Plasma Arc Machining- Process, Diagram , Application , Advantages and Disadvantages

Introduction:

Plasma-arc machining (PAM) employs a high-velocity jet of high-temperature gas to melt and displace material in its path. Called PAM, this is a method of cutting metal with a plasma-arc, or tungsten inert-gas-arc, torch. The torch produces a high velocity jet of high-temperature ionized gas called plasma that cuts by melting and removing material from the workpiece. Temperatures in the plasma zone range from 20,000° to 50,000° F (11,000° to 28,000° C).

This articles consist  Plasma arc machining working principle, plasma arc machining diagram, process, advantages and Disadvantages of plasma arc machining ,application of plasma arc machining.

Working Principle of PAM
In this process gases are heated and charged to plasma state. Plasma state is the superheated and electrically ionized gases at approximately 5000oC. These gases are directed on the workpiece in the form of high velocity stream. Working principle and process details are shown in Figure

 

plasma arc machninig working principle diagram
plasma arc machninig working principle diagram

Process Details of PAM

Details of PAM are described below.man

  • Plasma Gun
    Gases are used to create plasma like, nitrogen, argon, hydrogen or mixture of these gases. The plasma gun consists of a tungsten electrode fitted in the chamber. The electrode is given negative polarity and nozzle of the gun is given positive polarity. Supply of gases is maintained into the gun. A strong arc is established between the two terminals anode and cathode. There is a collision between molecules of gas and electrons of the established arc. As a result of this collision gas molecules get ionized and heat is evolved. This hot and ionized gas called plasma is directed to the workpiece with high velocity. The established arc is controlled by the supply rate of gases.
  • Power Supply and Terminals
    Power supply (DC) is used to develop two terminals in the plasma gun. A tungsten electrode is inserted to the gun and made cathode and nozzle of the gun is made anode. Heavy potential difference is applied across the electrodes to develop plasma state of gases.
  • Cooling Mechanism
    As we know that hot gases continuously comes out of nozzle so there are chances of its over heating. A water jacket is used to surround the nozzle to avoid its overheating.
  • Tooling
    There is no direct visible tool used in PAM. Focused spray of ho0t, plasma state gases works as a cutting tool.
  • Workpiece
    Workpiece of different materials can be processed by PAM process. These materials are aluminium, magnesium, stainless steels and carbon and alloy steels. All those material which can be processed by LBM can also be processed by PAM process.

    Applications of PAM
    The chief application of this process is profile cutting as controlling movement of spray focus point is easy in case of PAM process. This is also recommended for smaller machining of difficult to machining materials.

    Advantages of PAM Process
    Advantages of PAM are given below :
    (a) It gives faster production rate.
    (b) Very hard and brittle metals can be machined.
    (c) Small cavities can be machined with good dimensional accuracy.

    Disadvantages of PAM Process
    (a) Its initial cost is very high.
    (b) The process requires over safety precautions which further enhance the initial cost of the setup.
    (c) Some of the workpiece materials are very much prone to metallurgical changes on excessive heating so this fact imposes limitations to this process.
    (d) It is uneconomical for bigger cavities to be machined.

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