Topic 11 Advanced manufacturing

techniques

11.1 Joining 11.1.1 Describe friction welding. Friction welding is a completely mechanical solid phase process in which heat generated by friction is used to create the ideal conditions for a high integrity welded joint between similar or dissimilar metals. You can see an example of friction welding at: http://www.youtube.com/watch?v=cAXZYGZ8Yrg 11.1.2 Explain how two metal parts are welded using friction Diagrams should include two parts, one revolving, and the other fixed. By rotating a piece of metal against another which is fixed, heat is generated by the friction between the 2 components. The friction will generate enough heat to render each metal end molten. Pressure is constantly applied to the rotating piece via the fixed metal component, the 2 pieces fuse together and the process is complete. 11.1.3 Describe plastic welding. Consider hot air and friction welding techniques. Hot air welding is a plastic welding technique which is similar to gas welding of metals, though the specific techniques are different. A specially designed heat gun (hot air welder) produces a jet of hot air that softens the parts to be joined, as well as a plastic filler rod. Hot air/gas welding is a common fabrication technique for manufacturing smaller items such as chemical tanks, water tanks (black, grey, fresh & ballast), heat exchangers, and plumbing fittings. The materials being welded and the welding rod must be of the same or very similar plastic. Welding PVC to acrylic is an exception to this rule. 11.1.4 Explain how two plastic parts are welded together.

Only thermoplastics that do not burn or decompose when heated to their softening temperature can be welded.

11.1.5 Define permanent joining techniques. Basically a permanent joint is one that is intended to last the life time of a product where as a temporary joint is one which is intended to hold the item together but is removable easily at any stage without causing too much damage to the main product. 11.1.6 List a range of permanent joining techniques. Consider pop-rivets, brazing, welding and adhesives. 11.1.7 Discuss how permanent joining techniques lead to planned obsolescence and environmental issues. Permanent joins do not allow for the disassembly and easy maintenance of products. 11.1.8 Define adhesive. Glue or adhesive is a compound that adheres or bonds two items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry. 11.1.9 Identify a range of adhesives suitable for joining metals, woods and plastics. Polyvinyl acetate (PVA or PVAc) is a rubbery synthetic polymer. It is prepared by polymerization of vinyl acetate monomer, also referred to as VAM. As an emulsion in water, PVA is sold as an adhesive for porous materials, particularly wood, paper, and cloth. It is the most commonly used wood glue, both as "white glue" and the yellow "carpenter's glue." PVA is widely used in bookbinding and book arts due to its flexibility, and because it is non-acidic, unlike many other polymers. PVA is a common copolymer with more expensive acrylics, used extensively in paper, paint and industrial coatings, referred to as vinyl acrylics. It can also be used to protect cheese from fungi and humidity

Epoxy resin This is an expensive but versatile adhesive that will bond any clean dry materials. Equal amount of adhesive and hardener are mixed to start the chemical hardening process. Hardening begins immediately, but full strength is achieved after 1 or 2 days. In chemistry, epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction

between epichlorohydrin and bisphenol-A. Contact adhesive Contact adhesives as the name suggests stick on contact. They are used extensively for glueing large sheet materials such as thin laminates to kitchen worktop. Both surfaces must be coated with a thin layer of the adhesive. It is then

left to dry for approximately 15 minutes. As soon as the two coated surfaces are brought into contact there can be no repositioning. Contact adhesives can be used to stick dissimilar materials. Cascamite Cascamite is much stronger than PVA and is a waterproof, synthetic resin adhesive for use on general joinery - especially outside woodwork and boat building. It is supplied as a powder to be mixed with water. To use, push the two pieces together, rubbing the surfaces from side to side. This will ensure that air is not trapped and that the glue has been spread evenly. Use cramps such as G Cramps to lock the two pieces together. Leave for twenty four hours before removing the cramps.

Tensol cement

Plastics can be joined using a range of modern glues. Perhaps the best glue is Tensol Cement which joins plastics such as Acrylic together permanently. The glue is applied to the surfaces to be glued and they are pressed together. They should be clamped for 24 hours and this gives a permanent joint.

