The Mound Laser and Photonics Center - MLPC (Miamisburg, OH) recently developed a technique for using an Nd: YAG laser marking system to engrave EDM electrodes. It has done engraving in graphite such as Poco EDM-3 with excellent results, achieving depths of up to 0.045". Graphite is an excellent absorber of the Nd:YAG laser radiation and consequently can be engraved deeply. Metal electrodes (e.g., copper and NAK-55) also can be engraved to a depth of about 0.010" to 0.015", but it takes considerably longer. The advantages of laser engraving are described below.
Variety of Engraving
The laser can engrave numbers, letters and graphics such as logos. The characters can be engraved in normal orientation or in reverse. The artwork can be deep engraved into the EDM electrode or left standing - depending on requirements.
Detailed artwork from a customer can be converted for use in the laser in as little as five to 10 minutes, if a good electronic file is available. If artwork is not available, a file can be created to give the level of detail required. Letters as small as 0.020" tall can be engraved with excellent detail. The required depth, however, will usually specify the minimum detail size.
The laser can usually engrave a graphite electrode in five to 30 minutes, depending upon the complexity of the graphics and the depth required. Metal electrodes also can be engraved, but take longer. Often duplicates of electrodes are required, and with proper fixturing, this can be done quickly.
Depth of Engraving
Depth of engraving in graphite from 0.025" to 0.045" can readily be achieved. Metal electrodes are typically engraved between 0.010" and 0.015". Depth requirements determine the length of time required for the engraving.
Laser engraving of graphite is a very clean operation. Most material removal results in the formation of gaseous byproducts (e.g., CO2). Any residual dust that is formed in the engraving process is readily removed with a simple vacuum system. When engraving an electrode is finished, there is no dust or debris to be seen on the workstation. This is in clear contrast to a workstation around a CNC machine.
Once a satisfactory file for artwork has been created and converted by the laser, the artwork can easily be scaled in to achieve the desired size. Electronic files can readily be modified to adjust letter size and spacing while preserving the detail of the artwork. The laser has a finite kerf width that must be taken into account, and sometimes a graphic must be adjusted pixel by pixel. Through experience the proper way to achieve the desired effect in a minimum number of such trials was taught.
Processing of Electrodes
The key processing steps for the laser engraving of EDM electrodes are:
- Create a good electronic file (e.g. a 600 dpi bitmap);
- Manipulate the file (if necessary) to produce the desired features (e.g., character spacing) on the electrode;
- Fixture the electrodes for reproducibility; and,
- Engrave the electrodes.
Steps one through three setup the job. Anything that can be done by the customer - such as supplying fixturing and good artwork - speeds up the process. It is always good to work with the customer to minimize the time and cost associated with this up-front work. The engraving time is a fixed cost determined by the speed at which the laser removes the electrode material and the desired depth of engraving.