Machining Processes: Conventional vs. Non-Conventional Techniques
Maintenance Fundamentals
Importance of Maintenance
Maintenance is the activity of keeping machines, equipment, and systems in proper working condition so that they perform efficiently and safely throughout their service life.
Key Benefits of Maintenance
Increases Equipment Life – Regular maintenance reduces wear and tear.
Improves Reliability – Machines work smoothly with fewer breakdowns.
Ensures Safety – Prevents accidents due to machine failure.
Reduces Breakdown Cost – Early detection avoids major repair expenses.
Improves Productivity – Less downtime means higher output.
Maintains Product Quality – Properly maintained machines produce consistent quality.
Energy Efficiency – Well-maintained equipment consumes less power.
Types of Maintenance (with Examples)
1. Breakdown Maintenance (Corrective)
Maintenance carried out after equipment failure.
No planning before failure; used for non-critical equipment.
Example: Repairing a motor after it suddenly stops working.
2. Preventive Maintenance
Maintenance performed at regular intervals to prevent failures.
Scheduled maintenance; reduces chances of breakdown.
Example: Regular lubrication of machine parts or periodic replacement of belts.
3. Predictive Maintenance
Maintenance based on condition monitoring of equipment.
Uses vibration, temperature, or oil analysis; maintenance is done only when required.
Example: Replacing a bearing when vibration analysis shows abnormal readings.
4. Corrective Maintenance
Maintenance carried out to correct minor faults before failure occurs.
Improves performance; planned repair activities.
Example: Aligning a misaligned shaft or tightening loose bolts.
5. Routine Maintenance
Simple maintenance tasks carried out daily or frequently.
Performed by operators; keeps machines in running condition.
Example: Cleaning machines, checking oil level, tightening nuts.
6. Shutdown Maintenance
Maintenance performed when the plant or machine is shut down.
Used for major repairs; planned during holidays or off-production time.
Example: Overhauling a boiler during annual plant shutdown.
Total Productive Maintenance (TPM)
TPM (Total Productive Maintenance) is a modern maintenance approach that aims to maximize Overall Equipment Effectiveness (OEE) by involving all employees—from top management to shop-floor workers—in maintenance activities. The goal of TPM is zero breakdowns, zero defects, and zero accidents.
The House of TPM
The House of TPM is a conceptual model showing how TPM is built and sustained in an organization.
1. Roof of TPM
Goals of TPM: Zero breakdowns, zero defects, zero accidents, maximum OEE.
2. Pillars of TPM (8 Pillars)
These pillars support the TPM system and help achieve its objectives.
1. Autonomous Maintenance (Jishu Hozen)
Operators take responsibility for basic maintenance: cleaning, lubrication, inspection.
Example: Machine operators regularly clean and inspect their machines.
2. Planned Maintenance
Maintenance is scheduled based on time or condition; prevents unexpected breakdowns.
Example: Replacing worn-out parts during scheduled shutdowns.
3. Quality Maintenance
Focuses on preventing defects by maintaining machine conditions; ensures zero defects in production.
Example: Maintaining correct machine settings to avoid dimensional errors.
4. Focused Improvement (Kaizen)
Continuous improvement by small teams; eliminates losses and inefficiencies.
Example: Reducing setup time using SMED techniques.
5. Early Equipment Management
Maintenance considered during machine design and installation; reduces future maintenance problems.
Example: Designing machines for easy lubrication and inspection.
6. Training and Education
Improves skills of operators and maintenance staff; ensures proper machine handling.
Example: Training workers on fault detection and preventive maintenance.
7. Safety, Health, and Environment (SHE)
Ensures safe working conditions; aims for zero accidents.
Example: Installing safety guards and proper ventilation systems.
8. Office TPM
Applies TPM concepts to administrative and office functions; reduces losses in paperwork and processes.
Example: Reducing delays in purchase orders and maintenance approvals.
