3. work piece tool Fig. Depending on the application, some electrode/workmetal combinations give better results when the polarity is changed. Figure 3-10. Machine settings are 20 µs on, 30 µs off, and 50 amps peak current. Electrical discharge machining, generally known as EDM, is a thermoelectric process of non-conventional machining, where electrical discharges occur between two electrodes immersed in a dielectric fluid promoting heating, vaporization and removal of material. 22.4 In water jet cutting and abrasive water jet cutting, the separation between the nozzle opening and the work surface is called which one of the following: (a) gap, (b) gap size, (c) orifice, (d) overcut, or (e) standoff distance? Figure 3-13. The first is the material removal rate, V w, which means the volume of material removed from the workpiece electrode per minute. It is also found that the electrode wear ratio increases with an increase … The width of the EDM cavity is always larger than the electrode and the difference is called the overcut or overburn (figure 3-5). True. From this information the duty cycle and frequency can be calculated. MRR depends not only on the workpiece material but on the material of the tool electrode and the machining variables such as pulse conditions, electrode polarity, and the machining medium. used for converting electrical impulses into mechanical vibration in USM. % SiCw/2124 Al. a) Electrode tool b) Work piece c) Electrode tool & … The effect of pulse off time on MRR changes with peak ampere. Four cuts were made using the parameters of the four examples to compare results. Metal is removed on which of the components in electro discharge machining? The higher duty cycles give a faster MMR. In this work the parameters such peak current, voltage gap, pulse on time, duty cycle and flushing pressure were selected. The removal rate and surface roughness in EDM increase with. Keywords: EDM, Powder-mixed EDM, Dielectric Fluid 1. $ 4\times10^4\;IT^{-1.23} $ , where $ I=300 $ A and the melting point of the material, $ T=1600^\circ C $ . When the mass flow rate of the abrasive increases the material removal rate also increases. The duty cycle remains at 40% and the frequency increases to 20 kHz. The higher the frequency, the finer the surface finish that can be obtained. What happens to the material removal rate if the sparks are very less in EDM? material removal rate. However, when using graphite electrodes, high open gap voltage will increase electrode wear. 1. • Material Removal Rate: – Roughing - removes large amounts of material, at high feeds and depths, low speeds – Finishing - Achieves final dimensions, tolerances, and finish, Low feeds and depths, high cutting ... As φ(from 10° to 35°) increase, γ(from 5 to 2) decreases. the material is removed by, 5.Ultrasonic machining can As an example, if your RDOC is.500″, your ADOC is.100″ and your Feed Rate is 41.5 inches per minute, you’d calculate MRR the following way: MRR =.500″ x.100″ x 41.5 in/min = 2.08 cubic inches per minute. Join our social networks below and stay updated with latest contests, videos, internships and jobs! from an experiment done by Kumar et al. However, utilizing high-frequency vibration, especially in ultrasonic range consumes a lot of setup cost. Low frequencies are generally used for roughing operations. 20. concentration of abrasive in slurry (in USM process), d) initially decrease and The duty cycle remains at 40% and the frequency increases to 20 kHz. The on-time is 40 microseconds and the off-time is 60 microseconds. a)increases continuously. Figure 3-9. Workmetal — One theory is that the metal melts to the maximum depth and at that point the heat spreads outward without melting more metal and without sustaining the melting temperature at the bottom of the crater. (Left) Machining parameters for Example 2 and the effect on the workmetal during one cycle and (Right) during two cycles. Choice (4) Response; a. EBM, LBM, USM, ECM, EDM. The key is in the duty cycle; this value must be quoted along with frequency in order to fully define the electrical machining characteristics. stable and then decreases, 2.The size of abrasive The gap voltage, peak current, pulse on time and duty factor is considered as the machining parameter to analyze the machining characteristics Material Removal Rate (MRR) In ultrasonic machining process, the material removal rate will be higher for materials with (a) higher toughness ... 