Common problems and solving methods of aluminum parts in NC wire cutting

During the NC machining of aluminum parts, the problems of serious wear, short circuit, broken wire, track distortion and deformation of the workpiece are often occurred, and some products are directly discarded. Based on many years of experience, the author summarizes the key technical problems in the processing practice.
First, the wire cutting aluminum parts easily broken wire problem
The reason why the 1 wire cut aluminum piece is easy to break
The aluminum wire cutting, because the material is soft, chip removal difficult, and aluminum at high temperature is very easy to form a hard film processing, resulting in a large number of alumina or aluminum scraps easily stuck on the molybdenum wire, molybdenum wire to make contact with the feed block parts will soon grind groove. Soft aluminium and hard abrasive mixed together, filled in the trench, once was brought in, will put the trench crushed to death, will be cut off from the wire.
2 solutions
The molybdenum molybdenum wire is pinched off at the feed block problem under the wire frame feed block position adjustments, to prevent the feed groove block wear caused low efficiency, processing surface multiple cutting caused by the decline in the quality of materials and waste of broken wire wire.
Processing material thickness exceeds 40mm, the general processing of 3 ~ 4h after the feed block slightly rotated an angle, as shown in Figure 1b, the first rotating direction as shown in Figure 1a, 8h processing and then rotate the direction shown in Figure 1b, so that each processing after 8h rotation adjustment a feed block position to reduce the probability of the broken wire. The practical processing shows that the processing cost is greatly reduced and the economic benefit is improved by this method. Note that the feed block and the voltage of the electrode wire is generally in the 0.5 ~ 1mm. When the three points of one surface are cutting grooves, and rotary feed block 90 degrees, and so on until the four sides are cutting groove. Then, near the sampling line of the side pad a 1 ~ 2mm gasket, you can adjust the position of the feed block to the left, it is equivalent to a new feed block, saving the production cost.
For example: the thickness of each piece of aluminum for 2mm, a total of 8 pieces together at the same time processing, about 8h adjust the contact surface of the feed block, the daily processing of 8h, to sixth days of broken wire. Then use the micrometer molybdenum wire diameter is only 0.125mm (the original molybdenum wire diameter is 0.18mm). By adjusting the feed block position greatly to avoid the problem of broken wire wire feed block.

Of course, it must be noted that when the workpiece size accuracy requirements are relatively high, it is necessary to measure the diameter of the molybdenum wire, modify the amount of compensation in a timely manner to ensure that the size accuracy requirements.

