Dot Peening provides an inexpensive way to permanently mark various metal parts. Although a mature technology recent improvements have made it a good choice for Data Matrix DPM.
How does it work?
Diffuse on axis light gets “trapped” inside the indentation thus not reflecting any light back to the source, so it appears dark. Light hitting the flat surface reflects back to the source making it look light.
Dot peened tool needs a reasonably sharp point with a cone angle of 30° (120° included).
The dot depth to do spacing ratio should be adjusted so adjacent dots may touch, but do not overlap.