What is electric discharge machining

Electric discharge machining also is known as spark erosion.
It is the process of material removal based on the principle of metals by an interrupted electric spark discharge between the electrode tool and workpiece.

Working principle :

The main components of the EDM process are : 

• Electric power supply
• The dielectric medium 
• The workpiece and tool
• A servomotor

The basic process of EDM is really quite simple. The workpiece and the tool are electrically connected to D.C electric power supply. The workpiece is connected to the positive terminal of the electric source so that becomes the anode. The tool is a cathode. A gap is known as the 'spark-gap' in the range of 0.005 to 0.05 mm is maintained between the work piece and the tool.

In the spark gap produced spark is visible evidence of the flow of electricity. This electric spark produces intense heat with temperatures reaching 8000 to 12000 degree Celsius. The spark is controlled by very carefully and localized so that it affects the surface of the material only. 
The EDM process can be used in two different ways: 
1. A preshaped or formed electrode used as tool usually made from graphite is shaped to the form of the cavity it is to reproduce. The formed electrode is fed vertically down and the reverse shape of the electrode is eroded (burned) into the solid workpiece. 
2. A continuous-travelling vertical-wire electrode used as a tool and its diameter of a small needle or less is controlled by the computer. It follows a programmed path to erode the workpiece or cut a narrow slot to produce the required shape. 


The electrode ( Tools ) :

The shape of the tool will be basically the same as that of the product desired except that an allowance is made for side clearance and overcut.
The electrode materials generally used can be classified as metallic materials, non-metallic materials and a combination of metallic and non-metallic materials. Usually, copper, yellow brass, zinc and graphite are used for tools. Some low wearing tools are also used like silver-tungsten, copper-tungsten and metallized graphite. For commercial applications copper is best suited for fine machining. Aluminium is used for die-sinking while cast iron for rough machining.
One of the advantages of EDM is due to the fact that a tool made of a material softer than the workpiece material and which is a good conductor of electricity can be used to machine material of any hardness.
The wear of the tool in the EDM process due to electron bombardment is inevitable. 
The tool wears rates to determine the machining accuracy, tool movement, and tool consumption. 
The tool wear is the function of the rate of metal removal, the material of the workpiece, current setting, machining area, gap between the tool and workpiece and the polarity of the tool.

Wear ratio = Volume of work material removed / Volume of electrode consumed

Wear ratio = Depth of cut / Decrease in usable of the electrode

The wear ratio for carbon electrodes is up to 100:1.

For copper 2:1 

For brass 1:1

For copper tungsten 8:1

Purpose of Dielectric fluids :

• It used as a coolant for the workpiece and the tool. 
• It works as an insulating material during the charging of the condenser, as a result, perfect condition for efficacious spark discharge and its conduction when ionized is obtained. 
• The eroded materials are carried away by this medium. 
• It is a coolant in quenching the spark and prevents the arcing. 

Requirements of Dielectric fluids :

• Remain electrically nonconducting until the required break-down voltage has been reached.
• Breakdown electrically in the shortest possible time once the breakdown voltage has been reached.
• Have a good degree of fluidity.
• Be cheap and easily available.
• Be capable of carrying away the swarf particles.
• Inflammable. 
• It should be a hydrocarbon compound. 
• It should not produce toxic gases or vapours during the operation. 

Accuracy :

Tolerance value ( +- 0.05 ) mm could be easily achieved by EDM normal production.

By close control of the several variables tolerance ( +-0.003 ), mm could also be achieved.

Taper value id about to 0.005 to 0.05 mm per 100 mm depth.

An overcut of 5 to 100 micron is produced.

In no wear machining using graphite electrode a surface finish within 3.2 microns can be achieved.

Application of EDM :

The EDM provides economic advantages for making stamping tools, wire drawing and extrusion dies, header dies, intricate mould cavities.

It extremely used in aerospace industries, refractory metals, hard carbides and hardenable steels.

Some of its applications are following below :

• Drilling of micro-holes.
• Thread cutting.
• Helical profile milling.
• Wire-cutting EDM.
• Rotary forming.
• Curved hole drilling.
• Vacuum tubes.

