EDM is an important process in mold manufacturing, especially in injection mold manufacturing. However, some misunderstandings in the EDM process of the mold factory often lead to the failure of the machining accuracy, surface and efficiency to meet the requirements. The following will analyze the common misunderstandings of EDM in mold factories.
01
Use the electrode to touch the workpiece, and it is often "missed"
The method of using electrodes to directly touch the workpiece belongs to surface contact. There are inevitably more or less fine objects between the contact surfaces, and there are also clamping accuracy errors on the contact surfaces, which will directly affect the accuracy of edge finding and centering. Using this method, it is strictly required to wipe the contact surface clean, but due to the existence of human factors, the accuracy may be unstable.
For the numerical control electric discharge machine, it is recommended to use the method of the reference ball centering, which is a necessary method for the discharge of the mold factory. The usual practice is to:
Clamping the workpiece;
Place a datum ball on the bench;
Install the probe on the spindle head;
Use the probe to center the workpiece;
Use the probe to center the reference ball;
Remove the probe and install the electrode;
Subsequent electrodes are used to center the reference ball
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Since the centering process is a point-to-point sensory contact, a high-precision positioning accuracy of μm level can be achieved. In addition, the moving distance of the reference ball of the electrode is reduced, the stroke of the machine tool can be fully utilized, and the efficiency is also improved.
Of course, if the production process is more perfect, the eccentricity of the electrode can be measured by three coordinates outside the machine, and the eccentricity value can be transmitted to the EDM machine tool. There is no need to divide the center on the EDM machine tool, which can greatly improve the utilization rate of the machine tool , Improve the overall production efficiency of EDM.
02
Machine-made use of the same electrode material
Most domestic mold companies use red copper as electrode material. In today's pursuit of high-efficiency processing, have you ever investigated the processing advantages of graphite electrodes? Maybe you simply think that graphite electrodes are only suitable for large mold processing or rough machining. In fact, this kind of understanding is one-sided or still stays in the traditional modeling concept.
At present, more and more mold companies have begun to use graphite electrodes to greatly shorten the mold manufacturing cycle. Because whether it is the process of milling electrodes or electric discharge machining, the processing efficiency can be greatly improved, which is a significant advantage of graphite electrodes. In addition, the large electrodes made of graphite are light in weight, the narrow slit processing is not easy to deform, the CNC milling has no burrs, and the overall electrode can be designed to reduce the number of electrodes, etc., which fully reflect the advantages of graphite materials. Of course, graphite processing is not suitable for fine surface processing that requires Ra0.4μm or less.
For micro-machining, extremely low electrode loss is required. At this time, it is necessary to use high-quality copper electrodes or chrome-copper electrodes. For the electric discharge machining of high value-added parts, the use of more expensive copper-tungsten alloys can obtain smaller electrode losses, especially in the processing of hard alloy workpieces.
03
The electrode spark position is made too small, which greatly reduces the processing efficiency
Most enterprises are upgrading from traditional electric discharge machines to numerical control electric discharge machines. When many factories use numerical control electric discharge machines, the electrode spark position process still refers to traditional electric discharge machines. Take unilateral 0.05mm.
The small electrode spark position greatly limits the ability of CNC electric motors to use larger currents for high-speed machining. In fact, after high-speed plunge processing, the side of the cavity can be quickly smoothed only through translational processing, which is a process method to achieve the perfect effect of discharge surface, efficiency, and precision indicators. Here is a reference. The spark position of the rough machining electrode of the CNC discharge machine is 0.3~0.15mm on one side, and the finishing electrode is 0.15~0.05mm on one side. It is necessary to refer to the discharge area and the processing amount. If the area permits, the spark position should be made as large as possible to obtain even several times the processing efficiency.
04
Still using manual chucks to install and adjust electrodes
For strength or cost considerations, enterprises use traditional manual chucks to install and adjust electrodes. This method is simple and practical, and is widely used. However, some companies have purchased hundreds of thousands of CNC electric discharge machines, and still use manual chucks.
