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Welding

Leaving cert Engineering HL Q5

QuestionAnswer
Describe the main features of MMA Welding >Flux coated consumable electrode >Joint protected by gas from melting flux >Slag produced on top of weld >Electrode has to be changed often >Versatile process >Equipment light and portable
Describe the main features of MIG welding >Semi automatic process >Bare wire electrode fed to gun from a spool >Joint protected by inert gas (argon) >Very easy to do >Equipment big and bulky >No slag produced
Describe the main features of TIG welding >Non-consumable tungsten electrode >Filler rod added to weld by hand >Joint protected by inert gas (argon) >Very difficult and specialised >Used for Aluminium and stainless steel
Describe the main features of SAW welding >Fully automatic process set up on guide rail >Wire electrode fed from spool >Powder flux fed from hopper completely submerges the arc >excess flux sucked back into the hopper >used for straight lines eg bridges, ships, factory roofs
Describe the main features of Spot welding >Non-consumable copper electrode >Weld nugget formed between overlaping work pieces >No filler added >Very quick and easy to use >Used for sheet metals on car panels and filing cabinets
Describe the main features of Seam welding >Non-consumable copper motorised electrode rollers >Series of overlapping weld nuggets form air tight seal >No filler added >Quick and easy to use >Used to seal the edges of radiators
Describe the main features of Electro Slag welding >Fully automatic process >Used to weld very thick plate >Must be done vertically >Water cooled copper shoes enclose the weld pool >wire electrode and flux powder fed in >Weld pool rises until the whole gap is filled in
Describe three important safety features that minimise electrical hazards associated with manual metal arc welding; • MMA welding machines are protected from electrical surges. • Welding stations need to be free from dampness. • Cables and electrode holders are covered with plastic insulators. • Welding machines are earthed. • Power supplied can be adjusted to an a
Why is tungsten inert gas welding suitable for welding aluminium? Aluminium oxidises very quickly when heated. This tenacious oxide layer is overcome with the use of an inert gas, such as argon, and the cathodic action of the arc on the work-piece. Aluminium can be welded successfully in this way by TIG welding.
Explain the function of dissolved acetylene in oxy-acetylene welding If acetylene is compressed into a cylinder, it would explode under high pressure. Acetylene cylinders are packed with a porous material that is filled with acetone. The acetylene is dissolved into the acetone under pressure to prevent it from exploding.
Describe, with examples, the importance of colour coding in oxyacetylene equipment; It's important so the gasses don't get mixed up. Oxygen cylinder is black and acetylene is maroon, hoses and regulators are colour coded with oxygen as blue and acetylene as red.
Outline three safety precautions that should be observed in the preparation of equipment and materials for oxyacetylene welding; Oil & grease needs to be removed to minimise reaction with welding process Torch must be thoroughly cleaned before starting weld.Flashback arrestors need to be in place on fuel and oxygen line Correct colour coding of cylinders and hoses must be observed
Describe multi-run welds; A series of welds are run across the metals to be joined in multi-run welding. A superior weld is produced as each weld has a post heating effect on the previous run. The finished weld is stronger and more refined in structure than single run welds.
Outline two methods used to prevent porosity occurring in welds • Make sure the gas tank is not empty • Clean the material surfaces removing oil and grease • Eliminate moisture – the prime cause of weld porosity • Make sure gas flow is at correct pressure • Eliminate drafts and air
Describe the carburising flame used in oxy-acetylene welding. • Contains excess acetylene. • It has a working temperature of 3150oC. • Used to weld aluminium and alloy steel where it gives protection against oxidation. • Flame is bigger with the distinctive acetylene feather.
Describe the Oxidising flame used in oxy-acetylene welding. • Contains excess oxygen. • Has a working temperature of up to 3500°C. • Used to weld copper and brass, it would oxidise steel. • Flame appears smaller.
Describe the Neutral flame used in oxy-acetylene welding. • A balanced proportion of oxygen and acetylene. • Maximum combustion as all carbon from the acetylene is used. • Has a working temperature of up to 3300°C. • The most extensively used flame for oxy-acetylene welding.
Describe any three methods of joint protection when welding >Flux coating on the electrode in MMA welding >Inert gas pumped out of the gun in MIG/TIG welding >Arc submerged under flux powder in SAW welding >Acetylene flame
Describe three hazards associated with the use of manual metal arc welding in a school engineering room. >Other students might look at the arc and damage their eyes >Someone could trip on the wires >Appropriate ventilation >A welding apron should be worm to protect uniform
Outline the functions of the transformer, capacitor and rectifier in manual metal arc welding. A step-down transformer is used to change the mains voltage from 220V to a suitable level (80-100V) for welding The rectifier changes alternating current (AC) to direct current (DC) The capacitor is employed to provide a smooth supply of low voltage DC.
State two functions of the electrode coating in manual metal arc welding. • To generate a gas shield to protect welded joints from contamination by oxygen and nitrogen in the air. • To form a slag coating which protects the weld from oxidation and ensures a slow cooling rate for the weld • Helps to maintain the arc