Advantages and disadvantages of laser beam machining

Any solid material which can be melted without decomposition can be cut with the laser beam machining. To remove material from metallic or non-metallic surfaces, this process uses thermal energy. The high frequency of monochromatic light will fall on the surface and the material will be heated, melted and vaporized due to the impression of photons.
In this article, you can check it out some information on the advantages and disadvantages of laser beam machining to know more about it.

Advantages of laser beam machining : 

• No direct contact between tool and workpiece.
• No tool wear.
• Soft materials like rubber and plastics can be machined.
• Extremely small holes can also be machined.
• Machining of any material and also nonmetal is possible.
• Heat affected zone is small because of the collimated beam.
• Welding of dissimilar metal can also be performed efficiently.
• Any environment can be suitable for performing this process through transparent and magnetic fields.
• Drilling and cutting of areas not readily accessible are possible.

Disadvantages of laser beam machining : 

• One of the main disadvantages of that is it cannot be used to cut metals that have high heat conductivity or high reflectivity.
• Overall efficiency is extremely low.
• The process is limited to a thin sheet.
• Very low material removal rate.
• The machined hole is not round and straight.
• Cost is high.
• Output energy from LASER is difficult to control precisely.
• The laser system is quite troublesome since the life of the flash lamp is short.
• Too deep holes are not possible to drill.
• While machining some plastic bum or char is noticed.
• Experienced and skilled operators are required.
• Rate of production is low.

Application of laser beam machining

Laser beam machining applications :

• Suitable for exceptional cases like machining very small holes and cutting complex profiles in a thin and hard material like ceramics.
• Sheet metal trimming, blanking and resistor trimming.
• Used in mass micromachining production, not for mass material removal.
• Used in partial cutting or engraving.
• To drilling micro holes in turbine engine blades.
• In both soft and hard materials cutting.
• Scribing of any material.
• Patterning displays of all glass and plastic wafers and chips.
• Can be used for dynamic balance of rotating parts.
• Welding of non-conductive and refractory material.
• Jewellers also use laser welding on delicate pieces of jewellery.
• Laser beams perform intricate cuts in plastic.

Application of electron beam machining

Electron beam machining application : 

• To drill fine gas orifices.
• For use less than 0.002 mm work.
• In space nuclear reactors.
• Turbine blades for supersonic aero-engines.
• To produce metering holes in injector nozzles in diesel engines.
• To scribe thin films.
• To remove small broken taps from holes.
• In transmission assembly.
• To produce wire drawing die.

Advantages and disadvantages of electron beam machining

Electron beam machining is processed by a high-velocity focused stream of electrons which heats, melts and vaporizes the work material at the point of bombardment thus metal will be removed. Let us have a deep insight into the pros and cons of electron beam machining in this article. 

Advantages of electron beam machining :

• EBM is an excellent method for micro finishing.
• It can cut drill holes or cut slots which otherwise cannot be made.
• It is possible to cut any known material.
• No cutting tool pressure or wear occurred in this process.
• It is distortion free-machining so precise dimensions can be achieved.

Disadvantages of electron beam machining :

• High equipment cost.
• Highly skill operator required.
• Only small cuts are possible.

Advantages and disadvantages of EDM

Electric discharge machining also is known as spark erosion. It is the process of material removal based on the principle of metals by an interrupted electric spark discharge between the electrode tool and workpiece. Let us have a deep insight into the pros and cons that this process provided. 

Advantages of EDM : 

• It can be applied to all electrically conducting metals.
• Any complicated shape that can be machined.
• Machining time is less than conventional machining processes.
• It can also be employed for the extremely hardened workpiece.
• No mechanical stress is present in this process because of no contact between the tool and the workpiece.
• No burrs.
• Tolerances range +/- 0.005 can be achieved.
• Good surface finish can be attained.
• Creating small holes is not easily achieved by any other process other than EDM.
• Fragile and slender workplaces can be machined without distortion.
• The heat treatment process can be eliminated.
• Hard and corrosion-resistant surfaces, essentially needed for die making, can be developed by this process.
• Little or no polishing is required after the completion of the process.

Disadvantages of EDM : 

• Machining time is too long.
• Excessive tool wear.
• High specific power consumption.
• Profile machining of complex contours is not possible.
• Only able to machine conductive materials.
• The metal removal rate is slow.
• Reproduction of sharp corners is the limitation of the process.
• Surface cracking may take place in some materials owing to their affinity to become brittle at room temperature.
• Especially when higher energy per pulse is used.

