FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
A SYSTEM AND METHOD FOR REGULATING WIRE SPEED IN ELCTRO DISCHARGE MACHINE
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to Electrical Discharge Machine (EDM) and particularly to the Wire Electrical Discharge Machine (WEDM) which is used as a cutting tool for making through cavities in metallic blocks and more particularly to a system and method for regulating speed of cutting wire electrode in Wire Electrical Discharge Machine (WEDM) to reduce the consumption of wire in the cutting process.
B) BACKGROUND OF THE INVENTION
[0002] Electric discharge machining (EDM) is a manufacturing process whereby a required shape of an object called "work-piece" is obtained using electrical discharges (sparks). The material is removed from the work-piece by a series of rapidly recurring current discharges between two electrodes that are separated by a dielectric liquid and subjected to an electric voltage. One of the electrodes is called tool-electrode and is sometimes simply referred to as 'tool' or 'electrode', whereas the other is called work piece-electrode, commonly abbreviated as 'work piece'.
[0003] When the distance between the two electrodes is reduced, the intensity of the electric field in the space provided between the electrodes is expected to become larger than the strength of the dielectric and as a result the dielectric break down is occurred thereby allowing some current to pass between the two electrodes. The collateral effect of the passage of this current in that material is removed from both the electrodes. Once the current flow stops, a fresh dielectric liquid should be filled in the inter-electrode volume thereby enabling the removed electrode material and solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. The addition of new dielectric liquid in the inter-electrode volume is commonly referred to as

flushing. Also, a potential difference equal to the one before the occurrence of dielectric breakdown is restored between the two electrodes after a current flow so that a new dielectric breakdown can occur.
[0004] Electrical discharge machining (EDM) is a machining method primarily used for hard metals or those in which it is very difficult to perform the machining process with traditional techniques. EDM typically works with materials that are electrically conductive, although methods for machining insulated ceramics with EDM have also been proposed. EDM can cut intricate contours or cavities in pre-hardened steel without the need for heat treatment to soften and re-harden them. This method can be used with any other metal or metal alloy such as titanium, hastelloy, kovar, and inconel.
[0005] EDM is often included in the 'non-traditional' or 'non-conventional' group of machining methods together with processes such as electrochemical machining (ECM), water jet cutting (WJ, AWJ), laser cutting and opposite to the 'conventional' group of machining processes such as turning, milling, grinding, drilling and any other process whose material removal mechanism is essentially based on mechanical forces. Ideally, the EDM can be seen as a series of breakdown and restoration of the dielectric liquid in-between the electrodes.
[0006] The EDM mechanism is classified into two types such as sinker EDM and wire EDM. Sinker EDM sometimes is also referred to as cavity type EDM or volume EDM. Sinker EDM consists of an electrode and work- piece that are submerged in an insulating liquid such as oil or dielectric fluid. The electrode and work-piece are connected to a suitable power supply. The power supply generates an electrical potential between the two parts. As the electrode approaches the work-piece, dielectric breakdown occurs in the fluid forming an ionization channel and a small spark jumps. The resulting heat and cavitations vaporize the base material and to some extent, the electrode. These

sparks strike one at a time in huge numbers at seemingly random locations between the electrode and the work-piece. As the base metal is eroded and the spark gap is subsequently increased, the electrode is lowered automatically by the machine so that the process can continued without interruption. Several hundred thousand sparks occur per second in this process, with the actual duty cycle being carefully controlled by the setup parameters. These controlling cycles are sometimes known as "on time" and "off time". The on time setting determines the length or duration of the spark. Hence, a longer on time produces a deeper cavity for that spark and all subsequent sparks for that cycle create a rough finish on the work-piece. The reverse is true for a shorter on time. Off time is the period of time in which one spark is replaced by another. A longer off time, for example, allows the flushing of dielectric fluid through a nozzle to clean out the eroded debris, thereby avoiding a short circuit. These settings are maintained in micro seconds. The typical part geometry is to cut small or odd shaped angles. Vertical, orbital, vectorial, directional, helical, conical, rotational, spin and indexing machining cycles are also used.
[0007] In wire electrical discharge machining (WEPM), or wire-cut EDM, a thin single-strand metal wire, usually brass, is fed through the work-piece, typically occurring submerged in a tank of dielectric fluid. This process is used to cut plates as thick as 300mm and to make punches, tools and dies from hard metals that are too difficult to machine with other methods. The wire, which is constantly fed from a spool, is held between upper and lower diamond guides. The guides move in the x-y plane, usually being CNC controlled. Almost on all modern machines, the upper guide can also move independently in the z-u-v axis, giving rise to the ability to cut tapered and transitioning shapes (circle on the bottom square at the top for example) and can control axis movements in x-y-u-v~i-j-k-l-. This enables the user to program the wire-cut EDM to cut very intricate and delicate shapes. The wire is controlled by the upper and the lower diamond guides that are usually accurate and have a precision cutting path or kerf as small as 0.12 mm using a 0.1 mm brass wire, though the average cutting kerf that is achieved with the best economic cost and machining time may be varied. The wire-cut