Superglue (cyanoacrylate). Super glue is another adhesive that joins plastics together, very quickly. Great care must be taken when using this type of glue as it will just as easily glue fingers together. For this reason super glue is not used in schools. 11.1.10 Discuss the advantages and disadvantages of using adhesive bonding in products. Advantages: Disadvantages:

No finishing required Not as strong as metals Improved fatigue resistance Increasing the service temperature

decreases the bond strength Dissimilar materials can be joined Needs to be clamped while setting The bond is permanent Bonded structures are difficult to dismantle

for repair Adhesives seal and join at the same time Need to prepare the surfaces On Loading there is more uniform stress distribution

Health and safety aspects

Local stress concentrations are avoided Long bonding times Large areas can be bonded Small areas can be bonded accurately Adhesives prevent catalytic corrosion Reduced weight Stronger and stiffer products can be

designed. 11.2 Moulding

11.2.1 Define sprue, flash, parison, die, draft angle and injection moulding. A sprue is the passage through which molten material is introduced into a mold. During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. Flash Flashing of a part can occur for several reasons—from variations in the process or material to tooling trouble. Flash appears on the part's edge along the parting line of the mold or anyplace where the mold has metal meeting metal to form a boundary of the part.

Parison

Blow molding of plastic containers. (Counterclockwise from top) A molten polymer is extruded into a hollow, tube-shaped parison. A split mold is closed around the parison, which is expanded against the sides of the mold by a stream of air. Once the plastic has solidified, the mold is opened and the shaped bottle released.

Die A die is a specialized tool used in manufacturing industries to cut, shape and form a wide variety of products and components. Like molds and templates, dies are generally customized and uniquely matched

to the product they are used to create. Products made with dies range from simple paper clips to complex pieces used in advanced technology. Draft angle A draft angle describes the amount of taper for molded or cast

parts perpendicular to the parting line.Consider the fabrication of a hollow plastic box, without lid. Once the plastic has hardened around the mold, the mold must be removed. As the plastic hardens, it may contract slightly. By tapering the sides of the mold by an appropriate "draft angle", the mold will be easier to remove.If the mold is to be removed from the top, the box should taper in towards the

bottom, such that measuring the bottom internal dimension will yield a smaller length and width than measuring the top from which the mold is extracted. Injection moulding 11.2.2 Explain how an injection-moulded product is made. Diagrams must include the hopper, hydraulics, heaters, screw, sprue and mould.

Stage 1: Granulated or powdered thermoplastic plastic is fed from a hopper into the Injection Moulding machine. Stage 2: The Injection Moulding machine consists of a hollow steel barrel, containing a rotating screw (Archemidial Screw). The screw carries the plastic along the barrel to the mould. Heaters surround the barrel melt the plastic as it travels along the barrel. Stage 3: The screw is forced back as the melted plastic collects at the end of the barrel. Once enough plastic has collected a hydraulic ram pushes the screw forward injecting the plastic through a sprue into a mould cavity. The mould is warmed before injecting and the plastic is injected quickly to prevent it from hardening before the mould is full.

Stage 4: Pressure is maintained for a short time (dwell time) to prevent the material creeping back during setting (hardening). This prevents shrinkage and hollows, therefore giving a better quality product. The moulding is left to cool before removing (ejected) from the mould. The moulding takes on the shape of the mould cavity.

The image below shows an an Injection Moulding machine.

11.2.3 Outline the advantages of injection moulding. Consider initial capital investment, tooling, accuracy, quality control and quantity of product.

Initial Capital Investment : Injection moulds themselves can be surprisingly expensive,

sometimes upward of US$100,000. If the desired part quantity, however, is great enough, the mould cost becomes relatively insignificant, and the resulting plastic parts are very reasonably priced.

Tooling: The choice of material to build a mould is primarily one of economics.

Steel moulds generally cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel moulds are less wear resistant and are used for lower volume requirements or larger components.

Hardened steel moulds are heat treated after machining. These are by far the superior in terms of wear resistance and lifespan.

Aluminium moulds can cost substantial ly less, and when designed and machined with modern computerised equipment, can be economical for moulding tens or even hundreds of thousands of parts.

Beryllium copper is used in areas of the mould which require fast heat removal or areas that see the most shear heat generated.

