ME - Mechanical Engineering
Online resource for Mechanical Engineers

Electrogas welding (EGW) is an vertical positioned arc welding process, is used for welding the edges of sections vertically and in one pass with the pieces placed edge to edge (butt joint). It is classified as a machine-welding process, because for its operation requires special equipment. The weld metal is deposited into a weld cavity between the two pieces to be joined. The space is covered by two water-cooled copper dams(shoes) to prevent the molten slag from running off; mechanical drives move the shoes upward.
electrogas welding process
Schematic illustration of the electrogas welding process.
One or more electrodes are fed through a conduit and a continuous arc is maintained by flux-cored electrodes at up to 750 A or solid electrodes at 400 A. Power requirements is 20 kW. Shielding is done by means of an inert gas, such as argon or helium depending on the type of material being welded. The gas may be provided either from an external source, from a flux-cored electrode or from both the sources. The equipment of electrogas welding is reliable and training an operator is easy. Weld thickness is between 12 mm to 75 mm on steels, titanium and aluminum alloys.
Electrogas welding process is used in the construction of bridges, pressure vessels, thick-walled and large-diameter pipes, storage tanks, submarines and ships.
In Plasma-arc Welding (PAW) is an arc welding process, a concentrated plasma arc is produced and directed towards the weld area. The arc is stable and reaches temperatures as high as 33,000°C. A plasma is an ionised very hot gas composed of nearly same numbers of electrons and ions. The plasma starts between the tungsten electrode and the orifice by a low current pilot arc. What makes plasma-arc welding unlike other processes is that the plasma arc is concentrated because it is forced through a relatively small orifice. Operating currents usually are less than 100 A. When a filler metal is used it is fed into the arc as is done in Gas Tungsten-arc Welding. Arc and weld-zone shielding is supplied by means of an outer-shielding ring and the use of inert gases like argon, helium or mixtures.
There are two methods of plasma-arc welding:
  • In the transferred-arc method of plasma-arc welding(in pic left side), the workpiece being welded is part of the electrical circuit. The arc transfers from the electrode to the work piece hence the term transferred.
  • In the non transferred-arc method of plasma-arc welding(in pic right side), the arc occurs between the electrode and the nozzle and the heat is carried to the workpiece by the plasma gas. This thermal-transfer mechanism is similar to that for an oxy-fuel flame.
Plasma-arc Welding (PAW)
Two methods of plasma-arc welding processes (a) transferred and (b) non transferred
Compared to other arc welding processes, Plasma-arc Welding process has better arc stability, less thermal distortion and higher energy concentration, thus permitting deeper and narrower welds. PAW has higher welding speed ranges from 120 mm/min to 1000 mm/min. A variety of metals can be welded with part thicknesses less than 6 mm.
The high heat concentration can penetrate completely through the joint with thicknesses as much as 20 mm for some titanium and aluminium alloys. In the keyhole technique, the force of the plasma arc displaces the molten metal and produces a hole at the leading edge of the weld pool. Plasma-arc welding often is used rather than Gas Tungsten-arc welding for butt and lap joints because of its higher energy concentration, better arc stability and higher speed of welding. Proper training and skill are required for operator who works on this equipment.
The flux-cored arc welding process is shown in image below is similar to Gas Metal-arc Welding, except that the electrode is tubular in shape and is filled with flux. Cored electrodes produce a more stable arc, improve weld contour, and produce better mechanical properties of the weld metal. The flux in these electrodes is much more flexible than the brittle coating used on Shielded Metal-arc Welding electrodes, so the tubular electrode can be provided in long coiled lengths.
Flux-cored Arc Welding
Schematic illustration of the flux-cored arc-welding process.
The electrodes used in this welding process are usually 0.5mm to 4 mm in diameter and the power required is about 20 kW. Self-shielded cored electrodes also are available. They do not require any external shielding gas, because they contain emissive fluxes that shield the weld area against the surrounding atmosphere. Small diameter electrodes have made the welding of thinner materials not only possible but often preferable for using. Also small diameter electrodes make it relatively easy to weld joints in different positions and the flux chemistry permits the welding of many metals.
The Flux-cored arc Welding process combines the versatility of Shielded Metal arc welding with the continuous and automatic electrode feeding feature of gas metal-arc welding. The process is economical and versatile, so it is used for welding a variety of joints, mainly on steels, stainless steels, and nickel alloys. The higher weld metal deposition rate of the flux-cored arc welding process has led to its use in the joining of sections of all thicknesses. The use of tubular electrodes with very small diameters has extended the use of this process to work pieces of smaller section size.
A main advantage of using flux-cored arc welding is the ease with which specific weld-metal things can be developed. By adding alloying elements to the flux core, virtually any alloy composition can be produced. The process is easy to automate and is readily adaptable to flexible manufacturing systems and robotics.
The common rail is the most essential component of the direct fuel injection system.
Common Rail
Its role consists in accumulating highly pressurized fuel and distributing it to the injectors. The next-generation diesel and gasoline engines tend to become smaller and lighter for less fuel consumption and better performance, which increases the fuel pressure. This makes out of the common rail a component with very specific requirements. It should possess best mechanical properties in order to be strong and resistant to fatigue, loading, vibration and other environmental conditions.
Eventual common rail failure is always critical since the entire vehicle can be blocked or even set on fire. Exposed continuously to increased pressure and heat, its performance is crucial for the whole system.  Most common rail problems are related to the complex geometry of the components and possible cracks caused by material fatigue or during the manufacturing process. Therefore a special attention should be paid to the following: defining and keeping best parameters in the design phase, selecting high-quality resistant steels and excellent expertise in the forging manufacturing process. Following these guidelines guarantees perfection and reliable performance of the entire fuel direct injection.
Special attention should be paid to:
1. Design
The early stage of common rail’s development is essential for the later performance of that component. The right geometry and precise parameters prevent a lot of problems that occur later as defects in heading process or material fatigue. For example, modern gasoline engines are smaller and lighter which increases fuel internal pressure and requires common rails with complex shape. Hot forging offers a vast variety of shapes and sizes that can be achieved with high-quality equipment as forging hammers, mechanical presses, screw presses and other tools. Defining end-of-forging temperature, cooling and trimming parameters are also highly significant for most precise geometry.
2. Best material selection
The common rail itself acts as a common fuel storing rail and it is permanently exposed to heat and pressure.  Therefore, if the raw materials haven't been selected wisely, quality problems can occur. The most common rail problems related to material selection are shorter product life and reduced fuel accumulation volume.
3.  Strength
When forged, the common rail is made of stainless steel and consists only of one piece which eliminates the risk for cracks and leakages. Additionally, forging strengthens the material by closing empty spaces within the metal while deforming and shaping it with localized compressive forces.

