Machining ductile cast iron is getting much easier thanks to a new coated-carbide insert.

In machining ductile iron, Carboloy's TX150 turning-grade insert improves tool life, while resisting deformation and edge chipping.

Ductile cast irons are gaining in popularity and rapidly replacing gray cast iron and some low-strength steels. This increased use, especially in the automotive, heavy-duty equipment, and non-automotive transportation industries, has sparked the development of an insert specifically for the often tough-to-machine material.

Ductile cast irons have compositional similarities to gray cast iron, but generally contain additions of silicon, magnesium, and/or cerium needed for nodularization of the graphite content. Typically, ductile irons also contain substantial amounts of pearlite. Since there is a close relationship between pearlite content and material hardness, ductile iron will, in many cases, be both harder and less machinable than gray cast iron.

When machining either ductile irons or gray cast irons with a conventional wear-resistant coated cutting grade, microchipping invariably occurs and the cutting edges rapidly lose their sharpness. On the other hand, use of a conventional tough-coated grade will often result in rapid wear or plastic deformation of the substrate.

New cutting grade meets the needs
Introduced by Carboloy Inc., Detroit, TX150 is a new coated-carbide turning-grade insert specially developed for machining ductile irons. It is also effective with gray cast irons and high-strength alloy steels. TX150 grade inserts come with either a flat-top geometry or Carboloy's M5 chipgroove, which is a general-purpose groove to handle heavier cuts typically taken in cast irons

Cutting capabilities of Carboloy's TX150 grade are derived from two components. The first is a hard, deformation-resistant substrate well suited for machining cast irons. The second is a multi-layer coating that contains a thick film of highly wear-resistant titanium carbonitride applied by a new coating technique called medium temperature chemical vapor deposition (MTCVD). Because of MTCVD, the coating provides a free cutting edge with traditional CVD-coating hardness without compromising edge toughness.

In combination, the substrate/coating properties impart high resistance to both plastic deformation and edge chipping. These same properties also improve tool life in high-strength alloy steel applications.

Tests confirm capabilities
In applications on ductile irons, the TX150 turning-grade insert met the demands of machining 80- 55- 06 ductile iron and extended tool life. For example, while external turning and facing a differential housing at 525 sfm, feed of 0.02 ipr, and a 0.120-in. doc, the new insert tripled tool life against a competitive CVD-coated grade.

In another situation involving internal turning of a differential housing, TX150 inserts made a 0.04-in. doc at a cutting speed of 500 sfm and a feed of 0.015 ipr. Tool life increased by 50% over Carboloy's own universal grade. The new grade was also tested against a competitive CVD-coated grade in a rough O.D.-turning operation on a drive-train slip yoke. At a spindle speed of 750 rpm and a feed of 0.016 ipr, the TX150 grade extended tool life 11 times that of the currently used grade. Operators previously machining 10 parts per index were able to average 114 parts per index. The result was an 87% reduction in insert costs and a 90% reduction in total production costs when down-time for insert indexing was factored in.