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December 01, 2016
Forging process is perhaps the oldest metal working process and was known even during prehistoric days when metallic tools were made by heating and hammering.
Forging is basically involves plastic deformation of material between two dies to achieve desired configuration. Depending upon complexity of the part forging is carried out as open die forging and closed die forging.
In open die forging process, the metal is compressed by repeated blows by a mechanical hammer and shape is manipulated manually.
Forging process
Image source: Wikimedia Commons
In closed die forging, the desired configuration is obtained by squeezing the workpiece between two shaped between two shaped and closed dies.
In forging process the forces are applied on the raw material such that the stresses induced are greater than yield and less than ultimate so that material is experiencing plastic (or) permanent deformation to get required shape. But in forging operation force applied can be either continuous or intermittent impact loads.

Types of forging methods:

1 Based on the method of force application
  1. Hand forging (Drop hammer type)
  2. Machine forging (Mechanical or hydrostatic forging)

1.1 Hand forging:

Hand forging always uses drop hammer type. Because the continuous force by the human hand, it is not sufficient to produce the deformation in work piece.

1.2 Machine forging:

In machine forging because the required force is obtained from machine it is possible to use either continuous force application or intermittent impact load application.
2. Based on method of shape obtained
  1. Open die forging
  2. Closed die forging
  3. Semi die forging

2.1 Open die forging

  • In open die forging operation only drop hammer type of force application will be used.
  • Press forging is not used since there is no time fr changing the position of component.
Features of open die die forging:
  • Repeated impact blows are given on the work.
  • Less dimensional accuracy.
  • Suitable only for simple shapes of work.
  • Requires more skill of the operator.
  • Usually used for a work before subjecting it to closed die forging (to give approximate shape.
  • Dies are simple and less expensive.
  • It can be analyzed much easily.
  • it is the simplest of all forging operations.

2.2 Closed die forging

  • Closed die forging is also called as impression die forging because the shape of the dies is impressed on the component.
  • In this the type of forging force application may be either press forging type or drop hammer type will be used.
Features of closed die forging:
  • Closed die forging involves two or more steps:
    1. Blocking die: Work is rough forged, closed to final shape.
    2. Finishing die: Work is forged to final shape and dimension.
  • Both blocking die and finishing die are machined into the same die block.
  • More number of dies are required depending on the complexity of the job.
  • Two die halves close-in & work is deformed under high pressure.
  • High dimensional accuracy/close control on tolerances.
  • Suitable for complex shapes.
  • Dies are complex and more expensive.
  • Large production rates are necessary to justify high costs.

2.3 Semi closed die forging operation

  • Only drop hammer type of force application is possible.
  • In case of open die and closed die forging operations the volume of raw material required is remaining same as that of the volume of final finished component. But in case of closed die forging operation the volume of the raw material is about 10% to 20% more than final component to be obtained.
  • To accommodate the excess volume of material it is required to provide some open space dies also called gutter.
  • Because of provision of gutter the flash is produces in the forged component.
  • This flash is unwanted material which has to be removed by trimming operation.
  • Flash and gutter is used only in case of closed die operation but not in open die or semi closed die forging operation.

Advantages of forging:

Some common advantages of choosing forging operation are listed below:
  1. Forged parts possess high ductility and offers great resistance to impact and fatigue loads.
  2. Forging refines the structure of the metal.
  3. It results in considerable saving in time, labor and material as compared to the production process of similar item by cutting from a solid workpiece and then shaping it.
  4. Forging distorts the previously created unidirectional fiber as created by rolling and increases the strength by setting the direction of grains.
  5. The forged parts can be welded easily.
  6. Because of intense working, flaws are rarely found, so have high reliability.
  7. High accuracy may be obtained in forging operation.

Disadvantages of forging:

Few disadvantages of choosing forging operation are listed below:

