SEAM WELDING EXPLAINED !!

Seam welding is a resistance welding process in which overlapping sheets are joined by local fusion progressively, along a joint, by two rotating the circular electrodes. Fusion takes place because of heat, which is generated, from the resistance to electric current flow through the work parts which are held together under pressure by electrodes.


Principle of Operation (Procedure)
a) The work-pieces to be seam welded are cleaned, overlapped suitably and placed between the two circular electrodes which hold the work-pieces together by the pressure on electrode force.

b) Switch on the coolant supply (in some machines, the electrodes are cooled by external spray of water; in others, the electrodes are cooled by refrigerant fluid that flow inside the working electrodes).

c) Switch on the current supply. As the first current impulse is applied, the power driven circular electrodes are set in rotation and the work-pieces steadily move forward.

d) If the current is put off and on quickly, a continuous fusion zone made up of overlapping nuggets is obtained. It is known as stitch welding.

e) If individual spot welds are obtained by constant and regularly timed interruption of the welding current, the process is known as roll (spot) welding.

Advantages of Seam Welding

  • It can produce gas tight or liquid tight joints.
  • Overlap can be less than spot or projections welds.
  • Several parallel seams may be produced

Disadvantages of Seam Welding 

  • Cost of equipment is high as compared to spot welding set .
  • Welding can be done only along a straight or uniformly curved line.
  • It is difficult to weld thickness greater than 3 mm.

Applications of Seam Welding:

It is used for welding of stainless steels, steels alloys, nickel and its alloys, magnesium alloys etc.

DIFFERENCE BETWEEN TURRET AND CAPSTAN LATHE EXPLAINED !!

A lathe is a machine tool that rotates the workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, turning, with tools that are applied to the workpiece to create an object with symmetry about that axis.
There are basically two broad classification of semi-automatic lathe.They are:
  1. Turret Lathe
  2. Capstan Lathe 

TURRET LATHE :

>The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable

>It has additional turret, which is an indexable toolholder that allows multiple cutting operations to be performed, each with a different cutting tool.

>Need for the operator to perform set-up tasks in between, such as installing or uninstalling tools is not required.

>The turret head is directly mounted on the saddle and the saddle slides over the bed ways. (See figure.)
Fig:Turret Lathe
>Saddle is moved to provide feed to the tool.
>They are heavy and durable.
>More feed and depth of cut are provided for machining.
>It is use for mass production of large size equal part.
>It is accommodated with power chucks.

CAPSTAN LATHE :

>The capstan lathe also has a turret which contains multiple cutting tools but in case of capstan lathe the turret head is mounted on the ram and the ram is mounted on the saddle.(See figure)
Fig:Capstan Lathe 
>Saddle is locked at a particular point and the ram is moved to provide feed to the tool.
>They are lighter in construction.
>Only limited amount of feed and depth of cut are provided for machining.
>It is use for mass production of small size equal part.
>It have hand operated collet chucks.


Also see : LATHE AND OPERATIONS ON IT


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DIFFERENCE BETWEEN FIRST ANGLE AND THIRD ANGLE PROJECTION EXPLAINED !!

Orthographic projection  is a means of representing a three-dimensional object in two dimensions. It is a form of parallel projection, where all the projection lines are orthogonal to the projection plane, resulting in every plane of the scene appearing in affine transformation on the viewing surface. A lens providing an orthographic projection is known as an (object space) telecentric lens.

There are two types of drawing in orthographic , First Angle and Third Angle. They differ only in the position of the plan, front and side views.

First Angle Projection :

1.)In first angle projection, that object is assumed to be in the first quadrant. Hence, the top view is projected below, i.e. to the x-z plane - which lies below the object.
2.)The object is assumed to be positioned in between the projection planes and the observer.

