What Is EDM?
Application of EDM in mold manufacturing
Electrical discharge machining (EDM) and wire electrical discharge machining (EDM) are two of the most widely used special machining methods in mold parts processing. This section will only provide a brief overview of these two methods.
Electrical discharge machining (EDM) is a process that uses the high temperature generated by pulsed discharge between a tool electrode and a workpiece electrode in a specific medium to perform electro-erosion, machining the workpiece to achieve specific shapes, dimensions, and surface roughness requirements. EDM can process various high-melting-point, high-hardness, high-strength, high-purity, high-toughness, and high-brittleness metal materials. It is widely used for machining cavities, holes (round holes, square holes, irregular holes), curved holes (bent holes, threaded holes), as well as narrow slots, small holes, and micro-holes in various stamping dies, hot forging dies, die-casting dies, extrusion dies, plastic molds, and rubber molds.
Electrical discharge machining can be divided into electrical discharge forming (commonly referred to as EDM) and wire electrical discharge machining (commonly referred to as wire EDM) based on its application scope.
Electrical discharge machining (EDM) is mostly used for machining complex-shaped cavities and core grooves that cannot be penetrated by the mold, as well as for machining sharp corners and narrow grooves that cannot be completed by cutting (it is also used for perforation machining where dimensional accuracy requirements are not high).
Electrical discharge wire cutting equipment and examples
Electrical discharge wire cutting machine tools are divided into two types: slow wire cutting and fast wire cutting. Figure 1-27 shows a schematic diagram of the structure of a CNC fast wire cutting machine tool. The main body of the CNC fast wire cutting machine tool consists of a bed, wire frame, worktable, wire feeding mechanism, taper device, working fluid circulation system, etc.
1-Wire storage tube; 2-Wire holder; 3-Taper device; 4-Electrode wire; 5-Worktable;
6-Working fluid tank; 7-Bed; 8-Control box; 9-Control cabinet
In wire electrical discharge machining (EDM), the workpiece is fed by the relative movement of the worktable and the electrode wire. The worktable can move linearly in two coordinate directions, allowing the electrode wire to move relative to the workpiece in various planar curve trajectories.
The basic process of wire EDM is shown in Figure 1-28. The electrode wire starts from the wire-threading hole and performs electrical discharge machining along the dotted line trajectory until the entire machining contour is completed.
Figure 1-29 shows some parts machined by wire EDM. Figure 1-29(a) shows a hexahedron with a wire-threading hole near the edge. The electrode wire then starts from the wire-threading hole and machines along the contour, finally obtaining a part with a curved surface contour, similar to wire EDM machining of a punch. Figure 1-29(b) also shows a hexahedron with a wire-threading hole at the center. The electrode wire then starts from the wire-threading hole and machines along the contour, finally obtaining a part with a hexahedron exterior and a curved surface contour interior, similar to wire EDM machining of a die.
Figure 1-29(c) shows a narrow groove machined inside a disc part.Figure 1-29(d) shows a small core insert machined by wire EDM.
Electrical Discharge Machining Equipment and Examples
The electrical discharge machining (EDM) machine mainly consists of a bed, spindle head, column, worktable, working fluid tank, and control cabinet, as shown in Figure 1-30.
The worktable is generally capable of longitudinal and lateral movement, i.e., movement in both the X and Y directions, to achieve the required relative position between the tool electrode and the workpiece. The worktable is also equipped with a working fluid tank, which immerses the tool electrode and the workpiece in it, serving to cool and remove chips.
The control cabinet mainly consists of a pulse power supply and an automatic feed adjustment system. The pulse power supply converts the industrial frequency AC power into a unidirectional pulse current of a specific frequency to supply the discharge energy required for EDM. By adjusting the electrical parameters, different needs for roughing, intermediate, and finishing can be met. The automatic feed adjustment system ensures that a certain discharge gap is maintained between the electrode and the workpiece throughout the machining process through its own automatic control system, ensuring the stability of the EDM process.
Figure 1-31 shows parts processed by EDM. Figure 1-31(a) shows a square countersunk hole machined on a workpiece using a square electrode. Figure 1-31(b) shows a multi-cavity part machined using a single tool electrode through the translation of the worktable. Figure 1-31(c) shows a method of machining two cavities simultaneously using a single electrode. By rotating the machine tool spindle head, machining of multiple cavities can be achieved. Because electrodes wear out during machining, it is impossible to complete the machining process using only one tool electrode in actual machining. It is often necessary to prepare multiple electrodes to perform roughing and finishing of EDM separately.