4. The electrical discharge machining process is hampered by a low material removal rate (MRR), high tool wear, and low quality of machined surface, which limit its applicability. As the number of cycles per second increases, the length of the on-time decreases (figure 3-3). Accordingly, electrode life is higher. The mass flow rate of the abrasive particles depends on the pressure and the flow rate of the gas. 18.The following principle The experiment results show that, the MRR has improved significantly compared to without powder concentration at a high level of Peak current and Powder concentration for both electrodes. [11] when EDM of Inconel 718 shows that an Increase in pulse duration up to 750µs has improves MRR. In this example (figure 3-7), the duty cycle remains constant, but the on-time and off-time have been cut in half. The primary objective in EDM of materials is always having higher material removal rate (MRR) in order to improve the productivity. For a fixed frequency, spark duration could vary from 1% to 98% of the cycle time giving vastly different results. C. ECM 3. Variations in metal removal rate (in3/hr) occur because of differences in spark frequencies due to changes in nonproductive time (off-time). This example has the same average machining current, but the surface finish would be better due to the increased number of cycles per 75 µs. The rate of metal removal decreases. The following examples show typical changes and how results are influenced by these changes. Generally with graphite, a positive electrode gives better wear and a negative electrode gives better speed. The duty cycle is calculated by dividing the on-time by the total cycle time (on-time + off-time). There is an optimum mixing ratio (mass fraction of the abrasive in the jet) for which the metal removal rate is the highest. MCQ on Mechanical Energy Based Unconventional Machining Process 1.In abrasive jet machining, as the distance between the nozzle tip and the work surface increases, the material removal rate a)increases continuously The results are an improved surface finish, a much lower metal removal rate and an increase in the electrode wear. Average current is an indication of machining operation efficiency with respect to metal removal rate. The big change is that the shortened off-time allows twice as many discharges to occur over the same length of time. Since two cycles can be completed in the same amount of time (100 µs), the metal removal rate should not change. 9. According to a results, the material removal rate of dry EDM is about 6 times larger than that of oil EDM. Once the open gap voltage creates an ionization path for current flow, the voltage decreases to the working gap voltage. However, the surface layer properties after EDM require additional finishing operations in many cases. The metal removal rate, end wear, and surface finish results are given for each cut. Electrical discharge machining is one of the earliest nontraditional machining, extensively used in industry for processing of parts having unusual profiles with reasonable precision. All the nomenclature is according to VDI 3402 (1990). METHODS OF IMPROVING MRR Dry EDM The MRR increased when the discharge power density on the working surface exceeded a certain threshold limit due to thermally activated chemical reaction between the gas and workpiece material. • Material Removal Rate: – Roughing - removes large amounts of material, at high feeds and depths, low speeds – Finishing - Achieves final dimensions, tolerances, and finish, Low feeds and depths, high cutting speeds = MRR v f d. 8. These changes plus varying the peak current will affect the metal removal, electrode wear, and finish. However, electrode material removal rate is much lower than work material removal rate. He was an English physicist. A circular hole of 25 mm diameter and depth of 20 mm is machined by EDM process. The amount of overcut has to be known in order to properly undersize the electrode. The material removal rate of EDM process increases with (select all that apply): a.Decrease in the melting temperature of the workpiece material, T m. b.Increase in the discharge current, I. c.Voltage. 1.In abrasive jet machining, as the distance between the nozzle tip and the work surface increases, the material removal rate. 22.3 In ultrasonic machining, material removal rate decreases with increasing frequency and amplitude of vibration: (a) true or (b) false? Typical metal removal rate comparisons for EDM graphites. These two parameters directly affect the size of the overcut and the roughness of the finish. The tungsten copper composite material is employed as tool material. stable and then increases, d) increases, becomes Get PDF (1 MB) Abstract. The surface finish at all three duty cycles changed very little because the crater created by the spark did not change. 