A2 Technology

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Transcript A2 Technology

DT4 - Exam
A2 Technology
Product Design
Systems and Control Notes
Material Technology
Smart materials
Composite materials
Traditional materials
Smart Materials
Smart Materials
What are smart materials?
• Smart materials are materials that have
one or more properties that can be
significantly altered in a controlled fashion
by external stimuli, such as stress,
temperature, moisture, pH, electric or
magnetic fields.
What are the examples?
Piezoelectric materials
Shape memory alloys
Magnetic shape memory alloys
PH sensitive polymers
Halochromic materials
Chromogenic systems
What are Piezoelectric
• Piezoelectric materials are materials that
produce a voltage when stress is applied. Since
this effect also applies in the reverse manner, a
voltage across the sample will produce stress
within the sample. Suitably designed structures
made from these materials can therefore be
made that bend, expand or contract when a
voltage is applied.
• Buzzers are piezoelectric.
What are shape memory alloys?
• Shape memory alloys and shape memory
polymers are thermoresponsive materials
where deformation can be induced and
recovered through temperature changes.
What are shape memory alloys?
• An example is NiTinolTM (Nickel Titanium)
• Above its transformation temperature, Nitinol is
superelastic, able to withstand a large amount of
deformation when a load is applied and return to
its original shape when the load is removed.
Below its transformation temperature, it displays
the shape memory effect. When it is deformed it
will remain in that shape until heated above its
transformation temperature, at which time it will
return to its original shape.
Application of SMA
• Nitinol is used in medicine for
stents: A collapsed stent can be
inserted into a vein and heated
(returning to its original
expanded shape) helping to
improve blood flow. Also, as a
replacement for sutures where
nitinol wire can be weaved
through two structures then
allowed to transform into it's
pre-formed shape which should
hold the structures in place.
Further reading of SMA
• http://en.wikipedia.org/wiki/Shape_memory_alloy
Magnetic SMA
• Magnetic Shape Memory alloys are materials that
change their shape in response to a significant change in
the magnetic field.
PH sensitive polymers
• pH-sensitive polymers are materials which swell/collapse
when the pH of the surrounding media changes.
• The sensor is prepared by entrapping within a polymer
matrix a pH sensitive dye that responds, through visible
colour changes (see next slide) to spoilage volatile
compounds that contribute to a quantity known as Total
Volatile Basic Nitrogen (TVB-N).
PH sensitive polymers
• The ‘REF’ sample is outside the package. The others are
all inside. www.dcu.ie/chemistry/asg/pacquita/
Halochromic Materials
• Halochromic materials are commonly materials that
change their colour as a result of changing acidity. One
suggested application is for paints that can change
colour to indicate corrosion in the metal underneath
Chromogenic systems
• Chromogenic systems change colour in response to
electrical, optical or thermal changes. These include
electrochromic materials, which change their colour or
opacity on the application of a voltage (e.g. liquid crystal
displays), thermochromic materials change in colour
depending on their temperature, and photochromic
materials, which change colour in response to light - for
example, light sensitive sunglasses that darken when
exposed to bright sunlight.
• Flip a switch and an
electrochromic window can
change from clear to fully
darkened or any level of tint
• The action of an electric field
signals the change in the
window's optical and thermal
properties. Once the field is
reversed, the process is also
reversed. The windows
operate on a very low voltage
-- one to three volts -- and
only use energy to change
their condition, not to
maintain any particular state.
Kettles that change colour and
signs that glow-in-the-dark are two
recent examples of products
becoming ‘smarter’ as a result of
new materials. Colour-changing
thermochromic pigments are now
routinely made as inks for paper
and fabrics – and incorporated
into injection moulded plastics. A
new type of phosphorescent
pigment, capable of emitting light
for up to 10 hours, has opened up
entirely new design opportunities
for instrumentation, low-level
lighting systems etc.
• Photochromism is the reversible transformation of colour upon
exposure to light. This phenomenon is illustrated in sun glasses.
Quantum Tunneling Composites (or QTCs) are composite materials of
metals and non-conducting elastomeric binder, used as pressure sensors.
As the name implies, they operate using quantum tunneling: without
pressure, the conductive elements are too far apart to conduct electricity;
when pressure is applied, they move closer and electrons can tunnel
through the insulator. The effect is far more pronounced than would be
expected from classical (non-quantum) effects alone, as classical
electrical resistance is linear (proportional to distance), while quantum
tunneling is exponential with decreasing distance, allowing the resistance
to change by a factor of up to 1012 between pressured and unpressured
QTCs were discovered in 1996 and PeraTech Ltd was established to
investigate them further.
Smart Grease
Not really that new!
Composite materials
• Composite materials (or composites for
short) are engineered materials made from
two or more constituent materials with
significantly different physical or chemical
properties and which remain separate and
distinct on a macroscopic level within the
finished structure.
