AU2021103043A4

AU2021103043A4 - Optimize the process parameters of machining of gear on electrical discharge machining

Info

Publication number: AU2021103043A4
Application number: AU2021103043A
Authority: AU
Inventors: Abhinav Bhatnagar; Sumit Chauhan; Sachin Gupta; Akhilesh Kandwal; Amit Kumar
Original assignee: Roorkee College of Engineering
Current assignee: Roorkee College of Engineering
Priority date: 2021-06-03
Filing date: 2021-06-03
Publication date: 2021-08-05
Anticipated expiration: 2029-06-03

Abstract

Micro-wire EDM is an emerging technology in the field of Micro-machining to fabricate very complex micro products. This is used in the fields of dies, molds; precision manufacturing and contour cutting etc. any complex shape can be generated with high grade of accuracy and surface finish using CNC WEDM. The output of the process is affected by large no of input variables. Hence a suitable selection of input variables for the wire electrical discharge machining (WEDM) process depends heavily on the operator's technology & experience. In the present investigation an optimization of micro wire EDM has been carried out using Taguchi method. Using Taguchi's parameter design, significant machining parameters affecting the performance measures are identified as pulse off time, pulse on time, and current and optimal parameter setting is proposed. The effect of each control factor on the performance measure i.e. surface roughness, addendum circle, root circle, nose radius is studied individually using the plots of signal to noise ratio and analysis of variance. This work presents an experimental study in which wire EDM operations are performed on material SS-304 Steel plate. The effect of three machining parameters namely pulse on time, pulse off time and current are investigated. Trial run was conducted to establish the range of selected parameters. Subsequently pulse on time at three level , pulse off time at three levels and current at three levels are considered and 9 experiments as per the experimental plan of Taguchi's experimental design i.e. L9 OA are conducted . Five response variable namely Surface roughness, addendum circle, root circle, angle between top land and tooth face, and angle between bottom land and flank are measured. Signal to noise ratio for each response variable are computed. Subsequently, analysis of variance is used to obtain the percentage contribution of the parameters. The analysis of mean is performed to obtain optimum level of the machining parameters for multi performance characteristics. Analysis of variance is used to determine which machining parameters is significantly affected the multi performance characteristics and also to obtain the percentage contribution of each machining parameters towards the objective. 1 TOTAL NO OF SHEET:16 NO OF FIG.: 01 Ply.e supply Yf Spark-gap Workpiece Slot (kero guiedes Fig. 1.Principle of WEDM

Description

TOTAL NO OF SHEET:16 NO OF FIG.: 01

Ply.e

supply Yf

Spark-gap

Workpiece

Slot (kero guiedes

Fig. 1.Principle of WEDM

Australian Government

IP Australia

Innovation Patent Australia

OPTIMIZE THE PROCESS PARAMETERS OF MACHINING OF GEAR ON ELECTRICAL DISCHARGE MACHINING

Name and address of patentees(s)

Roorkee College of Engineering

Address: Roorkee College of Engineering Plot No.- 312 Roorkee-Haridwar Canal Road, Bajuheri, Roorkee-247667,Haridwar Uttarakhand,India.

Sumit Chauhan

Faculty of Roorkee College of Engineering Plot No.- 312 Roorkee-Haridwar Canal Road, Bajuheri, Roorkee-247667,Haridwar Uttarakhand,India.

Abhinav Bhatnagar

Amit Kumar

Akhilesh Kandwal

Complete Specification: Australian Government

FIELD OF THE INVENTION

Our Invention is related to optimize the process parameter of machining of Gear on Electrical Discharge Machining.

