Bad Welds?

[Old Machinist]

The tube on my LA535 loader passes all the way through and is welded on both sides. Same design on my JD loader.

Hard to believe they butt welded this tube. Kubota should recall these loaders and make them right.

 

[GreensvilleJay]

They built them right, for the designed load that they were made for, roughly 700#. If properly prepped and welded, it works just fine

Could it be made 'better' ? Sure, more engineering, steel, welding jigs, cutting holes, assembly time, etc. There's a LOT of cost in building anything,so to make it profitable , you build to 'specs' that allow you to have profit.

Kubota 'did the math' and what they do does work IF properly done.

Bet everyone here knows a house made with 2by12 walls is better, yet most are 2by6 construction.

 

[chim]

Wirefeed welding can be strong. I'm a hobbyist and the only training I have is the luxury of being coached by the weldors in the shop where I worked while doing some personal fab projects. I'll never be a real weldor, but very much enjoy tinkering. My "fancy well-equipped weld shop" consists of a sturdy steel table on wheels with a Wilton vise, MM175, Hypertherm 30AIR, Everlast 200STi, various De-Walt 20V tools and a driveway. There's no reason a pro (or a factory) can't do better than I can.

With that said, below are a couple pics of the DIY forks made here at home that show what a non-professional can do with fluxcore in the MM175. The starting point was a bought rectangular frame that already had the QA components on the tractor side. I added the two vertical stiffeners, headache rack and the slotted angle "chain grabber". Then I bought 5 bale spears with their tapered sockets to mount on the bottom of the frame with gussets for strength.

One picture shows one bale spear beinig stressed pretty good. I had a 10' piece of 3" EMT that served as a boom to reach out. It was slid onto the spear and two chains went from the far end of the EMT to the chain slots on the QA. The weight / force was sufficient to cause the EMT to slide toward the QA and the gusset to peel the EMT back like a Spam can opener. That left the EMT really bear down on the spear. Fortunately when the weight was removed everything went back into shape.

 

[Hugo Habicht]

Take a look at the loaders on larger models and you'll see that the loader arms are pierced with the torque tube welded on both sides of the arms providing way more torsional strength.

Keep in mind that having the torsion bar through the arms would weaken the arms, so that has to be taken into account.

As far as I can see the design is good but the welding was faulty. As a few people pointed out already: no penetration whatsoever. And that on a weld that looked good on the outside (first picture).

 

[jaxs]

I'm waiting to hear back from the dealership. Problem is, even if I get a new one under warranty, how long until that one breaks?

"How long until that one breaks ?"
Hopefully never but if they offer a replacement you can stack cards in your favor. Call around or better still have your dealer pull up inventory of loaders within number of miles you specify. Pay an expert welder to accompany you to inspect welds starting with closest until you find one with proper welds. THAT'S the loader you want.

My thinking is different shifts,different days and different plants turn out different welds so you are looking for a loader done right. That even applies to robotics which I don't think yours was. At minimum have a pro look at yours in person so you better understand what caused this to break. I say lack of penetration but I'm not a pro. Keep in mind this is not dealer's fault, be kind and thankful to your dealer. If dealer works for you, consider buying or doing something in appreciation.

I'm interested in how this unfolds,please let us know.

 

[Scm]

Not covered under warranty, going to have to have a real professional fix it the right way. Maybe Kubota should focus on quality instead of DEIs & SDGs.

 

[McMXi]

Keep in mind that having the torsion bar through the arms would weaken the arms, so that has to be taken into account.

Actually, no. Cutting a hole through the loader arms or any beam does weaken it for some load directions, but if the hole is centered on the neutral axis, the affect is minimized for loads that are in the same plane as the diameter of the hole. Then you have to account for the wall thickness of the tube in combination with the orientation, in addition to the welds on both sides and you end up with an even stronger cross section centered on the torque tube.

 

[Hugo Habicht]

This may well be. I have not done the maths. But in this case there would be a lot of material missing well outside the neutral axis.

 

[GreensvilleJay]

Well at the 'end of the day', I KNOW it took me 1/2 a day to remove all the 'other stuff', 7 minutes to transport to shop,he spent maybe an hour repairing it, 7 minutes to bring it home, then I spent another 1/2 day reattaching the 'other stuff' back on.
Biggest helper was printing the 'parts diagrams' , as some 'stuff' can go on 3 wrong ways and 1 correct !

