Engineering Unit 3 Section 11 Engineering Processes LO3. AC3.1 AC3.2
Joining Materials Joints between materials can be temporary or permanent. Joints can be formed with adhesives, frame joints, brazed or welded joints, or with fastening components such as nails, screws, bolts, and rivets. Types of joint Joints in wood can be made with screws, nails, glues and knock-down components, or with frame joints such as butt joints, halving joints, mortice-and-tenon, dovetail, and box joints. Joints in metal can be made by brazing, soldering, welding or using rivets. Joints in plastics can be made with plastic adhesive, rivets, bolts or machine screws. Most products are made from more than one piece of material, so when the product is assembled or fabricated the pieces need to be joined. Permanent and temporary joints Permanent joints are intended to stay put. They may make use of adhesives, nails, rivets, or one of the heat processes of brazing, soldering or welding. Assembly jigs are often used to hold components in place while they are being joined. For example, the parts of a steel roof frame can be put into the jig and then welded together. Temporary fixings usually involve components with a screw thread, such as screws, nuts and bolts, or one of the many knock down fixings on the market. Adhesives There are many types of adhesives to suit different materials. When you are choosing the right one for your product you will have to take into consideration the type of material, the strength of the bond required and the environment the product will work in - for example if you are gluing timber for outdoor use, you would not use polyvinyl acetate (PVA), because it is water soluble. Double-sided tape is widely used in industry, many parts of aircraft are held together with double-sided tape.
Joining Metals Oxyacetylene gas welding is commonly used to permanently join mild steel. A mixture of oxygen and acetylene, burns as an intense / focussed flame, at approximately 3,500 degrees centigrade. When the flame comes in contact with steel, it melts the surface forming a molten pool, allowing welding to take place. Oxyacetylene can also be used for brazing, bronze welding, forging / shaping metal and cutting. Oxy-Acetatline Cylinders Gas Cutting/Welding & Brazing Used for pipe work, thin sheet steels
Joining Metals Oxy-Acetatline Cylinders Gas Cutting/Welding & Brazing Used for pipe work, thin sheet steels When brazing, flux is applied to the joint, to prevent oxidation of the surfaces. The steel tube and plate are heated to bright red heat and the brazing rod (filler rod) applied to the joint. The end of the filler rod melts and flows around the joint, through capillary attraction. This gives a joint that looks like a line of bronze. Brazing is ideal for manufacture of bicycle frames, as it does not fracture as easily as steel welded joints Brazing and braze welding (bronze welding), can be used to join similar and also dissimilar metals such as: Mild Steel - Galvanized Steel Stainless Steel - Copper Mild Steel - Stainless Steel Stainless Steel - Copper-Nickel Mild Steel - Cast Iron
MIG Welding MIG welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the work piece metal(s), which heats the work piece metal(s), causing them to melt and join. POP RIVETING 1. The two pieces of plastic or aluminium are drilled to a size slightly larger than the rivet 2. The pop rivet is passed through both holes in the sheet plastic / aluminium. 3. The rivet pliers are pushed on to the pin of the rivet and the handles are pulled together. As this happens the pin head is pulled into the rivet and the end of the rivet is expanded. Eventually the pin will break off leaving the rivet permanently fixed in position holding the two pieces of plastic / aluminium together.
Soldering Soldering is a process in which two or more items (usually metal) are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes. Soldering is also used by plumbers to join copper pipes together in your homes.
Forging Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it is performed: cold forging (a type of cold working), warm forging, or hot forging (a type of hot working). For the latter two, the metal is heated, usually in a forge. Forged parts can range in weight from less than a kilogram to hundreds of metric tons. Forging has been done by smiths for millennia; the traditional products were kitchenware, hardware, hand tools, edged weapons, cymbals, and jewellery. (Heating Steel to Shape it) Producing decorative metal work/horse shoes etc Coal Forge Gas Forge Machine Forging/Drop Forge Blacksmith forging/shaping steel. Swords, horse shoes, blades Cold Chisel (cuts through metals when it is struck with a hammer )
Drilling COMMON DRILL BITS Good quality drill bits are manufactured from High Speed Steel (HSS). This type of steel keeps its sharp edge for along time and is capable of cutting through extremely resistant materials. Do not buy cheap carbon steel bits as they are a false economy. They will wear quickly an will not cut through resistant materials Twist drills come a range of sizes. the more common sets of twist drill range from 1mm to 10mm in diameter. When drilling the larger diameters it is wise to drill a smaller pilot hole first and then increase the diameter of the hole by drilling with a larger size. When drilling metals, use a lubricant such as oil. This will cool the drill bit as it cuts and lubricate the surface of the drill bit against the surface of the material being cut. Masonry bits are very similar to normal twist drills. However, tip is usually made from carbide steel. This is extremely tough and keeps its sharp edge even when drilling stone and brick. From time to time the tip will need grinding in order to re-sharpen the cutting edge. Hole Saws are used to drill large diameter holes, usually through thin wood boards. When drilling it is important to withdraw the saw/drill regularly to allow all the waste wood/chippings to escape from the hole. If this is not done the saw tends to jam. This can be dangerous. Hole saws are provided with a range of sizes of saws. The saw can be changed easily. The grub screw holds the saw firmly against the shaft of the drill bit so that it revolves at the same speed. Flat Bits are use to drill fairly large holes in wood boards and sections. They can be purchased in a range of sizes. A Plug Cutter is useful for cutting reasonably large holes through wood based materials. The wood collects inside the cylinder and can be removed quite easily, giving a disc of material. A Forsner Bit is used to cut blind holes in wood based materials. A blind hole is one that does not go all the way through the material being drilled.
