Method of manufacturing a corrugated metallic pipe and corrugated pipe produced by the method

A method of manufacturing a corrugated metallic pipe, including inserting into a smooth cylindrical metallic pipe a first mandrel having an axially extending corrugation having a predetermined shape and height, and radially expanding the first mandrel against cheek means, which surrounds the pipe and has a corrugation at least approximately corresponding to the corrugation of the first mandrel, to provide a first preformed corrugation on the metallic pipe, thereafter, inserting into the pipe with the first preformed corrugation, a second mandrel having an outer diameter corresponding to an inner diameter of the first corrugation, thereafter, radially displacing into corrugation hollows disc-shaped, axially spaced from each other, jaws which surround the pipe with the first preformed corrugation, and axially displacing the jaws toward each other, effecting folding up of the first preformed corrugation to obtain a final predetermined corrugation of the pipe.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of manufacturing a corrugated 
metallic pipe and which includes providing a mandrel having an axially 
extending corrugation having a predetermined shape and height, and 
inserting the mandrel into a smooth cylindrical metallic pipe and radially 
expanding the mandrel against cheek means, which surrounds the pipe and 
has a corrugation at least approximately corresponding to the corrugation 
of the mandrel, to provide a corrugation on the metallic pipe. The present 
invention also relates to a corrugated pipe formed by method. 
2. Description of the Prior Art 
The prior art discloses a plurality of methods and tools for manufacturing 
corrugated metallic pipes. Such methods and tools are disclosed, e.g., in 
German patents Nos. 3,035,234; 2,851,944; 2,909,142; 3,224,308; German 
publications DE-AS 2,407,226; DE-05 2,027,638; DE-OS 3,004,838; European 
Patent No. 298,852, French Patent No. 2,176,707, British patent 
publication No. 2,268,429; and U.S. Pat. No. 1,890,039. 
According to German patent No. 3,035,234, a shaft with a plurality of 
corrugation discs supported thereon is inserted into a to-be-corrugated 
pipe, with the pipe being acted upon from outside by another plurality of 
corrugation discs, which correspond to the corrugation discs provided 
inside the pipe but are offset relative to the inside corrugation discs. 
The outer corrugation discs are likewise mounted on a shaft. The rotatable 
discs are displaced simultaneously toward each other and are axially 
displaced on their respective shafts. This method is inapplicable to 
forming corrugations on pipes with a small cross-section because the 
corrugation discs carrying shafts should be very strong and, thus, should 
have increased dimensions so that they would not be deformed by an 
operational pressure generated during the formation of the pipe 
corrugation. 
According to German Publication DE-AS 2,407,226, a smooth cylindrical pipe 
is inserted into a matrix having a corrugated wall. Then, an elastic 
pressing member is inserted into the pipe and is compressed from opposite 
sides with dies, with the pipe being sectionally deformed. This method is 
very expensive and is applicable to forming corrugations only in pipes 
having thin walls. 
The German patent publication DE-OS 2,027,638, which corresponds to British 
patent No. 1,341,774, discloses inserting into a to-be-corrugated pipe of 
a radially expandable mandrel, with sector-shaped discs acting on the pipe 
from outside, with the discs being displaced radially against the pipe. 
The desired corrugation is obtained by simultaneous actions of the inner 
mandrel and the outer discs. 
According to German patents Nos. 2,851,944 and 2,909,142, the final 
corrugation is formed by forming one corrugation after another by applying 
inner pressure. This method and a tool for effecting the method are very 
expensive. However, the advantage of this method in comparison with the 
previously described methods consists in that the wall thickness of the 
pipe remains substantially unchanged in the corrugation region. 
German patent No. 3,224,308 discloses a tool with which a corrugation 
hollow is formed on a cylindrical pipe step by step. Shaped members are 
placed into the corrugation hollows of the preformed pipe from outside. 
Then, a high hydraulic pressure is generated inside of the pipe subjecting 
the pipe to an axial pressure force which shortens the pipe, whereby the 
pipe sections, which lie between the hollows supported by the shaped 
members are displaced outwardly. This method is likewise very expensive. 
According to European Patent No. 298,832, a radially expandable corrugated 
mandrel is inserted into a to-be-corrugated pipe. Sector-shaped cheek 
plates having a corrugation corresponding to the mandrel corrugation act 
on the pipe hammering it. The so obtained corrugation has a wall thickness 
which, because of stretching of the pipe in the corrugation region, is 
thinner than the thickness of the non-deformed wall. 