Outline two functions of the flux coating used in manual metal arc welding The flux coating in Manual Metal arc welding: • Helps to start the arc • Burns to give off a gas which prevents oxidation • Helps the formation of a slag on the weld • Additional alloy material can be part of the coating to improve weld strength
Explain why submerged arc welding (SAW) is suitable for welding steel girders. Its suitable for welding steel girders as it will give a long uninterrupted weld. As SAW is an automatic welding process, the weld joint will be of equal quality from beginning to end. SAW is also very suitable for the thickness of the girder material.
Outline two advantages of multi-run welds. Advantages of multi-run welds: • A superior weld is produced as each weld has a post heating effect on the previous run. • The finished weld is stronger and more refined in structure than single run welds.
Describe, with the aid of a suitable diagram(s), oxy-acetylene welding with reference to  equipment used Oxy-acetylene equipment include: • Acetylene cylinder • Oxygen cylinder • Oxygen and acetylene hoses • Welding torch • Pressure gauges • Flashback arrestors
Describe, with the aid of a suitable diagram(s), oxy-acetylene welding with reference to  flame types Three flame types: Neutral flame - equal portions of both gases; Oxidising flame - excess oxygen gas; Carburising flame - excess acetylene gas.
Describe, with the aid of a suitable diagram(s), oxy-acetylene welding with reference to  integrated safety features • The colour coding helps prevent any mix-up • The oxygen cylinder is usually thinner and taller. • The connections for the different gases have either left or right hand threads • The flashback arrestors prevent the flame returning to the cylinders.
Describe, with the aid of a suitable diagram(s), oxy-acetylene welding with reference to  applications. A neutral flame is used for general steel welding. An oxidising flame is used for brass and bronze welding. A carburising flame is used for aluminium alloys and alloy steel welding. A cutting torch can be attached instead of the welding torch
Outline the reasons for porosity in welding Porosity in welding: • The presence of moisture in the weld • Cylinder out of gas • Presence of paint, oil or grease • Weld nozzle is not close enough to weld • Shielding gas has been blown away due to drafts
Describe two hazards which may be encountered in underwater welding • If a diver surfaces too fast, he can get the bends • Sharks , •run out of oxygen • The ocean current can actually carry a welder off, • Nitrogen can build up in the diver's blood and create deposits. • drowning
Give two benefits of using resistance seam welding in the production of house radiators. • Creates a sealed unit • High speed welding • Easily automated • Suitable for high rate production • Economical.
Describe, with the aid of a suitable diagram The essential differences between Metal Inert Gas (MIG) welding and Tungsten Inert Gas (TIG) welding TIG - No-consumable electrode, uses foot pedal, fully manual, specialised and difficult to do, used on aluminium and stainless steel MIG - Consumable wire electrode, easy to use, semi-automatic, used on steel
Describe how multi-run welding can positively affect the quality of a weld Multi-run welds: • Multi-runs produce a superior quality weld which is more refined than a single run weld. • Multi-run welds have a post heating effect on the previous weld which will improve its quality.
Give two benefits of the formation of slag in manual metal arc welding Two benefits of the formation of a slag: • It minimises impurities in the weld. • To form a coating which protects the weld from oxidation. • It ensures a slow cooling rate for the weld. • It prevents cracking and brittleness
Describe two safety hazards associated with resistance spot welding • Flying sparks can cause fire and explosion. • Electric shock from wiring. • Hot metal and parts can cause burns. • Moving parts, such as tongs, tips and linkages, can injure fingers and hands. • Fumes from spot welding on parts coated with cleaners.
Outline three ways in which oxidation may be prevented during welding. Three ways oxidation can be prevented during welding: • Inert gas • Flux coating on electrode • Granulated flux • Secondary combustion envelope • Formation of a slag coating
State two reasons for the use of tungsten inert gas (TIG) welding for securing the stainless steel slide. Tungsten inert gas (TIG) welding is used as: • it is suited to stainless steel • A stronger, more durable weld is produced • As the metal is prone to oxidation, Argon gas acts as a shielding gas • A neat, spatter-free weld is usually produced
Describe how an acetylene cylinder is filled under low pressure. If acetylene is compressed into a cylinder, it would explode under high pressure. cylinders are packed with a porous material that is filled with acetone, this can absorb 25 times its own volume of acetylene. This is dissolved acetylene
Describe, with the aid of a diagram, the process of friction stir welding FSW Friction Stir Welding (FSW) works by using a non-consumable tool, which is rotated and plunged into the interface of two workpieces. The tool is then moved through the interface and the frictional heat causes the material to heat and soften.
Describe, with the aid of a diagram, the process of Linear Friction Welding (LFW) Linear Friction Welding (LFW) works by linearly oscillating one workpiece relative to another while under a compressive force. The friction between the oscillating surfaces produces heat, causing the interface material to soften and mechanically mix.
Describe, with the aid of a diagram, the process of Rotary Friction Welding (RFW) Rotary Friction Welding (RFW) is similar to LFW except that the workpieces are often round and are rotated relative to each other
Created by: todd.ciaran
 

 



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