EFFECT OF PROCESS PARAMETERS

High voltage gives high velocities in the electron beams. The mutual repulsion effects in the constituent electrons will be less marked at high velocities than at low velocities. Therefore, the higher the voltage, the sharper the possible focus. The sharper the possible focus, the deeper the penetration for a given power. The longer the working distance, the greater the depth of field, and greater the focus tolerance. This of course is related to convergence of the beam in respect to the work piece. High voltage beams have a narrower angle of convergence than low voltage beams. As penetration in a material is proportional to the energy density during welding, surface speed will also affect penetration. The slower the speed, the greater the penetration, however, if the speed is too slow the entire work piece will heat up and a massive heat affected zone will result. Therefore the lowest practical speed is limited to around 250 mm per minute. The factors, which influence weld depth, are as follows:

• Beam current
• Accelerating voltage
• Welding speed
• Joint material
• Joint design
• Focal point