1. Based on hole
The hole used as the reference should be finished with a coordinate grinder. The reference hole must be clean and free of dirt. The positioning accuracy based on the hole can generally reach 5-10 μm.
The method of finding the center of the electrode wire (fork centering) is to move the electrode wire in the reference hole, such as moving in the positive direction of x, when the electrode wire is in electrical contact with the hole wall, the electrode wire will reverse from this point (ie. x negative direction) move until the electrode wire is in contact with the hole wall at the other end, then the center point of the hole is coordinate x. It must be at the midpoint of this distance (the chord of the circle). Similarly, the coordinate Yo of the center point in the y-direction of the hole can be found. Xo, Yo is the center point position of the reference hole.
This method is only limited to finding the center point of the through hole, but for parts such as the positioning of the outer circle to find the center to cut the inner cavity, the positioning of the special-shaped hole as the center to position the cutting shape, and the blind hole as the center to locate and cut the inner cavity or shape , it is necessary to use the method of finding the center with the clamping tool, that is, the so-called "pre-hole positioning method". The part drawing of the cutting cavity is positioned by the shape. The positioning method of the pre-hole of the part is to find a backing plate with parallel upper and lower planes, punch a wire hole and a stop screw hole, and clamp the backing plate to the machine tool. In an appropriate position, first cut a hole with the same diameter as the outer diameter of the blank, and then put the blank into the hole, and the center coordinate of cutting this hole is the center coordinate value of the part to be cut in the future. Fasten the blank on the backing plate with the stop screw, then write the program for cutting the inner hole, then thread the electrode wire into the wire hole, and place the electrode wire at the center point of the part.
2 Based on the end face
The positioning accuracy based on the end face is not as high as the positioning accuracy based on the hole. This is because the positioning based on the end face is only one direction positioning, while the positioning based on the hole is based on the position of the two hole walls to determine its center. The positioning point is the positioning in two directions. Therefore, the positioning method based on the end face is relatively easy to generate errors, and it is difficult to achieve high precision requirements. Generally, when positioning is based on the end face, positioning errors are prone to occur due to different conditions (such as whether there is an oxide layer on the positioning surface, whether there is working fluid, the size of the wire tension, etc.). Therefore, in the positioning process, it is best to do more several times. The end face positioning fork is called "alignment". Alignment can also be done by the second-class fixture.
The structure of the second type of fixture is shown. The clamp body 1 is close to the locator 5 in the y-axis direction and the locator 4 in the X-axis direction. After the y-axis coordinate takes a certain value, the X-direction carriage is fed to cut the A surface, and then the x-axis coordinate takes a certain value. After the value is set, the carriage in the y direction is fed to cut the B side. At this time, the A and B surfaces cut out are not only parallel to the electrode wire, but also perpendicular to the electrode wire, which can be used as the precise positioning reference surface for clamping the workpiece.