Title of Invention	A METHOD FOR MANUFACTURING HOLLOW SHAFTS
Abstract	A method for manufacturing hollow shafts 11' having end portions 12', 16' of greater wall thickness and at least one intermediate portion 14 of reduced wall thickness, from a tube 11 having constant wall thickness using a mandrel 21 having diameters stepped over the length, which has a first longitudinal section 22 having a smallest diameter and at least one further longitudinal section 24 having a further larger diameter, having the following steps: reducing the external diameter of a first portion of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the first end portion 12', reducing the external diameter of a middle portion 14 of the tube 11 over the at least one further longitudinal section 24 of the mandrel 21 to produce the at least one intermediate portion 14', reducing the external diameter of a further portion 16 of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the second end portion 16'.

Title of Invention

A METHOD FOR MANUFACTURING HOLLOW SHAFTS

Abstract

A method for manufacturing hollow shafts 11' having end portions 12', 16' of greater wall thickness and at least one intermediate portion 14 of reduced wall thickness, from a tube 11 having constant wall thickness using a mandrel 21 having diameters stepped over the length, which has a first longitudinal section 22 having a smallest diameter and at least one further longitudinal section 24 having a further larger diameter, having the following steps: reducing the external diameter of a first portion of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the first end portion 12', reducing the external diameter of a middle portion 14 of the tube 11 over the at least one further longitudinal section 24 of the mandrel 21 to produce the at least one intermediate portion 14', reducing the external diameter of a further portion 16 of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the second end portion 16'.

