Introduction on Electric Discharge Machining (EDM)
Two conductive materials (electrode/workpiece) submerged in an insulating liquid, are connected to a source of current which is switched on and off. When the current is switched on, an electric voltage builds between the two parts. If the parts are brought together to a certain distance, the voltage is discharged and a spark jumps across. Where it strikes, the metal is heated up so much that it melts. Innumerable such sparks spray one after the other (never simultaneously), and gradually shape the desired form in the piece of metal.
Several hundred thousand such sparks must fly per second for efficient EDM.
Two different processes
In the case of die-sinking EDM, the required shape is formed in the workpiece with a three-dimensional electrode. By superimposed movements in the main axes X, Y, Z, C, varied shapes, indentations and cavities are created, such as cannot be achieved by any other machining system.
In the case of wire-cut EDM, the metal is cut with a special metal wire electrode. The wire travels along a pre-programmed path. By differing movements of the upper and lower wire guides, angled or conical surfaces can be produced to the highest accuracy and with the finest surface finish.
The performance of modern EDM equipment is extremely high: high cutting speeds, highly efficient automation, interlinking and storage of very long and recurring machining cycles. And thanks to electronic monitoring and fully automated correction of the EDM process, no supervision is required.
Introduction on High-Speed and High-Performance Milling
High Speed Cutting (HSC)
The typical application of this technology is the machining of complex three-dimensional surfaces. As the specific parameter of the process may be considered the workpiece surface machined per unit of time (cm2/min). NC programmes provide the geometric information either in form of coordinates or vectors. The data amount to be processed by the machine control is a function of distance between the coordinates and the programmed machining feed. Increasing machining feed demands improved calculation speed and intelligence of the control. High speed spindles are required to match the process. Mainly used cutting tools are ball nose end mills, flat end mills and toric end mills from solid carbide.
High Performance Cutting (HPC)
In contrast to High Speed Cutting, this technology mainly is used for the machining of twodimensional geometries. The cutting depth ap and the stepover ap along with the machining feed allow calculation of the material removal per unit of time (cm3/min). This process in particular is suitable when it comes to the removal of large volumes of material or the machining of difficult to cut materials. High power, high torque spindles are a must. Primarily used cutting tools are insert type milling heads, specific high performance end mills, drills, boring heads and special tooling.
The preceding definition is primarily directed towards the extreme facets of both processes. In reality the limit between High Speed Cutting (HSC) and High Performance Cutting (HPC) is not static, in fact it overlaps. The analysis of application and environment typically decides about which process will result in optimum machining performance.