Wire-cutting machine tool processing <br><br><br> Wire-cutting is the main processing method for punching parts. However, a reasonable process analysis is performed to correctly calculate the design wire-drawing path of the electrode wire in the NC programming, which relates to the machining accuracy of the mold. Through the determination of the threading hole and the optimization of the cutting line, the cutting process is improved, which is an effective and important way to improve the cutting quality and production efficiency.
The calculation of the actual trajectory <br> According to a large number of statistical data, the actual size after wire cutting processing is mostly in the vicinity of the median value (or "middle size") of the tolerance zone, so the dimension of the tolerance dimension in the die part drawing is The median value size should be used as the programming data for the actual cutting trajectory. The calculation formula is: median value size = basic size (upper deviation deviation).
For example: pattern size outer radius R25–0.04, where the bit size is 25 (0–0.04)/2=24.98 (mm).
Due to the characteristics of wire-cut EDM, there is always a discharge gap between the workpiece and the wire. Therefore, during the cutting process, the theoretical profile (pattern) of the workpiece and the actual trajectory of the electrode wire should maintain a certain distance, that is, the vertical distance between the center trajectory of the electrode wire and the contour of the workpiece, which is called the offset f0 (or the compensation value). .
F0=R wire δ electric type R wire——radius of wire electrode δ electric——Convex and concave mold of single-side discharge gap wire cutting processing die, should comprehensively consider electrode wire radius R wire, unilateral discharge gap δ electric and convex The unilateral fit gap δ between the die and the die to determine a reasonable gap compensation value f0.
For example: processing punching die (that is required to ensure the size of the punching of the workpiece), punching punch as a benchmark, so the punch compensation value is: f convex = R wire δ electric, die size should be increased δ match . While processing blanking die (that is, to ensure the size of the punched workpiece), based on the blanking die, the gap compensation value f of the die should be equal to the R wire δ, and the size of the punch should be increased by δ. see picture 1. The amount of offset will directly affect the machining accuracy and surface quality of wire cutting. If the offset is too large, the gap is too large, the discharge is unstable, affecting the dimensional accuracy; if the offset is too small, the gap is too small and the trim margin will be affected. The electrical parameters during the trimming process will be reduced in turn, and non-electrical parameters should be adjusted accordingly to improve the quality of the process.
According to practical experience, the fit clearance of the blanking die for wire-cutting should be smaller than that of the popular "large" gap die ("Handbook" recommended value). Because convex and concave mold wire cutting process, the surface of the workpiece will form a layer of the structure of the melted layer of crisp, the greater the electrical parameters, the worse the surface roughness, thicker melted layer. And with the increase in the number of die punching, this layer of crisp surface will gradually wear, so that the gap between the mold gradually increased to meet the "big" gap requirements.
Determination of threading holes <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> In general, the position of the threading hole is preferably selected at the intersection point of the known trajectory size or on the coordinate point for calculation, so as to simplify the calculation of the coordinate size in the programming and reduce the error. When cutting a die with a closed hole, the threading hole should be set in the center of the hole. This can not only accurately process the threading hole but also control the calculation of the coordinate trajectory conveniently, but the useless cutting stroke is long. For large hole cutting, the threading hole can be located near the corner of the machining track to shorten the useless stroke. When cutting the punch profile, the threading holes should be selected outside the profile, preferably near the starting point of the cut. When cutting a narrow groove, the threading hole should be set at the widest point of the pattern, and crossing of the threading hole and the cutting trajectory is not allowed. In addition, when two or more workpieces are cut from the same blank, separate threading holes should be provided. It is not possible to have only one threading hole to cut out all the workpieces at a time. When cutting a large punch, the conditional person may set a plurality of threading holes along the processing path so that the wire can be re-threaded and the cutting can be continued when the wire break occurs in the cutting.
