Advanced Machining Processes -GRK

 

Advanced Machining Processes 

1. Introduction

Advanced Machining Processes (AMP), also called Non-Traditional Machining Processes (NTMPs) or Unconventional Machining Processes, are modern manufacturing techniques used to machine materials and components that are difficult or impossible to machine efficiently using conventional processes such as turning, milling, drilling and grinding.

In conventional machining, material is generally removed by direct contact between a cutting tool and the workpiece. In advanced machining, material removal may be achieved using electrical energy, thermal energy, chemical energy, electrochemical action, mechanical erosion, or combinations of these methods.

Advanced machining processes are particularly important in the manufacture of:

  • Aerospace components
  • Automobile components
  • Dies and moulds
  • Turbine blades
  • Medical implants
  • Micro-components
  • Electronic components
  • Precision instruments
  • Hard and heat-resistant materials
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2. Need for Advanced Machining Processes

Conventional machining becomes difficult when:

  • The work material is extremely hard.
  • The material is brittle.
  • The component has a complex shape.
  • Very small holes are required.
  • The component is delicate or thin.
  • Heat-treated materials need to be machined.
  • Conventional cutting forces may damage the component.
  • Very high dimensional accuracy is required.
  • Micro-machining is required.
  • The component has difficult-to-access regions.

Examples

A conventional drill may struggle to produce a very small hole in a hardened turbine blade. An Electrical Discharge Machining (EDM) process can produce such holes without direct mechanical contact between the tool and workpiece.

Similarly, a laser beam can be used to produce very small holes and intricate profiles.

3. Classification of Advanced Machining Processes

Advanced machining processes can broadly be classified according to the primary form of energy used.

CategoryEnergy usedExamples
MechanicalMechanical energyUSM, AJM, AWJM
ElectricalElectrical dischargeEDM, WEDM
ElectrochemicalChemical + electricalECM, ECG
ThermalHeat energyLBM, PAM, EBM
ChemicalChemical reactionCHM
HybridCombination of energiesECDM, EDM-assisted processes

4. Conventional vs Advanced Machining

Conventional MachiningAdvanced Machining
Tool physically contacts workpieceContact may not be required
Cutting tool is generally harder than workpieceTool hardness may not be the primary requirement
Mechanical cutting actionElectrical, thermal, chemical or mechanical erosion
Cutting forces can be significantSome processes have very low cutting forces
Difficult to machine very hard materialsSuitable for hard materials
Tool geometry strongly influences machiningEnergy source determines material removal
Generally suitable for larger featuresCan produce micro-holes and complex shapes
Examples: turning, milling, drillingEDM, ECM, LBM, EBM, USM

5. Electrical Discharge Machining – EDM

Definition

Electrical Discharge Machining (EDM) is a thermal machining process in which material is removed from an electrically conductive workpiece through a series of controlled electrical sparks between the tool electrode and the workpiece.

There is no direct physical contact between the tool and workpiece.

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Principle

When a sufficiently high voltage is applied across a small gap between the electrode and electrically conductive workpiece, the dielectric fluid breaks down and a spark is produced.

The intense localized heat generated by the spark melts and vaporizes a small quantity of material.

Repeated sparks gradually produce the required shape.

Basic sequence

Electrical energy → Spark → Localized heating → Melting/vaporization → Material removal

Main Components of EDM

  1. Power supply
  2. Tool electrode
  3. Workpiece
  4. Dielectric tank
  5. Dielectric fluid
  6. Servo feed mechanism
  7. Pump and filtration system
  8. Control system

Common dielectric fluids

  • EDM oil
  • Deionized water

EDM Working

  1. The workpiece is connected to one terminal of the power supply.
  2. The tool electrode is connected to the opposite terminal.
  3. A small controlled gap is maintained.
  4. Dielectric fluid fills the machining zone.
  5. Voltage is applied.
  6. The dielectric breaks down.
  7. A spark occurs.
  8. The spark generates very high localized temperature.
  9. A small amount of workpiece material melts and vaporizes.
  10. The dielectric removes the debris.
  11. The process repeats thousands of times per second.

Advantages of EDM

  • Machines hardened materials.
  • No direct cutting force.
  • Produces complex shapes.
  • Suitable for intricate cavities.
  • Good dimensional accuracy.
  • Can produce small holes.
  • Suitable for dies and moulds.

Limitations

  • Workpiece must be electrically conductive.
  • Material removal rate can be relatively low.
  • Electrode wear occurs.
  • Power consumption can be significant.
  • Surface may contain a heat-affected/recast layer.
  • Dielectric handling is required.

Applications

  • Dies
  • Moulds
  • Punches
  • Turbine components
  • Hardened steel components
  • Small holes
  • Aerospace components

6. Wire Electrical Discharge Machining – WEDM

WEDM is a special form of EDM in which a continuously moving thin wire acts as the electrode.

