Note: Descriptions are shown in the official language in which they were submitted.
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FORENADE FABRIKSVERKEN
Forging blank for an internal threaded cylinder.
The present invention concerns a forging blank for an internal threa-
ded cylinder which is to be produced by cold forging around an external
threaded mandrel. By cylinder means in this case any kind of tube or part
of a tube of steel or other metal suitable for cold forging.
Internal threads in tubes or cylinders have earlier been produced
by turning or other cutting methodsi It has also been possible to produce
them by cold forging or hammering whereby a tube or cylinder shaped work-
piece is cold forged around an external threaded mandrel, which is later
removed from the tube or cylinder.
Cold forging involves several advantages compared to cutting methods.
By cold forging, a finer surface finish can be achieved than with cutting
methods, the material becomes harder as metal fibers are not cut, internal
stresses from earlier handling are eliminated, practically any type of
form of thread can be produced to extremely fine tolerances and cold forged
products are produced with an even and high quality etc.
In many cases with internal threaded tubes or cylinders, a starting
cone to the thread is required, specially where joining sleeves for rods
such as drilling rods are concerned, and it is required that the cylinder
screws easily to the rod. Earlier methods have been to grind, turn or in
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other ways produce the threads starting cone. Grinding or turning
involves an extra and cost increasing working step and there is
also the risk that such methods create burrs or damage to the
thread which would make it difficult to screw the rod into the
cylinder.
The invention therefore concerns a forging blank or work-
piece, which is shaped in such a way that the final forged threaded
cylinder is automatically given a starting cone at one end or at
both ends.
The invention provides forging blank for the production
of internally threaded cylinders by cold forging on an externally
threaded mandrel, wherein the forging blank along the major part
of its length has an outer diameter which exceeds the required
outer diameter of the final forged cylinder by an amount which
corresponds to the required profile depth of the cylinders internal
threads, and wherein the forging blank at one or more places is
formed on the outside with thicker or thinner parts intended to
form threads of lncreasing or decreasing profiles in the final
forged cylinder, and wherein the forging blank at one or both of
its ends is formed with a conically sloping part intended to form a
starting cone for the threads of the final forged cylinder. The
conically sloping end part causes a reduced material displacement
at the end, so that only a small amount of material is pressed into
the mandrel grooves. The cylinder is thus automatically given an
internal starting cone for the thread.
The invention will now be described in more detail with
reference to the accompanying drawings wherein:
Figure 1 shows diagrammatically and in an axial section a
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simple device or tool for the production of an internally threaded
cylinder;
Figure 2 shows in a larger scale a part of the device
shown in Figure 1 before cold forging; and
Figure 3 shows the final forged cylinder.
The tool shown in Figure 1 mainly comprises a forging tool
1, in which an externally threaded mandrel 2 and a forging blank
3 for a joining sleeve are set up. The forging blank is intended,
by the action of cold forging, to be worked into required form by
a number of forging hammers 4 of which only one is shown in the
drawing.
The forging tool 1 comprises an end socket 5 in which an
end positioner 6 with collar is loosely fitted. The surface of the
end positioner 6 is
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arranged to act as a s~op for the end 7 of the mandrel 2 and by varying the
axial width of end positioners collar, the mandrel s position in relation
to the forging blank 3 can be adjusted. The end socket 5 is arranged so that
its one end ~ acts as a holder for the one end of the forging blank 3. The
other end of the workpiece is supported by one end 9 of a driver 10, which
displaceably also supports the other end 11 of the forging workpiece 2.
The driver also comprises a spring loaded ram 12 whiçh forces the mandrel 2
against the end positioner 6 in the end socket 5. The tool 1 is rotatable
and for this purpose the end socket 5 is shaped with a journal 13 which can
be supported in a ball bearing and the driver 10 is similarly shaped with
a shaft end 14 which can be coupled to a motor to rotate the forging tool
together with the mandrel and forging blank.
The forging hammers 4 can be driven by excenters which intermittently
press the hammers against the workpiece while the tool is run past the ham-
mers. The workpiece is thereby successively worked from one end to the other
and is done so by enough force that the material of the forging blank is
displaced, whereby the worked material flows into the mandrel s 2 thread
grooves 15. The tool is held together by that the end socket 5 is hydrau-
lically or pneumatically loaded in an axial direction with a given force,
while the driver 10 is actuated in the opposite direction with a substantially
larger force, so that the tool is successively driven under the forging
hammers.
Simultaneously with the successive forging of the workpiece from one
end to the other, the workpiece increases in length in the same direction
as the hammers start working the blank, to the right as is shown in figure 1
and the blank must therefore be calculated shorter than the final length.
In many cases it is required that the threads in the final product are
of different height and according to the invention the workpiece can be for-
med thereafter so that the required form and si~e of the threads are auto-
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matically produced during forging and subsequent machining becomes un-
necessary. It may be required that one or two heavy threads are to be formed
in the cylinder's axial middle position, to achieve a locking effect for the
threaded rod or so that the rod cannot be threaded in more than to the slee-
ve's middle point. In the latter case the product may be formed as a thicke-
ning or bulge 16, as is indicated by figure 2.
A more usual requirement is however that the threads at the ends have
a starting cone to simplify screwing in the threaded rods. This is accomp-
lished by making the forging blank conically decreasing in diameter towards
its ends 17, whereby forging from the ends creates a successively increa-
sing amount of material which is pressed into the mandrel's threads 15,
whereby the thread height in the final product successively increases from
the cone's beginning 18 to its end point 19, from which point a constant
material displacement is maintained. The starting cones 17 can have a vary-
ing angle v depending on the required cone angle V required at the start
or end of the cylinder's thread 20. The starting point 18 of the blank's
cone 17 can lie over, on or even under the required level 21 for the final
forged cylinder's outer diameter, but normally the starting point lies a
little above the said level 21 so that some thread is formed at the beginning
of the cylinder.
In the shown case the threaded mandrel 2 is formed with a central cir-
cular groove 22 to form a central rib 23 in the forged cylinder, which is
intended as a safety measure so that the threaded rod cannot be screwed in
further than the sleeve's axial middle point.
The same effect can be obtained if the mandrel's thread grooves 15
are formed deeper at the sleeve's middle point or if the thread grooves 15
are formed throughout with a greater depth than the required profile depth
in the final forged product. In this latter case the threads are forged
down to a little play in relation to the base of the thread grooves 15,
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at all places except where the workpiece at the middle is formed with a
bulge 16, where the blank will be formed down to the base of the profile.
The larger profile depth at the cylinder's central threads act as stop so
that the threaded rod cannot be screwed in further than a certain position.
A practical embodiment of the invention is the production of a ioining
sleeve for drilling bars by using a forging blank which, according to the
invention has a length of approximately 165 mm, an inner diameter of
approximately 39 mm and an outer diameter of approximately 62 mm. At both
ends the forging blank is formed with ring shaped clamping part 24 for the
attachment of forging blank to the end socket 5 and driver 10, and from the
clamping ends the forging blank is conical with angle v of about 10 from
a diameter of approximately 54 mm. The cone 17, which gives a starting cone
in the cylinder, has a length of approximately 21 mm. After forging the
product'has an outer diameter of approximately'52 mm and the inside threads
formed by forging has a starting cone angle V of approximately 8.
The reader must understand that the description above and embodiments
of the invention shown on the drawings are only illustrative examples and
that many modifications can be made and exist within the scope of the
following claims.
