EP1107837B1 - Internal high pressure forming method for a workpiece - Google Patents

Abstract

A method and an apparatus are provided for internal high-pressure forming of a workpiece in a closed internal high-pressure forming die. The workpiece is expanded owing to the internal high fluid pressure exerted by a pressure generator and coming to rest on the cavity of the forming die. The workpiece and the forming die form friction partners in the areas of contact. In order to improve process reliability during the internal high-pressure forming of workpieces and to expand the scope of the method, vibration is imparted directly to at least one of the friction partners by a vibration generator during forming.

Description

The invention relates to a method for hydroforming a workpiece according to the preamble of the claim 1 and a device for performing the same according to the preamble of claim 11.

A method according to the preamble of claim 1 GB-A-2 240 944. A device according to the preamble of claim 11 is from CH-A-334 023 known.

A generic method or a generic device is also known from DE 94 07 812.2 U1. in this connection is a hollow profile forming the workpiece in a longitudinal the extension of the hollow profile divided internal high pressure forming tool inserted, after which this is closed. The hollow profile is then axially punched at both ends sealed. About the axial punch the interior of the hollow profile is filled. The axial punch are fluidly connected to a pressure generator. thereupon internal pressure is generated by means of the pressure generator of the hollow profile applied, whereby this expanded until it lies against the wall of the tool engraving. The tool engraving shows one of the hollow profile extension radially discharging branch into which the hollow profile material due to the high pressure inside Formation of a neck is pushed into it. Here too the material attaches itself to the branch wall. The expansion process within the branch is by one in the branch slidably guided counter slide stabilized, which supports the necking in the end area. Around the limits of failure with regard to bursting during the pure expansion, in which the length of the hollow profile shortens and thus a larger flare length of the neck is obtained by an additional axial force that is applied by retracting the axial punch, hollow profile material pushed to the junction, causing the Material thinning in the branch area responsible for bursting is at least partially compensated. Nevertheless limited when the hollow profile material is applied to the engraving wall, especially in the branch between the Tool and the hollow profile emerging and with increasing Internal high pressure, increasing friction - even if that Hollow profile on the outside with a lubricant is provided - the formability of the material is considerable This is especially true for materials with little Forming ability very problematic.

The invention has for its object a generic Method and a generic device to that effect to further develop that process reliability in hydroforming of workpieces is improved.

The task is according to the invention by the features of the claim 1 regarding the procedure and by the Features of claim 11 with respect to the device solved.

Due to the vibration excitation on one of the friction partners Workpiece - forming tool becomes the friction of the workpiece on the engraving wall between the maxima of the Vibration is reduced in the meantime, since there the investment power of the workpiece is lowered on the forming tool. That is, it takes place periodically during the forming process partial relief of the normal contact voltage between the workpiece and the tool. In drastic cases this can be such that the workpiece separates itself completely from the tool at short notice. Due to the associated reduction in friction however also the resistance for a flow or tracking the workpiece material is smaller towards the shaping point, so that more material moves to this location without failure can be. A thinning of material in the molding area is thus counteracted, one for the Forming more favorable material distribution, especially one achieved more uniform wall thickness distribution and / or the Degree of deformation can be increased. For example with a Branch from the engraving, i.e. in the formation of a neck this can mean an increase in the extension length. The process limits are e.g. with respect to the production of secondary form elements can be expanded. Of more can due to the increased material replenishment also narrower radii on the workpiece without the occurrence of a Cracks can be trained reliably. Overall will by the invention an improved forming of Workpieces made of materials with low deformability reached. By partially decoupling the process parameters from the tribological conditions achieved higher process stability. For an optimal Interpretation of the process with the greatest possible benefit for the the respective transformation is the vibration in its amplitude and frequency with regard to the workpiece material and the degree of deformation of the shape to be achieved, that is Geometry of the finished workpiece or other relevant Adapt process parameters accordingly. About that the body vibration of the friction partners also leads when using lubricants on the surface of the workpiece for a more even distribution of lubricants, which leads to a further reduction in friction. Due to the vibrating relative movement of the friction partners to each other and the activation of the brought Lubricant becomes an adhesive contact with a simultaneous reduction sliding friction largely avoided, or the transition from static to sliding friction (stick-slip effect) significantly reduced. This makes it a less demanding one Lubricant choice and / or a lower lubricant application or even a waiver of lubricant with warranty an improved forming possible.

Fig. 1 in einem seitlichen Längsschnitt eine erfindungsgemäße Vorrichtung, die aus mehreren Umformwerkzeugteilen mit Schwingungserregern besteht,

Fig. 2 in einem seitlichen Längsschnitt eine erfindungsgemäße Vorrichtung, mit einem Schwingungserreger, der mit dem Werkstück gekoppelt ist,

Fig. 3 ein Kraft-Zeit-Diagramm zur schwingungsanregenden Steuerung eines der Reibungspartner mit im Mittel steigendem Kraftverlauf,

Fig. 4 ein Kraft-Zeit-Diagramm zur schwingungsanregenden Steuerung eines der Reibungspartner mit im Mittel konstantem Kraftverlauf.