Every single production step of the common rail manufacturing process should undergo strict control. The manufacturing company should provide best design expertise, develop most resistant materials, use 100% controlled tools and apply best forging techniques.
Shielded Metal-arc Welding (SMAW) is the simplest and used for many joining processes. More than 50% of industrial and maintenance welding currently is performed by this welding process. In this welding operation electric arc is generated by touching the tip of a coated electrode against the workpiece and withdrawing it quickly to a distance sufficient to maintain the arc as shown in picture below. The electrodes are in the shapes of thin, long rods that are held manually. The heat generated melts a portion of the electrode tip, its coating and the base metal in the immediate arc area. The molten metal consists of a mixture of the base metal, the electrode metal, and substances from the coating on the electrode, this mixture forms the weld when it solidifies. The electrode coating de-oxidizes the weld area and provides a shielding gas to protect it from oxygen in the surroundings. A bare section at the end of the electrode is clamped to one terminal of the power source, while the other terminal is connected to the workpiece being welded. The current, which may be either DC or AC usually in the range 50A to 300 A.
Schematic illustration of the shielded metal-arc welding process.
For sheet-metal welding, DC is suitable because of the steady arc it produces. Power requirements generally are less than 10 kW.
A deep weld showing the buildup sequence of eight individual weld beads.
The Shield Metal-arc Welding process has the advantages of being relatively simple and requiring a smaller variety of electrodes. The equipment consists of a power supply, cables, and an electrode holder. The Shield Metal-arc Welding process commonly is used in general construction, shipbuilding, pipelines and other maintenance work. It is mainly useful for work in remote areas where a portable fuel-powered generator can be used as the power supply. Shield Metal-arc Welding is suited for workpiece of thickness 3 to 19 mm, although this range can be extended easily by skilled operators using multiple-pass techniques as shown in picture. The multiple-pass approach requires that the slag be removed after each weld bead. Unless removed fully, the solidified slag can cause severe corrosion of the weld area and lead to failure of the weld but it also prevents the fusion of welded layers. Before applying another weld, the slag should be removed completely by using wire brushing or weld chipping.
In Submerged-arc Welding (SAW), the weld arc is shielded by a granular flux consisting of lime, silica, manganese oxide, calcium fluoride and other compounds. The flux is fed into the weld zone from a hopper by gravity flow through a nozzle. The thick layer of flux completely covers the molten metal. Covered flux prevents spatter and sparks and suppresses the intense ultraviolet radiation and fumes characteristic of the Shield Metal-arc Welding (SMAW). Process. The flux acts as a thermal insulator by promoting deep penetration of heat into the workpiece.
The consumable electrode is a coil of bare round wire 1.5 mm to 10 mm in diameter, consumable electrode is fed automatically through a tube. Electric currents typically range from 300 A to 2000 A. The power supplies usually are connected to standard single-phase or three-phase power lines with a primary rating up to 440 V.
Submerged arc-welding process and equipment used
Schematic illustration of the submerged arc welding process and equipment. Unfused flux is recovered and reused
The flux is gravity fed, the SAW process is limited largely to welds in a flat or horizontal position having a backup piece. Circular welds can be made on pipes and cylinders-provided that they are rotated during welding. As image shows, the unfused flux is recovered, treated and reused. SAW is automated and is used to weld a variety of carbon and alloy steel and stainless-steel sheets or plates at speeds as high as 5 m/min. The quality of the Weld is very high with good toughness, ductility and uniformity of properties. The Submerged Arc Welding  process provides very high welding productivity, depositing 4 to 10 times the amount of Weld metal per hour as the Shielded Metal-arc Welding process. Typical applications include thick-plate welding for shipbuilding and for pressure vessels.
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Gas metal-arc welding (GMAW) also called as metal inert-gas (MIG) welding, In Gas metal-arc welding process the weld area is shielded by an effectively inert atmosphere of argon, helium, carbon dioxide or various other gas mixtures. The consumable bare wire is fed automatically through a nozzle into the Weld arc by a wire-feed drive motor. In addition to using inert shielding gases, de-oxidizers usually are present in the electrode metal itself in order to prevent oxidation.
Basic equipment used in gas metal arc welding operation
Basic equipment used in gas metal arc welding operation
Gas Metal Arc Welding process, formerly known as metal inert gas
Gas Metal Arc Welding process, formerly known as Metal Inert Gas
The temperatures generated in Gas metal-arc welding are low, GMAW method is suitable only for thin sheets and sections of less than 6 mm, otherwise incomplete fusion may occur. GMAW operation is easy to perform is commonly used for welding ferrous metals in thin sections. Pulsed-arc systems are used for thin ferrous and nonferrous metals. GMAW process is used for welding most ferrous and nonferrous metals and is used extensively in the metal-fabrication industry. Because of the relatively simple nature of the process, the training of operators is easy. This process is versatile, quick, economical and welding productivity is double that of the Submerged-arc Welding process.
Otto cycle consists of two isoentropic and two isochoric processes. Heat is supplied and heat is rejected by the cycle during isochoric process.
p-V and T-s diagram diagram for the air-standard otto cycle
Pressure-volume and Temperature-entropy diagram for the air-standard otto cycle
Where,
1-2: Adiabatic compression
2-3: Isochoric heat addition
3-4: Adiabatic expansion
4-1: Isochoric heat rejection

