The Analysis Of The Causes Of Molybdenum Wire Broken
1. Broken Wire Cause Of Molybdenum wire Own Reason:
1) Tension and Winding Speed
A. Improve the tension of molybdenum wire can decrease the influence of the wire vibration, thus improve the precision and cutting speed, and significantly reduce the broken wires, generally think that tension in 12 to 15 n more appropriate.
B. Wire winding speed will promote the molybdenum wire working liquid into the larger the thickness of the discharge gap of workpiece, to ensure the electric erosion product legend of exclusion and electro discharge machining stability. But winding wire speed is too high, molybdenum wire jitter severe, will damage the processing stability of machining accuracy and surface roughness, and easy to cause broken wires.Walking wire speed is too low, because of the large loss is also easy to broken wires, general experience with less than 10 m/s advisable.
2. Broken Wire Cause Of Thread Structure
1) Broken Wire Cause Of Transmit Wire Tube
A. Movement wire tube inside and outside circular coaxial, and lead to unbalanced inertia, prone to fold the wire during operation and cause broken wires.
B. The bearing and bearing parts of transmit wire tube often have clearance due to wear and tear, it’s very easy to cause jitter and broken wires.
C. Movement wire tube if there is no cut off the high frequency power supply, when reversing leads to molybdenum wire internal temperature is too high, resulting in burning wire in a short time, so need to check whether movement wire tube after the stroke switch failure
D. To keep the drum, roller rotating flexible, otherwise will cause godet system when running back and forth vibration and produce broken wires
E. Need to adjust the movement wire tube end the limit stop, and avoid wire tube out of the stroke limit and broken wires.
F. Should stop shortly after change of direction, to prevent the wire cylinder due to inertia super blunt bad transmission and snap of molybdenum wire.
2) Broken Wire related to the idler pulley and conductive block
A. If guide wheel and the conduction block due to wear to have groove, or roller bearing wear gap, it’s easy to cause the jitter of molybdenum wire and broken wires.
B. It should be ensured that the molybdenum wire and the conductive block, the processing work piece and the work surface contact is good, otherwise the high frequency power source is unable to connect with the molybdenum wire or the contact is bad.
3. Broken Wire When Machining Thick Workpiece
Thick workpiece generally refers to the thickness greater than 100mm of the workpiece. The main reason for broken wires is:
1) Broken wires when start cutting:
This is due to the initial cutting, molybdenum wire outside the workpiece, upper and lower guide wheel big pitch, cause molybdenum wire pulling jitter, the molybdenum wire and the workpiece gap is not stable, easy to form arc, the arc concentrated in a certain period, it will cause the broken wires. In EDM, arc discharge is the main cause of corrosion damage.
2) Broken wires in the process of cutting
When the molybdenum wire cutting in the workpiece after, because of the narrow kerf, emulsion is difficult to infiltrate, cutting seam electric corrosion products (carbon black and metal) is not easy to remove, processing conditions bad, kerf generated in the second and third discharge machining in, resulting in the kerf width, the gap in in poor state, the pulse forming arc discharge, causing the broken wire.
3) Broken wire at the end of cutting
When cutting is finished and there was a few millimeters, breaking even tens of microns of broken wire in addition to the above reasons and workpiece weight or workpiece material internal stress caused by the deformation caused by wired, solution is: can be made simple fixture, material factory before processing for the heat treatment necessary.
4. Broken Wire Related To Work Liquid
1) When the working fluid become black, the overall performance will be poor, very easy to cause broken wire. Therefore, we should always view its color, smell its taste, abnormal timely replacement, so that the working fluid to maintain a certain dielectric capacity. In particular, when the hard alloy is processed, the corrosion resistance is more, and the working fluid is easy to be penetrated and the mobility is poor.
2) How to identify the liquid soap
A. Around the new molybdenum wire and the workpiece on trial cut about 1 hour, observing the color of a molybdenum wire, if the greyish white, the cooling liquid can be thinner workpiece cutting, such as gray and white mixed with black spots or black, black bar diameter became fine and need to replace the new working fluid.
B. Open arc and path current. To start the operation of the wire tube, the artificial forced high frequency current is switched on, so that the molybdenum wire slowly closer to the workpiece, do not contact the workpiece, about spacing 1-1.5mm, then there should be no spark. Then to cool the workpiece, the molybdenum wire and workpiece space constitute a liquid path, if a spark is generated or ammeter reading values on the basis of the original load increased more than 10mA, no-load 30mA). At this time working fluid can not be reused.
5. Broken Wires Related To Electrical Parameters
1) According to the thickness of the workpiece to select a reasonable electrical parameters, the pulse interval to open some, so that it is conducive to the removal of metal particles. At the same time, the peak current of no-load voltage should not be too high, otherwise the single pulse energy becomes large, cutting speed is accelerated, it is easy to produce concentrated discharge and pull arc, causing broken wire. General no-load voltage is about 100V.
2) Choose proper discharge gap according to the thickness of the workpiece, discharge gap is too small, easily lead to short circuit, is not conducive to cooling and electrical erosion of exclusion; discharge gap is too large, it will affect the surface roughness and machining speed. When cutting large thickness of the workpiece, should try to use the wide pulse current, also discharge gap to corresponding larger, (which should generally be greater than 0.02 mm), so as to enhance the chip removal effect, improve the cutting stability.
6. Broken Wires Related To High Frequency Power Supply
1) The short circuit current peak is too large, that is, the number of power amplifier tube is too much, more than the current of the molybdenum wire can withstand, will make the molybdenum wire overheating, due to excessive fatigue and brittle fracture.
2) The negative wave of high frequency pulse is too large, and the negative wave of the pulse directly causes the molybdenum wire to increase, the loss of the wire is increased, the service life of the wire is reduced, and the broken wire is caused in short time.
3) Pulse width and pulse interval choice is undeserved, when processing large thickness of the workpiece, the pulse width is too large, will make the point discharge phenomenon in the discharge gap, burn molybdenum wire; pulse interval is too small, gap electric erosion matter cannot be fully discharged, deionization is not sufficient, also easy to break the wire. At this point in the molybdenum wire can be clearly seen burn marks (that is, black spots).
7. Broken Wires Related To The Movement Of The Working Table
1) The cutting precision of the work piece is ensured by the screw rod, and the gap between the screw rod and the nut is eliminated by the spring. If the screw rod lubrication or lack of spring force, will cause the work table is not uniform moving, in this case cutting, high-frequency current will appear frequent short circuit, if not timely troubleshooting, it is bound to cause broken wire.
2) When adjusting the frequency conversion tracking speed, the feed rate should be approximately equal to the working corrosion rate, so that the pulse utilization rate is high, the processing speed is fast, and the processing state is stable. Feed rate is too high, frequent short circuit, wire aging fast, in the current table can see current processing larger; the processing speed is too low, feed speed regulation is too slow, easy to make the discharge gap is not stable, arc discharge, burn easily broken molybdenum wire.
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