1 Introduction

Slow wire cutting machine tools are widely used and important. In the production and processing of plastic molds and fine 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 mold. Operating life, etc. Because of the high precision requirements for processing workpieces, if they are ignored in the processing process, the workpiece will be scrapped, and it will also have a negative impact on the cost of the mold and the processing cycle.

In the process of programming and operating the machine tool for slow wire cutting, combined with many years of production practice, according to the deformation problems and difficulties encountered in the process, several process treatment methods and processing operation plans are summarized

2 Punch processing technology

The punch plays an important role in the mold. Its design shape, scale accuracy and data hardness all directly affect the punching quality, service life and accuracy of the stamping parts of the mold. In practical production and processing, because of the residual stress and deformation inside the workpiece blank and the thermal stress deformation caused by electric discharge, the threading hole should be processed first for closed cutting, and the open cutting should be avoided as far as possible to cause deformation. If it is limited by the size of the workpiece blank and cannot be cut in the closed form, for square blanks, you should pay attention to choose the cutting path (or cutting direction) when programming.

Cutting the road should help to ensure that the workpiece remains in the same coordinate system with the fixture (clamping support frame) during the processing process, avoiding the influence of stress and deformation. The jig is fixed on the left end, and is cut counterclockwise from the left side of the gourd punch. The whole blank is divided into two parts according to the cut road. Because the data connecting the left and right sides of the blank is cut smaller and smaller, the right side of the blank is gradually detached from the fixture, unable to resist the internal residual stress and deform, and the workpiece deforms accordingly. 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, the rigidity is better, and stress deformation is avoided. Under normal circumstances, a reasonable cut road should separate the workpiece from the clamping part

The segment is arranged at the end of the total cutting procedure, leaving the pause point (Bridge) close to the clamping end of the blank.

The following focuses on the analysis of the cutting process of cemented carbide tooth punch. Under normal circumstances, when the shape of the punch is regular, the line cutting process will often reserve the connecting part (pause point, that is, the workpiece is not separated from the blank after the first rough cutting, and a small section of the cut is reserved. (Trajectory line) left in the plane orientation, after most of the finishing cutting, the reserved connection part is only cut once, and then flattened by the fitter, which can reduce the processing cost of the punch on the slow wire cutting .

Carbide punches are characterized by high data hardness and narrow and long shapes, which leads to slow processing speed and easy deformation. Especially in the case of irregular shapes, it is very difficult to fix the reserved parts for grinding. Therefore, the process can be appropriately adjusted during the slow wire cutting process, so that the shape accuracy reaches the requirements, and the grinding process of the suspension point before assembly by the fitter is eliminated.

Because of the high hardness of the cemented carbide and the large thickness of the cut, the processing speed is slow and the deformation is severe. Most of the shape processing and the processing of the reserved connection part (pause point) adopt the 4-cutting method and the cutting parameters of the two parts It is common to both offset and offset. The offset of the first cut electrode wire is increased to 0.5-0.8mm, so that the workpiece can be fully released of internal stress and completely change the deformation. After 3 times, there can be sufficient margin for precision cutting processing, which can make the final size of the workpiece Be assured.

The specific process analysis is as follows:

(1) Process the Φ1.0-Φ1.5mm threading hole in the proper orientation of the blank in advance with a perforator or EDM. The length of the imported cutting line l between the center of the threading hole and the outline of the punch is selected 5- 10mm.
(2) The width of the outline 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) In order to compensate the changed deformation, most of the residual deformation is left in the first rough cutting stage, and the offset is increased to 0.5-0.8mm. The next three times use the fine cutting method, because the cutting margin is small, and the deformation is also reduced.
(5) After the cutting of most of the shape is finished four times, the workpiece is blown dry with compressed air, and then the end surface of the blank is washed with an alcohol solution, cooled to dryness, and then used adhesive or liquid quick-drying glue (usually 502 fast Dry glue) Stick the metal sheet with a thickness of about 1.5mm flattened by the grinder to the blank, and then cut the reserved connection part of the workpiece according to the original 4 offsets (Note: Do not drop the glue into the spout Or drip on the reserved connection part of the work piece, so as not to cause non-conductive and can not be processed).
3 Deformation analysis in the processing of concave template

Before the online cutting process, the template has been cold-processed and hot-processed, and a large residual stress has occurred in the interior. The residual stress is a relatively balanced stress system. When the online cutting removes many waste materials, the stress is balanced with the balance. Destruction and release. Therefore, when the template is cut online, with the effect of the original internal stress and the thermal stress generated by the spark discharge, non-directional and irregular deformation will occur, resulting in uneven thickness of the cutting edge. , Affecting the processing quality and processing accuracy.

