Penetration in laser welding refers to the depth of fusion. It is the distance that fusion extends into the base metal or previous pass from the surface melted during welding. All welding requires the pieces of metal and filler metal to have complete fusion in order to have proper weld strength. Whether it was a deep or shallow penetration, the important thing is you have joined the metals together in one piece. However, there are circumstances where deeper penetration in laser welding is more beneficial.
Welders with limited skills benefit from laser weld penetration. With deeper weld penetration, the chances of achieving a complete fusion even in the presence of new welders are high. Complete fusion at the root of a weld joint is extremely important. This factor is affected by the welder’s skills. With deeper weld penetration, fusion is achieved even if the arc is not focused at a consistent distance.
If you achieve fusion beyond the root, the actual or effective theoretical throat (distance from the weld face to the root) is achieved. Deeper weld penetration allows a smaller to be made with absolutely the same strength level as a larger fillet weld made with lesser weld penetration.
Always take into account that problems may arise when there is lack of fusion in any part of a joint. Incomplete fusion is a weld defect area that will also affect the weld strength. This will then lead to weld failure.
Penetration welding is the most commonly used technique in the industry today. With a laser beam possessing a power density in excess of 106 – 107 W/cm2, any metal is vaporized at the point of contact. The ionized metallic vapour it produces is called plasma. Minimal distortion and a high work speed are then achieved with penetration welding. There is also a limited heat transfer to the adjacent material.