Thu Jun 09 09:44:48 CST 2022
Wire-cutting machine tools are widely used and important. They can ensure good dimensional accuracy in the production and processing of plastic molds and precision multi-station progressive molds, which directly affects the assembly accuracy of molds, the accuracy of parts, and the service life of molds. Wait.
Due to the high precision requirements of the workpiece, if there is a little negligence in the processing process, the workpiece will 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 operating the slow-moving wire cutting machine tool, combined with years of production practice, in view of the deformation problems and difficulties encountered in the processing process, several processing methods and processing operation plans have been summarized. Cutting machine, the machining accuracy is ±0.003mm, 99.9% brass electrode wire is selected, and immersion deionized water cooling.
The punch plays a very important role in the mold. Its design shape, dimensional accuracy and material hardness all directly affect the punching quality, service life and accuracy of the stamping parts.
In actual production and processing, due to the residual stress deformation inside the workpiece blank and the thermal stress deformation caused by discharge, the threading hole should be processed first for closed cutting (as shown in Figure 1), and the deformation caused by open cutting should be avoided as much as possible ( As shown in Figure 2) If the closed form cutting cannot be performed due to the size of the workpiece blank, for the square blank, care should be taken to select the cutting route (or cutting direction) when programming.
The cutting route should be beneficial to ensure that the workpiece and the fixture (clamping support frame) are always kept in the same coordinate system during the processing, avoiding the influence of stress deformation.
As shown in Figure 3, the fixture is fixed at the left end, and the cutting is performed counterclockwise from the left side of the gourd-shaped punch. The entire blank is divided into left and right parts according to the cutting route.
Because the material connecting the left and right sides of the blank is cut smaller and smaller, the right side of the blank is gradually separated from the fixture, which cannot resist the internal residual stress and deforms, and the workpiece is also deformed.
If as shown in Figure 4, cutting in a clockwise direction, the workpiece is left on the left side of the blank, close to the clamping part, and most of the cutting process keeps the workpiece and the fixture in the same coordinate system, which has better rigidity and avoids stress deformation. .
In general, a reasonable cutting route should arrange the cutting section where the workpiece and the clamping part are separated at the end of the overall cutting program, that is, leave the pause point (Bridge) close to the clamping end of the blank. The following focuses on analyzing the cutting process of cemented carbide tooth punch. Under normal circumstances, when the shape of the punch is regular, the wire cutting process often reserves the connecting part (pause point, that is, a small section of cutting trajectory line reserved so that the workpiece is not completely separated from the blank after the first rough cutting ) in the plane position. After part of the fine cutting is completed, the reserved connection part is only cut once, and then the fitter will grind it flat, which can reduce the processing cost of the punch in the slow wire cutting.
Due to the high hardness of the material and the narrow and long shape of the cemented carbide punch, the processing speed is slow and it is easy to deform. Especially in the case of its irregular shape, the grinding of the reserved connection part brings great difficulty to the fitter. Therefore, the process can be properly adjusted in the process of slow-moving wire cutting, so that the dimensional accuracy of the shape can meet the requirements, and the grinding process of the suspension point before assembly by the fitter is eliminated. Due to the high hardness of cemented carbide and large cutting thickness, the processing speed is slow and the torsional deformation is serious. Most of the shape processing and the processing of the reserved connection part (pause point) are cut in 4 times, and the cutting parameters and offset of the two parts are The amount (Offset) is the same. The offset of the first cutting electrode wire is increased to 0.5-0.8mm, so that the workpiece can fully release the internal stress and completely torsional deformation. In the next three times, there can be enough margin for fine cutting processing, so that the final size of the workpiece can be obtained. guarantee.
(1) Φ1.0—Φ1.5mm threading holes are processed by punching machine or EDM machine at the appropriate position of the blank in advance, and the length of the cutting line segment l between the center of the threading hole and the punch contour line 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 selected as 3-4mm.
(4) In order to compensate the torsional 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 3 times adopt the fine cutting method, because the cutting allowance is small, the deformation amount is also smaller.
