stamping design of blanket sheet.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * Long Pulse Laser Beam Machining The various undesirable effects associated with long laser pulse etching are illustrated here. The pulse duration in this example is 8 ns and the energy 0.5 mJ Example of a 25 μm (1 mil) channel machined in 1 mm (40 mils) thick INVAR with a nanosecond laser. INVAR is extremely stable. This sample was machined using a “long” pulse laser. A recast layer can be clearly seen near the edges of the channel. Large debris are also seen in the vicinity of the cut. (). * Short Pulse Laser Beam Machining Ultra-short laser pulses have opened up many new possibilities in laser-matter interaction and materials processing. The extremely short pulse width makes it easy to achieve very high peak laser intensity with low pulse energies. The laser intensity can reach 1014 ~ 1015W/cm2 with a pulse 1mJ when a sub-pico-second pulse is focused to a spot size of a few tens of micrometers. * Using short pulses laser intensity easily reaches the hundreds of terawatts per square centimeter at the work spot itself. No material can withstand the ablation forces at work at these power densities. This means that, with ultrafast laser pulses, very hard materials, such as diamond, as well as materials with extremely high melting points, such as molybdenum and rhenium, can be machined. The most fundamental feature of laser-matter interaction in the very fast pulse regime is that the heat deposited by the laser into the material does not have time to move away from the work spot during the time of the laser pulse. The duration of the laser pulse is shorter than the heat diffusion time. This regime has numerous advantages as listed below (/industrial/handbook/introduction.htm): Short Pulse Laser Beam Machining * Short Pulse Laser Beam Machining Because the energy does not have the time to diffuse away, the efficiency of the machining process is high. Laser energy piles up at the level of the working s