BACKGROUND OF THE INVENTION

Electrical discharge machining (EDM) is one of the must extensively used non-conventional, thermo-electric metal removal process which encodes material from the work place by a series of discrete spark between a work and a tool electrode immersed in a liquid dielectric medium. Electrical energy is used directly to cut the material in final shape. Melting and vaporization takes place by theses electrical discharges. The minute a mounts of the work material is then ejected and flushed away by the dielectric medium. The sparks occur at high frequency which continuously and effectively removes the work prices material by melting and evaporation. To initiate the machine process electrode and work piece are separated by a small gap known as 'spark gap' which results into a pulsed discharge causing the removal of material. The dielectric acts as a deionizing medium between two electrodes and its flow helps in vacating the resoliclified debris to assure optimal conditions for spark generation. In micro-wire EDM operation the work piece metal is cut with a special metal wire electrode that is programmed to travel along a definite path. Spark discharges and generated between a small wire electrode and a work piece to produce complex two dimensional and three-dimensional shapes according to a NC path. A very thin wire in the range of 0.18 mm in diameter as an electrode is used in the wire-cut EDM. The most prominent feature of a moving wire is that a complicated cutout can be early machined without using a forming electrode. The wire transport system of a wire EDM guarantees a smooth wire transport and constant tension of wire. The machine consists of a work piece contour movement control unit, work piece mounting table and wire driven part which ensures accurate movement of the wire oat constant tension. The purpose of WEDM is to achieve better stability and higher productivity, higher machining rate with accuracy. A large number of variables are involved in the process; also the nature of the process is stochastic. Hence even a highly skilled operator is unable to perform the optimal performance. Although WEDM machines available today have some kind of process control, still selection is very tough to ensure optimal setting.

These are the some important Features of Micro-wire EDM such as Electrode wear is negligible, Forming electrode to produce shape is not required, Machined surface are very smooth, Dimensional and Geometrical Tolerances are very tight, Straight hole production is possible with higher precision, Relative tolerance between punch and die is much higher and die life is extended, The machine can be operated unattended for long time at high rate, No special skills are required to run the machine, Any electrically conductive material can be machined irrespective of its hardness, This process allows the shaping and machining of complex structure with high machining accuracy in the order of micron. The surface roughness achievable is Rz = 0 pm.

OBJECTIVES OF THE INVENTION

There are a lot of parameters which affect the wire EDM machine performance. It is very though to derive exact and real mathematical models between machining performance and machining parameters. The reason is very complex mechanism involved in the process. The main objective is as follows: 1. The objective of the invention is to determine significant parameters affecting the performance of machining. 2. The objective of the invention is to discuss the cause effect relationship of machining parameters and the performance in WEDM. 3. The objective of the invention is to find out important parameters affecting the performance of machining. 4. The objective of the invention is the optimal machining parameters are obtained under constraint and requirements.

SUMMARY OF THE INVENTION

Principal of WEDM- The Spark Theory on a wire EDM is basically the same as that of the vertical EDM process. In wire EDM, the conductive materials are machined with a series of electrical discharges (sparks) that are produced between an accurately positioned moving wire (the electrode) and the work piece. High frequency pulses of alternating or direct current is discharged from the wire to the work piece with a very small spark gap through an insulated dielectric fluid (water).

Many sparks can be observed at one time. This is because actual discharges can occur more than one hundred thousand times per second, with discharge sparks lasting in the range of 1/1,000,000 of a second or less. The volume of metal removed during this short period of spark discharge depends on the desired cutting speed and the surface finish required. The heat of each electrical spark, estimated at around 15,000 to 21,0000 Fahrenheit, erodes away a tiny bit of material that is vaporized and melted from the work piece. (Some of the wire material is also eroded away) These particles (chips) are flushed away from the cut with a stream of DE-ionized water through the top and bottom flushing nozzles. The water also prevents heat build-up in the work piece. Without this cooling, thermal expansion of the part would affect size and positional accuracy. Keep in mind that it is the ON and OFF time of the spark that is repeated over and over that removes material, not just the flow of electric current. Major Components of Wire Electric Discharge Machine are

(1) Computerized Numerical Control (CNC) Think of this as "The Brains." (2) Power Supply Provides energy to the spark. Think of this as "The Muscle." (3) Mechanical Section Worktable, work stand, taper unit, and wire drive mechanism. (This is the actual machine tool.) Think of this as "The Body." (4) Dielectric System The water reservoir where filtration, condition of the water (resistivity/conductivity) and temperature of the water is provided and maintained. Think of this as "The Nourishment." Computer Numerical Control (CNC)-Today's numerical control is produced with the needs of the operator in mind. Programs, machine coordinates, cutting speeds, graphics and relevant information is displayed on a color monitor, with easy to use menu's.The control unit displays menu's that are designed to give top priority to operability. Characters and commands are input using the keyboard. The system is very easy to use, allowing the operator to quickly become familiar with it, resulting in his/her learning curve being drastically reduced.

