ME - Mechanical Engineering


Online Magazine for Mechanical Engineers

In soldering and brazing processes, the metal parts being joined are heated but not melted and molten filler material is made to flow between the two closely placed adjacent surfaces by the capillary action. A strong joint between the parts is formed on cooling to room temperature by the bond formed at the high temperature between the parent metal atoms and the filler metal atoms. These process are suitable for joining the dissimilar metals also.

Soldering

The American Welding Society (AWS) defines soldering as a joining process that takes place below 840°F, most of the brazing operations are done at temperatures ranging from 350 to 600°F.
Soldering is a metal joining process is used for making low mechanical strength joints. The Filler metal used has a low melting point and is called solder.
For metallic surface to be soldered, surface must be capable of being wetted by the solder. There must be liquid solubility between the solder and one or more of the constituents metals of each part to wet a surface. The atoms of at least one of the component metals of each part to wet a surface. The atoms of at least one of the component metals of the solder may form a solid solution with the metal being soldered but combination of two metals from the liquid solution may result in the formation of intermetallic compound.
The ability of joining solder to wet a surface depends on the cleanliness of the metallic surface. After cleaning, an extremely thin film of metallic oxide immediately forms on most of the metallic surfaces and inhibits its wetting by solder. Flux is used to dissolve the oxide film and also to protect the metallic surfaces thus uncovered until it has been effectively wetted by the solder.
In soldering joining process, the heat is supplied to the joint by soldering iron. The soldering iron may be heated electrically or by other means. The function of soldering iron is to heat the joint. The flat face of the soldering iron is held directly against the joint assembly so that the heat is transferred effectively to the parts being soldered.
Simple soldering joint
In soldering joining process, the heat is supplied to the joint by soldering iron. The soldering iron may be heated electrically or by other means. The function of soldering iron is to heat the joint. The flat face of the soldering iron is held directly against the joint assembly so that the heat is transferred effectively to the parts being soldered.
Solder:
Most of the solders used in soldering joining process are made of lead and tin alloys. Some solders also contain small amounts of cadmium and antimony. The amount of % composition of tin and lead determines the physical and chemical properties of joints made with solder. Bar, stick, fill, wire, strip are the different forms solder is available. Solder can be obtained in circular or semi-circular rings or any other desired shape. sometimes the flux can be included with the solder.
Fluxes:
The function of fluxes is to remove the non-metallic oxide film from the metal surface during the heating and soldering operations, so that clean metals may make mutual metallic contact. The flux does not constitute a part of the soldered joint. Commonly used fluxes in soldering joining process are Zinc chloride (Zncl2), ammonium chloride (NH4cl and hydrochloric acid (Hcl).

Brazing

The American Welding Society (AWS) defines brazing as a joining process that takes place above 840°F but below the melting point of the base metals. Most of the brazing operations are done at temperatures ranging from 1100 to 1500°F.
Since, Brazing joining process is done at high temperature, brazing is useful for joining thick metal parts for making relatively stronger joints. Both similar and dissimilar parts can be joined. The success of brazing operation depends upon that a fact that a molten metal of low surface tension will flow easily and evenly over the surface of a properly heated and chemically clean base metal, just as water flows over a clean glass plate.
During brazing the base metal of two pieces to be joined is not melted. An important requirement is that, similar to soldering, the filler metal must be wet the base metal surfaces to which it is applied. some diffusion or alloying of the filler material with the base metal takes place even through the base metal does not reach its solidus temperature.
The surfaces to be joined must be made chemically clean before brazing operation is started. however the fluxes are applied to remove oxides from the surfaces. Borax is the most commonly used flux during brazing process. It will dissolve the oxides of most of the common metals.

Brazing process is similar to soldering but the main difference between brazing and soldering is that brazing requires higher temperature than soldering.

Methods of Brazing:

Based upon the method of heating used in brazing process, different brazing methods have evolved. Two Commonly used methods of brazing are:
  • Torch Brazing:
    Torch brazing is widely used brazing method. Heat is produced, generally by burning a mixture of oxy-acetylene gas, as in the gas welding. A carbonizing flame is suitable for brazing purpose as it produces sufficiently high temperature needed for brazing.
  • Furnace Brazing:
    Furnace brazing is suitable for brazing large number of small or medium parts. Usually brazing filler metal in the granular or powder form or as strips is placed at the joint and then the assembly is placed in the furnace and heated. large number of small parts can be accommodated in a furnace and simultaneously brazed.

