DT1410 - Materials and Processes in DesignUNIT 5 - POWDER METALLURGY - PRINCIPLES OF MACHINING PROCESSES

Powder Metallurgy

Powder Metallurgy is one of the four major methods of shaping metals:

MachiningHot and Cold plastic

deformationCasting 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

The three most important methods of producing metal powders are:

AtomizationChemical methodsElectrolysis

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

Disadvantages of P/M

Lower corrosion resistance

Reduced plastic propertiesDuctilityImpact strength

Unit 5Powder MetallurgyPrinciples of Machining ProcessesCHAPTER 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=OeN1etkFsbk

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

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