Heat supplied during constant volume process 2-3
Heat supplied by the air during constant volume
Heat rejected during constant volume process 4-1
Heat rejected by the air during constant volume
The thermal efficiency of otto cycle can be written as
thermal efficiency of otto cycle
Stirling cycle consists of two isothermal and two isochoric processes. Heat rejection and heat addition takes place at constant temperature.
p-V and T-s diagram for the stirling cycle
Pressure-volume and Temperature-entropy diagram for the air-standard stirling cycle
Where,
1-2: Isothermal expansion
2-3: Constant volume cooling
3-4: Isothermal compression
4-1: Contant volume heating

From the p-V and T-s diagram of stirling cycle it is clear that the amount of heat addition and heat rejection during constant volume is same.

Heat supplied = Work done during isothermal expansion
Heat supplied in stirling cycle
Heat rejected by the air during isothermal compression
Heat rejected in stirling cycle
Work done = heat supplied - heat rejected
Efficiency of stirling cycle can be written as 
  Efficiency of stirling cycle
Welding joints
There are five types of welded joints for bringing two parts together for joining.
Five types of welded joints are butt joint, corner joint, lap joint, tee joint and edge joint.


Butt joint:

In Butt welded type, the parts lie in the same plane and are joined at their edges.

Corner joint:

The parts in a corner joint form a right angle and are joined at the center of the angle.

Lap joint:

Lap joint consists of two overlapping parts.

