Advanced machining processes

10 min readJun 14, 2021

Introduction :

Advanced machining processes are the material-removing processes different from conventional machining processes, in which a well-guided wedge-shaped tool removes the material in the form of chips by producing contact stresses. There are a variety of ways in which material is removed using these processes. One method is producing stresses in the work piece by different means but not with a well-guided wedge-shaped tool. There are several processes in this category, e.g., ultrasonic machining, water jet machining, and abrasive jet machining. Another method is utilizing the thermal effect to melt or vaporize the material. This is accomplished by laser beam machining, electron beam machining, and electrical discharge machining. Chemical and electrochemical machining processes provide very good surface finish by making use of principles of chemistry. Advanced machining processes have become popular and economical and are finding their use in industries.

Need of advanced machining processes :

Conventional machining was found to be unsuitable for machining of very hard material, for producing complicated and smaller shapes and for obtaining high accuracy, precision, and surface integrity. It prompted researchers to invent novel ways of removing the material. The newly invented processes were called unconventional or non-traditional machining processes. Most of these processes are now routinely employed by industries, and hence, a more appropriate name for these processes is advanced machining processes.

The classification of these processes is most widely recognized by classification based on type of energy required .

· Mechanical energy based processes

· Electrical energy based processes

· Chemical energy based processes

· Thermal energy based processes

In this blog, we are covering most of the important advanced machining processes.

Abrasive jet machining :

Abrasive jet machining is mechanical energy based process. It is the process of impinging the high-speed stream of abrasive particles by high-pressure gas or air on the work surface through a nozzle and metal removal occurs due to erosion caused by high-speed abrasive particles.

Working Principle of Abrasive Jet Machining:

It consists of a mixing chamber, gas filter, pressure gauge, regulator, and the nozzle.

The filtered gas at a pressure of 2 to 8 kg/cm2 is supplied to the mixing chamber containing the abrasive powder and vibrating at 50 Hz, where it mixes with abrasive particles and then enters into the connecting hose.

The abrasive and gas mixture comes out from the nozzle at a high velocity ranging from 150 to 300 meters/minute and impinges over the work surface causing abrasion action by repeated impacts and the material is removed by the erosion.

Abrasive power feed rate can be controlled by the amplitude of vibration of the mixing chamber.

The carrier gas should be cheap and non-toxic and easily available, It is generally air or nitrogen.

Abrasive generally used are Aluminum oxide, Silicon carbide or glass powder.

The nozzle is generally made by harder material such as ceramic or tungsten carbide to reduce abrasion wear.

The material removal rate depends on the diameter of the nozzle, jet pressure, composition of mixtures, Hardness of abrasive particles and work piece, Particle size, the velocity of jet and distance between work and nozzle.

Advantages of Abrasive jet machining are:

· The surface finish can be obtained smooth.

· The cost of equipment is low.

· Ability to cut heat-sensitive material without damage.

· Ability to cut intricate hole shapes in a hard and brittle material.

· The main advantages are its flexibility, low heat production.

Disadvantages of Abrasive jet machining are:

· The material removal rate is low.

· The process tends to environmental pollution. A dust collection system must be provided to avoid air pollution and health hazards. This can be eliminated by using abrasive water jet machining.

· AJM not suited for machining of soft material because the abrasive may get embedded in the work material.

Applications of Abrasive jet machining are:

· It is used in drilling and cutting of hardened metals.

· It is used for machining brittle and heat sensitive material like glass, quartz, sapphire, mica, ceramic etc.

· It is often used for cleaning and polishing of plastic, nylon and Teflon components, the frosting of the interior surface of the glass tubes, etching of markings on glass cylinders, etc.

Electric discharge machining (EDM)

This process comes under electrical energy based machining. EDM is also known as “Spark Machining” . Such name has been given for the fact that it removes the metal by applying a rapid series of repetitive electrical discharges. An electrode and the work piece is used for the conducting path of these electrical discharges. A continuously flowing fluid is always flowing to flush away the little amount of material that are removed. Repetitive discharge gives the workpiece a desired shape.

Working Principle : Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape.

Advantages of EDM

Metal having any hardness or brittleness and toughness can be machined.
Harder materials such as steel alloys or tungsten carbides which are used for molding and other non-conventional machining like forging and press tools can be reproduced.
Dies can be machined at hardened condition.
Complicated shapes can be reproduced.
Very fine holes can be done very accurately .
The accuracy is very high. Tolerance of 0.005 mm can be achieved.
Wear resistance surface can be made because workpieces produced with EDM have micro-craters which can contain lubricants effectively.

Disadvantages Electrical Discharge Machining

The power required for machining is much higher compared to the conventional machining. (120J/mm2)
There are chances of surface cracking when the materials become brittle at room temperature.
A thin layer usually ranging from 0.01 mm to 0,10 mm containing 4 % carbon may be deposited on the workpieces made of steel
The Material Removal Rate (MRR) is comparatively low (75 mm3/sec)
Reproducing sharp corners is difficult in EDM.
Sometimes the micro-structures are distorted and subsequently etching occurs.

Applications of EDM

Generally EDM is hugely used for machining burr free intricate shapes as well as narrow slots and blind cavities. Sinking of dies , plastic molding, die casting compacting, cold heading, extrusion, press tools, wire drawings are some of the examples of its application. Negative tool geometry can also be generated on a w/p if suitable tool can be made. EDM is very useful for machining small holes. It is also used to cut slot in diesel fuel injection nozzles. It is also used in air craft engines and brake valves etc.

