Objective: to master the selection principle of laser power and its influence on welding quality in the process of laser welding.
Read this article with the following questions:
- What is the weld forming factor? How to calculate?
- What is the basis for selecting laser output power during laser welding?
- What is the effect of decreasing laser output power on weld penetration and achievable welding speed?
1. Principle of double beam welding
Classification of laser welding
1) According to power density and weld formation characteristics:
- Heat conduction welding: power density (laser output power / focal spot area) ＜ 105W/cm2
- Deep penetration welding: power density > 106W/cm2
2) According to the laser output mode:
- Pulse laser welding
- Continuous laser welding
Fig. 1 Schematic diagram of pulsed laser welding and continuous laser welding
2. Selection of laser power P
The selection of P is determined according to the plate thickness. P determines the spot power density and can control the penetration depth and welding speed.
Fig.2 Curve of power density and metal temperature with time
3. Effect of laser power on penetration
As shown in the figure below, the greater the power P/kw, the deeper the penetration, and vice versa.
Fig. 3 Relationship between laser penetration and power
4. Influence of laser power on welding speed
Supplementary knowledge points:
Form factor (of the weld) is defined in GB / t3375-1994 as:
During fusion welding, the ratio of weld width (B) to calculated weld thickness (H) on the cross-section of a single weld（ φ= B/H), see Fig. 4 below.
When the weld forming factor is small, a narrow and deep weld will be formed.
In the center of the weld, due to regional segregation, more impurities will accumulate and poor thermal crack resistance, so the value of the forming factor cannot be too small.
For example, the forming factor of the weld should be greater than 1.3, that is, the width of the weld should be at least 1.3 times the calculated thickness of the weld.
Fig. 4 Laser power and speed determine the forming of weld
Fig. 5 Relationship between welding speed and laser power
5. Relationship between laser power, welding speed and penetration
Fig. 6 Changes of penetration and welding speed of low carbon steel under different power
The laser welding power determines the spot power density, and controls the welding penetration depth and welding speed;
With the increase of laser power, the welding speed and penetration can be increased.