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test 3 notes - Chp. 21 Theory of Metal Machining Machining...

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Chp. 21 – Theory of Metal Machining Machining is the most important member of the Material Removal Process family - a sharp cutting tool is used to mechanically remove material to achieve desired geometry - 3 principal machining processes are turning, drilling, milling Why maching is important commercially Machining can be applied to a wide variety of the work materials Machining can be used to create any regular geometries (Flat planes, round holes, cylinders) Introducing variations in tool shape and path, irregular geometriescan be created Machining can produce dimensions very close to tolerance ranges Machining is capable of creating very smooth surface finishes Disadvantages Machining is waistful of materials The chips generated are the waisted material Machining processes are time consuming Basic Types of Machining Turning – uses single point tool o Cutting tool with single cutting edge is used to remove material from rotating workpiece o This generates a cylindrical shape Speed – Primary motion – rotating part Feed – Secondary Motion – cutting tool moving slowly in a direction parallel to axis of rotation Drilling – multiple edge cutting tool o Used to create round holes Milling – Mutiple cutting edge tool o A rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or str8 surface Speed – rotation of the milling cutter Feed – lateral motion of the part Cutting Tools Basic Geometry A cutting tool has one or more sharp edges The cutting edge serves to separate a chip from parent material There are 2 surfaces connected to cutting edge of tool: o Rake Face
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o Flank Rake Face Directs the flow of newly formed chips This is oriented at an angle – α α is measured relative to a plane perpendicular to the work surface The Flank Provides clearance between the tool and newly generated work surface This in turn protects the new work surface from abrasion, which harm surface finish Cutting Conditions Primary motion – cutting speed – (v) Secondary Motion – feed –(f) Depth of cut – (d) Collectively these are the cutting conditions Material Removal Rates – MRR= vfd Chip Formation – Orthogonal Cutting Model Uses a wedge shaped tool in which the cutting edge is perpendicular to the direction of the cutting speed 2 elements of geometry – rake angle and clearance angle Rake angle determines the direction that the chip flows as it is formed Actual Chip formation and differences from Orthogonal Cutting 1 st – shear deformation process does not occur along a plane, but within the zone 2 nd – Secondary shearing resulting from friction between the chip and the tool as the chip slides along rake face of tool 3 rd - Formation of the chip depends on the type of material being machined and cutting conditions o A) Discontinuous Chip – Brittle materials are machined at low cutting
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test 3 notes - Chp. 21 Theory of Metal Machining Machining...

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