D1
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Powder-Metal Processing and Equipment
• Availability of a wide range of metal-powder compositions
• Net-shape forming and overall economics
• Automotive 70% of PM market
• The most commonly used metals in PM are iron, copper, aluminum, tin, nickel, titanium,
and the refractory metals. For parts made of brass, bronze, steels, and stainless steels,
prealloyed powders are used
• Competitive with processes such as casting, forging, and machining, particularly for relatively
complex parts made of high strength and hard alloys
• Although most parts weigh less than 2.5 kg, they can weigh as much as 50 kg
D2
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Production of metal powders
1. Powder production
2. Blending
3. Compaction
4. Sintering
5. Finishing operations
• Many processes depending on
requirements (more processes for same
powders)
• Microstructure, bulk and surface
properties, chemical purity, porosity, shape,
and size distribution
• Particle sizes produced range from 0.1 to
1000 mm
D3
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• Atomization
• Liquid-metal stream
• The stream is broken up by jets of
inert gas or air
• Parameters: temperature of the molten
metal, rate of flow, nozzle size, and jet
characteristics
• More spherical particles
• Rotating consumable electrode in He
D4
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• Reduction
• Metal oxide in gas (H2, CO), particelle fine ridotte
• Spongy and porous, sized spherical or angular
shapes
• Electrolytic Deposition
• Aqueous solutions or fused salts.
• Among the purest available powders
• Carbonyls
• E.g. Fe(CO)5 or Ni(CO)4 , reaction with CO
• Small, dense, uniformly spherical particles of high
purity
• Comminution
• Crushing, milling in a ball mill, or grinding of brittle
or less ductile metals into small particles
• With brittle materials, particles have angular shapes;
with ductile metals, they are flaky not particularly
suitable for powder-metallurgy applications
• Mechanical Alloying
• powders of two or more pure metals are mixed in a
ball mill
• Miscellaneous Methods
• Precipitation from a chemical solution, Production of
fine metal chips by machining, Vapor condensation.
• Nanopowders, Microencapsulated Powders
D5
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Blending and mixing
• Screen analysis
• Mesh size of 30 has an opening of 600 µm, size 100 has 150 µm
• Sedimentation, Microscopic analysis, Light scattering, Optical
methods, Suspending particles
• Particle Shape
• Aspect ratio (10 for flake-like or needle-like)
• Shape Factor
• Shape index, shape factor (SF) S/V
• Size Distribution, flow properties,
compressibility, density
• Different powders, homogeneity,
lubricants (0.25-5%), binders and additives
• Risks and practices
• Contamination or deterioration
• Work-hardening
• Mixing in air, in inert atmospheres (to avoid oxidation), or in
liquids (lubricants)
• Hazards
• Aluminum, magnesium, titanium, zirconium, and thorium
D6
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Compaction
• The presses used are actuated either hydraulically or mechanically
• Generally room temperature
• Green compact (very fragile)
• Correct size distribution
(if all particles are of the same size,
theoretical porosity at least 24 vol%)
• Effect of pressure and friction
(a) Compaction of metal powder to form a
bushing. The pressed-owder part is called
green compact. (b) Typical tool and die set
for compacting a spur gear.
D7
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
D8
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
A 7.3-MN mechanical press for
compacting metal powder
D9
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• Pressure ranges from 70 MPa for aluminumto 800 MPa for high-density iron parts
• Effect of the characteristics and shape of the particles, the method of blending, and the lubricant
• Press capacities are usually around 1.8 to 2.7 MN
• For small tonnage, crank- or eccentric-type mechanical presses are used
• For higher capacities, toggle or knuckle-joint presses are used
• Hydraulic presses with capacities as high as 45 MN can be used for large parts
• The higher the pressing speed, the greater is the tendency to trap air in the die cavity
D10
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Isostatic Pressing
• Cold isostatic pressing (CIP): flexible rubber
mold typically made of neoprene rubber,
urethane, polyvinyl chloride, or another
elastomer – Generally use of water – Most
common pressure is 400 MPa (up to 1000 MPa)
• Hot isostatic pressing (HIP): container
generally in high-melting-point sheet metal –
Pressurizing medium is high-temperature inert
gas or a vitreous (glass-like) fluid – Common
conditions 100 MPa and 1200°C – Almost 100%
density – Superalloys and Aerospace – High
costs and low productivity (less than 10.000
parts/year)
D11
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Miscellaneous Compacting and Shaping Processes
• Powder-injection Molding: The molded green parts are placed in
a low-temperature oven to burn off the plastic (debinding), or the
binder is removed by solvent extraction – Complex shapes, small
thickness (down to 5 mm)
• Powder forging: powder is fed into the roll gap in a two-high
rolling mill
• Extrusion: Hot process
• Pressureless Compaction: Porous metal parts
• Spray Deposition: Shape-generation process
Capabilities, with respect to part size and shape
complexity, available from various PM operations.
