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

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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