process uses water as a dielectric liquid since the resistivity and other electrical properties of water can be carefully controlled by filters and de-ionizer units. The water also serves the very critical purpose of flushing the cut debris away from the cutting zone. Flushing is an important determining factor for achieving the maximum feed rate that is available with a given material thickness and poor flushing situations necessitate the reduction of the feed rate.
[0008] Generally the wire speed defined by the present wire electrical discharge machining (WEDM) technology is lOmtr/min to 12mtr/min for Job referencing and rough machining stages. The wire used to get unwound from the spool during the start of the program, during the time of filling the tank with dielectric fluid and also during the cutting process. The machine used to start the job cutting process only after the tank was completely filled. The wire speed during this stage was specified as 7meter /min to lOmeter/min. This led to the wastage of wire during the non-cutting period of the machine. Further the operator has to make frequent changes of parameters in the job cutting machine which led to frequent wire breakage and consumes more wire for rough machining process.
[0009] Hence there is a need to provide a system and method to regulate the running speed of cutting wire electrode in EDM Machines to eliminate the excess usage of wire used by the wire electrical discharge machining (WEDM) in the job cutting process. Also there is a need to provide a process whereby the frequent change in settings required to be done by the operator for the job cutting process is reduced.
[0010] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

C) OBJECTS OF THE INVENTION
[0011] The primary object of the present invention is to provide a system and method to minimize the usage of cutting wire electrode used in the job cutting process in a wire electrical discharge machine (WEDM).
[0012] Another object of the present invention is to provide a system and method to reduce the wire speed during rough machining and job referencing stages.
[0013] Yet another object of the present invention is to provide a system and method to reduce the wire speed to zero during the filling of a tank with a dielectric liquid.
[0014] Yet another object of the present invention is to provide a system and method to reduce the necessity of changing the settings/parameters frequently by an operator for a job cutting process.
[0015] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0016] The various embodiments of the present invention provide a system and method for regulating the running speed of a cutting wire electrode in a wire electric discharge machine to reduce the usage of the wire in the metal cutting process and to reduce the frequency of changing the settings/parameters during the cutting process. .
[0017] According to one embodiment of the present invention, a wire speed regulating system in electro discharge machines comprising a tank enclosing a table

mounted with a job, is provided with a processor loaded with a wire cutting program. A servo motor is connected to the processor. A spool wound with a cutting wire electrode is connected to the servo motor. The processor displays a user interface to enable an operator to set the running speed of a cutting wire electrode during the job cutting process and during the process of filling the tank with a dielectric load to preset levels. The processor regulates the speed of the servo motor based on the input data to set the running speed of the cutting wire electrode to preset level during the job cutting process and during the tank filling process.
[0018] The preset running speed of the cutting wire electrode during the job cutting process and the preset running speed of the cutting wire electrode during the tank filling process are mutually different. The preset running speed of the cutting wire electrode during the job cutting process is 8 m/min. The preset running speed of the cutting wire electrode during the tank filling process is zero.
[0019] According to one embodiment of the present invention, a method is provided to regulate the running speed of a cutting wire electrode in electric discharge machine including a processor. The method involves mounting the job on a table, performing the job referencing process, loading a machining program in a processor, preparing the technology file and starting the program. The method further involves setting parameters with respect to a machining process, starting a rough machining process, starting a tank filling process, finishing the machining process and unloading the job. The parameters setting process with respect to a machining process involves displaying a user interface to enable the user to input the running speed of a cutting wire electrode to preset level based on a machining process to be performed.
[0020] The machining process is job cuttings process or a rough machining process or a dielectric liquid filling process in a tank that is provided to surround the table and

