Machining welding beads from I-beam unions
Machining welding beads from I-beam unions
(OP)
Hi there,
I am designing a "square" made with wide flange beams. It is made with HEB160 beams and the outer dimensions are roughly 700x800 mm2.The plan is welding it.

I am concerned about the accuracy of the whole system, what tolerances we have in the overall dimensions after welding. What is the typical precision one has in this kind of structures?
We plan to make a double V butt welding

One problem we face is the bead interferes with the parts which go bolted up and down this structure. So I was thinking about putting the welded assembly in a milling machine and getting rid off the upper and lower beads. Is this recommended? Just from one side of the V-butt-welding, maybe doing this is crazy...

thanks
I am designing a "square" made with wide flange beams. It is made with HEB160 beams and the outer dimensions are roughly 700x800 mm2.The plan is welding it.

I am concerned about the accuracy of the whole system, what tolerances we have in the overall dimensions after welding. What is the typical precision one has in this kind of structures?
We plan to make a double V butt welding

One problem we face is the bead interferes with the parts which go bolted up and down this structure. So I was thinking about putting the welded assembly in a milling machine and getting rid off the upper and lower beads. Is this recommended? Just from one side of the V-butt-welding, maybe doing this is crazy...

thanks





RE: Machining welding beads from I-beam unions
As to typical process capability (achievable tolerance), if you machine the holes before welding then generally wouldn't be great but I'm not close enough to that kind of industry to give a good idea. With accurately cut beams initially, the right fixturing and good technique etc. you may be able to do surprisingly well.
However, if putting the finished piece on a machine is a realistic option you could always consider drilling the holes after welding.
Important thing is functionally what tolerances do you need on the holes?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Machining welding beads from I-beam unions
I suggest you obtain a copy of AWS D1.1 or another structural welding standard that depicts typical joint details and "good industry practices."
If the assembly is to be machined, you should consider a thermal stress relief operation so you can more easily hold the necessary tolerances.
Best regards - Al
RE: Machining welding beads from I-beam unions
Grinding such welds flush is a standard process in many industries - but do it ONLY for the surfaces that must sit flat.
If the bottom of the assembly does not actually have to "flat" then you will probably find that your machinists can support a simple assembly on the milling machine ABOVE the milling machine plate for basic operations like drilling bolt holes with little problems. An automated milling machine can drill the holes, but you MUST decide where you need to index the clamped assemblies FIRST (before making jigs and fabrication assemblies!) so that all of your stacked tolerances end up with acceptable hole locations.
Alternative: Drill all of the holes, put the drilled parts into a jog with pegs or bolt studs to locate the already-drilled bolt holes, THEN weld the plates and beams together. But you will still likely get some weld shrinkage and frame warping as the welds cool.
RE: Machining welding beads from I-beam unions
Dave
Thaidavid
RE: Machining welding beads from I-beam unions
We need a precision better than 1 mm. This structure will sit on two parallel rails (two rollers each).
I am now concerned about the perpendicularity of the welds. Isn't perpendicular welding pretty standard? If one looks industrial buildings. What if we cut in the flange like this?:
We get two additional bead lines perpendicular to the original one.
About the machining the guys in the workshop will know; but do we really need to put it in the kiln? I guess not everybody anneals all the welded structures... but I am just guessing
thanks
RE: Machining welding beads from I-beam unions
With regards to the thermal stress relief, the maximum temperature is between 1150 and 1250 degrees F with a hold time of about 15 minutes for each 8 mm of thickness. This is to reduce the residual stresses to a tolerable level that will allow one to hold the necessary machining tolerances.
Best regards - Al
RE: Machining welding beads from I-beam unions
What is the load path between whatever you are putting on this and the rails?
RE: Machining welding beads from I-beam unions
To get a better fit with the mating part contact surfaces, it is common practice to weld local raised pads at the bolt hole locations, and then finish machine the pad faces after welding/stress relief. This approach does not require any material to be removed from the I-beam flanges.
RE: Machining welding beads from I-beam unions
MintJulep, I must admit the design is an overkill. Here are the forces, about 3t up and 2t down. They go directly to the beams perpendicular to the rails, the other two beams (parallel with the rails) are just connecting beams. I was thinking decreasing the size of these connecting beams, but I wanted continuity and everything connected on the flanges:
tbuelna, you mean an additional small plate welded and then machined?
thank you all
RE: Machining welding beads from I-beam unions
You could probably reduce the size of the connecting beams, but the detail shown provides rigidity. No dimensions are provided, but structural steel is typically provided in 20 or 40 foot lengths. So, if all four components can be cut from the same length, there is no cost savings if two 20 foot beams are cut to t he proper lengths and half of each twenty foot length is scrapped.
Best regards - Al
RE: Machining welding beads from I-beam unions
The plate assembly is certainly very rigid.
But! The twisting forces will be transmitted to the left-right rollers to the tracks - which are NOT rigidly attached to anything. Rather, the track rollers have a gaps between roller and roller body, roller and tracks, and the tracks themselves are only attached at intervals to the "floor" - whatever that might be.
Thus, your very rigid, very strong frame will stay rigid, but will easily rotate as a whole under that twisting motion.
RE: Machining welding beads from I-beam unions
Best regards - Al
RE: Machining welding beads from I-beam unions
Weld weld weld weld weld.
Grind a bunch of that weld off.
Stress relieve.
Machine holes.
That's a bunch of work, leading to a part that is far more expensive than it could be if is was designed to do what it needs to do.