These changes plus varying the peak current will affect the metal removal, electrode wear, and finish. MRR = 0.70 in3/hr EW = 6.3 % SF =300 µin Ra. However, speed is not usually the only consideration when cutting cavities. The metal removal rate, end wear, and surface finish results are given for each cut. He was an English physicist. a) Electrode tool b) Work piece c) Electrode tool & … It is also found that the electrode wear ratio increases with an increase … Electrode — A long on-time can put the electrode into a no-wear situation. The higher duty cycles give a faster MMR. Average current is an indication of machining operation efficiency with respect to metal removal rate. The optimization was performed in two steps using one factor at a time for preliminary evaluation and a Box-Behnken design involving three var… applications wherein increased importance is placed on the graphite electrode material utilized. This paper reviews the research trends in EDM process by using water and powder mixed dielectric as dielectric fluid. MRR = 0.28 in3/hr EW = 2.5 % SF = 350 µin Ra. The rate of metal removal remains the same. The on-time is 40 microseconds and the off-time is 60 microseconds. 7.Abrasives contained in a All work (metal removal) is done during on-time. The big change is that the shortened off-time allows twice as many discharges to occur over the same length of time. Accordingly, electrode life is higher. used for converting electrical impulses into mechanical vibration in USM. In this study, experiments were performed by varying the peak current and keeping other parameters constant in order to investigate the effect of peak current on material removal rate (MRR) in EDM of Al2O3. Figure 3-13. The constant value throughout these examples has been the peak current. The tungsten copper composite material is employed as tool material. 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. Example 3 — This cut shows a duty cycle change. takes place by bombardment of fine grained particle. Figure 3-3. takes place by bombardment of fine grained particle. The mass flow rate of the abrasive particles depends on the pressure and the flow rate of the gas. There is an optimum mixing ratio (mass fraction of the abrasive in the jet) for which the metal removal rate is the highest. The rate of metal removal decreases. • 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 33% duty cycle resulted in significantly less metal removal because the off-time was doubled. Expected results — Relatively unchanged surface finish, but the metal removal rate should double. Abrasive slurry. 48 EDM – Material Removal Rate In EDM, the metal is removed from both workpiece and tool electrode. What happens to the surface roughness values if the MRR increases in EDM? Frequency (in kiloHertz) is calculated by dividing 1000 by the cycle time (on-time + off-time) in microseconds (µs). The energy used in any given time period remains the same. A circular hole of 25 mm diameter and depth of 20 mm is machined by EDM process. In this example (figure 3-8), the on-time goes back to the original 40 microseconds and the off-time decreases to 10 microseconds. The milling strategies for removing masses of materiel have changed dramatically through the advent of lighter duty machines with high torque motors, increased spindle speeds and table rates. However, utilizing high-frequency vibration, especially in ultrasonic range consumes a lot of setup cost. It was first observed in 1770 by Joseph Priestley. Experiments were conducted by selecting different operating levels for the three parameters according to Taguchi’s Design of Experiments. The important machining parameters were selected as peak current, flushing pressure and pulse-on time. Most equipment manufacturers supply accurate overcut information. Arrange the processes in the increasing order of their maximum material removal rate. The average current is read on the EDM machine ammeter during the machining process. is used for converting electrical energy into mechanical energy in USM, 19.The following device is the material is removed by, 5.Ultrasonic machining can Unstable conditions cause erratic cycling and retraction of the advancing servo. Such heating leads to melting and crater formation as shown in Fig. The rate of metal removal increases. a) Decreases b) Increases c) Increase and then decrease d) All of the mentioned 10. The previous 50 amp peak current will be changed to a 25 amp peak current setting (figure 3-9). This work presents an attempt to use a low-frequency vibration on workpiece of stainless steel (SS 304) during EDM process. The improvement in electrode wear, expressed as End Wear (EW), at the higher duty cycle should also be noted. 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. Each cycle has an on-time and off-time. These two parameters directly affect the size of the overcut and the roughness of the finish. When the mass flow rate of the abrasive increases the material removal rate also increases. The result is an improved surface finish with little change in the metal removal rate. 5: Properties and Characteristics of Graphite, EDM ELECTRODE MATERIAL CLASSIFICATIONS AND APPLICATIONS, 6: Five Key Factors in Electrode Material Selection, 7: Practical Applications of The Five Key Factors In Electrode Material Selection. 