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Lesson 6.9CutChapter 6 · Cutting and non-traditional machining

Ultrasonic machining

A vibrating tool hammers abrasive grains into the surface

Ultrasonic machining makes a shaped tool vibrate about 20,000 times a second against hard, brittle material, through a paste of abrasive grains. Each blow chips away microscopic flakes, so the tool's shape slowly sinks into glass or ceramic without cracking it. It makes the square, star-shaped and slotted holes in glass and ceramic that a drill would shatter.

Ultrasonic machining: a real photo
Photo: Public domain, via Wikimedia Commons
A vibrating tool hammers abrasive grains into brittle materialCross-section of an ultrasonic machine, with a close-up of the tool tip (gap exaggerated)Workpiece (glass, ceramic)UltrasonicgeneratorTransducerHorn (sonotrode)ToolVibrates up and downabout 20,000 times a secondLight static forcefeeds the toolSlurry nozzleClose-up of the tool tipAbrasive slurryTool tiphammer blowEach blow chips outtiny flakesWorkpiece (glass)Real gap: about one grain wide123456WorkpieceTool, grains and machine partsAbrasive slurry (water and grains)
Ultrasonic machining · the machine and a close-up of the tool tipCircled numbers match the steps below; the close-up on the right magnifies the tool tip.

How it works

  1. Make the signal. A generator produces an electrical signal at typically 18–40 kHz (thousand cycles per second), just above the range of human hearing.

  2. Turn it into vibration. A piezoelectric transducer (a crystal stack that grows and shrinks with voltage) converts the signal into mechanical vibration.

  3. Amplify it. The horn, or sonotrode (a tapered metal bar), magnifies the motion to a few hundredths of a millimeter at the tool tip.

  4. Feed the slurry. A slurry (water mixed with abrasive grains such as boron carbide, silicon carbide or alumina) flows between the tool and the part.

  5. Chip. Each blow of the tool drives grains into the surface. Brittle material cracks off in microscopic chips; the tool itself never cuts directly.

  6. Feed and copy. A light, steady force pushes the tool down, so its exact negative shape sinks into the part. Fresh slurry carries the debris away.

Key facts

Materials
Hard, brittle materials: glass, quartz, sapphire, alumina and zirconia ceramics, silicon carbide, ferrite, carbides. Poor on soft, ductile metals.
Typical parts
Round and odd-shaped holes, slots, shallow cavities and engraving in brittle parts
Part size
Features from about 0.1 mm up to a few tens of millimeters; the tool face is usually small
Precision
Typically a few hundredths of a millimeter
Surface finish
Fine and matte, with no heat damage or burrs; smoother with finer grit, often Ra (average height of surface bumps) under 1 µm
Batch size it suits
From prototypes to large series (one part to 100,000 or more)
Tooling and machine cost
Tools are simple and soft (often low-carbon steel) but wear fast; machines from tens of thousands of dollars, more for CNC rotary versions
Speed
Slow: the tool typically advances a fraction of a millimeter to about a millimeter per minute

Strengths and limits

Strengths

  • Cuts glass, ceramics and gemstones without cracking them
  • Any hole shape, not just round
  • No heat, no chemical change, no burrs
  • Works on electrical insulators, unlike EDM and ECM

Limits

  • Slow, especially for deep holes
  • The tool wears and must be replaced or reshaped
  • Poor on soft, ductile metals, which dent instead of chipping
  • Deep holes taper, and slurry struggles to reach the bottom

Where it's used

  • ElectronicsHoles and slots in ceramic substrates, ferrite and quartz parts
  • OpticsShaped holes in glass, quartz and sapphire windows
  • AerospaceFeatures in technical ceramics and ceramic composites
  • Watchmaking and jewelryDrilling gemstones and sapphire parts
  • LaboratoriesGlass and quartz parts for scientific instruments

How to recognize it

  • Non-round holes (squares, stars, slots) cut into glass or ceramic.
  • Hole walls with a fine, frosted matte texture and no heat marks.
  • A slight taper in deep holes, and tiny chips along the exit edge.

Compare with

Sinker EDM6.6also copies a shaped tool into the part, but with sparks, so it only works on conductive materials.Waterjet cutting6.4also uses abrasive grains, but a jet carries them, cutting through-profiles rather than blind cavities.Grinding5.7abrasive too, but the grains are bonded into a spinning wheel instead of hammered loose.

Watch it

ADTW Study · An animation of the vibrating tool, slurry and cavity

Innovative learning of Engineering By MuthuKumar · The transducer, horn, tool and slurry feed explained

Berkness Company · Real footage from a machining shop

DMG MORI · The modern rotary variant: a spinning diamond tool that also vibrates

See real photos

Remember

  • A tool vibrating about 20,000 times a second hammers abrasive grains that chip away brittle material.
  • It is the shaped-hole method for glass, ceramics and gems, which drills and sparks cannot handle.
  • Look for odd-shaped holes in glass or ceramic with a frosted wall.

More in Cutting and non-traditional machining

All 100 processes
6.1Punching and shearingA punch shears shapes out of sheet against a dieOpen the lesson6.2Laser cuttingFocused light melts or vaporizes a narrow cutOpen the lesson6.3Plasma cuttingA superheated gas jet melts through conductive plateOpen the lesson6.4Waterjet cuttingVery high-pressure water, usually with abrasive, erodes a cutOpen the lesson6.5Wire EDMSparks from a thin moving wire cut through-profilesOpen the lesson6.6Sinker EDMSparks copy a shaped electrode into a blind cavityOpen the lesson6.7Electrochemical machining (ECM)Electrolysis dissolves metal in the shape of the toolOpen the lesson6.8Chemical machining and photochemical etchingA light-printed mask lets an etchant dissolve only bare metalOpen the lesson

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