the job. The running speed of the cutting wire speed is set to 8m/min during the execution of the job cutting process.
The running speed of the cutting wire electrode is adjusted to zero during the filling process of a tank with dielectric liquid. The running speed of the cutting wire electrode is adjusted to zero during the rough machining process.
[0021] According to one embodiment of the present invention, job alignment and clamping process includes placing the job on the table which is operated in the directions of x and y axis and clamping the job such that it is rigidly fixed to the table. The job referencing process includes drilling a hole at the center of the job through which the wire which is used to cut the job is made to travel. Also the job referencing process includes blocking the referencing edge and deriving the centre of the block. The wire for example a brass wire is made to pass through the hole. The wire speed is reduced using computer-numerically controlled (CNC) machine from IO-12meters /min to 8-10meters /min without losing the accuracy, surface finish and the time needed for completing the job cutting process.
[0022] The next stages in a wire electric discharging machining (WEDM) process are a program loading process, technology file preparation process and loaded program starting process. During this phase, the software program is prepared with the instructions on the size and shape of the job to be cut and a technology file containing these instructions and other control instructions is prepared. Further the technology file is loaded into a computer-numerically controlled (CNC) machine which intercepts these instructions and controls the wire guide accordingly to obtain the prescribed work-piece or job of preferred shape and size.
[0023] The technology loading process is followed by a tank filling process and a rough machining process. In this phase, the work-piece or job which is to be cut is

placed in a tank and the tank is filled by a dielectric liquid. Generally this dielectric liquid is pure water which acts as insulator between a wire electrode and the work-piece or job. Further rapid DC electrical pulses are generated between the EDM wire electrode and work-piece or job thereby removing the debris by spark erosion. When the tank is filled by a dielectric liquid, the computer-numerically controlled (CNC) machine is programmed such that the wire consumption is made zero during the filling of a tank with dielectric liquid. Also during the rough machining process, the computer-numerically controlled (CNC) machine is programmed such that the wire usage is constrained to 8mtr/min. This reduction in wire speed doesn't have any impact either on the cutting speed or the quality or the accuracy or the surface finish of the job.
[0024] After the cutting process, the job or work-piece is unloaded from the table. In this stage, the computer-numerically controlled (CNC) machine is programmed such that the wire usage is limited to 7mtr/min which further doesn't have any negative effect on the quality, accuracy or the speed of job processing. After the job cutting process is completed, the job or work-piece is unloaded from the table where it was clamped to obtain the final finished product.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0026] FIG. 1. illustrates a flow chart for explaining the method of reducing the wire electrode speed for regulating the wire speed in electro discharge machine according to one embodiment of the present invention.

[0027] FIG. 2 illustrates a front view of a graphical user interface displayed to enable the user to set the running speed of the cutting wire electrode during a rough machining process and job cutting process in a system for regulating the wire speed in electro discharge machine according to one embodiment of the present invention.
[0028] FIG. 3 illustrates a front view of a graphical user interface displayed to enable the user to set the running speed of the cutting wire electrode during a tank filling process in a system for regulating the wire speed in electro discharge machine according to one embodiment of the present invention.
[0029] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0030] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0031] The various embodiments of the present invention provide a system and method for regulating the running speed of a cutting wire electrode in a wire electric discharge machine to reduce the usage of the wire in the metal cutting process and to reduce the frequency of changing the settings/parameters during the cutting process.

[0032] According to one embodiment of the present invention, a wire speed regulating system in electro discharge machines comprising a tank enclosing a table mounted with a job is provided with a processor loaded with s wire cutting program. A. servo motor is connected to the processor. A spool wound with a cutting wire electrode is connected to the servo motor. The processor displays a user interface to enable an operator to set the running speed of a cutting wire electrode during the job cutting process and during the process of filling the tank with a dielectric load to preset levels. The processor regulates the speed of the servo motor based on the input data to set the running speed of the cutting wire electrode to preset level during the job cutting process and during the tank filling process.
[0033] The preset running speed of the cutting wire electrode during the job cutting process and the preset running speed of the cutting wire electrode during the tank filling process are mutually different. The preset running speed of the cutting wire electrode during the job cutting process is 8 m/min. The preset running speed of the cutting wire electrode during the tank filling process is zero.
[0034] According to one embodiment of the present invention, a method is provided to regulate the running speed of a cutting wire electrode in electric discharge machine including a processor. The method involves mounting the job on a table, performing the job referencing process, loading a machining program in a processor, preparing the technology file and starting the program. The method further involves setting parameters with respect to a machining process, starting a rough machining process, starting a tank filling process, finishing the machining process and unloading the job. The parameters setting process with respect to a machining process involves displaying a user interface to enable the user to input the running speed of a cutting wire electrode to preset level based on a machining process to be performed.

