unit 7 manufacturing processes: plastics and composites processing of plastics and composites

Unit 7Manufacturing Processes:Plastics and Composites

PROCESSING OF PLASTICS AND COMPOSITES

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Processing of Plastics and Composites

Composites: A materials category that

consists of a matrix or base material reinforced by another material.

The materials maintain their original identification but the properties of the combination are improved.


Composites:Matrix: In composite materials the matrix is

the outer layer of material in which the reinforcement is contained.

In metals, the background phase in which another phase is contained; steel is the matrix in which graphite flakes are present in gray cast iron.


Three Types of Composites:• PMCs – (Polymer Matrix Composites)

composite materials that have a reinforcing material in a polymer matrix.

• MMCs – (Metal Matrix Composites) composite materials that have reinforcing material in a metallic matrix.

• CMCs – (Ceramic Matrix Composites) composite materials that have reinforcing material in a ceramic matrix.


Three Types of Composites: Although the three types of

composites have some significant differences, they are similar in their general makeup.

Each has a polymer, metallic, or ceramic matrix.

The reinforcements used inside these matrices can vary.


Reinforcements:

The material added to the matrix of a composite to improve its properties, usually the strength or stiffness.


Composites differ from alloys, polymers, and ceramic compounds in that the matrix and reinforcement are separate from each other.

A material may be added to a metal, polymer, or ceramic for strengthening purposes and the material becomes part of the original material; reinforcements do not.


Reinforcements:

Vary from short or chopped fibers, flakes, and particles to filaments and wires to continuous woven fibers and honeycombs.

Short, discontinuous reinforcements increase mechanical strength

Better – continuous reinforcements which can transfer or redistribute a load throughout the composite.


PROCESSING METHODS FOR PLASTICS:

Blow molding

Injection molding

Extrusion


Blow Molding: Air is used to force a mass

of molten plastic against the sides of a mold shaped in the form of the desired end product.

Examples include: milk bottles, soft drink bottles, etc.

Extrusion Blow Molding

http://www.youtube.com/watch?v=ynsS2afrUzE




Injection Molding: A process in which the material to is

heated sufficiently to become fluid and then injected under pressure into a mold cavity.

There, it is cooled sufficiently to take the shape of mold, and then removed from the mold; polymers and ceramics are processed in this manner.

Metal die casting is very similar to injection molding.

Plastic Injection Molding

http://www.youtube.com/watch?v=jYkKBUFORco&feature=related




Extrusion: Usually under high pressure

and at elevated temperatures, forcing materials through a die containing the shape desired so that a shaped product is produced.

Metal and polymer shapes are produced using this method.

Extrusion

http://www.youtube.com/watch?v=WaB-dsB1Kfk&NR=1




OTHER MOLDING PROCESSES:Compression Molding

Thermoforming

Transfer Molding

Rotational Molding

Plastic Thermoforming

http://www.youtube.com/watch?v=U60mdDW5Ulc



Composites

Plastics and composites are fast replacing metals in a vast array of manufactured products

Why?

Because of the often high cost of metals and the large energy requirements in metal processing, and the high strength and light weight of plastics and composites.

Composites

NASA 360 Video

http://www.youtube.com/watch?v=tZhH2B-EI1IOr

http://www.youtube.com/watch?v=tZhH2B-EI1I

Composite Processing Methods

Methods to create and/or form the three types of composites:

PMCs – Prepregs Sheet-molding compound Molding Hand layup

Methods for forming Composites

To form PMCs (Polymer Matrix Composites)

Prepregs Sheet-molding compound Molding Hand layup Pultrusion Filament Winding Lamination

Methods for forming PMCs

Prepregs – an intermediate preimpregnated product:

Continuous strands of fiber are carefully aligned and then coated with the appropriate thermoplastic or thermoset resin

Made into sheets or tapes used to form a laminated product which is heated for curing

Pre-preg Materials

http://www.youtube.com/watch?v=IeST0vfDuhw&feature=related




Sheet-molding compound : Made from chopped fibers that

are deposited, with random orientation, on a resin-covered carrier film, such as polyethylene.

Another layer of resin covers the fibers

Then a top sheet or film (e.g. polyethylene) covers the resin.


Sheet-molding compound :

The resulting sandwich is pressed between rollers and coiled or kept as flat sheets.

Kept in a controlled environment for 24 hours to cure.

Sheet Molding Compounds

http://www.youtube.com/watch?v=IxaTwSBWz14




Molding: Some molding methods previously

discussed take advantage of the prepregs and molding compounds are compression and transfer molding.

In these cases the reinforcements are placed into the mold cavities before or during the application of the polymer.


Hand Layup:

The most common application of Hand Layup is the use of fiberglass.

Alternating layers of glass fiber fabric and resin are coated over a mold or form built in the shape of the desired end product.

Boat manufacturing is a popular application.

Automated Composite Lay-up

http://www.youtube.com/watch?v=y_TDd3bzDeM




Pultrusion: Fibers are pulled or drawn

through a liquid resin and then through a heated die that forms the desired shape.

Very much like extrusion except for the pulling rather than pushing of the material through the extrusion die.

Pultrusion

http://www.youtube.com/watch?v=4MoHNZB5b_Y




Filament Winding: Fiber is wound back and

forth on a cylindrical form. This method is used to

produce cylindrically shaped products such as tanks or other pressure vessels.

Filament Winding

http://www.youtube.com/watch?v=iOZl3v4RC18




Lamination: Laminating alternating layers of

resin containing the structural fiber.

Similar to the technique used with fiberglass; however, here the fibers are continuous throughout the material (in fiberglass, short pieces of glass fiber are randomly distributed throughout the resin).


