New technology addresses insert wear resistance, toughness dilemma

Achieving greater productivity and improving competitiveness is

important across all of manufacturing. Within the metalcutting

industry, research and development efforts continue to be focused on

developing increasingly productive technologies. Successes have come

over the years with frequent incremental increases in machine tool,

toolholding and cutting tool capability.

For example, advancements in machine tools have been noticeable and

numerous. Today’s equipment is capable of higher speeds, machining in

multiple axes, quick tool change, multi-spindle capability and much

more.

Toolholding, the critical connection between machine and tool, can be

accomplished using a number of methods and continues to improve,

providing accuracy and runnout in the tenths of thousandths. And,

cutting tools continue to evolve for all materials and intended

applications.

In the past, advancements in cutting tool technology have typically

been incremental. A new geometry, a new grade, a new coating on a

cutter body… all designed to improve quality, productivity or reduce

cost.

However, a recent introduction in the world of indexable carbide that

is much more than a slight improvement has been pioneered by Seco. The

tool is a coated cemented carbide grade developed for steel turning

that is providing results that are more revolutionary than evolutionary

for this significantly large and important market segment. However, the

real development was in the process used to develop the coating.

Metallurgists at Seco Tools have developed a methodology that

dramatically increases both the toughness and wear resistance of a

cutting insert-two features that have always been diametrically

opposed. In the past, in order to achieve improvement in one of these

properties you had to sacrifice at least some of the other. The ability

to increase both simultaneously virtually defied science.

Historically, aluminum oxide has been a consistent and proven coating

for steel turning applications. There are two different forms or phases

of aluminum oxide used for coatings: kappa and alpha. The difference

between the two forms is the crystal structure; the way the atoms are

arranged in the material.

When developing cutting tool (coating) materials, it is preferable to

use the alpha form of aluminum oxide for most applications. However, it

is much easier to deposit the kappa form. Consequently producers have

deposited the kappa form and then heat-treated it to transform it to

alpha. Unfortunately, this heating process results in a contraction in

volume, resulting in the formation of cracks in the coating.

There are a number of approaches to improving the performance of coated

products. Fine adjustments to the chemistry in the coating furnaces,

more careful structural control of the individual coating layers (as

there are numerous layers typically applied in both CVD and PVD

coatings), top and bottom grinding of the coated inserts and even

polishing the edges after coating. All are designed to provide

potential productivity and/or reliability gains to the end user.

For example, one reason that cutting tool manufacturers polish insert

edges on certain grades is to remove modest defects that naturally

occur during the coating process. This process is generally thought to

improve the smoothness and residual stress state of the cutting edge as

well as to reduce chip drag.

However, Seco’s new coating technology has made the polishing process

unnecessary. By carefully modifying the coating process, Seco has

learned how to control the crystal growth to improve both toughness and

wear resistance. This new methodology has been coined the Duratomic

process. This coating is more durable than other forms and provides the

user with a new level of toughness and wear resistance.

Essentially, this is a structural alteration of the aluminum-oxide

layer to create a coating that offers both long life and increased

cutting capability. Although these modifications are microscopic, the

results are impressive. Conventional aluminum oxide coatings have a

hardness of about 27.5 (GPa). Duratomic hardness is closer to

30.5(GPa), nearly an 11% increase. This translates directly to an

increase in abrasion resistance and, therefore, tool life. The coating

also runs cooler providing a full 35° centigrade reduction in a typical

application, enough to substantially reduce the tendency for the insert

to crater.

This article was supplied by Seco Tools, Fagersta, Sweden.secotools.com