Advantages of Soldering and Brazing:

  • Low temperature. Since the base metal does not have to melt, a low-temp heat source can be used. This minimized distortion and creates a smaller heat-affected zone.
  • Joints can be made be permanently or temporarily. Since the base metal is not damaged, parts can be disassembled at a any time by simply supplying heat. The parts then can be reused. The joint made by soldering or brazing process is solid enough to be permanent.
  • Metals of dissimilar can be joined. By using soldering and brazing process dissimilar metals can be easily joined, such as aluminum to brass, copper to steel and cast iron to stainless steel. It is also possible to join nonmetals, i.e. ceramics can be easily brazed to each other or to metals.
  • Speed of joining. Parts can be preassembled and furnace soldered or brazed in large quantities. A lower temperature means less time in heating.
  • Less chance of damaging parts. A heat source can be used that has a maximum temperature below that which may cause damage to the base material.
  • Parts of varying thickness can be joined. Very thin parts or a thick part and a thin part can be easily joined without burning through or overheating them.
  • Easy realignment. Parts can be easily realigned by reheating the joint, re-positioning the parts and allowing the filler metal to solidify.

References:
History of Manufacturing process and usage of materials and composites started dates back to the period 5000-4000 B.C. Recorded history of manufacturing by our ancients is older than actual history, the earliest forms of which were invented by the Sumerians around 3500 B.C. Primitive cave drawings, markings on clay tablets and stone, required some type of a brush and some kind of paint, as in the prehistoric cave paintings in Lascaux, France, estimated to be 15000 B.C period.
The manufacture of things for specific uses began with the production of various household artifacts, which were usually made of either stone, wood or metal. The materials were 1st used in making utensils and ornaments like gold, copper, iron, silver, lead, tin, bronze and brass. The process ways 1st employed involved largely casting and hammering, because they were comparatively straight forward to perform. Over the centuries, these simple processes gradually began to be developed into better and a lot of complex operations, at higher rates of production and increase in levels of product quality.

Anti-lock Brake System (ABS) is an automobile safety system that allows the wheels on a automobiles to continue tractive contact with the road surface as directed by driver steering inputs while braking, preventing the wheels from ceasing rotation and therefore avoiding skidding.

Advantages of Anti-lock Braking System (ABS):

  • ABS guarantees stable braking characteristics on all road surfaces, hence avoids overturning of the vehicle.
  • ABS reduces friction on wheels and road, thus increases efficiency of tires (up to 30%).
  • Vehicle with ABS can be stopped at a lesser distance than a non ABS vehicle.
  • Steering control is effective, i.e., vehicle can be steered smoothly while braking. Thus minimizes the accidents.
  • A driver without experience can drive ABS vehicle effectively, than an experienced driver on the non ABS vehicle.
Vehicle without Anti lock Braking System and with ABS
Image credits: nasva.go.jp

Disadvantages of Anti-lock Braking System (ABS):

  • Initial cost for ABS vehicle is high.
  • Maintenance issues arise as the whole braking system is controlled by engine control unit.
  • On concrete roads, the ABS vehicle stopping distance might be needed more.
Lagrange-d'Alembert principle is generally known as D'Alembert's principle, stated by French physicist and mathematician polymath Jean le Rond d’Alembert.
According to the d'Alembert's principle, the external forces acting on a body and the resultant inertia forces on a body are in equilibrium. This principle is a alternative form of Newton's Second law of motion but this principle suggests that the term "-ma" (product of mass and acceleration) of the body can be considered as a fictitious force, often called the inertia force or d'Alembert's force. Accordingly, the net external force F actually acting on the body and the inertia force Fi together keep the body in a state of fictitious equilibrium.
F + Fi = 0
The d'Alembert's principle gives the solution procedure of a dynamic problem, an appearance like that of a static problem and the above equation becomes equation of dynamic equilibrium.
Rolling Contact Bearings are also known as anti-friction bearing due to its low friction characteristics between ball and inner & outer rings. Rolling Contact Bearings are used for radial load, thrust load and combination of these both loads. Rolling Contact Bearings are often used due to its lower price, less maintenance cost and easy to operate.
Rolling Contact bearings are of two types they are:
  1. Ball bearing
  2. Roller bearing
The rolling contact bearings illustrated below represent a small set of the huge variety of ball and roller bearings.

