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MMM LECTURE NOTES FINAL.pdf

Fig material removal process in usmp in case of hard

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Fig., material removal process in USMP In case of hard and brittle materials such as glass, the machining rate is high and the role played by free impact can also be noticed. When machining porous materials such as graphite, the mechanism of erosion is introduced. The rate of material removal, in USM, depends, first of all, on the frequency of tool vibration, static pressure, the size of the machined area, and the abrasive and work piece material. The material removal rate and hence the mach inability by USM depends on the brittleness criterion which is the ratio of shearing to breaking strength of a material. According to glass has a higher machinability than that of a metal of similar hardness. Moreover, because of the low brittleness criterion of steel, which is softer, it is used as a
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Modern Manufacturing Methods tool material.the important parameters that affect the performance of USM, which are mainly related to the tool, work piece material, abrasives, machining conditions, and the ultrasonic machine. In USM, the material removal rate (MRR) can generally be described using the following formula., Factors affecting USM performance : The following Factors affecting from USMP are Working conditions Tools Abrasive slurry Work piece Tool oscillation. The amplitude of the tool oscillation has the greatest effect of all the process variables. The material removal rate increases with a rise in the amplitude of the tool vibration. The vibration amplitude determines the
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Modern Manufacturing Methods velocity of the abrasive particles at the interface between the tool and work piece. Under such circumstances the kinetic energy rises, at larger amplitudes, which enhances the mechanical chipping action and consequently increases the removal rate. A greater vibration amplitude may lead to the occurrence of splashing, which causes a reduction of the number of active abrasive grains and results in a decrease in the material removal rate. Abrasive grains. Both the grain size and the vibration amplitude have a similar effect on the removal rate. According to McGeough (1988), the removal rate rises at greater grain sizes until the size reaches the vibration amplitude, at which stage, the material removal rate decreases. When the grain size is large compared to the vibration amplitude,there is a difficulty of abrasive renewal in the machining gap.Because of its higher hardness, B4C achieves higher removal rates than silicon carbide (SiC) when machining a soda glass work piece 33 percent lower for tool steel, and about 35 percent lower for sintered carbide. Workpiece impact-hardness. The machining rate is affected by the ratio of the tool hardness to the workpiece hardness. In this regard,the higher the ratio, the lower will be the material removal rate. For this reason soft and tough materials are recommended for USM tools.
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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