5S in TPM (Workplace Organization)
The 5S system in Total Productive Maintenance (TPM) is a workplace organization method that improves efficiency, safety, and cleanliness.
Seiri (Sort) – Remove unnecessary items from the workplace.
Seiton (Set in order) – Arrange necessary items properly for easy access.
Seiso (Shine) – Clean machines and work areas regularly.
Seiketsu (Standardize) – Set standards to maintain the first three S’s.
Shitsuke (Sustain/Discipline) – Follow and maintain standards consistently.
Non-Conventional Machining Processes
What is EDM (Electrical Discharge Machining)?
EDM (Electrical Discharge Machining) is a non-conventional machining process in which material is removed from the workpiece by a series of controlled electrical sparks (discharges) between a tool (electrode) and the workpiece, both immersed in a dielectric fluid. EDM is mainly used to machine hard materials and complex shapes that are difficult to machine by conventional methods.
Working Principle of EDM
EDM works on the principle of spark erosion.
The tool (electrode) and workpiece are connected to a DC power supply.
A small gap (spark gap) is maintained between tool and workpiece.
When voltage is applied, electrical sparks occur across the gap.
The spark produces very high temperature (≈ 8000–12000°C).
This heat melts and vaporizes a small amount of material.
The molten material is flushed away by dielectric fluid.
Repeated sparks gradually remove material and produce the desired shape.
Important condition: The workpiece must be electrically conductive.
Advantages of EDM
Can machine very hard materials (hardened steel, carbides).
Suitable for complex and intricate shapes.
No cutting force → no mechanical stress.
High dimensional accuracy.
Can machine thin and fragile components.
Burr-free machining.
Disadvantages of EDM
Only works on electrically conductive materials.
Low Material Removal Rate (MRR).
Tool wear occurs.
High initial and operating cost.
Surface may have heat-affected layer.
Slower than conventional machining.
Applications of EDM
Die and mould making
Tool rooms
Aerospace components
Machining of hard alloys
Injection molds, punches, and dies.
Ques: A spark generator is used in which machining process?
Ans: A spark generator is used in the:
✅ EDM – Electrical Discharge Machining process
Explanation: In EDM, a spark generator produces controlled electrical pulses that create sparks between the tool (electrode) and the workpiece, which remove material by spark erosion.
Ques: Dielectric fluid is used in which type of machining process?
Ans: Dielectric fluid is used in:
✅ EDM – Electrical Discharge Machining
Explanation: In EDM, a dielectric fluid (such as kerosene or deionized water) is used to act as an insulating medium until the spark occurs, flush away molten material, and cool the tool and workpiece.
What is ECM (Electrochemical Machining)?
ECM (Electrochemical Machining) is a non-conventional machining process in which material is removed from the workpiece by electrochemical dissolution. It is the reverse of electroplating. ECM is mainly used to machine hard, tough, and electrically conductive materials with high accuracy and no tool wear.
Working Principle of ECM
ECM works on the principle of Faraday’s laws of electrolysis.
The workpiece acts as the anode (+).
The tool acts as the cathode (−).
A conductive electrolyte (NaCl or NaNO₃ solution) flows at high velocity through a small gap between tool and workpiece.
When DC voltage is applied, metal ions dissolve from the anode (workpiece), and material removal occurs in the shape of the tool.
The electrolyte flushes away metal ions and heat.
No contact occurs between tool and workpiece.
Advantages of ECM
Can machine very hard materials (superalloys, stainless steel).
No tool wear.
No cutting forces → no mechanical stress.
Excellent surface finish.
Complex shapes can be produced.
No heat-affected zone.
Disadvantages of ECM
High initial and operating cost.
Only works on electrically conductive materials.
Electrolyte handling and disposal problems.
Accuracy affected by stray current.
High power consumption.
Limited for very small features.
Applications of ECM
Turbine blades
Die and mould making
Aerospace components
Machining of hard alloys
Complex cavities and profiles
What is CHM (Chemical Machining)?