Thrust Ball Bearing:

Thrust ball bearing
A thrust ball bearing can support an axial load in one direction. These bearings are designed not to accommodate radial loads. The components of these bearings can be easily separated.



Deep Groove Bearing:

Deep groove bearing
In deep groove bearings balls are fitted well into the deep grooves, enabling the bearing to support axial loads in both directions. The bearing illustrated left side has a single row of balls.





Tapered Roller Bearing:

Tapered roller bearing
In tapered roller bearings the inner & outer rings and the rollers are tapered in order to simultaneously support axial and radial loads. In these bearings the ratio of the axial and radial loads supported depends on the angle between the roller and bearing axes. Higher the angle helps to support a larger axial load.




Angular Contact Ball Bearing:

Angular contact ball bearing
Angular contact ball bearings are able to with stand a large thrust load in single direction, in addition to radial loads.






Self-aligning Ball Bearing:

Self-aligning Ball Bearing
In Self-aligning ball bearings there are two sets of balls which one run on a pair of grooves on the inner ring, with a single outer-ring concave surface.







Needle Roller Bearing:

Needle Roller Bearing
Needle roller bearings has long and thin rollers, these bearings are used for applications where radial space is limited.






Spherical Roller Bearing:

Spherical Roller Bearing
In spherical roller bearings there is angular contact between the rollers and raceways, the bearings are able to with stand both axial and radial loads. the double set of rollers in spherical roller bearings permits the bearing to accommodate shaft misalignment. Notice that the rollers of the bearing illustrated left side are not cylindrical and hence the adjective `spherical'.



Cylindrical Roller Bearing:

Cylindrical Roller Bearing
The cylindrical roller bearings are able to withstand large radial loads. The bearing illustrated left side is a single-row bearing. These bearings played a seminal role in the development of the continuous rolling mill.





Wheel Hub Bearing:

Wheel Hub Bearing
Wheel Hub bearings are manufactured in large quantity annually for needs of the automotive industries. These bearings support the radial load due to the weight of the automobile, These bearings also support thrust loads developed when the motion of the automobile is not linear.




Source:
Mechanical Bearings PDF - University of Cambridge
Water hand pumps are manually operated pumps; They are used for bringing water from earth underground to earth surface and is used in every country for a variety of industrial, marine, irrigation and household purposes.
Image shown below is the typical design of Hand Pump.
Typical hand pump design

Hand Pump Parts:

  • Handle
  • Pump rod
  • water outlet
  • Piston
  • Piston valve
  • Foot valve
  • Rising main
  • Suction lift

Principle of Hand Pump:

There are several types of water hand pumps. Most commonly used hand pumps are positive displacement pumps, positive displacement pumps have reciprocating plungers or pistons. In a piston pump, the piston is fitted with the piston  valve (non-return valve) and slides vertically up and down within a cylinder which is fitted with a foot valve (non-return valve). Applying the force on handle of the water pump causes vertical movement of pump rods that are connected to the piston.
When the piston of the pump moves upwards, the piston valve closes and a vacuum is created below the piston valve, Piston valve causes water to be drawn into the cylinder through the foot valve, which opens. Simultaneously, water above the piston, held up by the closed piston valve, is displaced upwards. In a suction hand pump water flows outward through the delivery outlet; in a hand pump with a submerged cylinder it is forced up the rising main.
When the piton moves downwards in hand pump, the foot valve closes to prevent back flow of water and the piston valve opens to allowing the piston to move down through the water in the cylinder.

