dt1410 - materials and processes in design
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DT1410 - Materials and Processes in Design. Unit 5 - Powder Metallurgy - Principles of Machining Processes. Powder Metallurgy. Powder Metallurgy is one of the four major methods of shaping metals: Machining Hot and Cold plastic deformation Casting P/M. Powder Metallurgy. - PowerPoint PPT PresentationTRANSCRIPT
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DT1410 - Materials and Processes in DesignUNIT 5 - POWDER METALLURGY - PRINCIPLES OF MACHINING PROCESSES
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Powder Metallurgy
Powder Metallurgy is one of the four major methods of shaping metals:
MachiningHot and Cold plastic
deformationCasting P/M
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Powder Metallurgy
The Powder Metallurgy process is essentially the compression of finely divided metal powder into briquettes of desired shape that is then heated, but not melted to form a metallurgical bond between the particles.
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Powder Metallurgy
The basic conventional process of making P/M parts consists of two basic steps:Compacting (molding)Sintering
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Powder Metallurgy
Compacting: Loose powder (or a blend of different
powders) is placed in a die and is then compacted between punches.
Commonly done at room temperature Compounded part is known as a
briquette
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Powder Metallurgy
Sintering:
The briquette is heated to a temperature high enough to cause the powder particles to bond together by solid-state diffusion.
The powder particles also homogenize any alloy constituents into the powder.
Melting does not normally occur.
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Powder Metallurgy
After Sintering: The P/M part is now ready for
secondary operations: Sizing Machining Heat treating Tumble finishing Impregnating with oils, plastics, or
liquids
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Powder Metallurgy
http://www.youtube.com/watch?v=n_FW7Q2xO5o
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Metal Powders
A number of different metals and their alloys are used in P/M: Iron Alloy steel Stainless steel Copper Tin Lead
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Metal Powders
The three most important methods of producing metal powders are:
AtomizationChemical methodsElectrolysis
processes
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Powder Compaction
Compacting or pressing gives powder products their shape.
Pressing and Sintering techniques can be separated into two types: Conventional Alternative
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Powder Compaction
Conventional powder compaction: The powder is press
unidirectionally in a single- or double-acting press
Unlike liquids, which flow in all direction under pressure, powders tend to flow mainly in the direction of the applied pressure
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Powder Compaction
Alternative powder compaction can be classified into: Alternative compaction
methods Combined compaction and
sintering Alternative sintering
methods
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Powder Compaction
Advanced/Alternative Processes: Cold Isostatic Pressing (CIP)
The process of compacting a powder by exerting a constant high pressure at room temperature.
Hot Isostatic Pressing (HIP) The process of compacting
a powder by exerting a constant high pressure at elevated temperatures.
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Sintering
In solid-phase sintering the green compact part must be heated to 60 to 80% of the melting point of the constituent with the lowest melting point. Time required 30 minutes to 2
hours in a sintering furnace to produce the metallurgic bonds
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Characteristics of PM Parts
Superior engineered microstructures Consistent properties and quality Controlled porosity for filters/self-
lubrication Very low scrap loss Wide variety of shape designs Unlimited choice of alloys and composites Low cost, high volume production Good surface finishes Close dimensional tolerances Little or no machining required
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Advantages of P/M
Almost as strong as wrought steels
Lighter weight parts Ability to impregnate
with oils, fillers, other materials with desirable properties
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Disadvantages of P/M
Lower corrosion resistance
Reduced plastic propertiesDuctilityImpact strength
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Unit 5Powder MetallurgyPrinciples of Machining ProcessesCHAPTER 11 - PRINCIPLES OF MACHINING PROCESSES
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Principles of Machining Processes
Machining is essentially the process of removing unwanted material from wrought (rolled) stock, forgings, or casting to produce a desired shape, surface finish, and dimension.
