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Manufacturing Processes > Machining processes > Honing

 

Honing

 

Process description

The removal of small amounts of material by floating segmented abrasive stones mounted on an expanding mandrel, which rotates with low rotary speed and reciprocates along the surface of the workpiece.

Materials

All materials, including some ceramics and plastics.

Honing

Process variations

  • Horizontal and vertical honing machines with single or multiple spindles, are with either short or long stroke capability.
  • Honing can also be performed on lathes and drilling machines.
  • Internal and external cylindrical surfaces are honed commonly. Also, spherical, toroidal and flat surfaces can be honed, but are less common applications.
  • Single-stroke bore finishing and superfinishing using ‘superabrasives’ such as diamond and CBN, are related processes. Superfinishing is similar to honing, but performed on outside surfaces previously ground or lapped to improve finish.
  • Laser honing: for precise surface topographies.
  • Large range of stone geometries, abrasive materials, grain size, hardness grading, bond types and methods (co-axial and match honing) are available.
  • Automation aspects include in-process gauging and adaptive control to optimize cutting conditions and control accuracy.
  • Workpieces can be manually presented to honing mandrel.

Economic considerations

  • Production rates ranging 10–1000/h depending on number of spindles. Typically 60/h for single spindle machines.
  • Lead times short.
  • Very little material removed.
  • Suitable for all quantities.
  • Tooling costs varying, depending on degree of automation and size.
  • Equipment costs moderate.
  • Direct labor costs moderate. Skill level required is moderate to high (manual).
  • Finishing costs very low. Cleaning only required.

Typical applications

  • Any component where superior accuracy, surface finish and/or improvement of geometric features required on cylindrical features
  • Bearing surfaces
  • Pin and dowel holes
  • Engine cylinder bores
  • Rifle bores

Design aspects

  • Honing is performed to remove the minimum amount of material, usually between 0.02 and 0.2 mm.
  • Complexity is limited to nature of workpiece surface, i.e. cylindrical (internal and external), spherical, flat or toroidal.
  • Honing logically follows the grinding process to produce precision surfaces.
  • Surface features should be kept simple.
  • Chamfers are required on entrance to bores to facilitate easy access of honing tool.
  • Blind holes should have undercuts.
  • For small holes less than Ø15 mm, the maximum length that can be honed is 20 times the diameter of the hole. For best results, a length to diameter ratio of 1 is recommended.
  • Maximum length for large holes is 12 m.
  • Sizes ranging Ø6–Ø750mm+ for cylindrical honing

Quality issues

  • Interruptions on the workpiece surface, for example key seats and holes, reduce the quality of finish. Can be offset by increasing rotary speed of honing stone.
  • The process has the ability to correct geometrical inaccuracies, for example, bell-mouthing, barreling, tapers and waviness in holes, as well as removing machining marks.
  • Surface finish and accuracy is controlled by the stone grain size, feed pressure, area of contact, coolant access, stroke length, rotary speed and stone reciprocation speed, which when optimized ensure breakdown of the stone and good self-dressing characteristics.
  • Coolant also helps flush swarf from cutting area in long through holes, and blind holes.
  • Little heat is generated at surface, therefore, original surface characteristics of the component not altered.
  • Surface detail is excellent.
  • Surface roughness values ranging 0.025–1.6 µm Ra are obtainable.
  • Relatively soft and flexible materials tend to give inferior surface finish to hard materials.
  • A process capability chart showing the achievable dimensional tolerances is provided.

costing