Cool Boundary Case Study

the cool boundary of the arc. Also, the arc column continuously loses the charge carriers by radial migration to the cool boundary of the arc and therefore, imposing a greater requirement of potential for maintaining appropriate charge carriers between the electrode and weld plate.

The voltage principally determines the shape of the weld bead cross section and its external appearance. Increasing the welding voltage with constant current and welding speed produces flatter, wider, less penetrated weld beads and tends to reduce the porosity caused by rust or scale on steel. Higher voltage also bridges an excessive root opening when fit-up is poor. Increase in arc voltage also increases the size of droplets and hence decreases the number of droplets.

These characteristics are important to assure that the weld joint is properly filled, with a minimum of defects, particularly in multi-pass weld-ments. In this case, if the bead height is too great, it becomes very difficult to make subsequent weld passes that will have good fusion. The more peaked and narrow the weld bead, the greater the chance that poor fusion may occur. The weld bead characteristics may be altered via both size and shape. In order to change weld bead size, of weld metal deposited per linear foot (m) of the weld-ment must be changed. Welding current and travel speed are the welding parameters primarily used to control weld bead

For example a typical 10W laser can have peak power of the order of 5 kW. This is possible because the laser energy is delivered in a very short pulse. Peak power can be calculated as Pulse energy divided by pulse width. A pulse that has 1 Joule of energy delivered in 1 msec, will have a peak power of 1 kW. Keep in mind that the calculated value is the average for the pulse duration and actual peak power could be even greater since energy is not uniformly delivered over the duration of the pulse.

Fig. 3.2 Experimental set up for laser welding [Bhujbal and Tadamalle(2013)]

(b) Gap

Gap is the distance between the glass and the work-piece

(c) Laser speed Higher welding speed reduces the heat input to the base material leading to less volume of the base material melted. As mentioned earlier, the weld strength increases with increase in volume of the base material that is melted.

(c) Lens

It means the focus length of lens. Focus length is measure in mm.

(d) Defocus

Laser welding is a kind of high-energy welding. The defocus reflects the energy between the laser and the blanks. At the focus, the energy density is the highest. With the increase or decrease of the defocus, the energy density will be reduced.

3.3.2 Performance parameter of laser