Going through the strenuous course of completing a B. Tech degree is definitely an achievement. But for a mechanical engineer the struggle doesn't end there. Mechanical engineering is one of the oldest branches of engineering. It is also referred to as the mother of engineering. This field has a wide scope of learning and is extremely diverse. Most of the modern day inventions are contributed to this field of engineering.
Mechanical engineers have to understand various concepts like thermodynamics, mechanics, robotics, kinematics, fluid mechanics, heat transfer, CAD, CAM. All these concepts are universally used to create and design different type’s motor vehicles, manufacturing units, aircraft and aerospace parts and other assortments of machineries that are used every day and also at industries.
So once you are in final year or graduated in B. Tech/B.E in Mechanical Engineering from India, you have a variety of opportunities to explore. To get selected into the top PSU’s you would have to write the following exams GATE (Graduate Aptitude Test in Engineering), SAIL, GAIL, BARC etc.

You can also choose any one of the below mentioned specializations in Mechanical Engineering to do M.Tech / M.E by getting seat in top universities and colleges like IITs, NITs, BITS.

Production Engineering:

This is a combination of manufacturing technology and management science. A production engineer is someone that has both wide knowledge of various engineering practices and also aware of the challenges that are related to production. Their main goal is to achieve a smooth, judicious and economic production process.
Production engineering in short means application and design of manufacturing techniques. It is used to produce a specific product. It covers various areas like:
  • Specification, planning and coordination of the resources and their usage.
  • Analysis of productions processes, productability and systems.;
  • Application of equipment, methods and tooling.
  • Application of cost control techniques.

Industrial Engineering:

This specialization covers areas that deals with optimizing of complex systems and processes. It is concerned with the improvement, the implementation and the development of integrated systems of knowledge, people, money, information, energy, equipment, analysis, materials and synthesis. Industrial Engineering also covers physical, mathematical and social sciences that are put together with the principles and methods of engineering design to predict, specify, and evaluate what the results are.
Depending on the sub specialties involved, industrial engineering may also be known as Management Sciences, System Engineer, Ergonomics, and Safety Engineer etc.

Thermal Engineering:

This specialization deals with heating and cooling of equipment, processes and enclosed environments. A combination of theories and disciplines could be used to solve a specific thermal engineering issue like:
  • Thermodynamics
  • Fluid mechanics
  • Mass transfer
  • Heat transfer
Thermal engineering is practiced by both chemical engineers and mechanical engineers.
Material sciences Engineering: This specialization covers areas like design and discovery of new materials. It is a relatively new field in the engineering domain. It involves studying materials through materials paradigm i.e., properties, structure, synthesis and performance. Material Sciences origin reaches back to the fields of engineering, chemistry and mineralogy.
It has elements of physics and chemistry, and is at the front runner of nano technology and nano science research. However in recent years, materials science is widely known as a specific field of engineering and science

Automobile Engineering:

This specialization deals with the various aspects of automobile and its making. Modern automotive engineering, along with aerospace engineering and marine engineering, is a branch of automobile engineering, incorporating various elements like:
  • Mechanical
  • Electrical
  • Electronic
  • Software 
  • Safety engineering
These are applied to the design operation and manufacture of automobiles, motorcycles, trucks and buses along with their respective engineering subsystems.

Machine Design:

This specialization deals with the mathematical and physical basis of the subject and it is applied in various different fields. Broadly they cover subjects like mechanics, theories of elasticity, fracture and plasticity and design optimization.
Manufacturing: This area of specialization covers variety of courses like metallurgy, heat treatment, welding, casting, hot and cold forming and various other non-metallic materials like plastics, ceramics etc.

Fluid Mechanics / Environmental Fluid Mechanics:

This specialization deals with a broad range of applications relating to the principles of fluid mechanics and thermodynamics. Keeping their emphasis on industrial significance.