Finishing (of products) In this section we will look at Finishing Techniques of products and how the choice of finishes will affect the aesthetic characteristics and properties of the product. When designing a product it is vital that the correct finish is applied to ensure: It works well in its chosen environment It has the required aesthetic appeal for the chosen target market It improves the products performance Finishing can be broken down into two sub-categories. These are: Self Finishing Applied Finishing Self-finishing Self finishing is a term applied to materials that do not need any extra finishing techniques applied (e.g. Plastic). When plastic products are moulded (e.g. Injection Moulding) aesthetic finishes can be automatically applied if they are part of the mould, such as dimpled surfaces or glossy surfaces. Examples include: TV/Computer cases Kettles Car Parts (dashboards, bumpers, lights) Phone cases
Applied Finishing Applied finishes are those finishes that need an extra process in the manufacture of a product to ADD a finish to improve the look of the chosen material, improve its performance and to protect it from the environment. Examples of Applied Finishes: For Wood Paint Water based paints are used in school because they are non toxic and quick drying. Emulsion paint as used on walls at home can be used but ACRYLIC paints are tougher and more durable. A primer can be applied which will stick thoroughly to the surface and give a matt finish. Two or more topcoats of the coloured acrylic can then be applied. A foam roller gives an excellent finish, foam brushes can also be used. A light sanding between coats ensures a smooth final finish. Oil based paints can be used but are slow drying. Solvent based paints usually in aerosol cans will give a very good finish but the solvent is a fire risk and is also toxic. These paints can be used on metals as well. The use of a primer to ensure that the surface is chemically neutral is essential when painting metals, especially steels. Varnishes and Lacquers These are similar to paint but they are clear/translucent. They are available in matt, satin and gloss finishes the same as paint.
Oil Teak oil used on garden furniture is the best known. Linseed oil can also be used on many types of wood (linseed oil is the basis of traditional oil paint and is also used to make putty). Danish oil is a quick drying oil which can be used on any timber to enhance its appearance. Vegetable oils can be used on wooden food utensils. Wood stains colour the wood but need to be protected with varnish or lacquer. Coloured varnishes and oils are also available. Sanding sealer usually cellulose based (solvent). Very quick drying and used to seal the surface which is then sanded to flatten the surface before subsequent coats of paint or varnish are applied. Very effective when a wax finish is to be applied. Water based versions are now available. For Metals Iron and Steel - mild steel, tool steels. Steels rust (except stainless steel) so they need to be protected against moisture and air. Coating in oil or grease is effective as long as the coating is not removed. All of the steel that is delivered to the school is greasy. Plastic dip coating is very effective as it can change the appearance as well e.g. the shelves in fridges and dishwashers are plastic coated. In school the steel item is heated up to straw colour (blue is too hot), then dipped into a fluidising tank, where air is blown through the polythene powder to make it fluid enough for the item to be dipped in. The coated item is then removed and allowed to cool. Any excess coating is trimmed off with a knife.
Anodising (aluminium) Anodising is an electrical process which makes the oxide layer increase its thickness. This thicker oxide layer can be dyed any colour. Brasses and bronzes. These alloys are usually simply polished and lacquered or left unfinished. They are resistant to serious corrosion in normal use but do become dull. Enamelling (Metals) A powdered glass is melted and fused onto the metal. This requires high temperatures. This finish is very heat resistant. Portfolio Task Create an A3 Poster using text and images that answers all the below questions on FINISHING. 1). Why are finishes usually applied? 2.) Name three metal finishes? 3.) Name three wood finishes? 4.) Name a material that uses self-finishing? 5.) Name some products that wood stains are used on? 6.) Name some products that enamelling is used on? 7.) What is plastic dip-coating? 8.) What material can you anodise? 9.) What else should you use with sanding sealer? 10.) What oil should you use on wood which comes in contact with foods?