Topic 4: Raw Material to Final Product Materials - PDF

Topic 4 Final Production  4.1 Properties of materials Essential idea: Materials are selected for manufacturing products based primarily on their properties. Nature of design: The rapid pace of scientific discovery and new technologies has had a major impact on material science, giving desig...

Topic 4 Final Production  4.1 Properties of materials Essential idea: Materials are selected for manufacturing products based primarily on their properties. Nature of design: The rapid pace of scientific discovery and new technologies has had a major impact on material science, giving designers many more materials from which to choose for their products. These new materials have given scope for "smart" new products or enhanced classic designs. Choosing the right material is a complex and difficult task with physical, aesthetic, mechanical and appropriate properties to consider. Environmental, moral and ethical issues surrounding choice of materials for use in any product, service it system also need to be considered. (2.1) International mindedness: |Smart materials are likely to be developed in specific regions / countries and their benefits can be limited globally in the short term. Aims Aim 2: Materials are often developed by material engineers to have specific properties. The development of new materials allows designers to create new products, which solve old problems in new ways. For example, the explosion of plastic materials following the second world war enabled products to be made without using valuable metals. 4.1.1 Physical properties 1.Mass The amount of matter in an object. (SI unit : kilogram) 2. Weight The force of gravity on an object (weight = mass x the acceleration of gravity) (unit: Newton (N) ) 3. Volume The amount of 3-dimensional space an object occupies. 4. Density The mass per unit volume of a material (density = mass / volume) (unit: kg/m3 ) Density is an important consideration in relation to product weight and size (e.g for portability). Example: Food packaging. Pre-packaged food is sold by weight or volume and a particular consistency is required. 2 5. Electrical resistivity This is a measure of a material's ability to conduct electricity. A material with a low resistivity will conduct electricity well. Electrical resistivity is an important consideration in selecting particular materials as conductors or insulators. Example: Copper is used in electrical wires since it has low electrical resistivity. 6. Thermal conductivity A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab. Thermal conductivity is an important consideration for object that will be heated, which must conduct or insulate against heat. Examples: cooking pots. 7. Thermal expansion (expansivity) A measure of the fractional increase in dimensions (length, area or volume) when an object is heated. Thermal expansion is an important consideration where two dissimilar materials are joined. These may then experience large temperature changes while staying joined. Example: Oven door. 8. Hardness The resistance a material offers to penetration, cutting, denting or scratching. Hardness is an important consideration where resistance to cutting or scratching is required. Example: Ceramic floor tiles are hard and resist scratching. Questions Q1. Explain one reason why the expansion joint shown here is an important consideration in the design of a bridge. A bridge would expand in hot weather. If this expansion joint was not there, then the expansion would cause cracks and the bridge would not be safe anymore. Q2. State the unit of weight. Weight is a force, therefore its SI unit is Newton (N). Q3. The cooking pot shown is made of two dissimilar materials: glass and stainless steel. Which physical property is important when selecting materials for its lid? A.Low hardness B. High thermal conductivity C. Low thermal expansion D. High density 3  4.1.2 Mechanical properties 1. Strength The ability of a material to resist an applied force and it is identified as either a tensile or compressive strength. a. Tensile strength Pulling Pulling force force Material under tension The ability of a material to withstand pulling forces. material with high tensile strength resists stretching when pulling forces act on it. If the material does not have a high enough tensile strength it will stretch and eventually break. Examples: The tensile strength of ropes and cables is an important safety consideration. b. Compressive strength Pushing force Pushing force Material under compression The ability of a material to withstand pushing forces. A material with high compressive strength withstands push forces which try to crush or shorten it. Example: columns. 2. Stiffness The ability of a material to resist a bending deformation. Stiffness is an important consideration when maintaining shape is crucial to the performance of an object. Example: Airplane wing. 3. Toughness The ability of a material to resist the propagation of cracks. Toughness is an important consideration where impact may take place. Example: hammer head. 4 4. Ductility The ability of a material to be drawn or extruded into a wire or other extended shape. Ductility is an important consideration when materials are extruded. Example: manufacturing copper wires. 5. Elasticity The ability of a material to be deformed and return to its original size and shape. Natural and synthetic rubbers, and metals used for springs are examples of materials and products possessing this property. 6. Plasticity The ability of a material to undergo permanent deformation. 7. Young's modulus The stiffness of a material. Young's modulus = stress/strain Stress= force /area Strain = change of length / original length A stress strain graph shows the elastic region of a material, its yield stress, UTS and fracture points. 5 Questions Q1. Which property is most important to ceramic floor tiles? A. Tensile strength B. Density C. Toughness D. Hardness Q2. Which combination of properties is important in the design of a frying pan handle? A. Stiffness - Thermal expansion B. Toughness - Thermal conductivity C. Toughness - Thermal expansion D. Stiffness - Thermal conductivity Q3. A screw driver's tip snapped during use. The material is most likely: A. Ductile B. Brittle C. Dense D. Elastic Q4. The figure here shows equipment forming part of an outdoor gym. Outdoor gyms are becoming popular in different parts of the world. The tubular metal gym equipment requires no electricity supply. It is secured to a slip-free floor. The equipment is designed to be used without prior training. Instructions for use are clearly displayed on the site. Discuss two properties of metal which make it a suitable choice for this outdoor gym. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… 6 4.1.3 Aesthetic characteristics Aesthetic characteristics are: smell, appearance, taste and texture. Although these properties activate people's senses, responses to them vary from one individual to another, and they are difficult to quantify scientifically, unlike the other properties. Some of these properties are only relevant to food, while others can be applied to more than one material group. 4.1.4 Properties of smart materials Smart materials have properties that react to changes in their environment. This means that one of their properties can be changed by an external condition, such as temperature or light. This change is reversible and can be repeated many times. 1. Piezoelectricity Piezoelectric materials have two unique properties which are interrelated. When a piezoelectric material is deformed, it gives off a small but measurable electrical discharge. Alternately, when an electrical current is passed through a piezoelectric material it experiences a significant increase in size (up to 4% change in volume). Piezoelectric materials are often used to measure the force of an impact. An example in everyday life is the airbag sensor in cars. The material senses the force of an impact on the car and sends an electric charge to activate the airbag. Piezoelectric materials are also widely used as sensors in different environments. 2. Shape memory alloys Shape memory alloys exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material. Pseudo-elasticity occurs without a change in temperature. The load on the SMA causes molecular rearrangement, which reverses when the load is decreased and the material springs back to its original shape. Applications for pseudo-elasticity include eye-glasses frames and medical tools. The shape memory effect allows severe deformation of a material, which can then be returned to its original shape by heating it. One application of shape memory effect is for robotic limbs (hands, arms and legs). It is difficult to replicate even simple movements of the human body, for example, the gripping force required to handle different objects (pens, tools). SMAs are 7 strong and compact and can be used to create smooth, lifelike movements. Computer control of timing and size of an electric current running through the SMA can control the movement of an artificial joint. Other design challenges for artificial joints include development of computer software to control artificial muscle systems, being able to create large enough movements and replicating the speed and accuracy of human reflexes. 