Welding Shop Prepared by, Miftahul Mobin Chowdhury Lecturer, Department of Mechanical Engineering Rajshahi University of Engineering & Technology, RUET, Rajshahi Metal Joining processes: Joining processes include welding, brazing, soldering, mechanical fas-tening, and adhesive bonding. Mechanical fastening can be used to provide either temporary or permanent joints, while adhesive bonding, welding, brazing, and soldering processes are mainly used to provide permanent joints. What are different types of joining process? Joining includes welding, brazing, soldering, adhesive bonding of materials. They produce permanent joint between the parts to be assembled. What are the four types of permanent joining methods? What are the four types of permanent joining methods? Answer: The joining processes are (1) welding, (2) brazing, (3) soldering, and (4) adhesive bonding. Methods of Joining Metals ▪ Soldering ▪ Soldering-bits ▪ Soldering iron ▪ Soldering Flux ▪ Brazing ▪ Welding ▪ Riveting ▪ Mechanical Fastening ▪ Adhesive bonding Mechanical, Chemical & Metallurgical Joining Process: Mechanical joining •Mechanical energyRiveting •Caulking •Bolting •Shrink fitting •Folding Chemical joining •Chemical energyBonding Metallurgical joining (welding) Fusion welding •Electrical energyArc welding •Electron beam welding •Chemical energyGas welding •Light energyLaser welding Pressure welding •Electrical energyResistance welding:Resistance spot welding •Projection welding •Seam welding •Upset welding •Flash welding •Chemical energyExplosion welding •Mechanical energyCold pressure welding •Friction welding •Friction stir welding (FSW) •Ultrasonic welding •Diffusion welding Brazing/soldering •Electrical energyInduction heating brazing (soft brazing = soldering) •Chemical energyTorch brazing (flame brazing) •Light energyLight beam brazing •Laser brazing Metal Joining processes: https://www.slideshare.net/MechieProjects/metal-joining-processes-welding-riveting-bolting-brazing-soldering https://www.slideshare.net/Huai123/topic-7-joining-process-welding-brazing-soldering-fastening-160214 Joining of Metals: Method # 1. Soldering: There are various common methods of joining parts together used in Engineering works. Soldering is one of the techniques of the joining method, but thinner parts. A. What is Solder? Solder is an Alloy of Tin and Lead, sometime Antimony and Bismuth are also added. B. Types of Soldering: There are three types of Soldering: 1. Soft Soldering; 2. Hard Soldering; 3. Brazing. 1. Soft Soldering: Soft Soldering is a processes of joining two or more pieces of similar or dissimilar thinner parts by an alloy called ‘Solder’, which has a lower melting point than the base metals. The temperature required is approx. 300°C to 350°C for Soft Soldering. 2. Hard Soldering: In this process is required an extra external heat which comes from Blow-Lamp or Oxy-acetylene flame to melt the solder. Generally it is used for underground cable-joint of Telephone, Electric, etc. Metal Joining processes: 3. Brazing: Brazing is a kind of Hard Soldering. In this process, heat is applied from Oxy-acetylene flame. But in Soft Soldering no extra heat is required. D. Types of Soft Soldering and Its Composition: Types of Soft Soldering and Its Composition E. Equipment’s and Jointing Process of Soft Soldering: Equipment’s required for Soldering are: i. Soldering Iron ii. Open Hearth Furnace iii. Electrical Soldering Iron iv. Zinc Chloride Solution or Acid, Emery Paper, etc. F. How to Join by Solder: One point should be remembered—only thinner parts can be soldered by this process. A thin sheet, like Galvanized sheet, may be joined to another Mechanical process by Riveting and by Soldering to Soft Soldering. Before Soldering, the parts should be cleaned with ACID (Zinc Chloride solution) or liquid Fluxes to remove dust, oil and grease, and other foreign metals. The Soft Soldering Iron is heated by an open hearth furnace or by electrically. Thinner parts of Tin, Copper, Brass, Aluminium, etc. and electronic parts like Television and electrical goods can be repaired by this process. Metal Joining processes: 1. What is Solder? Classify the types of Soft Soldering. 2. What is the main composition of Solder? 3. Why is flux or acid used before Soldering? 