Full Text	003O91WO10 REDUCING TUBES OVER A STEPPED MANDREL TO MANUFACTURE TUBU- LAR SHAFTS HAVING AN UNDERCUT IN ONE OPERATION DESCRIPTION The present invention relates to a method for manufacturing hollow shafts having end portions of greater wall thickness and at least one intermediate portion of reduced wall thickness, particular a from a tube previously having con- stant wall thickness, using a mandrel having diameters stepped over the length, which has a first longitudinal section having a smallest diameter and at least one further longitudinal section having a further larger diameter. A method of this type is known from DE 101 18 032 A1. In this case, a first end portion of the tube is reduced freely in external diameter in a matrix without internal support, a middle tube portion having lesser wall thickness and larger external diameter is manufactured by stretching over an internal mandrel of constant diameter, and a second end portion of the tube is manufactured through reduction in external diameter in a matrix in the opposite drawing direction or through hammering without internal support. A method of the type cited, in which a first portion of a tube is reduced over a calibration mandrel which is intro- duced from the tube end discussed, and in which an interme- diate portion of the tube is reduced over a stretching man- drel, which is introduced from the other tube end, is known from DE 35 06 220 A1. The second end portion of the tube is reduced over the calibration mandrel again after changeover of the tube. The stretching mandrel comprises two longitu- dinal sections of different diameters having a conical transition area. The present invention is based on the object of providing a dimensionally accurate method, which may be performed effi- - 2 - ciently, for manufacturing hollow shafts of the above- mentioned type. This object is achieved by a method of the type cited hav- ing the following steps: reducing the external diameter of a first portion of the tube over the first longitudinal section of the mandrel to produce the first end portion of the hollow shaft, reducing the external diameter of at least one middle por- tion of the tube over the at least one further longitudinal section of the mandrel to produce the at least one interme- diate portion of the hollow shaft, reducing the external diameter of a further portion of the tube over another longitudinal section of the mandrel to produce the second end portion of the hollow shaft. This method has the advantage that all longitudinal por- tions of the hollow shaft are reduced over a single man- drel, the orientation of the direction of tube and mandrel to one another remaining the same. In this case, the method is applied in such a way that in the event of one or more changes of the relative position of mandrel and tube, the entire process up to manufacturing a finished hollow shaft may occur in a uniform feed direction of mandrel and tube in relation to one another without a tool change. For this purpose, the first end portion and one or more intermediate portions of the hollow shaft, having a reduced wall thick- ness in each case, may be produced with unchanged axial po- sition of the mandrel in relation to the tube. If the two end portions are to have the same cross-section, the second end portion is particularly also to be produced over the first longitudinal section of the mandrel. Furthermore, one or more further intermediate portions, each having an in- reased wall thickness respectively, and the second end por- tion of the hollow shaft may be produced with a changed ax- ial position of the mandrel in relation to the tube in each case, drawn out from the tube step-by-step. Finally, be- - 3 - tween the above-mentioned shaping steps, at least two in- termediate portions having alternating wall thicknesses, first increased in relation to the preceding wall thickness and then reduced again in relation to the last wall thick- ness, may be produced. The reduction of the external diame- ter of the tube is preferably performed through cold draw- ing using a matrix; alternatively, the reduction of the ex- ternal diameter of the tube is also possible through swag- ing, roll bending, or rolling, however. Furthermore, it is suggested that transitions between end portions and intermediate portions and transitions between intermediate portions of different wall thicknesses be formed by internal conical surfaces having a cone opening angle between 5 and 45°. A further embodiment provides that the wall thickness ratio between end portions and the ad- joining intermediate portion of smallest wall thickness is greater than 1.6. Preferred exemplary embodiments for performing the method according to the present invention are illustrated in the drawing and will be described in the following. Figure 1 shows, in a method for manufacturing a hollow shaft having a uniform middle intermediate por- tion, a) the tube in the starting state, b) the tube having inserted mandrel and applied matrix, c) the tube after the reduction of the first tube end to form the first end portion and the stret- ching of a middle intermediate portion, d) the tube before the reduction of the second tube end, e) after the reduction of the second tube end to form the second end portion, - 4 - f) the finished hollow shaft; Figure 2 shows, in a method for manufacturing a hollow shaft having a multiply stepped intermediate por- tion, a) the tube in the starting state, b) the tube having inserted mandrel and applied matrix, c) the tube after the reduction of the first tube end to form the first end portion and a first in- termediate portion and the stretching of a middle intermediate portion, d) the tube before the reduction of a second in- termediate portion, e) the tube after the reduction of a second in- termediate portion, f) the tube before the reduction of the second tube end, g) the tube after the reduction of the second tu- be end to form the second end portion, h) the finished hollow shaft; Figure 3 shows, in a method for manufacturing a hollow shaft having a multiply stepped intermediate por- tion in a second embodiment, a) the tube in the starting state, b) the tube having inserted mandrel and applied matrix, c) the tube after the reduction of the first tube end to form the first end portion and a first in- termediate portion and the stretching of a first thin-walled intermediate portion, d) the tube before the reduction of a thick- walled intermediate portion, e) the tube after the reduction of the thick- - 5 - walled intermediate portion and the stretching of a second thin-walled intermediate portion, f) the tube before the reduction of the second tube end, g) the tube after the reduction of the second tu- be end to form the second end portion, h) the finished hollow shaft. Figure 1 shows an illustration a of a tube 11 in the start- ing state, in which a first tube end 12 is identified on the left and a second tube end 16 is identified on the right, while a middle portion is identified by 14. It may be seen in illustration b that a matrix 31 is ap- plied to the left first tube end 12 and a mandrel 