Magnified Images of Laser Engraving on Wood, Acrylic, and Mild Steel.
Each small dot in this magnified image is a single “pulse.” More frequent pulses result in a tighter array and a finer surface finish.
Materials that are sensitive to thermal damange, like acrylic and rubber, are suited to higher-frequency engraving.
Do you want to take a look for yourself? USB Microscopes are available for public use in Small Hall Room 224.
“Pulse frequency is the number of cycles produced across the gap in 1 s. The higher the frequency, finer is the surface finish that can be obtained. With an increase of number of cycles per second, the length of the on-time decreases. Short on-times remove very little material and create smaller craters. This produces a smoother surface finish with less thermal damage to the workpiece. Pulse frequency is calculated by dividing 1000 by the total cycle time (on-time + off-time) in microseconds (44).”
The initial blast of the laser vaporizes all of the material in its path. Once it breaks through to the other side, it can begin following the cutting route. Oftentimes the laser creates a small fire on the underside of the material during the initial blast.
The materials above are acrylic, wood, and metal. As you can see, the more thermally sensitive material, the acrylic, has a slightly melted edge on the reverse side. The metal piece also has some visible melting.
