MMM LECTURE NOTES FINAL.pdf

The inlet water is typically pressurised between 1300

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method is not suitable for cutting hard materials. The inlet water is typically pressurised between 1300 4000 bars. This high pressure is forced through a tiny hole in the jewel, which is typically o.18 to 0.4 mm in diameter.
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Modern Manufacturing Methods Applications Water jet cutting is mostly used to cut lower strength materials such as wood, plastics and aluminium. When abrasives are added, (abrasive water jet cutting) stronger materials such as steel and tool steel can be cut. Advantages of water jet cutting There is no heat generated in water jet cutting; which is especially useful for cutting tool steel and other metals where excessive heat may change the properties of the material. Unlike machining or grinding, water jet cutting does not produce any dust or particles that are harmful if inhaled. Disadvantages of water jet cutting One of the main disadvantages of water jet cutting is that a limited number of materials can be cut economically. Thick parts cannot be cut by this process economically and accurately. Taper is also a problem with water jet cutting in very thick materials. Taper is when the jet exits the part at different angle than it enters the part, and cause dimensional inaccuracy . Material removal rate the abrasive particles from the nozzle follow parallel paths for a short distance and then the abrasive jet flares outward like a narrow cone. When the
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Modern Manufacturing Methods sharp-edged abrasive particles of Al2O3 or SiC hit a brittle and fragile material at high speed, tiny brittle fractures are created from which small particles dislodge. The lodged out particles are carried away by the air or gas. The material removal rate VRR, is given by Fig., material removal rate in AJM process. where K = constant N = number of abrasive particles impacting/unit area da = mean diameter of abrasive particles, μm ra = density of abrasive particles, kg/mm3 Hw = hardness number of the work material n = speed of abrasive particles, m/s The material removal rate, cut accuracy, surface roughness, and nozzle wear are influenced by the size and distance of the nozzle; composition,strength, size, and shape of abrasives; flow rate; and composition, pressure,and velocity of the carrier gas. The material removal rate is mainly dependent on the flow rate and size of abrasives. Larger grain sizes produce greater removal rates. At a particular pressure, the volumetric removal rate increases with the abrasive flow rate up to an optimum value and
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Modern Manufacturing Methods then decreases with any further increase in flow rate. This is due to the fact that the mass flow rate of the gas decreases with an increase in the abrasive flow rate and hence the mixing ratio increases causing a decrease in the removal rate because of the decreasing energy available for material removal.
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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