Presentation on theme: "Joining Metals Learning Intention: understand the processes of soldering, brazing, welding, riveting/pop riveting."— Presentation transcript:
1 Joining MetalsLearning Intention: understand the processes of soldering, brazing, welding, riveting/pop riveting
2 Permanent / Temporarythe method used will depend on the function, strength and quality of the product.
3 Soldering Three Rules of Soldering - All surfaces must be clean (no grease or dirt),Both parts must be hot so the solder will flow towards the heat,Flux must be used to clean the surface and encourage the solder to flow.
4 Fluxthe elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder/brazing rod) to re-oxidizeThe purpose of flux is to facilitate the soldering process. One of the obstacles to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil or oxidation. The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece. A freshly-cut apple turns brown, a bicycle fender becomes rusty and a copper penny suddenly turns green. What do all of these events have in common? They are all examples of a process called oxidation.Oxidation is defined as the interaction between oxygen molecules and all the different substances they may contact, from metal to living tissue. Technically, however, with the discovery of electrons, oxidation came to be more precisely defined as the loss of at least one electron when two or more substances interact. Those substances may or may not include oxygen. (Incidentally, the opposite of oxidation is reduction — the addition of at least one electron when substances come into contact with each other.) Sometimes oxidation is not such a bad thing, as in the formation of super-durable anodized aluminum. Other times, oxidation can be destructive, such as the rusting of an automobile or the spoiling of fresh fruit.We often used the words oxidation and rust interchangeably, but not all materials which interact with oxygen molecules actually disintegrate into rust. In the case of iron, the oxygen creates a slow burning process, which results in the brittle brown substance we call rust. When oxidation occurs in copper, on the other hand, the result is a greenish coating called copper oxide. The metal itself is not weakened by oxidation, but the surface develops a patina after years of exposure to air and water.
5 Joining Metals - Soft soldering Quick method of joining copper, brass and tinplate when little strength is required in the joint. Also for fixing electronic componentsSoldering is a process in which two or more metal items are joined together by melting and flowing 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.Soft solder – tin & lead
6 Silver / Hard Soldering Alloys of copper with either zinc or silver. Stronger join. Solder can be filed – soft solder can not."Hard" solders are alloys that melt at slightly lower temperatures than the corresponding metal pieces to be fused. Silver and gold jewelry require hard soldering. Copper, brass, and bronze components can also be fused with hard solders.
7 Brazing – typically for joining steel Melting point of filler rod above 450Very strong join.Can be used to braze copper and brass but skill is needed.Brazing is a way of bonding materials (usually metals) by melting a filler metal or alloy between the components you want to join. The filler metals used in brazing usually have melting points between 450°C and 1000°C, but must have a lower melting point than the material being joined. Brazing forms very strong, permanent joints.
8 Welding Strongest type of join The two pieces of metal are melted along the filler rod, fusing together as they cool..
9 Welding - oxy-acetylene a very hot flame is used
10 Welding - electric arc welding type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point.
11 Welding - electric arc welding Arc welding also know as stick welding uses a filler rod (electrode) that has flux, the MIG has a coil and uses gas to keep the weld area clean – clean up is necessary with ARC because of the flux rod, but not with the MIGArc better for thicker metal plate the process is generally limited to welding ferrous materials, though specialty electrodes have made possible the welding of cast iron,nickel, aluminium, copper and other metals
12 Welding - MIG Welding(Metal Inert Gas) Commonly used in schools.A form of electric arc welding but carbon dioxide gas surrounds the arc and prevents the oxidation of the molten steel. The joint is clean of slag and very strong. The arc is very bright and a protective eye shield must be used.. Originally developed for welding aluminium and other non-ferrous materials in the 1940s, was soon economically applied to steels. Today, commonly used in industries such as the automobile industry for its quality, versatility and speed. Because of the need to maintain a stable shroud of shielding gas around the weld site, it can be problematic to use the process in areas of high air movement such as outdoors.
15 Welding - Spot WeldingSpot welding used on sheet steel , stainless steel, Aluminium and light-alloys, galvanized sheets, brass and copperElectrodes which are copper tipped are brought together on either side of the joint. When the electric current flows a high temperature is produced, melting the metal at the point of contact. A spot weld is producedSpot welding can be used for joining many ferrous and non-ferrous alloys. The materials that are more easily welded by this process, are low alloy and steel, stainless steel, Aluminium and light-alloys, nickel and its alloys, galvanized sheets, brass and copper can also be welded.
16 Riveting components used for joining metal Rivets are used to join plates together and they have been used for hundreds of years. Before the widespread use of welding, rivets were used in heavy industries such as ship building. The steel plates used to build ships such as the Titanic and the naval Dreadnaughts of World War One were held together by steel rivets.Rivets have largely being replaced by techniques such as welding and brazing. However, joining plates together with rivets is still a useful technique especially if the plates to be joined are quite small.
18 A hole is drilled through both pieces of work, the rivet is placed through it, and its end beaten into a dome. A tool called a rivet set or rivet snap is used to finish the joint off neatly. Some rivets are countersunk.
19 RivetingCold Rivets can be used to permanently join plates together. Steel rivets are used for joining steel plates whilst aluminium rivets are used for aluminium plates. Rivets are available made from other materials such as copper and brass. The material of the rivet normally matches the material to be riveted together. In the case of perspex, aluminium or copper rivets are the most suitable because they are relatively soft and easy to shape.1. Rivets are made from either aluminium, steel, copper or brass. They are supplied in different lengths and diameters and must be cut to the exact length using a junior hacksaw.2. The head of the rivet is set to rest in the 'dome' of a ‘dolly’. A typical 'dolly' is shown on the left. This tool is held in an engineers vice and it supports the rivet’s head.3. The plates are placed over the rivet, resting on the top surface of the dolly.4. The plates are pushed over the rivet and in order to ensure that there are no gaps between them a rivet set is pushed pushed down, over the rivet's shaft. The rivet's shaft fits inside a small hole at the base of the rivet set. The rivet set is made from hardened steel as it is tapped at the top with a ball pein hammer. This closes any gap between the two plates.5. The ball pein hammer is reversed and used to expand the ‘tail’ of the rivet. This may take several slight taps. At this pint the rivet cannot be removed from the plates.6. The ball pein side of the hammer is used to form the rivet head. This takes time and should not be rushed. The head should form a dome.7. The final shaping of the rivet head is formed using the rivet snap. The plate should be permanently fixed together at this stage.
20 RivetingWith most rivets you need to get at both sides of the work to make the joint. Pop rivets enable you to complete the joint while only having access to one side of the work. They are usually used for joining thin sheets together.
21 Machine Screws Machine Screws Have a screw thread to fit into a threaded hole or a hexagonal nut. They can be used to join two or more pieces of metal or plastic.
22 Nuts and BoltsA bolt is only threaded for part of its length. Bolts normally have hexagonal heads.
23 Set screwHave a screw thread along the whole or most of their length, and normally have hexagonal heads