Difference between kinematics and dynamics

Kinematics and dynamics are two branches of mechanics that deal with the motion of a particle that plays an important role in robotics and mechanical engineering field. 

What is kinematics?

A study that describes the motion of bodies and the system of bodies without taking into consideration of the cause of motion. 

What is the dynamics?

A study of the motion of a particle along with their cause like force and torque.

Now let us have a deep insight into the comparison between them and check some difference between kinematics and dynamics. 

Key difference : 

Kinematics will give you the values of change whereas dynamics provide the reasoning behind it. 

Kinematics :

• Kinematics originates from the Greek word kinesis, meaning motion.
• Galileo worked on with his numerous experiments measuring displacement, velocity and acceleration of balls rolling down inclined planes.
• More concern with the movement in general.
• A description of how objects move.
• kinematics describes movement, acceleration, speed, of objects.
• Kinematics is based on the nature of force, nature of the body.
• Kinematics is the geometry of motion.
• Motion is teated geometrically without reference to things like cause and effects. 

Dynamics :

• Dynamics from the Greek word dunamis which means power.
• Newton worked on when he formulated his three laws.
• Concern about measuring the causes and quantity of it and how it contributes and relates to the movement.
• It deals with force and why objects move as they do.
• Dynamics describes forces applied to the objects.
• Dynamics is based on the concept of force.
• Dynamics is geometry + physics of motion.
• Motion is treated in terms of trajectories and time so force and motion come in. 

What is Kinematics and Dynamics

What is Kinematics?

It deals with the relative motion of different parts of a mechanism without taking into consideration the forces producing the motions.

Kinematics is the geometry of motion.

What is Dynamics?

It involves the calculations of forces impressed upon different parts of the mechanism.

Dynamics is geometry + physics of motion.

The forces can be either static or dynamics.

Dynamics is further subdivided into two groups :

• Kinetics
• Statics

Kinetics is the study of forces when the body is in motion. 

Statics is the study of forces when the body is stationary.

Absolute entropy definition

Definition of Absolute Entropy :

Answer :

• The increase in entropy of a substance as it goes from a perfectly ordered crystalline form at 0 K temperature where its entropy considers as zero.

Full form of ESC

What is the full form of ESC?

Answer :

• Electronic Stability Control

What does ESC mean?

ESC helps drivers to avoid crashes from skidding or losing control as a result of over-steering.

It is a fully computerized technology used to improve the safety of cars.


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Capstan and turret lathe

Introduction :
A capstan and turret lathe is a production lathe. It is used to manufacture any number of identical pieces in the minimum time.
These lathes were first developed in the United States of America by Pratt and Whitney in 1960.

Types of the machine :
There are two main types of horizontal lathe of this family are :

• The capstan or Ram type lathe
• The turret or Saddle type lathe

The capstan or Ram type lathe :

The ram-type lathe carries the hexagonal turret on a ram or a short slide.

The ram slides longitudinally on a saddle and clamp-on lathe bed ways.

This type of machine is lighter in construction and it is suitable for machining bar of smaller diameter. The tools are mounted on the square turret and six faces of the hexagonal turret.

Ram moves from left to right the feeding movement is obtained.

The turret or Saddle type lathe :

The hexagonal turret-mounted directly on a saddle and the whole unit moves back and forth on the bed ways to apply feed.
This type of turret lathe is heavier in construction and is particularly used for larger diameter bar work and chucking.work.

Principle parts of Capstan and Turret lathe :

Bed :
The bed is long box-like casting provided with accurate guide ways upon which are mounted the carriage and turret saddle.
The bed is designed to ensure strength, rigidity and permanency under heavy duty services.

Head stock :
The head stock is a large casting located at the left hand of the bed.
Different types of head stock maybe use that are listed below :

• Step cone pulley driven head stock
• The direct electric motor is driven head stock
• All geared head stock
• Perspective head stock

Cross-slide & Saddle :

In small capstan and turret lathe hand-operated cross-slide and saddle are used which are clamped on the lathe bed at the required position.

