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. Mechanics of USM 3. 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. Image Guidelines 4. Generally, stainless steels and low carbon steels are used for making the tools. The tool is gradually fed with a uniform force. Most transducers work on the magnetostrictive principle because of the high efficiency, high reliability in the 15-30 kHz range, low supply voltage, and simple cooling arrangement. When designing the tool, consideration should be given to the side clearance which is normally of the order of 0.06 mm to 0.36 mm, depending on the grain size of the abrasive. The range of sizes of USM machines varies from a light portable type having an input of about 20 W to heavy machines taking an input up to 2 kW. •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. The characteristic of variation of Δt, given by –. Shaw is generally well-accepted and, despite its limitations, explains the material removal process reasonably well. So, the material structure remains unaffected. The main purpose of the concentrator is to increase the amplitude to the level needed for cutting. The nature of variation of the mrr with the feed force (for various amplitudes) is shown in Fig. Aptitude Data Interpretation Verbal Reasoning Non Verbal Reasoning Verbal Ability Programming General Knowledge Puzzle. Ultrasonic Machining USM Process Parameters and Factors Affecting Ultrasonic Machining Rate, Working of ultrasonic machining equipment, USM applications, advantages and limitations, Types of Pattern Material - Application, Advantages And Limitation, 3-2-1 Principle of Location (Six Point Principle) Degree Of Freedom Controlled By 3-2-1 Location Principle - With Image, Different Types of Cutting Tools Materials and Their Properties, Basic Components of IC Engine and Their Function, Design and Working Principle of Simple Carburetor. But, then, with the boom in solid state electronics, the machining of electrically non-conducting, semi-conductive, and brittle materials became more and more important and, for this reason, ultrasonic machining again gained importance and prominence. 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. The material removal rate in EEM process depends on the concentration of powder particle, spherical head rotational speed during finishing operation. ... Material removal rate depends on melting point of work material. Material removal models in USM Theoretical analysis and experimental results have revealed that USM is a form of abrasion and material removal in the form of small grains by four mechanisms 1. 6.11. Therefore the optimum percentage of abrasives in the slurry is 40-60%. Material removal primarily occurs due to the indentation of the hard abrasive grits on the brittle work material. As the concentration of particle increases the material removal rate initially increases and then decreases. 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. Figure 6.23b shows how the amplitude of longitudinal vibration of the transducer-concentrator assembly is amplified. Therefore the optimum percentage of abrasives in the slurry is 40-60%. ____ can be used as abrasive carrying medium. Since the cutting force involved is very small, the process produces no appreciable stress and heating. The device for converting any type of energy into ultrasonic waves is the ultrasonic transducer. Wear ratio mainly depends on the brittleness of workpiece material i.e. 6.9, The various tool positions during a cycle are as shown in Fig. The important components of the machine are: The acoustic head (Fig. However, metals like aluminum, give very short life. Hammering of abrasive grains 3. Terms of Service 7. The actual nature of the variation is as shown in Fig. The machining time can be controlled easily because the process is stable when a suitable feed rate is selected 14.3 Abrasive Micromachining 14.3.1 Microgrinding Diamond microgrinding at the ductile mode is used for machining of brittle materials such as ceramics using a grinding wheel speed of 30-60 m/s, workpiece speed of 0.1-1.0 m/min. 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. Thus, a further increase in the concentration does not help. 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. 7. In USM the metal removal rate would... with increasing mean grain diameter of the abrasive material . In practice also, the mrr increases with the frequency (see Fig. The increase in frequency increase the number blows by the tool per second and cut more material from surface. In an USM operation, the surface finish depends mainly on the size of the abrasive grains. Mechanisms of Material Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. (v) All abrasive grains are identical and spherical in shape. His analysis is mostly applicable to plastic materials, however, most of the materials machined by ultrasonic machining are brittle. Coarse grains give higher MRR, but lower surface 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, … Magne-trostriction’ means a change in the dimension occurring in f… 9. 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. Hence, material removal due to these two factors has been ignored. generally above 16 kHz. Some physical properties (e.g., viscosity) of the fluid used for the slurry also affect the mrr. Diamond dust is used only for cutting diamonds and rubies. • The rate of material removal, in USM, depends, on the frequency of tool vibration, static pressure, the size of the machined area, and the abrasive and workpiece material. The tool material being tough and ductile wears out at a much smaller rate. 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. Content Guidelines 2. The grains used in the abrasive fluid are usually boron carbide or silicon carbide as they are rigid than others. Material removal in USM is due to: i) Hammering of the abrasive particles on the work surface by the tool. This is in a fairly good agreement with the theoretical prediction. Relation (6.11) indicates that the rate of material removal is proportional to d1/4, but actually it is proportional to d. This discrepancy between the theoretical prediction and the observed fact was explained by Shaw as follows. There is an optimum mixing ratio (mass fraction of the abrasive in the jet) for which the metal removal rate is the highest. 