What is the meaning of welding process?
Welding operation means the process of joining two metal parts together to produce a rigid joint.
What is fusion welding?
Fusion welding is defined as melting together materials using heat. Filler metals, which are metals are added to the weld area during welding. Lack of fusion between the materials could be a major drawback during this process.
What is an autogenous weld?
When filler metals aren’t utilized in fusion welds then the method is understood as autogenous welds.
What is oxyfuel-gas welding?
- Any welding process which uses a fuel gas combined with oxygen to provide a flame is named as oxyfuel-gas welding.
- Melting of metals at the joint takes place because of the flame which acts as a source of warmth.
- The most common gas welding process uses acetylene, the method is understood as oxyacetylene-gas welding and is employed for structural metal fabrication and repair work.
Which is the combustion process occurring in the inner core of the flame?
- The primary combustion process which occurs within the inner core of the flame involves the subsequent reaction.
- This reaction dissociates the acetylene into monoxide and hydrogen and produces about one-thirds of the full heat generated within the flame. The secondary combustion process is
- This reaction further consists of burning both the hydrogen and the CO which produces about two-third of the whole heat.
What are the equipment needed for Gas welding?
The details of welding equipments are listed below:
- High-pressure oxyacetylene welding equipment consists of two large steel cylinders.
- One is conventionally painted black and could be a long thin cylinder that contains oxygen-filled in at a air mass of 125-140 kg/ sq.cm.
- The other cylinder which is painted maroon and is shorter but of slightly larger diameter contains acetylene gas dissolved in acetone at a pressure of 16-21 kg/ sq.cm.
- Both these cylinders are fitted with valves which are normally kept in an exceedingly closed position.
- To draw gas from the cylinder, each cylinder is fitted with a pressure regulator with two gauges.
- The function of the pressure regulator is to cut back the pressure of the gas before delivering it.
- The two gauges indicate the pressure inside the cylinder and the reduced pressure of gas after the pressure regulator stage.
- The gases are carried from the pressure regulator to the welding torch (also called blow pipe) using rubber hose pipes.
- A welding torch connected to welding machine consists of various passages for oxygen and acetylene gases.
- Supply of those gases is controlled by pin valves.
- These two gases are then allowed to combine in a very mixing chamber before being driven out through the orifice of the blow pipe.
- These orifices are of various sizes and may be screwed on the blow pipe.
What are the different flame types in the welding process?
In oxyfuel gas welding, the proporation of acetylene and oxygen plays a vital role.
- Neutral flame:
At a ratio of 1:1 (i.e. when there’s no excess oxygen), the flame is claimed to be neutral.
- Oxidizing flame:
The flame is harmful when the content of oxygen is excess (especially for steels), because it oxidizes the metal. For this reason, a flame with excess oxygen is referred to as an oxidizing flame.
- Reducing or carburizing flame:
If the oxygen is insufficient for fuel combustion, the flame is understood as reducing or carburizing flame.
What is Filler metal?
The main function of filler metals is to provide additional metal during welding. They’re available as filler rods or wire and perhaps bare or coated with flux. The aim of flux is to retard oxidation of the surfaces of the parts being welded by generating a gaseous shield round the weld zone. The flux also helps to dissolve and take away oxides and other substances from the weld zone.
What is an oxyacetylene cutting?
- The oxyacetylene flame also can be used for cutting plate.
- This is done through a special “cutting torch”, which has an additional passage for high-pressure oxygen additionally to the standard passage for oxygen and acetylene gas.
- The process of flame cutting is an oxidation process.
- The place, where a cut is to be made is heated with the welding flame and when it’s hot, high-pressure oxygen is allowed to touch it.
- The cut needs to start either from the sting of the plate or a pilot hole should be drilled within the plate from which the cut can start is the only limitation of this process.
What is the principle of arc welding process?
- In arc welding, the source of warmth is an electrical arc.
- The temperatures reached in an electrical arc could also be as high as 5500°C.
- A spark is produced in an electrical circuit carrying current if the circuit is broken accidentally.
- An electric arc may be a spark created intentionally by a spot between the welding electrode and therefore the workpiece.
- Because of larger output and fewer oxidation, the standard of weld produced by an electrical arc is far better than a gas weld.
- Either A.C. or D.C. power supply is also used for arc welding.
- For A.C., an open-circuit voltage of about 75-80 V is required.
- The current requirement is however very heavy and therefore the welding machine should be capable of delivering 100-300 Amperes.
- D.C. supply is characterized by positive and negative terminals.
- Normally, the electrode is connected to a negative terminal and therefore the workpiece to a positive terminal.
- Such a meeting is named D.C. straight polarity.
What is a Heat affected zone?
- In the arc welding process, a good amount of warmth output takes place leading to the formation of a molten pool within the arc area.
- The heat is additionally conducted into the vicinity of the joint on either side.
- The temperature of the material on either side of the weld bead might not be as high because the freezing point of the metal, but, is incredibly near it.
- As we move off from the joint or weld bead, the metal is also heated to lesser temperatures.
- As the electrode travels over the joint and moves away, the heated metal cools as quickly because it was heated.
- If steel is being welded, this heating and quick cooling may end in the formation of martensitic and other structure which can be at risk of cracking.
Mention the various welding positions from the point of view of the welder?
There are 4 types of welding position techniques which might affect the quality of the weld.
a) Downhand welding position: This can be the foremost comfortable position for the welder to use and he can produce welds of excellent quality.
b) Horizontal welding position (on a vertical surface).
c) Vertical welding position (on a vertical surface).
d) Overhead welding process (say on the ceiling of the room): This is often the foremost difficult welding position. Not only the operator must turn his neck upwards and lift his arm to keep up an arc.
Note: The direction of movement of hand is also specified in the Fig. 5.
What is Electric Resistance welding?
- In electric resistance welding (ERW) methods, a high current is undergone the metal pieces to be joined together and also the heat is produced thanks to resistance within the current.
- The electric resistance welding process may be a pressure welding process and not a fusion welding process.
The following are the categories of electrical resistance welding processes which are described with diagrams::
- Spot welding process.
- Seam welding process.
- Butt welding process.
- Flash butt welding process.
1. Spot welding process:
Spot welding consists of joining of two pieces by placing them between two electrodes and spending an important current through them for a really short duration.
- Usually, spot welding is automatic and work on the subsequent weld cycle:
- Squeeze the 2 metal pieces along with light pressure.
- Pass heavy electrical phenomenon for a awfully brief time.
- Apply pressure and hold for a few time.
- Remove the pressure.
2. Seam welding process:
- A seam is produced by overlapping spot welds.
- The seam welding machine is comparable to a spot welding machine.
- In a seam welding machine, the electrodes are within the variety of copper rollers.
- The two work pieces which are to be joined pass between the rollers.
- The rollers exert pressure on the workpiece and also rotate at the identical time.
- The seam welding process leads to a successive series of spot welds being made.
3. Butt welding process:
- Welding two pieces of metal together, end to end, is termed butt welding.
- In butt welding, the ends are cleaned and made square in order that the 2 places touch one another over the whole cross-section.
4. Flash butt welding process:
- In this process, the tip preparation isn’t as detailed as within the butt welding process and also the ends need not be dead square.
- In this case, the present is switched on before bringing the 2 ends to be welded, close.
- This lead to flashing because the two ends almost touch one another but have a touch gap between them.
- This flashing or arcing generates heat and also the two metal end heat up to coalescence temperature.