Common Misunderstandings of EDM
The precision control and guarantee of EDM machining depends largely on positioning accuracy.In the commonly used Z-axis machining, the X and Y axes guarantee the position requirements of the cavity, and the Z axis guarantees the depth requirements of the machined cavity.There are many ways to achieve EDM positioning, including positioning methods that use contact sensing between the electrode and the workpiece.
As shown in the figure, it is widely used in mold enterprises
This positioning method is relatively simple and is very familiar to operators.
It can be found that if the precision requirements of EDM are very high and the positioning error requirements cannot be greater than 0.01 mm, such as in the processing of the half slider of the plastic mold, the matching and insertion parts of the upper and lower mold cores, it will be very difficult to use the above method in these cases. It is difficult to ensure stable positioning accuracy. Due to positioning tolerance, parts are repeatedly repaired and scrapped. Operators often complain that the machine tool has poor perception performance or low positioning accuracy.
In fact, the current EDM machine tool has a very high displacement accuracy. The situation of inaccurate positioning is that there is a misunderstanding in the selection of positioning methods.
Using the electrode to directly touch the edge of the workpiece, because the contact area is large, the burrs on the electrode or the workpiece, the presence of fine debris, the flatness, parallelism, and verticality of the electrode and the workpiece affect the positioning accuracy. Even if the workpiece and the electrode are wiped clean, it is difficult to ensure a positioning accuracy of 0.01 mm.
Indirect positioning with reference ball
For workpieces (electrodes) with special shapes or electrodes that are too large (too small) and require very high precision, there is only an indirect positioning method, that is, indirect positioning using a centering ball. This positioning method uses point contact to eliminate errors within the greatest range.
Advantages of using a centering ball for positioning:
▉ It is not only easy to ensure accuracy, but also can easily achieve centering when the workpiece has a complex shape;
▉ The process of the electrode finding the center of the centering ball avoids the electrode from moving a large stroke, saving operation time;
▉ For the processing of multiple workpieces, there is no need to use the electrode for multiple centering. It is sufficient to center the centering ball once, which saves a lot of operation time. The advantage is particularly obvious in multi-electrode processing.
How to use EDM ball
The centering ball is used in CNC machining and is a detection tool that can accurately determine the center position of the workpiece being processed.
It is installed on the spindle of the machine tool and used as a probe for the contour size of the workpiece. If a certain part is to be mass-produced, a standard part can be made first, clamped on the workbench, and then the coordinates of the contour can be detected with an edge finder and stored. Then, the next time the workpiece is clamped, this coordinate value can be used as a reference to correct the installation position of the workpiece, thereby ensuring that the feed position and coordinate setting deviation during each processing are within the theoretical deviation range of the machine tool, and improving the efficiency of installation and adjustment.
Use of EDM
1.Φ10 straight shank can be installed on cutting chuck or drilling chuck;
2. Use your fingers to gently press the side of the stator to make it eccentric by 0.5mm;
3. Make it rotate at a speed of 400-600RPM;
4. The spring force is small, which can prevent small milling cutters or small drill bits from breaking;
5. Make the stator contact the end face of the workpiece, and move it little by little to achieve full contact. The stator will not vibrate, just like a static state. If external force is applied at this time, the stator will shift out of position. The starting point of the sliding here is the required reference position;
6. The end face position of the workpiece itself is the coordinate position plus the 5mm radius of the stator.
7. Accuracy: static tolerance repeatability ±0.002mm.