T joint:

In a T joint, one joint is right angle to the other joint in the approximate shape of the letter "T".

Edge joint:

The parts in edge joint are parallel with at least one of their edges in common and the joint is made at the common edge(s).

butt joint, corner joint, lap joint, T joint and edge joint
Different types of loads are compression, tension, torsion and bending.
Compression, tension, torsion and bending loads.

Compression:

Compression loading is an effect in which the component reduces it size. During compression load there is reduction in volume and increase in density of a component.

Tension:

Tension is the act of stretching rod, bar, spring, wire, cable etc. that is being pulled from the either ends.

Torsion:

Torsion is the act of twisting of an rod, wire, spring etc. about an axis due to applied couple (torque).

Bending:

Bending is act of changing component from straight form into a curved or angular form.
A lathe machine is a mechanical device in which the work piece is rotated against a suitable cutting tool for producing cylindrical forms in the metal, wood or any other machinable material.
Lathe machine

Types of lathe machines:

  • Copy lathe machine
  • Automatic lathe machine
  • Turret lathe machine
  • Engine lathe machine
  • Bench lathe machine
  • Computer controlled lathe machine

Lathe machine parts:

Lathe machine parts
 image credits: iitb.ac.in

Operations that can be performed on lathe machine:

a) Straight turning
b) Taper turning
c) Profiling
d) Turning and external grooving
e) Facing
f) Face grooving
g) Cutting with a form tool
h) Boring and internal grooving
i) Drilling
j) Cutting off
k) Threading
l) Knurling
operations performed on lathe machine
image credits: iitb.ac.in
Foundry shop is the place where the metal casting is prepared by melting and pouring the molten metal into moulds. Some of the commonly used tools for moulding process in foundry shop are showel, trowel, riddle, rammer, draw spike, swab, vent wire and slick tool.

Showel:

Showel tool
Showel tool is used for mixing and tempering moulding sand and for moving the sand pile to flask.

Trowel:

Trowel tool
Trowel tool is used to shape and smooth the surfaces of the mould and for doing small repairs. They are made of steel and are relatively long and narrow.

Riddle:

Riddle tool
Riddle tool is a screen or sieve used to remove small pieces of metal and foreign particles from the moulding sand.

Rammer:

Rammer tool
Rammer tool is used to compress the moulding sand. The hand rammer is made of tool and resembles like a handless mallet with one end flat and the other end blunt edge.

Draw spike:

Draw spike tool
Draw spike tool is used to remove the pattern from the mould  and also for rapping the pattern gently the loosen it from the sand to assure a clean draw.

Swab:

Swab tool
Swab tool is made of flax or hemp and is used for applying water to the mould around the corners and edges of the patterns. This tool prevents the sand edges from crumbling, when the patern removed from the mould.

Vent wire:

Vent wire is a thin rod or wire carrying a pointed edge at one end and a wooden handle at the other end. Vent wire is used to make small holes called vents in the sand mould.

Slick tool:

Slicks tools are the spoon shaped trowels used for repairing or smoothening a mould surface.

Here are some of animations of the greatest mechanical principles and inventions, which shows greatness of human brain. Simple animation pictures are used to explain mechanisms of Boxer Engine, Geneva Drive, Radial Engine, Wankel Cycle.

1. Boxer Engine:

Boxer engine mechanism animation
A Boxer Engine is a flat engine IC engine with multiple pistons that move in a horizontal plane. The layout shown in animation has cylinders arranged in either side of a single crankshaft and it is sometimes known as horizontally opposed engine.

2. Geneva Drive:

Geneva drive mechanism animation
The Geneva drive is a gear mechanism that translates a continuous rotation into an intermittent rotatory motion. The rotating drive wheel has a pin that reaches into a slot of the driven wheel in regular intervals advancing driven wheel by one step. The drive wheel has a raised circular blocking disc that locks the driven the driven wheel in position between steps.

3. Radial Engine:

Radial Engine Mechanism animation

Radial Engine is a reciprocating type IC engine configuration in which the cylinders moves outward and then inwards in regular intervals from a central crankshaft. It looks like a stylised star when viewed from the front. The radial engine configuration was very common used in aircraft engines before turbine engines became in use.

4. Wankel Cycle:

Wankel Cycle mechanism animation
The Wankel engine is a type of IC engine using an eccentric point rotatory design to convert pressure into rotatory motion. Use of Wankel engine delivers advantages they are simplicity, smoothness, compactness, high RPM and a high power to weight ratio. Wankel Cycle engine is commonly referred to as a rotatory engine.