21 is in- serted into the interior of the tube, which essentially terminates with the left first tube end 12 and projects out of the right second tube end 16. The mandrel 21 has a first longitudinal section 22 having minimal diameter and a fur- ther longitudinal section 24 having a diameter which is es- sentially seated fixed in the tube 11. A conical transition section 27 is located between the first longitudinal sec- tion 22 and the further longitudinal section 24. Illustration c shows how two phases of the shaft manufac- turing have already been finished through a relative move- ment of matrix 31 (to the right) and mandrel 21 (to the left). Using the matrix 31, the first tube end has been re- duced in external diameter while increasing the wall thick- ness to produce a first shaft end 12' over the longitudinal section 22 of the mandrel 21. Furthermore, the middle por- tion has been reduced to form an intermediate portion 14' of the hollow shaft 11' over the second longitudinal sec- tion 24 of the mandrel 21. An internal conical transition area 17 has been formed over the transition section 27. - 6 - In illustration d, the mandrel 21 has been pulled back into a second axial position in relation to the matrix 31, the first longitudinal section 22 of the mandrel 21 being in- serted axially into the second tube end 16. In illustration e, the tube 11 is shown after the comple- tion of a third phase of the shaft manufacturing, the sec- ond tube end having been reduced in external diameter to manufacture a second shaft end 16' with wall thickness in- creased, the tube being supported radially on the inside on the longitudinal section 22 of the mandrel 21. An internal conical transition area 20 between the intermediate portion 14' and the second end portion 16' of the hollow shaft 11' is formed for this purpose solely by reducing the external diameter without internal support. In illustration f, the finished hollow shaft 11' having the two strengthened shaft ends 12', 16' and the intermediate portion 14' of reduced wall thickness is shown, two inter- nal conical transition areas 17, 20 being recognizable. In Figure 2, a tube 11 of constant wall thickness is shown in the starting state in illustration a. In illustration b, a matrix 31 is applied to the tube 11, while a mandrel 21 is inserted into the interior of the tube, which comprises a first, a second, and a further lon- gitudinal section 22, 23, 24 and conical transition sec- tions 27, 29 lying between them, which increase in diameter from the free end on the left to the end on the right. The matrix 31 is applied to the left tube end 12. The right tube end 16 may be axially supported. In illustration c, a partially finished hollow shaft 11' is shown after performing three manufacturing phases. By re- ducing the external diameter while increasing the wall thickness, a first shaft end 12' has been produced, which - 7 - is supported radially on the inside on the first longitudi- nal section 22 of the mandrel 21. A first intermediate por- tion 13 has also resulted with reduction of the external diameter and simultaneous stretching, which is supported on the longitudinal section 23 of the mandrel 21, and a second intermediate portion 14, which is supported on the longitu- dinal section 24 of the mandrel 21, has resulted with re- duction of the external diameter. In illustration d, the mandrel 21 is pulled back into an axial position in relation to the matrix 31 in which the longitudinal section 23 of the mandrel 21 is inserted into the second tube end 16 of the tube 11, which has not yet been shaped. The tube 11 is held axially in the matrix 31. Illustration e shows how a further intermediate portion 15 has resulted through reduction of the external diameter with partial stretching, whose wall thickness and length corresponds to the first intermediate portion 13 of the hollow shaft 11' and which is supported radially on the longitudinal section 23 of the mandrel 21. Illustration f shows how the mandrel 21 is again pulled to the right out of the matrix 31, in which the hollow shaft 11 is held axially, the first longitudinal section 22 of the mandrel 21 now being inserted into the last unshaped portion of the right tube end 16. In illustration g, it may be seen how a second shaft end 16' has been manufactured by reducing the external diameter using the matrix 31, which is supported internally on the longitudinal section 22 of the mandrel 21 with wall thick- ness reduction and whose length and dimensions correspond to the first shaft end 12' in the present case. The finished hollow shaft 11' is shown in illustration h, in which the two shaft ends 12', 16' and the intermediate - 8 - portions 13', 14', 15' may be seen. The transitions are each formed by internal conical transition areas 17, 18, 19, 20. The external diameter of the entire hollow shaft 11 is constant over the length, corresponding to the active diameter of the matrix 31. For both embodiments, it is to be noted here that in the practical application, the matrix 31 is preferably held axially fixed, while the entire relative motion is per- formed by the mandrel 21 having the tube 11 seated. Spe- cifically, a cylindrical intake area 32, an internal coni- cal reduction and stretching area 33, and an outlet cone 34 may be differentiated on the matrix. Instead of the cold drawing shown here using the matrix, milling or swaging or rolling of the external surface of the tube may also be ap- plied, the particular tool being axially displaced in the corresponding phases in relation to the mandrel in the di- rection corresponding with the matrix in each case. In Figure 3, a tube 11 of constant wall thickness is shown in the starting state in illustration a. In illustration b, a matrix 31 has been applied to the tube 11, while a mandrel 21 has been inserted into the interior of the tube, which comprises a first, a second, and a fur- ther longitudinal portion 22, 23, 24 and conical transition ares 27, 29 lying between each of them, which increase in diameter from the free end on the left to the end on the right. The matrix 31 is applied to the left tube end 12. The right tube end 16 may be axially supported. A partially finished hollow shaft 11' is shown in illustra- tion c after three manufacturing phases have been per- formed. A first shaft end 12' has been produced by reducing the external diameter while increasing the wall thickness, which is supported radially on the inside on the first lon- gitudinal section 22 of the mandrel 21. A first intermedi- - 9 - ate portion 13 has resulted, also with reduction of the ex- ternal diameter and simultaneous stretching, which is sup- ported on the longitudinal section 23 of the mandrel 21, and a first thin-walled intermediate portion 141, which is supported on the longitudinal section 24 of the mandrel 21, has resulted with reduction of the external diameter. In illustration d, the mandrel 21 is pulled back in rela- tion to the matrix 31 into an axial position in which the longitudinal section 23 of the mandrel 21 is inserted into the second, still unshaped tube end 16 of the tube 11. The tube 11 