20-08-2013, 01:08 PM
MANUFACTURING PROCESS OF A PISTON
INTRODUCTION
A piston is an important component of reciprocating engine helps to convert energy obtained by the combustion of fuel in cylinder into useful mechanical power.
It is like a disc which reciprocates within a cylinder.
It is either moved by the fluid or it moves the fluid which enters the cylinder.
PISTON IN IC ENGINE
The main purpose of the piston of an internal combustion engine is to transfer force from expanding gas in the cylinder to the crankshaft through a connecting rod.
It is located in a cylinder and is equipped with piston rings to provide a good seal between the cylinder wall and piston.
MANUFACTURING PROCESS
Casting
Heat treatment
Machining process
Pin fitting and Inspection
CASTING
The foundry is the beginning of the piston.
At the foundry the die is prepared by heating it to operating temperature for approximately one hour.
This process allows the die to readily accept the molten material when it is poured.
The molten material used for Piston is 10% Silicon content Aluminium or Aluminium alloys.
PROCESS
The process starts by heating the material to 700 degrees Celsius.
The material is then scooped up with a ladle from the crucible (the pot that holds the molten material).
This is then poured into the die through the sprue.
The material is then allowed to cool before it is removed from the die.
MACHINING PROCESS
Open end bore machining
Rough outer diameter turning
Grooves forming
Semi finish hole boring
Circlip grooving oil hole drilling in 3rd groove and skirt
Ring grooving and chamfering
Final outer diameter turning
Deburring and cleaning
Tin coating
Finish pin hole boring
CNC TURNING
Turning of the casting is carried out on CNC machinery.
This equipment is the most accurate and fastest available for this application with very tight tolerances and extremly fast spindle speeds. The following operations are performed on this machine:
Open end bore machining
Rough outer diameter turning
Grooves forming
REAMING
The final machining process for the piston is that of reaming.
This process involves the piston being placed in a bath of oil and reamed at different sizes to reach the final size required.
Since the pin boring process is only rough it is necessary to ream the pin bore a number of times to achieve the surface finish and size required.
DEFECTS
Since it’s a main reciprocating part of engine and hence it creates the problems of unbalancing due to its inertia.
Due to friction between wall of the cylinder and piston rings its life becomes short and it generates the unpleasant sound due reciprocating mechanism.
To transmit the energy of reciprocating piston, it is connected to a connecting rod and crank mechanism and due to these parts there occurs mechanical losses.
The motion of the crank shaft is not smooth, since energy supplied by the piston is not continuous and it is impulsive in nature.
To supply the fuel into the cylinder there is need of the valves and valve mechanism and during opening and closing of the valves, mechanical noise occurs and also mechanical vibration.
CONCLUSION
Although the piston appear to be a simple part, it is actually quite complex from the design and manufacturing stand point.
The efficiency and economy of the engine primarily depends on the working of the piston. So the working of the piston be more efficient.
It must operate in the cylinder with minimum friction and should be able to withstand the high explosive force developed in the cylinder and also withstand very high temperature ranging from 2000 C to 2800 C during operation.
To avoid the wear and unpleasant sound between cylinder walls and piston rings, piston rings should manufactured with wear resistant materials like cast iron and steel.
Lubrication problems should b avoided between cylinder walls n piston by providing oil grooves accurately.
Finally, the piston should be as strong as possible, however, its weight should be minimized as far as possible in order to reduce the inertia due to its reciprocating mass.