Cnc Wire cut ppt

1. CNC WIRE-CUT
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2. Safety Rules
• Always keep safety in mind.
• Wear eye protection and safety shoes at all times.
• Do not wear neckties, wristwatches, rings jewelry etc.
• Wear half sleeve shirt. Long sleeve shirt will be rolled above the elbow.
• Do not touch the wire while machine is in operation mode.
• Do not keep any material on the table or U/V covers.
• Make sure workpiece,Fixturing and table are properly grounded.
• Never attempt to break wire with hands, use appropriate cutting device.
• Do not watch the spark when skim cutting.
• Do get thoroughly familiar with STOP button and other controls as well as
alarms and interventions.
• Clean machine and area after each use.
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3. Machine Start Procedure
Stabilizer Switch On
Green Switch On
Machine Switch On
Emergency Switch Release
Power On
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MACHINE SPECIFICATION

5. Working Principle
ELECTRIC DISCHARGE MACHINING (EDM) is a process of repetitive
sparking cycles.
Graphical Representation of Sparking Cycles
Inter electrode Gap Current Waveform During Sparking
Where : TON : Pulse ON period
TOFF : Pulse OFF period
Td : Spark initiation period (Ignition Delay)
VP : Open Gap Voltage
Vg : Average Gap voltage
IP : Machining peak current
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6. WEDM
• Machine Tool:-
• The machine tool comprises of a main work table (called as X-Y table), an
auxiliary table (called as U-V table) and a wire drive mechanism. The
workpiece is mounted and clamped on the main work table. The main table
moves along X and Y axes, in steps of 0.5 micron, by means of servo
motors, and also the U-V table moves, in steps of 0.5 micron, by means of
servo motors. U & V axes are parallel to X & Y axes respectively.
• A traveling wire which is continuously fed from wire feed spool is caused to
travel through the workpiece and goes finally to the waste-wire box. Along
its traveling path, the wire is supported under tension, between a pair of
wire guides which are disposed on both (lower and upper) sides of the
workpiece. Lower wire guide is stationary whereas the upper wireguide is
supported by the U-V Table. The upper wireguide can be displaced
transversely, along U-V axes, with respect to the lower wire guide. It can
also be positioned vertically along Z axis by moving the vertical arm.
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7. WEDM
• Power supply
• The power supply unit comprises of Electric pulse generator, motor
driver units for X, Y, U, V axes and CNC controller.
• Dielectric Supply
• While the machining is continued, the machining zone is
continuously flushed with water passing through the nozzles on both
sides of the workpiece. The spark discharge across the workpiece -
wire electrodes causes ionization of the water which is used as a
dielectric medium.
• It is important to note that ionization of water leads to the increase in
water conductivity. An ion exchange resin is used in dielectric
distribution system, in order to prevent the increase in conductivity
and to maintain the conductivity of the water constant.
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8. WEDM
• Part Programming
• The geometry of the profile and the motion of the wire-electrode tool
along the profile is fed to the part programming system using
keyboard. The profile geometry is defined in terms of various
geometrical definitions of point, line and circle as the wire-tool path
elements on graphical screen, by using a totally menu driven
software. The wire compensation (for wire diameter and machining
overcuts) and taper angle can be specified for the total path or for
each path element separately. After the profile is fed to the
computer, all the numerical information about the path is calculated
automatically and its printout is generated. The entered profile can
be verified on the graphic display screen and corrected, if
necessary. After successful profile definition, the profile is recorded
by the computer on a floppy disc which can be used in the controller
for the execution.
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10. WEDM
• WIRE ELECTRODE
• The wire electrode is required to have a sufficient tensile strength
and should be of uniform diameter and free from kink or twist.
• The electrode wire material should be -
• - Brass / Diffused Brass / Zinc coated Brass
• - Diameter variation within ±0.002 mm
• - Tensile strength more than 50 Kgf/mm2
• - Even winding, free from breaks/kinks.
• 2.1 Wire diameter and Minimum corner radius.
• Wire diameter of the wire imposes a restriction on the minimum
achievable corner radius. (Refer Fig. 2.)
• Minimum corner radius = (0.5 * diameter) + overcut.
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11. WEDM
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12. WEDM
• Current carrying capacity of the wire.
• As a thumb rule, a brass wire of 0.2 mm in diameter can pass a current of
about 0.3 to 0.7 Amperes (A) in air, but, the same wire can easily pass a
current of about 6 to 9 A in water. While machining, therefore, wire should
always be surrounded by the water column to avoid wire breakage.
• Wire Tension (WT)
• Wire tension determines how much the wire is to be stretched between
upper and lower wire guides. More the thickness of job, more is the tension
required. Improper setting of tension may result in the job inaccuracies as
well as wire breakage. Following chart gives nominal values of wire tension
for different setting. Minimum tension (For 0 setting of WT) is approx. 200 ~
300 gms. Which can be adjusted by clutch adjustment provided on
feedspool mounting rod. This should be adjusted for different weight of
spools.
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13. WEDM
• WT TENSION (Gms.) Nominal Values
• 1 300
• 2 420
• 3 540
• 4 660
• 5 780
• 6 900
• 7 1020
• 8 1140
• 9 1260
• 10 1380
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14. WEDM
• Wire feed (WF)
• Due to spark erosion, the traveling wire-electrode becomes thin and brittle. Wire feed is the rate at
which the wire-electrode travels along the wire guide path. It is always desirable to set the wire
feed to maximum. This will result in less wire breakage, better machining stability, and slightly
more cutting speed. With wire feed set at 8 mt/min, on an average a 0.25 mm dia. brass wire
spool of 5 kg will last for 24 sparking hours.
• Setting WF at 15 will correspond to 15 mt/min (approx.)
• Overcut
• It is the lateral distance between the wire and workpiece during the sparking.
• Overcut is larger if -
• - machining gap voltage is higher
• - discharge energy is higher
• - wire tension is lower
• - guide span is higher
• - job thickness is higher
• - dielectric conductivity is higher
• - machining is unstable
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15. WEDM
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Wire Compensation (OFFSET) :
Wire compensation = (0.5* wire diameter) + overcut
Wire compensation can be to the left (G41) or right (G42) of
profile depending upon the direction of motion and wire being
inside or outside of profile as shown in figure .