is held axially in the matrix 31. Illustration e shows how a thick-walled intermediate por- tion 15, which is supported radially on the longitudinal section 23 of the mandrel 21, has resulted through reduc- tion of the external diameter with partial stretching. Fur- thermore, a second thin-walled intermediate portion 142, which is supported radially on the longitudinal section 24 of the mandrel 21, has resulted through stretching of an adjoining longitudinal portion over the longitudinal sec- tion 24 of the mandrel 21. Illustration f shows how the mandrel 21 has again been pulled out to the right from the matrix 31, in which the hollow shaft 11 is held axially, the first longitudinal section 22 of the mandrel 21 now being inserted in the last unshaped portion of the right tube end 16. In illustration g, it may be seen how a second shaft end 16', which is supported on the inside on the longitudinal section 22 of the mandrel 21 with wall thickness reduction and which corresponds in length and dimensions to the first shaft end 12' in the present case, has been manufactured by reducing the external diameter using the matrix 31. The finished hollow shaft 11' is shown in illustration h, - 10 - in which the two shaft ends 12', 16' and intermediate por- tions 13', 14', 15', 142' may be seen. The transitions are each formed by internal conical transition areas 17, 181, 191, 182, 192. The external diameter of the overall hollow shaft 11 is constant over the length, corresponding to the active diameter of the matrix 31. For embodiments, it is to be noted here that in the practi- cal application, the matrix 31 is preferably held axially fixed, while the entire relative motion is performed by the mandrel 21 having the tube 11 seated. Specifically, a cy- lindrical intake area 32, an internal conical reduction and stretching area 33, and an outlet cone 34 may be differen- tiated on the matrix. Instead of the cold drawing shown he- re using the matrix, milling or swaging or rolling of the external surface of the tube may also be applied, the par- ticular tool being axially displaced in the corresponding phases in relation to the mandrel in the direction corre- sponding with the matrix in each case. - 11 - List of reference numbers 11 tube, hollow shaft 12 tube end (first) 13 intermediate portion 14 intermediate portion 15 intermediate portion 16 tube end (second) 17 transition area having internal cone 18 transition area having internal cone 19 transition area having internal cone 20 transition area having internal cone 21 mandrel 22 first longitudinal section 23 second longitudinal section 24 further longitudinal section 27 transition section 29 transition section 31 matrix 32 intake area 33 reduction and stretching cone 34 outlet cone -12- 003091WO10 REDUCING TUBES OVER A STEPPED MANDREL TO MANUFACTURE TUBU- LAR SHAFTS HAVING AN UNDERCUT IN ONE OPERATION PATENT CLAIMS 1. A method for manufacturing hollow shafts (11') having end portions (12', 16) of greater wall thickness and at least one intermediate portion (14') of reduced wall thickness, from a tube (11) having constant wall thickness using a mandrel (21) having diameters stepped over its length, which has a first longitudi- nal section (22) having a smallest diameter and at least one further longitudinal section (24) having a further larger diameter, having the following steps: reducing the external diameter of a first portion (12) of the tube (11) over the first longitudinal section (22) of the mandrel (21) to produce the first end por- tion (12'), reducing the external diameter of at least one middle portion (14) of the tube (11) over the at least one further longitudinal section (24) of the mandrel (21) to produce the at least one second intermediate por- tion (14'), reducing the external diameter of a further portion (16) of the tube (11) over another longitudinal sec- tion (22) of the mandrel (21) to produce the second end portion (16). 2. The method according to Claim 1, characterized in that the first end portion (12') and one or more intermediate portions (13', 14') of the -13- hollow shaft (11'), having a reduced wall thickness in each case, are produced with an unchanged axial posi- tion of the mandrel (21) in relation to the tube (11). 3. The method according to one of Claims 1 or 2, characterized in that the second end portion (16) is produced over the first longitudinal section (22) of the mandrel (21). 4. The method according to Claim 3, characterized in that one or more further intermediate portions (15'), each having an increased wall thick- ness, and the second end portion (16') are each pro- duced with a changed axial position of the mandrel (21) in relation to the tube (11), drawn out step-by- step from the tube (11). 5. The method according to Claim 3, characterized in that at least two second intermediate portions (15', 142'), alternately having first in- creased, then reduced wall thickness, are produced - particularly with an unchanged axial position of the mandrel (21) in relation to the tube (11) in each case. 6. The method according to one of Claims 1 through 5, characterized in that the reduction of the external diameter of the tube (11) is performed through cold drawing using a matrix (31), through which the tube (11) is guided from one tube end (12), tube (11) and mandrel (21) jointly on one side and matrix (31) on the other side moving axially in relation to one an- other. - 14- 7. The method according to one of Claims 1 through 5, characterized in that the external diameter of the tu- be (11) is reduced through swaging, roll bending, or rolling. 8. The method according to one of Claims 1 through 7, characterized in that transition areas (17, 20) be- tween end portions (12', 16') and intermediate por- tions (13', 15') and transition areas (18, 19) between intermediate portions (13', 14', 15') of different wall thicknesses are formed by internal conical sur- faces having a cone opening angle between 5 and 45°. 9. The method according to one of Claims 1 through 8, characterized in that the wall thickness ratio between the end portions (12', 16') and the intermediate por- tion (14') of smallest wall thickness is greater than 1.6. A method for manufacturing hollow shafts 11' having end portions 12', 16' of greater wall thickness and at least one intermediate portion 14 of reduced wall thickness, from a tube 11 having constant wall thickness using a mandrel 21 having diameters stepped over the length, which has a first longitudinal section 22 having a smallest diameter and at least one further longitudinal section 24 having a further larger diameter, having the following steps: reducing the external diameter of a first portion of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the first end portion 12', reducing the external diameter of a middle portion 14 of the tube 11 over the at least one further longitudinal section 24 of the mandrel 21 to produce the at least one intermediate portion 14', reducing the external diameter of a further portion 16 of the tube 11 over the first longitudinal section 22 of the mandrel 21 to produce the second end portion 16'.