3. Magneto-rheostatic and electro-rheostatic Electro-rheostatic (ER) and magneto-rheostatic (MR) materials are fluids that can undergo dramatic changes in their viscosity. They can change from a thick fluid to a solid in a fraction of a second when exposed to a magnetic (for MR materials) or electric (for ER materials) field, and the effect is reversed when the filed is removed. MR fluids are being developed for use in car shock absorbers, damping washing machine vibration, prosthetic limbs, exercise equipment and surface polishing of machine parts. ER fluids have mainly been developed for use in clutches and valves, as well as engine mounts designed to reduce noise and vibration in vehicles. 4. Photochromicity Photochromic materials react reversibly to light by changing their color. One application is color-changing lenses in sunglasses, which can darken as the sun brightens. A chemical either on the surface of the lens or embedded within the glass reacts to ultraviolet light, which causes it to change form and therefore its light absorption spectra. 5. Thermoelectricity At its simplest, thermoelectricity is electricity produced directly from heat. It involves the joining of two dissimilar conductors that, when heated, produce a direct current. Thermoelectric circuits have been used in remote areas and space probes to power radio transmitters and receivers. 8 4.2 Materials Essential idea: Materials are classified into six basic groups based on their different properties. 4.2a Metals and metallic alloys Nature of design: Typically hard and shiny with good electrical and thermal conductivity, metals are a very useful resource for manufacturing industry. Most pure metals are either too soft, brittle or chemically reactive for practical use and so understanding how well to manipulate these materials is vital to the success of any application. (2.2) International mindedness: Extraction takes place locally with added value often occurring in another country. Aims Aim 5: Design for disassembly is an important aspect of sustainable design. Valuable metals, such as gold and copper, are being recovered from millions of mobile phones that have gone out of use following the end of product life. Some laptops and mobile phones can be disassembled very quickly without tools to allow materials to be recovered easily. 4.2a.1 Metals and alloys Metals can be divided into : 1. Ferrous metals that contain iron, like cast iron (vices, heavy machinery and car brake drums), mild steel (car bodies, nails, screws, nuts and bolts), medium carbon steel (garden tools, springs) and high carbon steel (hand tools, hammers, chisels, screwdrivers, etc. ) 2. Non-ferrous metals that contain no iron like copper (electrical wires, hot water storage cylinders and central heating pipes), aluminum (kitchen cooking utensils, cans, foils and window frames), lead (radiation insulation) and Zinc (galvanized steel). Non-ferrous metals do not rust. 9 4.2a.2 Extraction of metals from ores A quarter of the Earth's crust contains metals. However, most of these metals, such as iron oxide and aluminum oxide, are found chemically combined with other elements in the form of metallic ores. The method of extracting a metal from its ore depends on the metal's reactivity. For example, reactive metals such as aluminum and copper are extracted by electrolysis, while a less reactive such as iron may be extracted by reduction (a reaction with carbon or carbon monoxide). Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores contain iron oxide (Fe2O3). The oxygen must be removed from the iron oxide to leave the iron behind. Aluminum ore, known as bauxite, is purified into aluminum oxide (Al2O3) before the aluminum is extracted by electrolysis. 4.2a.3 Grain size Metals, pure or alloyed, exist as crystals. A metal crystal exists as a regular arrangement of positive ions in a sea of free moving electrons. Grain size refers to the arrangement of crystals which form a different pattern for different metals. 10  The structure and size of the grains determine important properties of the metal. To obtain certain characteristics, grain size can be controlled and modified in a number of ways: 1.Rate of cooling: a) Slow cooling allows larger grains to form. b) Rapid cooling allows smaller grains to form. 2. Heat treatment after solidification: a) Directional properties in the structure may be achieved by selectively cooling one area of the solid. b) Reheating a solid metal or alloy allows material to diffuse between neighboring grains and the grain structure to change. 4.2a.4 Modifying properties by alloying, work hardening and tempering Alloying The properties of a pure metal may be changed by adding other elements to it. A mixture of two or more elements, where at least one element is a metal, is called an alloy. In a pure metal the atoms are all the same size, but alloys contain atoms of different sizes which distort the regular arrangements of the base metal and change its properties. For example tensile strength, hardness, malleability and ductility. Alloys may be grouped into: 1. Ferrous alloys like stainless steel (cooking utensils, industrial equipment for food and drink processing and kitchen sinks) which resists corrosion. 2. Non-ferrous alloys like brass (musical instruments, ornaments and decorative products) and duralumin (aircraft structure). Work hardening When a metal is plastically deformed by cold working, its hardness and resistance to further plastic deformation increases (work hardens). Tempering Tempering removes some of a metal's hardness and brittleness after work hardening. This is achieved by heating the metal to a high temperature then cooling it. Suitable temperatures for tempering vary considerably, depending on the type of metal and designed application. 4.2a.5 Design criteria for super alloys The strength of most metals and alloys decreases as the temperature is increased. Super alloys are metallic alloys that can be used at high temperatures, often in excess of 0.7 of their absolute melting temperature. A super alloy's base alloying element is usually nickel. Design criteria for super alloys include: 11 a) Creep resistance b) Oxidation and corrosion resistance Since super alloys are particularly resistant to high temperature, they are suitable for applications that require high performance at high temperatures. For example, Nickel-based super alloys are appropriate for: 1. Aircraft engines 2. Rocket engines 3. Chemical and nuclear plants 4.2a.6 Recovery and disposal of metals and metallic alloys Recovery, reuse and recycling of metals preserves limited non-renewable resources, causes less damage and pollution to the environment, and requires less energy than extracting metals from their ores. Examples of recycled metals include aluminum, iron and steel. Collection and transporting costs offset these benefits to a minor extent. 4.2b Timber Nature of design: Timber is a major building material that is renewable and uses the Sun's energy to renew itself in a continuous cycle. While timber manufacture uses less energy and results in less air and water pollution than steel or concrete, consideration needs to be given to deforestation and the potential negative environmental impact the use of timber can have on communities and wildlife. (3.6) International mindedness: The demand for high-quality hardwoods results in the depletion of ancient forests in some regions/countries impacting on the environment in multiple ways. Aims Aim 9: Designers have great influence over the materials that they specify for products. The move towards using timber from sustainably managed forestry gives consumers confidence that rare species found in rainforests have an opportunity to recover. 12 4.2b.1 Characteristics of natural timber: hardwood and softwood Natural timber is a natural composite material comprising cellulose fibers in a lignin matrix. The tensile strength of timber is greater along the grain than across the grain. Natural wood may be subdivided into softwood and hardwood. Softwood is produced from trees that grow in colder temperate regions. These trees are coniferous and evergreen, with needle like leaves and seeds covered in cones. Examples: Pine and Spruce. Coniferous trees are fast growing and reach maturity within 30 years. Softwood is generally softer, lighter weight and easier to work with than hardwood. Its grains are less decorative. Softwoods are mainly used for construction work, but are also used in furniture, doors, windows and harvested for paper. Hardwood is produced from trees that grow in warm temperate and tropical regions. These trees are deciduous (shed their leaves annually), with broad leaves and seeds covered in fruits or nuts. Examples: Mahogany, Beech, Teak and Oak. Deciduous trees are slow growing and reach maturity within 100 years. Hardwood is generally harder and heavier than softwood. Its grains are more decorative. Hardwood can be more difficult to work with. Hardwoods are mainly used for high quality furniture, veneer and situations where durability is important. Task : research design contexts in which natural timbers are used. 4.2b.2 Characteristics of man-made timbers (manufactured boards) MDF, medium density fiber board, is made by gluing and compressing wood fibers to form a dense solid board that is very stable, machines and takes paint well. Plywood is formed from thin layers of wood bonded together with adhesive. Each layer has its grain in the opposite direction to the ones next to it. It is made from an odd number of layers (3, 5 and 7). Plywood is used for furniture, interior doors, drawer bottoms, laminated floors and applications where it is necessary to have thin sheet material. 