TO FORM MMCS (METAL MATRIX COMPOSITES)

Liquid Matrix

Powder-Metallurgy Techniques

Liquid-Solid Processing

Methods for forming MMCs

Liquid Matrix – the typical MMC methods involve casting the molten matrix around solid reinforcements:

Using conventional casting techniques

Or, by using pressurized gas on the liquid matrix to force it into and around a preformed reinforcement

Reinforcements are often made of metal sheet or wire, or a ceramic fiber.

Liquid Matrix Molding

http://www.youtube.com/watch?v=o0PGDRjoDUc



Methods for forming MMCs

Powder-Metallurgy Techniques

The reinforcement fibers, whiskers, or particles are carefully mixed with the powdered metallic matrix so that they are uniformly distributed in the mixture.

The mixture is then compacted, Then sintered


To form CMCs (Ceramic Matrix Composites)

The most common process used in producing CMCs is slurry infiltration, in which the slurry contains the ceramic matrix powder.

A fiber pre-form of the desired product is hot pressed and impregnated with the slurry, then sintered.

Tool and Die Making

Specialty tooling is required to hold or form plastic materials until steps are taken in the process that alter the state of the material to make it rigid.

Thus, Tool and Die Making – the processes of building specialty production tooling to support manufacture of a product – is an integral and indispensible part of forming plastics and composites.


PROCESSING OF OTHER INDUSTRIAL MATERIALS

Other Important Industrial Materials

THE MORE IMPORTANT INDUSTRIAL MATERIALS USED IN MANUFACTURING INCLUDE:

Glass

Ceramics

Wood, wood products, and paper

Fabrics

Rubber

Natural materials

Constructions materials


NONMETALLIC MATERIALS ARE USED IN CONJUNCTION WITH METALS IN ALL TYPES OF PRODUCTS.

IN MANY CASES THESE MATERIALS ARE REPLACING METALS BECAUSE THEY ARE:

More economical

Stronger

Lighter

Easier to process


Glass: Consists primarily of fused silica

(SiO2), a major constituent of beach sand.

Glass withstands chemical attack and large variations in temperature

Lead added to glass provides shielding from ionizing radiation

Can be fashioned into optical lenses


Glass: A relatively new/developing

technology in the use of glass is fiber optics.

Glass Manufacturing Processes include:

Pressing Blow and Blow Operations Press and Blow Operations


Ceramics: Ceramic engineering materials are

among the most researched and developing technologies in modern production.

Ceramics are made from the metallic oxides of such metals as silicon, aluminum, and magnesium.

Clay-based ceramics are becoming increasingly popular.


Ceramics: Important properties of ceramics

include: Resistance to high heat

levels High strength Chemically inert Heat reflective Can be as hard as diamonds

and as light as aluminum.


Wood, wood products, paper:

Structural lumber for construction

Plywoods and other laminates Hardwoods (furniture and

flooring) Paper


Fabrics:

Clothing and upholstery Natural

Cotton, wool, flax, silk Synthetic

Polyesters, nylons, other plastic polymers


Rubber:

Natural rubber or Latex Derived from the natural

gum of the rubber tree. Coatings, tubing, hose,

tires, etc. Processing methods

similar to those of plastics


Construction Materials:

Those from which structures are built

Engineering Materials: Those from which products are

made.


CORROSION AND PROTECTION OF MATERIALS

Corrosion and Protection of Materials

Because many materials, especially metals, react chemically with their environments, it is often necessary to provide protective coatings and coverings for them to prevent or to slow surface deterioration – corrosion.


METALS CORRODE BY TWO MAJOR PROCESSES:

Direct Oxidation

Galvanic Corrsion


Metal Corrosion – Direct Oxidation:

Most common metals exist in nature chemically combined with other elements as various oxides (ores).

There is a natural tendency for refined metals to revert to their natural state.

Because air and water are both common agents, and since oxygen makes up such a large percentage of each …


Metal Corrosion – Direct Oxidation:

Metals react with the oxygen present to revert back in varying degrees to their original oxide (ore) state.

The oxidizing process, direct oxidation, can occur slowly as normal rusting, or quickly, as in the case of steel heated to high temperatures.


Galvanic Corrosion:

A common type of corrosion process in which a potential difference through an electrolyte causes a deplating (corroding) of one of the metals.


Metal Corrosion – Galvanic Corrosion:

Galvanic Corrosion gets its name from the galvanic effect – the electric potential or voltage that results when two different metals are connected electrically in the presence of an electrolyte.

Electrolyte – a medium, usually a liquid, capable of conducting electric current.

Protection of Metals:

There are two principal strategies for protecting metals subject to direct oxidation:

1. Shielding the material from its environment by coating it with another material.

2. Establishing the chemical makeup of the parent material such that its environment does not cause it to degrade.


Cladding: Adding a layer of one metal to another metal:

To protect against corrosion

To improve mechanical characteristics such as hard facing

In some cases to improve appearance


Plating: The theory behind plating is that if

a thin layer of anticorrosive material can be “plated” to a base metal, then the material can be protected from corrosion.


Plating: The process of depositing a layer of

one metal on another, often done electrically, for the purpose corrosion protection, appearance, improved electrical conductivity, and other engineering requirements.


Plating: Common plating techniques:

Galvanizing Tin plating Electroplating

Coating an object with a thin layer of a metal through electrolytic deposition.

unit 7 manufacturing processes: plastics and composites processing of plastics and composites

Documents

composites composites

composites reinforcements

types of composites

composites processing

composites injection

related slide

metallic matrix

reinforcing material