Cutters – for shaping – Comprising tool of specific chemical composition
Reexamination Certificate
1999-02-19
2001-06-05
Tsai, Henry (Department: 3722)
Cutters, for shaping
Comprising tool of specific chemical composition
C407S118000, C407S032000
Reexamination Certificate
active
06241431
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
In the present specification by hard material is understood a compound, namely a carbide, oxide, oxycarbide, but in particular a nitride, nitrocarbide, oxynitride or nitrooxycarbide, of at least two of the metallic elements listed in the following, in particular of Ti and Al. By metallic elements are understood Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and Al.
If within the scope of the present application reference is made to a change of the composition of the hard material layer material in the active edge region, by that is understood a difference of at least 2 at % of a hard material layer metal component between a hard material layer in the active edge region and a hard material layer in the remaining regions of the tool.
Analogously, no change exists if the stated difference is less than 2 at %, in particular less than 1 at %.
By machining cross section f a
p
is understood the product “Vorschub x Schnitttiefe” {Advance x cutting depth} according to DIN 6580, Section 11.1.1, “Bewegungen und Geometrie des Zerspanungsvorgang” [Motions and Geometry of the Machining Process] (DN 6580, October 1985).
DE 38 25 399 as well as EP 0 352 545 disclose coating tools by means of a vacuum process with a layer of hard material, and therein especially with a (Ti,Al)N hard material layer. The coating takes place such that in the active edge region, i.e. in the region of the cutting edges, the hard material layer material has a changed composition compared with that on the remaining tool regions: according to DE 38 25 399 as well as EP 0 352 545 at the active edge regions of drills a thinning out of the aluminum is realized which is distinguishable on the tools by the reddish or yellowish coloration of these regions. Thinning-out ratios of 5 at % or 2 percent by mass of the Al are declared.
SUMMARY OF THE INVENTION
The process discovered, namely to change the hard material layer composition in the active edge region, is fundamentally represented as a measure for attaining a significant improvement of the quality of the coating.
Building generally on tools in which the provided hard material layer in the active edge region has substantially, and within the scope of measurability, an unchanged material composition as well as on tools in which, in contrast to the first stated, the composition of the hard material layer in the active edge region is changed, each relative to the hard material layer composition on the remaining tool regions, it is the task of the present invention to propose a process for the protective coating of machining tools as well as a set of at least two tools, by means of which substantially improved specific working properties are attained. In particular, as a working property to be improved is understood the service life of the tool or the decrease of the tool wear.
According to the process of the invention, onto the basic tool body a hard material layer is applied in any case but, specific to the tool stress, the composition of the hard material layer in the active edge region is either left with minimum changes relative to the composition of the hard material layer in the remaining coating regions on the tool basic body or is intentionally changed. The former, i.e. constant composition, is realized if the primary requirements to be made of the tools relate to adhesive strength of the hard material layer and only secondarily to hardness of the hard material layer. The second, in contrast, is realized if the primary requirements to be made of the tools relate to hardness of the hard material layer and only secondarily to adhesive strength of the hard material layer.
According to the invention it was consequently found that the estimating, previously described effective specifications of changed or unchanged compositions of hard material layers in the active edge regions of machining tools are not permissible, that namely, as a function of the working purpose of the tools, one time a hard material coating of constant composition and another time a hard material coating of varying composition in the active edge region in practice, i.e. when applying the tool, only leads to critical improvements: If tools for given application conditions are coated with the wrong coating technologies one of the two mentioned, therewith often an impairment of its working properties, in particular tool life, is obtained.
It could be shown, for example, that according to EP 0 352 545 with a thinning-out of the coating only in a few application fields of machining working better or at least equally good results can be achieved, compared to the application of corresponding tools with a lower or no, at least not measurable, difference in the concentration of the hard material layer. It should be pointed out in particular that the example mentioned in EP 0 352 545 with respect to service life of twist drills, based on the representative comparisons made according to the present invention, is erroneous in the case two completely identical, except for stated coating difference, and identically coated drills are present. By completely identical is therein understood the application of the same coating processes, in particular arc or sputtering processes, on identical tool bodies, and the adjustment of the realized or nonrealized concentration difference takes place exclusively by adjusting the voltage applied on the basic tool body during the coating with respect to ground or reference potential, referred to as bias voltage U
bias
in the following, and/or of the reactive gas partial pressure P
reactiv
in the vacuum coating receptacle with further process parameters remaining unchanged.
That the prior known thinning-out in the active edge region can effect critical disadvantages in the use of the tool, and that consequently it is necessary to assess very carefully according to the invention which process is applied at which time, can be seen, for example, by the fact that precisely the aluminum depletion of the hard material layer in the active edge region has negative effects on the wear through thermal stress of the hard material layer since through the aluminum thinning-out potentially now less aluminum reaches the surface of the hard material layer through diffusion and no continuous thermally insulating aluminum oxide layer can be formed there. The Al
2
O
3
layer on the surface is simultaneously worn out during the working process and formed again through Al diffusion. But precisely this phenomenon can critically influence the durability of a provided hard material layer with aluminum component under specific conditions of application.
According to the invention as explained in the following examples, it could be shown that tools with a hard material layer, in particular a (Ti,Al)N layer, comprising at least only a low or no longer measurable composition change of the material of the hard material layer in the active edge region, in many application cases yield a substantially better service life, even with increased cutting efficiency, than other tools, otherwise identical, with a composition change of the hard material layer in the active edge region. Especially good results can be achieved, in the case given first, if in the active edge region the change of one of the metal components of the hard material layer is less than 2 at %, preferably it is maximally 1 at % or no longer measurable.
Following another feature of the invention, when using arc vaporization for depositing the hard material layer, an as much as possible unchanged hard material layer composition in the active edge region is attained thereby that for the ratio U
BIAS
—of the electric basic tool body voltage relative to reference potential, usually ground potential, —to the partial pressure of the reactive gas p
reactiv
the following range is maintained:
1×10
−3
≦U
BIAS
/ p
reactiv
≦4×10
3
,
with the unit of voltage being “volt” and the unit of pressure “mbar”.
Furthermore the invention produces drills, roughing milling cutters, peripheral millin
Derflinger Volker
Wohlrab Christian
Zimmermann Harald
Notaro & Michalos P.C.
Tsai Henry
Unaxis Balzers Aktiengsellschaft
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