• The most primitive composite materials comprised straw and mud in
the form of bricks for building construction;
• the Biblical book of Exodus speaks of the Israelites being oppressed
by Pharaoh, by being forced to make bricks without straw being
provided. The ancient brick-making process can still be seen on
Egyptian tomb paintings in the Metropolitan Museum of Art.
• The most advanced examples perform routinely on spacecraft in
demanding environments. The most visible applications pave our
roadways in the form of either steel and aggregate reinforced
portland cement or asphalt concrete.
• Those composites closest to our personal hygiene form our shower
stalls and bath tubs made of fibreglass. Solid surface, imitation
granite and cultured marble sinks and counter tops are widely used
to enhance our living experiences.
There are two categories of constituent materials:
• Matrix (or binder) and reinforcement.
– At least one portion of each type is required.
The matrix material surrounds and supports the reinforcement materials by
maintaining their relative positions.
The reinforcements impart their special mechanical and physical properties
to enhance the matrix properties. A synergism produces material properties
unavailable from the individual constituent materials, while the wide variety
of matrix and strengthening materials allows the designer of the product or
structure to choose an optimum combination.
Engineered composite materials must be formed to shape. The matrix
material can be introduced to the reinforcement before or after the
reinforcement material is placed into the mold cavity or onto the mold
surface. The matrix material experiences a melding event, after which the
part shape is essentially set. Depending upon the nature of the matrix
material, this melding event can occur in various ways such as chemical
polymerization or solidification from the melted state.
• A variety of moulding methods can be used according to the enditem design requirements. The principal factors impacting the
methodology are the natures of the chosen matrix and reinforcement
materials. Another important factor is the gross quantity of material
to be produced. Large quantities can be used to justify high capital
expenditures for rapid and automated manufacturing technology.
Small production quantities are accommodated with lower capital
expenditures but higher labor and tooling costs at a correspondingly
slower rate. Most commercially produced composites use a polymer
matrix material often called a resin solution. There are many
different polymers available depending upon the starting raw
ingredients. There are several broad categories, each with
numerous variations. The most common are known as polyester,
vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene,
PEEK, and others.
• The reinforcement materials are often fibres but also commonly
ground minerals. The various methods described below have been
developed to reduce the resin content of the final product, or the
fibre content is increased. As a rule of thumb hand lay up results in a
product containing 60% resin and 40% fibre, whereas vacuum
infusion gives a final product with 40% resin and 60% fibre content.
The strength of the product is greatly dependent on this ratio, so this
increase in fibre content results in a dramatically stronger product.
• Fibreglass also known
as glass fibre) is material
made from extremely fine
fibres of glass. It is used
as a reinforcing agent for
many polymer products;
the resulting composite
material, properly known
as fiber-reinforced
polymer (FRP) or glassreinforced plastic (GRP),
is called "fiberglass" in
popular usage.
• Glassmakers throughout history have experimented with
glass fibers, but mass manufacture of fiberglass was
only made possible with the advent of finer machinetooling. In 1893, Edward Drummond Libbey exhibited a
dress at the World's Columbian Exposition incorporating
glass fibers with the diameter and texture of silk fibers.
What is commonly known as "fiberglass" today, however,
was invented in 1938 by Russell Games Slayter of
Owens-Corning as a material to be used as insulation. It
is marketed under the trade name Fiberglas, ® which
has become a generalised trademark.
Composites and Textiles
• Textile composites
• Textile composite materials consist of a polymer
matrix (thermoplastic or thermoset) combined
with a textile reinforcement. Materials of
particular interest to the group include
commingled glass/polypropylene fabrics, dry
fabrics (woven, warp-knitted or braided)
combined with thermoset resins via liquid
moulding, and carbon/epoxy thermoset
prepregs. Typical applications range from
structural parts for high volume cars to high
performance aerospace components.
Composites and Textiles
• Current activities are focused on prediction of processing and
mechanical properties, process modelling and the interactions
between manufacture and performance. Materials models are
developed from a geometric description for a general textile
structure. These are then implemented within models for
draping/forming and subsequent performance. Process modelling
for textile composites includes both formability (to eliminate wrinkles
and tears) and impregnation (to eliminate dry patches or lengthy fill
times). Using this approach, fabric iterations can be examined
quickly and cheaply for a wide range of textile styles including knits,
weaves, braids and hybrids
• http://www.nottingham.ac.uk/unimat/expertise/textiles/composites.ph
Composite Materials
• Further reading …
• Kevlar
• Carbon Fibre
Modern materials
Modern Materials
• Fabrics
– “Fast Skin”, Lycra, Polyester,
• Smart
– Nitinol, SMA, Thermo Chromic Film,
• Composites
– Plywood, MDF, carbon fibre, Kevlar
• Polymers
– Acrylic, H.I.P.S, polyester, nylon,
• Semi-conductors
– Silicon based semi-conductor
Modern Manufacturing methods
Modern Manufacturing Processes
Manipulating and shaping plastics
Cutting and shaping wood products
Forming and joining metals
Modern Manufacturing Processes
• Polymers
Injection Moulding
Blow Moulding
Rotational Moulding
Vacuum Forming
Injection Moulding
• Materials such as polystyrene, nylon,
polypropylene and polythene can be used
in a process called injection moulding.
