In the mold industry, especially in theplastic mold industry, EDM is a very important process link, which requires the design of a large number of electrodes (copper remover) for EDM.
1. Parts of the mold that need to be designed with electrodes
There are many deep slots, narrow slots and complex cavities on the mold surface, which are difficult to be machined by milling machine tools. This requires EDM. In addition, some parts with high machining accuracy and surface roughness are also commonly used in EDM.
(1) A part of a mold with a right or sharp angle
(2) The fillet is too deep and narrow
(3) An angle consisting of a curved surface and a straight or inclined wall
(4) There are deep and narrow parts in the mold structure
2. Electrode structure
There are two types of structure: integral electrode and mosaic electrode. The whole electrode is made of one piece of material, which is the most commonly used structure. When it is difficult to process the electrode with complex shape as a whole, it can be divided into several pieces, which can be inlaid and assembled as a whole after being processed respectively. The inlaid electrode can save materials, but the accuracy between the electrode inlays should be guaranteed.
Integral electrode and mosaic electrode
3. Experience in electrode design
(1) The die structure should be fully understood before designing the electrode. Distinguish the glue position, insert break position, rely break position, pillow position, etc. of the mold, confirm which parts need discharge processing, and whether the mold core and insert need to be assembled and discharged.
(2) The design of electrodes should be carried out in a certain order to prevent leakage. This is very important for electrode design of complex die.
(3) The design of electrode should consider the fabrication of electrode. The designed electrode should be easy to make, and it is better to use only one processing method. For example, it is very convenient to make complex electrode by CNC milling, and it is also easy to ensure the accuracy of electrode.
(4) For the mold with appearance and edge line requirements, the electrode can be designed as a structure that can process the integral cavity at one time; sometimes the integral electrode is difficult to process, has a dead angle that can not be processed, or is not easy to process, and the required cutter is too long or too small, then one more electrode can be considered, sometimes the partial angle electrode needs to be cleaned.
(5) The sharp angle, edge and other convex parts of the electrode lose faster than the flat parts in EDM. In order to improve the EDM accuracy, the electrode can be divided into the main electrode and the secondary electrode when designing the electrode. The main part of the cavity or the hole is processed by the main electrode first, and then the sharp angle, narrow slot and other parts are processed by the secondary electrode.
(6) For some thin electrodes with large height drop, the electrode is easy to deform in CNC milling and EDM. When designing the electrode, the structure of strengthening the electrode should be used.
(7) The electrode must extend a certain size in the direction of the opening of the processing position to ensure that there is no raised small rib at the mouth after the processing of the working position.
(8) In order to avoid the undesired discharge outside the machining part in EDM, some electrodes should be treated in the air.
(9) Reducing the number of electrodes should be considered in the design of electrodes. It is reasonable to combine some different processing parts on the workpiece as a whole or realize the processing of multiple positions by moving coordinates. As shown in the figure below, the same processing parts on the workpiece are processed with electrode moving coordinates.
Electrodes combined with different processing parts
(10) When designing electrodes, different parts with different processing requirements shall be designed separately to meet their own processing requirements. For example, the surface roughness requirements and dimensional accuracy of assembly parts and molding parts are different, so the electrodes of these parts cannot be mixed together.
(11) Design proper base for electrode. The base is the basis for correcting electrode and positioning in EDM, and also the basis for multiple processes of electrode. For example, in the process of wire cutting to remove the corner of the tool on the electrode, it is necessary to use the base for positioning. In addition, it is better to design a reference angle on the base which is convenient to distinguish the direction when the electrode is installed.
(12) EDM process should be considered when designing electrode. Select z-axis servo processing or lateral processing or multi-axis linkage processing; the electrode shall be easy to be clamped and positioned; chip removal and exhaust holes shall be set according to the specific situation.
(13) Determination of the number of electrodes. The determination of the number of electrodes mainly depends on the processing shape and quantity of the workpiece. Secondly, the material, processing depth and processing area of the workpiece should be considered.
(14) There are two ways to design the base of the electrode. One is to enlarge the base evenly on the basis of the largest shape of the electrode processing part. As a result, the X, y and Z coordinate values based on the base are often decimal. The second method is to first determine an integer for the X, y and Z coordinate values of the base datum. Obviously, the second method can avoid the operator's mistake of complex decimals in EDM.
(15) After the design of all electrodes of a set of mould is completed, the material preparation sheet shall be filled in (confirm the length, width, height, quantity and material of electrode blank according to the electrode requirements), the fabrication of electrode shall be arranged, and the drawing of EDM shall be designed (discharge coordinates, processing requirements and detailed remarks).
4. Determine the electrode scaling amount
The main factors to be considered in determining the electrode scaling amount are machining shape, machining size, machining allowance, machining accuracy requirements, machining surface roughness requirements, electrode and workpiece materials.