16. WEDM
• WATER DIELECTRIC
• 1. CHARACTERIZATION & SUITABILITY TO WIRECUT EDM :
• 1.1 The use of water as dielectric permits widening of spark gap to minimize
short circuit, resulting in high cutting speed.
• 1.2 Water has good wire electrode cooling effect (than kerosene, for
example).
• 1.3 It is non-flammable and its vapors are non-toxic.
• 2. DIELECTRIC STRENGTH :
• Since the insulation characterization of the dielectric fluid decides the
overcut, it is imperative to keep the conductivity as constant as possible.
During machining, the conductivity of dielectric water changes due to
generation of metallic ions and dissolution of ambient gases. The
conductivity can be decreased by passing the water through deionizer resin.
This is done automatically by the machine.
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17. WEDM
• FLUSHING :
• Flushing is important to achieve a stable machining
condition. It plays very important role as far as cutting
speed is concerned. Both the Nozzles (upper and lower)
should be just about 0.1 ~ 0.2 mm away from the
workpiece, otherwise cutting performance drops
considerably. Also both the nozzles should be checked
periodically for damages. Scratches or slight damage on
the contact edge affect cutting speed. Purity of the water
should be maintained by timely replacement of filters.
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18. WEDM
• SETTING UP AND OPERATION
• 1. Job Mounting :
• Mount the job and clamp it by maximum possible clamps. Dial the
top surface of the job by dial gauge. The dial gauge stand can be
mounted on the upper flushing assembly provision for the same is
provided. Make the wire vertical with the help of verticality block
provided along with the machine.
• 2. Job Reference Point :
• It is always desirable to have a reference point on the workpiece for
setting the work co-ordinate system (WCS). The programming
should be done with the reference to the WCS. The reference point
can be defined by the ground edges of the workpiece or the center
of a bored hole on the workpiece.
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19. WEDM
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Edge finding (EF) :
This function should be used to find the edge for setting work co-
ordinate system. Find the edge of the workpiece from a distance
of 2 - 5 mm. Refer Figure.
Remember that after edge finding, the wire center is away from
the workpiece edge by a distance equal to wire radius.

20. WEDM
• Center finding (CF) :
• This function should be used to find the center of the
reference hole. Center finding should be repeated at
least twice to verify consistency.
• Following care should be taken to perform CF and EF
functions.
• 2.2.1 Workpiece surface should be free from moisture,
rust, dust and grease etc.
• 2.2.2 Upper flushing assembly should not be wet
• 2.2.3 WF should be at 3 and WT at 6
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21. WEDM
(A) Machining Parameters:-
• TON : Pulse ON Time
• TOFF : Pulse OFF Time.
• IP : Peak current (A).
• VP : Pulse Peak Voltage setting
• WP : Flushing Pressure of Water Dielectric
• WF : Wire Feed rate setting.
• WT : Wire Tension setting
• SV : Spark Gap Set Voltage
• SF : Servo Feed Setting
• T : Threshold setting
• CC : Corner Control factor
• CRK : Radius compensation factor
• CS% : Cutting Speed Over-ride %.
• C DWELL : This parameter is used to provide Dwell (delay) in seconds
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34. Advantages
• Complex shapes that would otherwise be difficult to
produce with conventional cutting tools.
• Extremely hard material to very close tolerances.
• Very small work pieces where conventional cutting tools
may damage the part from excess cutting tool pressure.
• There is no direct contact between tool and work piece.
Therefore delicate sections and weak materials can be
machined without any distortion.
• A good surface finish can be obtained.
• Very fine holes can be easily produced.
• The part produced are burr free.
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35. Disadvantages
• Power consumption is high.
• Electrically non-conductive materials can’t
be machined.
• Only through profiles can be machined.
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36. Application
• Punches and dies used in Press Tool can
be made.
• For the production of moulds and dies.
• Used to cut out complex contours in
electrically conductive workpieces.
• Cylindrical pins as small as 5mm in
diameter can be machined.