2 Presentation Topic : Welding Group : 1 Group Members Muhammad Summair Hariss Bin Waheed Mohsin Mumtaz Jahanzeb Qdeeir Khaqan Asad Kashif Amin
3 What is WeldingJoin together (metal parts) by heating the surfaces to the point of melting with a blowpipe, electric arc, or other means, and uniting them by pressing, hammering, etc
4 Welding Welding conditions Parts are joined together by Fusion. Fusion is brought about by a combination of heat and pressure between parts being joined. In normal welding processes very high temperatures and little or no pressure is used.Welding conditionsSmooth joint surfaces that match each otherSurfaces clean and free from oxides, grease and dirt.Metals to be joined have same microstructure
5 Welding Preparation Weld Joints Welding Symboles Welding Techniques The metals should be good quality (no internal impurities)Welding PreparationBefore starting a weld, the joint edges should be carefully prepared.Beveling large edgesCleaning (Chemical/Mechanical)Weld JointsWelding SymbolesWelding Techniques
6 Weld Joints - Parts of a Weld Joint Joint rootGroove face, Root face and Root edgeRoot opening and BevelBevel angle, Groove angle and Groove radiusWeld Joints - Types of Weld JointButt JointLap JointT JointCorner jointEdge JointSplice Member
7 Joint Rootis that portion of a joint to be welded where the members are closest to each otherThe joint root may be either a point, line, or an areaThe joint roots are shown as shaded areas in (A)-(D) and lines in (E) (F)
8 Groove face, Root face and Root edge Groove face is “ that surface of a member included in the groove”Root face (land) is “that portion of the groove face within the joint root”Root edge is a root face of zero width
9 Root opening and BevelRoot opening is the separation between the work pieces at the joint rootBevel (chamfer) is an angular edge preparation
11 Welding Joints Butt Joint A joint between two members aligned approximately in the same plane
12 Lap JointA joint between two overlapping members
13 T JointA joint between two members located approximately at right angles to each other
14 Corner JointA joint between two members located at right angles to each other
15 Edge JointA joint between the edges of two or more parallel or nearly parallel members
16 Splice memberis “ the work piece that spans the joint in a spliced jointSingle-spliced butt jointDouble-spliced butt joint with joint filler
17 Basic components of a welding symbol Reference Line (Required element)ArrowTailReference Line must always be horizontal,Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area.
18 OTHER SIDE ARROW SIDE Weld Symbol Terminology Work Fillet Weld (Arrow Side Only)Fillet Weld (Both sides)
19 Welding Techniques Types of Welding There are many different methods of welding. The difference between them is outlined by two important featuresThe way the metal is heatedThe way additional filler metal if any is fed into the weldTypes of WeldingElectric arc weldingGas WeldingResistance WeldingFriction WeldingRobotic Welding
20 Electric Arc WeldingThe heat for fusion is supplied by an electric arcArc is formed between electrode and work this melts and fuses the joint edges
21 Manual Metal Arc (MMA) Applications Most widely used of all the arc welding processesCommonly called “stick” weldingApplicationsrepair work, structural steelwork,
22 Electric Arc welding Electrode In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together.,
23 The Electrode and Coating Coating is a combination of chemicalsCellulosic electrodes contain celluloseRutile electrodes titanium oxide (rutile)Basic electrodes contain calcium carbonate (limestone) and calcium fluoride (fluorspar)
24 Advantages of Electric arc welding Used with many electrode types & sizesUsed in all positionsUsed on great variety of materialsFlexibility in operator control makes it the most versatile of all welding processesLow cost of equipmentDis-advantagesRod becomes shorter & periodically needs replacingSlows production rate (% time welder welding)
25 Metal Arc Gas Shielded (MAGS) MIG MIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece.But we use very long electrode wire rolled on pulley.ApplicationsWelding Sheets and Heavy plates, productionwelding by robots on cars
26 MIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece; the electrode melts to form the weld bead. The main differenceis that the metal electrode is a small diameter wire fed from a spool and a sheilding gas is used. As the wire is continuously fed, the process is often referred to as semi-automatic welding.
27 Advantages Large gaps filled or bridged easily Welding can be done in all positionsNo slag removal requiredHigh welding speedsHigh weld qualityLess distortion of work piece
28 Equipmnt used in MAGS Three major elements are : Welding torch and accessoriesWelding control & Wire feed motorPower Source is TransformerShielding Gas
29 Welding torch and accessories GAS DIFFUSERNOZZLECONTACT TIPThe welding torch guides the wire and shielding gas to the weld zone.Brings welding power to the wire alsoMajor components/parts of the torch are the contact tip, shielding gas nozzle, gas diffuser, and the wire conduit
30 Welding control and wire feed motor Main function is to pull the wire from the spool and feed it to the arcControls wire feed speed and regulates the starting and stopping of wire feed
31 Sheilding GasPurpose of shielding gas is to protect the weld area from the contaminants in the atmosphereGas can be Inert, Reactive, or Mixtures of bothArgon, Helium, and Carbon Dioxide are the main three gases used in MAGS
32 Tungsten Arc Gas Shielded (TAGS) TIG TIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpieceApplicationsUsed in joining magnesium andAluminium, stainless steelsfor high quality weldingThin sheet material
33 In the TIG process the arc is formed between a pointed tungsten electrode and the work piece in an inert atmosphere of argon or helium. The small intense arc provided by the pointed electrode is ideal for high quality and precision welding.The electrode is not consumed during welding. When filler metal is required, it must be added separately to the weldpool. There are two currents one for starting the arc the other switched on using a trigger or foot pedal, this is a high frequency currentto maintain the arc, this is generated by a separte unit.