Full Text

003O91WO10
REDUCING TUBES OVER A STEPPED MANDREL TO MANUFACTURE TUBU-
LAR SHAFTS HAVING AN UNDERCUT IN ONE OPERATION
DESCRIPTION
The present invention relates to a method for manufacturing
hollow shafts having end portions of greater wall thickness
and at least one intermediate portion of reduced wall
thickness, particular a from a tube previously having con-
stant wall thickness, using a mandrel having diameters
stepped over the length, which has a first longitudinal
section having a smallest diameter and at least one further
longitudinal section having a further larger diameter.
A method of this type is known from DE 101 18 032 A1. In
this case, a first end portion of the tube is reduced
freely in external diameter in a matrix without internal
support, a middle tube portion having lesser wall thickness
and larger external diameter is manufactured by stretching
over an internal mandrel of constant diameter, and a second
end portion of the tube is manufactured through reduction
in external diameter in a matrix in the opposite drawing
direction or through hammering without internal support.
A method of the type cited, in which a first portion of a
tube is reduced over a calibration mandrel which is intro-
duced from the tube end discussed, and in which an interme-
diate portion of the tube is reduced over a stretching man-
drel, which is introduced from the other tube end, is known
from DE 35 06 220 A1. The second end portion of the tube is
reduced over the calibration mandrel again after changeover
of the tube. The stretching mandrel comprises two longitu-
dinal sections of different diameters having a conical
transition area.
The present invention is based on the object of providing a
dimensionally accurate method, which may be performed effi-

- 2 -
ciently, for manufacturing hollow shafts of the above-
mentioned type.
This object is achieved by a method of the type cited hav-
ing the following steps:
reducing the external diameter of a first portion of the
tube over the first longitudinal section of the mandrel to
produce the first end portion of the hollow shaft,
reducing the external diameter of at least one middle por-
tion of the tube over the at least one further longitudinal
section of the mandrel to produce the at least one interme-
diate portion of the hollow shaft,
reducing the external diameter of a further portion of the
tube over another longitudinal section of the mandrel to
produce the second end portion of the hollow shaft.
This method has the advantage that all longitudinal por-
tions of the hollow shaft are reduced over a single man-
drel, the orientation of the direction of tube and mandrel
to one another remaining the same. In this case, the method
is applied in such a way that in the event of one or more
changes of the relative position of mandrel and tube, the
entire process up to manufacturing a finished hollow shaft
may occur in a uniform feed direction of mandrel and tube
in relation to one another without a tool change. For this
purpose, the first end portion and one or more intermediate
portions of the hollow shaft, having a reduced wall thick-
ness in each case, may be produced with unchanged axial po-
sition of the mandrel in relation to the tube. If the two
end portions are to have the same cross-section, the second
end portion is particularly also to be produced over the
first longitudinal section of the mandrel. Furthermore, one
or more further intermediate portions, each having an in-
reased wall thickness respectively, and the second end por-
tion of the hollow shaft may be produced with a changed ax-
ial position of the mandrel in relation to the tube in each
case, drawn out from the tube step-by-step. Finally, be-

- 3 -
tween the above-mentioned shaping steps, at least two in-
termediate portions having alternating wall thicknesses,
first increased in relation to the preceding wall thickness
and then reduced again in relation to the last wall thick-
ness, may be produced. The reduction of the external diame-
ter of the tube is preferably performed through cold draw-
ing using a matrix; alternatively, the reduction of the ex-
ternal diameter of the tube is also possible through swag-
ing, roll bending, or rolling, however.
Furthermore, it is suggested that transitions between end
portions and intermediate portions and transitions between
intermediate portions of different wall thicknesses be
formed by internal conical surfaces having a cone opening
angle between 5 and 45°. A further embodiment provides that
the wall thickness ratio between end portions and the ad-
joining intermediate portion of smallest wall thickness is
greater than 1.6.
Preferred exemplary embodiments for performing the method
according to the present invention are illustrated in the
drawing and will be described in the following.
Figure 1 shows, in a method for manufacturing a hollow
shaft having a uniform middle intermediate por-
tion,
a) the tube in the starting state,
b) the tube having inserted mandrel and applied
matrix,
c) the tube after the reduction of the first tube
end to form the first end portion and the stret-
ching of a middle intermediate portion,
d) the tube before the reduction of the second
tube end,
e) after the reduction of the second tube end to
form the second end portion,