Besides executing NC data for positioning movement of the axes, the control amends these movements when using offsets, tapering, scaling, rotation, mirror images or axis exchange. The control also compensates for any pitch error compensation or backlash error in the axes drives, to ensure high accuracy positioning. The machine has multiple coordinate systems, and jobs can be programmed in absolute or incremental modes saving valuable programming time. For example, multiple jobs can be set-up on the worktable, while storing the separate reference points or locations of these jobs in specific coordinate registers.

One of the most important features that the control handles is offset. Programs are created and written for the center of the tool (wire) to follow the outline of the part. Let's say you are using a .010" diameter wire and it cuts a .012" slot with the power settings provided for the particular material. A .006" offset would be needed to put the part "on-size". Which side of the part (left or right) we apply the offset is determined by two factors; Are the part we are saving, the male (slug), or the female (opening)? & are we cutting the part in a clockwise or counterclockwise direction? Power Supply- When wire EDM machines were first introduced in the United States, they were equipped with power supplies that could achieve less than one square inch per hour. Today, most machines are rated to cut over twenty square inches per hour and faster. Faster or slower speeds are obtained depending on the work piece material, part thickness, and wire diameter, type of wire, nozzle position, flushing condition and required part accuracy.

Adaptive Control is yet another improvement where high speed circuitry has improved the spark gap sensitivity, reaction time of the servo motors, and changes to the power. With these improved capabilities, wire breakage is reduced to a minimum, making today's machines far more "forgiving" than in the past. Another feature is the anti-electrolysis circuitry that prevents the risk of electrolysis while cutting work pieces that are in the machine for extended periods. This AC circuit also eliminates the blue discoloration that appears when cutting titanium alloys with DC circuits and is a beneficial feature when cutting aluminum. Surface finishes on steel parts today are around sixty RMS for the roughing operations and surface finishes better than 0.5 p R max can achieved with multiple skim passes. In many cases, this eliminates or minimizes "benching", hand polishing, or lapping of parts that have fine finish requirements. Wire Path- When wire EDM was first introduced, copper wire was used on the machines because it conducted electricity the best. But as speeds increased, its limitations were soon discovered. The low tensile strength of copper wire made it subject to wire breaks when too much tension was applied. Poor flush ability was another problem, due to coppers high thermal conductivity. A good portion of the heat from the EDM spark was transferred to the wire and carried away from the work zone instead of using that heat to melt and vaporize the work piece. There is a vast array of wires to choose from with brass wire normally being used however, molybdenum, graphite, and thick and thin layered composite wires are available for different applications. Needs for various wires include: optimizing for maximum cutting speeds, (coated or layered wire) cutting large tapers, (soft brass) or cutting thick work pieces (high tensile strength with good flush ability).

Wire diameters range from .004" through .014" with .010" being the most commonly used. The wire originates from a supply spool, then passes through a tension device (different diameter wires require different amounts of tension to keep it straight). It then comes in contact with power feed contacts where the electric current is applied. The wire then passes through a set of precision, round diamond guides, and is then transported into a waste bin. The wire can only be used once, due to it being eroded from the EDM process. (The used brass wire is sold to the scrap dealer for recycling) Automatic Wire Threading (AWT)- The demand for automatic wire threading (AWT) and dependent reliability has been met with new and improved designs. This feature allows multiple openings to be cut in die blocks, progressive dies, production, and prototype work pieces automatically and unattended without the intervention of an operator, resulting in higher productivity. With the addition of the programmable "Z" axis, work pieces of different thickness, can also be machined. For example, the die openings and dowel pin holes can be machined on a one inch thick die block, then the machine can be programmed to move to another location and machine the punches on a two or three inch thick work piece.