3.)The views are obtained by projecting the images on the respective planes.
4.)First Angle Projection is commonly used in all countries other than United States. The Indian Standard Institution (ISI) recommend the use of First Angle Projection method now in all the institutions.
5.)In first angle projection right view come in left of front view and top view come at the bottom of front view.
Fig : First Angle Projection

Third Angle Projection:

1.)In the third angle projection method, the object is assumed to be in the third quadrant. i.e. vertical Plane is in front of the object and the Horizontal Plane is above the object.
2.)For the third angle projection plane of projection is placed between the object and observer.
3.)Third Angle Projection is commonly used in United States of America.
4.)In third angle projection right view come on right side of front view and top view comes at the top of front view.
Fig:Third Angle Projection

Major differences between first angle and third angle projection:


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DIFFERENCE BETWEEN HOLE,SLOT AND GROOVE EXPLAINED !!

We generally get confused in three terms that are HOLE,GROOVE and SLOT.These terms might look similar but there are basic differences that make them different from each other.Again,it is an important interview question.

HOLE :-

1.)A hole may be defined as the circular cutout through the material.
2.)The hole may be upto a certain depth or throughout the material.
3.)In the figure below, (a) is throughout hole and (b)is upto a certain depth.

GROOVE :-

1.)A groove is a long and narrow indentation built into a material, generally for the purpose of allowing another material or part to move within the groove and be guided by it.
2.)Example includes a depression on the entire circumference of a cast or machined wheel, a pulley or sheave. This depression may receive a cable, a rope or a belt.

SLOT :-

1.) A narrow, elongated depression  for receiving or admitting something like coin or a letter.
2.)A slot is cut into a flat plate or normal to the axis of a cylinder.
3.)You can simply understand that a slot can be through or blind but a groove is always blind(having some depth).

DIESEL CARS VS PETROL CARS : WHICH ONE YOU SHOULD BUY? WE HAVE THE ANSWER !

Should you buy a petrol car or diesel car?
This is probably the first question that comes to mind when you think about buying a car.
The question is simple but the answer is not. In this article we are going to share pros and cons of a Diesel Engine and Petrol Engine.
Usually, Diesel Engine cars will run on Diesel or Bio-diesel only. The Petrol Engine car can run on petrol and can run on CNG when a suitable CNG kit is fitted on that engine. CNG kits are not available for Diesel Engine cars as Petrol and Diesel engine have some fundamental differences which make diesel engines not-suitable for CNG. Lets see these differences in detail.

Petrol / Gasoline Engine Car :

  1. Petrol Engine cars are less noisy as compared to the Diesel Engine cars of similar type.
  2. Petrol Engine cars give less fuel mileage (miles per gallon / KM per liter) when compared to diesel engine cars of similar type.
  3. Petrol engine cars have better acceleration and top speed compared to Diesel Engine cars.
  4. Petrol Engine cars have lower torque at lower engine speed when compared to a diesel engine cars. This means that a petrol car will face more difficulty climbing uphill when compared to a Diesel engine car.
  5. Petrol Engine cars are cheaper to maintain and initial cost is also cheaper.
  6. Petrol Engine is more efficient at higher speeds. This means it gives a better mileage on highway /freeway driving compared to city-driving mileage.
  7. Petrol Engine can be run on CNG by fitting a CNG kit to the petrol Engine of the car.
  8. It is more economical to buy a petrol engine car if you travel only a few miles a day, this is because the initial cost of petrol engine car is low and maintenance cost is low.

Diesel Engine Car :

  1. Diesel Engines cars are noisy when compared to the similar petrol engine cars.
  2. Diesel Engines cars are more fuel efficient compared to the petrol engine cars. Diesel Engines deliver more miles per gallon / more KM per liter of Diesel when compared to the petrol engine cars of similar type.
  3. Diesel Engine cars have low peak power and acceleration compared to similar capacity petrol engine car.
  4. Diesel Engine cars have higher torque at lower engine speed when compared to a petrol engine cars. This means that a diesel engine car can carry heavy loads uphill more easily as compared to a petrol engine car. So if you drive in a hilly terrain, you will find diesel car better compared to a petrol car.
  5. Diesel Engines usually have higher maintenance cost when compared to petrol engines.
  6. Diesel Engine cars are more fuel efficient at low engine speeds as compared to petrol engine cars. This means diesel engine car will give better fuel efficiency in city-driving conditions as compared to the petrol engine cars. 
  7. Diesel Engines can not run on CNG directly by fitting a CNG kit. This is because petrol engines have spark plug and they have compression ratios which suit the CNG fuel, but the diesel engines work on compression ignition without use of spark plug and  have much higher compression ratio than what is suited for CNG. Although there is some research going on to use CNG in diesel engine is some different way, but that technology is still in labs and will take some time to become feasible and available in passenger cars.
  8. It is more economical to buy a Diesel engine cars if you travel more than 20 miles a day or so because the high initial cost and high maintenance cost is offset by the low running cost of  diesel engine car.