  1. Rapid oxidation in forging of metal surface at high temperature results in scaling which wears the dies.
  2. It is difficult to maintain close tolerances in forging operations.
  3. Forging is limited to simple shapes and has limitation for parts having undercuts etc.
  4. Some materials are not readily worked by forging.
  5. The initial cost of forging dies and the cost of their maintenance is high.
  6. The metals gets cracked or distorted if worked below a specified temperature limit.
  7. The maintenance cost of forging dies is also very high.
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December 01, 2016
Actual suction:
During the suction stroke the atmospheric air must be entered into the engine cylinder. Then the suction pressure must be below the atmosphere air. At the start of the suction stroke the piston speed is less, hence less air will enter into the cylinder. Then the difference between the atmosphere pressure and the suction pressure will be less at the start of the suction stroke. Then the piston picks up the speed, where more air enters inside. The pressure difference is considered to be higher. Finally the piston slows down and come to rest at bottom dead center. Hence the pressure difference will also be less. Actual suction process will be given by like 0 –a^1  – 1
Actual compression:
Due to heat carried away by cold water, the actual compression process is Polytropic. In account of heat loss the work input for the actual compression process will be more. Hence area in the p-v diagram for actual compression will be lesser. Hence the slop for the actual compression process will be higher than the adiabatic index. Process is given by 1-c-2^1
Actual heat addition:
Heat addition takes place during the changing direction of the piston at the top dead center. The volume first decreases and later increases. Further, the pressure increases throughout heat addition. The pressure increases through heat addition. The actual heat addition process is given by  2^1– d –3^1
Actual Expression:
Due to heat carried away by cold water the work output from the polytrophic expansion process is less. The expansion process is given by the line is  3^1– e –4^1
Heat rejection:
The actual heat rejection is not a constant volume process. During heat rejection the piston under goes change in direction at bottom dead center. The volume initially increases and then decreases. The pressure decreases throughout heat rejection. It is given by the line  4^1– f – e^1.
Actual Exhaust:
During exhaust the leftover exhaust gas is pushed out by the upward motion of the piston depending on the piston speed, the actual exhaust process is given by 1- b^1 – 0
The area formed by the combustion of the suction and exhaust process is known as pumping of engine loss.
The following area must be taken as negative
(0 – a^1 – 1- 1^1 – b^1 – 0). The area available due to the other operation is treated as positive where the net area is determined.
h_m=\frac{net \:\: area}{length \:\:\: of \:\:\: diagram}
imep=h_m \times Spring \:\:\: scale
The ratio of net actual indicated work done to the ideal indicated work done is defined as diagram factor of engine.

df = IWD actual/ IWD ideal.
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December 01, 2016
  • In the 2 stroke engine it consists of one cycle with one rotation
  • In the 4 stroke engine it consists of one cycle with two rotations.
  • The inlet and the exhaust valves of the 4 stroke engine are replaced by 3 ports in a 2 stroke engine.
  • In 2 stroke engine the lubrication oil must be mixed with the petrol
  • In case of 4 stroke engine the lubrication and the fueling must take place separately
  • In the 2 stroke engine due to the presence of the lubrication oil, some of the lubrication oil must be combusted during the time of heat addition. Hence there is more friction and loss of work in 2 Engine
  • The power available in the 2 stroke engine is only 70% of the calculated power
  • In 4 stroke engine the power available is 90% of the calculated power
  • In 2 stroke engine the transfer port and the exhaust port are opened at the same time. Hence some fresh air fuel mixture will be escaped out of the engine cylinder, due to which there is loss of fuel.
  • For single cylinder engine the size of the flywheel is bigger than the 4 stroke engine.
  • Due to the above reason the 2 stroke engine on the roads are replaced by the 4 stroke engine
  • The overall efficiency of a 4 stroke engine is much higher than that of a 2 stroke engine.

Difference in between the petrol engine and diesel engine
  • The temperature at the end of the compression is less for the petrol engine.
  • Thus a spark plug is needed for the compression. In case of the diesel engine the temperature at the end of the compression is above the self-ignition temperature of the fuel.
  • Hence the fuel ignited is allowed to enter the cylinder due to the high temperature.
  • No spark plug is required for the diesel engine.

