Wire cutting - is impulse discharge machining, machining parts required to be a good conductive properties.
1. Speed wire EDM components.
Mainly by the host, machine tools, electrical boxes, work tank,glue stick adaptive pulse power and numerical control system and other components shown in Figure 1.
2. WEDM processing principles.
(1) line cutting - CNC EDM wire cutting short.
(2) working principle: the use of mobile as a tool electrode wire,glue gun and wire and workpiece through the pulse current, the use of the corrosive effect of pulse discharge cutting of the workpiece.
(3) Because it is the use of wire electrodes, therefore, can only make contour cutting.
(4) Work shown in Figure 2.
(5) When the workpiece and the gap between the wire electrode enough to be impulse voltage breakdown, the spark discharge between the workpiece and cutting.
(6) l by the directives issued by NC device, control stepper motor 11, drive X, Y two pallets move, can process a curvilinear contour of the workpiece.
3. WEDM Category:
(1) According to the different control methods, WEDM is divided into: Electrical model by WEDM; optical tracking WEDM; digital control of WEDM.
(2) According to the wire electrode wire to go different ways, CNC wire cutting machine is divided into: Fast wire EDM; walking WEDM.
1) Fast Wire EDM:
① wire electrode run faster (300-700m/min).
② bidirectional reciprocating operation, that is, the electrode wire can be used repeatedly until the wire electrode to a certain degree of wear and tear or broken wire up.
③ wire electrode is used: molybdenum wire (Φ0.1 ~ Φ0.2mm).
④ working solution is usually as follows: saponification solution or emulsion fluid.
⑤ loss of the electrode wire and the electrode wire movement to influence the process of change, and its precision wire walking worse than the surface roughness is higher;
⑥ dimensional accuracy: 0.015 ~ 0.02mm;
⑦ surface roughness Rɑ: 1.25 ~ 2.5μm.
⑧ general size precision can reach: 0.01mm, the surface roughness Rɑ is: 0.63 ~ 1.25μm.
2) wire cutting beds:
① low speed wire electrode (0.5 ~ 15m/min).
② wire electrode can only be one-way movement, not reusable, it can avoid the electrode loss on the processing accuracy.
③ wire electrode: copper, brass, tungsten, molybdenum and various alloys, the diameter is generally 0.1 ~ 0.35mm.
④ working solution: deionized water, kerosene.
⑤ dimensional accuracy: ± 0.001mm.
⑥ surface roughness: Ry0.3μm.
4. Wire cutting process indicators:
Process indicators are commonly used: cutting speed, precision and surface roughness.
(1) Cutting speed:
1) line cutting is the kerf of the workpiece processing.
2) Cutting speed (or processing speed), said:
① wire center electrode per unit time by cutting through the effective area (mm2/min);
② feed rate (mm / min) Additional line cutting thickness.
(2) precision:
Precision include: the shape of the workpiece to be machined precision and position accuracy.
1) The shape accuracy:
① the shape of the workpiece to be machined precision XY plane is seen from the shape of the plane processing accuracy (ie, dimensional accuracy), Z is processed to the vertical surface.
② of shape accuracy: the linearity requirements of cutting surface is smaller. Namely: the surface to be machined to uniform and smooth, vertical small.
③ CNC wire cutting of the workpiece is mostly drum-type, that is, the central recessed parts,
④ speed wire, by contrast, is generally the central protruding parts.
2) Position Accuracy:
① location accuracy - is the relative position between the cutting contour deviation.
② the determinants of positional accuracy:
a. precision machine tool itself, that the mechanical precision and control of machine tool accuracy;
b. operation of the selected targeting.
3) Surface Roughness:
① surface roughness - refers to the processed surface of the micro-roughness profile.
② that roughness parameters are: Rɑ, Rz, Ry.
③ CNC wire cutting surface roughness by the following formula: Ry = kz tk0.38 Ip0.34.
Where: κz is a constant; tk pulse width (μs); Ip is the peak pulse current (A).
5. The factors that affect the process indicators:
Can be divided into consumption and non-power factors.
(1) electric parameters on the impact of process indicators:
Electric quantity - is the variable pulse parameters, including pulse peak, pulse width, pulse frequency and supply voltage.
1) pulse peak current on machining process criteria:
In the other parameters unchanged, the increase of pulse peak current will increase the energy of single pulse discharge, processing current also increases. Significant increase in cutting speed, surface roughness variation.
2) pulse width on machining process criteria:
① in the processing of the current situation remains unchanged, so that pulse width and pulse stop time proportional change.
② pulse width increases, cutting speed increases, but the pulse width increases to some value, the processing speed is no longer with the pulse increases.
③ line cutting does not exceed the pulse width of 50μs.
④ increase the pulse width, the surface roughness increased.
3) pulse frequency on the processing process criteria:
① single pulse energy under certain conditions, increase the number of pulse discharge, namely, increasing pulse frequency, processing speed will increase.
② In theory, a single pulse energy constant, the machined surface roughness are the same.