Final Verdict :

Diesel has its major advantage of low fuel cost(now a days the difference between cost of petrol and diesel per liter is not much) and better mileage but when it comes to service and maintenance it will cost you more than petrol. This leads to a very logical answer –  Don’t just buy a car considering its great mileage and cheaper fuel price; buy a car after calculating the overall running cost and the tenure that you would want to keep it for. If you want to keep a car for long and drive more than 80-100km a day, diesel can be a valid option. Otherwise, if your running is quite less and you don’t prefer keeping a car for more than 3-4 years, go for petrol.

6 THINGS NOBODY TOLD YOU ABOUT YOUR TYRES !!

A lot of vehicle owners don’t bother about tyres except for filling up air, and getting the occasional ‘alignment-balancing’ done. Often, not knowing enough about tyres causes a lot of repairs, expenses and even accidents. Here are 10 things every vehicle owner must know about tyres.

1.)Proper inflation is everything

Over-inflation is bad. Under-inflation can be fatal. Always, make sure that your car’s tyres run the same pressure specified by the automaker. While underinflation can cause punctures, and even tyre bursts at high speeds, over-inflation can cause suspension damage, a poor ride and also loss of control at high-speeds.

2.)Burn-outs kill tyres

Burn-outs may look spectacular but they can simply destroy a car’s tyres by causing, 1. Flat spots that make the tyres prone to bursts. 2. Heavy tyre wear. 3. Loss of grip due to the tyre wear. A bald tyre will not just heat up faster and cause a tyre burst, but also dissipate water poorly, causing aquaplaning in the monsoons, potentially leading to a nasty accident.

3.)Regular wheel alignment and balancing = long lasting tyres and suspension

Wheel alignment, balancing and rotation of tyres needs to be done according to manufacturer specified intervals. This interval varies from car to car. Consult your manual for the exact interval. For most cars, it’s 10,000 kilometers. Yes, even suspension lasts longer on balanced tyres rather than unbalanced ones. For even tyre wear, rotation of tyres is important. Also, make sure that you take your car for alignment-balancing if you experience the steering ‘pulling to one side’ or vibrations on the steering-wheel.

3.Say NO to Overloading 

Overloading a vehicle stresses tyres beyond its carrying capacity, increasing wear, and also the potential for failure. Each time a vehicle is overloaded, a tyre gets weakened, and obviously, this can have dangerous consequences. So, never overload a vehicle. Should it be unavoidable, cut speed by at least 30 % to give yourself some margin of safety.

4.)High speeds on cement roads are ‘tyre-killers’

Cement/concrete roads (found on most expressways) cause much higher tyre wear than tar roads. This is because they cause the tyres to heat up more. So, when you’re on such a road, make sure that you stick to the speed limit. Driving at high-speeds – significantly higher than the speed limit – can easily cause a tyre burst.

5.)Fat tyres are more for looks than performance

Fat tyres make a lot of cars look good, but are wholly unnecessary as far as performance goes. Fat tyres cut fuel efficiency, increase tyre noise in many cases, and also make cars go slower due to higher rolling resistance and weight. If you have to upsize, make sure that the new tyres are within the ‘advisable rolling diameter’ that will suit your car. There are many online tyre-size calculators that will help you figure this out.

