[ekbmuts]

From a larger sheet, I plasma cut two pieces of 11ga diamond plate both 1-1/2" x 48". I'm replacing some missing stair nosing on a steel staircase.

So far so good, even though the cuts were a little wavy. I flap-disced all the edges to get rid of the roughness. It was at that point that I noticed that each piece was bent, even though the cut was relatively straight. In other words, placed on a flat table, the pieces laid flat but when placed on edge, they were both like a seesaw.

Regardless, I took a large piece of 1/4" angle, clamped my two pieces of cut diamond plate to it, straightened them out and welded them into a stair nose. I welded the outside edge and penetrated fully. They welded easy enough. I waited for the new piece to air-cool entirely before removing the clamps.

When I took the clamp off, I had a bow along the weld seam. Placed on a table to make a "V" shape, I had a good 1/4" bow - 1/4" off the table at the highest point.

I took a propane torch and tried to heat the piece to bend it back straight but with little success. Then I hit the inside of the "V" with my TIG torch, just to give it some extra heat. That straightened it immediately but not evenly.

What am I missing here? There must be some basics to this that someone could give me a brief rundown on.

I'm also interested: Is there a way to prevent the plasma cutter from distorting the metal along the cut edge?

Any advice would, as usual, be very appreciated.

THKS. Jon

[cj737]

Heat causes distortion, no two ways around it. The thinner the material, the worse the distortion.

Depending upon how you welded the “nosing”, you either trapped stress into the part or worse, caused more distortion by repetitive heat cycles for lightweight metal. Hard to know without seeing the piece or knowing your technique.

[Poland308]

Diamond plate never bends evenly. Unless you use a lower die in the press that is made of special compression rubber.

[ekbmuts]

Fair enough.

Question: Does clamping only minimize the distortion effect rather than nullify it? Even though I clamped it to my larger piece of angle iron dead straight and allowed it to air-cool, it still came out warped.

Jon

[weldin mike 27]

You need to preset your parts against any possible bending. That means you put a packer under the middle, clamp the ends and weld. When it bends, hopefully it won't go back past flat. How much use need preset is trial and error. And the time you need to keep it clamped after welding.

[Arno]

Question: Does clamping only minimize the distortion effect rather than nullify it?

Because steel (like many other materials) has 2 ways of deforming:

• Elastic
• Plastic

The first is like loading a spring. You can deform steel and if you don't overdo it it will 'spring back'.

Plastic deformation is when the change is permanent and 'set' after you remove any force.

They go hand-in-hand though, which is why you always need to bend pieces a little further than the desired angle (esp. when cold forming) as the initial movement is elastic and only then becomes plastic. Once you remove the bending force it will spring back a little from the elastic amount of force.

In your case the part may be clamped to a fixed piece, but the stresses from the expansion and contraction during welding of the metal still put a lot of force into the part. It's not visible as long as it's clamped but they are there..

Once you then remove the clamps it basically 'springs back' to the form the stresses in the part dictate it in an elastic manner as if you have wound up a spring with the stresses from the welds.

Sometimes you can minimise it by adjusting your pattern of welding so various 'pull' and 'push' forces from the welds (almost) nullify or cancel eachother out so when the piece is released from a backing piece it won't want to twist or buckle.

Bye, Arno.

[ekbmuts]

Hey Arno, Thanks a lot for your input. Certainly a fascinating subject.

I did a little research myself and found a pretty interesting and scientific approach to it. It was put together by a German engineer. Lots of theory and a bunch of practical. Here's a link in case anyone is interested:

https://www.youtube.com/watch?v=w1XPDzunbY0

Thanks everyone again.

Jon