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Introduction to

Hybrid Machining Processes

presented by

Dr. P. SahaDepartment of Mechanical Engineering

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What is hybrid machining?

Conventional Process

Unconventional Process

Improved New

Process

Unconventional Process 1

Unconventional Process 2

Improved Process

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Why to develop a hybrid machining process ?

• To make use of the combined or mutually enhanced advantages, and/or

• To avoid or reduce some adverse effects the constituent processes produce when they are individually applied.

Adverse effects

Advantages

Machinability,

MRR,

Surface finish,

Accuracy etc.

Burr,

HAZ,

Residual stress etc.

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What is hybrid machining ?

Improvement of machining processes by combining different physico-chemical interactions

(thermal, chemical, electro-chemical and mechanical interactions).

Thermal

Chemical

Mechanical

Electro-chemical

Improved Process

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Interactions

• Thermal

• Electrochemical

• Chemical

• Mechanical

Energy carriers

• Photon

• Electron

• Ion

• Plasma

• Abrasives

• Cutting Edge

• Fluid Jet

Working media

• Solid

• Electrolyte

• Fluid

• Dielectric

• Gas

• Photon

Combining different physico-chemical interactions through

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Categories of hybrid processes

• All constituent processes are directly involved in the material removal,

• Only one of the participating processes directly removes the material while the others only assistin removal.

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Classification

1. Hybrid thermal processes

2. Hybrid electrochemicalprocesses

3. Hybrid chemical processes

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1. Hybrid thermalprocesses

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Example 1-1

Electrochemical Discharge Machining

• Thermal (Electrical Discharge) machining +

• Electrochemical machining

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1-1. Electro chemical discharge machining

ECDM process components

• Electrochemical machining

hybridized with

• Electrodischarge machining

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Surface formation in ECDM

(1.1 continued) …

Electrochemical discharge machining

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Work piece

(+)

Tool

(-)

Oxide film

Spark action breaks off oxide film

Gas bubbles

Gap spark

Gap spark

Electrolyte surface

(1.1 continued) …

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Pulsed voltage waveform

Due to the background dc voltage electrochemical

action goes on while electrical discharge stops during

pulse off time. Voltage during pulse on time is set above

the breakdown threshold leads to EDM.

(1.1 continued) …

Electrochemical discharge machining

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Advantages

• significantly smoother surface

• depth of HAZ significantly reduced or eliminated.

• High machining rates• Burrs at the edges are

absent

Disadvantages

• applied only to electrically conductive materials

• low accuracy• difficulty in handling the

electrolyte.• cannot produce internal

and external sharp edges

(1.1 continued) …

Electrochemical discharge machining

• MRR can be as much as 5 to 50 times greater than ECM and EDM

• especially effective when dealing with materials with tensile strength higher than 1500 N/mm2 and heat resistance alloys.

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Example 1-2

Abrasive Electro Discharge Machining

• Electro discharge machining

hybridized with

• Mechanical abrasion

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Abrasive Electro Discharge Machining

AEDM schematic

(1.2 continued) …

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Abrasive Electro Discharge Machining

(1.2 continued) …

Process components of AEDM

• Mixing silicon carbide powder into dielectric reduces electrical

capacitance across the discharge gap by increasing the inter-electrode

gap size.

• As a result is higher dispersion of

sparks and improvement in the discharge characteristic, especially in the machining of large work piece area.

• Obtain mirror finishing of complex shape and more uniform and crack free affected layer.

• Produces a die without the need of removing the affected layer, i.e. without polishing it.

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Example 1-3

Abrasive Electro Discharge Grinding

• Electro discharge machining

hybridized with

• Mechanical abrasion

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Abrasive Electro discharge grinding (AEDG)

AEDG schematic

Material removal mechanism

in AEDG

(1.3 continued) …

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Example 1-4

Electro Discharge Machining Ultrasonic Assisted

• Electro discharge machining

hybridized with

• Ultrasonic machining

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Electrodischarge machining ultrasonic-assisted

EDMUS schematic

(1.4 continued) …

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Electro Discharge Machining Ultrasonic-assisted

Process components of EDMUS

Acoustic wave and cavitations phenomena improve the flushing and material removal from the surface craters.

Less liquid metal is recast

Useful for micro drilling and production of slots and grooves.

(1.4 continued) …

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2. Hybrid chemical processes

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Example 2-1

Laser Assisted Chemical or Electrochemical Interactions

• Chemical / electrochemical process

hybridized using a thermal source

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• An increase in temperature leads

to acceleration of kinetic reactions on

heated surfaces enhancedch anodic

dissolution or cathodic deposition in

chemical or electrochemical

interactions.

