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Metallic Processing Routes

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Joao Cardoso

on 3 January 2014

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Transcript of Metallic Processing Routes

Metallic Processing Routes
These have been widely used throughout the industry, in order to obtain desired final products and to process them in the most efficient and fastest way possibility
Nickel powder and its processing route
Nickel powder kindly given by DURIT®
This is a process used in manufacturing industry to cast a continuous length of metal
Continuous Casting

The powder can be produced through different routes:
Solid state reduction
Atomization from the melt

Powder Metallurgy
Shaped casting is used to conform pieces with irregular design using molds. It’s a non continuous process

Shaped Casting
General aspects
Different sintering processes

Solid-state reduction
The ore goes through a furnace, mixed with carbon (coke) that will reduce the mineral
Once finished, a cake sponge of the metal (i.e. iron, copper) remains, that will then be crushed, separated from the non-metal and sieved to produce the powder
There are no refining operations involved, so the purity relies only on the purity of the ore

Solid-state reduction
Typically the particles originated are irregular and even porous, due to the formation of gases during the reduction process
[10] copper oxide and reduced copper

Gas/water atomization
By creating a thin stream of molten metal and subjecting it to a high pressure gas jet, the metal is disintegrated and turned into thousands of small droplets
Typically the particles are very even in shape (spherical) and have a good dimensional range control

Gas/water atomization
The process is here represented, and the shape of the particles varies depending on the use of gas or water (gas gives more spherical particles)
Consists on depositing metal in a spongy powdery state (typically from solution or mineral) by applying an electrical current, on which the metal will be reduced from its ionic state
For process control several variables are taken under consideration, such as current density, electrolyte concentration and solution temperature

The reduction of metal ions occurs under oxidative reduction of the corresponding minerals (or if they’re dissolved in a solution) by the action of strong reactants (for the reduction of Ti it is used molten CaCl2, at temperatures as high as 900ºC)

Particle obtained from electrolysis and chemical processing
The final properties of the powders obtained in either way may vary and always require further processing before the melt, to obtain the best homogenization possible
Shape is typically very irregular and with great variation in size
[12] nickel particles from electrolysis

What is sintering
Sintering is a method used to create solid compacts out of pressed powders (ceramic or metal), at a temperature below the melting point of the main constituent, in order to increase its strength by bonding at an atomic level all the grains
During the firing process, atomic diffusion drives powder surface elimination in different stages, starting from the formation of necks between powders to final elimination of small pores at the end of the process.

Sintering - general aspects
The sintering process is governed by the following parameters:
temperature and time
particle size
composition of the powder mix
density of the powder compact
composition of the protective atmosphere in the sintering furnace

Sintering Stages
Burn-off zone
The lubricants (contained in the compacts) are burned off between 250 °C and 700 °C
Hot zone
The iron powder parts are sintered at 1120 – 1150 °C
Carbon restoring zone
Superfically decarbonized parts can be recarbonized at 800 – 900 °C
Cooling zone
The sintered patrs are cooled down to approx. 250 – 150 °C, before being exposed to air

Sintering Stages
Different types of sintering processes
Spark plasma sintering (fast method)
Hot isostatic pressing (expensive method)
Cold isostatic pressing
Microwave heating
Hot pressing
Inductive heating
Indirect resistance heating
Direct hot pressing


Spark Plasma Sintering (SPS)
Use of the DC current generating heat internally
Full density and controlled porosity
Pre-forming and binders not necessary
Retains nanometric particle structure
Saving of times and energy (heating rates exceeding 300 °C/min)
Ease of use
Spark Plasma Sintering (SPS)
Hot Isostatic Pressing (HIP)
Pressure acts from every direction
Use of the inert gas up to 2000 bar
Use of temperature up to 2000 °C (for nickel 1320 °C)
Time and energy are not spared in this process (heating rates normally 10 °C/min)

Hot isostatic Pressing (HIP)
In this process a bar of metal is forced through a die orifice by a compressive force.

The extrude piece that emerges has the desired shape and a reduced cross-sectional area

Products: rods and tubing that have rather complicated cross-sectional geometries

This process is used in aluminum and copper alloys but, using the proper lubricant, it can be used in steel.