4. An electronic part of Television has been disconnected at the inside, wire. How and what measure would you take to repair the same? Name the type of Solder which would be required to join the T.V. parts and a Tin made Mug or Bucket. Joining of Metals: Method # 2. Brazing: ❑ Brazing may be defined as “Hard Soldering”. Brazing is a method of joining metals by the use of a fusible alloy consisting largely of Brass, and melting at a temperature above 600°C. Brazing produces a much stronger joint than soft soldering but requires greater heat from Oxy-acetylene flame. But it should be remembered that it is a temporary joint. It can be easily separated after heating of the welded bronze metal. ❑ In this process, non-ferrous or alloy filler metal is used whose melting point is higher— about 1,000°F (540°C)—but lower than that of the metals being welded. The Bronze or Brass filler rod should be coated with a flux of a deoxidizing agent. This operation is called “fluxing the rod”. ❑ Moreover, the operation Tinning is very important in Bronze welding or Brazing. By moving the flame around the starting point of the weld, the base metal gradually becomes red hot. Tinning is an operation in which a molecular union between the Bronze filler metal and the base metal is achieved. The strength of weld mainly depends upon the molecular union. Metal Joining processes: Joining of Metals: Method # 3. Brazing Flux: ❑ Flux is a chemical compound or mixture of deoxidizing agent used as powder, paste, liquid, granular, and gaseous. The flux employed in Brazing operations depends entirely upon the type of operation and the Brazing alloy being employed. ❑ When metals are heated in contact with air, oxygen from oxides cause poor quality low strength welds, or, in some cases, may even make welding impossible. For this reason it is generally desirable to add a flux to the welding area— this being a substance capable of dissolving the oxide. ❑ It is important to know that “The ordinary grades of mild steel provide an exception to the rule, because they may be successfully welded without the use of a flux. The reason is that mild steel contains considerably, more silicon and manganese which act as deoxidizing and fluxing agents.” ❑ No single flux is suitable for all metals. So it is necessary to choose a flux developed specially for the particular metal being welded. For ferrous materials, borax, sodium carbonate, sodium bicarbonate, and sodium silicate have been found to give excellent results, together with small additions of vigorous deoxidizing substances. ❑ Purposes of Flux: ❑ Firstly, Flux serves several purposes. Flux acts as a good insulator and concentrates heat in a relatively small welding zone—thus improving the fusion of the welding rod and the melted parent metal. ❑ Secondly, the molten portion of the flux floats as a liquid blanket over the molten pool of the electrode and parent metal, protecting it from the atmosphere and reducing to a minimum its pick-up of Oxygen and Nitrogen. Metal Joining processes: Joining of Metals: Method # 4. Riveting: Rivets are used when it is required to connect permanently two or more pieces of heavy section metal. Light gauge sheet can also be joined by Riveting. It is required specially in heavy sections such as, Bridge, Wagon, Tanker, Boiler, etc. In engineering rivets are usually made of wrought iron or mild steel. A rivet consists essentially of three parts—the Head, the two types of Rivets: (1) Snap head rivet; and (2) Pan head rivet. Process of Riveting: There are four processes of riveting: riveting; (1) Single riveting; (2) Double (3) Chain riveting; and (4) Zig-Zag riveting. The holes in the plates are either punched (light gauge sheet) or drilled (in heavy section). Punching is liable to damage the plates, especially when they are of hard wrought iron. On the best work, plates are ‘tacked’ or clamped together by a few bolts here and there along the seam. So the remaining holes may be drilled through both plates without any danger of trouble arising through holes being out of alignment. A Burr is usually left after every drilling operation as a riveted joint may aid shear. Metal Joining processes: Welding: Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the pplication of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building. Types of welding GAS Welding ARC Welding GAS WELDING Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch The temperature generated during the process is 33000c. When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld. Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas. GAS WELDING EQUIPMENT 1. Gas Cylinders Pressure Oxygen – 125 kg/cm2 Acetylene – 16 kg/cm2 2. Regulators Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depends upon the thickness of the work pieces welded. 3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve Gas welding Schematic: Gas welding Schematic: Gas welding FLAMES PRODUCED DURING GAS WELDING Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame. Addition of more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c). Used for welding steels, aluminium, copper and cast iron oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c) Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (30000c). Advantages of Gas welding. 1.Simple Equipment 2.Portable 3.Inexpensive 4.Easy for maintenance and repair Disadvantages Of Gas welding 1.Limited power Density 2.Very low welding speed. 3.High total heat input per unit length 4.Large Heat affected Zone 5.Severe Distortion 6.Not recommended for welding reactive metals such as titanium and Zirconium. Flames in gas welding: Gas welding & Arc welding: GAS WELDING 1. Heat is produced by the Gas Flame 2. The Flame temperature is about 3200C 3. Separate Filler rod introduced 4. Suggested for thin materials 5. Gas welded parts do not have much strength 6. Filler metal may not be the same parent metal 7. Brazing and soldering are done using gas. ARC WELDING 1. Heat is produced by Electric Arc 2. The temperature of Arc is about 4000oC 3. Arc Producing as well as filler rod material is the electrode. 4. Suggested for medium and thick materials 5. Arc welded parts have very high strength 6. Filler metal must be same or an alloy of the parent metal 7. Brazing and soldering can’t be carried out by electric arc. ARC WELDING Uses an electric arc to coalesce metals Arc welding is the most common method of welding metals Electricity travels from electrode to base metal to ground 1.Arc welding Equipments • A welding generator (D.C.) or Transformer (A.C.) • Two cables- one for work and one for electrode • Electrode holder • Electrode • Protective shield • Gloves • Wire brush • Chipping hammer • Goggles Electric arc Welding: Arc Welding: Arc Welding: 2.Electrode Electrode is a thin rod made up of same as that of parent material. Flux is coated over the electrode to avoid oxidation. It is mostly connected to the negative polarity. Two Basic Types of AW Electrodes Consumable – consumed during welding process Source of filler metal in arc welding Nonconsumable – not consumed during welding process Filler metal must be added separately Consumable Electrodes Forms of consumable electrodes • Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less in diameter and must be changed frequently • Weld wire can be continuously fed from spools with long lengths of wire, avoiding frequent interruptions In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal. Nonconsumable Electrodes Made of tungsten which resists melting Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool 3.Flux A substance that prevents formation of oxides and other contaminants in welding, or dissolves them and facilitates removal Provides protective atmosphere for welding Stabilizes arc Reduces spattering 4.STEPS FOLOWED IN ARC WELDING : • Prepare the edges to be joined and maintain the proper position • Open the acetylene valve and ignite the gas at tip of the torch Arc welding: • Hold the torch at about 45deg to the work piece plane • Inner flame near the work piece and filler rod at about 30 – 40 deg • Touch filler rod at the joint and control the movement according to the flow of the material Advantages Most efficient way to join metals Lowest-cost joining method Affords lighter weight through better utilization of materials Joins all commercial metals Provides design flexibility Disadvantages • Manually applied, therefore high labor cost. • Need high energy causing danger • Not convenient for disassembly. • Defects are hard to detect at joints. Difference between Gas Welding and Arc Welding Difference between Gas Welding and Arc Welding Different types of welding: https://www.brainkart.com/article/Metal-Joining-Process_5740/ https://www.slideshare.net/pradeepbolisetti/welding-and-types Arc welding Types of welding Types of welding SMAW: TIG welding: MIG Weldding: Welding defects: Welding joints:
