Hello
friends! How are you? I am Amy from TAGUTI EDM Co., Ltd in Suzhou. So
happy to see you! Welcome to “One month, one talk”. This month the topic
is “Discipline on electrical discharge wire cutting” Ok, let’s begin.
About the main tech indexes:
1/ The wire cut speed,
The speed is guaranteed some roughness on the surface in the wire cut process, in the unit time, the total area that the middle wire in the wire cuts on the workpieces, the unit is mm2/min. The max wire speed is at the condition of disregarding the directions and roughness, it gets to the max wire cut speed. In general, the speed is between 40 and 80 mm2/min. It has some relationship with electric current.
2/ Machining precision/ working accuracy,
Machining precision means the together of the precision in size, shape and position. Machining precision is an aggregative indicator, it includes the precisions in the control of cutting track, Accuracy of mechanical transmission, Workpiece clamping positioning accuracy and Pulse power parameter fluctuations, the error in the diameter of the electrodes, loss & shaking, The change of working liquid smudgy degree, proficiency of the operator.
3/ Surface roughness,
In China and Europe, we show arithmetical mean deviation of the (roughness) profile “Ra(μm)”, but in Japan, they use “Rmax”.
4/ Wire electrode wastage,
To high speed EDM machines, the wire will be reduced after cutting the area of 10 000 mm2 , the reduction is not less than 0.01mm. But to slow speed EDM machines, due to the wire is one-off, so it makes no sense to discuss about the wastage.
About: The influence of electric parameters on the technical index
1/ the peak discharge current has an effect on technic index,
The peak discharge current increases, single pulse energy increases, the discharging trace in workpiece increases. So the cutting speed is improved, surface roughness number value increases, the wastage of wire is increased but the machining precision reduces. So the bigger peak discharging current for the first cutting and machining the thicker workpieces. The current has the limited range, when reaches a certain critical value, if continue adding the current, then the stability of machining variation becomes bad, the machining speed becomes slow, and even broken wire.
2/ pulse width ti
At
the same condition, adding the pulse width ti, improving the speed of
the wire cutting, the worse of the surface roughness. This is because
when add the width, single pulse energy increases, the discharging trace
in workpiece increases. The same time the wire wastes too much. When
the width reaches a certain critical value, the speed reduces instead.
3/ pulse interval
At the same conditions, reduce the interval, pulse frequency improves, so the times of discharging adds, and average current increases, and improve the cutting speed.
4/ polarity
The pulse width is narrow, so in fact we use positive polarity to make, if not, the speed will be slower and the big wastage.
Non-electrical parameter
1/ The choice of electrodes,
At present the common electrode materials are molybdenum wire, tungsten wire, Molybdenum-tungsten alloy wire, brass wire, Copper tungsten filament and etc.
Adopt
tungsten wire, the higher speed, but after discharging, the wire is
brittle and broken wire easily. So it is used little. Melting point of
moly wire is lower than tungsten wire, Low tensile strength, but good
tenacity. In the process of frequent change snap hot and cold, the wire
can’t be embrittlemented and be broken wire easily.
Tungsten-molybdenum wire (half-half) whose machining effect is better
than Tungsten wire and moly wire, and at the same time the mixture wire
has the both wire’s characters, the service time is longer and the
machining speed is higher than moly wire. Copper-tungsten has a better
machining effect, but the tensile strength is a little worse, with more
expensive and rarely source, so it is seldom used in the industry. Brass
wire whose machining speed is faster, and good machining stability, but
bad tensile strength and great loss.
At present, moly wire is widely used in high speed wire cut EDM machining and brass wire whose diameter is at least 0.1mm is used in slow speed wire cut EDM machining.
