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Plasma Arc Welding:
Before going to study plasma arc welding lets have an overview of arc welding first. So
Arc welding :
Lets first know about the Arc welding, How it works, Advantages and Disadvantages…
Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals when the cool result in a binding of the metals.
Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created.
Since the joining is an intermixture of metals the final weldment potentially has the same strength properties as the metals of the parts.
A problem that arises in arc welding is contamination of the metal with elements in the atmosphere (O, H, N, etc). There can also be a problem with the surface that is not clean.
The solution to this Includes,
- Gas shields: An inert gas is blown into the weld zone to drive away other atmospheric gases.
- Flux: A material that is added to clean the surface this may also give off a gas to drive away unwanted gases.
Arc welding circuit diagram:
An AC or DC power sources, fitted with whatever controls may be needed, is connected by work cable to the workpiece and by an electrode cable to electrode holder of some type, which makes electrical contact with the welding electrode.
An arc is created across the gap when the energized circuit and the electrode tip touches the workpiece and is withdrawn yet still within close contact. The arc produces a temperature of about 6500-degree centigrade at the tip.
This heat melts both the base metal and the electrode producing a pool of molten metal sometimes called a creator. The creator solidifies behind the electrode as it is moved along the joint.
This result is a fusion bond.
Advantages of Arc welding:
- The process gives high deposition rates.
- Welding speed is high.
- Wire consumption is low.
- The consumption of electrical energy is low, as a maximum of 97 % of heat energy can be utilized.
- Any length can be welded without any interruption.
- High-quality Welds are achieved with no fusion defects, no porosity and slag inclusions.
Disadvantages of Arc welding:
- Arc is invisible, it can be controlled only by measuring arc voltage and current.
- It can be used only in the down hand welding position.
Plasma Arc Welding:
Plasma arc welding is a liquid state welding process in which, the metal to metal joint forms in a molten state. The hot ionized gases are known as Plasma. These hot ionized gases used to heat the work plates, and the joint is created due to fusion.
Main Parts or component:
- Filler Material
- Power Supply
- Plasma Console
- Water re-circulator
- Plasma Welding Torch
- Torch Accessory Kit (Tips, ceramics, collets, electrodes set-up gages)
- In Plasma arc welding there is no filler material is used. If the filler material is used, then it is directly fed into the weld zone.
- PAW process needed a high power DC supply to generate the electric spark in between the tungsten electrode and welding plates.
- This welding can weld at low 2 amp and maximum current which it can handle is about 300 amp. It needs about 80volts for proper working.
- The power source consists of a transformer, rectifier and control console.
Plasma welding torch:
- This is the most important part of the PAW(Plasma Arc Welding) process.
- This torch is quite similar as used in TIG welding.
- PAW torches are water cooled because the arc is contained inside the torch which produces high heat, so a water jacket is provided outside the torch.
- In Plasma arc welding (PAW) is an arc welding process, a concentrated plasma arc is produced and directed towards the weld area.
- The arc is stable and reaches temperatures as high as 33,000°C.
- A plasma is an ionized very hot gas composed of nearly the same numbers of electrons and ions.
- The plasma starts between the tungsten electrode and the orifice by a low current pilot arc. What makes plasma-arc welding unlike other processes is that the plasma arc is concentrated because it is forced through a relatively small orifice. Operating currents usually are less than 100 A.
- When filler metal is used it is fed into the arc as is done in Gas Tungsten-arc Welding. Arc and weld-zone shielding are supplied by means of an outer shielding ring and the use of inert gases like argon, helium or mixtures.
Advantages, Disadvantages, Application of Plasma Arc Welding:
Advantages / Merits:
- Torch design allows better control of the arc.
- This method provides more freedom to observe and control the weld.
- The higher the heat concentration and plasma jet allow faster travel speeds.
- The high temperature and high heat concentration of plasma allow keyhole effect.
- This provides complete penetration with single pass welding of many joints.
- Heat affected zone is smaller compared to GTAW(Gas tungsten arc welding).
- It uses less current input as compared to another welding process.
Disadvantages / Demerits:
- It produces wider welds and heat affected zones compare to LBW and EBW.
- Plasma welding equipment is very costly. Hence it will have a higher startup cost.
- It requires training and specialization to perform plasma welding.
- It produces ultraviolet and infrared radiation.
- The method produces higher noise on the order of about 100dB.
- The torch is bulky and hence manual welding is a bit difficult and requires training as mentioned.
Application / Uses:
- This welding is used in marine and aerospace industries.
- This is used to weld pipes and tubes of stainless steel or titanium.
- It is mostly used in electronic industries.
- Also, this is used to repair tools, die, and mold.
- This is used for welding or coating on a turbine blade.
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