- 4 -
f) the finished hollow shaft;
Figure 2 shows, in a method for manufacturing a hollow
shaft having a multiply stepped intermediate por-
tion,
a) the tube in the starting state,
b) the tube having inserted mandrel and applied
matrix,
c) the tube after the reduction of the first tube
end to form the first end portion and a first in-
termediate portion and the stretching of a middle
intermediate portion,
d) the tube before the reduction of a second in-
termediate portion,
e) the tube after the reduction of a second in-
termediate portion,

f) the tube before the reduction of the second
tube end,
g) the tube after the reduction of the second tu-
be end to form the second end portion,
h) the finished hollow shaft;
Figure 3 shows, in a method for manufacturing a hollow
shaft having a multiply stepped intermediate por-
tion in a second embodiment,
a) the tube in the starting state,
b) the tube having inserted mandrel and applied
matrix,
c) the tube after the reduction of the first tube
end to form the first end portion and a first in-
termediate portion and the stretching of a first
thin-walled intermediate portion,

d) the tube before the reduction of a thick-
walled intermediate portion,
e) the tube after the reduction of the thick-

- 5 -
walled intermediate portion and the stretching of
a second thin-walled intermediate portion,
f) the tube before the reduction of the second
tube end,
g) the tube after the reduction of the second tu-
be end to form the second end portion,
h) the finished hollow shaft.
Figure 1 shows an illustration a of a tube 11 in the start-
ing state, in which a first tube end 12 is identified on
the left and a second tube end 16 is identified on the
right, while a middle portion is identified by 14.
It may be seen in illustration b that a matrix 31 is ap-
plied to the left first tube end 12 and a mandrel 21 is in-
serted into the interior of the tube, which essentially
terminates with the left first tube end 12 and projects out
of the right second tube end 16. The mandrel 21 has a first
longitudinal section 22 having minimal diameter and a fur-
ther longitudinal section 24 having a diameter which is es-
sentially seated fixed in the tube 11. A conical transition
section 27 is located between the first longitudinal sec-
tion 22 and the further longitudinal section 24.
Illustration c shows how two phases of the shaft manufac-
turing have already been finished through a relative move-
ment of matrix 31 (to the right) and mandrel 21 (to the
left). Using the matrix 31, the first tube end has been re-
duced in external diameter while increasing the wall thick-
ness to produce a first shaft end 12' over the longitudinal
section 22 of the mandrel 21. Furthermore, the middle por-
tion has been reduced to form an intermediate portion 14'
of the hollow shaft 11' over the second longitudinal sec-
tion 24 of the mandrel 21. An internal conical transition
area 17 has been formed over the transition section 27.

- 6 -
In illustration d, the mandrel 21 has been pulled back into
a second axial position in relation to the matrix 31, the
first longitudinal section 22 of the mandrel 21 being in-
serted axially into the second tube end 16.
In illustration e, the tube 11 is shown after the comple-
tion of a third phase of the shaft manufacturing, the sec-
ond tube end having been reduced in external diameter to
manufacture a second shaft end 16' with wall thickness in-
creased, the tube being supported radially on the inside on
the longitudinal section 22 of the mandrel 21. An internal
conical transition area 20 between the intermediate portion
14' and the second end portion 16' of the hollow shaft 11'
is formed for this purpose solely by reducing the external
diameter without internal support.
In illustration f, the finished hollow shaft 11' having the
two strengthened shaft ends 12', 16' and the intermediate
portion 14' of reduced wall thickness is shown, two inter-
nal conical transition areas 17, 20 being recognizable.
In Figure 2, a tube 11 of constant wall thickness is shown
in the starting state in illustration a.
In illustration b, a matrix 31 is applied to the tube 11,
while a mandrel 21 is inserted into the interior of the
tube, which comprises a first, a second, and a further lon-
gitudinal section 22, 23, 24 and conical transition sec-
tions 27, 29 lying between them, which increase in diameter
from the free end on the left to the end on the right. The
matrix 31 is applied to the left tube end 12. The right
tube end 16 may be axially supported.
In illustration c, a partially finished hollow shaft 11' is
shown after performing three manufacturing phases. By re-
ducing the external diameter while increasing the wall
thickness, a first shaft end 12' has been produced, which

