The Meaning of Ductility
In order to successfully deal with ductile materials, strategies such as chip control features on inserts, wiper style inserts, through tool coolant, interrupted cuts, chip breakers, and high pressure coolant can be considered.
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Ductility arrives in our shops as indicated by burrs.
Ductility is the ability of a material to deform plastically without fracturing. In the materials usually machined in our shops, ductility is measured by determining the percent of elongation and the percent reduction of area on a specimen during a tensile test.
Ductility is often indicated by chip control issues in certain steels, as the chip readily deforms, but does not separate from the workpiece. This can result in persistent burrs attached to the work.
Ductility can also mean long, stringy chips that can form a dreaded “birds nest,” engulfing the tool and workpiece. Long necklace chips are another sign of ductile materials in machining (see below).
Short chips curled into “sixes and nines” showing a bit of heat discoloration are typical of less ductile materials and ductile materials machined at proper parameters using chipbreakers and high pressure coolant delivery.
Chips that look like sixes or nines showing a bit of heat discoloration are desired for safe practice.
In our machining practice, we would prefer materials that are “crisp” rather than ductile. In order to successfully deal with ductile materials, strategies such as chip control features on inserts, wiper style inserts, through-tool coolant, interrupted cuts, chipbreakers and high pressure coolant can be considered. Dialing in the appropriate feeds, speeds and depth of cut are crucial, too.