The larger capstan lathes are usually used two designs of the carriage like :

• Conventional type carriage
• Side hung type carriage 

The turret saddle and auxiliary slide :

The turret saddle bridges the gap between two-bed ways and the top face is accurately machined to provide a bearing surface for the auxiliary slide.

The hexagonal turret is mounted on the auxiliary slide.

Capstan and turret lathe mechanism :

The carriage, cross-slide and turret slide may be fed into the work by hand or power. 

The various mechanism for machining. 

• Turret indexing mechanism
• Bar-feeding mechanism

Capstan and turret lathe operation :

In this lathe operations are similar to that of the centre lathe machine.

The usual operations performed in this lathe are :

• Straight turning
• Shoulder turning
• Taper turning
• Chamfering
• Thread cutting
• Facing
• Knurling
• Forming
• Drilling
• Reaming
• Boring
• Counter boring
• Tapping
• Undercutting
• Parting off 

Cutting speed, feed and depth of cut are similar to the simple lathe machine.

Full form of PDI in automobile

What is the full form of PDI?

Answer :

• Pre Delivery Inspection

What does PDI mean?

It is the inspection only to make sure that the vehicle is 100% perfect condition and make a finishing touch before the customer takes delivery. 

In the inspection finishing touch such as following.

• Feeling the car up with gas 
• Washer fluid 
• Engine oil
• Installing the radio and license plate brackets
• Bolt checking
• Check for damage 

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Difference between capstan turret and engine lathe

A capstan and turret lathes are the development of an engine lathe. The capstan lathe was first developed in the United States of America by Pratt and Whitney in 1860. These types of lathe are the development of an engine lathe so they possess certain basic difference as their construction, operation and use. Let us have a deep insight into the comparison and difference between them. 

Difference :

• The headstock of a turret lathe is similar to that of an engine lathe in construction but it has a wider range of speeds.
• Engine lathe required motor of 3 h.p. to drive its spindle and other parts whereas capstan and turret lathe requires high power as 15 h.p. for a high rate of production.
• The tailstock of and engine lathe is replaced by a turret in turret lathe thus it resembles a big six-sided nut with can carry six tools for rotating jobs on the other side engine lathe holds one tool of limited size.
• Turret lathe it acts like production machines while engine lathe is used for various types of odd jobs within limits.
• In a turret lathe, combination cuts can be taken while in centre lathe this type of arrangement is quite uncommon.
• The labour cost required to operate a capstan and turret lathe is less than that required in centre lathe.
• Capstan and turret lathe are not usually fitted with lead screws for cutting threads similar to an engine lathe.
• In capstan and turret lathe one time setting of job then you must not change the tools while in engine lathe you can change tools as per your requirement.
• Turret movement can be controlled automatically. engine lathe tool movement can control manually. 
• In capstan and turret lathe number of speeds is more in engine lathe number of speeds is less.
• Capstan and turret lathe is suitable for mass production while engine lathe is not suitable for that.
• Capstan and turret lathe tool is centred automatically while an engine lathe tool is centred manually after changing the tool.

Summary : 

An engine lathe is a versatile machine capable of machining any types of jobs with different sizes and shapes. The machine is not suitable for production unit because time is taken to set different tools on the tool post of lathe after each and every operation.

On the other hand capstan and turret lathe is a mass-production machine. They are unsuitable where only one or a few jobs are to be machined. The high initial setting time compared to an engine lathe.

Factors affecting charge efficiency

There is a various factor affecting charge efficiency. let we check it out below :

• The compression ratio.
• The amount of heat picked up during passage of the charge through the intake manifold.
• The valve timing of the engine.
• The resistance offered to air-fuel charge during its passage through induction manifold.

Internal combustion engine efficiency

We expressing engine performance in terms of power, it is also essential to express in terms of efficiency. 
Various efficiency are listed below : 

• Air-standard efficiency
• Brake thermal efficiency
• Indicated thermal efficiency
• Mechanical efficiency
• Relative efficiency
• Volumetric efficiency
• Scavenging efficiency
• Charge efficiency
• Combustion efficiency

we can discuss various engine efficiency one by one.

• Air-standard Efficiency :

The air-standard efficiency is also known as thermodynamic efficiency. It is mainly a function of compression ratio and other parameters.

