Introduction to Hybrid Machining Processesmech14.weebly.com/.../6/1/0/...ps_hybrid_machining.pdf ·...
Transcript of Introduction to Hybrid Machining Processesmech14.weebly.com/.../6/1/0/...ps_hybrid_machining.pdf ·...
4/12/2018 P Saha IIT Kharagpur 1
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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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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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
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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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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