(5) After the 4th cutting process of most of the shapes is completed, dry the workpiece with compressed air, then wash the end face of the blank with alcohol solution, dry it in the air, and then use a binder or liquid quick-drying glue (usually 502 quick-drying glue). glue) stick the metal sheet with a thickness of about 1.5mm that has been ground by the grinder on the blank (as shown in Figure 6), and then cut the reserved connection part of the workpiece according to the original 4 offsets (note: do not put the The glue drips into the water nozzle or onto the reserved connection part of the workpiece, so as not to cause non-conductivity and cannot be processed).
Before the wire cutting process, 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. release. Therefore, during the online cutting process of the template, with the effect of the original internal stress and the influence of the processing thermal stress generated by the spark discharge, non-directional and irregular deformation will occur, so that the thickness of the subsequent cutting cuts will be uneven, affecting the The processing quality and processing accuracy are improved.
In view of this situation, for templates with relatively high precision requirements, 4 cuts are usually used. In the first cutting, all the scraps of the holes are cut off. After the scraps are taken out, the automatic shifting and automatic threading functions of the machine tool are used to complete the second, third and fourth cuttings. As shown in Figure 7, a cut for the first time, take scrap → b cut for the first time, take scrap → c cut for the first time, take scrap → ... → n cut for the first time, take scrap → a cut for the second time →b cutting the 2nd time →...→n cutting the 2nd time →a cutting the 3rd time →...→n cutting the 3rd time →a cutting the 4th time →...→n cutting the 4th time, the processing is completed. This cutting method can make each hole have enough time to release the internal stress after processing, and can minimize the mutual influence and micro deformation of each hole due to different processing sequences, and better ensure the processing size of the template. precision. However, the processing time is too long, the consumption of wearing 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 allows the template, the first unified processing can be used to keep the waste material unchanged, and the subsequent 2, 3, and 4 times can be combined for cutting (that is, a cutting the second After the first time, do not shift or cut the wire, then cut the 3rd and 4th times →b→c...→n), or omit the 4th cut and do 3 cuts. After cutting in this way, the shape and size are basically in line with the requirements. Refer to Table 1 and Table 2 for the reference values of machining allowance, machining accuracy and surface roughness for each of the 4th and 3rd cuts. Preliminary estimation, the displacement between the holes, thread threading, wire cutting, water supply, water release, etc. are calculated in 1min. Using this cutting method, processing a template with 100 holes will save about 9h of processing time each time, and about 30h of cutting time will be saved for 4 times. It not only improves the production efficiency, but also reduces the cost consumption, so the manufacturing cost of the template is also reduced.
Machining allowance, machining accuracy and surface roughness for each of the 4 cuts
Machining allowance, machining accuracy and surface roughness for each of the 3 cuts
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 very small (such as R0.07—R0.10mm), the filament must be replaced (such as Φ0.10mm). However, compared with thick wire, the processing speed of thin wire is slow and expensive (mostly imported wire is required). If the entire hole is machined with filament, it will prolong the machining time and cause waste. After careful comparison and analysis, we firstly increased the corner radius appropriately, cut all the holes with thick wire to meet the size requirements, and then replaced the filament to uniformly trim the corners of all holes to the specified size. The wire cutting process of rectangular tooth-shaped concave template (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) Demagnetization and shutdown.
(3) Replace the Φ0.10mm filament. Move the wire conveyor to an unused location. If the conveyor belt has been used in all 3 positions and the effect of biting the filament is not good, replace the conveyor belt with a new one.
(4) Find the center again.
(5) Modify the corner radius of the graphics, reprogram, avoid the contour lines of other holes, and trim the corner radius of the hole to R0.07mm.
The multi-hole concave die, fixing plate and stripper plate take into account the micro-deformation caused by the residual stress and processing heat of each hole during the processing, so in actual production, the method of consistent processing sequence of the holes is adopted to ensure the shape of the holes. The consistency of hole position deformation ensures the coaxiality of the holes of the die, the fixing plate and the stripper plate.
Wire-cut wire cutting machine tools have high processing precision and strong functions, but the processing cost is high. In order to give full play to the role of the machine tool and create good economic benefits, it is necessary to carry out 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 operating skills of the machine tool, reasonable selection of water and electrical parameters, reducing wire breakage during processing, and constantly summarizing experience and lessons in practice, so as to maximize the potential of the machine tool and improve production efficiency.