Bent plate after welding. How to prevent?
Bent plate after welding. How to prevent?
(OP)
I am faced with a design problem that involves welding bending a flat plate. The flat plate is 23.5x23.5x.38 –inches. I’m welding a two 3.00x3.00-inch tubes about 9 inches apart along the center line of the plate. In addition I’m welding 2 L brackets near the center of the plate about 3 inches apart. All this welding on one side of the plate is causing the plate to bend, as would be expected. I’m looking for design ideas that will result in a flat plate after welding.
One common solution is to pre-bend the plate in the opposite direction that the weld bends it, however this plate is being used on two sides of a box and is not symmetrical.
Thank you for your replies.
One common solution is to pre-bend the plate in the opposite direction that the weld bends it, however this plate is being used on two sides of a box and is not symmetrical.
Thank you for your replies.
Cooperjer
Mechanical Engineer





RE: Bent plate after welding. How to prevent?
Give your weld fixture the ability to clamp your plate into a pre-stressed postion. Trial and error will need to be done to determine the correct pre-stress.
Don't weld, bolt.
Straighten plate after welding.
Machine plate after welding.
Stiffener on plate to resist distortion.
If you closely examine the plate around the 3 x 3 tube you will probably find a localized out of flat condition also. How flat do you want the plate after welding?
RE: Bent plate after welding. How to prevent?
Have you considered welding to a thicker plate and then doing a post weld stress relieve followed by machining the plate down to the right thickness.
regards desertfox
RE: Bent plate after welding. How to prevent?
The only continuous labor cost is for shoveling the chips out of the CNC mill, and some of them do that for you, too.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Bent plate after welding. How to prevent?
This is a good question. On two corners of the plate a shaft protrudes out opposite of the 3x3 tubes about 6-inches. This shaft has a plastic roller on it. Any deflection in the plate due to welding or pre-welding manufacturing, as the plate has holes in it, causes the corners to bend toward the 3x3 tube side. This bending prevents the roller from riding flat on the rails. The result of course is increased wear on the rollers and rail. Thus far testing has shown a deflection of about in the plate of .06 to .09 inches due to welding. The addition of the weight of the machine on the rollers causes an additional .06 to .09 inches of deflection in the plate. There is no black and white answer to how flat I want the plate.
A post welding process may be a possibility. I’ll check with fabrication and get their opinion.
Thank you for the responses.
Cooperjer
Mechanical Engineer
RE: Bent plate after welding. How to prevent?
to the other side to help bring it
back to a nearer flat condition.
RE: Bent plate after welding. How to prevent?
I would practice heating on a piece of scrap plate before trying this on your welded assembly.
RE: Bent plate after welding. How to prevent?
Cooperjer
Mechanical Engineer
RE: Bent plate after welding. How to prevent?
RE: Bent plate after welding. How to prevent?
His answer was, has it been welded on?
I answered yes.
His answer was that you had better say a prayer.
You will be able to straighten some SS parts but the very next one will get catty wampus, not telling where it will go.
RE: Bent plate after welding. How to prevent?
RE: Bent plate after welding. How to prevent?
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Bent plate after welding. How to prevent?
Thank you again.
Cooperjer
Mechanical Engineer
RE: Bent plate after welding. How to prevent?
RE: Bent plate after welding. How to prevent?
Are the tubes welded continuously along the length of the sheet or are they stitch welded? Stitching can reduce the amount of distortion. Another variation of this is to stitch while alternating sides of the tube.
I have had some experience with heat straightening on mild steel and it is easy to turn "some" distortion into a "lot" so I would be very cautious on a stainless assembly. If this is your first go at this, plan on sacrificing at least a couple before you have consistency. How much are you willing to risk?
Griffy
RE: Bent plate after welding. How to prevent?
If so, how many of what size?
Is the total deflection from welding and operating load .120" and .180"?
How are the L brackets welded. flat side or on edge with flat side up?
One possible way out if your design will allow it cap/plug the end of the tubes and plug weld from the opposite side with whatever stitch welding is needed on the tube side.
A secret trick that may work on the plate if there aren't too many holes.
Assuming this is a mechanical contrivance.
If I understand correctly the plate has bent up leaving the bottom convex. Turn the assembly upside down lay a straight edge across the plate and find just where the plate starts to break away from the straight edge. Get your best light handed tig welder and let him do a very light fusion pass along a line at the point where plate starts to breakaway from the straight edge. The line will probably not be symmetrical. Only weld where there is a break. You might have to do slightly over lapping parallel passes in the worst area.
RE: Bent plate after welding. How to prevent?
I thought about mentioning redundant 'compensating' welds on the opposite side. We try to keep this type of correction as a 'last resort' in production (cycle time, mat'l, added heat / cooling, etc.) But, it does work.
I've even seen on a high volume, large tubular mig-welded assembly, (where multiple fixtures are in use) an inline probe check that provides feedback to a PLC which in turn calls up a "corrective action" and directs a robot to provide a suitable compensatory weld(s) to pull the assembly back towards nominal.
The "corrective action" table was compiled through empirical data collection and a loose DOE. This effort was well rewarded with a dramatic increase in overall CpK ratings.
regards,
Hydroformer
RE: Bent plate after welding. How to prevent?
Hope some of these help.
Mark
RE: Bent plate after welding. How to prevent?
RE: Bent plate after welding. How to prevent?
Cooperjer
Mechanical Engineer