Plasma Arc Cutting

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Plasma Arc Cutting
MENG 439
Dr. L. K. Gaafar
Prepared by Eng. Ahmad Hassan Sayed
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Plasma Arc Cutting

• PAC is a thermal material removal process that is
  primarily used for cutting thick sections of
  electrically conductive materials.
• Plasma can be defined as a superheated,
  electrically ionized gas.

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PAC Process

• PAC uses a high velocity jet of plasma
  (Temperatures range from 10,000 to 14,000 oC) to
  cut through the metal by melting it.
• The high gas flow rate facilitate the removal of
  molten metal through the kerf
• Stream pressures can reach up to 1.4 MPa.

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Gases Used

• Primary Gases
• Gases that are used to create the plasma arc.
  Examples are nitrogen, argon, hydrogen, hydrogen,
  or mixture of them
• Secondary Gases or Water
• Surrounds the electric arc to aid in confining
  it and removing the molten material.

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System Components

• Torch
• Power Supply
• Arc Starting Circuit

www.twi.co.uk/j32k/servlet/ getFile/jk51.html
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System Components
A. The Torch

• The torch is the holder of the consumable
  electrode and nozzle.
• Responsible for forming the arc and maintain it
  in a vortex.

Groover 626
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System Components
A. The Torch

• Types of Torches
• Air Plasma Torch
• Oxygen-Injected Torch
• Water Injected Torch
• Dual Gas Torch

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Types of Torches
Water Injected (Benedict 340)
Air Plasma (Benedict 337)
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System Components
B. Power Supply

• Constant DC current source.
• Speed and cut thickness are determine by the
  amount of output current.

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System Components
C. Arc Starting Circuit

• High frequency generator circuit that produces a
  high AC Current.
• To start the arc, the AC current ionizes the
  cutting gas, which makes it conductive to allow
  the DC current to flow through it.

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Types of Arcs

• Transferred Arc
• the generated arc is between the electrode and
  the work-piece.

Benedict 336
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Types of Arcs

• 2. Non-Transferred Arc
• the generated arc is between the electrode
  and the nozzle and heat is carried to the
  work- piece by the plasma gas.

Benedict 336
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Advantages - Disadvantages

• Cuts any metal.
• 5 to 10 times faster than oxy-fuel.
• 150 mm thickness ability.
• Easy to automate.

• Large heat affected zone.
• Rough Surfaces
• Difficult to produce sharp corners.
• Smoke and noise.
• Burr often results.

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Applications

• Pipe industry preparing pipe edges for welding.
• industries for shape cutting

Cpam.engr.wesc.edu
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Other Plasma Uses

• Plasma Arc Welding (PAW)- plasma arc is produced
  and aimed at the weld area to weld.
• Applications- Used for butt and lap joints
  because of higher energy concentrations and
  better arc stability.

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Safety Precautions

• Machine the heat affected zone (0.75-5 mm).
• Regulate gas pressure (approx. 1-1.4 MPa).
• Maintain constant distance between torch and work
  piece.
• High labor safety (i.e. goggles, gloves, etc).
• Proper training for operators.
• Protection against glare, spatter and noise from
  the plasma.