Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
2001-04-06
2004-04-20
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S577000, C427S580000, C427S249170, C427S249180, C427S249190, C427S255320, C427S284000, C427S255394, C407S032000, C407S119000, C408S144000
Reexamination Certificate
active
06723391
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
Definitions
In the present specification hard material means 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. Metallic elements means 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, this means 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 %.
Machining cross section f a
r
means the product “Vorschub×schnitttiefe” {Advance×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).
German Patent DE 38 25 399 as well as European Patent 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.
The invention starts from the understanding that generally, tools have a hard material layer in their active edge region which is substantially, and within the scope of measurability, an unchanged material composition. In contrast, the composition of the hard material layer in the active edge region is changed relative to the hard material layer composition on the remaining tool regions according to the present invention. The invention proposes 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, working properties such as the service life of the tool or decrease of the tool wear, are improved.
According to the process of the invention, a hard material layer is applied onto the basic tool body but is selected for the specific stress the tool is meant to endure. 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 found that by changing or not changing the compositions of the hard material layers in the active edge regions as a function of the working purpose of the tools, that is, by either providing a hard material coating of constant composition or a hard material coating of varying composition in the active edge region, critical improvements were realized. If tools for given applications, are coated with the wrong coating technique of the two mentioned, often an impairment of the tools' working properties, in particular tool life, results.
It could be shown, for example, that according to EP 0 352 545 with a thinning-out of the coating only in a few fields of machining, better or at least equally good results can be achieved, compared to the application of corresponding toots 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 where two completely identical, except for stated coating difference, and identically coated drills are present. The phrase completely identical here means an application of the same coating processes, in particular arc or sputtering processes, on identical tool bodies, and the adjustment of the realized or not realized concentration difference 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.
It can be seen 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, for example, by the fact that precisely the aluminum depletion of the hard material layer in the active edge region has negative effects on 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 the hard material layer with aluminum component under specific conditions.
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 only a low or no longer measurable composition change of the material of the hard material layer in the active edge region, in many applications yield a substantially better service life, even with increased cutting efficiency, than other tools that are 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 when 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
, has the following range of values:
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 milling cutters and hobbing machines with as much as possible unchanged composition of the hard material layer in the active edge region, and front-end milling cutters and ball-end milling cutters with changed composition of the hard material lay
Derflinger Volker
Zimmermann Harald
Beck Shrive P.
Markham Wesley D.
Notaro & Michalos P.C.
Unaxis Balzers AG
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