Cutting and threading of the wire are controlled by codes in the program. If there is a wire break during machining, the machine returns to the start point of that opening, re-threads the wire and move through the program path to the position where it broke, powers up, and continues cutting as if the wire had never broken. Some EDM's can also re-thread the wire through the slot. The threading process of the automatic wire threaded takes place automatically if there is a broken wire or by a command in the program. In a wire break situation, the end of the wire is clamped while the supply wire is drawn back, Annealing and separating the wire, while leaving a sharp point on the end of the supply wire. The wire tip segment that was clamped is disposed of in a wire tip disposal unit. The supply wire is then directed into the lower guide. The wire then proceeds to the back of the machine where it is discarded in a scrap wire bin.AWT offers the ability to cut multiple openings in a work piece without operator intervention. Parts with multiple openings or even several jobs are cut overnight while many jobs can be cut over the weekend without operator intervention. Dielectric System- Wire EDM uses de ionized water as the dielectric compared to Vertical EDM's that use oil. The dielectric system includes the water reservoir, filtration system, deionization system, and water chiller unit. During cutting, the dirty water is drained into the unfiltered side of the dielectric reservoir where the water is then pumped and filtered through a paper filter, and returned to the clean side of the dielectric tank. Following filtration, the clean water is measured for conductivity, and if required passes through a vessel that contains a mixed bed of anion and action beads. This mixed bed resin (the ion exchange unit) controls the resistivity of the water to set values automatically.

The clean water fills the clean side of the dielectric reservoir and proceeds to the cutting area. Used water is drained and returned to the unfiltered side of the dielectric reservoir to complete the cycle. A water chiller is provided as standard equipment to keep the dielectric, work piece, worktable, control arms, and fixtures thermally stable.

During the cutting process the chips from the material that is being eroded, gradually changes the water conductivity level. Resistivity levels of the water are set according to the cutting requirements of the work piece material being machined.

Advancements in Taper Cutting- Most Wire EDM's are equipped with a programmable "Z" axis giving precise control of the upper guide assembly to ensure accurate tapers. The rigid U and V axis is positioned away from the work area to avoid moisture, contamination and deflection from the high pressure flush. These axes provide movement to the top portion of the wire to produce taper angles of up to +/- 30 degrees. Both conical and oblique cylindrical radii can be programmed, and the size of the top and bottom radii of the part can also be programmed. Tapering values can be changed within the program. This is useful for mold applications or form tools that have different side and frontal taper relief angles. Die blocks are normally machined first with their taper relief, then straight cut for their die land.

The machine control knows where the upper and lower guide are in relation to the work table. The amount of taper angle and direction the wire is tilted in relation to the program path is in the program. The operator only needs to input where the taper should intercept the work piece in relation to the work table surface. For small production runs, parts are made by cutting laminated stacks of material, this is also great for cutting prototype parts. Independent programming of the U & V axes is for work pieces that have a different shape on the top and bottom. The independent, simultaneous movement of all four axes (X, Y, U, V) makes machining extrusion dies, airfoil shapes, and "squirrels" (a square shape on the top, and a circle on bottom of the work piece) quite easy.

Introduction to Taguchi Method- Process optimization is the discipline of adjusting a process to optimize some specified set of parameters without violating some constraint. The most common goals are minimizing cost and maximizing efficiency. This is one of the major quantitative tools in industrial decision-making. When optimizing a process, the goal is to maximize one or more of the process specifications, while keeping all others within their constraints. Many methodologies have been developed for process optimization such as Taguchi method, six sigma, lean manufacturing and others.

Taguchi method is a statistical methods developed by Mr. Genichi Taguchi. He revolutionized the manufacturing process in Japan through improving the quality of manufactured good sat minimum cost. Taguchi as an engineer understood that all manufacturing processes are affected by outside influences called as noise. However, Taguchi realized methods of identifying those noise sources, which have the greatest effects on product variability. His ideas have been adopted by the manufacturers around the globe which results in creating superior production at much lower costs. Taguchi's techniques have been used widely in engineering design (Ross 1996 and Phadke 1989). The Taguchi method contains system design, parameter design, and tolerance design for the best product quality. The main trust of Taguchi's techniques is the use of parameter design, which is an engineering method for product or process design that focuses on determining the parameter settings producing the best levels of a quality characteristic with minimum variation. Taguchi designs provide a powerful and efficient method for designing processes that operate consistently and optimally over a variety of conditions. To determine the best design, it requires the use of a strategically designed experiment, which exposes the process to various levels of design parameters. Taguchi's Rule for Manufacturing- Taguchi realized that the best opportunity to eliminate variation is during the design of a product and its manufacturing process. Consequently, he developed a strategy for quality engineering that can be used in both contexts. The process has three stages:

