CNC wire cutting technology and skills of CNC machine tools

Slow wire cutting machine tools are widely used and important. In the production and processing of plastic molds and precision multi-station progressive molds, they can ensure good dimensional accuracy, which directly affects the assembly accuracy of the mold, the accuracy of the parts, and the use of the mold. Life span etc. Due to the high precision requirements of machining workpieces, any negligence in the machining process will cause the workpiece to be scrapped, and it will also have a negative impact on the manufacturing cost and processing cycle of the mold.
In the process of programming and operation of slow-moving wire cutting machine tools, combined with many years of production practice, in view of the deformation problems and difficulties encountered in the processing process, several processing methods and processing operation plans are summarized

2 Punch processing technology
The punch plays an important role in the mold. Its design shape, dimensional accuracy and material hardness directly affect the punching quality, service life and accuracy of stamping parts. In the actual production and processing, due to the residual stress deformation inside the workpiece blank and the thermal stress deformation caused by the electric discharge, the wire hole should be processed first for closed cutting, and the deformation due to open cutting should be avoided as much as possible. If you are limited by the size of the workpiece blank and cannot be cut in a closed form, for the square blank, you should pay attention to choosing the cutting route (or cutting direction) when programming.
The cutting route should be beneficial to ensure that the workpiece is always kept in the same coordinate system with the fixture (fixture support frame) during the machining process to avoid the influence of stress and deformation. The clamp is fixed at the left end, from the left side of the gourd-shaped punch, the cutting is carried out in a counterclockwise direction, and the whole blank is divided into two parts on the left and right according to the cutting route. As the material connecting the left and right sides of the blank becomes smaller and smaller, the right side of the blank gradually separates from the fixture and cannot resist the internal residual stress and deforms, and the workpiece is also deformed. If cutting in a clockwise direction, the workpiece remains on the left side of the blank, close to the clamping part. Most of the cutting process keeps the workpiece and the fixture in the same coordinate system, which has good rigidity and avoids stress deformation. Under normal circumstances, a reasonable cutting route should arrange the cutting section that separates the workpiece from the clamping part at the end of the total cutting program, that is, leaving the pause point (Bridge) near the clamping end of the blank.
The following focuses on the analysis of the cutting process of the cemented carbide tooth-shaped punch. Under normal circumstances, when the shape of the punch is regular, the wire cutting process will often reserve the connection part (pause point, that is, a small section of the cutting track line reserved for the workpiece to be completely separated from the blank after the first rough cutting. ) Stay on the plane position. After most of the fine cutting is completed, the reserved connection part will only be cut once, and then the fitter will smooth it, which can reduce the processing cost of the punch in the slow-moving wire cutting.
Cemented carbide punches are slow in processing speed and easily deformed due to the high hardness of the material and the narrow and long shape. Especially in the case of irregular shapes, the grinding of the reserved connecting parts brings great difficulty to the fitter. Therefore, the process can be appropriately adjusted during the slow-moving wire-cutting processing stage, so that the shape and size accuracy can meet the requirements, and the process of grinding the suspended point before the fitter assembly is eliminated.
Due to the high hardness of the cemented carbide and the large cutting thickness, the processing speed is slow and the torsion deformation is serious. Most of the shape processing and the processing of the reserved connection part (pause point) adopt 4 cutting methods and the cutting parameters and offset of the two parts The Offset is the same. The wire offset of the first cutting is increased to 0.5-0.8mm, so that the workpiece can fully release the internal stress and completely torsion deformation. There will be enough margin for fine cutting in the next 3 times, so that the final size of the workpiece can be obtained. Guarantee.
The specific process analysis is as follows:
(1) Pre-process the Φ1.0-Φ1.5mm threading hole in the appropriate position of the blank with a punching machine or an EDM, and the length of the lead-in cutting line between the center of the threading hole and the contour line of the punch is selected to be 5-10mm .
(2) The width of the contour line of the punch and the edge of the blank should be at least 1/5 of the thickness of the blank.
(3) The connection part (pause point) reserved for subsequent cutting should be selected near the center of gravity of the workpiece blank, and the width should be 3-4mm.
(4) To compensate for torsional deformation, leave most of the residual deformation in the first rough cutting stage, and increase the offset to 0.5-0.8mm. The precision cutting method is used for the next 3 times, and the deformation is also reduced due to the small cutting margin.
(5) After the 4th cutting process for most of the shapes is completed, the workpiece is blown dry with compressed air, and then the end face of the blank is washed with an alcohol solution, and then dried, and then used with a binder or liquid quick-drying glue (usually 502 quick-drying Glue) Stick a metal sheet with a thickness of about 1.5mm that has been ground by a grinder on the blank, and then cut the reserved connection part of the workpiece according to the original offset of 4 times (Note: Do not drop the glue into the nozzle or drip To the reserved connection part of the workpiece, so as not to cause non-conductive and unable to be processed).

