METHOD OF MAKING ENDMILLS

PROCEDE DE PRODUCTION DE FRAISES

English Abstract

The present invention relates to an endmill provided with cutting edges of cBN
or PCD and consisting of a shank part and a part containing the cBN or PCD
brazed to the shank. The latter part is in the form of a disc in which the
superhard material is present in a groove in the envelope surface and extends
from one end surface to the other. After brazing the disc to the shank, the
body obtained is ground to an endmill with cutting edges formed of superhard
material. In a preferred embodiment, the shank is provided with a tenon
against which the part containing the superhard material is brazed. This
minimises the risk of braze joint failure and provides an endmill with several
cutting edges which can be achieved at a low cost.

French Abstract

L'invention concerne une fraise dotée d'arêtes de coupe en nitrure de bore cubique ou en diamant polycristallin, comprenant une partie queue et un élément contenant le nitrure de bore cubique ou le diamant polycristallin. Cet élément, fixé à la queue par brasage, a la forme d'un disque dans lequel le matériau extra-dur est présent dans une rainure pratiquée à la surface de l'enveloppe et s'étend de la face d'une extrémité à la face de l'autre extrémité. Une fois le disque fixé à la queue par brasage, le corps ainsi obtenu est usiné pour donner une fraise dotée d'arêtes de coupe en matériau extra-dur. Dans un mode de réalisation préféré, la queue est dotée d'un tenon sur lequel l'élément contenant le matériau extra-dur est fixé par brasage. Cela réduit le risque de défaillance aux points de brasage et permet la fabrication à faible coût d'une fraise pourvue de plusieurs arêtes de coupe.

Claims

4
Claims
1. Endmill provided with cutting edges of cBN or PCD
and consisting of a shank part and a part containing the
cBN or PCD brazed to the shank characterised
in that said shank is provided with a tenon against
which the part containing the superhard material is
brazed.
2. Endmill according to the preceding claim
characterised in that said tenon is round.
3. Endmill according to claim 1
characterised in that said tenon is tapered.
4. Endmill according to claim 1
characterised in that said tenon is of
non-round shape.
5. Endmill according to claim 1
characterised in that said tenon extends at
least part way into the part containing the superhard
material.
6. Method of making an endmill provided with at
least one cutting edge of cBN or PCD and consisting of a
shank part and a part containing the cBN or PCD
characterised in comprising the steps
providing a cemented carbide disc preferably with a
cylindrical cross section provided with at least one
body of a superhard material in a groove in the envelope
surface and extending from one end surface to the other
brazing said cemented carbide disc to a shank
grinding the obtained body to form an endmill with
cutting edges formed from the superhard material.
7. Method according to claim 6
characterised in that said cemented carbide
disc is made using the following steps
providing a cemented carbide bar
grinding at least one groove in said bar

5
filling said groove with a powder mixture containing
cBN and/or diamond
heat treating said cemented carbide bar at a
temperature and pressure where cBN and/or diamond is
stable and cutting said bar into discs.
8. Method according to claim 6
characterised in said cemented carbide disc
is made using the following steps
providing one or more cemented carbide discs
grinding at least one groove in said discs
filling said groove in said discs with a powder
mixture containing cBN and/or diamond
heat treating said cemented carbide discs at a
temperature and pressure where cBN and/or diamond is
stable whereby the discs are separated from each other
in such a way that they do not sinter together.
9. Method according to any of claims 6 - 8
characterised in the step of brazing said
shank part to the part containing the superhard material
with the aid of a tenon formed in the end of said shank
part and a hole extending at least partway through said
part containing the superhard material.
10. The product according to any of claims 6 - 8.