Thermal effect on reaction rate

(2.1 continued) …

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where ,

To

and Ts

= initial and final of surface temperature respectively,

= the increment in the temperature,

io

= current density without heating i.e. current density

at = 0,

E0

= the activation energy, and

R = gas constant.

The effect of temperature on the rate of

CHM/ECM processes is described by following

Arrhenius equation:

(Current density iL,

determines the rate of

dissolution/deposition)

(2.1 continued) …

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Laser Assisted CHM

The thermal action of focused laser radiation may locally

accelerate chemical etching reactions on the surface of work

piece, which is submerged in a suitable etchant.

Principle of laser-induced selective wet chemical etching

Laser

Etchant

Job

Groove

Heated area @ T0C

(2.1 continued) …

Interac-

tion

time

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Main advantages of the process

• low thermal load on the work piece

• high localization of etching reactions

• high etch rates

• precise machining with micron resolution

Some possible reactions in liquid etchant:

Titanium machining by artho-phosphoric acid:

2Ti + 2H3PO4 2TiPO4 + 3 H2

Copper machining by potassium hydroxide:

Cu + 2KOH + ½ O2 K2CuO2 + H2O

Laser Assisted CHM

(2.1 continued) …

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Application of Laser Assisted CHM

Ceramics fabrication: A ceramic can be etched at a

rate of 200 µm/s in KOH solution using Nd-YAG laser

beam the method is applied to the fabrication of

superconductive ceramic or diamond membranes.

Fabrication of semiconducting devicies: Using laser

assisted etching, semiconducting devices are etched 10 to 100 times faster than with conventional

procedures.

Metal fabrication: An argon ion laser and wet etching

are usually combined.

(2.1 continued) …

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Microspiral fabricated from Titanium by Nd-YAG

laser-induced wet chemical etching in H3PO4

Laser Assisted CHM

SEM micrographs of grooves

etched in Titanium

(2.1 continued) …

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3. Hybrid electrochemical

processes

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3. Hybrid Electrochemical Processes

ECD : Electrochemical Dissolution

LB : Laser Beam

MA : Mechanical Abrasion

FJ : Fluid Jet

US : Ultrasonic

ECML : Laser Assisted ECM

ECG : Electrochemical Grinding

ECH : Electrochemical Honing

ECS : Electrochemical Super finishing

ECB : Electrochemical Buffing

USMEC : Ultrasonic Assisted Electrochemical Machining

USMEC

ECG

ECH

ECS

ECMLECB ECDLB

MA

FJ

US

Mechanical Abrasion

Ultrasonic

Fluid JetLaser Beam

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Example 3-1

Electro Chemical Grinding

• Electro chemical machining

hybridized with

• Mechanical abrasion

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3.1 Electrochemical Grinding (ECG)

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Electrochemical dissolution and Mechanical abrasion in the

Machining Gap during ECG

(3.1 continued) …

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Electro Chemical Honing (ECH)(3.1 continued) …

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Applications of Electro Chemical Honing (ECH)

Removing roundness error

Correcting straightness error

Correcting small taper

ECH effects on bore errors

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Example

Electro Chemical Discharge Machining

Working Media: Electrolyte

Example:

3.2 Electrochemical Discharge Wire-Machining,

3.3 Electrochemical Discharge Drilling,

3.4 Electrochemical Discharge Grinding

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Due to the background dc voltage electrochemical action goes

on where as electrical discharge stops during off time.

Special Pulsed Power Supply for

Electrochemical Discharge Machining

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Wire Electro chemical discharge machining

Wire electro-chemical discharge machining

(3.2 continued) …

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Electro chemical discharge drilling

Electro chemical discharge drilling

(3.3 continued) …

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Electro Chemical Discharge Grinding

ECDG schematic

(3.4 continued) …

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Electro Chemical Discharge Grinding

Hybridization of three processes in ECDG

(3.4 continued) …

Material removal mechanism in ECDGmech14.weebly.com

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3-5 Ultrasonic assisted electrochemcialmachining

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Ultrasonic assisted electrochemcial machining

Useful for machining composite material having non-conductive inclusionsion/reinforcements in a conductive matrix (Metal matrix composite)

MRR reaches its maximum level with minimum gap set by the size of the statically presses abrasive grains

Voltage : 3-15 V

Current density : 5-30 A/cm2

Frequency : 20 kHz

Amplitude : 8-30 micron

(3.5 continued) …

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and many more such hybrid processes

are possible …

Thank You

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