CHM (Chemical Machining) is a non-conventional machining process in which material is removed from the workpiece by controlled chemical dissolution using a suitable etchant. There is no mechanical force or cutting tool involved. It is mainly used for producing thin, delicate parts and complex shapes with good surface finish.
Working Principle of Chemical Machining
CHM works on the principle of chemical etching.
Areas of the workpiece not to be machined are covered with a maskant.
The workpiece is immersed in a chemical etchant.
The exposed areas react chemically with the etchant.
Material is removed gradually by chemical dissolution.
After achieving required depth, the workpiece is removed and cleaned.
⚠️ The material removal rate depends on: Type of material, Etchant used, Temperature and concentration.
Advantages of Chemical Machining
No cutting forces → no mechanical stress.
Suitable for thin and delicate components.
Good surface finish.
Can machine complex shapes.
No tool wear.
Burr-free machining.
Disadvantages of Chemical Machining
Low material removal rate.
Accuracy is limited.
Etchant disposal causes environmental issues.
Maskant preparation is time-consuming.
Not suitable for thick materials.
Difficult to control depth precisely.
Applications of Chemical Machining
Aerospace components, Printed circuit boards (PCB), Decorative engraving, Thin sheet metal parts, Weight reduction of aircraft panels
Ques: Which machine is used for making tool and die?
Ans:
✅ EDM (Electrical Discharge Machining) machine
Reason: It can machine very hard materials, is suitable for complex and intricate shapes, and is widely used in tool rooms and die manufacturing. Other machines like Milling, Grinding, and CNC machining centers are also used depending on the work.
What is EBM (Electron Beam Machining)?
EBM (Electron Beam Machining) is a non-conventional machining process in which material is removed from the workpiece by a high-velocity focused beam of electrons. The kinetic energy of electrons is converted into intense heat, which melts and vaporizes the material. EBM is mainly used for micro-machining and high-precision work on very hard materials.
Working Principle of EBM
EBM works on the principle of conversion of kinetic energy into thermal energy.
Electrons are emitted from a heated tungsten filament (electron gun).
These electrons are accelerated by a high-voltage DC supply.
Magnetic and electrostatic lenses focus the beam.
The focused electron beam strikes the workpiece, producing very high temperature (≈ 10,000°C).
Material melts and vaporizes from the surface.
Machining is carried out in a high vacuum to avoid scattering of electrons.
Advantages of EBM
Very high precision and accuracy.
Can machine very hard and brittle materials.
Suitable for micro holes and fine features.
No cutting force; minimal tool wear.
Narrow heat-affected zone.
Disadvantages of EBM
Very high initial and operating cost.
Requires high vacuum.
Low material removal rate.
Limited to small workpieces.
Requires skilled operator; safety precautions needed due to radiation.
Applications of EBM
Micro drilling of small holes, Aerospace components, Nuclear industry, Medical devices, Precision electronic components
What is LBM (Laser Beam Machining)?
LBM (Laser Beam Machining) is a non-conventional machining process in which material is removed from the workpiece by a high-energy, highly focused laser beam. The intense laser energy melts and vaporizes the material to produce the required shape. LBM is suitable for hard, brittle, and difficult-to-machine materials and for micro-machining operations.
Working Principle of LBM
LBM works on the principle of conversion of light energy into heat energy.
A laser source generates a high-energy coherent laser beam, focused by optical lenses to a very small spot.
When the focused laser beam strikes the workpiece, temperature rises rapidly (≈ 2000–3000°C or more), and material melts and vaporizes.
An assist gas (oxygen or nitrogen) removes molten material.
No physical contact occurs between tool and workpiece.
⚠️ The workpiece need not be electrically conductive.
Advantages of LBM
No cutting force or tool wear.
Can machine very hard and brittle materials.
High precision and accuracy.
Suitable for micro-holes and thin sections.
Narrow heat-affected zone.