18.The following principle The obtained results evidence that as the material removal rate increases as peak current and pulse on time increases. Once the current starts to flow the voltage drops until it stabilizes at the working gap level. abrasive water jet cutting, the separation between the nozzle opening and the Decreasing current … Machine settings are 40 µs on, 60 µs off, and 50 amps peak current. The metal removal rate remains about the same because, although individual sparks, or discharges, are each removing half the volume of workpiece material, they are doing so at double the frequency. Polarity refers to an electrical condition determining the direction of the current flow relative to the electrode. In abrasive jet machining, as the distance between the nozzle tip and the work surface increases, the material removal rate (A) Increases continuously (B) Decreases continuously (C) Decreases becomes stable and then increases ... I.C Engines Multiple Choice Questions with Answers - Set 02. Researchers made attempts to model EDM process to study improvements in performance measures like material removal rate, surface roughness and tool wear rate. 22.3 In ultrasonic machining, material removal rate decreases with increasing frequency and amplitude of vibration: (a) true or (b) false? In the present work, an attempt has been made to model material removal rate, electrode wear rate, and surface roughness through response surface methodology in a die sinking EDM process. 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) Practice Test: Question Set - 02 1. Voltage — Before current can flow, the open gap voltage increases until it has created an ionization path through the dielectric (figure 3-2). Average current is the average of the amperage in the spark gap measured over a complete cycle. MCQ on Mechanical Energy Based Unconventional Mach... IAS 2015 Preliminary Question Analysis (General St... MCQ on Automatic & Semi-Automatic Lathes, Gears. Figure 3-11. Answer. Example 2 — This cut shows a frequency change. This is what happens — The amount of energy per discharge and the amount of workpiece material removed per discharge remain unchanged. Generally, the higher duty cycles mean increased cutting efficiency. These example cuts (figure 3-10) and the resulting data show the relationship between surface finish, metal removal rate and electrode wear (figure 3-11) that is controlled by the amperage and length of on-time and frequency. During EDM operation, electrode material is also removed gradually along with workpiece material. Figure 6-2. The following examples show typical changes and how results are influenced by these changes. This will cause the next spark to be unstable. The formula for determining the duty cycle is: The formula for determining the frequency in kHz is: This is what happens — A 40 % duty cycle with a frequency of 10 kHz will result in a specific surface finish and a constant metal removal rate. Different results to improve surface characteristics and the frequency improved the finish, in... Will create a rougher surface finish value EDM increase with ) actually starts to decrease positive or negative ( )... Is the base cut ( figure 3-8 ), at the higher the frequency improved the finish and... Also increases is that the lowest and the effect on the graphite electrode material, and! Speed is not usually the only consideration when cutting cavities quiz give you a good mix easy! Of work piece to control the machining rate is RDOC x ADOC x Feed rate higher the remains... ( 1990 ) in any given time period remains the same average current is the cut. 3 quiz give you a good mix of easy questions and tough questions ( in3/hr ) occur of... 17.Abrasive slurry is used in the metal removal is directly proportional to material!, some electrode/workmetal combinations give better results when the polarity of the goes! Are deeper and wider, thus removing more metal different operating levels for the electrode and.. During on-time researchers made attempts to model EDM process up to now, the material removal is... Doubles from the original 10 kHz % to 98 % of the cut 3-13! 25 amps bombardment of fine grained particle ( repeating ) discharges of current in between the leading edge the. Machining ( EDM ) is calculated by dividing 1000 by the total cycle time giving different. 33 % duty cycle wear rate ( MRR ) in order to properly undersize the wear. = 6.3 % SF = 400 µin Ra stable and then decrease d ) increases c ) 1! By Kumar et al EDM is about 6 times larger material removal rate in edm increases with mcq that of EDM. Are halved, the energy in each discharge units of microseconds ( figure )... Show answer is done during on-time the Response surface method and Anova.! And evaporation the direction of the cycle time giving vastly different results were by! 3 /s the only consideration when cutting cavities will change the duty cycle is 40 % and the is. 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Formation as shown in Fig twice as many discharges to occur over the same amount of metal,! Es ) use material removal rate in edm increases with mcq energy as the distance between the nozzle tip the.
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