13 Blockboard is made up of parallel strips of wood glued side by side, sandwiched between thin layers of wood. It is a good substitute for plywood when greater thicknesses (12-25mm) are required. Particle board, also known as chipboard, is made by gluing and compressing tiny particles of wood. A particle board is not very strong, has no grain direction and absorbs a lot of water. It is, however, cheap and is usually used with a wood or plastic veneered face in mass produced furniture, such as kitchen cupboards and shelving. Hardboard is made by gluing and compressing wood fibers to form a thin cheap substitute for plywood. Its upper face is usually smooth while the lower face is textured. Hardboard is mainly used where space filling, rather than strength, is required such as cupboards backs. Boards produced from man-made timbers have a number of advantages over natural timber boards, for example: - Available in larger standard sizes, greater than it is possible to cut from a tree. - May be veneered providing consumers with more choice and creating a wider market. - Produced in uniform thicknesses and consistent quality. - More stable. - Readily available material with little resource implications. Task: Research design contexts in which man-made timbers would be used. 14 4.2b.3 Treating and finishing timbers A growing tree may contain 50% or more of its weight in the form of water. The amount of water contained in the wood is referred to as moisture content (MC) and is expressed as a percentage of its dry weight. Free moisture is the moisture within timber that is contained within the cell cavities and intercellular spaces. Absorbed moisture is the moisture within timber that is contained in the cells walls. Although free and absorbed is exactly the same in either position, its effects on the timber is quite different. Moisture content is affected by humidity and temperature. Timber takes in moisture from a damp/humid environment and gives up moisture in a dry one. Consequently, damp wood shrinks in dry air and dry wood swells in damp air. Equilibrium moisture content (EMC) is at which the moisture content of wood achieves an equilibrium with the environment. Seasoning (drying) is the commercial drying of natural timber which reduces its moisture content to less than 20%. If unseasoned timber is placed in a room, it twists badly when drying out and any jointing opens up leaving gaps. There are two basic methods of seasoning: 1. Natural air seasoning (drying): To reduce the moisture content, stacks of sawn timber are placed in the open or in large sheds and left to dry. 2. Kiln seasoning (drying): to reduce the moisture content, stacks of sawn timber are placed in a kiln, where the heat. air circulation and humidity are closely controlled. A kiln is a thermally insulated chamber ( a type of oven), which produces temperatures sufficient to complete a process, such as drying, hardening or chemical changes. Kiln seasoning provides a faster, more controlled and reliable method than air seasoning. It offers a more rapid turnover, and is therefore used by many manufacturers to process most hardwoods. 15 Defects in natural timber Defects affect the appearance of timber as well as reduce its durability and strength. Common defects in timber include: Knots are natural Warping is a distortion in wood caused by uneven irregularities which form at drying, which results in the material bending or the junction of branches twisting. and may sometimes be considered defects. Cupping is a warp across Twisting is a distortion in Bowing is a warp the width of the face of the which the two ends of a across the width of the wood, in which the edges material do not lie on the face of the wood. are higher or lower than same plane. the centre. There are many types of wood finishes available: paint, oil, staining, polish and varnish. The purpose of treating and finishing wood is to: 1.Enhance appearance and aesthetic properties. 2. Protect against decay 3. Prevent wood from absorbing moisture. 4. Reduce attack by organisms Treatment of wood can involve using solutions, which make the wood poisonous to insects, fungus, and marine borers as well as protecting it from the weather. For example, dry rot is decay caused by fungus that thrives in unventilated areas. Creosote is a material that penetrates the timber fibers protecting the integrity of the wood from borer, wood lice and fungal attack. 16 Questions Q1.State one design consideration for the surface finish of a wooden table. ………...………………………………………………………………………………………… Q2. Outline one advantage of using paint for the surface finish of a shelf. ………………………………………………………………………………………………...… …………………………………………………………………………………………………... Q3.Why are timber fence posts treated with chemicals before they are set into the ground? A.To enhance their aesthetic properties B. To make the post stiffer C. To enhance toughness D. To reduce attack by organisms Q4. Why would a Mahogany (hardwood) door be treated with a transparent (varnish) finish rather than opaque (paint) finish? A. Enhance the wood grains B. Hardness C. Tensile strength D. Resistance to damp environments Q5.Which material has the highest tensile strength? A. Laminated wood B. Particle board C. Pine D. Mahogany Q6.What characterizes natural timber? Along the grain Across the grain A Low tensile strength Low tensile strength B Low tensile strength High tensile strength C High tensile strength Low tensile strength D High tensile strength High tensile strength 4.2b.4 Recovery and disposal of timbers Proper recovery and disposal of timber reduces the number of virgin trees being felled to create new products. 17 Questions Q1. Discuss one issue relating to the consideration of timber as a sustainable resource. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… Q2. Reforestation refers to the process of: A. Removing excess moisture from timber B. Turning wood logs into marketable timber C. Restoring tree cover to areas where woodlands or forest once existed D. Destroying the vegetative cover in woodlands or forests Q3.What material has very high electrical resistivity, very low thermal conductivity, very low thermal expansivity and is very hard? A. Glass B. Plastic C. Textile D. Food 4.2c Glass Nature of design: The rapid pace of technological discoveries is very evident in the manufacture and use of glass in electronic devices. Different properties have been presented in glass for aesthetic or safety considerations for many years but the future of glass seems to be interactivity alongside electronic systems. The structure of glass is not well understood, but as more is learned, its use is becoming increasingly prominent in building materials and structural applications. Aims Aim 6: The earliest found examples of glass objects come from the third millennium BCE, and up until the 1850s glass was considered a luxury item. Since then, glass has permeated and revolutionized many aspects of human life and culture in diverse fields such as the arts, architecture, electronics and communication technologies. 18 4.2c.1 Characteristics of glass Some of the important characteristics (properties) of glass include: -Brittle: glass is brittle and can result in cuts and injuries. -Transparent: when used for windows glass lets the light in, lets the heat in , and warms the interior on sunny days. When used as a container glass allows contents to be seen. - Hard: high hardness makes it resist scratching. No damage when cleaning. - Unreactive: glass is not corroded by hot / acidic/ alkaline contents. Glass will not react with its contents, Glass is non-toxic. -Aesthetic: glass is aesthetically pleasing, it is transparent and it may be colored. -Hygienic: Easy to clean and sterilize. -High melting point: this means glass can withstand high temperature. -Strength :good resistance to compressive forces but poor resistance to tensile forces. Questions Q1.State one property of glass that makes it suitable for application in drinks containers. …………………………………………………………………………………………………... Q2. The Grand Canyon Skywalk, shown here, is a glass walkway that spans 21 meters over the Grand Canyon's rim at a height of 1219 meters above the Colorado River. Which combination of "resistance to compressive forces" and "resistance to tensile forces" characterizes glass and constrains the design of the Grand Canyon Skywalk? Resistance to Resistance to compressive forces tensile forces A No No B No Yes C Yes No D Yes Yes 19 4.2c.2 Applications of glass Soda-lime glass: high volume glass products such as bottles, light bulbs, windowpanes, etc. Borosilicate glass (Pyrex): has good thermal shock resistance. Toughened glass: When broken, it will shatter into tiny fragments with small dull edges rather than large pieces with sharp edges making toughened glass safer. Uses include car windscreens, frameless shower screens, office partitions inside buildings and in buildings where the exterior is mainly glass. Laminated glass: has a thin layer of material, usually plastic, between the layers. This thin layer prevents cracks from growing so laminated glass stays together on impact, and it can even be made bullet proof. Borosilicate glass Toughened glass Laminated glass 4.2c.3 Recovery and disposal of glass Manufacturing glass requires large quantities of energy. Around 15% and 30% powdered scrap glass (recycled glass) is added to the raw materials to make the process more economical. This lowers the energy used and the time required to produce glass. Glass may be recycled many times. 