Welded Steel Hydraulic Reservoir Squareness

Hi Chris,

I had a similar problem many years ago. The root cause was found to be the welding sequence. We started welding on the left and continued to the right until we were done. It warped. What we did was change the sequence such that we welded here then there so that we didn't get a heat build up, and the warpage was reduced.

If your concerned about it rocking after it's done, why not add feet and have them machined after welding, they would end up flat.

Just some Ideas here.

I'd have thaught the basic reservior could be built without mounting points and then welded to mounting points which are pre-assembled onto an accurate jig at the correct locations.

This way you get the best of both worlds, cheap, low tolerance easy to build reservoir, but accurately positioned mounting points.

Sorry if I'm miowwing up the wrong tree, or you've been there done that....after all I'm just a cat... why are you even reading this?

I'm reading this on the notion that there are smarter cats out there than me, and as I have run into a brick wall with this one, I don' t know where else to turn.

Apparently, if we even suggest to the welding shop that it could be done better, the first thing they will do is charge us more, just to talk about it... so this is more of a quality control issue i guess. I had a meeting today with other managers, and they seem to be consistent with the idea of putting up with the basic imperfections, and just trying to weed out the really bad ones... so maybe I should focus more on basic measuring tools and methods.

:)

Chris

This tank has broad surfaces and a lot of points for welding. I understand that the flatness of the broad sides will never be perfect due to the welding stresses, but I would not agree with your current shop's issues concerning squareness.

I think Labyguy has already pointed out that the sequence of assembly and welding needs to be refined. Surely the shop is using even a rudimentary type fixture to hold the parts in position during the initial tack and subsequent weld and not just holding the pieces with a couple of clamps and a piece of angle iron? In my opinion, they are being lazy and welding each joint in an uninterrupted pass.

It can be done, as weldments are available that prove that excellent craftsmanship is available. Me? I would send the drawing to several qualified shops, express your concerns and see what they can do. I realize that you may have done this-more than once. The price may rise, but we know that there is no price for correct quality-just the price for poor quality.

Ing. Robert Forbus

IMO,

Its all layout, fixturing and execution. If you can't do it yourself, it makes it VERY difficult to tell a vendor ho to do it. Elbow grease thats how you fix it. To check to see if it is fixed you need a gage or fixture for checking tolerances my 2 cents worth

As mentioned above, correct welding procedure should help immensely. What type of welding process is used, perhaps switching to MIG would help too if that is not the process already employed. In your picture it looks like there are pieces of angle in the corners, can they be welded on last on a flat surface to provide feet all in a level plane. Is there any reason you can't bend up the tank and just weld in the baffles, the ends and the seam left after the bending ? Could you build the tanks out of an extruded tube if you could find an appropriate size and weld in the ends and baffles. If you need different size tanksyou could adjust the length accordingly. Could tube tanks be an option ?

John

Why not simply make the feet, or fixing points adjustable, that way you could achieve the tolerances with a simple adjustment one you are able to place the unit back on a level surface, alternatively, in vestigate the possibility of outsourcing the manufacture, thus obviating the need for further investment. Depending upon production numbers any additional cost could be amortised in reverse by deducting a suitable amount towards thefigure that would have have been paid for the additional machinery.

The added advantage of outsourcing is that presumably the manufacturer would be able to achieve better tolerances without the additional investment in machinery and you would be able to use more than one source to ensure that if one failed consistently to provide quality you would have another to fall back on. You would then be able to order as and when required so that deliveries were concurrent with manufacturing schedules.

If the tolerances were better the additional costs of having failures would be eliminated, including fitting and disassembly and re-fitting times.

Hope that helps.

They can stitch weld with cooling time between weld. Would be harder to keep it liquid tight due to overlapping weld. Also time consuming.

They can stress relieve before and after weld.

You can design it with more bend to reduce weld. Bend the bottom long edges up and weld on top to keep bottom flat. Don't full weld the baffle inside.

All the above will add to cost. Weld mounting point/plate at bottom is cheapest.

Pineapple

I would see if you can find a shop that can 'break' (bend) the major section(s) of the tank into one 41"x20"x41" 'U' shape 96" long that would form the front, back and bottom of the tank (two less 96" welds, integrity and stability) or do it in two 41"x20" 'L' shapes, (still reducing welding though not quite so stable on the bottom).

Recess the end plates in the above mentioned form, to the thickness of the plate (a bit of fitting involved at the slight radii). Tack on the outside, then stitch weld on the inside; grind out exterior tacks and sequence weld. The interior stitches will limit the amount of distortion from the exterior continuous weld.

Make sure the big adapter fittings are welded into the end plates prior to fitting them. Careful TIG welding for these fittings will usually keeps distortion at bay.

You could also modify the baffles (with holes, slots or triangular openings at the lower corners) such that they are welded at intervals to the bottom plate. You can do this for the top plate as well and plug weld the baffles. This will help maintain squareness.

In any case of what you do, the work should be heavily jigged, as others have said.