[0001] The present invention relates to a roll-shaped thin plate metal profile, the strength
and/or shaping properties of which vary partially in its longitudinal direction.
[0002] The material content of roll-shaped profiles available today does, in its longitudinal
direction, exhibit constant strength and/or shaping properties. Accordingly, these
prior art profiles have a strength, which is constant along all of its length, which
per se is not a disadvantage in most applications. However, in the fields where e.g.
the weight of the profiles may be of importance, e.g. within the aircraft and motor
car industry, this is a drawback, since it is not necessary for the profile to have
the same strength and shaping properties along all of its length. Instead, in those
cases it would be enough if the profile had a sufficient strength corresponding to
the calculated load or stress. It has also proved difficult, when the roll-shaped
profiles consist of ultrahigh strength steel, later to carry out some form of shaping,
e.g. embossing on the surface of the profile, bending it or carrying out a subsequent
punching of the material.
[0003] The object of the present invention is to provide a roll-shaped metal profile of
the kind mentioned above, at which the disadvantages enumerated above have been eliminated.
The features characterizing the invention are set out in the claims.
[0004] Thanks to the invention there has now been provided a roll-shaped thin plate metal
profile, which in an excellent manner fulfils its purpose and, in addition thereto,
at the same time is both simple and cheap to manufacture. By use of the profile according
to the invention it becomes possible to match the width of the flat blank, from which
the profile is made, to the relevant stress. In this way the weight can be reduced
with maintained bending stress strength. The profile according to the invention can
be manufactured both as I-beams and tubes having a circular or square cross-section.
In those load cases, when the profile is clamped at its one end and the force is applied
at the other end, the greater material area is at the clamped end. If the profile
is loaded between two support points, the greater material cross-sectional area should
be at the center. In order to facilitate a finishing shaping or machining of the profile
either the blank, from which the profile is made, or the finished profile is exposed
to a partial heating to above 300°C, which produces a remaining reduction of the rupture
and tensile limits of the profile material.
[0005] Some chosen preferred embodiments of the invention will now be described with reference
to the drawing, in which
- Fig. 1
- shows a profile-blank having varying width and used to produce a profile in the shape
of a tube according to the invention,
- Fig. 2
- shows a completed tube or post according to the invention made from the profile blank
in Fig. 1, four different cross-sections through the tube being illustrated,
- Fig. 3
- shows an alternative embodiment of a blank for a profile constituted by an I-beam,
- Fig. 4
- shows, at four different cross-sections, a roll-shaped profile in the form of an I-beam
made from the blank in Fig. 3,
- Fig. 5
- shows a cross-section through a profile, which according to the invention has been
given a tubular shape, and
- Fig. 6
- shows in a compacted manner the roll-forming steps starting from a blank exhibiting
a varying width and generating the profile shown in Fig. 5.
[0006] As appears more in detail from the embodiment of the invention illustrated in Figs.
1 and 2, one has here started from a flat blank 1 of varying width, which is intended
to match the strength properties desired in the completed profile 2, which is in detail
and in cross-section illustrated in Fig. 2. This profile 2 is intended to form a post
or a strut for e.g. a vehicle and the flat blank 1 of the profile 2 does at its base
3 have a width greater than that at its top portion 4. In this way the completed post
or tube will have its greatest strength at the lower portion, or mounting portion,
where the stress is highest, in the case that the post or strut is to be used to support
e.g. a road sign or as a strut in a vehicle or the like. The upper portion 4 of the
profile 2, where the stresses are not so high, has been made weaker. In this way there
has been provided a profile 2, which both has a lower weight and where the material
consumption is lower compared with conventional profiles having a uniform cross-sectional
profile.
[0007] Figs. 3 and 4 illustrate an alternative embodiment relating to a blank 7 and its
profile 5 forming an I-beam to be used in the back support of a motor car chair, in
which the highest stress in the profile 5 is at the mounting end 6. Figs. 5 and 6
show an alternative embodiment, according to which the blank 11 for the profile 10
is tubular and exhibits inwardly folded portions 8, 9, the extension of which in the
transverse direction of the profile 10 varies in the longitudinal direction. Consequently,
also in this embodiment material is conserved, the strength of the profile 5, 10 being
highest in the places where it is most exposed to forces. In the above-mentioned tubular
profiles 2, 5, 10 having a non-linear material content one has thus attained a lower
weight completely or partly maintaining the strength against bending stresses. When
the profile 2, 5, 10 is manufactured it is shaped starting from a flat metallic blank
1, 7, 11 in long, rolled strips, which are cut before or after having been given a
roll profile. The profile 2, 5, 10 can also be manufactured from prestamped blanks
of formate sheet. If the roll profiling starts from a strip, the width thereof can
be varied in a non-linear manner in the way that material is separated by cutting,
stamping, nibbling or by different shearing methods. If the roll profiling starts
from blanks, the width thereof can be varied according to the methods described above.
[0008] Roll-shaped profiles 2, 5, 10 of an ultrahigh stress steel having a tensile limit
above e.g. 700 N/mm
2 must partially be given a greater plastic deformation than that which the starting
material tolerates without rupturing. According to the invention this can be achieved
in the way that the blank, or the completed profile, is partially heated to above
300°C, resulting in a remaining reduction of the rupture and tensile limits, which
facilitates a subsequent shaping. This shaping may consist in e.g. a bending of the
profile or in a punching or embossment of the material, which process is then facilitated.
The heating can be carried out according to different methods, e.g. induction heating,
laser heating or with the use of hot dies. In certain cases it could also be suitable
to heat portions of the completed profile 2, 5, 10 in order to attain a reduction
of the rupture and tensile limits in preparation of a subsequent treatment.
[0009] In the motor car manufacturing industry the thickness difference between plates to
be welded together butt to butt must not be too great. The thickness ratio 1:2 is
suitable. However, in the use of sheets of a high-stress material having a tensile
limit exceeding 700 N/mm
2, the critical parameter is not the thickness but rather the strength of the material.
The reason for this is that such sheets have a strength about 6 times that of an ordinary,
soft sheet. To get a smooth transition between the materials one can heat the ultrahigh
strength steel sheet at the transition to the ordinary, soft sheet to a temperature
above 300°C in locations along all of the edge secured to the soft sheet. Accordingly,
this partial heating is used on the one hand to facilitate a subsequent treatment
of the ultrahigh strength steel and, on the other, to achieve a soft transition in
the weld joint between it and an ordinary, soft sheet. If this treatment is not carried
out the weld joint will rupture due to the different strength properties of the two
materials.
[0010] A partial heating of the ultrahigh strength sheet is also carried out in such portions
of the sheet which shall be adapted to serve as deformation zones in e.g. vehicles.
This is done to diminish the damages, which otherwise would occur upon a collision,
namely if certain exposed portions of a vehicle are more easily deformed than other
portions also consisting of that ultrahigh strength material.
1. A method for attaining a reduction of the rupture and tensile limit of a metal blank
or metal profile of an ultra-high strength material, characterized in that the blank or profile is exposed to a heat treatment by partial heating to above 300°
C within selected portions of the sheet in order to produce a remaining reduction
of the rupture and tensile limit to facilitate a subsequent shaping or to produce
deformation zones.
2. A method according to claim 1, characterized in that said tensile limit amounts to above 700 N/mm2.