There are plethora of industries that have high demand mechanical engineers like Aerospace Industry, Steel Plants, Aviation Companies, Armed Forces, Thermal Plants, Automobile and Auto parts industry etc. Plus if you plan to complete your masters and PhD, you could join as a professor at any reputed university.
Screw thread is a continuous helical groove of specified cross-section produced on the external or internal surface. A screw thread formed on a cylinder is known as straight or parallel screw thread, while screw thread formed on a cone or frustum is known as tapered screw thread.
Axis of a thread: This is a imaginary line running longitudinally through the centre of the screw.
Crest: Crest of thread is the top most surface joining the two sides.
Root: Root of thread is the bottom of the groove between the two flanks.
Flank: Flank of thread are straight edges which connect the crest with root of thread.
Pitch: Pitch of a thread is the distance measured parallel to the axis from a point on a thread to the corresponding points on adjacent thread forms in the same axial plane and on the same side of axis.
Depth of thread: Depth of a thread is the distance between the crest and root of the thread.
Screw Thread Terminology
Major diameter: It is an imaginary largest diameter of thread which would touch the crests of internal or external thread.
Minor diameter: It is an imaginary smallest diameter of thread which would touch the roots of an external thread.
Pitch diameter: It is a theoretical diameter between the major and minor diameter of screw threads.
Basic profile of screw threads
Helix angle: On straight thread, It is the angle made by the helix of the thread at the pitch line with the axis.
Lead angle: On straight thread, It is the angle made by the helix of the thread at the pitch line with plane perpendicular to the axis. Lead angle is measured in an axial plane.
Flank angle: Flank angle is the angle made by the flank of a thread with the perpendicular to the axis of a thread.
Included angle: Included angle is the angle between the flanks or slope of the thread measured in an axial plane.
The lead: It is the distance the nut moves parallel to the screw axis when the nut is given one turn. For a single thread as shown in the figure above, the lead is the same as the pitch of the screw thread.

  • The ease with which welding of a give material can be done without producing any defect is called Weldability.
  • Weldability can also be defined as the capability of a metal to be welded under the fabrication conditions imposed satisfactorily in the intended surface.
  • The metal should not require expensive or complicated or extracting procedures in order to produce a sound joint.

Factors affecting Weld Ability:

Melting point, thermal conductivity, reactivity, coefficient of thermal expansion, electrical resistance and surface condition of material are factor that affect weld abiliy.
1. Meting point of metal: Materials with medium melting point can be welded very easily.
2. Thermal conductivity: Material with High Thermal conductivity (K) are treated as difficult to weld materials.
3. Reactivity: If the material reacts with air, water or surroundings it become difficult to weld.
4. Coefficient of thermal expansion of metals: Material with high thermal expansion coefficient, it becomes difficult to weld.
5. Electrical resistance: Higher the electrical resistance of the material, it becomes difficult because it requires lot of heat energy.
6. Surface condition: The material with dirty surface it becomes difficult to weld.

From the above mentioned factors whichever the material is influenced by maximum number of factors, the corresponding material is treated as very difficult to weld and whichever the material is influenced by least number of factors, the corresponding material is treated as very easy weld material.
Steam Engines powered most of the trains from 1800s to 1950s. Steam locomotives are railway locomotive that produce its pulling power. Fuel for these steam locomotives engines is produced by burning combustible material, usually coal or wood to produce steam in a boiler.
The image below is steam locomotive train engine, not all components are present on all locomotives and not all possible components are labelled in the illustration below.
Steam Locomotive train
1.Tender, 2.Cab, 3.Whistle, 4.Reach rod, 5.Safety valve, 6.Generator, 7.Sand dome, 8.Throttle Lever, 9.Steam dome. 10.Air pump, 11.Smoke box, 12.Main steam pipe, 13.Smoke box door, 14.Hand rail, 15.Trailing truck, 16 Foot board/Running board, 17.Frame, 18.Brake shoe and brake block, 19.Sand pipe, 20.Coupling rods, 21.Valve gear, 22.Connecting rod, 23.Piston rod, 24.Piston, 25.Valve, 26.Valve chest.

Steam Locomotive Components
27.Firebox, 28.Boiler tubes, 29.Boiler, 30.Super heater tubes, 31.Throttle valve, 32.Super heater, 33.Chimney 34.Headlight, 35.Brake hose, 36.Water compartment, 37.Coal bunker, 38.Grate, 39. Ash pan hopper, 40.Journal box, 41.Equalising beams, 42.Leaf Springs, 43.Driving wheel, 44.Pedestal or saddle, 45.Blast pipe, 46.Pilot truck, 47.Coupling.

