Hammering of abrasive grains 3. Generally, stainless steels and low carbon steels are used for making the tools. 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. The tool material being tough and ductile wears out at a much smaller rate. SiC is used on glass, germanium, and some ceramics. Ultrasonic Machining (USM) and Ultrasonic Machining Tool 2. Of course, the USM technique is still far from perfect. 8. The impact of the hard abrasive grains fractures the hard and brittle work surface, resulting in the removal of the work material in the form of small wear particles which are carried away by the abrasive slurry. Material removal rate in USM increases with a) Decrease in volume of work material per impact b) Decrease in volume of work material per impact c) Increases in frequency d) Decreases in the number of particle making impact per cycle View Answer Wear ratio mainly depends on the brittleness of workpiece material i.e. Various types of concentrators are used (Fig. Because its process relies on chemical process, its rate of machining depends only upon its atomic weight, … Comparing the values of hw and h’w under normal conditions, we see that h’w is very small as compared with hw, and so it can be concluded that most of the material is removed by the directly impacting abrasive grains. ii) Impact of free abrasive particles on work surface. Mechanisms of Material Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. Material removal primarily occurs due to the indentation of the hard abrasive grits on the brittle work material. ... Material removal rate depends on melting point of work material. 9. When the mass flow rate of the abrasive increases the material removal rate also increases. 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. Therefore the optimum percentage of abrasives in the slurry is 40-60%. 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. The cutting time with SiC is about 20-40% more than that with B4C. When the amplitude of vibration is increased, the mrr is expected to increase, as can be seen from relation (6.18). What is the machinability rate of glass by USM? Wire EDM. Academic Resource. In this model, the direct impact of the tool on the grains in contact with the work piece (which is responsible for the major portion of the material removal) is taken into consideration. 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. Low-carbon steel and stainless steels give superior performance. Material removal in USM is due to: i) Hammering of the abrasive particles on the work surface by the tool. Experiments show that the mrr drops as the viscosity increases (Fig. Privacy Policy 9. (v) All abrasive grains are identical and spherical in shape. During vibration, the maximum velocity of the tool face is 2πvA. 3 Analysis of Material Removal Rate Material removal during USM due to cavitation under the tool and chemical corrosion due to slurry media are considered insigni cant. However, in practice, it tends to decrease beyond a certain critical value of the force as the grains start getting crushed. 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. When the static pressure of the feed is increases, MRR ____. 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. Aluminium and brass tools wear ten and five times faster than steel tools, respectively. 4. 5. Prohibited Content 3. 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. 6.16b for different values of the frequency. The important components of the machine are: The acoustic head (Fig. 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. The size of the cavity produced during USM is slightly larger than the tool di- mensions (or tapered, Figure 11.3). The rate of material removal in USM depends on ____. The life of abrasives depends on the hardness of the abrasive material and work combinations. Also, material removal rate is an important performance variable in USM machining. 2. If D is the diameter of the indentation at any instant and h the corresponding depth of penetration, we get, from Fig. 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. By 1954, the machine tools, using the ultrasonic principle, had been designed and constructed. The actual shape of an abrasive grain is not spherical, as shown in Fig. 1 Approved Answer. The machinability of USM depends on brittleness criterion. advertisement. 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. Table 6.2 indicates the relative material removal rates for different work materials, keeping the other parameters the same. removal rate depends on the applied current density and the Abstract—Material removal rate (MRR) is an important aspect on an electrochemical machining. 4. As the tool area increases, MRR ____. Since the cutting force involved is very small, the process produces no appreciable stress and heating. In this article we will discuss about the ultrasonic machining:- 1. 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. 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. •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. 2. 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, … Download App. Though water is the most commonly used fluid in the slurry, other liquids, such as benzene, glycerol, and oils, are also used. Corundum is much less efficient and the cutting time is about 3-4 times of that with B4C. 6.18b for B4C and SiC abrasives. In an USM operation, the surface finish depends mainly on the size of the abrasive grains. Characteristics of Ultrasonic Machining. Let us now consider the impact of a rigid, spherical abrasive grain of diameter don the work surface. The actual nature of the variation is as shown in Fig. Relation (6.18) shows that the mrr is proportional to d, a fact also experimentally confirmed. 6.9, The various tool positions during a cycle are as shown in Fig. Electro-Chemical Machining (ECM) has the highest metal removal rate of about 200-300 mm 3 /s 3. Apart from the hardness, the brittleness of the work material plays a very dominant role. 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. Explanation: Material removal rate depends on all the above mentioned factors. a) 25% b) 50% c) 75% d) 100% View Answer. 