Plasma Arc Machining

It is also one of the thermal machining processes. Here the method of heat generation is different than EDM and LBM.

Working Principle of PAM: In this process, gases are heated and charged to plasma state. Plasma state is the super heated and electrically ionized gases at approximately 5000⁰C. These gases are directed on the work piece in the form of high velocity stream. Working principle and process details are shown in Figure:

Process Details of PAM: 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 DC 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 work piece 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 hot, plasma state gases works as a cutting tool.

Work piece: Work piece 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 alsorecommended 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 initialcost is very high.

(b) The process requires over safety precautions which further enhance the initial cost of thesetup. (c) Some of the work piece 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.