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Welding Sheet Metal

Cut and Etch Weld Testing

How to use cut and etch technique to test a weld

Macro etch test is a technique used to test a weld by revealing the structure of the base material and weld. It’s a destructive testing method that is used to evaluate the characteristics of the weld. First, the sample is cut to expose the profile of the weld. This allows us to see how the weld is adhering to the base metal, and also shows us other characteristics like penetration or cracks.

After cutting, the sample is published to reveal create a smooth surface before etching. The cutting process usually leaves a coarse trace on the material, so polishing helps reveal the finer details of the weld and produces a smoother surface.

MIG cut weld

Profile of a MIG weld after cutting

MIG polished weld

The polished surface of the weld with a 240 grit sandpaper

After polishing to the required level, different acid-based solutions can be used to etch the surface and reveal even more detail. A combination of ethanol and nitric acid is usually used. Other industrial-grade rust removers can also be used for this purpose (for example, Rust Off from Bunnings Warehouse or other phosphoric acid solutions). Make sure you use proper personal protection equipment (P.P.E – such as gloves and eye protection) and follow the local regulations for disposal of these solutions as they are usually classified as harmful and corrosive.

MIG weld etching

The etchant acid reacting with the metal 

weld cut and etch details

The profile after etching revealing the weld boundary

After etching the sample in the acid-based solution for a few minutes, the boundaries of the base metal and weld become visible. The visual inspection at this point can reveal additional information about the weld. For example, the following photos show the effect of different wire feed rates on a MIG weld.

Effect of MIG wire feed speed on the welding tested by cutting and etching

6 m/min wire feed speed

8 m/min wire feed speed

10 m/min wire feed speed

Based on these tests, it can be seen that 10 m/min is too fast for the feed speed and there is no penetration or proper adhesion as the wire melts up too quickly to provide proper welding. 8 m/min provides a better weld penetration compared to 6 m/min, however, the operator needs to adjust the hand movement to cover the base of the weld and both sides properly.

Low magnification microscopes can also be used to examine the finer structure of the weld. That’s why polishing should be done to achieve a finer surface finish before etching.

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How is sheet metal made?

What is sheet metal?

Sheet metal is a metal that is shaped into thin, flat pieces by hot and cold rolling industrial process. Sheet metal is one of the basic forms of metalworking and can be cut and bent into various shapes.

How is sheet metal made?

Sheet metal is made by running hot slabs of metal through a series of roughing rolling stands that makes them thinner and longer. To make them even thinner, these sheets go through finishing rolling stands and are then cooled and rolled into coils.

Aluminium Welding Melbourne

What are metal pickling and pickled and oiled steel?

Pickling is a surface treatment method used to remove impurities such as stains, inorganic contaminants, rust or scale from the surface of the metal after manufacturing by using an acid bath.

Aluminium forms a protective layer of oxide when exposed to atmospheric air that protects the aluminium from further rusting and oxidisation. However, steel can rust after going through pickling. To protect steel from rusting, a thin film of oil is usually used to protect the steel, and hence the term ‘pickled and oiled steel’.

What are the different types of sheet metal finish?

Sheet metal coils after hot rolling and pickling can be used as what is known as a hot band. If special finishing is needed, further processing is done starting with cold rolling to make the sheets even thinner. After that, the sheet metal coils can go through other finishing processes.

  • Galvanising is the process of zinc coating the steel sheets for corrosion resistance
  • Tinning is the process of tin coating the steel sheets for food cans
  • Anodising is used for aluminium to create a thicker protective oxide layer
  • Annealing is used to make the metal sheets easier to bend and form
  • Tempering is used to add hardness and create surface textures in the metal sheets using special rollers

Westberg Sheetmetal offers sheet metal parts in a wide array of materials including:

  • Aluminum
  • Stainless steel
  • Bronze/Brass
  • Copper
  • Steel

To further customize parts, Westberg Sheetmetal offers post-processing options to add to sheet metal parts such as:

  • Plating
  • Welding
  • Inserts
  • Powder Coating
  • Other custom finishes upon request
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