What Does 'Ductility' Mean?

The ability of a material to deform plastically without fracturing, is called ductility. 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 work piece. This can result in persistent burrs attached to the work .

Ductility arrives in our shops as indicated by burrs.

Ductility can also mean long stringy chips that can form a dreaded "birds nest" engulfing the tool and work piece.

Birds nest chips present a very real danger to operators. Ductility can hurt!

Long necklace chips are another sign of ductile materials in machining.

Long continuous chips resulting from ductile material can be controlled to keep them away from work piece and tool.

Short chips curled into "sixes and nines" showing a bit of heat discoloration are typical of less ductile materials and dutile materials machined at proper parameters using chip breakers 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, chip breakers, and high pressure coolant can be considered.

Dialing in the appropriate feeds, speeds and depth of cut are crucial too.

Birdsnest photo courtesy Garage Journal

All other photos by author.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which you can finish reading here.