Tool Materials and
Non-traditional Machining Processes
Tool Materials
• Tool failure modes identify the important properties that a tool material should possess: – ‐ Toughness ‐ to avoid fracture failure
– ‐ Hot hardness ‐ ability to retain hardness at high temperatures – ‐ Wear resistance ‐ hardness is the most important property to resist abrasive wear
Cubic Boron Nitride
• Next to diamond, cubic boron nitride (cBN) is hardest material known
• Fabrication into cutting tool inserts same as SPD: coatings on WC‐Co inserts • Applications: machining steel and nickel‐based alloys • SPD and cBN tools are expensive
Range of Applicable Cutting Speeds and Feeds for a number of Tool Materials
.
Hot Hardness
Cutting Fluids
• Fluids address two major problems:
‐Heat generation at the shear zone
‐Friction at the tool‐chip interface and tool‐
work interface
Types : ‐ Coolants (Oil‐water mixtures)
‐Lubricants (Special lubricants that involves formation of thin solid salt layers on the hot and clean material surface by reaction.
Cutting Fluids
• Cutting oil (petroleum,animal, vegetable mineral oils)
• Emulsified oils (Oil droplets suspended in water)
• Chemical fluids (Chemicals in water)
• Semi‐chemical fluids (Small amounts of emulsified oil added to increase lubrication
characteristics
NON‐CONVENTIONAL MACHINING
Why do we need it?
• Very high hardness/strength material
• Complex shapes or small diameter holes as in turbine blades and fuel injection nozzles
• Very rigorous surface finish and dimensional tolerance requirements
• Temperature and residual stresses in the work piece not desirable/acceptable
Turbine Blade Machining
Non‐Conventional Machining
¾Mechanical Energy Process
‐ Ultrasonic Machining (UM)
‐ Water (WJC) and Abrasive Jet Machining
¾Electrical Energy Processes
‐ Electrochemical Machining (ECM)
‐ Electrochemical Grinding (ECG)
¾Thermal Energy Processes
‐ Electric Discharge Process (EDM)
‐ Electron Beam Machining (EBM)
‐ Laser Beam Machining (LBM)
¾ Chemical Process
‐Chemical Machining (CHM)
Ultrasonic Machining
Tool is excited at a frequency of 20,000 Hz with a magnetostrictive transducer.
Ultrasonic Machining
Magnetostriction
Water Jet or Abrasive Water Jet Machining
A fine (0.1 – 0.4 mm dia.), high pressure (400 MPa), high velocity ( 900 m/s)
stream of water is directed at the work surface to cause cutting.
Plastic, Textile, Composites, Tile, Carpet, Leather and Cardboard
Water Jet or Abrasive Water Jet Machining
Complex shapes can be machined using CNC WJC
Electrochemical Machining (ECM)
• Machining by passage of current, that is electrochemical dissolution. It is basically de‐
plating process.
• Generally used to machine complex cavities, particularly in the aerospace industry for the mass production of turbine blades, jet‐engine parts and nozzles
Electrochemical Machining (ECM)
Tool : Copper, Brass, Stainless steel
Electrolyte: NaCl solution, HCl, or H2SO4
Electrochemical Machining (ECM)
• Electrolyte pumped at very high flow rates to remove dissolved “metal ions” to prevent precipitation and “deposition” at cathode.
• DC voltage: 5 – 25 V; Current: 5 – 40000 A
Top: Turbine blade made of a nickel alloy
(b) Thin slots on 4340‐steel roller‐bearing cage
(c) Integral airfoils on a compressor disk
Electrochemical Machining (ECM)
1
2
4
5
3
Electrochemical Machining set up at ME dept
Electric Discharge Machining (EDM)
• Basic EDM system consists of a shaped tool
and work piece connected to a DC power
supply.
• Tool: Usually graphite, Brass, Cu, Cu‐W;
Diameter can be as low as 0.1 mm
• Dielectric fluid (mineral oil, kerosene, distilled
and de‐ionized water) between tool and work
piece
• Apply high enough voltage to create spark
discharges through the fluid
• Small amount of material is removed from the
work piece surface
• Voltage: 50 – 380 V; Current: 0.1 – 500 A
• Discharge is repeated at rates between 50
and 500 kHz
Electric Discharge Machining (EDM)
Electric Discharge Machining (EDM)
KI
MRR = 1.23
T
EDM Wire Cutting
EDM Wire Cutting
Uses
• Production of die cavities for for large automotive–body components
• Deep small diameter holes
• Narrow slots in turbine blades
Laser Machining
Laser Micromachining
Micro pattern machined
on a steel plate
200 micron holes on
Ti6Al4V alloy
Process
Resolution
μm
Surface
Roughness μm
Side Effects
Mechanical
100
6.3-1.6
Burring, requires
polishing
EDM
100
4.75-1.6
Electrode wear, rough
finish, slow and unclean
process
Chemical
Etch
250
6.3-1.6
Undercutting
LIGA
5
1-2
Synchrotron source:
very expensive
Nd: YAG
Laser
50
1
Redeposition
Excimer
Laser
5
> 1 μm (nm
range)
Recast Layer, aspect
ratios
Ultrafast
Laser
<1
nm range
Higher power ranges
may require vacuum
environment
Laser Micromachining
Process
Parameters
Effect
Wavelength,
Feature size
Focal length of lens
Feature shape
Beam shape
(Gaussian/square
wave)
Beam energy,
Size of heat affected
zone
Pulse width
Depth of focus
Aspect ratio
Vacuum or inert gas
Amount of
environment
redeposition, size of
recast layer
Micromachining in 18μm Thick Aluminum Foil
(a) Array of shots (b) Thru-hole drilled after 33 shots at a
pulse energy of 14μJ
Thru-holes Drilled in 25μm Thick
Brass Foil
56μJ/pulse
27μJ/pulse
Chemical Machining
• Oldest non‐traditional process. Used to engrave metals and hard stones, and deburring
• More recently used in the production of printed‐circuit board and microprocessor chips
• Uses the concept of chemical dissolution of metals for machining
Chemical Machining
This is basically etching using strong chemical
Steps
•
•
•
•
Cleaning
Masking
Etching
Demasking
Various parts made by chemical machining
(L)
Missile
skin‐panel
contoured
by
chemical
machining
(R) Weight reduction of space launch vehicles by chemical machining
aluminium‐alloy plates
The best of the best guys from all over the country join IITK. Now in a
competitive grading system, though the class is consisted of the best guys there
must be some guys who will not do as good as the rest... does that mean they
are not up to... ?? Assume a class consisting of Einstein, Dirac, Feynman, S N
Bose , Lagrange.... you put them in a system like this.... some of them are
definitely going to get 'F' grade. Do the present grading system .. that mostly
measure how much better or how much poorer you are compared to your
neighbor in the class... is justified enough??