 

[Sidekick]

Those are classic stress riser cracks. Mig welding is notorious for causing these and it is usually caused by using a too small of a filler wire. I don’t think that’s the case here. I suspect the quality of the tube steel is the issue. Steel is made with tolerances for amounts of carbon and other alloys. I suspect this run of tubing might be outside of the standard but I don’t know if Kubota uses certificates to monitor their steel or not. I assume they would but maybe these parts are done outside of the factory.

In 2021 and 2022 I was told Kubota was having a hard time getting properly speced steel and the best stuff was going into the larger expensive tractors. Also worker shortages caused the best workers to be assigned to the expensive stuff. That's one of the reasons production numbers were low and my side by Sidekick was 8 months late. Wonder if this was made in that time frame.

 

[GreensvilleJay]

Mine was bought in 2018.... dang almost 7 years ago.

 

[McMXi]

This may well be. I have not done the maths. But in this case there would be a lot of material missing well outside the neutral axis.

The maths is complex, in part due to the geometry. I use SolidWorks in my job and spent a few minutes this afternoon modelling a section of a loader arm with the torque tube butt welded to and also piercing the loader arm. I then ran a stress and displacement study on both and there's only a tiny difference in the deflection under a vertical load which confirmed that the hole isn't reducing the strength of the loader arm. I also ran a torsional study but that's more complicated in terms of where to fix the model and to really capture all of the relationships. I might need to model an entire loader for that.

 

[Runs With Scissors]

My thinking is different shifts,different days and different plants turn out different welds so you are looking for a loader done right.

Being from very near Detroit, I have heard my whole life that "You don't want to buy a car that was built on a Monday or Friday."

I have no idea if thats actually true, nor do I know how the "average Joe' could tell, but thats the saying anyway.....

 

[hagrid]

I'll be "that guy" and guess that this is a material issue and not a welding issue.

 

[TheOldHokie]

I'll be "that guy" and guess that this is a material issue and not a welding issue.

 

[Flintknapper]

I'll be "that guy" and guess that this is a material issue and not a welding issue.

My thought as well. The weld itself is intact. (welding metal being many times stonger than the base metal). Inferior base metal pulled away from the loader arm.

I would agree with others that insuffcient penetration of the weld plays a part in the failure. But I would wager (already poor quaility) steel became crystalline at the weld site due to the heat of the process.

So even IF the weld had penetrated more, failure would likely have occured anyway.

The only other plausible explanation IMO, would be the metal became 'work hardened' (owing to flex at that site) and I doubt the engineers would not have accounted for that.

 

[Old Machinist]

Most loaders I've seen are designed with the torque tube passing through both arms and welded on both sides. Cutting holes in the arms may weaken them if the tube wasn't welded in but the tube should add that strength back and then some. Plus it gives you a handy hole for a rake or shovel handle.

 

[McMXi]

I'll be "that guy" and guess that this is a material issue and not a welding issue.

It could be hydrogen embrittlement (hydrogen assisted cracking) which is one of the reasons for 7018 welding rods that are called low hydrogen rods by some. That would be a welding issue.

We're all guessing here, but I'm not guessing when I say that doubling the weld length i.e. welded on both sides of a tube or beam, doubles the required shear stress to cause failure. If piercing the frame doesn't significantly reduce the strength in the major load plane then it's a small loss for a large gain.

 

[Flintknapper]

Most loaders I've seen are designed with the torque tube passing through both arms and welded on both sides. Plus it gives you a handy hole for a rake or shovel handle.

^^^^^

Or to store some chain.

 

[Chanceywd]

Looking at the OP 's picture I have to wonder about the design of welding that tube to the fish plate. The thickness of that could have been flexing above the cross tube on both sides leading to the break starting there. You can see there is more metal to flex above the tube as compared to below the tube.
It appears all the that plate fractured and stayed with its weld to the tube.

Not a professional welder or metallurgist just thinking if it had been thru both sides it couldn't have flexed the fish plate like that. It may have been a design to keep it from doing the exact same thing if welded to just one side of the arm metal box directly and it failed to live up to that.

Bill