Wire Electrical Discharge Machining(WEDM)

It is a primary type of EDM in which a very thin wire of diameter ranging from 0.02 to 0.3 mm is used as an electrode in wire cut EDM. It cuts the workpiece with electrical discharge just like a band saw. In this process either workpiece or the wire is moved. The spark discharge phenomenon is used for eroding the metal which is same as the conventional EDM. In wire cut EDM the wire acts as an electrode as a result complicated shapes can be cut easily without forming electrode.

Laser beam machining

This process comes under thermal energy based processes. It is a non-conventional machining process in which the work piece is being holed by the laser machining process. To remove the material from the work piece the process used thermal energy.

Principle:

Laser Machining is based on the LASER and conversion or process of Electric Energy into Light Energy and into Thermal Energy.

Negatively charged electrons in the atomic model rotate around the positively charged nucleus in orbital paths. It depends on the number of electrons, electron structure, neighboring atoms, and the electromagnetic field.

Every orbital of electrons is associated with different energy levels. An atom is considered to be at ground level at absolute zero temperature at this; all electrons occupy their lowest potential energy.

The electrons at the ground state move to a higher state of energy by absorbing energy like an increase in electronic vibration at elevated temperatures.

High voltage is applied at the ends that lead to discharge and gas plasma will be formed. Population inversion and lasing action will take takes place due to energy transformation.

The laser has one 100% reflector and the other one is partial reflector.100% the reflector directs the photons inside the gas tube and the partial reflector allows only some part of the laser beam that will be used for processing of materials.

The laser beam produced is focused on the work piece that has to be machined. When the laser strikes the work piece, the thermal energy impinges on the work piece.

Advantages of laser beam machining are:

· Any material can be machined including non-metal.

· The production rate is high.

· There is no direct contact between the tool and the work.

· There is no tool wear.

· No mechanical force on the work.

· The heat-affected zone is very small.

· Heat treated and magnetic materials can be welded, without losing their properties.

Disadvantages of using laser beam machining:

· The overall efficiency of Laser machining is very low.

· Not able to drill too deep holes.

· It’s having a high cost.

· A very low rate of metal-removing.

Applications of laser beam machining

· Soft materials like rubber, plastic can be machined.

· Extremely small holes can be machined.

· Used for making very small holes.

· Mass macro machining production.

Electrochemical Machining (ECM)

This processes comes under the chemical based processes. This process works on the Faraday law of electrolysis which state that if two electrodes are placed in a container which is filled with a conductive liquid or electrolyte and high ampere DC voltage applied across them, metal can be depleted form the anode (Positive terminal) and plated on the cathode (Negative terminal). This is the basic principle of electrochemical machining. In this machining process, tool is connected with the negative terminal of battery (work as cathode) and work-piece is connected with the positive terminal of battery (work as anode). They both are placed in a electrolyte solution with a small distance. When the DC current supplied to the electrode, metal removed from work-piece.

Advantages of ECM :

A single tool can be used to machining large number of work-piece. Theoretically no tool wear occur.
Machining of metal is independent on strength and hardness of tool.
ECM gives very good surface finish.

Disadvantages of ECM :

High initial cost of machine.
Design and tooling system is complex.
Fatigue property of machined surface may reduce.
Non conductive material cannot be machined.
Blind hole cannot be machined form ECM.
Space and floor area requirement is high compare to conventional machining.

Plasma Arc Machining

This process comes under the thermal energy based processes. It is used to remove material from the workpiece. In this process, a high velocity jet of high-temperature gas is used to melt and remove material from the workpiece. This high velocity of hot gas is also known as plasma jet.
When a gas or air is heated at a temperature of more than 5000 °C, then it will start getting ionized into positive ions, negative ions and neutral ions. When the gas or air is ionized its temperature reaches from 11000 °C to 28000 °C and this ionized gas is called plasma.
The gas or air is heated with arc and the plasma produced by heating gas is used to remove material from the workpiece. So the whole process is called Plasma Arc Machining.

Working of Plasma Arc Machining:

When a D.C power is given to the circuit, a strong arc is produced between the electrode (cathode) and the nozzle (anode).
A gas usually hydrogen (H2) or Nitrogen (N2) is passed into the chamber.
This gas is heated to a sufficiently high temperature of the order of 11,000°C to 28,000°C by using an electric arc produced between the electrode and the nozzle.
In this high temperature, the gases are ionized and a large amount of thermal energy is liberated.
This high velocity and high-temperature ionized gas (plasma) is directed on the workpiece surface through the nozzle.
This plasma jet melts the metal of the workpiece and the high-velocity gas stream effectively blows the molten metal away.
The heating of workpiece material is not due to any chemical reaction, but due. to the continuous attack of plasma on the workpiece material. So, it can be safely used for machining of any metal including those which can be subjected to the chemical reaction.

Advantages of Plasma Arc Machining:

· Hard as well as brittle metals can be easily machined with this process.

· Plasma Arc Machining gives a faster production rate.

· Small cavities can be machined using this process with good dimensional accuracy.

· It can be used for rough turning of very hard materials.

Disadvantages of Plasma Arc Machining:

· Plasma process cuts by melting, a characteristic feature is the greater degree of melting towards the top of the metal resulting in top edge rounding, poor edge squareness or a bevel on the cut edge.

· The equipment used in Plasma Arc Machining are very costly.

· Metallurgical changes take place on the surface of the workpiece.

· The consumption of inert gas is high.

· As oxidation and scale formation takes place, shielding is required.

Applications of PAM:

· It is also used in the nuclear submarine pipe system.

· Used in welding rocket motor case.

· Used in welding of stainless-steel tubes.

· It is used for profile cutting.

Conclusion:

In our blog, many advanced machining processes are described. Not a single process is suitable for machining all materials and/or manufacturing all features. Every process has a pros and cons. which we also mentioned earlier. We hope this blog helps our reader to understand various concepts related to Advanced Machining Processes.

Some useful YouTube links for more understanding :