EP0706843A1 - Method and device for the production of curved workpieces - Google Patents

Abstract

The method for producing a bent workpiece by combined extrusion and bending is characterised by the fact that the workpiece is bent immediately after its exit from the die of the extrusion press by means of an appropriate tool (a guide roll, for example).

Description

The invention relates to a method for the production of curved workpieces by a combination of extrusion and bending and a device for performing the method.

Extrusion processes for various materials are known in various forms. Mainly aluminum, copper alloys, but also steel and titanium are used. The extrusion process for aluminum is described in detail in the aluminum pocket book, pages 269 - 296.

• Bauteile in der Bauindustrie wie z. B. Fensterprofile, Handläufe an Brückengeländer und Treppenhäusern sowie Träger für Brückenkonstruktionen
• im Waggonbau Konstruktionsprofile und Profilversteifungen in Differential- und Großprofilbauweise
• in der Flugzeugindustrie Sitzschienen, Stringerprofile, Spanten, Fußbodenquerträger
• in der Automobilindustrie Konstruktionselemente wie Fensterrahmen, Dachreling oder dekorative Bauteile wie Zierleisten und Blenden.

Typical extrusions include:

• Components in the construction industry such. B. window profiles, handrails on bridge railings and stairwells and beams for bridge constructions
• In wagon construction, construction profiles and profile stiffeners in differential and large profile construction
• in the aircraft industry seat rails, stringer profiles, frames, floor cross members
• in the automotive industry, construction elements such as window frames, roof rails or decorative components such as moldings and trims.

In the applications mentioned, curved profiles are often also required. These can be used in the form of hollow and solid profiles, whereby multifunctional construction elements are also increasingly required.

From US 5 305 626 (Reynolds Aluminum Holland BV) a method for extruding curved profiles is known in which different frictional resistances on the inner surface of the extrusion die ensure local deceleration or acceleration of the flow process during the extrusion. As a result of the different friction conditions, a curved workpiece shape emerges from the die, which is guided over a curved outlet section, but is not further deformed in the process.

This method has not been successful so far, since it is only profitable for large quantities due to the complex design of the inner contour of the die.

The object of the present invention is to develop a method and a device of the type mentioned at the outset which, with simple means, enable a defined curvature in the case of extruded products in a repeatable, approximately calculable manner, the cross-sectional areas in the bent state also being compared in the case of complicated hollow profile cross sections the cross-sectional areas of the straight profile should remain unchanged. “Complex cross-sections” are understood to mean in particular those with large wall thickness differences, but also those profiles which have a small wall thickness in relation to the circumscribing circle of the extruded profile.

This object is achieved according to the invention by a device and a method according to claims 1 and 5.

With the new process, it is possible to ensure high dimensional accuracy and shape accuracy of curved profiles even over great lengths.

Since the shaping tool can act on the emerging strand in a space free of contact surfaces after the strand has emerged from the die, any bending radii are possible. When exiting the die, the workpiece is subjected to a bending or shear force at the same temperature, as a result of which the stress distribution in the press channel of the extrusion die is influenced.

In principle, it is possible to set any solid angles by appropriately guiding the bending device during the forming process. Usually, the bending device is also moved in the pressing plane, so that simple feed movements of the bending devices are sufficient.

If desired, a ring shape of the workpiece can also be generated with the device according to the invention. For this purpose, the forming tool is brought into a suitable position and fixed there. Alternatively, the workpiece can also be produced with a constant curvature or with an increasing or decreasing curvature as a helical tube or in a spiral shape.

Special devices for pressing solid or hollow profiles are not required in the procedure according to the invention. So z. B. a simple role can be used as a forming tool for both a curved square tube and a curved square rod. It is only necessary to ensure that the geometry of the press, in particular the arrangement of the crosshead, is designed so that it cannot hinder the bending process. In the case of large bending lengths, a support to prevent bending due to its own weight should also be arranged below the workpiece.

However, multiple devices can also be used for bending the extruded profiles, which, however, exert their lateral forces on the extruded profile one after the other. For example, to create spatially curved profiles, one or more guide rollers can be provided on separate delivery devices one or more roller cages arranged one behind the other can be combined.