10. The basic USM process involves a tool (made of a ductile and tough material) vibrating with a very high frequency and a continuous flow of an abrasive slurry in the small gap between the tool and the work surface. The geometrical features are decided by the process. Therefore the optimum percentage of abrasives in the slurry is 40-60%. removal rate depends on the applied current density and the Abstract—Material removal rate (MRR) is an important aspect on an electrochemical machining. 2. If we assume that during the indentation caused by such an impinging grain the contact force increases linearly with the indentation, then –. The thickness of any wall or projection should be at least five times the grain size of the abrasive. 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. Let us now consider the impact of a rigid, spherical abrasive grain of diameter don the work surface. With an increase in static loading (i.e., the feed force), the mrr tends to increase. 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. Disclaimer 8. It also depends on the size of grains of the abrasive slurry, the rigidity and the viscosity as well. 6.17a. The diameter of the circle circumscribed about the tool should not be more than 1.5 to 2 times the diameter of the end of the concentrator, and the tool should be as short and rigid as possible. 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. In a hollow tool, the walls should not be made thinner than 0.5 mm to 0.8 mm. The rate of material removal in USM depends on ____. 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. The use of ultrasonics in machining was first proposed by L. Balamuth in 1945. (iv) The chemical action associated with the fluid used. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. Throwing of abrasive grains 2. The maximum metal removal rate is 3 mm®/s and the power consumption is high. Also, material removal rate is an important performance variable in USM machining. The cutting rate in USM depends on 1. 6.17b. 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)). By 1954, the machine tools, using the ultrasonic principle, had been designed and constructed. Material Removal Rate 15. The actual shape of an abrasive grain is not spherical, as shown in Fig. The time spent on ultrasonic machine entirely depends on the frequency of the vibrating tool. USM Application. 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. Ultrasonic Machining (USM) has metal removal rate of about 5-10 mm 3 /s. 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. Though water is the most commonly used fluid in the slurry, other liquids, such as benzene, glycerol, and oils, are also used. ... Material removal rate depends on melting point of work material. The cutting time with SiC is about 20-40% more than that with B4C. It should be noted that the system has to be held to the main body at a nodal point, as shown. 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. 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. Therefore the optimum percentage of abrasives in the slurry is 40-60%. Vibration frequency and amplitude: The frequency of vibration is directly proportional to the material removal rate. (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. Wire EDM. Since the mrr increases as C1/4, the increase in the mrr is quite low after C has crossed 30%. 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. Machinability rate of glass by USM is ____. 2. 4. Prohibited Content 3. 6.16b for different values of the frequency. The major USM process variables effecting material removal rate, accuracy, and surface finish are tool/horn design, power, amplitude, abrasive size and frequency. Aluminium and brass tools wear ten and five times faster than steel tools, respectively. SiC is used on glass, germanium, and some ceramics. When the static pressure of the feed is increases, MRR ____. 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. Limitations of the Process. So, the corresponding maximum kinetic energy of the abrasive grain is given by –, Where ρ is the density of the abrasive material. •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. When the amplitude of vibration is increased, the mrr is expected to increase, as can be seen from relation (6.18). 6.15. 6.18b for B4C and SiC abrasives. However, during cutting through a hole, chipping may occur at the exit side of the hole. 1 Approved Answer. Figure 6.13 shows a grain reflected by the tool. 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. Instead of having a smooth surface, it has projections of average diameter d1. Ultrasonic machining is an abrasive process which can create any material into hard and brittle form with the help of its vibrating tool and the indirect passage of abrasive particles towards the work piece. The tool material, being tough and ductile, wears out at a much slower rate. As the tool area increases, MRR ____. This is also confirmed by relation (6.18). 6. As the tool vibrates, it leads to indentation of the abrasive grits. Account Disable 12. Again, the actual characteristic is somewhat different from the theoretically-predicted one. (ii) The rate of work material removal is proportional to the number of particles making impact per cycle. 14. 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. The figure below shows a qualitative relationship between the material removal rate and lambda i.e. Figure 6.9 shows the indentation caused by such an impact at an instant of time. (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. 4. The life of abrasives depends on the hardness of the abrasive material and work combinations. The model proposed by M.C. Ultrasonic machining (USM) using loose abrasive particles suspended in a liquid slurry for material removal is considered an effective method for manufacturing these materials. It is clear that the surface finish is much more sensitive to the grain size in the case of glass. An instrument showing the movement of the tool indicates the depth of machining. Electro-Chemical Machining (ECM) has the highest metal removal rate of about 200-300 mm 3 /s 3. 6.19a). Uploader Agreement. [gravityform id="1" title="false" description="false" ajax="true"]. In recent years, various types of ultrasonic machine tools have been developed. 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. What is the machinability rate of glass by USM? Corundum is much less efficient and the cutting time is about 3-4 times of that with B4C. In this article we will discuss about the ultrasonic machining:- 1. Material removal primarily occurs due to the indentation of the hard abrasive grits on the brittle work material. 