French Patent No. 2,176,707 likewise discloses a radially expandable 
corrugated mandrel. As outer jaws, a plurality of gears, which surround 
the pipe, are used. The gears are so arranged that they coincide with the 
mandrel corrugation. The gears are supported on a slide displaceable along 
the pipe. With this arrangement, thinning of the pipe material in the 
corrugation region is also unavoidable. 
British publication No. 2,268,429 discloses a radially expandable mandrel 
divided in an axial direction into a plurality of discs the outer surfaces 
of which form a corrugation. From the outside, the pipe is surrounded with 
sector-shaped disc-like jaws which, together with the mandrel, form the 
pipe corrugation. A similar method is disclosed in U.S. Pat. No. 
1,890,039. 
German patent publication No. 3,004,838 discloses a method for producing a 
corrugated pipe with a distinctive transverse corrugation. The device for 
forming the corrugation includes a plurality of axially spaced jaws. A 
to-be-corrugated pipe is inserted into the device, with the outer surface 
of the pipe engaging the jaws. After the pipe is inserted, it is sealed at 
its opposite ends, and a high hydrostatic pressure is generated in the 
interior of the pipe, causing bulging of the pipe sections located between 
the spaced jaws. Then, press pistons are applied while the high 
hydrostatic pressure is maintained inside the pipe. This causes folding of 
the bulged pipe sections. During application of the high hydrostatic 
pressure in the interior of the pipe, the axial sections of the pipe, 
which engage the jaws, are stretched out. This causes thinning of the wall 
in the region of these axial sections resulting in their weakening. During 
the subsequent axial displacement of the jaws, while the high hydrostatic 
pressure is maintained, which is necessary not only for further 
displacement outward of the pipe bulging sections but also for providing 
an adequate fiction force between the jaws and the pipe sections which 
engage them, the wall thickness of the jaw engaging pipe sections is 
further reduced. Thus, the finished corrugated pipe has a smallest wall 
thickness in the regions of the corrugations hollows. The above-mentioned 
friction force should be sufficiently high in order to prevent sliding of 
the jaws relative to the pipe during displacement of the jaws against the 
small bulge sections of the pipes, which are located between the jaws, 
which sliding would not permit to obtained a corrugation with 
predetermined dimensions. Generally, such corrugated pipes are used with 
steering columns of motor vehicle and serve as intermediate 
energy-absorbing elements during an accident. The corrugated pipes, which 
are located inside of the steering columns, serve for transmitting a 
rotational torque in steering motor vehicles. The corrugated pipe, which 
is produced with the above-discussed method have the smallest wall 
thickness in its interior region, and it is this region which is subjected 
to the highest stress during the transmission of the rotational torque. 
Therefore, for forming corrugated pipes used in steering columns, pipes 
with an increased wall thickness are selected so that the corrugated pipe 
is not subjected to inadmissible stress even in its inner region which is 
subjected to the highest stresses. 
Accordingly, an object of the present invention is a method of 
manufacturing corrugated pipes with a very distinctive corrugation in 
which the wall thickness of the corrugated pipe in its interior region is 
not only retained but is rather increased. 
Another object of the invention is a method of manufacturing of a 
corrugated pipe in which the ratio of a height of a single corrugation 
protrusion to a length of the corrugation protrusion is approximately 1:1. 
SUMMARY OF THE INVENTION 
These and other objects of the invention, which will become apparent 
hereinafter, are achieved by providing a method of manufacturing a pipe 
having a predetermined corrugation and which includes providing a 
plurality of first mandrel having each an axially extending corrugation 
having a predetermined shape and height, with the heights of the first 
mandrels progressively increasing from one first mandrel to another first 
mandrel, inserting the first mandrels into a smooth cylindrical metallic 
pipe, radially expanding the first mandrels against exchangeable 
complementary cheek means, and displacing the complementary check means, 
which surrounds the pipe and has a corrugation at least approximately 
corresponding to the corrugation of the inserted first mandrel, radially 
inward to provide a first preformed corrugation on the metallic pipe. 
Thereafter, a second mandrel having an outer diameter corresponding to an 
inner diameter of the first corrugation is inserted into the pipe having 
the first preformed corrugation. Thereafter, disc-shaped, axially spaced 
from each other, jaws, which surround the pipe with the first preformed 
corrugation, are radially displaced into corrugation hollows and then are 
axially displaced toward each other, effecting folding up of the first, 
preformed corrugation to obtain a final predetermined corrugation of the 
pipe. 
