Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 Background and Brief Description OI Invention
It is known in the art of manufacturing gears to
utilize cuttin~ to~ls which have two basic forms of
cutting blades included on the tool for contacting a
workpiece. A first type of cutting blade is designed
to form a rough tooth slot in a work blank and is
referred to as a "roughing" cutting blade or tool. The
second type of cutting blade is designed to complete
the specific geometry of the tooth form of the gear
being manufactured, and this type of blade is referred
to as a "finishing" cutting blade or tool. A typical
tool which includes both forms of cutting blades and
which is designed for manufacturing straight bevel
gears is illustrated and discussed in Wildhaber, et al,
U.S. Patent 2,620,709 dated December 9, 1952. This
patent provides information about the type of
cutting tools which are the subject of this specification.
~ n recent years, there has developed an interest
in treating cutting tools in some way to extend the
life of the tool and to permit higher cutting speeds
and greater productivity. Various forms of coating
treatments are now available and offer varying degrees
of improvement in tool life, cutting speed, and/or
quality of finish. However, it has no~ been learned
that ~he use of coating materials sometimes changes the
basic cutting characteristics of known cutting tools so
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as to introduce changes in the tooth geometry or finish
of a given gear-cutting job. In the case of the
cutting tools of the type described above in which
roughing and finishing blades are included on a single
cutter body, it has been necessary to provide considerable
adjustment in machine settings in order to compensate
or modifications in tooth geometry or fin~sh introduced
by the use of coating materials on the cutting blades
themselves. This requirement for machine adjustment
reduces the desireability of using coating materials
because many of the set-up procedures for given machines
operating to produce specific forms of gears are well
known and established in manufacturing plants and would
be subjec-t to extensive monitoriny to compensate for
changes introduced by coated cutting tools. Thus, a
manufacturing operation would not only have to adjust
machines according to whether coated or uncoated cutting
tools were being used, but would also have to create
a system for assuring that such adjustments are made
at the appropriate times. This would result in aaditional
lost time between production runs and could lead to
possible scrap losses for work performed with incorrect
settings. ~urthermore, it has been found, in certain
instances, to be nearly impossible to fully adjust for
the errors introduced by otherwise very acceptable
coating materials in the specific Gleason machines
which utilize the type of cutting tool disclosed
herein.
The present invention involves a rather remarkable
discovery that substantially all of the expected
advantages of coating of tools (e.g., increased tool
life, higher speed cutting, and improved quality
of finish) can be obtained with presently known coating
materials if the coating material is applied only to
the roughing cutting blades of the tool and not to the
finishing cutting blades of the tool. Thus, the
roughing cutting blades which are removing substantial
amounts of metal from a work blank are provided with
the additional advantages obtained with the use of
coating materials, while the finishing cutting blades,
which remove very little material, are able to finish
the gear teeth profiles to precise and known geometric
profiles without a need for adjusting machines from
their traditional settings for doing a particular job.
Thus, even though the discovery is a relatively simple
concept, it is one which has significant impact on the
ease with which production machines can be used ~or
manufacturing various types of gears. Productivity can
be increased without sacrificing quality of finish or
precision of shape, and all of this can be done without
a need for relearning specific machine settings for a
specific job. In addition, the invention produces the
quite unexpected result of providing for all of these
benefits through a use of a lesser amount of expensive
coating material since only the roughing blades of a
given process need be coated in accordance with the
discovery of this invention.
These and other features and advantages of the
invention will be discussed below where reference will
also be made to the accompanying drawing as briefly
described below.
Brief Descri tion of Drawin
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The drawing shows an elevational view of a typical
cutter head having roughing and finishing cutting
blades incorporated in its structure.
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Detailed Description of Invention
Referring to the drawing, a typical cutting tool
is illustrated. The tool includes a cutter body 10
upon which are secured a number of cutting blade
segments 11 and 12. Each cutting blade segment is
designed with a plurality of cutting blades extending
outwardly therefrom so that an assembly of a number of
such segments on a cutter body 10 produces a tool of
the t~pe shown. Such tools are well known in the art
ancl are mounted for rotation on well known machinery
which provides for a rotation of the tool relative to a
workpiece mounted on a spindle. In addition, relative
transversing motion is provided between the tool ana
the workpiece so that the rotating tool can advance
along the length of a tooth slot being formed. In
this way, a completed tooth slot can be formed with
a single rotation of the tool.
Tools of this type are designed to include a
number of roughing cutting blades 14 arranged in series
about one portion of the cutter body 10 together with a
number of finishing cutting bla~es 16 arranged in
series about a different portion of the cutter body 10.
In the illustrated embodiment, forty-four roughing
cutting blades 14 are carried on eleven blade segments
11, while twenty finishing cutting blades are carried on
five blade segments 12. In addition, although not
pertinent to the present invention, the tool may be
provided with a chamfering device 18 positioned between
the two series of cutting blades.
- 30 In accordance with the invention, it has been
discovered that only the roughing cutting blades 14
need be coated with a material to increase their
hardness for improving tool life and cutting speed. In
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fact, by not ~oating the finishing cutting blades with
the same material, it has been discovered, quite
unexpected]y, that the overall speed and precision of
the process can be greatly improved. Thus, the finishing
blades 16 are left in their sharpened condition without
a need for additional treatment of the type provided
for the roughing cutting blades which are illustrated.
As an example of a specific coating material that
may be applied to the roughing blades, the following
has been used successfully:
1~ Titanium Nitriae (TiN) was applied to a
twenty-one inch (di~neter~ cutting tool
manufactured from M2 steel. Coating was
applied by a known physical vapor deposition
process at ab~ut 1000 degrees F. Distortion
was minimized (tool tolerance requirements
were on the order of 0.0002 inches).
2. The coated tool was tested on a Gleason
No. 725 REVACYCLE machine on a standard
production job. The machine was operated
so as to rough and finish each tooth slot in
a single pass of the tool relative to the
workpiece.
Although the invention has been described with
reference to a specific form of cutting tool which can
be greatly improved through the use of a coating on
only its roughing blades, it is contemplated that the
basic relationship between roughing ana finishing tools
can be maintained in other processes and with other
forms of equipment. For example, tools of the type
illustrated are also manufactured with only roughing
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blades on a single cutter body and with only finishing
blades on a single cutter body. In accordance with the
basic discovery of this invention, it would be possible
to provide a coating on only the cutter body having the
roughing blades for forming the roush tooth slots on a
gear blank while omitting any use of coating on a
separate cutter head ~7hich carries only finishing
blades. These and other variations are intended $o be
includea within the scope of this invention as more
completely defined in the claims which follow.