- 7 -
is supported radially on the inside on the first longitudi-
nal section 22 of the mandrel 21. A first intermediate por-
tion 13 has also resulted with reduction of the external
diameter and simultaneous stretching, which is supported on
the longitudinal section 23 of the mandrel 21, and a second
intermediate portion 14, which is supported on the longitu-
dinal section 24 of the mandrel 21, has resulted with re-
duction of the external diameter.
In illustration d, the mandrel 21 is pulled back into an
axial position in relation to the matrix 31 in which the
longitudinal section 23 of the mandrel 21 is inserted into
the second tube end 16 of the tube 11, which has not yet
been shaped. The tube 11 is held axially in the matrix 31.
Illustration e shows how a further intermediate portion 15
has resulted through reduction of the external diameter
with partial stretching, whose wall thickness and length
corresponds to the first intermediate portion 13 of the
hollow shaft 11' and which is supported radially on the
longitudinal section 23 of the mandrel 21.
Illustration f shows how the mandrel 21 is again pulled to
the right out of the matrix 31, in which the hollow shaft
11 is held axially, the first longitudinal section 22 of
the mandrel 21 now being inserted into the last unshaped
portion of the right tube end 16.
In illustration g, it may be seen how a second shaft end
16' has been manufactured by reducing the external diameter
using the matrix 31, which is supported internally on the
longitudinal section 22 of the mandrel 21 with wall thick-
ness reduction and whose length and dimensions correspond
to the first shaft end 12' in the present case.
The finished hollow shaft 11' is shown in illustration h,
in which the two shaft ends 12', 16' and the intermediate

- 8 -
portions 13', 14', 15' may be seen. The transitions are
each formed by internal conical transition areas 17, 18,
19, 20. The external diameter of the entire hollow shaft 11
is constant over the length, corresponding to the active
diameter of the matrix 31.
For both embodiments, it is to be noted here that in the
practical application, the matrix 31 is preferably held
axially fixed, while the entire relative motion is per-
formed by the mandrel 21 having the tube 11 seated. Spe-
cifically, a cylindrical intake area 32, an internal coni-
cal reduction and stretching area 33, and an outlet cone 34
may be differentiated on the matrix. Instead of the cold
drawing shown here using the matrix, milling or swaging or
rolling of the external surface of the tube may also be ap-
plied, the particular tool being axially displaced in the
corresponding phases in relation to the mandrel in the di-
rection corresponding with the matrix in each case.
In Figure 3, a tube 11 of constant wall thickness is shown
in the starting state in illustration a.
In illustration b, a matrix 31 has been applied to the tube
11, while a mandrel 21 has been inserted into the interior
of the tube, which comprises a first, a second, and a fur-
ther longitudinal portion 22, 23, 24 and conical transition
ares 27, 29 lying between each of them, which increase in
diameter from the free end on the left to the end on the
right. The matrix 31 is applied to the left tube end 12.
The right tube end 16 may be axially supported.
A partially finished hollow shaft 11' is shown in illustra-
tion c after three manufacturing phases have been per-
formed. A first shaft end 12' has been produced by reducing
the external diameter while increasing the wall thickness,
which is supported radially on the inside on the first lon-
gitudinal section 22 of the mandrel 21. A first intermedi-

- 9 -
ate portion 13 has resulted, also with reduction of the ex-
ternal diameter and simultaneous stretching, which is sup-
ported on the longitudinal section 23 of the mandrel 21,
and a first thin-walled intermediate portion 141, which is
supported on the longitudinal section 24 of the mandrel 21,
has resulted with reduction of the external diameter.
In illustration d, the mandrel 21 is pulled back in rela-
tion to the matrix 31 into an axial position in which the
longitudinal section 23 of the mandrel 21 is inserted into
the second, still unshaped tube end 16 of the tube 11. The
tube 11 is held axially in the matrix 31.
Illustration e shows how a thick-walled intermediate por-
tion 15, which is supported radially on the longitudinal
section 23 of the mandrel 21, has resulted through reduc-
tion of the external diameter with partial stretching. Fur-
thermore, a second thin-walled intermediate portion 142,
which is supported radially on the longitudinal section 24
of the mandrel 21, has resulted through stretching of an
adjoining longitudinal portion over the longitudinal sec-
tion 24 of the mandrel 21.
Illustration f shows how the mandrel 21 has again been
pulled out to the right from the matrix 31, in which the
hollow shaft 11 is held axially, the first longitudinal
section 22 of the mandrel 21 now being inserted in the last
unshaped portion of the right tube end 16.
In illustration g, it may be seen how a second shaft end
16', which is supported on the inside on the longitudinal
section 22 of the mandrel 21 with wall thickness reduction
and which corresponds in length and dimensions to the first
shaft end 12' in the present case, has been manufactured by
reducing the external diameter using the matrix 31.
The finished hollow shaft 11' is shown in illustration h,

- 10 -
in which the two shaft ends 12', 16' and intermediate por-
tions 13', 14', 15', 142' may be seen. The transitions are
each formed by internal conical transition areas 17, 181,
191, 182, 192. The external diameter of the overall hollow
shaft 11 is constant over the length, corresponding to the
active diameter of the matrix 31.
For embodiments, it is to be noted here that in the practi-
cal application, the matrix 31 is preferably held axially
fixed, while the entire relative motion is performed by the
mandrel 21 having the tube 11 seated. Specifically, a cy-
lindrical intake area 32, an internal conical reduction and
stretching area 33, and an outlet cone 34 may be differen-
tiated on the matrix. Instead of the cold drawing shown he-
re using the matrix, milling or swaging or rolling of the
external surface of the tube may also be applied, the par-
ticular tool being axially displaced in the corresponding
phases in relation to the mandrel in the direction corre-
sponding with the matrix in each case.

