Pro Tip, Weld a Crack in Thin Metal




Introduction: Pro Tip, Weld a Crack in Thin Metal

Last week my uncle asked me to weld two cracks on the bonnet/hood of his car.
These occurred on the place where the locking mechanism was mounted.

He cleaned the location where I needed to weld, but because of this there was a small crack/gap of 1-2 mm. In this instructable I will explain how you can weld this properly.

I recreated this with a piece of 0.8mm zincor plate.

My welding table is based on this instructable

Step 1: Step 1: the Materials

The things I used

  • The metal to weld
  • Welding gloves
  • Welding mask
  • A Mig/mag welder
  • Angle grinder
  • Work gloves
  • Safty goggles
  • The welding table. In a real live situation it is probably not possible to use this.
  • Welding pliers
  • Hearing protection
  • A flat piece of cupper

Step 2: Step 2: Flat Piece of Copper

The trick to weld a crack in thin metal is to use a flat piece of copper.

This has two advantages

  • Copper will spread the heat over a larger part of the metal so you a burn trhough is less likely
  • The underside of the welded part will be flat, this is handy when you can not reach the underside of the weld and this needs to be flat, this was the case on the bonnet.

For the flat copper I used a piece of copper tubing wich I flattend on my anvil (piece of train rail)
Make sure you clean the piece before welding

Step 3: Step 3: Trepare the Part

This is the part I created with a piece of zincor plate.

I locked the copper between the the metal and the welding tabe using my small welding pliers

Step 4: Step 4: Weld

Start welding.

I have a 155 amp mig/mag welder, for this I have it in the lowest setting with the wire speed between 1 and 2.
At the moment I have 0.8mm of welding wire in my machine.

When you weld take your time, it is better to weld it in three shorter bits then in one long and have a burn trough.
With the copper you see that a burn trough does not happen so fast.

When there is a burn trough the copper ensures that the molten metal does not fall through

Step 5: Step 5: Clean

After the fun part, the cleaning up

To clean this part I used an angle grinder with sandpaper. Dont forget to wear the correct protection.
On the last photo you see how flat the underside of the piece is

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    5 Discussions


    2 years ago

    This is a great tip. Thank you.


    2 years ago

    Did you clean the zink off the zincor plate before welding?

    I thought that welding stuff like that caused toxic fumes...


    Reply 2 years ago

    For this small bit I didn't do it, but for larger parts i always remove a small part of the zinc


    2 years ago

    Yep good if you use MIG a lot . Same setup for TIG but easier I think and the one I prefer is gas. You can bring the gas pressures right down and take your time for an excellent join . So how do you keep the copper strip behind the weld on the bonnet ?


    Reply 2 years ago

    I made a smaller copper strip and hold it with a small C-clamp