Can machine non-conductive materials.
Disadvantages of LBM
High initial and operating cost.
Low material removal rate for thick sections.
Heat-affected zone may cause micro-cracks.
Limited depth of cut.
Requires skilled operator; high power consumption.
Applications of LBM
Micro drilling, Cutting thin sheets, Aerospace and electronic industries, Medical instruments, Precision components
What is USM (Ultrasonic Machining)?
USM (Ultrasonic Machining) is a non-conventional machining process in which material is removed from the workpiece by the abrasive action of fine abrasive particles driven by a tool vibrating at ultrasonic frequency (≈ 20–40 kHz). USM is mainly used to machine hard, brittle, and non-conductive materials.
Working Principle of USM
An electrical generator produces high-frequency electrical signals converted into mechanical vibrations by a transducer (magnetostrictive or piezoelectric).
The tool vibrates vertically with very small amplitude (≈ 10–50 µm).
An abrasive slurry (water + abrasive particles like SiC or Al₂O₃) is fed between the tool and workpiece.
Abrasive particles strike the workpiece surface due to tool vibration.
Material is removed by micro-chipping and erosion.
The shape of the cavity produced is the same as the tool shape.
Advantages of USM
Can machine very hard and brittle materials.
Suitable for non-conductive materials.
No heat-affected zone, chemical, or thermal damage.
Good surface finish.
Complex shapes can be produced.
Disadvantages of USM
Low material removal rate.
Tool wear is high.
Not suitable for ductile materials.
Limited depth of cut.
Abrasive slurry handling is difficult; high equipment cost.
Applications of USM
Machining glass, ceramics, quartz
Semiconductor and electronic industries
Precision holes and cavities
Jewel and watch industries
Aerospace components (brittle materials)
What is PAM (Plasma Arc Machining)?
PAM (Plasma Arc Machining) is a non-conventional machining process in which material is removed from the workpiece by a high-temperature plasma jet. The plasma is an ionized gas capable of melting and blowing away material from the surface. PAM is mainly used for cutting hard and electrically conductive metals.
Working Principle of PAM
PAM works on the principle of thermal energy of plasma.
A gas (argon, nitrogen, hydrogen or air) is forced through a constricted nozzle.
An electric arc is struck between the Tungsten electrode (cathode) and the Workpiece (anode).
The gas gets ionized due to the arc and converts into plasma, reaching temperatures of 11,000–30,000°C.
This intense heat melts the metal, and the high-velocity plasma jet blows away the molten material.
Advantages of PAM
Very high cutting speed; faster than oxy-fuel cutting.
Can cut thick and hard metals.
Narrow heat-affected zone.
Can be used for automation.
Good surface finish compared to gas cutting.
Disadvantages of PAM
High equipment and operating cost.
High noise and intense light; produces fumes and radiation.
Limited accuracy for very thin materials.
Electrode wear occurs; requires skilled operator.
Applications of PAM
Cutting stainless steel and aluminium, Shipbuilding and automobile industries, Heavy fabrication work, Aerospace industry, Structural steel cutting
Comparison: Conventional vs. Non-Conventional Machining
Difference Between Conventional and Non-Conventional Machining
| Basis | Conventional Machining | Non-Conventional Machining |
|---|---|---|
| Tool | Sharp cutting tool required | No sharp cutting tool |
| Material Removal | Mechanical cutting action | Thermal / electrical / chemical energy |
| Cutting Force | Present | Negligible or zero |
| Hard Materials | Difficult to machine | Easily machinable |
| Tool Wear | High | Very low to none |
| Accuracy | Moderate | High |
| Examples | Turning, Milling, Drilling | EDM, ECM, LBM, EBM, USM, CHM, PAM |
Acronym Explanations
LASER → Light Amplification by Stimulated Emission of Radiation
TPM → Total Productive Maintenance
USM → Ultrasonic Machining
AJM → Abrasive Jet Machining