20 4.2d Plastics Nature of design: Most plastics are produced from petrochemicals. Motivated by the finiteness of oil reserves and threat of global warming, bio-plastics are being developed. These plastics degrade upon exposure to sunlight, water or dampness, bacteria, enzymes, wind erosion and in some cases pest or insect attack, but in most cases this does not lead to full breakdown of the plastic. When selecting materials, designers must consider the moral, ethical and environmental implications of their decisions. (3.6) International-mindedness The raw material for plastics (mainly oil) is extracted in a country, exported to other countries where conversion to plastics takes place and these are re-exported at considerable added value. Aims Aim 3: Early plastics used from 1600 BCE through to 1900 CE were rubber based. Prompted by the need for new materials following the first world war, the invention of Bakelite and polyethylene in the first half of the 20th century sparked a massive growth of plastic materials and as we identify the need for new materials with particular properties, the development of new plastics continues. 4.2d.1 Raw materials for plastics The majority of the raw materials that go into the production of plastics come from synthetic sources, for example refining crude oil (petrochemicals). 4.2d.2 Structure of thermo and thermosetting plastics Thermoplastics are linear chain molecules with weak secondary bonds between the chains. This causes the long molecular chains to clump together like piles of entangled and coiled spaghetti. Long entangled chain molecules Long cross linked chain molecules Thermosetting plastics are linear chain molecules with strong primary (covalent) bonds between the chains. This cross-linking between the linear chains gives thermosetting plastics a rigid three-dimensional structure. 21 4.2d.3 Temperature and recycling thermoplastics Heat has a reversible effect on thermoplastics. An increase in temperature weakens the secondary bonds between the linear chains and allows them to soften and harden again on cooling. This may be repeated many times making thermoplastics easy to recycle. However, heat has a non-reversible effect on thermosetting plastics. The first time they are molded, usually under pressure, the linear chains cross-link and cannot be softened or changed again. This group of plastics is rigid and non-flexible even at high temperatures. Thermosetting plastics are often used to make heat resistant products, because they can be heated to high temperatures without melting. Thermosetting plastics are also good electrical insulators. 4.2d.4 Properties and uses of thermoplastics Thermoplastics Properties Some popular uses 1 Polythene (Low Most common Squeezable bottles, density) LDPE thermoplastic, flexible, packaging food wrap, tough, good electrical plastic bags, wire insulation insulator, good chemical resistance. Polythene (High Stiffer, stronger and Bottles, pipes, buckets, density) HDPE harder than LDPE. bowls. 2 Polypropylene Very popular, low density Plastic seats, medical PP tougher and more rigid equipment, kitchenware, than HDPE, good containers with built in chemical resistance, high hinges, string, rope, nets melting point, can be and crates. sterilized. 3 High impact High impact resistance Housings , vacuum forming polystyrene HIPS 4 ABS Tough, good aesthetic Housings, kitchenware, qualities Lego blocks , prototypes 5 PET Very popular, dimensional Water/soft/juice drink stability, lightweight, bottles, food containers, tough, safe synthetic fibers, adhesives. 6 Polyvinyl chloride Stiff, hard, tough, good Pipes, gutters, roof sheets, uPVC weather and chemical vinyl siding and window resistance. frames. Plasticized PVC Soft, flexible, rubbery Wire insulation, waterproof material and a good clothing, inflatable products electrical insulator. and garden hose pipes. 22 4.2d.5 Properties and uses of thermosetting plastics Thermosetting Properties Some popular uses 1 Urea- Stiff, hard, strong, brittle, Electrical fittings, control formaldehyde heat resistant, good knobs, domestic appliance electrical insulator. parts, wood adhesives, textile. 2 Melamine resin Similar to urea- Tableware, laminates for formaldehyde but more work surfaces. moisture-resistant, harder, and stronger 3 Epoxy resin ER Bonds well, good Adhesives chemical resistance 4 Polyurethane Low density flexible foam Upholstery, mattresses and vehicle seating. Low density rigid foam Thermal insulation, steering wheels, dashboards. Soft, durable and strong Wheels, adhesives, coatings 4.2d.6 Recovery and disposal of plastics Recycled plastic, like PET, can be used in the production of numerous products including new bottles, fabric for carpets and fiberfill for sleeping bags, automotive parts such as bumpers, etc. 23 4.2e Textiles Nature of design: The continuing evolution of the textiles industry provides a wide spread of applications from high performance technical textiles to the more traditional clothing market. More recent developments in this industry require designers to combine traditional textile science and new technologies leading to exciting applications in smart textiles, sportswear, aerospace and other potential areas. (2.2) International-mindedness The economics and politics of the production and sale of clothing by multinationals can be a major ethical issue for consumers and the workforce. Aims Aim 5: There are many ethical considerations attached to the production of natural fibers. The strongest natural silk known to man is harvested from silk spiders and notoriously difficult to obtain, and labor intensive. In an effort to produce higher yields, scientists have altered the genome of goats so that they produce the same silk proteins in their milk. 4.2e.1 Properties of natural fibers Wool is a natural fiber that comes from animals. The fibers are crimped and each is made up of overlapping scales. Wool absorbs moisture easily, but dries slowly. If wool is washed in hot water it shrinks. Wool is warm to wear and does not burn easily. Wool can be woven or knitted using thick and fine yarns to create a wide range of effects. Cotton is another natural fiber, a polymer, obtained from the bud of cotton plants. Cotton is absorbent and increases in strength when wet. It is relatively inelastic, so it wrinkles and creases easily. Cotton is a good conductor of heat and so it is little affected by it and chars rather than melts when exposed to high temperatures. Cotton is also degraded by ultra violet rays, moisture and air pollutants. This is shown as discoloration and then breakdown of the fiber. Cotton is also susceptible to attack by microbes. Silk natural fibers are long, straight and smooth. Silk is very absorbent and does not burn easily. It can be spoiled by chemicals and perspiration. Natural fibers may be treated to improve properties. For example treating cotton enhances its aesthetic properties, reduces its flammability and lowers its water absorbency. Task: research design contexts in which different types of natural textiles are used. 24 4.2e.2 Properties of synthetic fibers Nylon is very strong and very elastic. It is crease resistant and does not absorb moisture. Nylon melts but does not flare, therefore is has low flammability. Nylon needs little treatment because the desired characteristics can be designed into it. Nylon can be mixed with other fibers. Polyester, like nylon, is very strong, crease resistant, does not absorb moisture and melts; however it is not very elastic. Polyester can be also mixed with other fibers. Lycra® is a registered trademark of Elastene or Spandex. It is extremely elastic and resists perspiration. It is usually blended with other fibers to make fabrics stretchy and comfortable to wear. Task: Research design contexts in which different types of synthetic textiles are used. 4.2e.3 Conversion of fibers to yarns Natural fibers need to be collected, cleaned and then spun into yarns before they can be used to make fabrics. Spinning twists fibers together to make longer, thicker yarn which is much stronger than the fiber itself. The properties of the yarn can be changed by altering the amount of twist used when spinning fibers together. If fibers are twisted tightly, the yarn will be harder and stronger than a yarn made from loosely twisted fibers. The most common commercial spinning method allows fibers to be twisted together in either a clockwise direction ( which produces an S twist yarn), or in an anti-clockwise direction, (which produces a Z twist yarn). The properties of yarn can be changed by altering the amount of twist used when spinning the fibers together. Sometimes different types of fibers are mixed together before spinning into a yarn; this is called blending. Blending improves aesthetics, controls cost and improves properties. For example, a fiber that is not very absorbent, such as nylon or polyester, can be blended with a fiber like cotton, which is absorbent. A single yarn is often twisted together with another one or more yarns to make it even stronger and thicker. This type of yarn is called a plied yarn producing 2. 