You can choose the EDM wire based on the machining needs and tech condition. Around a range of machining, you can choose the bigger diameters’ EDM wire. Bigger diameter, more tensile strength, bear more current, Strong electric gauge is used, that can improve the output pulse energy and improve the machining speed finally. In the meanwhile, thick wire electrode, kerfs width, the excluded condition of discharge products is good and stable processing. So in further, that can improve pulse efficiency and machining speed. But you have to consider that if the wire is much too thick, it is very hard to make sharp corners in workpieces. What is the result? The machining precision is reduced and kerfs are too wide that make the materials removal rate becomes big. It will have an effect in the speed; it is not wise to choose a much too smaller diameter, lower tensile strength and broken easily, narrow kerfs, bad excluded condition and unstable process to make the slower speed. The advantage of thin EDM electrodes is that you can get a smaller diameter sharp corners, the machining precision is improved in some degree. The diameter of moly wire between 0.10mm to 0.25mm is commonly used in high speed wire cut EDM machining.
2/ Wire travelling speed
To high speed wire cut EDM machines, in some special range, along with
the improvement of the velocity, it is good for the end of the pulse
discharge channel deionization quickly. Meanwhile, high speed movement
can bring work fluid into thicker workpieces’ discharging gaps. So it is
make for chip removal and guaranteed the stable machining process. We
can see that in some special process, along with the increasing of the
wire speed, improving the machining speed. The same way for slow speed
wire cut machines. This kind of moving type is very stable, shaking
little, so it can make good surface roughness and machining precision;
but if it is too slow, the discharging products can’t be removed in
time. The result is short circuit and unstable discharging in the EDM
process.
The optimal speed for slow speed wire cut EDM machines have
some related with the workpieces, EDM wire and diameter, etc. Now you
can see the recommended speed in operating manual.
3/ EDM wire moves back and forth
You will find Black and white stripes in high speed EDM cut processing.
EDM wire moves back and forth. It also makes inclination. When the wire
works up and down, entrance and exit have different size. The
wide-mouthed end is the entrance and the narrow one is exit, thus on the
same cut surface the height of the ends are different. This point has
an effect on the precision and surface roughness.
But you won’t find
the above phenomenon in slow speed wire cut EDM machining. Because the
wire is one-off, don’t need to change the directions, and keep work
fluid and removal products balance in the discharging gaps, so you can’t
see Black and white stripes in the workpiece. Due to slow speed system,
the slow speed and stable state. In this good process, it is not easy
to make big Machine shake and that avoid the stripes.
4/ The tension of the wire electrodes
a. At the start step, the tension becomes more and the cut speed
becomes faster, do you know the reason? In the process, the wire
electrode becomes smaller amplitude, the kerfs width is narrow, so the
speed is faster. If the tension is very weak, one side it will shake a
lot and result to short circuit frequently, unstably and the machining
accuracy is not high; on the other side, the wire is too loose to make
the electrodes curve seriously in the process of machining under
discharging pressure, the cutting track becomes backward and off tracks.
And in the machining process, there will be errors in shape and size.
But the tension is too strong, the cut speed won’t continue increasing,
on the contrary, it is broken wire easily. The reason of broken wire is
due to the control of wire’s tensile strength. So at practice
processing, the start cut wire’ tension should be weak to make sure the
wire not broken. When in precision machining, the tension should be
strong to reduce the wire’s shake to improve the machining precision.
b.
At the same working conditions, different working fluids make different
machining speed, surface roughness. The speed of WEDM is on the basis
of the dielectric coefficient, mobility, detergency and so on. The
fluids include kerosene, deionized water, emulsified liquid, detergent
liquid, alcoholic solution, etc. But at the condition of the work
solution like kerosene and alcoholic solution, the slow wire cut speed,
free-burning, so it is rarely used now. At present, emulsified liquid is
widely used in high speed wire cut EDM machining procedure, the speed
is fast in the process. Deionized water is used in slow speed wire cut
EDM machining procedure.
We discuss about some elements make a
difference in the machining technic index. In the last paragraph, we
talk a little about the operating solution, but time is limited, we will
continue discussing it in next month. OK?
OK!
It is time to say goodbye to you, all my friends. But I want to say
something about our factory: TAGUTI. If you want EDM consumables and
parts, TAGUTI can help you, even our price is not cheap as others, but
stable quality can help you make more profit than others. I think it is
one of the reasons I recommend to you. Any questions, contact us! My
name is Amy, see you next month. Bye~
