Comb crack

A comb crack is a multiple crack formation on cutting tools across the cutting edge, reminiscent of a comb . Comb cracks are stress cracks that occur as a result of strong temperature differences when cutting machine tools with interrupted cuts : the tool is heated during the cut, while the air or cooling lubricant cools it down considerably when it is idle between cuts .

The development of comb cracks is explained as follows: In the cutting wedge , the heat from the cutting creates a temperature gradient. There are compressive stresses in the surface layer and tensile stresses in the underlying layers of the tool material because the heated surface layer can only expand to a limited extent. The tension is reversed when it cools down. As soon as the elastic limit is exceeded, the surface tensions lead to plastic compression when heated and to plastic expansion when cooled . These periodic deformations cause cracks along the temperature gradient to form on the surface, which progress into deeper layers.

literature

• Herwart Opitz: Investigations into the use of hard metals in roughing and finishing milling of steel with cutter heads, Springer, Wiesbaden 1966, pp. 12-16. ISBN 978-3-663-07448-9

Web links

• Comb cracking (accessed July 2, 2020)
• Basics of machining - engineering book (accessed July 2, 2020)
• Assessment of wear and errors in turning (accessed July 2, 2020)
• Machining technology glossary German - English (accessed July 2, 2020)
• Machine tools (accessed on July 2, 2020)