Thursday, 12 January 2017

Ultrasonic welding:


Ultrasonic welding is a cold-joining process(I.e.,solid- state welding).In this case ,a bond is produced by ultrasonic vibratory energy in the weld region.The equipment necessary for ultrasonic welding is shown in fig.It includes a transducer,a velocity transformer with a sonotrode tip and a suitable anvil.The prob induces lateral vibrations on workpieces such that surface films are broken and bond results due to slip between clean surfaces under pressure.The operation should be stopped as soon as weld is complete. This is to avoid bonding of prob with upper workpiece.


ADVANTAGES:

1) Absence of generated heat.

2) Dissimilar metals can be joined.

3) No oxidation and distortion

4) The welding time is only about one second or less.

DISADVANTAGE:

1) The maximum thickness is limited to 0.3 to 2.5mm


APPLICATIONS:

The ultrasonic welding is employed for spot welding and seam welding of thin strips or foils.It can also be used for welding aluminium up to 2.5mm thick.The process is mostly used for welding dissimilar metals such as aluminium to stainless steel and aluminum to copper l.It has been used for refractory metals such as titanium and zirconium. 

SUBMERGED ARC WELDING:


Submerged arc welding is used for the production of long continuous weldings.In this case,a bare electrode (1.5-10mm) in the form of continuous wire is used; and the arc is struck between electrode wire and work piece under the flux,consisting of lime,silica,magnesium oxide,calcium fluoride and other elements.The flux is fed as a powder in front of the electrode.the flux near the arc melts and forms a protective coating of slag, which is easily detached from finished weld.The rate of cooling of the weld metal is slow,and it is also protected from atmosphere while cooling.The principle of submerged arc welding is shown in fig.In this case,an automatic feeding device ensures that the gap between the electrode and the base metal is constant.Electric current usually range between 300A and 2000A.The power supply is from a standard single or three phase power lines with a primary rating up to 440V.




ADVANTAGES:

The process offers the following advantages:

1)High rate of deposition

2)No visible arc with little fumes and spatter

3)Smooth weld surface for long lengths

4)High quality welds of excellent penetration,and

5)Weld area is free from surface ripples.

LIMITATIONS:

The process has the following limitations:

1) process is not flexible,and reqires costly equipment.

2) Slag must be removed after each pass

3) Process is not suitable for thin plates and for overhead welding,and limited to the flat or horizontal position welds.

APPLICATIONS:

Developed in the 1940s,submerged arc welding (SAW) Process is best suited for the continuous welding of components having 12 to 50mm thickness. This process is used to weld a variety of carbon and alloy steel,and stainless steel sheets.Typical applications are the welding of pressure vessels,boiler plates and pipes.

Wednesday, 11 January 2017

METHODS OF APPLICATIONS OF CUTTING FLUIDS :



The method of application of a cutting fluid is very important and depends on the particular operation. These methods vary from hand applications such as use of brush or oil-can to high pressure applications.For high production. The following methods are used.

   1)Flood method,

   2) Jet method,and

   3) Mist method.

1) Flood method :

In this method,a reciprocating pump is used to force the coolant over the work and tool.The outlet of the pump is connected to a nozzle through flexible pipe.The nozzle can be adjusted to direct the stream of the fluid at the cutting zone.This is the most common method of application of cutting fluid.


2) jet method :

In jet method,a small jet of fluid at high speed is directed at the point of metal separation from the underneath the tool.In high-speed jet system gear or vane type pump is used to maintain high pressure.


3) Mist method :

In mist method,the fluid is passed through a specially designed nozzle to form very fine droplets(mist).This mist is directed at the cutting zone at high speed.It has better cooling effect than flood or jet methods.

METHODS OF LUBRICATION:

Various methods are used to apply the lubricant to the machine tools.Lubricating oil is generally applied to sliding parts with the help of oil-can.Lubricants are also applied by the following systems.

       1)Gravity feed system.

       2) Pressure feed system.

In the gravity feed system lubricant is applied to the sliding parts through oilcups which are located at the higher levels of sliding parts l.In this oil flows to the parts due to gravity.

Pressure feed system is generally used in automobiles where lubricants are applied under pressure by using oil pump which is situated below the engine.

Monday, 9 January 2017

Law of conservation of energy:

Total energy in a system is constant.Energy cannot be created cannot be destroyed but one form of energy is converted into another form


ADVANTAGES AND LIMITATIONS OF BROACHING:

Broaching is an interesting machining process which is used in mass production. It has certain advantages and limitations as compared to the other machining processes.these are given below.

ADVANTAGES :

1) Fast and simple process.

2)High degree of accuracy and finish is possible.

3)Any shape of profile can be easily machined.

4) Machining process is completed with one stroke of broach.

5) Life of broach tool is high.

6)Cutting temperature and tool wear is low.

7) Doesn't require a highly skilled operator.

8)Cutting force acts in the clamping direction I.e.,it doesn't tends to lift the workpiece from fixture.

9)cutting fluids can be applied more easily and effectively.

10)Most economical for mass production of components.



LIMITATIONS:

1) Not economical for small quantity productions.

2)Cost of broach is high.

3) Tool grinding (broach sharpening) is difficult and expensive.

4) Not suitable to machine a surface having obstruction.

5) The work must be strong enough to with stand cutting forces.

6) Very light and delicate jobs cannot broached easily.

7)Large amount of metal cannot be removed by broaching.

APPLICATIONS OF BROACHING :

The operation of broaching was originally developed for machining small,internal surfaces such as key way in a small diameter which is relatively difficulty for slotter.Broaching is widely used in present day industry for machining a large variety of jobs which were formerly milled or shaped.

Internal broaching is used for machining and sizing of round holes,square,hexagonal,and many other shapes of holes.Internal keyways,splines and gears are easily produced by broaching.External or surface broaching is increasingly used in mass production as an alternatively to milling.It can machine plane or complex shapes easily and economically.