Due to the high degree of precision involved in steel fabrication processes, poorly executed operations can give rise to a significant number of defects. These defects need to be rectified during production so that resiliency and durability of the finished product is not compromised and quality is not adversely impacted. Each sheet metal process comes with its own unique set of defects and this also corresponds to the type of end product being developed. This blog is the first of a two-blog series which will look to discuss the defects generated due to two common metal operations – bending and welding – and corresponding solutions in this regard.
Bending Defects and Solutions
Sheet metal bending is an important sheet metal process due to its ability to draw a variety of part geometries without tooling, as well as fast lead times, high repeatability, and automation in metal fabrication. It also allows products to be manufactured from one piece of metal, utilizing heat induction bending services, thus resulting in lower costs, improved strength, and simplified assembly.
Cracks in the bending angle – The two major reasons for cracks in a drawn part are poor metal pliability and having a very small bending radius. To avoid the occurrence of these defects, usage of softer metals, or increasing metal malleability by heating and then cooling slowly is recommended.
Hole deformation – The location of the hole can be deformed by the friction between the concave die surface and the outside surface during the bending process. Such defects can be resolved by raising the pressure of the ejector plate or by adding a hard spot on this plate to increase the friction between the aforementioned surfaces so that they do not slide.
Uneven concave piece bottom – These defects are usually caused by the use of an ejection device, due to insufficient force or uneven material. Therefore, it is required to ensure that the ejection device is set to the correct measure of force, or removed altogether and that the material is evenly leveled before the start of the bending process.
Welding Defects and Solutions
Welding is commonly used to join two or more pieces of sheet metal together. Be it MIG Welding (Gas Metal Arc Welding), TIG Welding (Gas Tungsten Arc Welding), Shielded Metal Arc Welding (SMAW), or Flux Cored Arc Welding (FCAW), several defects may be faced if the proper technique is not used.
Spatter – Spatter occurs when molten material droplets are formed near the welding arc. It is usually caused by high currents, wrong polarity, or insufficient gas shielding. To avoid spatter, reduction of the current and arc length and increase of the torch-to-plate angle is suggested. Cleaning the gas nozzle can also help.
Porosity – These defects are caused when hydrogen, nitrogen, and oxygen are absorbed in the molten weld pool. Upon solidification, they are trapped in the weld. Grease, moisture, paint, and rust can also cause porosity. To prevent this issue, ensuring the plate edges are clean and dry, using fresh welding materials, and checking the welding torch for leakages can help.
Undercut – Undercut occurs when high voltages or long arc lengths are used. Utilizing an incorrect electrode or one that is too large relative to the thickness, as well as a fast travel speed of the torch, can also cause this problem. Such defects can be averted by using an electrode that is just the right size, ensuring that the torch is moved slowly, and avoiding holding near the vertical plate if a horizontal fillet weld is being made.
It is evident that sheet metal plays a vital role in the manufacturing industry due to its ability to undergo a variety of processes. In practice, it is not possible to achieve a “zero-error” production, hence it is vital that defects are rectified immediately so that the final product fits business requirements. Ultimately, quality is the holy grail for the customer – and customer is king!