Unconventional Machining Questions and Answers

Answer: A

The matching is P-2, Q-3, R-1, S-4.

1. EDM removes material by electric sparks, so the work must be electrically conductive (P-2).
2. Ultrasonic machining uses abrasive slurry hammered by a vibrating tool, ideal for hard, brittle non-conductors such as glass (Q-3).
3. Chemical machining dissolves material by etching with no mechanical or thermal load, leaving no residual stress (R-1).
4. Ion beam machining removes material atom by atom, so it is used for nano-scale machining (S-4).

The other options swap EDM and USM (which would make EDM cut glass) or put nano-machining against chemical machining.

Answer: B

Metal is removed by melting and vaporization.

In electric discharge machining, a pulsed voltage between the tool and the workpiece, both immersed in a dielectric, breaks down the dielectric and produces a spark. Each spark creates a plasma channel at several thousand degrees, which melts and vaporises a tiny crater of metal; when the pulse ends, the collapsing channel and the flushing dielectric carry the molten debris away.

Ion displacement and corrosive (electrochemical) reaction describe electrochemical machining, not EDM. Plastic shear is the mechanism of conventional chip-forming processes such as turning and milling.

Answer: D

The material removal rate increases, becomes stable and then decreases as the stand-off distance grows.

Very close to the work, the jet has not yet reached full speed over its cross section and the abrasive that bounces back off the surface interferes with the incoming stream, so removal is low. As the nozzle moves back, the jet develops fully and the removal rate rises to a broad maximum over a range of stand-off distances. Further back still, the jet diverges and the particles lose velocity to air drag, so they strike a larger area with less energy and the removal rate falls.

A steady rise or a steady fall each describe only one side of this peaked curve, and 'decreases, becomes stable and then increases' is the curve turned upside down.

Answer: B

Ceramics and glass are machined by ultrasonic machining.

Ultrasonic machining removes material by abrasive grains hammered against the work by a tool vibrating at about 20 kHz. It works best on hard, brittle materials that fracture in small chips, such as glass and ceramics.

Electric discharge machining, electrochemical machining and transferred-arc plasma machining all need an electrically conducting workpiece, so they cannot cut glass or most ceramics.