Image courtesy: Panther
Rolex Submariner Date Oyster, 40 mm, steel watch
If you have ever wondered ever why Rolex Watches are so expensive you can watch this video made by Watchfinder & Co, on demonstration of Rolex Submariner DATE Oyster, how it is being disassembled each part, showing the intricacies work involved in hand making the time piece in exquisite detail.
Airplanes are travelling machines that are manufactured to transport human beings and luggage from one location to another. Airplanes travel in air very faster compared to roadway vehicles, trains and ships.
Airplanes are manufactured in manufactured in different shapes and sizes according to the need and desire. When Airplane is travelling it has to lift its own weight, the fuel, the passengers and the luggage. 
Parts of an airplane are wing, jet engine, cockpit, fuselage, slats, spoiler
Parts of an airplane and their function are mentioned below in tabular form.
S.No
Airplane part
Function of the airplane part
1
Wing
Generate lift to hold airplane in air.
2
Jet Engine
Generate thrust to overcome the drag and to move in forward direction
3
Cockpit
Pilot sit here to control and command the plane.
4
Fuselage (Body)
Holds all parts together
5
Slats
To increase airplane lift during takeoff and landing
6
Spoiler
To reduce plane speed
7
Aileron
Roll the wings side ward direction
8
Flaps
Increase lift and drag of airplane during takeoff and landing
9
Elevator
Deflect the tail of the airplane up and down motion
10
Rudder
Deflect the tail direction to the left and right side
11
Vertical Stabilizer
To maintain the balance of the airplane from swinging side ward directions
12
Horizontal Stabilizer
To maintain the balance of the airplane from moving up-and-down

Reference: Parts of Airplane and function - NASA Website
Boston Dynamics - Robot spotBoston Dynamics is an robotics design company owned by Google in 2013, they began as spin-off from the MIT. Boston Dynamics Technical team of engineers and scientists develop robots that run and move carefully like animals.

Spot is a smaller robot designed by Boston dynamics company. Spot robot is an electrically powered and hydraulically actuated four-legged robot. This robot has a sensor head that helps it navigate and negotiate rough terrain. It weighs 72.5 kilograms.

Rivet is used to connect two or more plates inserted through the hole in plates and pressed on the other side.
Rivets
The diameter of the rivet hole for a given plate is given by the Unwin's formula:
d = 6*(t)^(0.5)
where, t = Thickness of plate in mm and
d = Diameter of rivet in mm which is used to denote dimension of the rivet.

Types of Rivets:

For steel plates the rivets are generally made in low carbon steel. The rivets in copper add to resistance against corrosion and aluminium rivets can be used to lower the weight of the structure.
Different types of Rivets
Rivets with counter sunk head and oval counter sunk rivets shown in bottom image are not as strong as button head rivets.  Counter sunk head and oval counter sunk rivets are used only when protruding rivet heads are objectionable. Pan heads and conical heads are less frequently used and are difficult to produce. Tubular rivets have special deviation from solid rivet shank. Tubular rivets are used in aircraft's.

Types of Riveted joints:

The classification of riveted joints can be done in following ways:

1. According to purpose of rivets:

Based on purpose the riveted joints can be classified into three types:
1.1 Strong Joints:Strong rivet joints strength is the only criterion. These joints are used in engineering structure such as trusses, beams and machine frames.
1.2 Tight Joints: Tight rivet joints provide strength as well as are leak proof against low pressures. Joints in reservoirs, containers and tanks fall under this group.
1.3 Strong Tight Joints: Strong tight rivet joints are used in boilers and pressure vessels and ensure both strength and leak proofness.
Classification of rivets based on purpose has no sound basis and is arbitrary. This classification of rivets helps to understand the basis of design and manufacturing.

2. According to position of plates connected:

According to the position of plates connected riveted joints are classified into two types:
2.1 Lap joint: In a lap joint the edges of plates are simply laid over each other and riveted.
2.2 Butt joint: In Butt joint plates lie in the same plane and jointed through cover plates.

Reference: Riveted Joints PDF by IGNOU - The People's University