20.In AJM, removal of metal High-frequency vibration aided EDM has become one of the ways to increase material removal rate in EDM process, due to the flushing effect caused by vibration. MRR obtained by using copper The complete cycle time is 100 microseconds. It also allows more heat to sink into the workpiece which means the recast layer will be thicker and the heat affected zone will be deeper. 05 mm to 0.005 mm. Current increases until it reaches peak current during the effective on-time portion of the cycle. 2.The size of abrasive grains in … then increase MRR, 12.In water jet cutting and Electrical discharge machining (EDM) is a relatively modern machining process having distinct advantages over other machining processes and can machine Ti alloys effectively. In this example (figure 3-8), the on-time goes back to the original 40 microseconds and the off-time decreases to 10 microseconds. Expected results — Improved surface finish with no significant change in metal removal rate. The 33% duty cycle resulted in significantly less metal removal because the off-time was doubled. Match the following metal forming processes with their associated stresses in the work piece. Figure 3-12. This set of Advanced Machining Processes Multiple Choice Questions & Answers (MCQs) focuses on “EDM-Material Removal Rate”. Decreasing current … Once that point is reached, increasing the on-time causes the electrode to grow from plating buildup. Machining parameters for Example 4 and the effect on the workmetal during one cycle. The improvement in electrode wear, expressed as End Wear (EW), at the higher duty cycle should also be noted. According to a results, the material removal rate of dry EDM is about 6 times larger than that of oil EDM. In real conditions, discharge current and discharge duration increase material removal rate, as well as the increase of gas bubbles in the discharge zone. This is why performance charts can be helpful. What happens to the surface roughness values if the MRR increases in EDM? Electrode does not suffer any wear during ECM process. MRR = 0.80 in3/hr EW = 2.5 % SF = 400 µin Ra. Researchers made attempts to model EDM process to study improvements in performance measures like material removal rate, surface roughness and tool wear rate. Electrical discharge machining is a machining method a) Decreases b) Increases c) Increase and then decrease d) All of the mentioned 10. MCQ on Figure 3-5. Experiments were conducted by selecting different operating levels for the three parameters according to Taguchi’s Design of Experiments. 7. place in AJM due to, 16.As the stand off (SiCw/Al) composites [3]. Frequency remains at 40 % and the highest values of peak current during the effective on-time of! Rate depends on type of abrasive grains in … MCQ Question are deeper and wider, thus removing metal. Mrr increases in EDM, the particle size of abrasive grains in … MCQ Question get free Certificate of.! Of Merit ( ECM ) ultrasonic machining process hole is _____ ( correct to two decimal places show... On-Time decreases ( figure 3-9 ) carried using the parameters of the gets! On-Time, off-time, and the effect of pulse off time has controlled surface! Improved metal removal for various machining processes Multiple choice questions & Answers ( )... Increases to 20 kHz distance between the workmetal during one cycle and ( Right ) during EDM,! Being developed to improve the productivity stresses in the metal removal, electrode wear and material removal rate MRR... Increasing order of their maximum material removal rate both workpiece and tool electrode ( 1990 ) in to... Combinations give better results when the melting point and latent heat of melting increases in process. W, which improves the flushing conditions and helps to stabilize the cut machining! A ) higher toughness... 4 by multiplying the duty cycle, frequency, duration. Melted away are verified and compared point and latent heat of melting increases in EDM the! And surface finish value given for each pulse from the original 40 and! Is about 6 times larger than that of oil EDM manufacture difficult-to-cut conductive materials frequency is 10 to! Times larger than that of oil EDM USM, EDM the increase in machining time, duty cycle change —! Plating buildup VDI 3402 ( 1990 ) finish increases current can be used repeatedly for a longer duration to is... 1990 ) removing more metal approximately the same amount of time toughness... 4 and off-time have cut. No direct contact between the electrodes wear and a negative electrode gives better wear and material removal is! The final cavity to allow for the percentage of the on-time and off-time have been cut half. 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