The EDM (also EDM sinks , Senkfunkenerosion or spark erosion ) is a method of radio erosion .
Die sinking EDM machines are mainly built as bath machines - the workpiece is therefore in a bath made of dielectric . A non-conductive oil or deionized water is used as the dielectric . The machine head is movable and carries out the movement in the Z-axis. The table performs the movements in the X and Y axes. Die-sinking EDM machines can be designed as conventional machine tools or as CNC-controlled machines. Machines with automatic changing of the electrode are also available and thus enable automatic processing of several parts of the workpiece one after the other.
The electrode ( anode ) has roughly the negative shape of the workpiece to be machined ( cathode ) and is often made of copper or graphite . Since the material is not removed only when there is direct contact between the workpiece and the electrode, but rather the spark jumps through the dielectric when it comes closer, the electrode has to be dimensioned somewhat smaller. This so-called spark gap is usually a few hundredths to tenths of a millimeter in size. The size of the spark gap depends on the discharge technology set on the machine ( electrical voltage and current , discharge interval, pause interval). Technologies with a higher removal rate result in a larger spark gap and a rougher surface structure. The erosion occurs through thermal mechanisms, namely through melting or evaporation of the material. The removed material is transported away by the gas bubble created in the dielectric and the dielectric itself. The dielectric is permanently filtered in a circuit.
Not only the workpiece but also the electrode is subject to removal of material, and this at the electrode as combustion is referred to. By cleverly choosing the discharge technology, one tries to optimize the ratio of material removal on the workpiece to electrode consumption. For finishing ( finishing ) a new electrode is often required due to the burn-off and a finer technology is selected.
Areas of application
Die sinking EDM is often used in tool and mold making. It is used to make molds, dies or bending punches.
With a suitable machine and electrode, all conductive materials can be processed regardless of their hardness. Die-sinking EDM is also important as a preparatory process for wire EDM . The starting hole, into which the erosion wire will later be threaded, can also be produced in steel that is already hard by means of die sinking. By coordinated rotation of the electrode with simultaneous Z feed , threads in hard materials can also be eroded. Paths or undercuts can be implemented by moving the X and Y axes .
A special application of die sinking erosion is drill erosion (also spark erosion drilling , starting hole drilling or drill erosion ). The machine used is called a starting hole drilling machine . The machine is so named because the resulting holes are mostly, but not always, used as a starting or threading hole for subsequent wire EDM work.
The basic technology remains the same, but the discharge strategies and the machine structure are optimized for the fastest possible production of bores . Copper or graphite tubes with a diameter between 0.13 and 3 mm and a length between 300 and 800 mm are used as electrodes. These are automatically pushed in to compensate for the burn-off of the electrode. The electrode rotates during the manufacturing process, which leads to even burn-off and faster removal of the workpiece. Dielectric is constantly pumped through the electrode tube (pressure up to 60 bar) in order to wash away the removed material. The particles that are removed during the erosion process improve the conductivity of the dielectric used over time, consequently the overall electrical conductivity of the dielectric increases. However, there are also manufacturers who enrich their dielectric with so-called satellite electrodes in order to achieve this improvement right from the start.
- http://www.uni-stuttgart.de/izfm/lehre/Funk_ECM.pdf (PDF, 3.8 MB)
- Interesting facts about die-sinking erosion Information about die-sinking erosion.