The method according to the present invention permits to eliminate the 
drawbacks of a corrugated pipe, which is produced by the method disclosed 
in German Publication No. 3,004,838, with simple means. By using a 
multi-step formation of the pipe corrugation with a plurality of tool 
elements having appropriate shapes and dimensions, a very distinctive 
corrugation is formed in which the wall thickness of the interior region 
is not only retained but is even increased. This results from pressing 
inward of the small inner corrugation hollows which leads to the reduction 
of the inner diameter in comparison with the diameter of the initial 
cylindrical pipe, which results in material accumulation. The distinctive 
corrugation results in such deformation of the inner region in the area of 
small inner hollows that their flanks are sharply inclined, with the mean 
flank angle being at least 45.degree. and, preferably, 65.degree.. During 
subsequent folding, a simple tool can so support the inner region that 
during the pleating or folding step, the pipe sections located between the 
jaws are not subjected to any significant inner pressure. The jaws engage 
in the little folded hollows and are not displaced therefrom during their 
subsequent axial displacement. A reliable form-locking connection is 
provided between the foldable pipe corrugation and the outer jaws which 
insures a reliable retention of the pipe sections, which are located 
between the jaws, during the axial displacement of the jaws, without a 
need to provide an outwardly acting pressure inside the pipe. 
The present invention permits to produce corrugated pipes which have, in 
their inner circular region, a wall thickness greater than the wall 
thickness of the smooth cylindrical pipe, which make the so produced 
corrugated pipes especially suitable for their designated purpose, as they 
have an increased thickness in the region where the highest stresses are 
generated during the transmission of the rotational torque. 
In order to transform the preformed corrugation into the predetermined 
distinctive corrugation, the jaws are arranged pairwise in a plurality of 
parallel planes, and each jaw has a semi-circular recess, the limiting 
surface of which has a stepped profile with the step height corresponding 
to the height of the predetermined corrugation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, manufacturing of corrugated metallic 
pipes is effected as follows. A mandrel 2 is inserted into a smooth 
cylindrical pipe 1. Two mandrels 2 are inserted into the pipe 1 from 
opposite sides. However, often the mandrel 2 can be inserted only from one 
side. The mandrel 2 is formed of a plurality of sector-shaped sections 3 
between which, for effecting a radial expansion, a wedge-shaped shaft 4 is 
introduced (in a direction indicated with arrow 5). For holding the pipe 
1, there are provided outer cheeks 6 which are likewise sector-shaped. 
Along their length L, both the outer cheeks 6 and the sections 3 are 
provided, on their adjacent sides, with cophasal, substantially 
identically formed corrugations 7 and 8, with the corrugation trains 
having relatively small hollows and relatively elongate crests. 
Such a tool can be used only when several similar tools are used in a 
manufacturing process. Separate tools distinguish from each other by the 
shape of their corrugations. The first tool has a relatively small 
corrugation, i.e., a corrugation with a small height, with the corrugation 
height increasing from a tool to a following tool. For the sake of 
simplicity and clarity, only one corrugating tool is shown in the 
drawings. 
The smooth surface of the pipe 1, which lies between the mandrel 2 and the 
outer cheeks 6, is deformed by the radial expansion of the mandrel 2 and 
by the radial displacement of the cheek 6 toward the mandrel 2 (in the 
direction of arrow 11). Thereby, the pipe 1 is provided with the 
corrugations along the length L which distinguish from tool to tool until 
they acquire the shape shown in FIG. 2 at an increased scale. FIG. 2 shows 
that the corrugations hollows 9 are relatively small and the corrugation 
crests 10 have a relatively large extent. With the corrugation 20 shown in 
FIG. 2, the corrugation length L exceeds the corrugation height H by 
several times, e.g., by three to four times. With such shape of the 
corrugation 20, the length L, of the corrugation hollow 9, which is 
directed toward the pipe inside, constitute only a fraction of the length 
l.sub.2 of the outwardly directed corrugation crest 10. This ratio, e.g., 
amounts to about from 0.3 to 0.6, with the lengths l.sub.1, l.sub.2 being 
measured at the half of the corrugation height H. The corrugation hollow 9 
is shaped so and has such a depth that the mean flank angle .alpha. is at 
least 45.degree. and, preferably, 60.degree. and more. 