[0035] The machining process is job cuttings process or a rough machining process or a dielectric liquid filling process in a tank that is provided to surround the table and the job. The running speed of the cutting wire speed is set to 8m/min during the execution of the job cutting process.
The running speed of the cutting wire electrode is adjusted to zero during the filling process of a tank with dielectric liquid. The running speed of the cutting wire electrode is adjusted to zero during the rough machining process.
[0036] According to one embodiment of the present invention, a wire electric discharge operation is used for the removal of material which is done by a succession of moving electrical discharges (sparks), separated from each other by a uniform time interval. The phenomenon is therefore unitary and periodic. The discharges are produced by the voltage source (off- load voltage) of more than 20 volts, and always takes place in the dielectric fluid. Generally brass wire mounted on a spool is fed through a hole made in a metallic block and used to cut a through profile by electro discharge machining.
[0037] A wire electric discharge machine (WEDM) comprises a table operated in X and Y directions by ball screw mechanism which is powered by servo motors and optical reading scale for displacement measurement. The metallic block is mounted on the table for cutting operation. The table is surrounded by a tank which is filled by dielectric fluid. The EDM wire is generally mounted on a spool which rotates to unwind the wire during various operations of the machine. The wire is made to pass through a hole made in the metallic block and its free end is connected to the wire drive roller which is mounted on lower wire guide chamber. The cutting operation takes place in dielectric fluid submerging both the steel block and EDM wire. The profile being cut is separated from the EDM wire by a gap called SPARK gap. The job acts as Cathode and EDM wire acts as Anode having high voltage difference. The energy is transferred to the job in the form of spark that melts away the work piece causing profile cutting action.

[0038] The wire speed defined by machine technology is lOm/min to 12m/min for job referencing and rough machining processes. The wire speed is specified as 7 to 10 m/min during the tank filling process. The wire speed is reduced to 8m/ min during job referencing and rough machining processes while the wire speed is kept at zero during the tank filling process. The accuracy, surface finish and machining time are remained unchanged.
[0039] The wire speed was further reduced to 7m / min for rough machining but frequent breakage of wire is occurred frequently. Hence the speed was frozen at 8m/min for rough machining process. The referencing point is found unchanged even after reducing the wire speed to 8m/min.
[0040] FIG. 1. illustrates a flow chart for explaining the method of reducing the wire electrode speed for regulating the wire speed in electro discharge machine according to one embodiment of the present invention. With respect to FIG.l, the stepwise procedure involved in the wire electric discharging machining (WEDM) process are Job alignment and clamping process(lOl), Job referencing process(102), Program loading and technology file preparation process (103), program starting process (104), Tank filling process followed by rough machining process (105), Finishing machining process (106) and job unloading process (107).
[0041] The job alignment and clamping process (101) includes placing the job on the table which is operated in the directions of x and y axis and clamping the job such that it is rigidly fixed to the table. The job referencing process (102) includes drilling a hole at the center of the job through which the wire which is used to cut the job is made to travel. Also the job referencing process (102) includes blocking the referencing edge and deriving the centre of the block. The wire for example a brass wire is made to pass through the hole. The wire speed is reduced using computer-numerically controlled

(CNC) machine from 10-12meters /min to 8-I0meters /min without losing the accuracy, surface finish and the time needed for completing the job cutting process.
[0042] The next stages in a wire electric discharging machining (WEDM) process are a program loading process, technology file preparation process and loaded program starting process. During the program loading process and technology file preparation process (103), the software program is prepared with the instructions on the size and shape of the job to be cut and a technology file containing these instructions and other control instructions is prepared. Further the technology file is loaded into a computer-numerically controlled (CNC) machine which intercepts these instructions and controls the wire guide accordingly to obtain the prescribed work-piece or job of preferred shape and size.
[0043] The technology loading process is followed by a tank filling process and a rough machining process (105). During the tank filling process (105), the work-piece or job which is to be cut is placed in a tank and the tank is filled by a dielectric liquid. Generally this dielectric liquid is pure water which acts as insulator between a wire electrode and the work-piece or job. Further rapid DC electrical pulses are generated between the EDM wire electrode and work-piece or job thereby removing the debris by spark erosion. When the tank is filled by a dielectric liquid, the computer-numerically controlled (CNC) machine is programmed such that the wire consumption is made zero during the filling of a tank with dielectric liquid. Also during rough machining process, the computer-numerically controlled (CNC) machine is programmed such that the wire usage is constrained to 8mtr/min. This reduction in wire speed doesn't have any impact either on the cutting speed or the quality or the accuracy or the surface finish of the job.
[0044] After the cutting process (106), the job or work-piece is unloaded from the table. In this stage, the computer-numerically controlled (CNC) machine is programmed such that the wire usage is limited to 7mtr/min which further doesn't have any negative