PF = powder forging.
D12
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Punch and Die Materials
• Most common die materials are air- or oil-hardening tool steels with a hardness range from 60 to 64 HRC
• Tungsten-carbide dies are used for more severe applications
• Too large clearance between punch and die allows the metal powder to enter the gap (wear, < 25 µm )
• Die and punch surfaces must be lapped or polished for increasing life
Sintering
• Green compacts are heated in a controlled atmosphere furnace to a temperature below the melting point
• Most common gases: H2, N2, hydrocarbons, NH3
• An oxygen-free atmosphere is essential for iron and iron-based compacts
• A vacuum generally is used for sintering refractory-metal alloys and stainless steels
D13
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• The sintering mechanisms are diffusion, vapor-phase transport, and liquid-phase sintering
• In spark sintering loose metal powders are placed in a graphite mold, heated by electric current
•
• The sintering mechanisms are diffusion, vapor-phase transport, and liquid-phase sintering
• In spark sintering loose metal powders are placed in a graphite mold, heated by electric current
• Depending on temperature, time, and processing history different structures and porosities can be obtained
• Temperature is 70-90% of Tm, time from 10 min (Cu, Fe) up to 8 h (Ti)
• Generally, with density less than 80% of its theoretical density, the pores are interconnected.
• Continuous-sintering furnaces: Burn-off chamber, High-temperature chamber and Cooling chamber
D14
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
D15
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
D16
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
Secondary and Finishing Operations
• Coining and sizing: dimensional accuracy and improvement of strength and surface finish
• Impact forging: good surface finish, good dimensional tolerances, and a uniform and fine grain size
• Machining, Grinding, Plating, Heat treating
• Fluid impregnation: 30 vol% of oil in bearings
• Infiltration (slug of a lower-melting-point metal is placed in contact with the sintered part)
• Elctroplating
Design Considerations
• The shape of the compact must be
kept as simple and uniform as
possible
• Provision must be made for ejection
• PM parts should be made with the
widest acceptable dimensional
tolerances for tool life
• Part walls generally should not be
less than 1.5 mm thick
• Simple steps if the size doesn’t
exceed 15% of the overall part length
D17
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• Letters can be pressed if they are
oriented perpendicular to the direction of
pressing
• Flanges or overhangs can be produced
but long flanges can be broken upon
ejection
• A true radius cannot be pressed into the:
chamfers or flats are preferred
• Keys, keyways, and holes can be formed
during powder compaction
• Notches and grooves can be made if they
are oriented perpendicular to the pressing
direction.
• Dimensional tolerances of sintered PM
parts are usually on the order of ±0.05 to
0.1 mm
D18
University of Rome Tor Vergata
Manufacturing Technologies Faculty of Engineering
Bachelor's Degree in Engineering Sciences
• Near-net shape
• High initial cost of punches, dies, and equipment
• Generally economical over 10,000 pieces
• Cost increases significantly with HIP and PIM
• Labor costs are not as high in other processes
• Skills required are not as high
Economics
Yearly global flow of ferrous powder for structural applications. Sankey diagram, the material flows from left to right and the
width of the lines are proportional to the mass. Most data sources used to make the diagram are from 2010 to 2015
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