Accuracy: The moulds can be manufactured by either CNC machining or by using Electrical Discharge Machining processes. Establishing the correct tolerances with respect to the product function is of economic importance. The designer should be aware that dimensions with tight tolerances have a big influence on the costs of both product and mould. Even slightly over specifying tolerances may adversely influence tool costs, injection molding conditions, and cycle time. It is recommended to indicate only critical dimensions with tolerances on a drawing.

Quality control: If the product has been designed using CAD and the mould has been made using CAM the product can be virtually tested using an analytical computer software program

Quantity: The quantity of pieces from the injection moulder will depend on the number of cavities per die, the cycle time and the amount needed by the manufacturer. Injection moulders can run 24/7 with very little human interface. It is advisable for a moulder to produce mass pieces as start up costs are high.

11.2.4 Discuss how standardized bottle caps have constrained bottle design, but have cut costs for manufacturers. Bottle caps can be classed as standardized parts. Bottle tops are injection moulded, while bottles are normally made by blow moulding. It is financially beneficial for a blow moulding company to use off-the-shelf bottle tops instead of purchasing an injection moulding machine and new tooling. The advantage of using standard components is that it speeds up manufacturing and costs as the same units can be used around the world. 11.2.5 Describe how a blow-moulded product is made. The d iagram shows B low m o u l d i n g o f p l a s t i c containers. A molten polymer is extruded into a hollow, tube-shaped parison. A s p l i t m o l d i s c l o s e d around the parison,

which is expanded against the sides of the mold by a stream of air through the air inlet. Once the plastic has solidified, the mould is opened and the shaped bottle released. 11.2.6 Explain how a rotational-moulded product is made. Diagrams must include the mould, filling the mould, heater chamber, rotation and cooling chamber.

Rotational moulding is a versatile process for creating many kinds of mostly hollow plastic parts. The phrase is often shortened to rotomoulding.

The process was developed in the 1940s but in early years was used little because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted

in a significant increase in usage.

Diagrams must include the extruder, parison, the mould and air inlet. 11.2.7 Explain how a compression -moulded product is made. Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, and heat and pressure are maintained until the molding material has cured. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms. Diagrams must include the mould, pre-form, hydraulic press, finished part and flash material.

Flash Material

11.2.8 Discuss why some products have to be made using compression moulding. Consider the heat the product must withstand, quantity and type of product to be made. Refer to thermosets. Compression and Transfer Molding is accomplished by placing a pre-weighed amount of material in a matched metal mold and closing the mold. The heat and pressure cause the material to liquify and flow into the voids in the tool where it chemically reacts and hardens into the final shape. Very large shapes can be molded in compression presses.

11.2.9 Describe how a vacuum-formed product is made. Diagrams must include the vacuum chamber, former, platen, heater, air in and out.

Vacuum forming, commonly known as vacuforming, is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto or into a single-surface mold, and held against the mold by applying vacuum between the mold surface and the sheet.

The vacuum forming process can be used to make most product packaging, speaker casings and even car dashboards.

Normally, draft angles must be present in the design on the mold (a recommended minimum of 3°), otherwise release of the formed plastic and the mold is very difficult.

11.2.10 Identify manufacturing methods suitable for thermoplastics and thermosets. Thermoplastics: vacuum forming, blow moulding, injection moulding and rotational moulding.

Thermosetting plastic: compression moulding.

11.3 Casting Casting is a manufacturing process by which a liquid material is (usually) poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solid casting is then ejected or broken out to complete the process. Casting may be used to form hot liquid metals or various materials that cold set after mixing of components (such as epoxy, concrete, plaster and clay). 11.3.1 Describe lost wax casting.

