What Is Peening in Welding?

As you complete a fillet welding process, the fatigue strength of the metal can reduce a lot. It is still a possibility if you use clamps to keep the metal steady. Peening a metal sheet can increase its fatigue strength and decrease the stress inside it. It is true that the process actually does not remove or reduce internal stress.

Instead, it simply redistributes it in the crack. When you peen a weld joint, it stretches the joint during its cooling process. Thus, the stress gets distributed. In this article, we will talk about various peening types and other necessary information.

Why Is Peening Done?

Peening is done on a weld joint to balance the internal surface stress and the tensile stress inside the metal. Without doing this, the joint can get cracked and reduce the fatigue strength of the metal sheet. It also creates stress corrosion, decreasing the quality of the metal.

During a peening process, the form of the welding joint is changed with the use of an air-hammer as the weld beads keep cooling. These beads will spread as a result, which will decrease the stress caused by the metal shrinking. Keep in mind that the outer welding layer would expand sideways as you peen. But the bulk material’s elasticity stops that from happening.

What is a Peen Body Part?

Instruments used for a shot peening are blasting machines that can help you bombard the metal parts as required. An automated shot peening machine normally contains these parts-

1. Gun rods.
2. Traveling guns.
3. Media feeds that can be adjusted.
4. Mechanisms that let you load or unload the metals.

In roto peening, several metal flaps are used. In needle peening, people use steel needles. Finally, the hammer peening requires a good-old ball-shaped hammer peen. Keep in mind that the instruments you get are perfect as something wrong can ruin the peening process.

Types of Peening in Welding

Shot Peening

Shot peening is one of the most common peening techniques. Spherical metal parts are shot towards the welding joint at high velocity using an air hammer. One must load the air-hammer with round particles created from several material types and in several sizes.

You can either use a manual or automatic peening machine in order to complete the process. It depends on the welding area and type. Air with high velocity is applied that shoots the round metal parts on the welding surface. Shot peening is an excellent way to improve joint quality and life.

Hammer Peening

Hammer peening is probably the simplest peening technique for most people. All you need is a hammer and the welded metal. All you got to do is hit the weld with the side of the hammer that is round-shaped. However, you must not apply too much pressure. Hitting more than necessary may make the metal too brittle.

During hammer peening, the stress gets relieved from welds with high stress and low fatigue strength. It is almost similar to needle peening in a way but is much easier. Also, it uses a round rod or hammer instead of needles.

Needle Peening

You may find some similarities between the hammer and needle peening processes. In this peening, one will use a cluster of needles to hit the welding spot. The needle impact will move on the beads in a Crisscross pattern. It means that there will be a lot of hits on the beads from the needle than the hammer peening.

To do it, people use a de-scaling gun that hits the needle on the metal, returns them, and repeats the process. The needles will be of hardened steel, and their tips have to be radial-shaped.

Roto Peening

Like shot peening, the roto peening will focus on compressing the welded area. The main instrument here is a number of flaps. These flaps have metal carbide shots placed upon wire fibers. The side-extended flaps will help you create a spindle.

To form the spindle, the flaps will be installed on a drilling machine, which will be rotated at around 3000rpm speed. This speed will determine how much energy to provide on the welding. As the flaps hit the weld, they create the peening on the beads.

What Happens If I Skip the Peening Process?

Skipping the peening process after a weld may seem normal at first, but it possesses great risk. A structure will have countless welding spots on it. Not applying peening means that the welding may stay with high stress and reduced fatigue strength. As a result, the metal will remain brittle.

It may cause any megastructure to collapse, resulting in loss of valuables, injury, or even death. So, the process must not be skipped and done very carefully.

Final Note

Peening is an important part of welding. It prevents weld distortions and balances the stress concentration in the weld puddle. Neglecting it may cause stress corrosion and a lack of fatigue resistance. Both of these are pretty dangerous for a megastructure or any structure in general.

It is ideal to get good at all the peening processes if possible. The hammer peening is useful when there is a lack of peening machines. Meanwhile, the shot peening and roto peening provide a better result.