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MATERIAL REMOVAL PROCESS - Coggle Diagram
MATERIAL REMOVAL PROCESS
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FUNDEMENTAL IN CUTTIING
TEMPERATURE
- Excessive temperature lowers the strength, hardness, stiffness, and wear resistance of the cutting tool; tools also may soften and undergo plastic deformation; thus tool shape is altered
- Increased heat causes uneven dimensional changes in the part being machined, making it difficult to control its dimensional accuracy and tolerances.
- Excessive temperature rise can induce thermal damage and metallurgical changes in the machined surface, adversely affecting its properties.
TEMPERATURE DISTRIBUTION
- Because the sources of heat generation in machining are concentrated in the primary shear zone and at the tool–chip interface, it is to be expected that there will be severe temperature gradients in the cutting zone.
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MACHINABILITY
The machinability of a material is usually defined in terms of four factors:
- Surface finish and surface integrity of the machined part.
- Tool life
- Force and power required
- The level of difficulty in chip control.
CUTTING TOOL MATERIALS
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HIGH SPEED STEELS
- developed to machine at higher speeds than was previously possible
- suitable especially for (a) high, positive rake-angle tools (b) interrupted cuts, (c) machine tools with low stiffness that are subject to vibration and chatter, and (d) complex and single-piece tools
- available in wrought (rolled or forged), cast, and powder-metallurgy forms.
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CAST COBALT ALLOYS
- not as tough as high-speed steels and are sensitive to impact forces
- less suitable than high-speed steels for interrupted cutting operations.
- used only for special applications that involve deep, continuous roughing cuts at relatively high feeds and speeds
CARBIDES
- cannot be used as effectively where high cutting speeds (hence high temperatures) are involved.
- necessary to improve plant productivity because of their high hardness over a wide range of temperatures, high elastic modulus, high thermal conductivity, and low thermal expansion, carbides are among the most important, versatile, and cost-effective tool and die materials for a wide range of applications.
TYPES
TITANIUM CARBIDE
- consists of a nickel-molybdenum matrix.
- higher wear resistance than tungsten carbide but is not as tough
- suitable for machining hard materials (mainly steels and cast irons) and for cutting at speeds higher than those appropriate for tungsten carbide
TUNGSTEN CARBIDE
- consists of tungsten-carbide particles bonded together in a cobalt matrix.
- The amount of cobalt present, ranging typically from 6 to 16%, significantly affects the properties of tungsten-carbide tools
- used for cutting steels, cast irons, and abrasive nonferrous materials and largely have replaced HSS tools because of their better performance.
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CUTTING FLUIDS
FUNCTION
- Reduce friction and wear, thus improving tool life and the surface finish of the workpiece.
- Cool the cutting zone, thus improving tool life and reducing the temperature and thermal distortion of the workpiece.
- Reduce forces and energy consumption
- Flush away the chips from the cutting zone, and thus prevent the chips from interfering with the cutting process, particularly in operations such as drilling and tapping
- Protect the machined surface from environmental corrosion.
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LATHE
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SPECIFICATIONS
- Its swing, the maximum diameter of the workpiece
- The maximum distance between the headstock and tailstock centers.
- The length of the bed
OPERATIONS
FORM TOOLS
- to produce various shapes on solid, round workpieces by moving the tool radially inward while the part is rotating
BORING
- performed inside hollow workpieces or in a hole made previously by drilling or other means
DRILLING
- mounting the drill bit in a chuck in the tailstock quill.
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MILLING MACHINE
TYPES OF
PROCESS
PERIPHERAL MILLING
- the axis of cutter rotation is parallel to the workpiece surface.
- The cutter body, which generally is made of high-speed steel, has a number of teeth along its circumference
- Cutters for peripheral milling may have straight or helical teeth, resulting in orthogonal or oblique cutting action
FACE MILLING
- the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface.
END MILLING
- important and common machining operation because of its versatility and capability to produce various profiles and curved surfaces.
- The cutter, called an end mill has either a straight shank (for small sizes) or a tapered shank (for larger cutter sizes) and is mounted into the spindle of the milling machine.
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ABRASIVE MACHINING
- One of the best methods for producing accuracy and fine finishing on parts is abrasive machining
- a small, hard particle having sharp edges and an irregular shape, unlike the cutting tools described earlier
- capable of removing small amounts of material from a surface through a cutting process that produces tiny chips.
- used in finishing processes for heat-treated metals and alloys and for very hard parts in applications such as (a) finishing of ceramics and glasses, (b) cutting off lengths of bars, structural shapes, masonry, and concrete, (c) removing unwanted weld beads and spatter, and (d) cleaning surfaces with jets of air or water containing abrasive particles.
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