Die EDM is an important process in die factory. Some factories have good technical level and can process high-quality molds, but some enterprises can't, even if they use very high-end CNC EDM machines. The effect is still very unreasonable. This paper summarizes some main technical misunderstandings of EDM, which is very helpful to the actual production of the factory.

Myth 1: contact the workpiece with electrode in the middle and often "offset"

Many mold factories still use the method of electrode contacting the workpiece, which is a very serious problem. Using electrodes to directly contact the workpiece belongs to surface contact. There are inevitably more or less small objects between the contact surfaces, and there are clamping accuracy errors on the contact surfaces, which will directly affect the accuracy of edge finding and alignment. Using this method, the contact surface is strictly required to be wiped clean, but the accuracy will be unstable due to human factors. For NC EDM machine, it is suggested to use reference ball centering method, which is a necessary method for EDM in die and mould factory. The usual approach is:

Clamp the workpiece;

Place a reference ball on the workbench;

Install the probe on the spindle head;

Centering the workpiece with a probe;

Align the probe with the reference ball for centering;

Remove the probe and install the electrode;

The subsequent electrodes are centered on the reference ball.

Because the alignment process is point-to-point sensing contact, it can be realized μ M high precision positioning accuracy. In addition, the moving distance of the electrode in the process of indexing the reference ball is reduced, the stroke of the machine tool is fully utilized, and the efficiency is improved.

Myth 2: the same electrode material is used in the same way

Most domestic mold enterprises use copper as electrode material. In pursuit of efficient processing today, have you studied the processing advantages of graphite electrode? You may simply think that graphite electrode is only suitable for large mold machining or rough machining. In fact, this understanding is one-sided, or still stays in the traditional concept of mold manufacturing.

At present, more and more mold enterprises begin to use graphite electrode to greatly shorten the mold manufacturing cycle. Because both milling electrode and EDM process can save about 50% of the time, which is a significant advantage of graphite electrode. In addition, the large graphite electrode has light weight, the slit is not easy to deform, CNC milling has no burr, and the overall electrode can be designed to reduce the number of electrodes, which fully reflects the advantages of graphite. Graphite material. Of course, even if Ra0.4 is required μ Fine surface processing below M can also achieve good graphite processing, but this is not necessary.

For micromachining, very low electrode loss should be sought. At this time, we should choose high-quality copper electrode or chromium copper electrode. For the EDM of high value-added parts, the expensive copper tungsten alloy can be used to obtain less electrode loss, especially in the machining of cemented carbide workpiece.

Myth 3: the electrode spark position is too small, which greatly reduces the machining efficiency.

Most companies upgrade from traditional EDM machines to CNC EDM machines. When many factories use NC EDM machines, the electrode spark position process still refers to the traditional EDM machine. For example, the spark position side of rough machining electrode is 0.15mm and that of finish machining electrode is 0.06mm

The position of small electrode spark greatly limits that NC EDM can not use large current for high-speed machining. In fact, after high-speed cutting machining, the side of the cavity can be quickly trimmed only by translational machining. This is a process method to achieve the perfect effect of discharge surface, efficiency and accuracy. This is a reference. One side of the rough machining electrode spark position of the NC EDM machine is 0.3 ~ 0.15mm, and one side of the finish machining electrode is 0.15 ~ 0.1mm. It is necessary to refer to the discharge area and processing quantity. If the area allows, increase the spark position as much as possible to obtain machining efficiency, even several times.

Myth 4: manual chuck is still used for electrode installation and adjustment.

For strength or cost reasons, the company uses traditional manual chucks to install and adjust electrodes. This method is simple, practical and widely used. However, some enterprises have purchased hundreds of thousands of CNC EDM machines and are still using traditional chucks.

Using the traditional manual chuck, the actual utilization rate of the machine tool is not high. When the production efficiency can not be met, we can only spend more money to increase the discharge machine tool. In fact, a good horse needs a saddle. The NC machine tool shall be equipped with 3R quick clamping and positioning fixture, which can save the manual measurement process, reduce the frequent standby of the machine tool and improve the production efficiency.

Myth 5: using CNC machine tools, there is no side impact and oblique impact function

NC EDM machine can realize side impact and multi axis machining. Some injection molds have thin and deep glue positions around the molding inserts, which is very suitable for side punching.

Clear the R angle of the remaining tool after discharge. It is a relatively common type of machining. If x, y and Z axis linkage mode, i.e. inclined machining, is adopted, the discharge phenomenon due to the small area of the machining part can be avoided. Stable, local electrode wear.

Myth 6: large area high finish machining is difficult to meet the requirements

For example, the company's mold EDM belongs to large area (more than 30 square centimeters), the surface is required to be below vdi18, and the spark texture is required to be uniform, such as TV remote control cavity. Then EDM is a headache. The texture often needs to be repaired again and again, and the machining efficiency is also very low.

If it is batch EDM for large area and large cavity molds, the mixed powder processing technology should be considered, which can greatly improve the processing efficiency and make it easier to obtain large-area fine lines or mirrors.

Myth 7: incorrect surface quality control of EDM

Some mold enterprises do not have high requirements for molds, and the discharge parts must be polished afterwards. In this case, die EDM pursues vdi18 (Ra0.8) μ m) Even the requirements of mirror processing, and complain that the discharge speed is too slow and the delivery time is too late.

Enterprises should correctly control the discharge surface quality according to the different requirements of molds, and distinguish whether the discharge priority is efficiency or quality. For most post polished parts, EDM can reach vdi22 (ra1.25 μ m) Or above. For fine parts, more fine machining can be carried out to avoid polishing deformation. It should be emphasized here that when pursuing the requirements of high-quality fog surface below vdi22, the discharge time will be greatly increased and the electrode loss will also be increased.

Myth 8: misunderstanding of mirror EDM

For mold enterprises that have not been in contact with mirror EDM, they will be interested in this technology. Unfortunately, due to the lack of practical experience, some of their misconceptions led to the handling of failed cases.

In fact, it is not difficult for CNC EDM to realize mirror machining, such as vdi7 (Ra0.2 μ m) It is very difficult to process the secondary mirror of level. Whether high-quality mirror effect can be achieved depends largely on the material of the workpiece in addition to the selected processing parameters. SKD11, DC53, fake S136 and other materials can not achieve good mirror effect in any case, so we must determine the material first and then decide to conduct mirror discharge, otherwise it may waste time and fail to meet the requirements. For the electrode, there is no such strict requirement, and it is not necessary for the electrode to be mirror polished.

The main experience of image processing is time control. How much area and time are set, experienced masters can flexibly realize efficient mirror production. Without experience, they can only rely on CNC machine tool expert system.

The above misunderstandings of EDM deserve the attention of all mold factories. In fact, a small improvement in a factory process may create great value or improve quality and efficiency. This is also the value of experience!