In view of this situation, the template with relatively high precision is generally selected for 4 times of cutting. The first cut will cut off the waste material of all types of holes. After removing the waste material, the machine will be automatically shifted and threaded to complete the second, third and fourth cuts. 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 the second time → a cut the third time → …… → n cut the third time → a cut the fourth time → …… → n cut the fourth time , Processing is over.

This cutting method can release the internal stress at a time when each hole is processed, and can reduce the interaction and micro deformation of each hole due to the different processing order to a minimum, and better ensure the processing of the template Scale accuracy. However, the processing time is too long, and the consumption of wearing parts of the machine tool is large, which increases the cost of making the template. In addition, the machine tool itself will also creep with the prolongation of the processing time and the shaking of the temperature. Therefore, according to practical measurement and comparison, the template can choose the first common processing to take the same material under the condition that the processing accuracy allows, and the back 2, 3, and 4 times are cut together (that is, a cut After the second time, do not shift or tighten the wire

Then cut the third and fourth times → b → c … → n), or omit the fourth cut and do the third cut. After the incision is completed in this way, the shape and position scales basically meet the requirements. Refer to Table 1 and Table 2 for the reference values ​​of machining allowance, machining accuracy, and appearance roughness in each of 4 and 3 cuts. As a preliminary budget, the displacement, threading, thread cutting, water supply, water supply, etc. between the holes are calculated in 1 minute. Selecting this cutting method, processing a template with 100 holes will save about 9h of processing time each time, and cut 4 times to save about 30h, so that the machine tool is expensive to cut the wire with slow walking wire. In other words, it not only improves the production power, but also reduces the cost and consumption, so it also reduces the cost of making the template.

4 Processing technology of small corners of concave template holes

Because the larger the diameter of the cut wire, the larger the radius of the corner of the cut hole. When the corner radius of the template hole is very small (such as R0.07-R0.10mm), it must be replaced with a thin wire (such as Φ0.10mm). However, compared with thick silk, the processing speed of thin silk is slow and expensive (mostly imported silk). If the entire hole is processed with filaments, the processing time will be prolonged, causing spoilage. After careful comparison and analysis, it is adopted to increase the corner radius appropriately, cut all types of holes with thick wire to reach the standard requirements, and then replace the fine wires to jointly trim the corners of all types of holes to reach the regular size.

The following is the wire cutting process of the rectangular tooth concave template (the inner corner radius is R0.07mm).

(1) First use Φ0.20mm to cut the wire to process the template hole to the required standard, and process the inner corner to R0.15mm.
(2) Demagnetization and shutdown.
(3) Replace the Φ0.10mm filament. Move the cut wire conveyor belt to an unused position. If all three orientations of the conveyor belt have been used and the function of biting the filament is not secure, replace the new conveyor belt.
(4) Find the center from the beginning. The cutting wire guide insert with 2 diamond cones (this guide insert is for AGIE company’s slow-moving wire cutting machine). The point support can accurately locate the lower deviation point of the cutting wire and make the cutting wire accurate Oriented. When the diameter of the cut wire is Φ0.20mm, the center of the straightening is at point b, when the diameter of the cut wire is Φ0.10mm, the center of the straightening is at a, | ab | = | bo |-| ao | = 0.1 〖 KF (〗 2 〖KF)〗-0.05 〖KF (〗 2 〖KF)〗 = 0.0707mm. Therefore, the coordinate value of replacing the Φ0.10mm filament from the beginning to the center should be about 0.0707mm away from the original center coordinate value.
(5) Modify the radius of the corner of the figure, program from the beginning, avoid the outline of other type holes, and modify the corner radius of the type hole to R0.07mm.

5 Processing sequence of multi-hole concave die, fixed plate and discharge plate

Multi-cavity cavity die, fixed plate, and unloading plate take into account the small amount of deformation caused by the residual stress and processing heat during the processing of each type of hole, so in practice, the common method of processing the hole is selected to ensure its type. The commonality of hole orientation deformation then ensures the coaxiality of the holes in the die, fixed plate and discharge plate.

6 Conclusion

The machine tool with slow wire cutting has high processing precision and strong function, but the processing cost is high. If you want to fully play the role of the machine tool and create good economic benefits, you must carry out reasonable processing technology analysis and technical function analysis on the workpiece to fully understand the machine tool. Structural functions and proficiency in machine tool operation skills, reasonable selection of water and electrical parameters, reduction of wire breakage during processing, and continuous summing up of experience and lessons in practice, so as to maximize the potential of the machine tool and increase production power.

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