DT1410 - Materials and Processes in Design Unit 5 - Powder Metallurgy - Principles of Machining Processes

Powder Metallurgy Machining Hot and Cold plastic deformation Casting Powder Metallurgy is one of the four major methods of shaping metals: Machining Hot and Cold plastic deformation Casting P/M

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.

Powder Metallurgy The basic conventional process of making P/M parts consists of two basic steps: Compacting (molding) Sintering

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

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.

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

Powder Metallurgy http://www.youtube.com/watch?v=n_FW7Q2xO5o

Metal Powders A number of different metals and their alloys are used in P/M: Iron Alloy steel Stainless steel Copper Tin Lead

Metal Powders Atomization Chemical methods Electrolysis processes The three most important methods of producing metal powders are: Atomization Chemical methods Electrolysis processes

Powder Compaction Compacting or pressing gives powder products their shape. Pressing and Sintering techniques can be separated into two types: Conventional Alternative

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

Powder Compaction Alternative powder compaction can be classified into: Alternative compaction methods Combined compaction and sintering Alternative sintering methods

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.

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

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

Advantages of P/M Almost as strong as wrought steels Lighter weight parts Ability to impregnate with oils, fillers, other materials with desirable properties

Lower corrosion resistance Reduced plastic properties Disadvantages of P/M Lower corrosion resistance Reduced plastic properties Ductility Impact strength

Unit 5 Powder Metallurgy Principles of Machining Processes Chapter 11 - Principles of Machining Processes

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.

Basic Machining Processes Turning Characteristics Work rotates, tool moves for feed Type of Machine Lathe & vertical boring mill http://www.youtube.com/watch?v=O eN1etkFsbk

Parting on the Lathe http://www.youtube.com/watch?v=1mkg73G0Vho&playnext=1&list= PL8D35020DEFB12A92

Turning – Horizontal Lathe

CNC Turret Lathe Videos http://www.machinetools.net.tw/lathe/taiwan_cnc_turret_lathes.htm

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

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

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

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

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

Basic Machining Processes Planing Characteristics Work reciprocates while tool is stationary Tool is movable, worktable is not Type of Machine Planer

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

Basic Machining Processes Vertical Bandsawing Characteristics Endless band moves downward, cutting the workpiece Workpiece moves Type of Machine Vertical bandsaw

Basic Machining Processes Vertical Bandsawing Characteristics Endless band moves downward, cutting the workpiece Workpiece moves Type of Machine Vertical bandsaw

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

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

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

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

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

Basic Machining Processes Drilling/Reaming Characteristics Drill or reamer rotates while work is stationary Type of Machine Drill presses Vertical milling machine

Basic Machining Processes Drilling/Reaming Characteristics Drill or reamer rotates while work is stationary Type of Machine Drill presses

Basic Machining Processes Drilling/Reaming Characteristics Work turns while drill or reamer is stationary Type of Machine Engine lathes Turret lathes Automatic Screw Machines

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

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.

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).

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.

Motion and Parameters: Speed, Feed, and 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.

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.

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

Basic Machining Processes Cutting Tool Geometry:

Basic Machining Processes Cutting Tool Geometry:

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