The diameter of the threading hole should be suitable, generally Φ2mm ~ Φ8mm. If the hole diameter is too small, it will not only increase the difficulty of drilling but also make it difficult to thread; if the hole diameter is too large, the workload of the fitter will increase. If more holes are required for cutting, the hole diameter is too small, and the arrangement is more dense, a smaller threading hole (Φ0.3 mm to Φ0.5 mm) should be used to prevent the threading holes from being opened or interfered with each other.
Cutting path optimization <br> Reasonable or not cutting path will affect the size of the workpiece deformation.
Therefore, optimizing the cutting route is conducive to improving the cutting quality and shortening the processing time. The arrangement of the cutting line should be conducive to the workpiece in the process of the process is always maintained in the same coordinate system with the clamping bracket, to avoid the impact of stress and deformation, and to follow the following principles.
(1) In general, it is preferable to arrange the starting point of cutting near the holding end, and to arrange the cutting section separated from the holding portion of the work piece at the end of the cutting course, and to set the stop point near the holding end of the blank.
(2) The starting point of the cutting line should be selected where the surface of the workpiece is relatively flat and has little effect on the work performance. For workpieces with high precision requirements, it is better to take the starting point of cutting in the prefabricated threading hole on the blank. It is not allowed to cut directly from the outside of the blank so as to avoid deformation of the workpiece.
(3) In order to reduce the deformation of the workpiece, the cutting route should keep a certain distance from the outline of the blank, generally not less than 5mm.
For some specific process requirements in line cutting, optimization of cutting routes should be focused.
(1) Secondary (or multiple) cutting method For some recessed cavity parts with complex shapes, wall thicknesses, or large cross-sectional changes, secondary cutting methods should be used to minimize distortion and ensure machining accuracy. Normally, the part with high accuracy is required to leave 2mm to 3mm margin before the rough cutting. After the workpiece is released from deformation, the precision cutting is performed to the required size. In order to further improve the cutting accuracy, before the fine cutting, leaving a 0.20mm ~ 0.30mm margin for semi-fine cutting, that is, 3 times cutting method, the first rough cutting, the second semi-cut, the third time For fine cutting. This is an effective way to improve the accuracy of the die line cutting.
(2) Sharp angle cutting method When the workpiece is required to be cut into "sharp angles" (or "clear angles"), method 1 may be used to add a small section of the ultra-cut path to the original route, as shown in Figure 2 A0-A1 In the segment, the maximum retardation point of the wire cutting is reached at the point A0 of the program, and then it proceeds to the additional point A1 and returns to point A0. Then, the original program is executed again, and the sharp corner can be cut. It is also possible to use the cutting route shown in Figure 3 for the second method. Add an over-cutting small square or small triangular route at the sharp corners as an additional procedure. This ensures that sharp edges are sharply cut.
3) Cut-off of the corner line During the EDM process, the actual position of the electrode wire is delayed by the position of the X, Y coordinate axis of the machine tool due to the reaction force of the discharge, resulting in a poor corner accuracy.
The hysteresis movement of the electrode wire will cause the outer arc of the workpiece to be excessively deficient, while the inner arc will be insufficiently machined, resulting in a decrease in the precision at the corner of the workpiece. For this reason, for corners where the accuracy of the workpiece is required, the drive speeds of the X and Y axes should be automatically adjusted so that the actual movement speed of the wire electrode is synchronized with the X and Y axes. That is, the higher the machining accuracy, the slower the driving speed at the corners.
(4) Small fillet cutting method If the radius of the fillet required by the pattern is found to be smaller than the offset when cutting, the “root cut†phenomenon will occur at the corner. For this reason, it should be clear that the smallest fillet in the contour of the pattern must be greater than the offset of the last pass, otherwise a finer diameter electrode wire should be selected. In the main cutting and initial cutting processing, different fillet radii can be set according to the different offsets during processing, that is, different fillet radius subroutines are programmed for the same contour, and the subprograms The radius of the fillet should be greater than the offset of the cut so that small fillets can be cut and a good fillet cut quality can be achieved.
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