6.)High-performance tyres wear out much faster

High-performance tyres can offer great grip but they also wear out faster. If you drive a budget car mainly for commuting and stick to sane speeds, there’s no real benefit of fitting high-performance tyres to your car. Such tyres are quite expensive, and also need to be replaced much earlier.

MECHANICAL PROPERTIES OF MATERIAL,EVERY MECHANICAL ENGINEER MUST KNOW !!!

The mechanical properties of a material are those which effect the mechanical strength and ability of material to be molded in suitable shape. 

Some of the typical mechanical properties of a material are listed below-

#1. Strength:

The ability of material to withstand load without failure is known as strength. If a material can bear more load, it means it has more strength. Strength of any material mainly depends on type of loading and deformation before fracture. According to loading types, strength can be classified into three types.

a. Tensile strength:
b. Compressive strength:
3. Shear strength:

According to the deformation before fracture, strength can be classified into three types.

a. Elastic strength:
b. Yield strength:
c. Ultimate strength:

#2. Homogeneity:

If a material has same properties throughout its geometry, known as homogeneous material and the property is known as homogeneity. It is an ideal situation but practically no material is homogeneous.

#3. Isotropy:

A material which has same elastic properties along its all loading direction known as isotropic material.

#4. Anisotropy:

A material which exhibits different elastic properties in different loading direction known as an-isotropic material.

#5. Elasticity:

If a material regain its original dimension after removal of load, it is known as elastic material and the property by virtue of which it regains its original shape is known as elasticity.

Every material possess some elasticity. It is measure as the ratio of stress to strain under elastic limit.

#6. Plasticity:

The ability of material to undergo some degree of permanent deformation without failure after removal of load is known as plasticity. This property is used for shaping material by metal working. It is mainly depends on temperature and elastic strength of material.

#7. Ductility:

Ductility is a property by virtue of which metal can be drawn into wires. It can also define as a property which permits permanent deformation before fracture under tensile loading. The amount of permanent deformation (measure in percentage elongation) decides either the material is ductile or not.

Percentage elongation = (Final Gauge Length – Original Gauge Length )*100/ Original Gauge Length

If the percentage elongation is greater than 5% in a gauge length 50 mm, the material is ductile and if it less than 5% it is not.

#8. Brittleness:

Brittleness is a property by virtue of which, a material will fail under loading without significant change in dimension. Glass and cast iron are well known brittle materials.

#9. Stiffness:

The ability of material to resist elastic deformation or deflection during loading, known as stiffness.  A material which offers small change in dimension during loading is more stiffer. For example steel is stiffer than aluminum.

#10. Hardness:

The property of a material to resist penetration is known as hardness. It is an ability to resist scratching, abrasion or cutting. 

It is also define as an ability to resist fracture under point loading.

#11. Toughness:

Toughness is defined as an ability to withstand with plastic or elastic deformation without failure. It is defined as the amount of energy absorbed before actual fracture.

#12. Malleability:

A property by virtue of which a metal can flatten into thin sheets, known  as malleability. It is also define as a property which permits plastic deformation under compression loading.

#13. Machinability:

A property by virtue of which a material can be cut easily.

#14. Damping:

The ability of metal to dissipate the energy of vibration or cyclic stress is called damping. Cast iron has good damping property, that’s why most of machines body made by cast iron.

#15. Creep:

The slow and progressive change in dimension of a material under influence of its safe working stress for long time is known as creep. Creep is mainly depend on time and temperature. The maximum amount of stress under which a material withstand during infinite time is known as creep strength.

#16. Resilience:

The amount of energy absorb under elastic limit during loading is called resilience. The maximum amount of the energy absorb under elastic limit is called proof resilience.  

#17. Fatigue Strength:

The failure of a work piece under cyclic load or repeated load below its ultimate limit is known as fatigue. The maximum amount of cyclic load which a work piece can bear for infinite number of cycle is called fatigue strength. Fatigue strength is also depend on work piece shape, geometry, surface finish etc.

#18. Embrittlement:

The loss of ductility of a metal caused by physical or chemical changes, which make it brittle, is called embrittlement.