3 Deformation analysis in the processing of concave template
Before online cutting processing, the template has been cold processed and hot processed, and a large residual stress has been generated inside, and the residual stress is a relatively balanced stress system. When a large amount of waste is removed by online cutting, the stress will be destroyed as the balance is destroyed. Release it. Therefore, during the online cutting of the template, with the effect of the original internal stress and the processing thermal stress generated by the spark discharge, non-directional and irregular deformation will occur, which will cause the thickness of the subsequent cutting to be uneven and affect Improve the processing quality and processing accuracy.
In view of this situation, the template with relatively high precision requirements is usually cut 4 times. The first cutting cuts off all the waste material of the hole. After removing the waste material, the automatic shifting and automatic threading function of the machine tool will complete the second, third, and fourth cutting. a cut the first time, take the waste → b cut the first time, take the waste → c cut the first time, take the waste →……→n cut the first time, take the waste → a cut the second time → b cut the second time →……→n-cut 2nd time→a-cut 3rd time→……→n-cut 3rd time→a-cut 4th time→……→n-cut 4th time, processing is completed.
This cutting method can make each hole have enough time to release the internal stress after processing, can reduce the mutual influence and micro deformation of each hole due to the different processing sequence to the minimum, and better ensure the processing size of the template Accuracy. However, the processing time is too long, the consumption of vulnerable parts of the machine tool is large, and the manufacturing cost of the template is increased. In addition, the machine tool itself will also produce creep with the extension of processing time and temperature fluctuations. Therefore, according to the actual measurement and comparison, if the processing accuracy of the template is allowed, the first uniform processing can be used to take the waste material unchanged, and the subsequent 2, 3, and 4 times can be cut together (that is, a cuts the second After the second, do not shift or cut the wire and then cut the 3rd and 4th times→b→c……→n), or save the 4th cutting and do 3 cuttings. After the cutting is finished, the shape and position are basically in line with the requirements after measurement. Refer to Table 1 and Table 2 for the reference values ​​of machining allowance, machining accuracy, and surface roughness for each of the 4 and 3 cuts. For a preliminary estimation, the displacement between the holes, threading, cutting, watering, watering, etc. are all calculated at 1min. Using this cutting method, processing a template with 100 holes will save about 9 hours of processing time each time, and a total of about 30 hours will be saved for 4 times. This way, for the use of expensive slow-moving wire cutting machine tools, It not only improves the production efficiency, but also reduces the cost and consumption, so the manufacturing cost of the template is also reduced.

4 The processing technology of the small corners of the concave template hole
As the diameter of the selected cutting wire is larger, the corner radius of the cut hole is also larger. When the corner radius of the template hole is required to be very small (such as R0.07-R0.10mm), it must be replaced with a thin wire (such as Φ0.10mm). However, compared with thick filaments, the processing speed of fine filaments is slower and expensive (mostly imported filaments are required). If the entire hole is processed with filaments, it will extend the processing time and cause waste. After careful comparison and analysis, the corner radius is appropriately increased, all the holes are cut with thick wire to meet the size requirements, and then the corners of all the holes are uniformly trimmed to the specified size by replacing the thin wire.

The following is the wire cutting process of the rectangular tooth-shaped concave template (the inner corner radius is R0.07mm).
(1) First, use Φ0.20mm cutting wire to process the template hole to the required size, and process the inner corner to R0.15mm.
(2) Demagnetize and shut down.
(3) Replace the Φ0.10mm filament. Move the cutting wire conveyor belt to an unused position. If all 3 locations of the conveyor belt are used and the effect of biting the filaments is not good, replace the conveyor belt with a new one.
(4) Re-align the center. The cutting wire guide plug-in with 2 diamond cones (this guide plug-in is dedicated to AGIE slow-moving wire cutting machine tool) point support can make the lower deflection point of the cutting wire be accurately positioned, so that the cutting wire can be guided accurately. When the diameter of the cutting wire is Φ0.20mm, the alignment center is at point b, when the diameter of the cutting wire is Φ0.10mm, the alignment center is at point a,｜ab｜=｜bo｜-｜ao｜=0.1〖KF( 〗2〖KF)〗-0.05〖KF(〗2〖KF)〗=0.0707mm. Therefore, changing the Φ0.10mm filament to re-align the center coordinate value should be about 0.0707mm different from the original center coordinate value.
(5) Modify the corner radius of the figure, reprogram, avoid the contour lines of other holes, and trim the corner radius of the hole to R0.07mm.
5 Processing sequence of multi-hole die, fixed plate and discharge plate
The multi-hole die, fixed plate, and unloading plate take into account the micro-deformation caused by the residual stress and processing heat of each hole in the processing process, so in actual production, the method of consistent hole processing order is adopted to ensure its shape. The uniformity of the hole position deformation ensures the coaxiality of the hole of the die, the fixed plate and the discharge plate.

6 Conclusion
The slow-moving wire-cutting machine tool has high processing accuracy and strong functions, but the processing cost is high. To give full play to the role of the machine tool and create good economic benefits, it is necessary to conduct reasonable processing technology analysis and technical performance analysis of the workpiece, and fully understand the structure of the machine tool Performance and proficiency in the operation skills of the machine tool, reasonable selection of water and electrical parameters, reduce wire breakage during processing, and constantly sum up experience and lessons in practice, so as to maximize the potential of the machine tool and improve production efficiency.