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Joint Rootis that portion of a joint to be welded where the members are closest to each other

The joint root may be either a point, line, or an area

The joint roots are shown as shaded areas in (A)-(D) and lines in (E) (F)

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

Root opening and Bevel

Root opening is the separation between the work pieces at the joint rootBevel (chamfer) is an angular edge preparationBevel angle, Groove angle and Groove Radius

Robotic welding

Robots 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.Weld Joints -Parts of a Weld JointJoint root Groove 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 MemberT JointA joint between two members located approximately at right angles to each other

Corner Joint

A joint between two members located at right angles to each other

Edge Joint

A joint between the edges of two or more parallel or nearly parallel membersSplice memberis the work piece that spans the joint in a spliced joint

Single-spliced butt jointDouble-spliced butt joint with joint fillerWelding conditions continued.

The metals should be good quality (no internal impurities)Welding Preparation

Before starting a weld, the joint edges should be carefully prepared. Beveling large edges Cleaning (Chemical/Mechanical)Weld JointsWelding SymbolsWeld defectsWelding TechniquesWeld Symbol TerminologyARROW SIDE OTHER SIDEWorkFillet Weld (Arrow Side Only)Fillet Weld (Both sides)Touch electrode against work withdraw electrode to establish arc. Heat of arc melts base metal, the electrodes metal core, and any metal particles in electrodes covering. Heat also melts, vaporises, or breaks down chemically

non-metallic substances in covering for arc shielding. Mixing of molten base metal and filler metal from electrode produces coalescence required to effect joining.

AdvantagesDis-advantagesUsed with many electrode types & sizesUsed in all positionsUsed on great variety of materialsFlexibility in operator control makes it the most versatile of allwelding processesLow cost of equipment Rod becomes shorter & periodically needs replacing Slows production rate (% time welder welding)

The Electrode and CoatingCoating is a combination of chemicalsCellulosic electrodes contain celluloseRutile electrodes titanium oxide (rutile)Basic electrodes contain calcium carbonate (limestone) and calcium fluoride (fluorspar)

Produce gas to shield weld pool from oxidisising effects of atmosphere Fluxing elements help weld pool to form Helps slag to form-removes impurities Slag slows down cooling preventing Brittleness Can contain alloying elements or additional filler metalFunction of Electrode CoatingEquipment used in MMAAC power sourceTakes power directly from mains power supply. It use a transformer to supply the correct voltage to suit the welding conditions.

DC power sourceTwo typesDC generatorTransformer-rectifierDC GeneratorAn electricity generator is driven by a motor. The motor can be electric, petrol or diesel. The generator provides DC current for the arc

Transformer-rectifierA transformer with an electrical device to change AC to DC, this is known as a rectifier. It has the advantage of being able to supply both DC and AC

Basic Transformer-rectifier circuit (AC to DC)On/Off switchStep Down Transformer Bridge RectifierSmothingCapacitorHigh AC Voltage230VLow AC Voltage 10-50VDC output+_ABCDABCDTransformerA transformer converts AC current at one voltage to AC at a higher or lower voltageStep DownStep Up

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 difference is 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. AdvantagesLarge gaps filled or bridged easilyWelding can be done in all positionsNo slag removal requiredHigh welding speedsHigh weld qualityLess distortion of work piece

Equipmnt used in MAGSThree major elements are :

Welding torch and accessoriesWelding control & Wire feed motorPower SourceShielding Gas

Welding torch and accessoriesThe 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

NOZZLECONTACT TIPGAS DIFFUSERWelding 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

Welding power source

Positive (+) lead is connected to the torchNegative (-) lead is connected to the work piece

Sheilding GasPurpose of shielding gas is to protect the weld area from the contaminants in the atmosphere Gas can be Inert, Reactive, or Mixtures of bothArgon, Helium, and Carbon Dioxide are the main three gases used in MAGS

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 current to maintain the arc, this is generated by a separte unit.AdvantagesSuperior quality weldingCan be used in mechanised systemsUsed to weld aluminium and stainless steelsFree of spatterLow distortion

Equipment used in TAGSPower sourceElectrodesTIG must be operated with a constant current power source - either DC or AC Electrodes 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.

