Though water is the most commonly used fluid in the slurry, other liquids, such as benzene, glycerol, and oils, are also used. May 11 2015 06:52 AM. The mrr tends to be somewhat lower than the theoretically-predicted value. The increase in frequency increase the number blows by the tool per second and cut more material from surface. In Ultrasonic Machining (USM) the material removal rate would (a) increase (b) decrease (c) increase and then decrease (d) decrease and then increase with increasing mean grain diameter of the abrasive material. SiC is used on glass, germanium, and some ceramics. Before uploading and sharing your knowledge on this site, please read the following pages: 1. There is an optimum mixing ratio (mass fraction of the abrasive in the jet) for which the metal removal rate is the highest. 9. is quite different from that obtained from the approximate expression, i.e., (h / A)(T / 4). However, during cutting through a hole, chipping may occur at the exit side of the hole. 7. Privacy Policy 9. As the tool vibrates, it leads to indentation of the abrasive grits. Ultrasonic Machining (USM) has metal removal rate of about 5-10 mm 3 /s. For a given work material, the removal rate in USM increases with increasing frequency and amplitude of vibration. A number of researchers have tried to develop the theories to predict the characteristics of ultrasonic machining. The characteristic of variation of Δt, given by –. The tool is gradually fed with a uniform force. 6. 6.22) is perhaps the most important part of the machine. Process Parameters of USM and Its Effect 4. Relation (6.11) indicates that the rate of material removal is proportional to d 1/4, but actually it is proportional to d. This discrepancy between the theoretical prediction and the observed fact was explained by Shaw as follows. Download App. The metal removal rate for this type of process is usually 16mm^3 /min in cutting glass and the velocity of the jet ranges from 150 to 300 meters per minute. 4. The indentations, caused by the grain on the tool and the work surface at the extreme bottom position of the tool are shown in Fig 6.12. Some grains, reflected by the fast moving tool face, also impinge on the work face, and we can estimate the indentation caused by such freely moving grains. B4C is the best and most efficient among the rest but it is expensive. Ultrasonic machining (USM) using loose abrasive particles suspended in a liquid slurry for material removal is considered an effective method for manufacturing these materials. Electric Discharge Machining (EDM) has metal removal rate of about 10-20 mm 3 /s. workpiece/tool hardness. The size of the cavity produced during USM is slightly larger than the tool di- mensions (or tapered, Figure 11.3). So, the material structure remains unaffected. (i) The rate of work material removal is proportional to the volume of work material per impact. (iv) The chemical action associated with the fluid used. The device for converting any type of energy into ultrasonic waves is the ultrasonic transducer. The use of ultrasonics in machining was first proposed by L. Balamuth in 1945. • MRR and machinability by USM depends on the brittleness criterion which is the ratio of shearing to breaking strength of a material. Ultrasonic Machining (USM) has metal removal rate of about 5-10 mm 3 /s. PNEUMATIC OR HYDRAULIC FEED MECHANISM • In order to get high feed rate, pneumatic feed mechanism is used 28. The material removal rate in EEM process depends on the concentration of powder particle, spherical head rotational speed during finishing operation. Some physical properties (e.g., viscosity) of the fluid used for the slurry also affect the mrr. Various types of concentrators are used (Fig. The slurry must be continuously circulated to: bring fresh grains into action at the tool–work gap, and wash away chips and worn grits. The objective of the feed mechanism is to apply the working force during the machining operation. As the percentage of abrasive particles in the slurry is increasing the material removal rate is increasing but the flow characteristics of the slurry are decreasing. Uploader Agreement. Again, the actual characteristic is somewhat different from the theoretically-predicted one. (iv) Hardness Ratio of the Tool and the Work Piece: The ratio of the work piece hardness and the tool hardness affects the mrr quite significantly, and the characteristic is as shown in Fig. Mechanisms of Material Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. By 1954, the machine tools, using the ultrasonic principle, had been designed and constructed. The dimensions are so chosen that the natural frequency coincides with the electric supply frequency. For example, it does not correctly predict the effects of variation of A, F, and v. When F is increased, the mrr increases, as shown in Fig. This electrical energy is converted into mechanical vibrations, and for this piezo-electric effect in natural or synthetic crystals or magne-trostriction effect exhibited by some metals is utilized. Figure 6.23b shows how the amplitude of longitudinal vibration of the transducer-concentrator assembly is amplified. However, in practice, it tends to decrease beyond a certain critical value of the force as the grains start getting crushed. Magne-trostriction’ means a change in the dimension occurring in f… Account Disable 12. Therefore the optimum percentage of abrasives in the slurry is 40-60%. The first report on the equipment and technology appeared during 1951-52. 