  • For the separate entry of the fuel after the compression stroke, a nozzle is provided for the diesel engines.
  • In case of the petrol engine they do not have the nozzle.
  • In petrol engine the air and the fuel, are mix inside a carburetor before entering the engine cylinder. In diesel engine there is no mixing of air and fuel before suction stroke. Hence diesel engine does not have a carburetor.
  • Heat addition must take place at the constant volume for petrol engine. It takes place at the constant pressure for diesel engine
  • For the same compression ratio, the efficiency of a petrol engine is higher than that of the diesel engine. This is theoretical.
  • In an actual practice the compression ratio of a diesel engine is 1.5 times to 2 times more than that of a petrol engine.
  • Hence the diesel engine efficiency is much higher.
  • Under some conditions the air fuel ratio for the petrol engine must be 16 and for the diesel engine case the ratio of the air fuel mixture must be 25 to 35.
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December 01, 2016
Technically, mechanical engineering is the application of the principles and problem-solving techniques of engineering from design to manufacturing to the marketplace for any object. Mechanical engineers analyze their work using the principles of motion, energy, and force — ensuring that designs function safely, efficiently, and reliably, all at a competitive cost.
Mechanical engineers make a difference. That’s because mechanical engineering careers center on creating technologies to meet human needs. Virtually every product or service in modern life has probably been touched in some way by a mechanical engineer to help humankind.
This includes solving today’s problems and creating future solutions in health care, energy, transportation, world hunger, space exploration, climate change, and more.
Being ingrained in many challenges and innovations across many fields means a mechanical engineering education is versatile. To meet this broad demand, mechanical engineers may design a component, a machine, a system, or a process.  This ranges from the macro to the micro, from the largest systems like cars and satellites to the smallest components like sensors and switches. Anything that needs to be manufactured — indeed, anything with moving parts — needs the expertise of a mechanical engineer.  
What do mechanical engineers do?
Mechanical engineering combines creativity, knowledge and analytical tools to complete the difficult task of shaping an idea into reality.
This transformation happens at the personal scale, affecting human lives on a level we can reach out and touch like robotic prostheses. It happens on the local scale, affecting people in community-level spaces, like with agile interconnected microgrids. And it happens on bigger scales, like with advanced power systems, through engineering that operates nationwide or across the globe.
Mechanical engineers have an enormous range of opportunity and their education mirrors this breadth of subjects. Students concentrate on one area while strengthening analytical and problem-solving skills applicable to any engineering situation.
Disciplines within mechanical engineering include but are not limited to:
·         Acoustics
·         Aerospace
·         Automation
·         Automotive
·         Autonomous Systems
·         Biotechnology
·         Composites
·         Computer Aided Design (CAD)
·         Control Systems
·         Cyber security
·         Design
·         Energy
·         Ergonomics
·         Human health
·         Manufacturing and additive manufacturing
·         Mechanics
·         Nanotechnology
·         Production planning
·         Robotics
·         Structural analysis
Technology itself has also shaped how mechanical engineers work and the suite of tools has grown quite powerful in recent decades. Computer-aided engineering (CAE) is an umbrella term that covers everything from typical CAD techniques to computer-aided manufacturing to computer-aided engineering, involving finite element analysis (FEA) and computational fluid dynamics (CFD). These tools and others have further broadened the horizons of mechanical engineering.
What careers are there in mechanical engineering?
Society depends on mechanical engineering. The need for this expertise is great in so many fields, and as such, there is no real limit for the freshly minted mechanical engineer. Jobs are always in demand, particularly in the automotive, aerospace, electronics, biotechnology, and energy industries.
Here are a handful of mechanical engineering fields.
In statics, research focuses on how forces are transmitted to and throughout a structure. Once a system is in motion, mechanical engineers look at dynamics, or what velocities, accelerations and resulting forces come into play.Kinematics then examines how a mechanism behaves as it moves through its range of motion.
Materials science delves into determining the best materials for different applications. A part of that is materials strength — testing support loads, stiffness, brittleness and other properties — which is essential for many construction, automobile, and medical materials.
How energy gets converted into useful power is the heart of thermodynamics, as well as determining what energy is lost in the process. One specific kind of energy, heat transfer, is crucial in many applications and requires gathering and analyzing temperature data and distributions.
Fluid mechanics, which also has a variety of applications, looks at many properties including pressure drops from fluid flow and aerodynamic drag forces.
Manufacturing is an important step in mechanical engineering. Within the field, researchers investigate the best processes to make manufacturing more efficient. Laboratory methods focus on improving how to measure both thermal and mechanical engineering products and processes. Likewise, machine design develops equipment-scale processes while electrical engineering focuses on circuitry. All this equipment produces vibrations, another field of mechanical engineering, in which researchers study how to predict and control vibrations.   
Engineering economics makes mechanical designs relevant and usable in the real world by estimating manufacturing and life cycle costs of materials, designs, and other engineered products.
What skills do mechanical engineers need?
The essence of engineering is problem solving. With this at its core, mechanical engineering also requires applied creativity — a hands on understanding of the work involved — along with strong interpersonal skills like networking, leadership, and conflict management. Creating a product is only part of the equation; knowing how to work with people, ideas, data, and economics fully makes a mechanical engineer.
What tasks do mechanical engineers do?
Careers in mechanical engineering call for a variety of tasks.
·         Conceptual design
·         Analysis
·         Presentations and report writing
·         Multidisciplinary teamwork
·         Concurrent engineering
·         Benchmarking the competition
·         Project management
·         Prototyping
·         Testing
·         Measurements
·         Data Interpretation
·         Developmental design
·         Research
·         Analysis (FEA and CFD)
·         Working with suppliers
·         Sales
·         Consulting
·         Customer service
How much do mechanical engineers earn?
Like careers in many other engineering fields, mechanical engineers are well paid. Compared to other fields, mechanical engineers earn well above average throughout each stage of their careers. According to salary.com, the median starting salary for a Mechanical Engineer I in the United States is just under $63,000, with the top ten percent earning close to $75,000.
The future of mechanical engineering
Breakthroughs in materials and analytical tools have opened new frontiers for mechanical engineers. Nanotechnology, biotechnology, composites, computational fluid dynamics (CFD), and acoustical engineering have all expanded the mechanical engineering toolbox.

Nanotechnology allows for the engineering of materials on the smallest of scales. With the ability to design and manufacture down to the elemental level, the possibilities for objects grows immensely. Composites are another area where the manipulation of materials allows for new manufacturing opportunities. By combining materials with different characteristics in innovative ways, the best of each material can be employed and new solutions found. CFD gives mechanical engineers the opportunity to study complex fluid flows analyzed with algorithms. This allows for the modeling of situations that would previously have been impossible. Acoustical engineering examines vibration and sound, providing the opportunity to reduce noise in devices and increase efficiency in everything from biotechnology to architecture.
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