Sheilding GasArgon Argon + Hydrogen Argon/Helium Helium 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.Shielding gas is selected according to the material being welded.

The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the work piece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. There is no visible arc light, welding is spatter-free and there is no need for fume extraction. Submerged Arc Welding (SAW) Equipmnt used in SAWSAW is normally operated with a single wire on either AC or DC current. Common variants are: twin wire triple wire single wire with hot wire addition metal powdered flux addition All contribute to improved productivity through a marked increase in weld metal deposition rates and/or travel speeds. WireFluxFluxes used in SAW are granular fusible minerals The flux is specially formulated to be compatible with a given electrode wire type so that the combination of flux and wire yields desired mechanical properties. All fluxes react with the weld pool to produce the weld metal chemical composition and mechanical properties

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 joined Additional Filler Metal is fed in by hand into the weld pool, at regular intervals where it becomes molten and joins with the parent metal.

The Oxy-acetylene welding Flame Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes, copper)Neutral Equal acetylene & oxygen (low carbon steel, mild steels).Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys)Inner ConeSecondary Combustion envelopeAcetylene featherMax. Temp. Zone

CarburisingNeutralOxidisingThe Oxy-acetylene welding Flame The Oxy-acetylene welding Flame

Primary Combustion zoneThe oxy-acetylene flame has two distinct zones. The inner zone (Primary combustion Zone) is the hottest part of the flame. The welding should be performed so as the point of the inner zone should be just above the joint edges. C2H2 + O2 2CO + H2The outer zone the secondary combustion envelope performs two functionsPreheats the joint edgesPrevents oxidation by using some of the surrounding oxygen from weld pool for combustion and gives off carbon dioxide and water vapour

Secondary Combustion zoneCO + H2 + O2 CO2 + H2OEquipment used in O-A welding The oxygen and acetylene hose pipesGases usedGas pressure RegulatorsFlashback arrestorWelding torch/Welding nozzleFiller rods and fluxes

The oxygen and acetylene hose pipes

Reinforced rubber hoses. Acetylene hose has left hand thread couplings and colour coded red.Oxygen hose has right handed thread couplings and colour coded blueGases usedOxygen extracted from air and compressed into cylinders at high pressure. Cylinder is black. Oil should never be brought into contact and should not be used on fittingsAcetylene (C2H2) is a fuel gas. Cannot be compressed directly as explodes at high pressures. Cylinders are packed with porous material which is filled with acetone Acetone absorbs acetylene. Cylinder colour coded maroonGas Pressure Regulators

One gauge indicates the pressure of the cylinder and the other indicates the pressure in the supply pipe to the torch. Welding torch

Oxygen 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. MixerNeedle valves

Flashback Arrestors These 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.Filler Rods and fluxes Filler rods are used when additional filler metal is required in the weld area 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 Spot welding Seam Welding

Spot welding Ideal 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.Seam welding

The rollers allow the workpiece to move through the welder continously. A stream of electrical pulses pass through the rollers and welds the jointResistance Welding Benefits High speed welding Easily automated Suitable for high rate production Economical Resistance Welding Limitations Initial equipment costs Lower tensile and fatigue strengths Lap joints add weight and material Advantages of Robotic welding Faster production ratesEfficent continous operationSafe working practiceReliable and consistent weldsFull automationCost effectiveExamplesAutomated welding of motor vehicles skeletel frames and bodies.Robotic welding Terms Lead through programming Teaching robot movements through guiding it manually through a sequence of operations. These are recorded to memeoryMachine Vision Area of vision robot has, limits which robot sensors can operateWorking enevelope The area within which a robot can operate. Where the work is caried out by robotic armYaw left and right movment of robotic armRoll rotation of robot about one of its axisDegrees of freedom These are the number of independent movements of the arm joints( or actuators) the robot has.