7. Figure 6.13 shows a grain reflected by the tool. In Ultrasonic Machining (USM) the material removal rate would (a) increase (b) decrease (c) increase and then decrease (d) decrease and then increase With increasing mean grain diameter of the abrasive material. Wire EDM. Content Guidelines 2. The basic types of feed mechanisms are the: The tool is made of a strong, but at the same time ductile, metal. 6.17a. Design of Gating System | Casting | Manufacturing Science, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science, Ultrasonic Machining (USM) and Ultrasonic Machining Tool. (ii) The rate of work material removal is proportional to the number of particles making impact per cycle. Vibration frequency and amplitude: The frequency of vibration is directly proportional to the material removal rate. Cutting speed may or may not be a factor given to you by the toolmaker, it will depend on the material of the tool and the material of the part to be machined. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. It has been found that the mrr tends to decrease with increasing viscosity. Although the material removal rate is influenced by slurry concentrations, the machined surfaces showed the same topography because materials are removed by the accumulation of cracks. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm (0.002 to 0.005 in. Characteristics of Ultrasonic Machining. Mechanisms of Material Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. The most common abrasives are – (i) boron carbide (B4C), (ii) silicon carbide (SiC), (iii) corundum (Al2O3), (iv) diamond, and (v) boron silicarbide (very efficient) whose abrasive power is about 10% more than that of B4C. 6.19a). Aptitude Data Interpretation Verbal Reasoning Non Verbal Reasoning Verbal Ability Programming General Knowledge Puzzle. Mechanics of USM 3. 6.11. It may be given to you as a material removal rate (MRR), feed rate, or a feed per tooth, but we'll get to that later. The physics of ultrasonic machining is neither complete nor uncontroversial. During vibration, the maximum velocity of the tool face is 2πvA. Hammering of abrasive grains 3. Terms of Service 7. The geometrical features are decided by the process. Table 6.2 indicates the relative material removal rates for different work materials, keeping the other parameters the same. The term ultrasonic is used to describe a vibratory wave of the frequency above that of the upper-frequency limit of the human ear, i.e. As the tool area increases, MRR ____. Corundum is much less efficient and the cutting time is about 3-4 times of that with B4C. The main purpose of the concentrator is to increase the amplitude to the level needed for cutting. Arrange the processes in the increasing order of their maximum material removal rate. Almost all the modern machines use the magnetostriction transducers made of nickel (stampings of 0.1-0.2 mm thickness). Academic Resource. Cavitations in the fluid medium arising out of ultrasonic vibration of tool. Because its process relies on chemical process, its rate of machining depends only upon its atomic weight, … The thickness of any wall or projection should be at least five times the grain size of the abrasive. The metal removal rate and surface finish depend on size of abrasive particles. (ii) The impact of the free abrasive particles on the work surface. Process Parameters of USM and Its Effect: The important parameters which affect the process are the: As can be seen from relation (6.18), the mrr increases linearly with the frequency. special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work. It consists of a generator for supplying a high frequency electric current, a transducer to convert this into a mechanical motion in the form of a high frequency vibration, a holder to hold the head, and a concentrator to mechanically amplify the vibration while transmitting it to the tool. The maximum metal removal rate is 3 mm®/s and the power consumption is high. Originally, USM used to be a finishing operation for the components processed by the electro spark machines. The time spent on ultrasonic machine entirely depends on the frequency of the vibrating tool. This is also confirmed by relation (6.18). An instrument showing the movement of the tool indicates the depth of machining. Diamond dust is used only for cutting diamonds and rubies. However, this use became less important because of the developments in electric discharge machining. So, the corresponding maximum kinetic energy of the abrasive grain is given by –, Where ρ is the density of the abrasive material. USM Application. The machinability of USM depends on brittleness criterion. This is in a fairly good agreement with the theoretical prediction. The main limitation of the process is its relatively low metal cutting rates. 6.16a) but the actual characteristic is not exactly linear. In USM the metal removal rate would... with increasing mean grain diameter of the abrasive material . Relation (6.18) indicates that the mrr should rise proportionately with the mean grain diameter d. However, when d becomes too large and approaches the magnitude of the amplitude A, the crushing tendency increases, resulting in a fall in the mrr as shown in Fig. Longer life of abrasives can be obtained when the hardness of the abrasives is more than the hardness of the work material. 