Description

CA 02290023 1999-11-09
WO 98/56528 PCT/SE98/01113
1
Method of making endmills
This invention relates to an endmill with cBN (cubic
boron nitride) or PCD (polycrystalline diamond) in the
cutting edges and a method of making the same. The
purpose of the method is to decrease the cost compared
to existing methods.
An endmill is used for machining of grooves, pockets
and slots and consists of a cylindrical holder with
cutting means at the end. It can be made of high speed
steel, or solid cemented carbide, but it can also
consist of a steel holder with cemented carbide inserts
as cutting means. For certain applications metal cutting
inserts having cutting edges formed of a superhard
material, such as PCD, are usually used for the
machining of non-ferrous alloys such as brass, magnesium
and aluminium, and the like, whereas inserts with
cutting edges formed of a superhard abrasive, such as
cBN are usually used for the machining of cast iron and
hardened steel and the like.
There are several types of PCD or cBN endmills on
the market today. Essentially there are two different
methods to manufacture them. One method includes
sintering cBN or diamond powder under elevated pressure
and temperature into a solid cylindrical body which is
then brazed onto a shank and finished into an endmill.
The other method includes bonding a layer of cBN or
diamond under elevated pressure and temperature to a
substrate, usually a cemented carbide disc, from which
smaller pieces, "chips", are cut out. These chips are
then brazed onto a cemented carbide rod and ground to
the finished shape. Tools produced that way are normally
quite expensive due to the many steps the product must
undergo before it is finished.
CONFIRMATION
coPY

CA 02290023 1999-11-09
WO 98/56528 PCT/SE98/01113
2
The object of the present invention is therefore to
provide a method, where an endmill with several cutting
edges can be achieved but at a substantially lower cost.
Fig 1 shows the principle of the method where
1 is the element that will form the cutting part,
2 is the shank
3 is the braze joint and
4 is a tenon
5 is a top view of the element 1 after shaping to
expose the cutting edges.
According to the method of the present invention the
starting point is a cemented carbide disc preferably
with a binder phase content of >10 wt-% provided with
superhard bodies according to the teachings of US
5,676,496. The cemented carbide disc is made from a
cemented carbide rod with a circular, square, triangular
or other suitable cross section preferably with a center
hole. Into this rod one or more grooves are ground
throughout its whole length and parallel to its axis.
The groove can be straight but it can also be helical.
The number of grooves and their location depend on the
type of disc that is to be produced. The shape of the
grooves can be made in different ways. It is important,
however, that they have a rounded or plane shape. Their
size shall be such that the cutting work essentially is
performed by the superhard material. After HP/HT
sintering the rod is cut into discs of desired
thickness.
Alternatively, in one or more cemented carbide discs
at least one groove is ground and filled with a powder
mixture containing cBN and/or diamond after which the
discs are treated at a temperature and pressure where
cBN and/or diamond is stable. During this treatment the
discs are separated from each other in such a way that
they do not sinter together.
I I T

CA 02290023 1999-11-09
- WO 98/56528 .~ PCT/SE98/01113
The shank 2 is preferably made in cemented carbide
preferably with a binder phase content of >10 wt-%. The
diameter of the shank is somewhat smaller than the
diameter of the disc with superhard materials. The other
end of the shank is provided with clamping means.
The PCD/cBN disc is then brazed together with the
shank.
In a preferred embodiment the end of the shank where
the PCD/cBN disc is brazed is ground down to form a
tenon, 4. The shape of the tenon is generally
cylindrical but it may alternatively be tapered, square,
triangular, elliptical or other non-round shape. The
diameter (or equivalent) of the tenon is about 15 - 40
of the diameter of the shank and is designed to fit
within the center hole of the disc 1 although the tenon
does not have to extend through the entire length of
that center hole.
The PCD/cBN disc is then brazed together with the
shank using the tenon as guide and braze joint, 3. It is
according to the invention essential that brazing is
made only at the tenon. This will minimise the risk of
braze joint failure.
After brazing the tool obtained is ground in such a
way that cutting edges are formed from the superhard
bodies as shown in the top view 5 of Fig 1.

Representative Drawing