- 11 -
List of reference numbers
11 tube, hollow shaft
12 tube end (first)
13 intermediate portion
14 intermediate portion
15 intermediate portion
16 tube end (second)
17 transition area having internal cone
18 transition area having internal cone
19 transition area having internal cone
20 transition area having internal cone
21 mandrel
22 first longitudinal section
23 second longitudinal section
24 further longitudinal section
27 transition section
29 transition section
31 matrix
32 intake area
33 reduction and stretching cone
34 outlet cone

-12-
003091WO10
REDUCING TUBES OVER A STEPPED MANDREL TO MANUFACTURE TUBU-
LAR SHAFTS HAVING AN UNDERCUT IN ONE OPERATION
PATENT CLAIMS
1. A method for manufacturing hollow shafts (11') having
end portions (12', 16) of greater wall thickness and
at least one intermediate portion (14') of reduced
wall thickness, from a tube (11) having constant wall
thickness using a mandrel (21) having diameters
stepped over its length, which has a first longitudi-
nal section (22) having a smallest diameter and at
least one further longitudinal section (24) having a
further larger diameter,
having the following steps:
reducing the external diameter of a first portion (12)
of the tube (11) over the first longitudinal section
(22) of the mandrel (21) to produce the first end por-
tion (12'),
reducing the external diameter of at least one middle
portion (14) of the tube (11) over the at least one
further longitudinal section (24) of the mandrel (21)
to produce the at least one second intermediate por-
tion (14'),
reducing the external diameter of a further portion
(16) of the tube (11) over another longitudinal sec-
tion (22) of the mandrel (21) to produce the second
end portion (16).
2. The method according to Claim 1,
characterized in that the first end portion (12') and
one or more intermediate portions (13', 14') of the

-13-
hollow shaft (11'), having a reduced wall thickness in
each case, are produced with an unchanged axial posi-
tion of the mandrel (21) in relation to the tube (11).
3. The method according to one of Claims 1 or 2,
characterized in that the second end portion (16) is
produced over the first longitudinal section (22) of
the mandrel (21).
4. The method according to Claim 3,
characterized in that one or more further intermediate
portions (15'), each having an increased wall thick-
ness, and the second end portion (16') are each pro-
duced with a changed axial position of the mandrel
(21) in relation to the tube (11), drawn out step-by-
step from the tube (11).
5. The method according to Claim 3,
characterized in that at least two second intermediate
portions (15', 142'), alternately having first in-
creased, then reduced wall thickness, are produced -
particularly with an unchanged axial position of the
mandrel (21) in relation to the tube (11) in each
case.
6. The method according to one of Claims 1 through 5,
characterized in that the reduction of the external
diameter of the tube (11) is performed through cold
drawing using a matrix (31), through which the tube
(11) is guided from one tube end (12), tube (11) and
mandrel (21) jointly on one side and matrix (31) on
the other side moving axially in relation to one an-
other.

- 14-
7. The method according to one of Claims 1 through 5,
characterized in that the external diameter of the tu-
be (11) is reduced through swaging, roll bending, or
rolling.
8. The method according to one of Claims 1 through 7,
characterized in that transition areas (17, 20) be-
tween end portions (12', 16') and intermediate por-
tions (13', 15') and transition areas (18, 19) between
intermediate portions (13', 14', 15') of different
wall thicknesses are formed by internal conical sur-
faces having a cone opening angle between 5 and 45°.
9. The method according to one of Claims 1 through 8,
characterized in that the wall thickness ratio between
the end portions (12', 16') and the intermediate por-
tion (14') of smallest wall thickness is greater than
1.6.

A method for manufacturing hollow shafts 11' having end portions 12', 16' of greater wall thickness and at least one
intermediate portion 14 of reduced wall thickness, from a tube
11 having constant wall thickness using a mandrel 21 having
diameters stepped over the length, which has a first longitudinal section 22 having a smallest diameter and at least one
further longitudinal section 24 having a further larger diameter,
having the following steps:
reducing the external diameter of a first portion of the tube
11 over the first longitudinal section 22 of the mandrel 21 to
produce the first end portion 12',
reducing the external diameter of a middle portion 14 of the
tube 11 over the at least one further longitudinal section 24
of the mandrel 21 to produce the at least one intermediate
portion 14',
reducing the external diameter of a further portion 16 of the
tube 11 over the first longitudinal section 22 of the mandrel
21 to produce the second end portion 16'.

A METHOD FOR MANUFACTURING HOLLOW SHAFTS

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