Built up edge

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Schematic diagram showing a built up edge.

In machining, specifically cutting operations, a built-up edge (BUE) is an accumulation of material against the rake face that seizes to the tool tip, separating it from the chip.[1]

Formation

Because

micrometres thick) forms.[1]

The conditions necessary for a noticeable edge to build up are that:

  • the cutting speed is low.[2] This is because at high cutting speeds the metal moving away from the workpiece becomes hot enough to recover before seizing onto the tool, preventing the formation of a BUE.[3]
  • the metal being cut is one that work-hardens and is reluctant to recover.[2] A BUE will not form with pure metals since they do not work-harden much. Conversely, alloys, such as steel, do work-harden and recover less so they are prone to forming a BUE.[3]

Effects on the cutting process

The built up edge effectively changes tool geometry and rake steepness. It also reduces the contact area between the chip and the cutting tool,[1] leading to:

  • A reduction in the power demand of the cutting operation.[1]
  • Slight increase in tool life, since the cutting is partly being done by the built up edge rather than the tool itself.[4]

However, the formation of BUEs have negative effects on the quality of the workpiece,[1] specifically:

  • Excessive work hardening at the surface of the workpiece.[1]
  • Poor surface finish, since bits of the BUE eventually break off and stick to the workpiece. These bits tend to be problematic since, due to the work-hardening they underwent, they are very hard and so become abrasive.[1]
  • A reduction in the dimensional control of the process, due to the dynamically changing geometry of the cutting tool.

See also

References

  1. ^ a b c d e f g The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 14. Milton Keynes: The Open University.
  2. ^ a b The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 14 and 15. Milton Keynes: The Open University.
  3. ^ a b The Open University (UK), 2001. T881 Manufacture Materials Design: Block 2: Cutting, page 15. Milton Keynes: The Open University.
  4. ISBN 978-0-07-008769-9
    .
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