• These are thermoplastics - this means
when they are heated and then pressured
in a mould they can be formed into
different shapes.
Injection Moulding
Injection Moulding
Injection Moulding
Injection Moulding Dies
Injection Moulding
Advantages of Injection moulding
The advantages of injection moulding are
that a large number of components can be
produced in a short time and all with a
consistently good finish and quality.
However when using with thermosetting
plastics they can cure in the hopper or the
screw, this causes a clog and halts
• Extrusion occurs one of two ways, either direct or
indirect extrusion. In direct extrusion the material is fed
through the die either using a ram or with a screw like
the one used in the injection moulding. However the
indirect extrusion works by forcing the die onto the
material so that the material is forced through the die.
• Direct extrusion can be used to produce a continuous
extrusion which can later be cut to the desired length.
Only simple shapes can be produced and often the
quality of the finish is quite poor.
Blow moulding
High pressure air blown in to inflate form to shape of the mould
Rotational moulding
Rotational moulding is very
different from other plastics
moulding techniques, and
those differences generate its
advantages. Rotational
moulding is a unique, openmoulding, low-pressure, hightemperature process that uses
biaxial rotation and heat to
produce hollow one-piece
plastic parts. Plastic footballs
are made like this
Rotational moulding
This process can be completed
in school. Moulds or formers are
made from a dense material,
such as MDF. High Impact
Polystyrene, is placed in the
vacuum former and heated.
Once the HIPs is soft the former
is pressed into the plastic and
the air is evacuated.
Cutting and Shaping
• Is it a place to go for a walk or a collective
name for a complex family of materials?
• Hardwood
• Softwood
• Manufactured Wood
Deciduous trees
Man made
Oak, Beech, Horse chestnut,
cherry, apple, Ash,
Pine, Cedar, Redwood
Plywood, MDF, chipboard,
modelling plywood, flexiply
Shaping WOOD
Forming ‘METAL’
• Is this a collective name for a variety of
metallic substances or…
• …do we only have one metal in the world?
• Ferrous
– Containing iron
• Steel
• Iron
• High carbon steels
• Non Ferrous
– No iron
• Copper, gold, silver, aluminium, zinc,
• ALLOYS http://en.wikipedia.org/wiki/Alloy
– Mixture of metals
Duralumin (durable aluminium)
– List of alloys
Shaping and forming METAL
• Riveting
• Brazing
• Soldering
Turning METAL
Turning METAL
• Melting two metals
(aluminium, steel) and
joining them with a
filler metal to fuse
both together.
• The filler must be the
same metal e.g. steel
for steel etc
• Heating two pieces of
steel and joining them
with a filler of brass to
join both together.
Brazing doesn’t fuse
the pieces together.
• The correct term for joining two dissimilar
materials together is…
Reactive Synthetic Glues
Urea resin glue
(1 part)
• Urea resin glue
(2 part)
Reactive Synthetic Glues
• Cyanoacrylate
– “Super glue” is a brand of this type of glue
• Epoxy
– “ARALDITE” is a brand of this type of glue
• Polyurethane
– “TITEBOND” is a brand of this type of glue
• Urea Resin
– “Cascemite” is a brand of this type of glue
Reactive Synthetic Glues
• Characteristics of reactive synthetic
– Used to permamnently bond dissimilar
materials together
– Give a stronger, waterproof bond
– Curing times vary
Reactive Synthetic Glues
• Contact adhesives “EVOSTICK”
• Contact adhesive is one which must be applied to both surfaces and
allowed some time to dry before the two surfaces are pushed
together. Some contact adhesives require as long as 24 hours to dry
before the surfaces are to be held together. Once the surfaces are
pushed together, the bond forms very quickly, hence, it is usually not
necessary to apply pressure for a long time. This means that there is
no need to use clamps, which is convenient.
• Natural rubber and Neoprene are commonly used contact
adhesives. Both of these elastomers undergo strain crystallization.
• Contact adhesives find use in laminates, such as bonding Formica
to a wooden counter, and in footwear, for example attachment of an
outsole to an upper
• Polyvinyl acetate (PVA or PVAc) is a rubbery
synthetic polymer. It is prepared by
polymerization of vinyl acetate monomer, also
referred to as VAM. Partial or complete
hydrolysis of the polymer is used to prepare
polyvinyl alcohol. Hydroylized alcohol product is
typically in the 87% to 99% range (converted
PVA). It was discovered in Germany by Dr. Fritz
Klatte in 1912.