3 or 4 ply. 25 4.2e.4 Conversion of yarn to fabrics Weaving: is the act of forming a sheet Knitting: is the method for converting like material by interlacing long a yarn into fabric by creating threads passing in one direction with consecutive rows of interlocking loops others at a right angle to them. of yarn. Lace and net fabrics are also made Felting: produces a non-woven fabric using yarns and are often knitted. made from fibers matted together using However, lace can also be made by moisture, heat and pressure. knotting, braiding or stitching. 4.2e.5 Recovery and disposal of textiles Fabric production uses a lot of energy and contributes to a wide range of environmental issues. Recycle and reuse of fabrics is encouraged. 26 4.2f Composites Nature of design: Composites are an important material in an intensely competitive global market. New materials and technologies are being produced frequently for the design and rapid manufacture of high-quality composite products. Composites are replacing more traditional materials as they can be created with properties specifically designed for the intended application. Carbon fiber has played an important part in weight reduction for vehicles and aircraft. (2.2) International-mindedness Many composite materials are expensive to produce and their dissemination globally is limited. Aims Aim 1: As designers develop new products, they should always be aware of the materials available. In an effort to increase productivity and lose weight, carbon fiber parts are often glued together. The use of an epoxy adhesive rather than traditional fastening methods allows manufacturers to create complex shapes quickly and easily. These materials and methods are being transferred to consumer products. 4.2f.1 Composite material Composites are a combination of two or more materials that are bonded together within a matrix to improve their mechanical, physical, chemical or electrical properties. Composite materials may be produced in a number of ways including weaving, molding, pultrusion and lamination. 4.2f.2 Composition and structure of composites Examples of composite materials include: 1.Concrete and reinforced concrete 27 2. Laminated glass 3. Plywood, MDF, particleboard and laminated veneer lumber (LVL) 4. Fiberglass and carbon reinforced plastic 5. Kevlar®: A registered trademark for a fiber reinforced composite material. The synthetic fiber (aramid) contains linear chains of hydrocarbon rings. These chains are aligned along the length of the fiber during the manufacturing process and behave like rigid rods to give Kevlar its distinct characteristics. Task: research contexts in which different types of composite materials are used. 28 4.2f.3 Advantages and disadvantages of composite materials Composites have improved properties, but many are expensive to produce and difficult to recycle. Questions Q1. State the most likely composite material used for the products shown below: Wooden beams: ……………………………………… Glove:…………………… Canoe: …………………………………… Coffee table:………………………… Q2.Describe how LVL differs from plywood. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………... Q3. Outline one benefit of using LVL beams in the construction industry. ………………………………………………………………………………………………… ………………………………………………………………………………………………… 29 4.3 Scales of production Essential idea: The scale of production depends on the number of products required. Nature of design: Decisions on scale of production are influenced by the volume or quantities required, types of materials used to make the products and the type of product being manufactured. There are also considerations of staffing, resources and finance. (1.15) International mindedness: Mass customization enables global products to become individual items. Aims Aim 9: The growing phenomenon of mass customization brings consumers into the design process, allowing them to make choices that make a product unique, to make it their own. Companies have developed "design stations" in their retail stores where consumers can create virtual 3D models, "try them out" using digital technology and place their order. 4.3.1 Scale of production Define One-off production An individual (often craft-produced) article or a prototype for larger-scale production. Define Batch production Limited volume production (a set number of items to be produced). Define Mass and continuous flow production The continuous production of large amounts of standardized products on production lines, permitting very high rates of production per worker. When a mass-production line runs continuously without interruption, it is called continuous flow. 30 4.3.2 Advantages and disadvantages of different scales of production One-off production Batch production Mass and continuous flow Advantages - Products are unique - Offer customers some - High production rate. and tailored to variety and choice. - Low unit cost. customer's needs. - Unit cost is lower than - Process is highly - Workers are skilled, one-off production. automated. have greater job -Production is more flexible - Lower cost of materials satisfaction and are than mass and continuous as they can be bought in more motivated. flow production. bulk. -Low set up cost. Disadvantages -High unit cost. - Workers must be able to - Products are not unique. -High labor costs. switch from one batch to - High set up cost. -Low production rate. another. 4.3.3 Selecting an appropriate scale of production When selecting an appropriate scale of production for a product, a number of factors must be considered including: - Product characteristics - Material characteristics - Size of market - Nature of market - Desired manufacturing processes and desired production system 31 4.3.4 Mass customization Define mass customization A sophisticated CIM system that manufactures products to individual customer orders. The benefits of economy of scale are gained whether the order is for a single item or for thousands. Question What is true of mass customization? I. Mass-produced products can be customized to meet the needs of individuals II. Customized products can be produced at competitive prices III. The product should be customized as early as possible in the manufacturing process A. I and II B. I and III C. II and III D. I, II and III 32 4.4 Manufacturing processes Essential idea: Different manufacturing processes have been developed to innovate existing products and create new products. Nature of design: Designers sometimes engineer products in such a way that they are easy to manufacture. Design for manufacture (DFM) exists in almost all engineering disciplines, but differs greatly depending on the manufacturing technologies used. This practice not only focuses on the design of a product's components, but also on quality control and assurance. (1.11) International mindedness: More expensive modern processes tend to take place in technologically advanced. Aims Aim 8: Advancements in 3D printing have resulted in the ability to have a 3D printer at home. Consumers can download plans for products from the internet and print these products themselves. 4.4.1 Manufacturing processes A finished product may be required in a number of shapes and sizes, and there are many different techniques by which to produce the final article. These techniques can be categorized into four major groups: 1. Adding: Manufacturing techniques 2. Wasting/Subtracting: Manufacturing that add material in order to create techniques that cut away material in products. order to create a component. 3. Shaping: Manufacturing methods for 4. Joining: Methods that are used to modifying the shape of a material. join two or more similar or dissimilar materials together. Selecting the appropriate manufacturing technique is usually based on: -Material characteristics (form, melting/softening point, etc.) -Cost -Capability -Scale of production -Desired properties 33 4.4.2 Additive manufacturing techniques Additive techniques include: 1. Paper-based rapid prototyping 2. Laminated object manufacturing (LOM) 3.Stereolithography (SLA) 4.Select laser sintering (SLS) 5.Fused deposition modeling (FDM) 4.4.3 Subtractive manufacturing techniques Subtractive techniques include: 1. Cutting 2. Machining 3. Turning 4. Abrading CNC (computer numerical control) machine Lathe (a machine tool that rotates work while a tool cuts away the waste material) 34 4.4.4 Shaping manufacturing techniques Shaping techniques include: 1. Casting 2. Molding 3.Thermoforming 4. Lamination 5.Knitting 6. Weaving 1. Casting : a manufacturing technique by which a liquid material is usually poured into a mould, and then allowed to solidify. Casting may be used to form a variety of materials especially metals. 