System design is a design at the conceptual level, involving creativity and innovation. In Parameter design the concept is established, the nominal values of the various dimensions and design parameters need to be set, the detail design phase of conventional engineering. This is sometimes called robustification. Tolerance design with a successfully completed parameter design and an understanding of the effect that the various parameters have on performance, resources can be focused on reducing and controlling variation in the critical few dimensions. Basically Eight Steps in Taguchi Methodology

Step-1: Identify the main function, side effects, and failure mode Step-2: Identify the noise factors, testing conditions, and quality characteristics Step-3: Identify the objective function to be optimized Step-4: Identify the control factors and their levels Step-5: Select the orthogonal array matrix experiment Step-6: Conduct the matrix experiment Step-7: Analyze the data predict the optimum levels and performance Step-8: Perform the verification experiment and plan the future action 1.6.3 Orthogonal Array& array Selector

BRIEF DESCRIPTION OF THE DIAGRAM

1. Principle of Wire EDM 2. Product/ Process System 3. Diag. Of Stainless Steel (SS-304) 4. Wire Electric Discharge Machining 5. Working Diagram of Wire Electric Discharge Machine 6. Effect of shielding gas on weld geometry 7. Inclination fixture made for welding 8. Welding specimen by GMAW process

DESCRIPTION OF THE INVENTION

Material Selection and Its Properties- To perform this experiment material selected is Stainless Steel SS-304. Chemical composition of this stainless steel is given in table 3.1. Physical properties of this alloy are as follows: Density is 8.03 g/cm3, Poisson's ratio is 0.275, Elastic modulus is 193 GPa, tensile strength is 621 MPa, yield strength is 290 MPa and thermal conductivity is 100 C. The selected Stainless Steel SS-304 is available in the form of flat rectangular bar of cross sectional area 63mm X 6mm and length of 610mm is purchased from local market.

Wire EDM Machine- The system consists of a CNC control, power supply with anti electrolysis circuitry, automatic wire threading, and held pendant, programmable Z-axis, water chiller and filtration system.

Experimental Methodology: STEER CORPORATION DK7712 NC WEDM machine was used to perform the experiments. Molybdenum wire with 0.18mm diameter was used in the experiment. The work piece material ,SS-304 hot die steel with 100mmx100mmx5mm was used. During the experiment external gear having diameter of 10 mm was cut. Molybdenum wire with 0.18 diameters was used in the experiment.

Experimental Setup for Testing- In this set up main focus is on testing Gear manufacturing of stainless steel (SS-304). In our project Surface roughness testing machine that was prepared after gear manufacturing is visually inspected for any kind of defect and its mechanical property i.e. Surface roughness is also verified.

WIRE EDM- Machine-Wire EDM's are manufactured in various sizes and styles of flush or submerged type machines to fit the needs of the consumer. Large scale EDM's can handle work pieces weighing over ten thousand pounds and can cut over twenty inches thick. Automatic Wire Threaders (AWT) is usually standard equipment on most models. In addition to the X-Y table travels, wire EDM's have U / V travels for providing the movement to cut tapers. Most machines can cut tapers of 20-30 degrees depending on work piece thickness.

Testing specimen-The specimen is made of stainless steel ss-304 plate. The gear manufacturing was obtained by machining of stainless steel SS-304 with the help of wire EDM machine and molybdenum wire use as a tool. The gear is inspected by surface roughness tester machine and stereo zoom microscope, for measuring Ra (surface roughness) and gear profile. Figure 3.6 shows the specimen

ANALYTICAL PROCEDURE

Design of experiments- It is based on Taguchi's concept which have been in developed into an engineering method of quality improvement referred to as quality engineering in Japan and as robust design in the west, which is discipline engineering process that seeks to find best trade off a product design. Concepts technique used in robust design Taguchi's concept such as "quality", S/N Ratio, Orthogonal arrays Degree of freedom and analysis of variance

" may be synthesis in engineering studies. The quality lose function is considered as an innovative means for determining the economic advantage of improving system safety or operational safety .orthogonal arrays are used to study many parameters simultaneously with a minimum of time and resources to produce an overall pictures for more detailed safety based design an operational decision making. The Signal to noise ratio is employed to measure quality.