Lost-wax casting is the process by which a bronze is cast from an artist's sculpture; in industrial uses the modern process is called investment casting. An ancient practice, It is more appropriate to use the term "lost mould" rather than "lost wax" since the technique employs other materials besides wax, such as tallow, resin, tar, and even textile. Because the mould is destroyed to unveil the cast item,

11.3.2 Describe how lost wax cast products are made. Consider preparation of the master pattern; injection of wax to create copy; creation of a wax tree to make a wide range of small parts from the same metal; covering wax with ceramic or plaster of Paris; removal of wax; and the addition of the final chosen material. 11.3.3 Explain how a range of products are made using lost wax casting. Jewellery, dental implants, hip replacements and wind instrument keys. http://www.expertvillage.com/video/515_lost-wax-casting.htm http://www.youtube.com/watch?v=gVe3VeQfyzw

11.3.4 Describe high-pressure die casting. Die casting is mainly used for low-melting alloys. Molten metal is forced into a mould under high pressure. High pressure die casting is a manufacturing process in which molten metal (aluminum) is injected with a die casting machine under force using considerable pressure into a steel mold or die to form products. Because of the excellent dimensional accuracy and the smooth surfaces, most high pressure die castings require no machining except the removal of flash around the edge and possible drilling and tapping holes. High pressure die casting production is fast and

inexpensive relative to other casting processes. 11.3.5 Describe how high-pressure die cast products are made. Draw a diagram to include holding furnace, injector, gooseneck and die. 11.3.6 Explain how a range of products are made using high-pressure die casting. Consider hip replacements, disk drive chassis and carburettors. 11.3.7 Outline two advantages and two disadvantages of high-pressure die casting. Advantages: high accuracy, good surface finish, thin walls, and high rate of production. Disadvantages: high plant costs, high tooling costs, cannot be used for a wide range of alloys, and limitations on maximum size that can be cast.

11.4 Forming Thermo set composites and contact moulding 11.4.1 Describe the process of spray-up.

Spray-up is carried out on an open mould, where both the resin and reinforcements are sprayed directly onto the mould. The resin and glass may be applied separately or simultaneously “chopped” in a combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate. Wood, foam or other core material may then be added, and a secondary spray-up layer embeds the core between the laminates (sandwich construction). The part is then cured, cooled and removed from the reusable mould. Spray-Up is a faster process and is less labour

intensive than hand lay-up. Several drawbacks include possibility of more air entrapment and a difficulty in controlling thickness and resin-to-glass ratios.

11.4.2 Identify products that could be made using spray-up processes. For example, pleasure boats and swimming pools. 11.4.3 Describe the process of hand lay-up. In hand lay-up processing, fibreglass continuous strand mat and/or other fabrics such as woven roping are manually placed in the mould. Each ply is sprayed with catalysed resin and the resin is worked into the fibre with brushes and rollers to wet-out and compact the laminate. 11.4.4 Identify products that could be made using hand lay-up processes. Products of varying sizes that do not need a high accuracy finish, for example, prototypes. Hand Lay-Up is well suited for low volume production of product. This method can be used for both both corrosion barrier and the structural portion. 11.4.5 Describe the process of filament winding. This process is primarily used for hollow, generally circular or oval-sectioned, components, such as pipes and tanks. Fibre tows are passed through a resin bath before being wound on to a mandrel in a variety of orientations, controlled by the fibre feeding mechanism, and rate of rotation of the mandrel. Filament winding machine design varies with part geometry. Filament winding is an excellent process for fabricating round equipment such as

11.4.6 Identify products that could be made using filament winding processes. For example, fishing rods and rowing oars. 11.4.7 Describe the process of vacuum bagging.

This process is basically an extension of the wet lay-up process where pressure is applied to the laminate once laid-up in order to improve its consolidation. This is achieved by sealing a plastic film over the wet laid-up laminate and onto the tool. The air under the bag is extracted by a vacuum pump, and thus up to one atmosphere of pressure can be applied to the laminate to consolidate it.

More details about Vacuum bagging can be found at: http://www.youtube.com/watch?v=mgBSMmqzSJM 11.4.8 Outline the benefits of using vacuum bagging when using composite layup techniques.

• Large products are possible • Top quality products through the use of pre-pregs • Clean production method • Low moulding costs.

Prepregs are specially formulated resin matrix systems, that are reinforced with man-made fibers such as carbon, glass and aramid. When cured at elevated temperatures, the themoset resin undergoes a chemical reaction that transforms the prepreg into a solid structural material that is highly durable, temperature resistant, exceptionally stiff and lightweight. Initially developed for the aerospace industry, prepregs are now used in a wide range of applications - from golf clubs to satellite arrays, and from wind turbine rotor blades to life-saving Formula 1 monocoques. Prepregs are supplied to customers in roll form, to be stored frozen and defrosted before use. When cured at elevated temperatures and under pressure, prepregs form molded components that are extremely strong and stiff. A broad range of formulated resins are used to impregnate the woven and unidirectional reinforcements.