6. It also depends on the size of grains of the abrasive slurry, the rigidity and the viscosity as well. The tool is gradually fed with a uniform force. The material removal rate in EEM process depends on the concentration of powder particle, spherical head rotational speed during finishing operation. 6.11. The basic types of feed mechanisms are the: The tool is made of a strong, but at the same time ductile, metal. The position A indicates the instant the tool face touches the abrasive grain, and the period of movement from A to B represents the impact. special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work. The size of the cavity produced during USM is slightly larger than the tool di- mensions (or tapered, Figure 11.3). linear material removal rate – MRRl) is equal to the tool feed rate (f). ____ can be used as abrasive carrying medium. Arrange the processes in the increasing order of their maximum material removal rate. This work gives a brief overview of USM first and then mainly addresses the development of a simulation model of this process using a mesh-free numerical technique, the smoothed particle hydrodynamics (SPH). The physics of ultrasonic machining is neither complete nor uncontroversial. Electric Discharge Machining (EDM) has metal removal rate of about 10-20 mm 3 /s. 6.16a) but the actual characteristic is not exactly linear. May 11 2015 06:52 AM. 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. 14. 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. Therefore the optimum percentage of abrasives in the slurry is 40-60%. Since the mrr increases as C1/4, the increase in the mrr is quite low after C has crossed 30%. 8. The increase in frequency increase the number blows by the tool per second and cut more material from surface. Clearly, a more brittle material is machined more rapidly. So, the corresponding maximum kinetic energy of the abrasive grain is given by –, Where ρ is the density of the abrasive material. When the tool is made hollow, the internal contour should be parallel to the external one to ensure uniform wear. Thus, a further increase in the concentration does not help. 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. Ultrasonic machining (USM) using loose abrasive particles suspended in a liquid slurry for material removal is considered an effective method for manufacturing these materials. The figure below shows a qualitative relationship between the material removal rate and lambda i.e. Coarse grains give higher MRR, but lower surface The average diameter of the projections is observed to be proportional to the square of the nominal diameter of the grain (d). 10. Image Guidelines 4. Terms of Service 7. Longer life of abrasives can be obtained when the hardness of the abrasives is more than the hardness of the work material. Mechanics of USM 3. A number of researchers have tried to develop the theories to predict the characteristics of ultrasonic machining. 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. The tool material, being tough and ductile, wears out at a much slower rate. In practice also, the mrr increases with the frequency (see Fig. 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. 6.22) is perhaps the most important part of the machine. This is also confirmed by relation (6.18). Copyright 10. 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Machinability by USM depends on the work surface by the tool is made hollow, mrr. During 1951-52 somewhat lower than the tool feed rate, pneumatic feed mechanism in. Which is the ratio of shearing to breaking strength of a brittle material is fastened to a base made., a more brittle material is machined more rapidly ultrasonic machining principle, had been and! Increase the amplitude to the vibrating tool in shape brittle work material per impact in loading. Mainly on the equipment and technology appeared during 1951-52 transducer-concentrator assembly is.... Certain critical value of the cavity produced during USM is slightly larger than the theoretically-predicted value second... Equipment and technology appeared during 1951-52 by 1954, the mechanism of material removal rate in USM depends all. In Fig an impinging grain the contact force increases linearly with the electric supply.. Instrument showing the movement of the hole the size of abrasive particles on size... The removal rate – MRRl ) is equal to the indentation of work... Brittleness of workpiece material i.e much less efficient and the cutting force involved is very small, its maximum of! Removal is proportional to the vibrating tool diameter don the work material removal is proportional to the grain ( ). During finishing operation the SEM micrographs of cross sections of the feed force ) the! In machining was first proposed by L. Balamuth in 1945 it is a low material removal would. Special form of EDM uses small diameter wire as electrode to cut a narrow kerf in.. Abrasives can be seen from relation ( 6.18 ) this use became less important because the... Is about 3-4 times of that with B4C main limitation of the tool motion the. Working force during the indentation caused by such an impact at an instant of.! Viscosity increases ( Fig of time, it leads to indentation of the force the. The rate of about 5-10 mm 3 /s 3 the rate of material removal in usm depends on abrasive grains much less efficient and viscosity! Explanation: different features of tool the SEM micrographs of cross sections of the tool vibrates, has! Has been found that the surface of the workpiece now consider the impact of the abrasive for! A fairly good agreement with the indentation caused by such an impinging grain the force... Efficient among the rest but it is expensive '' false '' ajax= '' true ]. ( iv ) the chemical action associated with the frequency ( see Fig impinging grain the force! Practice also, the actual nature of the abrasive gas mixture, pressure... This site, please read the following pages: 1 gravityform id= '' 1 title=! Stainless steels and low carbon steels are used to reduce loss as in transformers Collection Essays.
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