The required forming force can be applied to the profile both by rollers and by fixed tools. But there are also other active media such. B. gases, fluids or electrical / magnetic fields can be used to generate a suitable forming force. Instead of a forming roller or a fixed sliding block, the zone of influence of the active media must be brought close to the workpiece in the case of the use of active media; for example, when using electromagnetic fields, a suitably shaped magnetic coil must be brought in the immediate vicinity of the strand.

Figur 1:

prinzipieller Aufbau einer erfindungsgemäßen Strangpreß- und Biegeeinrichtung mit Andrückrolle;

Figur 2:

prinzipieller Aufbau einer erfindungsgemäßen Strangpreß- und Biegeeinrichtung mit einer Gleitfläche

Figur 2a:

erfindungsgemäße Vorrichtung mit einem Rollenkäfig;

Figur 3:

prinzipieller Aufbau einer erfindungsgemäßen Vorrichtung zur Herstellung von gekrümmten Werkstücken mit einer, ein Druckmedium erzeugenden Druckquelle;

Figur 4:

Prinzipbild zur Herstellung von gedrillten Profilquerschnitten.

The invention is explained in more detail below with the aid of several exemplary embodiments. Show it:

Figure 1:

basic structure of an extrusion and bending device according to the invention with pressure roller;

Figure 2:

basic structure of an extrusion and bending device according to the invention with a sliding surface

Figure 2a:

device according to the invention with a roller cage;

Figure 3:

basic structure of a device according to the invention for the production of curved workpieces with a pressure source generating a pressure medium;

Figure 4:

Block diagram for the production of twisted profile cross sections.

According to FIG. 1, the extrusion device consists of a punch 1, a block receiver 2, into which the punch 1 can be inserted in the direction of the arrow, and a die 4, which, as seen in the pressing direction, is supported against a crosshead 5.

In the block receiver 2 is the metal heated to the extrusion temperature, for example in the form of an aluminum block 3, which is pressed out of the die in the form of a strand 6 in the pressing direction when the die 1 is actuated.

Immediately after the strand 6 emerges from the die 4, at a distance a from the crosshead 5, there is a pressure roller 7 which exerts a force acting transversely to the direction of extrusion on the workpiece, here the strand 6.

The bending radius R can be influenced by displacing the pressure roller 7 transversely to the extrusion direction. It is readily apparent to the person skilled in the art how he can position or orient the pressure roller 7 by means of a suitable control or regulation in such a way that a predetermined course of curvature is achieved both in a flat and in a spatial configuration. This allows not only the formation of the workpiece curvature in one plane, but also anywhere in space with multiple changes in the feed direction, so that very complex workpiece geometries can be produced with the device according to the invention.

In Figure 2, a further embodiment of the extrusion and bending device according to the invention is shown. Instead of a pressure roller 7, a sliding surface 8 generating a transverse force is shown immediately following the die holder 5. Like the pressure roller 7, this can be adjustable or, as shown in the exemplary embodiment according to FIG. 2, can be arranged in a stationary manner. This allows curved structures to be produced in a simple manner. According to Figure 2a, a roller cage is used in a corresponding manner to apply the transverse force, so that depending on the positioning relative to the die different radii R₁ and R₂ can be applied to the strand.

So far, a particular difficulty with the bending of extruded profiles has been to achieve dimensional stability while maintaining all dimensions of the parts before and after bending. This applies in particular to spatial structures in the case of open profile cross sections, which are particularly sensitive to lateral pressure or to different frictional resistances.

According to the prior art, a change in structure, a hardening of the workpiece and different internal stress distributions, along with a change in geometry (e.g. constriction of the wall thickness, pillow-shaped distortion) was unavoidable during bending processes. Now, with the method according to the invention, a straight or arbitrarily curved workpiece (profile) with always the same geometry and always the same structural and strength properties can be produced in a conventional extrusion die.

With the device according to the invention it has now been possible to solve the manufacturing problems of curved problems in that the workpiece is deformed simultaneously with or immediately after the shaping extrusion process with a precisely metered force. This means that the state of tension during the production of the workpieces is influenced directly during the extrusion, since the extruded sections are bent at the same time as the extrusion process. The workpieces leave the extrusion device with a defined curved longitudinal axis, the curvature of the workpiece being adjustable in a defined manner in the longitudinal axis.

