Blog- Near-Dry EDM
NEAR DRY EDM
Group members:
BHOSALE DNYANESHWAR SUBHASH - 14
GHOLAP OMKAR BABASAHEB - 25
MANDLIK RUSHIKESH ANNASAHEB - 42
KHAIRNAR JAYESH LOTAN - 39
WAGHMODE KIRAN MITTHU - 73
Introduction
The electric discharge machining treatment is widely used for the production of complex profiles, electrically conductive material, high temperature resistance and high strength. Due to its wide application in industry, and so on, it has become the most popular process setting for conventional machining processes such as turning, milling, drilling, etc. Despite its many advantages, so the process tolerates a number of limitations, such as low material removal rate (MRR) and has a high consumption rate (TWR), as well as weak surface integrity, and in some cases. In the past, several attempts have been made to overcome these limitations associated with the growth of techniques, such as rotating the electrode by ultrasonic vibration and suspending powder in a dielectric liquid. Although these methods have a great research perspective, in practice they are used only for small applications. Further restrictions in EDM process may be related to environmental pollution and labeling. During the process material removal must have a consistent set of thermal energy generated by a series of discrete electrical sparks created between the tool and the operation of electrodes that are immersed in a dielectric medium, typically hydrocarbon oils. Oils and serious toxic fumes can cause injury to the operator's health and the environment. To overcome the limitations of the EDM process, dry and almost dry varieties were introduced, and SO on. - Dry EDM process, the use of pressurized natural gas, such as a dielectric, it is necessary that the almost dry EDM process uses a combination of liquid and gas (two-phase) as a dielectric medium, and is environmentally friendly. In this section, you will find information about these two models, environmental (i.e. Dry and Almost Dry EDM).) The EDM process is combined with the development of research in this area.
Electric Discharge Machining (EDM)
Amongst the un-conventional machining processes, EDM is the most popular un-conventional machining process because it is capable to machine any electrically conductive material irrespective of its hardness and toughness; and can cut complex geometries, shapes and features efficiently. It is also called as spark erosion machining. It has a wide area of application in different fields like mold and die manufacturing, aerospace and automotive industries, electronics and medical instruments, etc. With increase in demand of products made from hard metals and alloys especially difficult-to-machine materials, more interest has gravitated towards the EDM process.
Classification of EDM
flow diagram of classification of electric discharge machining processes. There are several categories of EDM processes according to the type of dielectric medium used. These variants are conventional EDM, powder mixed electric discharge machine (PMEDM), dry EDM and near-dry EDM. Wire EDM, micro EDM and rotary EDM are tool based EDM process variants. Whereas, magnetic-field assisted EDM (MFAEDM) is workpiece based EDM process. Furthermore, the ultrasonic assisted EDM comes under both categories (tool or workpiece).
Dry and near Dry EDM
Dry and near dry EDM processes must be resistant to process changes and SO on. These processes are classified based on the use of a dielectric medium. It is carried out using gas as a dielectric medium, which is usually called dry, and so on. A high-speed gas flow is provided through a tubular electrode, which is the molten material of the object you want to remove, and remove. At that time, the higher the gas velocity for the plasma formed from the last spark, and the lower the temperature in the treatment zone. First of all, the National Aeronautics and Space Administration (NASA) has shown the possibility of using an inert gas, such as a dielectric medium . Then investigated the possibility of using in mixtures of various gases, such as a dielectric medium. So in this version of the process, and so on, they called it dry, and SO on. It is used for high F and low gas rate dielectric liquids like oxygen, nitrogen, hydrogen, and compressed air through a tubular electrode between the interelectrode gap. It is usually used to solve environmental protection problems, which leads to increased processing performance. It was measured six times higher than that of the usual, with the same set of resistor conditions .
Process parameters
In process parameters on dry and near-dry EDM, belong to one of four categories, which are as follows
- Electrical parameters
- Non-electrical parameters
- Tool electrode based parameters
- Near-dry based (dielectric) parameters.
Principles :
In dry EDM, tool electrode is formed to be thin walled pipe. A high velocity gas jet from a pipe tool electrode reacts with the work piece material under high temperature caused by arc discharge and enhances the evaporation and melting of the work piece at the discharge spot.