Mechanical way of deforming a single piece of a normally hot metal. This can be achieved in two different ways: by the application of successive blows or by continuous squeezing.

Forged articles have outstanding grain structures and the best combination of mechanical properties.

Open die forging

Two dies, with simple geometric
shape, strike and deform the workpiece.

The metal is never completely confined or
restrained in the dies.

Closed die forging

This is a process in which the dies
move towards each other and
covers the workpiece in whole or
in part.
Coming from above, the impact of
the top die on the raw material
forms it into the required forged form.

This process consists of passing a piece of metal between two rolls through a space smaller than the material thickness
A reduction in thickness results from compressive stresses exerted by the rolls.

Wire drawing
Drawing is the pulling of a metal piece through a die having a tapered bore by means of a tensile force that is applied on the exit side
A reduction in cross section results, with a corresponding increase in length.

The total drawing operation may consist of a number of dies in a series sequence

Rod, wire and tubing products are commonly fabricated in this way.

This process transforms a flat metal sheet in a new object with a new shape (flat or concave), but without a substantial alteration in thickness.

Usually, this process is preformed at room temperature.

Deep drawing
The process
The metallic powder will be treated in the same way as a ceramic, following these steps:
Powder pressing
Sintering for 4 hours at 1150 ºC (to ensure maximum densification)
Analysing the piece and possible manual forging for shape and outer microstructure refinement
Sand Casting
Mold made of sand, various types of molds could be done with sand, like: green sand, dry sand and skin dry sand
Is a relatively cheap method, and more than 70% of the metals are conformed using sand molds
Sufficiently refractory to be used in high melting temperature metal foundries
Shell Molding
Mold produced applying sand covered with a resin on a permanent pattern
Used to pieces that require high precision and normally with small or medium size
[1] http://www.doral.com.au/view/products/what-we-produce
[2] http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=266
[3] http://www.cam.ac.uk/
[4] “Materials Science and Engineering- an introduction”, William D. Callister, Jr.; 7ed Edition;John Wiley & Sons, Inc.; 2007
[5] http://www.welded-steelpipes.com/
[6] http://www.substech.com/dokuwiki/doku.php?id=deep_drawing
[7] Notes from "Metallurgic Technology"
[8] http://www.harperintl.com/news-and-events/harper-chosen-by-allomet-corporation-for-advanced-rotary-furnace-for-unique-metal-powder-processing/
[9] http://mpi-eg.com/MPI/what-is-pm.html
[12] Notes from "Desenvolvimento Microestrutural"
[13] Picture from: German, R. M., Sintering Theory and Practice, John Wiley & Sons, New York, 1996
[14] http://riad.usk.pk.edu.pl/~mnykiel/iim/KTM/MP/DOWNLOAD/pdf/CHAPT06.PDF
[15] http://sps.fdc.co.jp/whats/whats3.html
[16] http://www.azom.com/article.aspx?ArticleID=5769
[17] http://www.vam.ac.uk/content/journals/conservation-journal/issue-11/sand-cast-aluminium/
[18] http://www.mdunas.com.br/cascas.htm
[19] http://www.compuland.com.br/boldor/shell.htm
[20] http://www.substech.com/dokuwiki/doku.php?id=die_casting
[21] http://www.afsinc.org/about/content.cfm?ItemNumber=6920
[22] http://www.spuncast.com/
[23] http://www.custompartnet.com/wu/investment-casting
Die Casting
Mold produced from two hard metal machined parts
Mostly used to non-ferrous metals: Zn, Cu, Al...
Relatively expensive method, used to large scale production to dilute the investment
Good surface finish and good final dimensions

Centrifugal Casting
A permanent mold spinning that force the poured metal against the mold wall
Good technique to conform thin wall cylinders
Good mechanical properties obtained, used to produce pressure vessels, pipes, train wheels, flywheels...
Investment or lost-wax casting
Good method to produce small castings of high-performance alloys, that requires accuracy
Expensive general process, however, has lower equipment costs than other techniques,
Used in small and high added value productions
Powder Production
Investment or lost-wax casting
Centrifugal Casting
Die Casting
Shell Molding
Sand Molding
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