This process is explained in more detail in FIG. 3 on the basis of a geometric view. It should be assumed that the strand 6 emerging from the die 4 is bent by a pressure source 10 which produces a gas cushion 11.

As a starting point for the geometric considerations, it is assumed that there are exactly parallel cuts 12a, 12b in the strand 6 when entering the die 4. The closer these cuts 12a, 12b migrate to the exit end of the die 4, the more their plane parallelism is reduced, so that after the strand 6 exits the die 4, an angle α can be measured between the originally plane-parallel cuts 12a, 12b. It is clear from this that the pressure source 10 arranged at a distance a from the die outlet end exerts a reaction on the profile formed in the extrusion die. In other words: The workpiece cross sections formed in the extrusion die 4 are influenced in such a way that they do not emerge from the die parallel to one another, but are at an angle to one another, the size of the angle being determined by the geometry and the positioning or orientation of the device applying the transverse force.

In the following, a method for determining the feed path of the bending or guiding tool as a function of the contour of the bent workpiece and the press path at a constant radius is shown.

The workpiece contour is linked to certain geometric boundary conditions during manufacture. Because of the manufacturing process, the contour must match the die and be tangential to the exit axis, ie perpendicular to the exit plane.

If a constant radius is to be established, the infeed path z can be determined by the secant equation at a known distance a from the exit plane depending on the radius; $$\text{z = R -}\sqrt{{\text{R}}^{\text{2nd}}\text{-}\frac{{\text{A}}^{\text{2nd}}}{\text{4th}}}{\text{with A}}^{\text{2nd}}\text{= 2 a}$$

If the contour to be produced is generally described as a space curve in a coordinate system, the coordinates per se can be determined for any point and a tangent vector for this point can also be calculated using the methods of curve geometry. With this tangent vector, which is identical to the exit axis according to the conditions mentioned above, the feed path of the guide tool can be determined using simple calculations. It is also possible to determine the length of the contour, so that the infeed path can be specified as a function of the press path. The contour can be available as a function or as a table of values for the control program of a manipulator or the like. Figure 2 shows the geometric approach for any contour.

• Allgemeine Beschreibung der Kontur durch einen Kurvenparameter: F = f(x(λ),y(λ),z(λ)), Gewählt: λ = x. Daraus ergibt sich: F = f(x,y(x),z(x)).
• Die Länge der Kurve für ein bestimmtes x läßt sich über folgende Formel ermitteln:
  
• Der Tangenteneinheitsvektor ergibt sich durch folgende Berechnung: $$\overline{{\text{<figure-callout id="1" label="e" filenames="imgf0001.png" state="{{state}}">e</figure-callout>}}_{\text{1}}}\text{(}\mathit{\text{x}}\text{)=}\frac{\mathit{\text{d}}\overline{\mathit{\text{r}}}\text{(}\mathit{\text{x}}\text{)/}\mathit{\text{dx}}}{\left|\mathit{\text{d}}\overline{\mathit{\text{r}}}\text{(}\mathit{\text{x}}\text{)/}\mathit{\text{dx}}\right|}$$
  
• Mit Hilfe des Tangenteneinheitsvektors kann im 2-dimensionalen Raum die Gleichung einer Geraden bestimmt werden, die senkrecht auf diesem Vektor steht und im Abstand a von der Austrittsebene verläuft.
• Der Schnittpunkt dieser Geraden mit der Raumkurve ist der Kontaktpunkt des Werkzeuges mit der Werkstückkontur. Daraus ergibt sich im 2-dimensionalen Raum der Zustellweg z.
• Da für jedes x eindeutig eine Raumkurvenlänge s, die der ausgepreßten Länge entspricht, und ein Zustellweg z bestimmt werden kann, kann z als Funktion von s dargestellt werden.
• Für den 3-dimensionalen Raum ist die Berechnung aufwendiger, aber auch möglich.
  • c) es sind Bewegungen in beliebiger Raumrichtung möglich, wobei die Führungsrolle beispielsweise durch einen Manipulator gesteuert wird;
  • d) es lassen sich Torsionsbewegungen zur Erzeugung eines verdrillten Stranges durchführen.