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Working principle

A thin electrically conductive wire passes continuously through the workpiece while controlled electrical discharges remove material.

The wire does not normally touch the workpiece.

Common wire material

  • Brass
  • Zinc-coated brass

Applications

  • Punches
  • Dies
  • Precision components
  • Intricate profiles
  • Tool manufacturing
  • Aerospace parts

Advantages

  • Very complex profiles can be produced.
  • High accuracy.
  • Suitable for hardened materials.
  • Narrow cutting width.
  • No conventional cutting forces.

7. Electrochemical Machining – ECM

Definition

Electrochemical Machining (ECM) removes material from an electrically conductive workpiece by controlled electrochemical dissolution.

It works on the principle of electrolysis.

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Principle

The workpiece acts as the anode (+) and the tool acts as the cathode (−).

An electrolyte flows through the small gap between them.

When direct current is supplied, metal is removed from the workpiece through an electrochemical reaction.

Basic principle

Workpiece → Anode

Tool → Cathode

Electrolyte → Conducts electric current

Working

  1. The workpiece is connected to the positive terminal.
  2. The tool is connected to the negative terminal.
  3. Electrolyte flows through the machining gap.
  4. DC current is supplied.
  5. Electrochemical dissolution occurs at the workpiece.
  6. Material is removed without direct tool-workpiece contact.
  7. Electrolyte carries away machining products.

Advantages

  • No tool wear due to mechanical contact.
  • No cutting forces.
  • No thermal damage from sparks.
  • Can machine complex shapes.
  • Suitable for hard electrically conductive materials.
  • Good surface finish possible.

Limitations

  • Workpiece must be electrically conductive.
  • Electrolyte handling is required.
  • Corrosion-related issues can occur.
  • High power consumption.
  • Equipment cost is relatively high.

Applications

  • Turbine blades
  • Die sinking
  • Aerospace components
  • Deburring
  • Profiling
  • Drilling of complex holes

8. Electrochemical Grinding – ECG

Electrochemical Grinding combines:

  • Electrochemical machining
  • Conventional grinding

The majority of material removal occurs through electrochemical dissolution, while the grinding wheel removes the remaining material and surface film.

Applications

  • Carbides
  • Hardened steels
  • Surgical needles
  • Aerospace components
  • Precision grinding

9. Ultrasonic Machining – USM

Definition

Ultrasonic Machining (USM) is a mechanical advanced machining process in which abrasive particles suspended in a slurry are driven against the workpiece by a vibrating tool.

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Principle

A tool vibrates at ultrasonic frequency, generally around 20 kHz or higher, with a small amplitude.

Abrasive particles between the tool and workpiece impact the surface and cause microscopic chipping and erosion.

Common abrasives

  • Aluminium oxide
  • Silicon carbide
  • Boron carbide
  • Diamond

Working

  1. Tool is connected to an ultrasonic transducer.
  2. Transducer produces high-frequency vibration.
  3. Abrasive slurry is supplied between tool and workpiece.
  4. Tool vibrates at high frequency.
  5. Abrasive particles impact the workpiece.
  6. Small particles are removed.
  7. Tool gradually reproduces its shape on the workpiece.

Suitable Materials

USM is particularly useful for:

  • Glass
  • Ceramics
  • Carbides
  • Quartz
  • Gemstones
  • Hardened brittle materials

Advantages

  • Machines brittle materials.
  • Very low thermal damage.
  • Low cutting forces.
  • Complex shapes can be produced.
  • Good surface finish.

Limitations

  • Low material removal rate.
  • Tool wear occurs.
  • Generally less suitable for soft and ductile materials.
  • Abrasive slurry handling is required.

10. Abrasive Jet Machining – AJM

Definition

Abrasive Jet Machining removes material using a high-velocity stream of fine abrasive particles carried by compressed air or gas.

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Principle

The high-speed abrasive particles strike the workpiece and cause:

  • Erosion
  • Micro-cutting
  • Brittle fracture

Abrasives

  • Aluminium oxide
  • Silicon carbide
  • Glass beads

Applications

  • Cleaning
  • Deburring
  • Engraving
  • Cutting thin materials
  • Surface finishing
  • Glass machining

11. Abrasive Water Jet Machining – AWJM

AWJM uses a high-pressure water jet containing abrasive particles to cut materials.

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Working

High-pressure water passes through a small orifice, producing a high-speed jet. Abrasive particles are introduced into the jet, and the resulting mixture cuts the workpiece.

Advantages

  • No significant heat-affected zone.
  • Low mechanical forces.
  • Can cut many materials.
  • Suitable for thick sheets.
  • Environmentally useful in some applications.

Applications

  • Steel plate cutting
  • Aluminium
  • Composites
  • Stone
  • Glass
  • Aerospace materials
  • Automotive components

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