③ In fact, Fast thread cutting, when the pulse frequency increase, the process will follow the current increases, causing a significant change to the cutting of different stripes, cut along the workpiece surface roughness variation.
4) Power supply voltage on the impact of process parameters:
① peak current and the processing of current conditions remain the same, increasing the supply voltage, can significantly improve the cutting speed, but has little effect on surface roughness.
② difficulty in the chip, small energy, small roughness conditions, as well as high-impedance, high melting point material cutting, the higher the supply voltage will improve the processing stability, cutting speed and machining surface quality will be improved.
(2) non-electric parameters on the impact of process indicators;
1) take the wire speed:
① the impact of cutting speed: the main chip by changing the conditions to achieve.
② help improve the walking speed wire: wire electrode to the working fluid discharge into the large gap in the workpiece thickness; electric erosion products of the discharge, so that the processing stability, and increase processing speed.
③ take the wire speed is too high: increase will lead to mechanical vibrations, reduces machining accuracy and surface roughness increases, and could easily lead to broken wires.
④ The Fast thread cut, should consider changing the speed of the wire electrode commutation generated by cutting the impact of stripes on the surface roughness.
2) The process of wire tension on indexes of:
① increase the tension of wire can reduce the vibration of wire processing to improve machining accuracy and cutting speed.
② If the excessive increase of wire tension, frequently cause broken wires and the impact of processing speed.
③ electrode wire tension fluctuation of processing a great influence on the stability and processing quality, the use of constant tension wire tension device can reduce the volatility.
3) electrode wire on the processing process criteria:
① for silk and silk the thickness of the material aspects;
② wire electrode material: wire cut more brass and copper wire used as electrode materials, Fast thread cut use more molybdenum wire and tungsten molybdenum alloy as the electrode material.
③ The thickness of wire: wire radius increases, the electrode wire to increase the value of allowing the pulse current can improve the processing speed, but the surface roughness increases. General, the use of thick rough cut piece cut wire electrode; cut with a fine cut wire electrode for high roughness of the workpiece.
4) The thickness of the workpiece on the machining process criteria:
① cutting thin workpiece;
Easy access and full of working fluid discharge gap, is conducive to the process of chip removal and elimination of the working fluid electrolyte in the positive and negative ions.
But the piece is too thin, the electrode wire is easy to shake, not conducive to the machining accuracy and surface roughness.
② cutting thick workpiece;
Difficult to access, and full of working fluid discharge gap, so the processing stability of the poor, but not easy to shake the electrode wire, so the machining accuracy and surface roughness better rent.
5) the working fluid on the impact of process indicators:
① The role of the working fluid: dielectric, cooling, chip removal, etc.;
② The processing speed and processing quality:
Workpiece machined with kerosene was dark gray;
Deionized water, the workpiece machined gray;
Emulsion of the workpiece machined with silver white.
③ the resistivity of the working fluid on the processing speed of:
Speed wire EDM device working fluid purification facilities are generally not, the working fluid use of time can not be too long;
LSWEDM deionized water as much, it should be changed regularly ion exchange resins.
6. Line cutting processing forms:
Line cutting can be divided into planar processing, secondary processing and cutting taper and so on.
(1) plane processing;
Graphic processing - refers to the electrode wire is always in the process is strictly vertical, the electrode wire only in the X, Y direction, the two-dimensional shape processing.
(2) taper processing;
Taper processing - is in the process, through the X, Y, U, V-axis control, three-dimensional processing to achieve the upper and lower profiled.
Processing during the taper need to specify the value of the variable:
A: definition of the taper to be machined, Z1: procedures height;
Z2: processing speed display height, Z3: the lead from the mouth to the table surface (equal to ΔZ3 S Z5);
ΔZ3: Z3 used to determine the parameters, the parameters of the device after installation automatically determined by the system;
S: upper guide surface of the mouth and the workpiece gap, after clamping the workpiece measured with a feeler, and generally 0.1 ~ 0.2mm appropriate.
Z4: The following guidance from the mouth to the surface of the table, the parameters of the device after installation automatically determined by the system; Z5: Faced with the program height should be non-procedural.
(3) secondary cutting:
1) The second cutting - precision machining allowance in advance to stay out of a first cutting, and precision machining allowance for the left, the processing conditions to finishing conditions, reduce the offset section, and then cutting processing.
2) can be divided into 1 to 5 times cutting, known as the secondary cutting method.
Second cutting the following three purposes:
① cutting can be removed at the beginning of the first joint of the convex part left.
② to improve the surface roughness. Gradually changing the electrical conditions during each cut, reducing single pulse energy, improve the surface roughness.
③ improve dimensional accuracy.
Heat-treated materials, will produce internal stress, this stress is in a stable condition in the interior, but after a wire cutting electric discharge machine processing, it will destroy this steady state, so that the internal stress release, resulting in distortion.
After the piece of rough, 1 to 4 times further finishing can improve the surface roughness, dimensional accuracy but also modified.