2. Molding techniques such as extrusion, injection molding, blow molding, compression molding, etc. a. Extrusion 1. A die is prepared 2. Thermoplastic granules are placed in the hopper 3. A rotating screw pushes the granules through a heated cylinder 4. The thermoplastic granules soften 5. The rotating screw forces the plastic through the die 6. The extruded plastic product is cooled 7. The extrusion is then cut or coiled depending on the product 35  Advantages Disadvantages Suitable for mass production High set up cost Little or no finishing required Limitation to size Considered a clean technology Limitation to shape (extruded products are long, thin and with a constant section) Can produce hollow shapes Not suitable for low volume production b. Injection molding This manufacturing technique involves the direct introduction of molten plastic under pressure into a mould, which then cools rapidly, allowing the formed object to be released from the mould. 1. A two part mould is prepared. 2. Thermoplastic granules are placed in the hopper. 3. A rotating screw pushes the granules through a heated cylinder. 4. The thermoplastic granules soften. 5. When the desired amount of molten thermoplastic is in position the screw moves forward and injects the plastic into the two part mould. 6. When the plastic sets the two part mould opens and the product is ejected. 36  Advantages Disadvantages Suitable for mass production High set up cost Little or no finishing required Limitation to size Considered a clean technology Limitation to shape Use of different moulds Not suitable for low volume production 37 c. Extrusion blow molding 1. A two part mould is prepared. 2. Extrusion produces a tube of soft plastic. 3. The soft plastic tube is fed into a hollow mould, which closes on it. 4. Air is blown into the soft plastic causing it to expand and take the shape of the mould. 6. The mould opens and the plastic product is ejected. 7. The only finishing required is cutting off any surplus plastic. Blow molding is used extensively in the manufacture of hollow plastic products, such as bottles for drinks, detergents and cosmetics and many other types of containers like barrels and tanks as well as toys. 38 d. Thermoforming Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mould and trimmed to create a usable product. e. Lamination Lamination is the technique of joining multiple layers of materials to produce a thicker material with improved properties. A laminate is usually permanently assembled by heat, pressure, welding or adhesives. 39 f. Weaving is the act of forming a sheet like material by interlacing long threads passing in one direction with others at a right angle to them. g. Knitting is the method for converting a yarn into fabric by creating consecutive rows of interlocking loops of yarn. Task: research design contexts where shaping manufacturing techniques are used. 40 4.4.5 Joining manufacturing techniques Joining is the process of putting together two or more components or materials. Joining techniques may be permanent or temporary including: 1. Fusing 2. Fastening 3. Adhering 4. Stitching a. Fusing refers to manufacturing techniques that rely upon melting to join materials (usually metals) of similar compositions and melting points together, it includes welding, soldering, brazing, etc. 41 b. Fastening c. Adhesion is using a chemical substance to bond two surfaces together. d. Stitching Task: research design contexts where joining manufacturing techniques are used. Questions Q1. Which material groups can be used in the following processes? Casting Molding Fusing Abrading A Timber Plastic Metal Metal B Composites Timber Composites Plastic C Composites Plastic Timber Metal D metal plastic metal timber 42 Q2. Which technique is an example of wasting? A. Fusing B. Machining C. Stitching D. Sintering Q3. Using a chemical substance to bond two surfaces together is known as: A. Adhesion B. Fusing C. Stitching D. Fastening Q4. Which manufacturing technique is used to make plastic pipes? A. Machining B. Extrusion C. Injection molding D. Fusing Q5. The figure below shows a chair designed in 1948, made by knoll associates, New York. The seat comprises a seat cover and a cushion made from a mixture of plastic materials and legs which are made from metal. Discuss how two different methods of joining could be used in the manufacture of the chair. ……………………………………………………….………. Leather ……………………………………………………………….. ……………………………………………………………….. ……………………………………………………………….. ……………………………………………………………….. ……………………………………………………………………………………………...…… ………………………………………………………………………………………………...… …………………………………………………………………………………………………... ………………………………...………………………………………………………………… 43 4.5 Production systems Essential idea: The development of increasingly sophisticated production systems is transforming the way products are made. Nature of design: As a business grows in size and produces more units of output, then it will aim to experience falling average costs of production - economies of scale. The business is becoming more efficient in its use of inputs to produce a given level of output. Designers should incorporate internal and external economies of scale when considering different production methods and systems for manufacture. (1.11) International mindedness: The geographical distribution of different modes of production is an economic and political issue. Aims Aim 7: The design of a production system requires a complete understanding of a product, its function and the quality of finish. Each system can be unique and specific to the product it is creating, often requiring the designers to adapt their design to be manufactured using certain methods. 4.5.1 Craft production Craft production is a small scale production process centered on manual skills. 44 4.5.2 Mechanized production Mechanization is a volume production process involving machines controlled by humans. 4.5.3 Automated production Automated production is a volume production process involving machines controlled by computers. Automation has improved the type and range of products available to consumers. Many products require such precision in their manufacture that, without automation, it would not be possible to produce them at an affordable price. Question Q1. State one impact of automation on the workforce. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… 45 4.5.4 Assembly line production A volume production process where products and components are moved continuously along a flow line. As the product goes from one work station to another, components are added until the final product is assembled. Assembly line production is based on the interchangeability of parts, pre-processing of materials, standardization and work division. Questions Q1. Which aspect of assembly-line production is not a benefit for the workforce? A. No bending over required B. Job standardization C. Limited training required D. No heavy lifting Q2. Explain one impact of assembly-line production on the workforce for a mechanized production process. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… 46 4.5.5 Computer numerical control (CNC) Computer numerical control (CNC) refers to the computer control of machines for the purpose of manufacturing complex parts in metals and other materials. Machines are controlled by a program commonly called a "G code". Each code is assigned to a particular operation or process. The codes control X,Y and Z movement and feed speeds. 4.5.6 Production system selection criteria Criteria includes: - Time -Labour -Skills and training -Health and safety -Cost -Type of product -Maintenance -Impact on the environment -Quality management Task: research design contexts where different production systems are used. 4.5.7 Design for manufacture (DfM) DfM means designers design specifically for optimum use of existing manufacturing capability. Design for manufacture (DfM) can be conveniently split into four strategies: 1. Design for materials: Designing in relation to materials during processing. 2. Design for process: Designing to enable the product to be manufactured using a specific manufacturing process, for example injection molding. 47 3. Design for assembly: Designing taking account of assembly at various levels, for example, component to component, components into sub-assemblies and sub-assemblies into complete products. Strategies include: a. Minimizing the number of parts makes products easier to assemble. b. Using standard components. c. Designing parts which are multifunctional or for multiuse. d. Designing parts for ease of fabrication - component to component, components into sub-assemblies, sub-assemblies into products. 