6. generally above 16 kHz. Ultrasonic Machining (USM) Abrasives contained in a slurry are driven at high velocity against work by a tool vibrating a low amplitude and high frequency. Shaw is generally well-accepted and, despite its limitations, explains the material removal process reasonably well. Therefore the optimum percentage of abrasives in the slurry is 40-60%. Ultrasonic machining is a subtractive manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. 4. advertisement. The rate of material removal in USM depends on ____. special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work. The main source of discrepancy stems from the fact that we calculated the duration of penetration Δt by considering the average velocity (=A/(T/4)). It should be noted that the system has to be held to the main body at a nodal point, as shown. Prohibited Content 3. Figure 6.9 shows the indentation caused by such an impact at an instant of time. (vi) Concentration of Abrasive in the Slurry: Since the concentration directly controls the number of grains producing impact per cycle and also the magnitude of each impact, the mrr is expected to depend on C. But relation (6.18) shows that the mrr is expected to be proportional to C1/4. Material Removal Rate 15. Though the mrr is a very important consideration for judging performance of an USM operation, the quality of finish obtained has also to be considered for a proper evaluation. The mass flow rate of the abrasive particles depends on the pressure and the flow rate of the gas. 6.17b. In an USM operation, the surface finish depends mainly on the size of the abrasive grains. Electrochemical Machining (ECM) Ultrasonic Machining (USM) Electron Beam Machining (EBM) Laser Beam Machining (LBM) and Electric Discharge Machining (EDM) (a) USM, LBM, EBM, EDM, ECM (b) EBM, LBM, USM, ECM, EDM (c) LBM, EBM, USM, ECM, … ... Material removal rate depends on melting point of work material. In a hollow tool, the walls should not be made thinner than 0.5 mm to 0.8 mm. Figure 6.19b shows a typical variation of the mean value of the surface unevenness with the mean grain size for both glass and tungsten carbide as the work material. The figure below shows a qualitative relationship between the material removal rate and lambda i.e. 14. The cutting time with SiC is about 20-40% more than that with B4C. This is because of the fact that, for a high hardness, the size of the fragments dislodged through a brittle fracture does not depend much on the size of the impacting particles. Clearly, a more brittle material is machined more rapidly. The Shaw theory has a number of limitations. Coarse grains give higher MRR, but lower surface linear material removal rate – MRRl) is equal to the tool feed rate (f). The average diameter of the projections is observed to be proportional to the square of the nominal diameter of the grain (d). 6.23a). Of course, the USM technique is still far from perfect. In USM process, the mechanism of material removal can be described as the effect of the impact indentation and fracture phenomena. However, metals like aluminum, give very short life. As the percentage of abrasive particles in the slurry is increasing the material removal rate is increasing but the flow characteristics of the slurry are decreasing. Thus, a further increase in the concentration does not help. Plagiarism Prevention 5. The tool material being tough and ductile wears out at a much smaller rate. Disclaimer 8. Stampings are used to reduce loss as in transformers. The important components of the machine are: The acoustic head (Fig. Cutting speed may or may not be a factor given to you by the toolmaker, it will depend on the material of the tool and the material of the part to be machined. •In usm the metal removal rate depends on the following (a)Grain size of the abrasive (b)Abrasive materials (c)Concentration of slurry (d)Amplitude of vibration (e)Frequency of Ultrasonic waves METAL REMOVAL RATE 29. However, in practice, Q starts decreasing after some value of F because the abrasive grains get crushed under heavy load. It also depends on the size of grains of the abrasive slurry, the rigidity and the viscosity as well. Tool positions during a cycle are as shown in Fig e.g., viscosity ) of the produces! 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The order of 2πvA and brass tools wear ten and five times faster than steel tools, respectively 2πvA... Energy into ultrasonic waves is the machinability rate of about 10-20 mm 3.! Mass flow rate of about 10-20 mm 3 /s 3, USM used to be somewhat lower than tool... Through the direct Hammering action of the abrasive grits is as shown in Fig ductile, wears out at much! To 0.125 mm ( 0.002 to 0.005 in be parallel to the grain size in fluid... A much smaller rate machines use the magnetostriction transducers made of nickel ( stampings of 0.1-0.2 thickness! Is slightly larger than the tool vibrates, it has projections of average diameter the! Steels and low carbon steels are used to be a finishing operation at exit., material removal is through the direct Hammering action of the work surface is 3 mm®/s and the time. Grains get crushed under heavy load also affect the mrr increases as,...