7. Privacy Policy 9. Experiments show that the mrr drops as the viscosity increases (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. The objective of the feed mechanism is to apply the working force during the machining operation. However, in practice, it tends to decrease beyond a certain critical value of the force as the grains start getting crushed. Its function is to produce a vibration in the tool. The metal removal rate and surface finish depend on size of abrasive particles. Stampings are used to reduce loss as in transformers. USM Application. Manufacturing Science, Machining Processes, USM. Characteristics of Ultrasonic Machining. workpiece/tool hardness. The slurry must be continuously circulated to: bring fresh grains into action at the tool–work gap, and wash away chips and worn grits. 3. … 8. Low-carbon steel and stainless steels give superior performance. B4C is the best and most efficient among the rest but it is expensive. Process Parameters of USM and Its Effect 4. The mass flow rate of the abrasive particles depends on the pressure and the flow rate of the gas. 6.23a). Before uploading and sharing your knowledge on this site, please read the following pages: 1. The basic types of feed mechanisms are the: The tool is made of a strong, but at the same time ductile, metal. A number of researchers have tried to develop the theories to predict the characteristics of ultrasonic machining. 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. • MRR and machinability by USM depends on the brittleness criterion which is the ratio of shearing to breaking strength of a material. 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 first report on the equipment and technology appeared during 1951-52. Wear ratio mainly depends on the brittleness of workpiece material i.e. Figure 14 presents the SEM micrographs of cross sections of the surface machined by USM. For a given work material, the removal rate in USM increases with increasing frequency and amplitude of vibration. The mrr tends to be somewhat lower than the theoretically-predicted value. The size of the cavity produced during USM is slightly larger than the tool di- mensions (or tapered, Figure 11.3). In USM dominant in material removal is ____. 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 abrasive gas mixture, jet pressure, abrasive particle size and hardness are mainly responsible for the metal removal rate. 5. (i) The rate of work material removal is proportional to the volume of work material per impact. 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. 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. When the tool is made hollow, the internal contour should be parallel to the external one to ensure uniform wear. Fig 1.4 is quite different from that obtained from the approximate expression, i.e., (h / A)(T / 4). The machinability of USM depends on brittleness criterion. 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. Academic Resource. 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. special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work. When the mass flow rate of the abrasive increases the material removal rate also increases. PNEUMATIC OR HYDRAULIC FEED MECHANISM • In order to get high feed rate, pneumatic feed mechanism is used 28. Electric Discharge Machining (EDM) has metal removal rate of about 10-20 mm 3 /s. 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. Relation (6.18) shows that the mrr is proportional to d, a fact also experimentally confirmed. In USM process, the mechanism of material removal can be described as the effect of the impact indentation and fracture phenomena. Content Filtration 6. Mechanisms of Material Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. linear material removal rate – MRRl) is equal to the tool feed rate (f). The reasons of material removal during USM are believed to be: (i) The hammering of the abrasive particles on the work surface by the tool. 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). Various types of concentrators are used (Fig. The main limitation of the process is its relatively low metal cutting rates. Apart from the hardness, the brittleness of the work material plays a very dominant role. 2. Report a Violation 11. It is a low material removal rate machining process. Longer life of abrasives can be obtained when the hardness of the abrasives is more than the hardness of the work material. special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work. advertisement. (iii) The rate of work material removal is proportional to the frequency (number of cycles per unit time). The actual variation is shown in Fig. 1. Arrange the processes in the increasing order of their maximum material removal rate. The Shaw theory has a number of limitations. 4. Miller assumed that the material removal rate depends upon work-hardening and plastic deformation of the workpiece. 6.14. The dimensions are so chosen that the natural frequency coincides with the electric supply frequency. 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. Table 6.2 indicates the relative material removal rates for different work materials, keeping the other parameters the same. a) 25% b) 50% c) 75% d) 100% View Answer. (ii) The impact of the free abrasive particles on the work surface. If the distance travelled by the tool from the position A to the position B is h (the total indentation), then-, Since the flow stress σ and the Brinell hardness H are the same, equations (6.6) and (6.7) yield –. linear material removal rate – MRRl) is equal to the tool feed rate (f). Download App. Wire EDM. However, in practice, Q starts decreasing after some value of F because the abrasive grains get crushed under heavy load. Components of Ultrasonic Machining 5. Explanation: Material removal rate depends on all the above mentioned factors. 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. 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 Clearly, a more brittle material is machined more rapidly. 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. Lower than the tool face is 2πvA / a ) ( T / the rate of material removal in usm depends on ) not made... 6.23B shows how the amplitude of vibration is increased, the rigidity and the viscosity well... We assume that during the indentation of the abrasive grains are identical and in! 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