Dielectric Mediums in Dry and Near-Dry EDM
Generally, dry-EDM utilizes compressed air as a dielectric medium. It was found that the MRR is increased due to the enlarged volume of discharged crater and more frequent occurrence of discharges when using oxygen. In near-dry EDM, mixture of liquid and gas used as dielectric medium. mixed different gases such as helium, oxygen and nitrogen with water. It was found that mixture of oxygen-water provided highest MRR and surface roughness as well. Further, The MRR produced by glycerin-air dielectric medium was approximately three times higher than the EDM oil-air and water-air combinations at best parametric settings (current 15 A, duty factor 0.80, flushing pressure 80 psi). generates high thermal energy and gaseous pressure in IEG when it decomposes with discharge. It is apparent that glycerin generates concentrated explosion at IEG, thus increasing material removal. However, glycerin-air dielectric medium produced slightly higher TWR than other dielectric mediums but it was approximately negligible because wear ratio (ratio of TWR and MRR in percentage) of the process was less than one percent. Furthermore, it was observed that recast layer produced by EDM oil-air and water-air were 0.52m and 0.40m, respectively, while combination of glycerin-air did not produce any measurable recast layer .
Comparison of Dry, Near-Dry and Conventional EDM
This section highlights the advantages of dry and near-dry EDM over conventional EDM in terms of various machinability.
Productivity: The MRR of near-dry EDM was nearly 50–60% higher than conventional EDM. In conventional EDM, carbon particles and other debris particles are generated during spark erosion . Further, due to inefficient flushing they do not flush away from the IEG effectively. Subsequently, they disturb the erosion process resulting in ineffective sparks which results in low MRR. In near-dry EDM high pressure dielectric medium provides better flushing than conventional EDM. This reduces debris accumulation problem at IEG resulting in higher MRR. Several investigations have been conducted where it was found that near-dry EDM achieves higher MRR as compared to conventional EDM. the MRR of near-dry EDM was marginally higher than dry EDM. It can be attributed to the fact that two phase (liquid and air) dielectric medium eliminates debris reattachment problem. Consequently, lower down chances of possible short circuiting. This phenomenon improves MRR in near-dry EDM. It was also interestingly observed that, conventional EDM produced very high TWR at higher values of current than near-dry and dry EDM process.
Environmental aspects: These processes are green because there is no generation of hazardous gases/fumes; and no waste is produced from the dielectric liquid. There is no risk of fire hazards because no flammable dielectric is used.
Efficiency: Highly efficient due to high MRR and fine surface finish. Further, TWR in dry and near-dry EDM processes is negligible.
Space requirements: These processes do not require large floor space because they do not need a huge dielectric circulation unit.
Machining Time and Cost:
As die sinking EDM requires the use and subsequently production of tool electrodes, machining time is longer and costs higher than cutting methods such as milling by machining centre. Cost of EDM with oil is more because of cost of oil and greater electrode wear.
Advantages : Some of the advantages of EDM include machining of:
• 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.
Disadvantages : Some of the disadvantages of EDM include:
• The slow rate of material removal.
• For economic production, the surface finish specified should not be too fine.
• The additional time and cost used for creating electrodes for ram/sinker EDM.
• Reproducing sharp corners on the workpiece is difficult due to electrode wear.
• Specific power consumption is very high.
• Power consumption is high.
• Drilling of micro-holes, thread cutting, helical profile milling, rotary forming, and curved hole drilling.
• Delicate work piece like copper parts can be produced by EDM.
• Can be applied to all electrically conducting metals and alloys irrespective of their melting points, hardness, toughness, or brittleness.
• Other applications: deep, small- dia. holes using tungsten wire as tool, narrow slots, cooling holes in super alloy turbine blades, and various intricate shapes.
• EDM can be
economically employed for extremely hardened work piece.
FUTURE SCOPE :
Very less work has been reported on MRR improvement. Also on
material like water hardened die steel, molybdenum high speed steel have non
tried as a work materials in near-dry EDM and powder mixed EDM. The same may be
tried in future works.
Conclusion
In essence, dry and near-dry EDM are the environmentally friendly variants of EDM. These processes are capable to generate high surface integrity and to achieve high productivity along with minimum hazard, wastages and pollution, and thus attain overall sustainability which makes them the sustainable substitutes to the conventional EDM.
References
1. Jain VK (2002) Advanced machining processes. Allied Publishers Pvt. Ltd., New Delhi, pp 126–159
2. Davim JP (2013) Nontraditional machining processes. Research Advances Springer. doi:10. 1007/978-1-4471-5179-1
3. Schumacher BM (2004) After 60 years of EDM the discharge process remains still disputed. J Mater Process Technol 149(1–3):376–381
4. Puertas I, Luis CJ (2003) A study on the machining parameters optimization of electrical discharge machining. J Mater Process Technol 143–144:521–526
5. El-Hofy H, Youssef H (2009) Environmental hazards of nontraditional machining. In: Proceedings of the 4th IASME/WSEAS international conference on energy & environment (EE’09), pp 140–145
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