Geometric basics for determining the delivery route:

• General description of the contour using a curve parameter: F = f (x (λ), y (λ), z (λ)), selected: λ = x. This results in: F = f (x, y (x), z (x)).
• The length of the curve for a specific x can be determined using the following formula:
  
• The tangent unit vector results from the following calculation: $$\overline{{\text{<figure-callout id="1" label="e" filenames="imgf0001.png" state="{{state}}">e</figure-callout>}}_{\text{1}}}\text{(}\mathit{\text{x}}\text{) =}\frac{\mathit{\text{d}}\overline{\mathit{\text{r}}}\text{(}\mathit{\text{x}}\text{) /}\mathit{\text{dx}}}{\left|\mathit{\text{d}}\overline{\mathit{\text{r}}}\text{(}\mathit{\text{x}}\text{) /}\mathit{\text{dx}}\right|}$$
  
• With the help of the tangent unit vector, the equation of a straight line that is perpendicular to this vector and runs at a distance a from the exit plane can be determined in 2-dimensional space.
• The intersection of this straight line with the space curve is the contact point of the tool with the workpiece contour. This results in the delivery path z in the 2-dimensional space.
• Since a space curve length s, which corresponds to the pressed length, and a feed path z can be determined unambiguously for each x, z can be represented as a function of s.
• For 3-dimensional space, the calculation is more complex, but also possible.
  • c) movements in any spatial direction are possible, the guide roller being controlled, for example, by a manipulator;
  • d) torsional movements can be carried out to produce a twisted strand.

In any case, it must be ensured that the bend at a distance a from the exit plane allows reaction via the extruded product into the shaping zone of the extrusion press. This means that there are no contact surfaces for the extruded profile to be bent in the space between the transverse force or extruded surface and the exit plane of the strand.

Under this condition, the bending process takes place during the extrusion process by superimposing stress in the plastic state. The profile cross-sections emerging from the die are identical to the cross-sectional areas that would be produced in straight extrusion. The wall thicknesses are unaffected by the bending and are absolutely true to shape over long press lengths even with twisted profile sections.

4 shows the production of twisted profile sections. The strand 15 emerging from the die 14 is inserted into a roller cage 16, the roller axis 17 of which is rotated by an angle β with respect to the vertical profile edge 18. The hatched area 19 represents the profile opening in the die 14 in a view against the pressing direction. The roller cage in front of the die is thus twisted by an angle β against the orientation of the profile.

Claims (12)

Process for the production of curved workpieces, in particular solid and hollow profiles with complex cross sections, by a combination of extrusion and bending, characterized, that the workpiece is bent simultaneously with or immediately after the shaping extrusion process by a force acting transversely to the extrusion direction on the workpiece. Method according to claim 1, characterized, that the curvature of the workpiece occurs when it emerges from the extrusion die. The method of claim 1 or 2, characterized, that the force acting on the workpiece to form different bending radii during the extrusion process is varied according to direction and strength. The method of claim 1 or 2, characterized, that a force component acts as a tensile or compressive force in the shaping extrusion process on the cross-sectional areas of the resulting profile walls. Device for carrying out the method for producing curved workpieces by a combination of extrusion and bending consisting of a block heating system, an extrusion device with a die, which has an exit plane at the exit of the strand, and devices for block handling, shearing or conveying devices and a cooling section, characterized, that seen after the die in the extrusion direction, a shear force generating device is arranged which can be pressed against the emerging strand, wherein in the space between the extrusion surface and the exit plane there is a bending zone free of contact surfaces. Device according to the preceding claim, characterized, that the device generating a transverse force consists of a roller that can be pressed against the emerging strand. Device according to one of the preceding claims, characterized, that the device applying a transverse force consists of one or more sliding surfaces. Device according to one of the preceding claims, characterized, that the device applying a transverse force consists of a cage with rollers or sliding surfaces. Device according to one of the preceding claims, characterized, that the device applying a transverse force consists of a pressure source producing a gas cushion. Device according to one of the preceding claims, characterized, that the device generating a lateral force consists of an induction coil. Device according to one of the preceding claims, characterized, that the transverse force is applied to the strand via an infeed path which runs essentially parallel to the strand exit plane. Device according to one of the preceding claims, characterized, that the passage cross sections of the die and roller cage are rotated or offset from one another about the extrusion axis to produce a helically curved strand.

Images