effect on the quality, accuracy or the speed of job processing. After the job cutting process (106) is completed, the job or work-piece is unloaded from the table where it was clamped to obtain the final finished product (107). The frequency of cutting processes performed in a cycle is decided by accuracy of job required.
[0045] FIG. 2 illustrates a front view of a graphical user interface displayed to enable the user to set the running speed of the cutting wire electrode during a rough machining process and job cutting process in a system for regulating the wire speed in electro discharge machine according to one embodiment of the present invention. With respect to FIG.2, the wire speed is reduced to 8m/ min during job referencing and rough machining processes. The accuracy, surface finish and machining time are remained unchanged. In the "machine parameters" block it is recorded that wire speed (WS) is 8.0 and in the "speed" block it is indicated as 2.692 mm/min which resulted in less usage of wire used for job cutting purpose.
[0046] FIG. 3 illustrates a front view of a graphical user interface displayed to enable the user to set the running speed of the cutting wire electrode during a tank filling process in a system for regulating the wire speed in electro discharge machine according to one embodiment of the present invention. With respect to FIG.3, the wire speed is kept at zero during the tank filling process. The accuracy, surface finish and machining time are remained unchanged. In the "wire" block it is recorded that wire speed (WS) is reduced to Omts/min from 7mts/min which resulted in less usage of wire during this stage.
G) ADVANTAGES OF THE INVENTION
[0047] The various embodiments of the present invention provide a system and method for reducing the running speed of cutting wire electrode in an electro discharge

machines such that the excess usage of wire is re4uced during the wire electric discharging machining (WEDM) process.
[0048] The system and method reduces the wir£ speed during rough machining
and job referencing stages without losing the consistency in quality, time and accuracy
of the job finishing. The system and method reduces the wire speed to zero during the
filling of a tank with a dielectric liquid. The system and method is provided to
reduce the necessity of changing the settings/parameters frequently by an operator fox a job cutting process.
[0049] Although the invention is described with varices specific embodiments, it will be obvious, for a person. skilled in the. act to practice the invention with, modifications. However, all such modifications are deemed to be within the scope of the claims.
[0050] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A wire speed regulating system in electro discharge machines comprising a tank
enclosing a table mounted with a job, the system comprising:
A processor loaded with a wire cutting program;
A servo motor connected to the processor;
A spool wound with a cutting wire electrode connected to the servo motor;
Wherein the processor displays a user interface to enable an operator to set the
running speed of a cutting wire electrode during the job cutting process and
during the process of filling the tank with a dielectric load to preset levels.
2. The system according to claim 1, the preset running speed of the cutting wire electrode during the job cutting process and the preset running speed of the cutting wire electrode during the tank filling process are mutually different.
3. The system according to claim 1, wherein the preset running speed of the cutting wire electrode during the job cutting process is 8 m/min.
4. The system according to claim 1, wherein the preset running speed of the cutting wire electrode during the tank filling process is zero.
5. The system according to claim 1, wherein the processor regulates the speed of the servo motor based on the input data to set the running speed of the cutting wire electrode to preset level during the job cutting process and during the tank filling process.

6. A method to regulate the running speed of a cutting wire electrode in electric
discharge machine including a processor, the method comprising:
Mounting the job on a table;
Performing the job referencing process;
Loading a machining program in a processor;
Preparing the technology file;
Starting the program;
Setting parameters with respect to a machining process;
Starting a rough machining process;
Starting a tank filling process;
Finishing the machining process; and
Unloading the job;
Wherein the parameters setting process with respect to a machining process
involves displaying a user interface to enable the user to input the running speed
of a cutting wire electrode to preset level based on a machining process to be
performed.
7. The method according to claim 6, wherein the machining process is a job cutting process,
8. The method according to claim 6, wherein the running speed of the cutting wire speed is set to 8m/min during the execution of the job cutting process.
9. The method according to claim 6, wherein the machining process is a dielectric liquid filling process in a tank that is provided to surround the table and the job.
10. The method according to claim 6, wherein the running speed of the cutting wire
electrode is adjusted to zero during the filling process of a tank with dielectric
liquid.

11. The method according to claim 6, wherein the machining process is a rough
machining process.
12. The method according to claim 6, wherein the running speed of the cutting wire
electrode is adjusted to 8m/min during the rough machining process.