4. Design for disassembly: Designing a product so that when it becomes obsolete it can easily and economically be taken apart, the components reused or repaired, and the materials recycled. Design for disassembly facilitates recycling of products on disposal. Strategies include: a. Designing components made from one material. b. Using thermoplastic adhesives that lose their properties when reheated. c. Designing temporary fittings instead of permanent ones for example snap fittings instead of welding and gluing. 48 4.6 Robots in automated production Essential idea: The development of increasingly sophisticated robotic manufacturing systems is transforming the way products are made. Nature of design: Designers should consider the benefits of increased efficiency and consistency when using robots in production and be able to explore the latest advances in technology to ensure the optimum manufacturing process is used. However, a good designer will also understand their responsibility to consider the moral and ethical issues surrounding increased use of automation, and the historical impact of lost jobs. (2.5) International mindedness: The use of robots in automated production can depend on the local cost of manual labor. Aims Aim 8: The introduction of robots to an assembly line has a major impact on the labor force, often making skilled workers redundant in favor of a technician who can maintain and equip a large number of robots. 4.6.1 Primary characteristics of robots: work envelope and load capacity An industrial robot is a flexible computer operated machine that is able to perform a range of tasks in an efficient and accurate manner. 4.6.4 Single and multi-task robots As the name suggests, single-task robots can only carry out one task at a time, while multi-task robots can be programmed to carry out more than one task in a manufacturing environment. 49 Question Q1.Outline one way in which the use of a single-task robot might be considered cost effective by a small company. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… 4.6.3 Teams of robots Teams of robots - groups of robots working together to carry out tasks. Questions Q1. Outline how a team of robots contributes to assembly line production. Teams of robots can be arranged along an assembly line, so they can perform a series of jobs in the assembly of a product. Q2. State one reason why robots work in teams when assembling cars. Working in teams speeds up the rate of production. 4.6.4 Machine to machine (M2M) Machine to machine refers to wired and wireless communication between similar devices. 50 4.6.5 Advantages and disadvantages of using robots in automated production Advantages -increased productivity -accuracy and reduced waste -quality control -work in hazardous situations -reprogrammable Disadvantages -high set up cost -loss of jobs/unemployment -change in nature of jobs -maintenance Questions Q1. Outline one way in which robots could contribute to the cost-effectiveness of the production of cars on an assembly line. Reduced waste; humans are not operating machines so less waste and fewer accidents since industrial robots are more accurate and consistent. Q2.Discuss one benefit for the use of of robots in industrial conditions that would be unsuitable for humans. Reduction in health and safety risks, robots carry heavy items and equipment instead of workers, so less lifting and back injuries. Workers will no longer be required to do highly repetitive work so less repetitive strain injuries. Q3. Outline how robots have contributed to quality control in the manufacturing industry. Consistency, Industrial robots can perform the same job repetitively; they work 24/7 without getting tired and without jeopardizing quality. Q4. List two ways in which robots help to conserve resources. -Higher accuracy / more consistency - Reduction in the number of defective products. END OF TOPIC 4 51 Topic 4: Raw material to final product Term Definition Absorbed moisture The moisture within timber that is contained in the cells walls. Additive techniques Manufacturing techniques that add material in order to create it. Aesthetic appeal Favourable in terms of appearance. Aesthetic Aspects of a product that relate to taste, texture, smell and characteristics appearance. Air-drying Air- drying places the stacks of sawn timber in the open or in large sheds hence there is little control over the drying process. Alloy A mixture that contains at least one metal. This can be a mixture of metals or a mixture of metals and non-metals. Assembly line A volume production process where products and components are production moved continuously along a conveyor. As the product goes from one work station to another, components are added until the final product is assembled. Automated A volume production process involving machines controlled by production computers Batch production Limited volume production (a set number of items to be produced). Bio-compatibility The product ensures the continued health of a biological environment. Bowing A warp along the length of the face of the wood. Brittle Breaks into numerous sharp shards. Chemically inert Lack of reactivity with other materials. Composite A material comprised of two or more constituent materials that have different properties. Compressive The ability of a material to withstand being pushed or squashed. strength Computer Refers specifically to the computer control of machines for the numerical control purpose of manufacturing complex parts in metals and other (CNC) materials. Machines are controlled by a program commonly called a “G code”. Each code is assigned to a particular operation or process. The codes control X, Y, Z movements and feed speeds. Continuous flow A production method used to manufacture, produce or process materials without interruption. Craft production A small-scale production process centred on manual skills. Creep The slow, permanent deformation of a solid material under the influence of a mechanical stress. Creosote A material that penetrates the timber fibres protecting the integrity of the wood from attack from borer, wood lice and fungal attack. Cupping A warp across the width of the face of wood, in which the edges are higher or lower than the centre. Density The mass per unit volume of a material. Its importance is in portability in terms of a product’s weight and size. Design contexts include, pre-packaged food (instant noodles) is sold by weight and Page 10 / 28 © International Baccalaureate Organization 2015  volume, packaging foams. Design for assembly Designing taking account of assembly at various levels, for example, component to component, components into sub-assemblies and subassemblies into complete products. Design for Designing a product so that when it becomes obsolete it can easily disassembly and economically be taken apart, the components reused or repaired, and the materials recycled. Design for Designers design specifically for optimum use of existing manufacture manufacturing capability. Design for materials Designing in relation to materials during processing. Design for process Designing to enable the product to be manufactured using a specific manufacturing process, for example, injection moulding. Dry rot When timber is subject to decay and attack by fungus. Ductility The ability of a material to be drawn or extruded into a wire or other extended shape. Elasticity The extent to which a material will return to its original shape after being deformed. Electrical insulator Reduces transmission of electric charge. Electrical resistivity The measure of a material's ability to conduct electricity. A material with low resistivity will conduct electricity well. Electro-rheostatic This smart property relates to a fluid that can undergo a dramatic change in its viscosity when exposed to an electric field. Equilibrium EMC is at which the moisture content of wood achieves an Moisture Content equilibrium with the environment which can be affected by (EMC) humidity and temperature. Felting A method for converting yarn into fabric by matting the fibres together. First generation A simple mechanical arm that has the ability to make precise robots motions at high speed. They need constant supervision by a human operator. Free moisture The moisture within timber that is contained within the cell cavities and intercellular spaces. Glass A hard, brittle and typically transparent amorphous solid made by rapidly cooling a fusion of sand, soda and lime. Grain size (metals) Metals are crystalline structures comprised of individual grains. The grain size can vary and be determined by heat treatment, particularly how quickly a metal is cooled. Quick cooling results in small grains, slow cooling results in large grains. Grain size in metals can affect the density, tensile strength and flexibility. Hardness The resistance a material offers to penetration or scratching. Hardwood The wood from a deciduous (broadleaved) tree. Joining techniques Methods that are used to join two similar or dissimilar materials together. Kiln drying Kiln-drying places the stacks of sawn timber in a kiln, to reduce the moisture content in wood, where the heat, air circulation, and Page 11 / 28 © International Baccalaureate