• Brake thermal Efficiency :

The brake thermal efficiency is based on brake power of the engine. These efficiency give an idea of the output generated by the engine with respect to heat supplied in form of fuel.

• Indicated thermal Efficiency :

The indicated thermal efficiency is based on indicated power of the engine.
In modern engine an it is almost 28% obtained with gas and gasoline spark-ignition engines having a moderate compression ratio. 

• Mechanical Efficiency :

Mechanical efficiency takes into account the mechanical losses in an engine.
There is various mechanical losses in the engine :
Friction losses as in case of pistons, bearing, gears, valve mechanisms etc.
Power is absorbed by engine such as fuel pump, lubricating oil pump, water circulating pump, radiator and distributor etc.
Ventilating action of the flywheel. 
Charging in cylinder with fresh charge and discharging the exhaust gases during the exhaust stroke.
In general, mechanical efficiency of engines varies from 65 to 85%.

• Relative Efficiency :

The relative efficiency is the ratio of actual efficiency obtained from an engine to the theoretical efficiency of the engine cycle.

Relative efficiency = Actual brake thermal efficiency / Air-standard efficiency

• Volumetric Efficiency :

Volumetric efficiency is defined as the ratio of the actual mass of air drawn into the engine during a given period of time to the theoretical mass which should have been drawn in during that same period of time.

n_v = ṁ_act / ṁ_th 

• Scavenging Efficiency :

In case of two-stroke engines scavenging efficiency is defined as the ratio of the amount of air or gas-air mixture, which remains in the cylinder, at the actual beginning of the compression to the product of the total volume and air density of the inlet.

• Charge Efficiency :

The charge efficiency shows how well the piston displacement of a four-stroke engine is utilized. Various factor affecting the charge efficiency.

• Combustion Efficiency :

Combustion efficiency is the ratio of heat liberated to the theoretical heat in the fuel.
For a well adjusted engine it is varies form 92% to 97%. 

Advantages and disadvantages of two stroke engine

A two-stroke cycle engine is a type of internal combustion engine that completes a single crankshaft revolution power cycle with two-piston strokes. This engine provided some advantages and disadvantages comparing with a four-stroke engine. Let us have a deep insight into the pros and cons of the two-stroke engine in this article.   

Advantages of two-stroke engine : 

• Simpler in design because don't have valve only port.
• Power developed is twice as compared to same dimensions four-stroke engine with the same operating speed.
• The work required to overcome the friction of the exhaust and suction strokes is saved.
• Burnt gases do not remain in the clearance space because of scavenging.
• Two-stroke engines can work in any position since oil flow is not a concern with any valves to worry about.
• It occupies lesser space.
• Lighter in weight because the lighter flywheel is used.
• Easy to maintain.
• Less cost.
• It produces Uniform torque.
• Power to weight ratio is high.

Disadvantages of two-stroke engine : 

• A high-speed two-stroke engine is less efficient.
• When the inlet valve of the engine is opened for the intake of the air-fuel mixture, the exhaust valve is also open so the part of the fuel is wasted this increase fuel consumption and reduce overall efficiency.
• Effective compression is less in case of a two-stroke engine.
• These engines are liable to cause heavier combustion of lubricating oil.
• With heavy loads, it gets heated due to excessive heat produced.
• Thermal efficiency is also less.
• It causes pollution and smoky.

Types of two-stroke engine

A two-stroke engine is which it completes its cycle of operation in one complete revolution of the crankshaft in other word in two stroke of the piston.

Two-stroke engine are basically two types and its depend on the scavenging method.

Types of two-stroke engine are listed below :

• Crankcase Scavenged Engine
• Separately Scavenged Engine

The details of above two types of engine are describe below :

Crankcase scavenged engine :

It is one of the simplest types of two-stroke engine. In this engine the charge is compressed in the crankcase during the expansion stroke. 

There are three ports in this engine :

• Intake port at the crankcase 
• Transfer port 
• Exhaust port 

Through the transfer port compressed charge passes into the engine cylinder and flushing the products of combustion is called scavenging.

Separately scavenged engine :

It is same engine as crankcase engine but in this engine uses external device like a blower to scavenge the products of combustion is called externally or separately scavenged engine.