34 Advantages Superior quality welding Can be used in mechanised systems Used to weld aluminium and stainless steelsLow distortion
35 Equipment used in TAGS Power source Electrodes TIG must be operated with a constant current power source - either DC or ACElectrodesElectrodes for DC welding are normally pure tungsten. In AC welding, as the electrode will be operating at a much higher temperature, It should be noted that because of the large amount of heat generated at the electrode, it is difficult to maintain a pointed tip and the end of the electrode assumes a spherical or 'ball' profile.
36 Sheilding GasShielding gas is selected according to the material being welded. Argon Argon + Hydrogen Argon/HeliumHelium is generally added to increase heat input (increase welding speed or weld penetration). Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.
37 Gas Welding (Oxy-acetylene) A number of welding processes use a flame produced by burning a mixture of fuel gas and oxygen. The gas usually used is Acetylene but other gases are also used.Separate cylinders and a hose pipe from each cylinder transports the gases to a torch.Gas and fuel mix in the torch3100°C.
38 During the welding heat from the flame is concentrated on the joint edges until the metal melts and starts to flow. When the molten metal from both sides melts it starts to fuse, when the metal cools down the two parts become Permanently joinedAdditional Filler Metal is fed in by hand into the weld pool, at regular intervals where it becomes molten and joins with the parent metal.
39 The Oxy-acetylene welding Flame CarburisingThis kind of flame is used for welding High carbon steel & cast iron.Amount of acetylene gas is high in carburising.NeutralA flame resulting from the burning of gases supplied in the proper proportions for perfect combustion as approximately equal volumes of acetylene and oxygenOxidisingWidely used for cutting and not suitable for welding. When the amount of oxygen increases, the flame shortens but temperature goes too high.
40 Gases usedOxygen extracted from air and compressed into cylinders at high pressure. Cylinder is black.These cylinder have no welding joint these are complete tube like cylinders. Pressure contains 1800 psiAcetylene (C2H2) is a fuel gas. Cannot be compressed directly as explodes at high pressures. Cylinder colour coded maroon. We made these cylinders by welding three parts. Pressur contains 250 psi
41 Gas Pressure Regulators One gauge indicates the pressure of the cylinder and the other indicates the pressure in the supply pipe to the torch.
42 Welding torchOxygen and acetylene are delivered to the torch by separate hoses. Each gas is controlled by a valve on the torch. The two gases mix in the torch and after they are ignited burn at the nozzle.
43 Flashback ArrestorsThese are positioned on both the fuel gas and oxygen supply between the hose and the regulator. Their purpose is to prevent the return of a flame through the hose into the regulator.Back FireBack fire is a process in which aTiny fire particle goes into the cylinderThrough torch and pipe. As a resultIt cause big blast.
44 Filler Rods and fluxesFiller rods are used for welding the parts to each other. they come in different diameters.Fluxes protect the weld pool from contamination by oxygen and nitrogen, they are normally in paste form placed on a heated filler rod before welding begins.11
45 Advantages of gas welding Disadvantages of gas welding The equipment is inexpensi ve, simple and is easily portable.Useful for welding light metals such as automobile bodies and repair works.Alarge variety of material can be welded.Welds can be produced at reasonable cost.Equipment must always be handled carefully as in certain circumstances acetylene is explosive.A high temperature flame from a hand held torch is dangerous when handled carelessly.It causes more distortion.The process is not satisfactory for heavy sections.
46 Resistance weldingResistance welding uses the application of electric current and mechanical pressure to create a weld between two pieces of metal. Weld electrodes conduct the electric current to the two pieces of metal as they are forged together. The welding cycle must first develop sufficient heat to raise a small volume of metal to the molten state. This metal then cools while under pressure until it has adequate strength to hold the parts together.
48 Spot weldingIdeal for joining light sheet metal. The electrodes are made from copper. Pressure is applied to the electrodes and an electric current is passed through the circuit. The high resistance between the joint faces causes rapid heating and fusing of a small globule of metal from both faces.
49 Seam weldingThe rollers allow the workpiece to move through the welder continously. A stream of electrical pulses pass through the rollers and welds the joint
50 Resistance Welding Benefits High speed welding Easily automated Suitable for high rate production EconomicalResistance Welding Limitations Initial equipment costs Lower tensile and fatigue strengths Lap joints add weight and material
51 What is Friction Welding Friction welding is a solid state joining process that produces coalescence by the heat developed between two surfaces by mechanically induced surface motion.
52 Friction weldingOne part is held stationary while the other part is rotatedWhen the parts are hot enough the rotation is stopped and the parts forged togetherWorkpiecesNon-rotating viseMotorChuckSpindleHydraulic cylinderBrake
53 Advantage of frictional welding Disadvantages of frictional welding Easily joins dissimilar metals.Friction welds are higher strength.Friction welds often cost less.Friction welds minimize the Heat Affected Zone.No need of furnace .A machine of sufficient power is needed.T oo high power needed.Tight concentricity requirements.
54 Robotic weldingRobots are driven using actuators which control the robotic arm from an input signal. They can use hydraulic (large robots), pneumatic(small actuators with simple control movements) or electrical principles of operation.A computer sends instructions in electrical signals or pulses. An interface converts these digital pulses into analogue electricity for the motors. The robot is fitted with sensors which can send feedback on the position of the robot.
55 Advantages of Robotic welding Faster production ratesEfficent continous operationSafe working practiceReliable and consistent weldsFull automationCost effectiveExamplesAutomated welding of motor vehicles skeletel frames and bodies.