dana 44 that came from the factory with 2 short side shafts in it. He asked if I caught it under warranty and I said yes, but only because I was swapping in some stronger shafts and he said that was a good thing for Dana because that would be terrible expensive for them to get caught with that error.
Most of my mechanical engineering career was spent on racing vehicles, and the QC requirements were very simple - win the darn race! I only worked on production vehicles for about 3 years, and they weren't road-going vehicles, so I didn't have to deal with all that FMVSS crap, but I have a brother and some friends who spent careers in engineering in the Motor City, and we'd trade war stories. My time spent in racing helped me hone my diagnostic skills because sponsors don't like it if you break something in the Sunday morning warm up and don't make it to the grid that afternoon, so you learn how to solve problems quickly, or you look for a new career.
OP
It could be. I'm trying to think through the failure mode of putting two short sides in...it would have to potentially lock the axle up and cause a loss of control to make it to recall status.
I'm sure Dana found out about it...I've been in warranty review meetings and they aren't any fun at all. I bet it triggered some problem solving events.
OP
I spent 10 years in tier 1 supply before I got tired of the grind. I miss the engineering, but not the ruthlessness of it all. I got to do and see some REALLY neat stuff in that time. I've been on GM's test track in Milford, been in the wind tunnel, seen cars in clay, etc. I once got a early build prototype F150 for the weekend to use as my own. It was amazing, but man...they whip you. You are beholden to the company and it better be your #1 priority. It gets better the further away from OEM you go, but its still automotive and the profit margins are so thin...I guess that's the trade off for contracted manufacturing.
That is cool. When I was in school I'd fantasize about working in automotive or aerospace. Had offers from boeing and lockheed but they didn't feel right, and I ended up in wood products. Not flashy but it pays the bills. And I get to bring my pup in with me.
You made the right choice. The college I graduated from was recruited heavily by Boeing. To a man, every classmate who went to work there eventually got laid off. They hire and fire based on contracts in hand. No contract, no job. Wouldn't be bad if it wasn't as cyclical as it is. My wife's uncle was an electrical engineering graduate of the same college as mine. Boeing was his first job. Got laid off after 2 or 3 years and spent the rest of his career at AC Delco. He had nothing good to say about Boeing.
Vtx531
TJ Addict