The corrugation 20 shown in FIG. 2 is produced in several operational steps 
with several tools. The separate tools so differ from each other that the 
corrugation is formed with ever increasing complementing surface of the 
tools, i.e., the corrugation height H increases from one tool to another, 
with the flank angle becoming steeper and steeper. As a rule, a double 
increase in dimensions of a set of tools is sufficient. With such a 
formation of the corrugations shown in FIG. 2, not only the wall thickness 
of the pipe 1 remains substantially unchanged, but it even increases in 
the bottom regions of the corrugation hollows 9. The increase of the 
thickness in these regions results from the flow of material toward the 
interior of the pipe which is caused by the displacement of the cheek 6 
radially against the pipe 1. 
Such preformed pipe 1 which, in the example shown in the drawings, is 
closed at one end and has, at that closed end, an extension 12. The 
preformed pipe 1 is placed on a cylindrical mandrel 13 having a smooth 
outer surface. The mandrel 13 is formed, preferably, in the same way as 
the mandrel 2 shown in FIG. 1, but with the separate sector-shaped 
sections having, as it has already been mentioned above, smooth surfaces. 
The mandrel 13 is expanded radially, by introducing a wedge-shaped shaft, 
to such an extent that its outer diameter contacts the inner diameter of 
the corrugations 20, i.e., the inner surfaces of the corrugation hollows 9 
of the preformed pipe 1 lie on the smooth cylindrical outer surface of the 
mandrel 13. 
The mandrel 13 is arranged between jaws 15 as shown in FIGS. 4-6. A plan 
view of a jaw 15 is shown in FIG. 7. The jaws 15 lie in a plurality of 
planes and are arranged pairwise with respect to the mandrel 13, as shown 
in FIG. 4. Each of the jaws 15 has a semi-circular recess 16 limited by a 
stepped surface 17, with the height h of the step corresponding to at 
least the height to which the preformed corrugation, which is shown in 
FIG. 2, should be corrugated. By using appropriate guide and positioning 
means (not shown), the jaws 15 are so positioned that the projecting 
portions of the jaws 15 lie in the planes of the corrugation hollows 9 of 
the corrugations 20 of the pipe 1. These jaws 15 are displaced toward the 
mandrel 15, which extends through the pipe 1 (FIG. 5), so that the 
projecting portions of the jaws 15 extend into the corrugation hollows 9, 
with the jaws 15 encompassing the pipe 1. Because of the increased wall 
thickness of the corrugation hollows 9 and steep flanks, form-locking 
positions of the jaws 15 is obtained, which insures a following proper 
pleating, without any pressure being generated in the interior of the pipe 
1. The mandrel 15 insures an adequate support for the corrugation hollows 
during pleating. 
Finally, a die 18 is advanced against the uppermost jaw 15 and displaces 
the pairs of jaws 15, which are spaced from each other, toward each other, 
with the lowermost jaw 15 being supported by a stop designated with an 
arrow 19 (FIG. 6). By the mutual displacement of the jaws 15, first, the 
flat corrugation crests 10 fold up with a simultaneous reduction of the 
length l, forming a pipe with a very distinctive corrugation. A very 
distinctive corrugation, according to the present invention, is a 
corrugation with a ratio of a corrugation protrusion length to the 
corrugation protrusion height being approximately 1:1. Upon the 
corrugation having been formed, the die 18 is displaced upward, the jaws 
15 are displaced sidewise away from the pipe 1, and the mandrel 13 is 
radially contracted by the wedge shaft being withdrawn therefrom. Then, 
the finished corrugated pipe 1 is taken off from the mandrel 13. The 
corrugated pipe 1 may represent a single pipe or be formed of several 
pipes inserted one into another. 
As it have been discussed above, a corrugation pipe produced by the 
disclosed method has a corrugation with a ratio of a corrugation 
protrusion length to corrugation protrusion height of approximately 1:1 
This ratio proved to be optimal for the intended use of the corrugation 
pipe as an intermediate energy-absorbing element of a steering column of a 
motor vehicle. Experiments have show that the corrugation pipe with the 
corrugation protrusions having the foregoing ratio is optimally deformed 
under a predetermined force. 
Though the present invention was shown and described with reference to the 
preferred embodiments, various modifications thereof will be apparent to 
those skilled in the art and, therefore, it is not intended that the 
invention be limited to the disclosed embodiments or details thereof, and 
departure can be made therefrom within the spirit and scope of the 
appended claims.