Opposite Side Welding Finish for 18ga SM

[D.Wu]

Hello,

I have a fairly noob question but I hope to learn.

We currently have a product (a cabinet) with a very high aesthetic requirement, it is 18ga 1020 sheet metal that is powder coated with a glossy finish.

The main method that I use to weld everything together are 1/4" plug welds from the inside.

The issue is that from the other side (exterior side) of the plug weld, the heat from welding creates a very slight but annoying visual defect that is very perceivable at an angle because of the glossy paint, basically a heat penetration mark that deforms the sheet metal.

Anyway to eliminate this? I have tried lowering the voltage of the welder but this causes poor penetration and all the welds break easily.

Is there a specific grinding method to do this? Already tried grinding with a 40 then 80 grit wheel, minimized but still perceivable.

Is this the best finish I can get?

I have attached a picture to illustrate the problem.

 

[berkshire]

No matter how you try , you are not going to get rid of this. You can minimize it by clamping a copper bar heatsink on the back face. The weld affects the structure of the steel which is why it shows up even after grinding ,sanding or polishing. If the part you are plug welding to the inside of the cabinet is big enough, like a bracket or a shelf you could look at gluing the part in using VHB tape.
B.E.

You are judged not by what you know, but by what you can do.

 

[D.Wu]

Thank you for the reply!

 

[MintJulep]

The likely cause of the visible defect is the difference in wetability of the surface.

Probably a combination of physical roughness and surface energy-surface tension.

The tech support team of your powder coat manufacturer should be able to offer some suggestions.

Did you know that you can use the "Upload Image" button on the posting toolbar to insert an image inline with your post?

 

[Tmoose]

So the defect is "a heat penetration mark that deforms the sheet metal."

If so, it sounds like sanding does not remove enough material in a controlled fashion to flatten or at least blend the surfaces.

What happens if you paint the surface around the defect with Dykem, or a black magic marker, and use a fine flat file to dress the defect area?
Does a mechanical depression remain ?

If you find there is a mechanical depression, and this was regular painting There are sandable high build primers that are very effective at filling in scratches and low spots, without having to use a filler or spot putty, etc..

This link suggests there are similar products that can handle powder coating' temperatures.

https://forum.caswellplating.com/fo...e-to-fill-pits-in-metal-before-powder-coating