What is N material group?
Aluminum is a malleable, silvery-colored metal. It is remarkable for its resistance to oxidation and low density. It represents on average 8% of the mass materials from the solid surface of our planet. Aluminum is too reactive to exist in its native state in the natural environment: on the opposite, it is found in combined form in more than 270 different minerals, its main mineral being bauxite.
Aluminium alloys have become desirable materials to address the weight reductions required by the
transportation industry. When pure, aluminium is soft and corrosion resistant material. Alloying with
elements like copper or magnesium for example provides the materials with higher strength properties.
Silicon is added to give the aluminium alloy an abrasion resistance, but these results in a high wear
rate of the insert if the cutting speed is not reduced.
ISO N Pentagram
Seco classifies the machinability of materials based on 5 important properties: abrasiveness, ductility, strain hardening, thermal conductivity and hardness.
ABRASIVENESS, is defined as variations in hardness caused by alloying elements that are able to form hard carbide, oxide and intermetallic particles. This results in excessive wear on the cutting edges. Some examples of highly abrasive materials are Ni‑ alloys and carbon fibre reinforced plastics.
DUCTILITY, which results in adhesion and built‑up edge, refers to a high elongation at fracture for a material. This is one of the key difficulties in machining aluminiums and titanium alloys.
STRAIN HARDENING occurs when cutting hardens a surface in comparison to the bulk material. This is a well‑known challenge to overcome when machining Ni‑based alloys.
THERMAL CONDUCTIVITY refers to heat conduction of the material. The lower the thermal conductivity of a workpiece material, the more the heat will concentrate on the cutting edge, which results in excessive cutting edge temperatures.
HARDNESS is a material’s resistance to deformation. The higher the hardness, the greater the force needed to deform the material. High hardness results in high heat generation as well.
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Basic guidelines for ISO N materials e.g. for aluminium machining:
- The ductility and adhesive nature of these materials towards cutting materials are your main concern (leading to build up edge wear and cracking of the cutting edges)
- Use big depth of cut and high feed
- Use high cutting speeds to avoid as much as possible the formation of build-up edges on the cutting tool
- Use dedicated carbide grades and sharp cutting geometry
- Emulsion cooling is advised, JETSTREAM cooling gives good results
ISO N Tab extract
Inline Content - Survey
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