Two, deformation of the workpiece
1 reasons for the deformation of the workpiece
The workpiece blank manufacturing, machining, heat treatment, the uneven heating, internal force and deformation of organization transformation, such as the role of the internally generated residual stress, a certain period of time without outside influence under the condition of stress distribution is relatively balanced, but the WEDM Process, because the workpiece material is a large number of cut and cut off, also can change the stress distribution, with the passage of time and gradually tends to balance, so that the workpiece deformation. This deformation phenomenon is more obvious for aluminum alloy parts.
2 solutions
(1) cutting process before the stress parts in the first heat treatment to eliminate internal stress, so that the large stress deformation will not occur in order to stabilize the size of the parts. Of course, different materials, processing methods are not the same.
(2) the outer contour machining method of outer contour processing usually can not through the wire hole can be cut from the blank side, as shown in Figure 2a, this method is very easy to break because the blank after the material release stress deformation, resulting in decreased machining accuracy. In order to avoid and reduce the deformation of the production, can be used to cut through the wire hole processing method, to maintain the rough outline of the closed, as shown in Figure 2B, can minimize the stress and deformation in the processing process.
(a) outside cut (b) to play through the wire hole processing
(3) using the two cutting method for machining accuracy of parts, it is best to use the two cutting method.
As in the process shown in Figure 3 a bullet tail, with a V shaped iron clamp one end of the diameter of 8mm, and the other end is hung. By processing the normal processing after the micrometer measurement, near V iron processing size is 2.00mm, and the other end processing size is only 1.86mm. This is online cutting process, because the workpiece material is cut to change the stress distribution of the workpiece deformation.
Processing method of improvement is the thickness of the first intermediate processing have increased from 2mm to 2.4mm, leaving 0.2 margin in the first cutting side, (with a diameter of 0.18mm molybdenum wire when rough machining to fast). The first time after the original cutting blanks by internal stress balance is destroyed, and reached a new balance, then second times finishing, finishing the measurement of the size of 1.99mm, to test the required size.
Three, aluminum parts cutting easy to short circuit and cutting track distortion problem
1 Analysis of the causes of the problem
In the daily processing, cutting large thickness of the workpiece is difficult, because the restriction of EDM erosion condition, workpiece thickness to a certain extent, not enough coolant into the workpiece, gap of electric erosion products not normally excluded, processing is not stable, there is no current until the discharge short-circuit occurs, in the cutting process the aluminum at this phenomenon is more likely to happen.
Usually off the assembly line cutting machine tools with short circuit protection function, once the short circuit, the machine tool bed immediately stop moving, keep in situ not move to wait for processing. However, in the processing of aluminum, aluminum is soft and light, because the chip is difficult, sometimes after a short circuit discharge point by the processing zone transfer to feed block, block and the molybdenum wire is fed by spark discharge, although between the workpiece and the wire electrode in a short-circuit state, but the machine discharge status is normal, so the machine does not because of the workpiece and the molybdenum wire between the short circuit and achieve short circuit protection, this machine is still in accordance with the normal procedures for cutting, processing the workpiece discharge can not process normal shape and size by molybdenum wire in aluminum workpiece soft pull groove, causing the cutting track distortion, leading to the workpiece scrapped. As shown in Figure 4 of the processing gear, the first two parts of the processing of the cutting track distortion and the workpiece scrapped.
2 ways to solve
(1) the first is to optimize the process parameters according to different thickness set different wire cutting parameters. Through many experiments, processing Aluminum Alloy materials may be appropriate to reduce the pulse width, this is because the pulse width decreases, the single pulse energy is decreased, the discharge mark is small, also can reduce the size and quantity of alumina particles, reduce feed block wear. Relative to increase the pulse gap, it is conducive to chip removal, reduce wire bonding, improve the stability of cutting, and improve the surface roughness of the workpiece. If the pulse gap is too small, the discharge product can not be ruled out, the discharge gap is too late to eliminate ionization, which will make the processing become unstable, easily lead to broken wire or cutting track distortion.
The feed rate of the set is smaller than the actual corrosion rate of the workpiece, and the machining state is open, and the cutting speed is slow. Because the melting point and the vaporization point of the aluminum alloy are low, the amount of the same discharge energy is increased, and the discharge gap is large. Due to the discharge gap, the pulse voltage can not be timely breakdown between the liquid medium, greatly reducing the pulse utilization rate, at the same time too much distance between the wire electrode leads to the increase of amplitude, the process becomes unstable, even caused by broken wires. When the feed speed is greater than the actual set of possible erosion speed (called tracking or feed), then processing is easy to short circuit, the actual feed and cutting speed but also decreased, but not by the electric erosion elimination of aluminum, lead wire breaking and short-circuit suffocated. Therefore, the reasonable adjustment of variable frequency feed, so that it can achieve a better processing state. The entire variable frequency feed control circuit has many adjustment links, most of which are installed in the control cabinet of the machine tool, the general should not change. There is a knob mounted on the console panel, can be processed according to the specific circumstances of the knob on the right position, to ensure that the current meter, voltage meter reading, molybdenum wire jitter is small, processing in the best tracking state.
Such as the processing of thick workpiece, generally at the beginning (5mm) processing, because the electrode wire is easy to shake, the cooling liquid concentration is high, should be added to a single pulse energy, increasing the pulse interval, at least the pulse width and pulse interval ratio (1: 8), which is to ensure that the single pulse energy and enough the electrical erosion to exclude the sufficient time interval, while reducing the machining current, generally below 2A. When the processing is stable, then the corresponding reduction of the pulse interval, the processing of the current increase of about 3A, the voltage of about 75V. The average value of the discharge of the molybdenum wire is not increased, the ability to form a spark discharge, the explosive force of the spark is enhanced. Therefore, the electrical parameters should be appropriate to take a larger, otherwise it will make the processing is not stable, the quality of processed parts decreased.
The requirement of cutting speed and surface roughness is the two technological indexes, so it is necessary to pursue high cutting speed in order to meet the need of surface roughness.
(2) according to the workpiece thickness discharging gap not suitable is too small, otherwise prone to short-circuit, discharge is not conducive to cooling and corrosion materials; the discharge gap is too large, will affect the surface roughness and machining speed. When cutting thick workpiece, should try to use a larger diameter of molybdenum wire, large pulse width, so that the discharge gap increases, enhance chip removal effect, improve the stability of cutting.
(3) maintain the coolant cleanliness and timely replacement of new coolant, impurities and reflux cooling liquid in the table with the filter to filter the impurities in the cooling liquid, then the coolant outlet put a layer of sponge adsorption cooling liquid, the effect is very good. In order to improve the chip removing ability, the processing track can be prevented, the detergent and the soap block can be added in the cooling liquid, so that the washing performance is good, the chip discharging ability is increased, and the chip removal condition is improved. At the same time in a timely manner to adjust the position of the block rotation feed or to change a new feed block, always clean up the chip at the particle feed, and the feed block between the molybdenum wire keeps good contact state, avoid the emergence of discharge phenomenon, which can effectively avoid the distortion caused by cutting track work piece scrapped.
Four, the conclusion
From the actual operation of the cutting line, analyzed in aluminum processing, easy to produce alumina particles, resulting in a decrease in conductivity, feed block wear, broken wires and short circuit phenomenon, seriously affect the processing quality and efficiency problems, summed up in practice problems and solutions. These methods and measures are practical and feasible, which have good effect on improving the quality of wire cut processing, reducing broken wire, short circuit and cutting track distortion of aluminum parts.