Metal deforming – By application of fluent medium – or energy field – Using fixed die
Reexamination Certificate
2002-02-05
2004-07-20
Larson, Lowell A. (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
Using fixed die
C072S370220
Reexamination Certificate
active
06763693
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for forming an initial section or like component featuring a hollow interior to a final shape by means of high internal pressure in the sealed hollow interior using a medium that can flow, in particular forming until the final section comes into contact with the wall of a shape-determining space. Further, the invention also relates to a section with a space delimited by section walls, in which two section walls each determine a corner region of the cross-section, in particular an initial section for carrying out this process.
In the high-internal-pressure-forming (HIPF) process a hollow section is expanded by means of internal pressure. In addition, by means of at least one stem engaging the part in question, the hollow section may be displaced and widened, compressed or expanded.
German Patent DE 35 32 499 C1 describes a device for hydraulic expansion of a length of pipe by using a plug-like cylindrical probe which can be introduced into the pipe and, using at least a pair of sealing rings spaced a distance apart, forms a circular space which is filled with compressive medium for the purpose of expanding the tube. Each of the sealing rings is situated in a ring-shaped grooved with a u-shaped in cross-section, in the probe and initially upon introducing the probe into the tube, has an outer diameter which at most is the same as the outer diameter of the probe. Before starting the expansion process, in order to seal the ring-shaped gap between the probe and the tube, compressive medium is introduced into the ring-shaped grooves via a feed pipe connected to the medium supply line and applies compressive force radially to the sealing rings. The feeding of the compressive medium to the ring-shaped space is performed solely by way of at least one of the grooves and is controlled by a sealing ring acting as a valve, which closes off an opening between the groove and the ring-shaped space until it has achieved its sealing function by elastic expansion. That groove is provided with at least one inclined slit at its edge neighboring the ring-shaped space. If the pressure in the ring-shaped space between the two seals is increased, the wall of the tube begins to expand in this region.
This internal high pressure forming or hydroforming process is finding ever increasing application in the automobile industry as an economical means for manufacturing car body components. Mainly steel tubes are employed as starting material. The final contour of the component to be shaped this way is generally much more complicated than the simple circular cross-section of the starting material. As a rule, the HIPF process results in regions which are much more heavily deformed than other regions and which are correspondingly thinner. If these regions are subjected to a high degree of loading in use, the initial sheet must be sufficiently thick; this however results in an unnecessary amount of material in the less heavily formed regions. This disadvantage is contrary to the requirement of obtaining the lowest possible weight in the component.
Recently aluminium alloys have been included along with steel as starting material for HIPF processes. As with steel there are manufacturing processes in which tubes of aluminium sheet are employed as starting material; alternatively, extruded aluminium sections may also be employed for that purpose. For economic reasons extruded steel sections do not come into question here. The use of extruded sections has the decisive advantage that the shape of the initial section is almost without limit.
HIPF processes using extruded sections are employed mainly to be able to produce high precision parts. To that end the present state of the art tends to make the shape of the initial section as close as possible to that of the final section in order to employ relatively small degrees of deformation in the HIPF-process. In particular with curved components that are to be bent in advance or where the section cross-sections feature sharp corners, this approach is usually not successful. Also, attempts to keep the degree of deformation small generally results in its non-uniform distribution. As a result—and due to the pre-shaping from the bending process—spring-back effects are produced causing the desired precision to be achieved only in exceptional cases using that process. Likewise as a rule, sharp corners which exhibit a large ratio of wall thickness to outer radius cannot be filled out using this process.
In HIPF-processes using steel pipes it is normal to carry out pre-shaping prior to the actual shaping process (bending and HIPF)—this e.g. in order to arrive at a more favourable cross-section for bending or in order to make it even possible to place the part in the HIPF shaping tool.
SUMMARY OF THE INVENTION
In view of the above, the object of the present invention is to provide a specific cross-section of an extruded section which achieves a favorable distribution of deformation in the HIPF-process; the elastic spring-back of the component after removal from the HIPF shaping tool should be minimized and dimensional accuracy achieved to the desired degree of precision.
In accordance with the present invention, in order to shape-form the initial section featuring at least one corner region, the wall sections adjacent to the corner region are pre-shaped in a curved manner—as viewed in cross-section—counter to the direction of applied pressure, and subsequently reshaped by applying the high internal pressure of the medium that can flow in the direction in which the pressure is applied, displacing the corner region. If there are at least two corner regions present, the wall lengths between the corner regions are accordingly pre-shaped counter to the direction in which the pressure is applied and reshaped—likewise by applying the high internal pressure of the medium that can flow, displacing the corner regions in the direction in which the pressure is applied.
In practice the reshaping will mainly concern angles that are almost right angles, whereby the section cross-sections need not have rectangular shaped contours. However, other sizes of angle can be reshaped, in particular corners running to a peak with angles of less than 45°.
It has been found favorable to carry out the displacement of the corner region in the direction of the line bisecting the angle or its line of symmetry. In the initial section this corner region should also be of greater thickness.
The local degree of deformation can be created in the initial section in the form of oversizing with respect to the final contour of the final section, this by means of a doming—inward pointing curvature in the section cross-section. It is also possible to introduce the degree of deformation in the initial section in the form of undersizing with respect to the final contour of the final section.
Usefully, therefore, the requirements for precise light weight construction are met i.e. the initial section is designed in such a manner that at the end of the HIPF process the component exhibits an accumulation of material mainly in those places where, for reason of strength, this is required. In order to achieve the above mentioned goals:
the local degree of deformation of the section wall is controlled by curvature in the cross-section and by lengths of section with local undersizing and, in this connection, the internal stress oriented in the longitudinal direction;
section corners are made more pointed;
those lengths of section which should undergo little or no deformation are made thicker;
section cross-sections are curved in advance.
Controlling the local degree of deformation by means of dome-like, inwards pointing curvature of the cross-section, and section lengths that are undersized locally, is achieved using the following principle.
The inwards pointing curvature of the cross-section is important here; especially with regard to cross-sections whose section walls are curved in the final component, it is emphasized that it depends on the relative curvature and
Gehrig Markus
Leppin Christian
Schwellinger Pius
Alcan Technology & Management Ltd.
Larson Lowell A.
Ostrolenk Faber Gerb & Soffen, LLP
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