Using the traditional manual collet, the actual utilization rate of the machine tool is not high. If the production efficiency cannot be satisfied, it can only spend more capital investment to increase the discharge machine tool. In fact, a good horse needs a good saddle, and the CNC machine should be equipped with a 3R quick clamping and positioning fixture, which can save the process of manual metering, reduce the frequent standby of the machine tool, and improve production efficiency.
05
Using CNC machine tools, without the function of side beating and oblique beating
The CNC electric discharge machine can realize side cutting, oblique cutting and multi-axis linkage processing. For example, some molding inserts of injection molds have relatively thin and deep glue spots around them, and these parts are very suitable for side punching.
The R angle of the tool left after EDM cutting is a relatively common type of processing. If the method of X, Y, and Z three-axis linkage is used, that is, oblique processing, it can avoid the occurrence of unstable discharge due to the small area of the processing part. The phenomenon of local loss of electrodes.
For the oblique gate processing on the mold, many factories process it according to the Z-vertical by tilting the mold. In fact, it can be completed by using the oblique punching function of the CNC EDM machine tool, and the processing of the oblique gate can be realized by setting the starting point and the end point. When designing the electrode, it is necessary to design the electrode according to the oblique method.
Some factories are equipped with high-end CNC EDM machines, and the machine tools are also equipped with C-axis. However, when processing the corner gate of the mold insert, the C-axis function will not be used. In order to realize the processing of the corner gate, the insert is divided into two halves for inlaying. In fact, it can be done using the servo machining of the C axis.
06
It is difficult to meet the requirements of large-area high-gloss processing
If the EDM of the company's molds is of a large area (more than 30 square centimeters), and the surface is required to be below VDI18, a uniform spark texture is required, like a TV remote control type cavity. Then electrical discharge machining is a headache. It is often trimmed repeatedly for the texture, and the processing efficiency is also very low.
If large-area and large-cavity molds are to be processed in batches, powder mixing processing technology should be considered, which can greatly improve processing efficiency and make it easier to obtain large-area fine textures or mirror surfaces.
07
Improper EDM Surface Quality Control
Some mold companies do not have very high requirements for the molds they manufacture, and the discharge parts basically need to be polished later. In this case, the mold electric discharge machining is pursuing the requirements of VDI18 (Ra0.8μm) or even mirror surface processing, but at the same time complaining that the discharge speed is too slow and the delivery time is too late.
Enterprises should correctly control the quality of the discharge surface according to the different requirements of the mold, and clearly distinguish whether the priority of discharge is efficiency or quality. For most of the processed parts that will be polished later, it is sufficient for the electrical discharge machining to reach VDI22 (Ra1.25μm) or above. For subtle parts, it can be processed finer in order to avoid polishing deformation. What needs to be emphasized here is that when pursuing the high-quality matt surface requirements below VDI22, the discharge time will be greatly increased, and the electrode loss will also increase.
08
Mistakes in mirror EDM
Mold companies who have not been in contact with mirror EDM will be very interested in this technology. Unfortunately, due to lack of practical experience, some of their incorrect cognitions can easily lead to processing failures.
In fact, for CNC electric discharge machines, it is not difficult to achieve mirror surface processing, but sub-mirror surfaces like VDI7 (Ra0.2μm) are extremely difficult to process. Whether a high-quality mirror effect can be achieved, in addition to the selected processing parameters, depends largely on the material of the workpiece. Some materials such as SKD11, DC53, and counterfeit S136 cannot achieve a good mirror effect anyway, so it must be Judge the material and then decide to carry out mirror discharge, otherwise it may waste time and fail to meet the requirements.
The main experience of mirror processing is time control. No matter how large the area is, how much time should be set. Experienced masters can flexibly realize high-efficiency mirror production.
