1. Power density
This aspect appears a most crucial parameter in laser machining. Due to the power density the face layer is exposed to heating up to the boil point in microseconds. This will result in significant evaporation.
Consequently, density of higher power is especially effective when your task is to punch, engrave or cut.
For low-power densities the facing temperatures reach the boil point and last a few milliseconds.
Prior to the evaporation of the face layer, the down layer approaches the melt point. At this point it is simple to form a suitable fusion welding.
Thus, when conducting laser welding, the power densities are within 10 ^ 4 ~ 10 ^ 6 W / cm ^ 2.
2. Form of Laser Pulse Wave
The forms of laser pulse waves are crucial in the laser weld process, particularly while welding sheets.
If highly intensive beams hit the face of materials, the surface of metals reflect 60-98 percent of laser energy. The reflective performance varies depending on the face temperatures.
During exposure to a laser pulse, the reflective performance of metals change considerably.
3. Laser pulse breadth
This aspect is of no less importance in the laser weld process.
It is a significant specification differing from such treatment operations as material removing and fusion. It also defines the costs and volumes of technological outfit.
4. The effects of defocus on the welding performance
Laser weld process needs some defocus as the power densities in the central area of laser core are extremely great and the evaporation into pores is easy.
Allocation of power densities is considerably even along the layers coming out of laser core.
Defocus can be of positive and negative types. The positive type implies the location of focus planes above the work piece. The case is just opposite for the negative type.
As the theories of geometric optics suggest, the equality of distances within the negative and positive defocusing layers and the weld plane provides similar power densities upon the according plane. Still, the melting pool shape differs. The negative defocus delivers higher levels of penetration depending on the shapes of melting pool.
More than one experiment has indicated that at laser heat 50~200 us materials get exposed to melting, form fluid-phase metals and vaporize in parts, shape high-pressure streams, spray at extremely rapid rates and emit dazzling light.
Meanwhile, vapors of extreme concentration move the fluid metal to the edges of the bath forming a recess in its central part.
In case of negative defocus the inner power densities of materials are more compared to the surfaces. The formation of a strong melt and vapors as well as transmitting the light to the deeper parts of materials is easier.
Consequently, while realizing a practical application, if deep penetration is needed, negative defocus is suitable. Positive defocus is proper to weld thinner materials.
5. Weld speed
This aspect affects the heat input per unit of time.
In case of slower weld speed, the heating input appears larger. This will cause work piece burning.
In case of rapid speeds, the heating input is smaller. This, in its turn, might bring on improper welding performance.