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Melin’s Harder Tool Coatings

Melin’s Tool coatings available from Cutting Tools Chicago aka General Cutting Tools, harder than AlTiN coatings are applied via a process that combines AlTiN particles with an amorphous silicon nitride (Si3N4) matrix.

Seeing is believing, but it may require testing first.  That was the case for toolmaker Melin Tool Co. when it was presented a coating called nACo, which the coating company said was harder, more wear resistant and had a higher hot hardness than AlTiN.

Melin Tool performed in house tests on nACo, which refers to nanocomposite, applying the coating to a series CCMG 45 six flute end mill for cutting hardened steel and comparing its tool life to the same style end mill coated with AlTiN.  “We found about a 27 percent increase in tool life with the nACo coating,” said Mike Wochna, Melin Tool’s president.

Also, the nACo coated tool had a hardness of 45 GPa vs. 38 GPa for the AlTiN coated tool.  “It creates a harder surface,” Wochna said of nACo.

Besides end mills, Melin Tool offers the nACo coating on its high performance, through coolant drills and ball nose end mills for making dies and molds.  All three types of tools are made from 91 HRC solid carbide and are for cutting work piece materials of about 45 HRC to 65 HRC.  In all cases, the tools are usually for cutting hardened steel, cast iron, high-silicon aluminum and superalloys.

Moreover, nACo has a high hot hardness.  As a nanocomposite coating, it can withstand heat up to 1,200°C before it starts to oxidize and break down.

Filling the Spaces

nACo’s hardness results from its nanocomposite structure.  The coating consists of nanocrystalline AlTiN grains embedded in an amorphous Si3N4 matrix.  According to the coating and coating equipment company, Platit AG, Grenchen, Switzerland, this structure increases hardness partly because the matrix acts as a diffusion barrier, preventing the grains from growing.  “The smaller the grains, the higher the hardness,” said Bo Torp, sales manager of Platit Inc., Libertyville, IL.

The matrix also contributes to the coating’s hardness.  Torp compared the grain and matrix to wet sand.  On a beach, a person’s feet usually sink into dry sand, but they won’t sink, or sink as far, in wet sand.  The reason is the space between the grains is occupied by water, not air.  Consequently, wet sand has a higher resistance, is harder.  Likewise, the matrix occupies the space between the grains and makes the coating harder.

nACo’s nanocomposite structure can increase a machine shop’s productivity and reduce its costs.  “You can improve feeds and speeds, or you can start running dry,” Torp said.

Melin Tool applies the coating in house with a Platit Pi80 coating machine.  Torp estimated that the coating is appropriate for 90 percent of carbide tools.  He added that it’s mainly unsuitable for HSS tools because the substrate usually is not hard enough to sustain the coating.  nACo, however, can be applied to other styles of cutting tools and can be used when cutting different work piece materials.

General Cutting Tools is an authorized distributor for Melin Tools.

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