11.4.9 Identify products that can be made using vacuum bagging processes. For example, laminated curved furniture. Model aircraft wings Guitar cases http://www.youtube.com/watch?v=nZeQHSgpVwM Surf boards Further information can be found at: www.epoxi.com www.resininfusion.com Advantages of Contact Moulding techniques:

• The use of reinforcing fibres results in high strength • Other performance additives, such as flame retardants can be incorporated • Versatile in terms of size

and shape • Allows thick sections to

be produced •

11.4.10 Explain how a curved shape is produced in timber using lamination. Thin layers of ply or veneers are laid onto a former, then glued and clamped. To eliminate spring-back on tight curves, a fast drying adhesive should be used. Thicker timber can be steamed and shaped over a former. Some spring-back is likely to occur, but it is possible to reduce this by combining lamination and steaming.

11.4.11 Discuss how lamination can be used to strengthen material. The structure of a timber is such that all fibres run along its length. Laminating more than one timber together but with fibres running at right angles increases the strength in all directions.

Engineered timber

Engineered timber is a generic term used to describe a wide range of wood-based products that have been engineered to

provide enhanced performance characteristics. This improves their suitability for particular end uses, especially in demanding structural situations, but may also be designed to improve other characteristics such as durability. Usually these products are composites that combine wood or wood fibre with adhesives and possibly other materials. Some reasons for engineering solid timber into such composites include:

• to overcome the dimensional limitations of sawn timber • to improve performance; structural properties and stability • to transform the natural orthotropic product into one with more homogenous

properties • to optimise the use of a valuable resource and minimise waste.

Engineered timber can take several forms:

Board materials such as oriented strand board (OSB), medium density fibreboard (MDF), plywood etc. are available for a wide range of structural, decorative and utility uses.

Structural timber composites produced in large sections for use as beams, columns and other structural components. Products include glued laminated timber (glulam), parallel strand lumber (PSL) and laminated veneered lumber (LVL).

Timber I-joists comprise a timber flange, typically solid timber or LVL (laminated veneer lumber) and a panel product web, usually OSB (oriented strand board). They offer a number of benefits over traditional sawn joists, including low weight, no moisture movement and greatly reduced risk of squeaks.

Structural Composite Lumber (SCL):

Structural composite lumber (SCL), which includes laminated veneer lumber (LVL), laminated strand lumber (LSL) and oriented strand lumber (OSL), is a family of engineered wood products created by layering dried and graded wood veneers or flakes with waterproof adhesive into blocks of material known as billets. Cured in a controlled process, SCL is typically available in various thicknesses and widths and is easily worked in the field using conventional construction tools.

Strong, Reliable and Consistent

In SCL billets, the grain of each layer of veneer or flakes runs primarily in the same direction. The resulting products out-perform conventional lumber when either face- or edge-loaded. SCL is a solid, highly predictable and uniform engineered wood product that is sawn to consistent sizes and is virtually free from warping and splitting.

Making the Best Use of Resources

One important benefit of SCL is that the veneering, flaking and gluing process enables large timbers to be made from relatively small trees of many species, thereby providing for efficient utilization of wood fiber resources.

11.4.12 Describe how LVL differs from plywood. Consider material cross-section and grain direction. http://www.wooduniversity.org/ 11.4.13 Discuss how forming techniques have enabled designers to be more flexible in the way they approach the design process. Material choice, environment and cost factors can be more widely addressed Topic 2 Language review Key word Have

heard of it Can use in a

sentence Can

define Can give a clear

example to explain

1 Friction welding 2 Plastic welding 3 Permanent joining 4 Adhesive 5 Sprue 6 Flash 7 Parison 8 Die 9 Draft angle 10 Injection moulding 11 Blow moulding 12 Rotational moulding 13 Compression moulding 14 Vacuum forming

15 Thermoplastic 16 Thermosetting plastic 17 Lost wax casting 18 High pressure die casting 19 Spay-up 20 Composite Lay-up 21 Filament winding 22 Vacuum bagging 23 Lamination 24 LVL