Orthogonal arrays- Taguchi's has developed a system of tabulated designs (arrays) that allow for the maximum number of main effects to be estimated in an unbiased (orthogonal) manner, with a minimum number of runs in the experiment. Orthogonal arrays [6] are used to systematically vary and test the different levels of each of the control factors. Commonly used Oas includes the L4, L9, L12, L18, and L27. The columns in the OA indicate the factor and its corresponding levels, and each row in the OA constitutes an experimental run which is performed at the given factor settings. Typically either 2 or 3 levels are chosen for each factor. Selecting the number of levels and quantities properly constitutes the bulk of the effort in planning robust design experiments.

Signal to noise ratio and ANOVA approach- The S/N ratio developed by Dr. Taguchi [6] is a performance measure to choose control levels that best cope with noise. The S/N ratio takes both the mean and the variability into account. In its simplest form, the S/N ratio is the ratio of the mean (signal) to the standard deviation (noise). The S/N equation depends on the criterion for the quality characteristic to be optimized. While there are many different possible S/N ratios, three of them are considered standard and are generally applicable in the situations such as Biggest-is best quality characteristic (strength, yield), Smallest-is-best quality characteristic (contamination), and Nominal-is-best quality characteristic (dimension).

In addition to the Signal to Noise Ratio (S/N ratio), the obtained results have been tested using statistical Analysis of Variance (ANOVA) with Pareto chart to indicate the impact of process parameters on surface roughness. The reason of combining Pareto chart with Analysis of Variance was to detect causes applying the principle that 80 percent of the problems usually stem from 20 percent of the causes. Pareto ANOVA technique of analysis has been used in this experimentation to analyze data for process optimization in past research also. Pareto ANOVA is a simplified ANOVA method, which uses Pareto principle. It is a quick and easy method to analyze result of parameters design. It does not require an ANOVA table and therefore, does not use F-test. The calculations of these tables are done by the use of standard orthogonal arrays. The preferred parameter settings are then determined through analysis of the "signal-to-noise" (SN) ratio where factor levels that maximize the appropriate SN ratio are optimal. There are three standard types of SN ratios depending on the desired performance response. Smaller the better (for making the system response as small as possible)

SNs = 101g

Nominal the best (for reducing variability around a target):

SN r = tog

SNL = -10 log =1 V

Larger the better (for making the system response as large as possible):

These SN ratios are derived from the quadratic loss function and are expressed in a decibel scale. Once all of the SN ratios have been computed for each run of an experiment, Taguchi advocates a graphical approach to analyze the data. In the graphical approach, the SN ratios are plotted for each factor against each of its levels. Finally, confirmation tests should be run at the "optimal" product settings to verify that the predicted performance is actually realized. 2. 5 Steps applied in Taguchi methods Taguchi proposed a standard procedure for applying his method for optimizing any process. The steps suggested by Taguchi-

Determine the quality characteristic to be optimized: The first step in the Taguchi method is to determine the quality characteristic to be optimized. The quality characteristic is a parameter whose variation has a critical effect on product quality. Identify the noise factors and test conditions: The next step is to identify the noise factors that can have a negative impact on system performance and quality. Identify the control parameters and their alternative levels: The third step is to identify the control parameters thought to have significant effects n the quality characteristic. Control (test) parameters are those design factors that can be set and maintained. The levels (test values) for each test parameter must be chosen at this point. Design the matrix experiment and define the data analysis procedure: The next step is to design the matrix experiment and define the data analysis procedure. First, the appropriate orthogonal arrays for the noise and control parameters to fit a specific study are selected. Conduct the matrix experiment: The next step is to conduct the matrix experiment and record the results. Analyze the data and determine the optimum levels for control factors: After the experiments have been conducted, the optimal test parameter configuration within the experiment design must be determined. To analyze the results, the Taguchi method uses a statistical Journal of Engineering Research and Studies E-ISSN976-7916 JERS/Vol.III/ Issue I/January-March, 2012/70-74 measure of performance called signal to noise (S/N) ratio. Predict the performance at these levels: The final step is an experimental confirmation run using the predicted optimum levels for the control parameters being studied.