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Basic Machining Processes
Turning Characteristics
Work rotates, tool moves for feed Type of Machine
Lathe & vertical boring mill http://www.youtube.com/watch?v=Oe
N1etkFsbk
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Parting on the Lathe
http://www.youtube.com/watch?v=1mkg73G0Vho&playnext=1&list=PL8D35020DEFB12A92
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Turning – Horizontal Lathe
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CNC Turret Lathe Videos
http://www.machinetools.net.tw/lathe/taiwan_cnc_turret_lathes.htm
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Basic Machining Processes
Milling Characteristics
Cutter rotates and cuts on periphery Work feeds into the cutter and can be
moved in 3 axes. Type of Machine
Horizontal milling machine
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Basic Machining Processes
Face Milling Characteristics
Cutter rotates to cut on its end and periphery of vertical workpiece
Type of Machine Horizontal mill, profile mill, machining
center
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Basic Machining Processes
Vertical Milling Characteristics
Cutter rotates to cut on its end and periphery
Work moves on 3 axes for feed or position
Spindle also moves up or down Type of Machine
Vertical milling machine, machining center
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Basic Machining Processes
Vertical Milling Characteristics
Cutter rotates to cut on its end and periphery
Work moves on 3 axes for feed or position
Spindle also moves up or down Type of Machine
Vertical milling machine, machining center
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Basic Machining Processes
Shaping Characteristics
Work is held stationary and tool reciprocates
Work can move in 2 axes while toolhead can move up or down
Type of Machine Horizontal and vertical shapers
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Basic Machining Processes
Planing Characteristics
Work reciprocates while tool is stationary
Tool is movable, worktable is not Type of Machine
Planer
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Basic Machining Processes
Horizontal Sawing Characteristics
Work is held stationary while saw either cuts in one direction (bandsawing)
Saw reciprocates while being fed downward
Type of Machine Horizontal bandsaw,
reciprocating cutoff saw
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Basic Machining Processes
Vertical Bandsawing
Characteristics Endless band moves downward,
cutting the workpiece Workpiece moves
Type of Machine Vertical bandsaw
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Basic Machining Processes
Vertical Bandsawing
Characteristics Endless band moves downward,
cutting the workpiece Workpiece moves
Type of Machine Vertical bandsaw
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Basic Machining Processes
Broaching Characteristics
Workpiece is stationary while a multi-tooth cutter is moved across the surface
Each tooth cuts progressively deeper Type of Machine
Vertical/horizontal broaching machine
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Basic Machining Processes
Horizontal Spindle Surface Grinding Characteristics
Rotating grinding wheel moved up or down feeding into workpiece
Worktable holds piece and can move in 2 axes
Type of Machine Surface grinders
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Basic Machining Processes
Vertical Spindle Surface Grinding Characteristics
Rotating grinding wheel can be moved up or down feeding into workpiece
Circular table rotates Type of Machine
Blanchard-type surface grinders
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Basic Machining Processes
Cylindrical Grinding Characteristics
Rotating grinding wheel contacts turning workpiece that reciprocates from end to end
Workhead can be moved into and away from workpiece
Type of Machine Cylindrical grinders
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Basic Machining Processes
Centerless Grinding
Characteristics Work is supported by a work rest
between a large grinding wheel and a smaller feed wheel
Type of Machine Centerless grinder
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Basic Machining Processes
Drilling/Reaming Characteristics
Drill or reamer rotates while work is stationary
Type of Machine Drill presses Vertical milling machine
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Basic Machining Processes
Drilling/Reaming Characteristics
Drill or reamer rotates while work is stationary
Type of Machine Drill presses
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Basic Machining Processes
Drilling/Reaming Characteristics
Work turns while drill or reamer is stationary
Type of Machine Engine lathes Turret lathes Automatic Screw Machines
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Basic Machining Processes
Boring Characteristics
Work rotates, tool moves for feed on internal surfaces
Type of Machine Engine lathes Horizontal/vertical Turret lathes Vertical boring mills
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Motion and Parameters:Speed, Feed, and Depth of Cut
Cutting Speed:The rate at which the
workpiece moves past the tool or the rate at which the rotating surface of the cutting edge of the tool moves past the workpiece.
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Motion and Parameters:Speed, Feed, and Depth of Cut
Feed Motion: the advancement of the
cutting tool along the workpiece (for lathes) or the advancement of the workpiece past the tool (for milling machines).
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Motion and Parameters:Speed, Feed, and Depth of Cut
Feed Rate:The distance that a
cutting tool moves in either one revolution (feed per revolution) or in one minute (feed per minute) in a machining operation.
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Motion and Parameters:Speed, Feed, and Depth of Cut
Depth of Cut: The thickness of the layer
of material sheared from a workpiece by a cutting tool in a machining operation.
The depth of cut determines the width of the chips produced in the machining operation.
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Basic Machining Processes
Machinability: the ease or relative ease
with which a workpiece can be machined
compared by measuring the power required and cutting tool life for each workpiece material.
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Basic Machining Processes
Cutting Tool Geometry: Tool Geometry (shape)
varies considerably depending on the machining application.
The shape and angle of cut of the tool are key to the proper removal of material
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Basic Machining Processes
Cutting Tool Geometry:
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Basic Machining Processes
Cutting Tool Geometry:
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Basic Machining Processes
Chip Formation/Chip Control: Chips that are shaped like
“9”s are preferred. This means the tool geometry, cutting speed, and depth are correct
Many cutting tool have “chip-breaking” geometries that help to produce the desired chip shape