Tool Material

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

Mechanical Energy Process‐ Ultrasonic Machining (UM)‐Water (WJC) and Abrasive Jet Machining

Electrical Energy Processes‐ Electrochemical Machining (ECM)‐ Electrochemical Grinding (ECG)

Thermal Energy Processes‐ Electric Discharge Process (EDM)‐ Electron Beam Machining (EBM)‐ Laser Beam Machining (LBM)

Chemical Process‐Chemical Machining (CHM)

Non‐Conventional Machining

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 MachiningA 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


Tool : Copper, Brass, Stainless steelElectrolyte: NaCl solution, HCl, or H2SO4

• 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

4

3

1

2

5


Electrochemical Machining set up at ME dept

Electric Discharge Machining (EDM)

• Basic EDM system consists of a shaped tooland work piece connected to a DC powersupply.

• Tool: Usually graphite, Brass, Cu, Cu‐W;Diameter can be as low as 0.1 mm

• Dielectric fluid (mineral oil, kerosene, distilledand de‐ionized water) between tool and workpiece

• Apply high enough voltage to create sparkdischarges through the fluid

• Small amount of material is removed from thework piece surface

• Voltage: 50 – 380 V; Current: 0.1 – 500 A

• Discharge is repeated at rates between 50and 500 kHz


23.1TKIMRR =

EDM Wire Cutting

Uses

• Production of die cavities for for large automotive–body components

• Deep small diameter holes

• Narrow slots in turbine blades

EDM Wire Cutting

Laser Machining

Micro pattern machinedon a steel plate

200 micron holes on Ti6Al4V alloy

Laser Micromachining

Process Resolutionμm

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,Focal length of lens

Feature size

Beam shape (Gaussian/square

wave)

Feature shape

Beam energy,Pulse width

Size of heat affected zone

Depth of focus Aspect ratioVacuum or inert gas

environmentAmount of

redeposition, size of recast layer

(a)Array of shots (b) Thru-hole drilled after 33 shots at a pulse energy of 14μJ

Micromachining in 18μm Thick Aluminum Foil

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 machiningaluminium‐alloy plates

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Tool Material

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