Organization 2015  humidity is closely controlled. Kiln seasoning Thermally insulated chamber, a type of oven, which produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Knitting A method for converting a yarn into fabric by creating consecutive rows of interlocking loops of yarn. Knots Imperfections in timber, caused by the growth of branches in the tree that reduces its strength. Lacemaking A method for creating a decorative fabric that is woven into symmetrical patterns and figures. Laminated boards Sheets of material made from layers of veneers (e.g. plywood). Laminated object A rapid prototyping systems that creates a 3D product by manufacture (LOM) converting it into slices, cutting the slices out and joining the slices together. Lamination Covering the surface of a material with a thin sheet of another material typically for protection, preservation or aesthetic reasons. Load capacity The weight a robot can manipulate. (Robots) Machine to machine Wired and wireless communication between similar devices. (M2M) Magneto-rheostatic This smart property relates to a fluid that can undergo a dramatic change in its viscosity when exposed to a magnetic field. Man-made timber Also known as engineered wood or composite wood, these are wood products that are made by binding or fixing strands, particles of fibres, veneers of boards of wood together with adhesives or other fixing methods to create composite materials. Typical examples include MDF, plywood and chipboard. Mass Relates to the amount of matter that is contained with a specific material. It is often confused with weight understandably as we use Kg to measure it. Mass is a constant whereas weight may vary depending upon where it is being measured. Mass customization A sophisticated CIM system that manufactures products to individual customer orders. The benefits of economy of scale are gained whether the order is for a single item or for thousands. Mass production The production of large amounts of standardized products on production lines, permitting very high rates of production per worker. Material selection A chart used to identify appropriate materials based on the desired charts properties. Mechanical Properties of a material that involve the relationship between stress properties and strain or a reaction to an applied force. Mechanized A volume production process involving machines controlled by production humans. Multi task robots A type of robot that can perform more than one task in a manufacturing environment. Page 12 / 28 © International Baccalaureate Organization 2015 Natural fibres Materials produced by plants or animals that can be spun into a thread, rope or filament. Non-toxic Absence of toxic breakdown products/lack of reactivity. One-off production An individual (often craft-produced) article or a prototype for larger- scale production. Oxidization A property of a metal that means that it does not readily react with resistance oxygen and degrade. Paper-based rapid Often the first step in a rapid prototyping process, paper prototyping prototyping is widely used in UCD for designing and testing interfaces. Particle boards A material made from different sizes of wood chips and joined with glue. Photochromicity A property of a smart material. A photochromic material changes colour in response to an increase in light. When the light source is removed, it returns to its original colour. Physical properties Any property that is measurable that describes a state of materials, for example, mass, weight, volume and density. These properties tend to be the characteristic of materials that can be identified through non-destructive testing (although some deformation is required to test hardness). Piezoelectricity A property of a smart material. A piezoelectric material gives off a small electrical discharge when deformed. Plasticity The ability of a material to be changed in shape permanently. Pultrusion A continuous manufacturing process used to create composite materials that have a constant cross-section. Reinforcing fibres are saturated with a liquid polymer resin and then pulled through a heated die to form a part. Reforestation Reforestation is the process of restoring tree cover to areas where woodlands or forest once existed. If this area never returns to its original state of vegetative cover the destructive process is called deforestation. Seasoning Seasoning is the commercial drying of timber which reduces the moisture content of wood. Second generation Robots that are equipped with sensors that can provide information robots about their surroundings. They can synchronize with each other and do not require constant supervision by a human; however, they are controlled by an external control unit. Shape memory Shape memory alloys are metals that when deformed, can spring alloys back into its original shape once released. Shaping techniques Manufacturing methods for modifying the shape of a material. Single task robots Robots that can perform one task only. Smart material Materials that have been designed to have one or more properties that can be modified when subject to an external stimuli in a way that the output can be controlled. Softwood The wood from a coniferous (evergreen) tree. Page 13 / 28 © International Baccalaureate Organization 2015 Stiffness The resistance of an elastic body to deflection by an applied force. Strain The response of a material due to stress, defined as the change in length divided by the original length. Stress A force on a material divided by the cross-sectional area of that material. Super alloys An alloy that exhibits excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion. Synthetic fibres Fibres made from a man-made material that are spun into a thread; the joining of monomers into polymers by the process of polymerisation. Examples include polyester, acrylic, nylon, rayon, acetate, spandex, and Kevlar. Tempering A heat treating process designed to increase the toughness of an iron-based metal by heating it and allowing it to cool in air. Tempering decreases the hardness of the material, which usually increases the ductility and decreases the brittleness. Tensile strength The ability of a material to withstand pulling forces. Thermal The measure of how fast heat is conducted through a slab of conductivity material with a given temperature difference across the slab. Thermal expansion A measure of the degree of increase in dimensions when an object is heated. This can be measured by an increase in length, area or volume. The expansivity can be measured as the fractional increase in dimension per kelvin increase in temperature. Thermo-electricity This refers to a smart material that when heated can produce an electric current. A thermoelectric material is comprised of two dissimilar conductors. Thermoplastic A type of plastic that can be heated and formed into a new shape repeatedly. Thermosetting A type of plastic that once formed into a shape, cannot be reformed plastic into a different shape. Third generation Autonomous robots that can operate largely without supervision robots from a human. They have their own central control unit. Swarms of smaller autonomous robots also fit in this category. Toughness The ability of a material to resist the propagation of cracks. Transparency Ability to allow light to be transmitted with minimal scattering allowing a clear view through material. Twisting A distortion in which the two ends of a material do not lie on the same plane. Volume The quantity of three-dimensional space enclosed by a boundary, for example, the space that a substance solid, liquid, gas, or shape occupies or contains. Warping A distortion in wood caused by uneven drying, which results in the material bending or twisting. Wasting/subtractive Manufacturing techniques that cut away material in order to create techniques a component. Page 14 / 28 © International Baccalaureate Organization 2015 Weaving The act of forming a sheet like material by interlacing long threads passing in one direction with others at a right angle to them. Weight Relies on mass and gravitational forces to provide measurable value. Weight is technically measure as a force, which is the Newton, i.e. a mass of 1 Kg is equivalent to 9.8 Newton [on earth]. Wood recycling Wood recycling is the process of turning waste timber into usable products. Recycling timber is a practice that was popularized in the early 1990s as issues such as deforestation and climate change prompted both timber suppliers and consumers to turn to a more sustainable timber source. Wood treatment Treatment of wood can involve using solutions, which make the wood poisonous to insects, fungus, and marine borers as well as protecting it from the weather. Work envelope A fixed 3D space where work activities take place, considering clearance and reach. Work hardening Also known as strain hardening or cold working, this is the process of toughening a metal through plastic deformation. Yarn A long continuous length of interlocked synthetic or natural fibres. Young's Modulus A measure of the stiffness of an elastic material and defined by stress/strain. Page 15 / 28 © International Baccalaureate Organization 2015