WE CLAIMS

1. Our Invention is Discharge pulse can be classified into four pulse types by combination of some of the time periods and gap voltage characteristics .The proportion of short circuit and sparking frequency can be used to monitor and evaluation of the gap condition. 2. Our Invention is if we set the long pulse interval and high table feed, it causes the gap to become smaller which results an increase in short ratio. 3. Our Invention is the increase of work piece thickness equivalent to surface roughness result in the formation of much debris in the spark gap leading to the increase of short ratio. 4. Our Invention is a pulse interval control strategy has been proposed according to the classification of discharge pulse to improve the abnormal machining conditions.

5. Our Invention is in order to assess influence of various factors means and signal to noise ratio

for each control factor are to be calculated. Levels of input parameters (i.e. pulse on time, pulse off time and current) are selected as per orthogonal array selector and results of surface roughness test specimen for each trial. The analysis of variance (ANOVA) was conducted to study the significance of machining parameters on surface roughness based on their P-value and F-value at 5% level of significance. 6. Our Invention is an experimental study in which wire EDM operations are performed on material SS-304 Steel plate. The effect of three machining parameters namely pulse on time

,pulse off time and current are investigated. Trial run was conducted to establish the range of selected parameters. Subsequently pulse on time at three level , pulse off time at three levels and current at three levels are considered and 9 experiments as per the experimental plan of Taguchi's experimental design i.e. L9 OA are conducted. Five response variable namely Surface roughness, addendum circle, root circle, angle between top land and tooth face, and angle between bottom land and flank are measured. Signal to noise ratio for each response variables are computed. Subsequently, analysis of variance is used to obtain the percentage contribution of the parameters. The analysis of mean is performed to obtain optimum level of the machining parameters for multi performance characteristics. Analysis of variance is used to determine which machining parameters is significantly affected the multi performance characteristics and also to obtain the percentage contribution of each machining parameters towards the objective.

The results of the present study the following conclusion are drawn: (a) The optimum combination of machining parameters and their level in surface roughness areA3,B3,C1 (b) The optimum combination of machining parameters and their levels for decreasing the deviation in addendum circle are A3, B2, C2 (c )The optimum combination of machining parameters and their levels for decreasing the deviation in root circle are A2, BI, C2 (d) The optimum combination of machining parameter for angle between top land and tooth face are A2,B1,C3. (e ) The optimum combination of machining parameter for angle between top land and tooth face are A2,B3,C1. (f) Pulse on time, pulse off time ,and current are significantly affect the surface roughness, addendum circle, root circle, angle between top land and tooth face, angle between bottom land and flank. (g) The percentage contribution of surface roughness are current (41.95%), pulse off time (29.12%), pulse on time (27.36%). (h) Pulse on time is least significant factor for surface roughness. (i) The percentage contribution of addendum circle are current (33.82%), pulse on time (33.25%), pulse off time (32.69%). (j) Pulse off time is least significant factor for addendum circle. (k) The percentage contribution of root circle are pulse off time (59.55%),pulse on time (26.31%), current(13.33%). Current is least significant factor for root circle. (1) The percentage contribution of angle between top land and tooth face are current (41.23%), pulse off time (38.21%), pulse on time (32.56%). (m) Pulse on time is least significant factor for angle between top land and tooth face. (n)The percentage contribution of angle between bottom land and flank are current (38.31%), pulse on time (26.43%), pulse off time (23.64%). (o)Pulse off time is least significant factor for angle between bottom land and flank.

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Fig. 1.1Principle of WEDM

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Table 1.2 Array Selectors

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Figure 3.1 Stainless Steel SS-304 flat

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Fig3.2: Wire EDM Machine

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Figure 3.3 Wire EDM Machine

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Fig. 4.1.1: Main effect plot

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Fig4.1.2: Normal probability plot of the residuals.

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Graph 4.2.1: Mean Effect Plot for S/N Ratio

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Graph 4.2.2: Normal probability plot of the residuals

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Graph 4.3.1 Effect Plot for S/N Ratio

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Fig4.3.2: Normal probability plot of the residuals

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Graph 4.4.1: Main effect plot for S/N ratio

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Graph 4.4.2. Normal probability plot of the residuals

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Graph 4.6.1: Main effects plot for S/N ratio

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Graph 4.6.2: Normal probability plot of the residuals.