Fast wire in the professional terminology is called: high speed reciprocating wire EDM wire cutting machine
Slow wire is called low speed unidirectional WEDM in professional terms
The wire speed of reciprocating WEDM is 6-12 m / s. The biggest characteristic of the product is that it has 1.5 degree taper cutting function, and the processing thickness can be more than 1000 mm. It is used in all kinds of medium and low-grade mold manufacturing and special parts processing, and has become one of the most widely used machines in China’s CNC machine tools. However, due to the fact that the reciprocating WEDM machine can not implement constant tension control on the electrode wire, and the computer gong processing, the electrode wire jitters greatly and is easy to break in the process of processing. Because the electric grade wire is used repeatedly, it will cause electrode wire loss, machining accuracy and surface quality reduction.
The electrode wire of low-speed WEDM uses copper wire as tool electrode and generally moves unidirectionally at the speed of less than 0.2m/s. A pulse voltage of 60-300v is applied between the copper wire and the processed materials such as copper, steel or superhard alloy, and a gap of 5-50um is maintained. The gap is filled with insulating medium such as deionized water (close to distilled water), which causes spark discharge between the electrode and the workpiece This is consumed and corroded, and numerous small pits are etched on the surface of the workpiece. Through the monitoring and control of NC control and the execution of servo mechanism, the discharge phenomenon is uniform and consistent during the machining of mechanical parts, so that the processed products can be processed into products with the required size and shape accuracy. At present, the accuracy is up to 0.001mm, and the surface quality is close to the grinding level. The electrode wire is no longer used after discharge, and no resistance anti electrolysis power supply is adopted. Generally, it is equipped with automatic threading and constant tension device. It has the advantages of stable, uniform, small jitter, high machining accuracy and good surface quality, but it is not suitable to process large thickness workpieces. Due to the precise structure of the machine tool, high technology content, high price of the machine tool, the use cost is also high.
It can form plastic parts with deep holes and complex shapes.
Under heat and pressure, the plastic can be heated quickly and evenly through the mold pouring system to ensure short hardening time.
The dimensional accuracy of plastic parts is easy to ensure and the flash of parting surface is thin. It is difficult to extrude plastics with fluidity less than 80mm. The forming pressure is higher than that of the glue pressing method. The consumption of plastic must be increased (pouring part).
Injection method: the granular or powdered plastic is heated and melted into the flowing state in the barrel of the injection machine, and then the whole cavity is filled with a narrow nozzle and the pouring system of the mold with a very high pressure and poor speed. After a certain period of setting, the mold is opened, and the plastic parts can be taken out from the mold. The characteristics of injection molding: short forming cycle, easy to realize. The dimensional accuracy of plastic parts is easy to guarantee.
The mold is usually designed to be fixed. When there are many metal inserts in the plastic parts, the installation of the inserts is more difficult. Plastic mould can be divided into thermosetting plastic pressing mould, thermosetting plastic extruding mould, thermosetting plastic injection mould and thermoplastic injection mould.
According to the form of material cavity, thermosetting plastic pressing mold can be divided into:
(a) Open die, that is, the cavity is the feeding cavity;
(b) Semi closed die, that is, the cross section of the feeding chamber;
(c) The feeding cavity is the continuous part of the cavity, and the forming pressure is completely transmitted to the pressed plastic parts through the upper die.
According to the structure, it can be divided into:
(a) Mobile press mold,
(b) Fixed press mold.
Factors affecting the quality of EDM
There are many factors affecting the processing quality, which are related to the selection of electrode materials, electrode manufacturing, electrode clamping and alignment, the selection of machining standards and the appropriateness of operation process. To prevent the production of waste products, the following should be noted.
Correct selection of electrode materials
In cavity machining, graphite is a common electrode material. However, due to the variety of graphite, not all graphite materials can be used as electrode materials for EDM. Special graphite with high strength, high density and high purity should be used. Copper electrode is often used in precision. One is: the discharge end of EDM, which is used to process cavity, lettering, etc., and is usually made into the required shape. The material is graphite, copper or aluminum (rare). The other is: the discharge end of WEDM is made of molybdenum wire. Its principle is to apply high-frequency and high-voltage to the discharge end through the electric control part. When the electrode (molybdenum wire) contacts with the grounding end (workpiece), it will form high-frequency ignition and generate high temperature, which will quickly dissolve the workpiece surface (a very small gap) in contact with molybdenum wire, which is called wire cutting.
The so-called multi electrode machining refers to the parts to be processed with high precision, and the discharge parts should be discharged twice or more. In the early stage, it is rough discharge machining with larger translation, and the later is fine discharge machining with small translation.
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