Expedient embodiments of the invention can be found in the subclaims; otherwise, the invention is explained in more detail below with reference to two exemplary embodiments shown in the drawings; shows:

1 in a lateral longitudinal section an apparatus according to the invention, which consists of several forming tool parts with vibration exciters,

2 shows a device in accordance with the invention in a lateral longitudinal section, with a vibration exciter which is coupled to the workpiece,

3 shows a force-time diagram for the vibration-stimulating control of one of the friction partners with an average increasing force curve,

4 shows a force-time diagram for the vibration-stimulating control of one of the friction partners with an average constant force curve.

In Fig. 1 is a device 1 for expanding internal high pressure forming of a workpiece 2 shown in this embodiment formed by a hollow profile but also from two superimposed boards may exist for the purpose of expanding the boards. The device 1 includes a hydroforming tool 3, which in a Upper tool 4 and a lower tool 5 is divided, which with their engravings 6 the mold space 7 for the to be expanded Form hollow profile 2. The upper tool 4 has a radial branch 8 protruding from the main direction of the molding space 7 in which a the internal high pressure within the hollow profile 2 counteracting stamp 9 of the device 1 is guided. The controlled controllable Counter stamp 9 serves to stabilize the material flow of the workpiece material when the branch is formed 8 true-to-contour neckline 10 and thus serves one reliable molding at this point of the hollow profile 2, the counter-punch 9 receding as the neck length increases.

Furthermore, the upper tool 4 has several tool parts 11, 12 and 13, the tool part 11 having a housing forms to the hollow profile 2 open upper receiving space 14, in which the other two tool parts 12 and 13, which for the widening forming essential section of the engraving 6 include, held movable relative to the hollow profile 2 are. In Fig. 1 it can be seen that the tool parts 12 and 13 radially to the rectilinear section of the Hollow profile 2 are movable. However, it is also conceivable that the tool part 13 alone, the area of the branch 8 limited, radial to itself when subjected to internal high pressure forming neck 10 is movable. Here, the tool part 13 is on a side wall 15 of the receiving space 14 is slidably supported. Farther it is conceivable that the tool parts 12 and 13 with each other are connected in one piece and both radially to the straight line Part of the hollow profile inserted into the forming tool 3 2 as well as axially to this and thus radially to the neck 10 of the hollow profile 2 are displaceable. Although in only half of the device 1 is shown in the drawing is, their complete formation is mirror-symmetrical to be presented on the central axis 16.

The lower tool 5 has a lower one which is open at the top Recording space 17 in which a tool part 18 of the lower tool 5, which essentially includes the lower engraving, is guided for lifting. The hollow profile 2 is the further sealed at both ends by a sealing stamp 19, which during the forming process is either rigid at one time assumed position of use while ensuring a tight metallic clamp connection between the hollow profile 2 and the sealing cone 20 of the sealing plunger 19 remains or the one corresponding to the expansion of the Hollow section 2 resulting axial shortening of the hollow section 2 is trackable. The seal can also be used instead of the sealing cone 20 via a suitable radial seal. Otherwise, it is also conceivable by additional application an axial force on the hollow profile 2 by means of Seal 19 hollow profile material in the area of the bulge of the hollow profile 2, that is, the branch 8 of the forming tool 3, from the ends of the hollow profile 2, so that the process safety of training the Necking 10 can be increased further. For the following described inventive method for forming of the hollow profile 2, it is not absolutely necessary that the tool parts 11, 12, 13 and 18 can all be moved are. Depending on requirements, these can also be arranged rigidly be or only one or two tool parts can be moved.

It is also conceivable that the tool parts 11, 12 and 13th all of them vibrate during the forming process, but that guided along the tool parts 12 and 13 and radially to the hollow profile 2 tool part 11 oscillating with higher Amplitude is excited. This has the advantage that the friction relief particularly strongly on the end of the hollow profile lying pushing area affects, so that Feeding material there is made considerably easier and thus the areas of higher degrees of deformation like the area the neck 10 due to the increased material offer can be formed particularly reliably. The Friction relief for the rest of the engraving area 6 remains due to the also vibrating tool parts 12 and 13 maintained.

After the hollow profile 2 is inserted into the forming tool 3 was closed, after which the sealing stamp 19th be moved into their sealing position of use. The counter stamp 9 is in its starting position with its End face 21 is flush with the engraving 6 of the upper tool 4. Then a feed hole inside the Sealing plunger 19 pressure fluid introduced into the hollow profile 2, after which the pressurized fluid by means of a high pressure generating plant, which are fluidly connected to the feed bore is high tension. By unfolding the internal high pressure the hollow profile 2 widens, whereby whose walls on the engraving 6 of both the upper tool 4 as well as the lower tool 5.

In the area of the branch 8, the counter-stamp 9 gradually becomes retracted, the hollow profile material as a bubble in the free by the withdrawal of the counter-stamp 9 Expansion space displaced by means of the internal high pressure becomes. This bubble lengthens the further the counter-stamp 9 is moved back and lies on the wall of the branch 8 to form the neck 10.

When the hollow profile 2 is applied to the engraving 6 or in the Neck 10 on the wall of branch 8 forms that Hollow profile 2 for the further forming process with the forming tool 3 a friction partner because of the hollow profile material for further shaping, i.e. for further flow to the forming point, the static friction on the forming tool, to which it is pressed by high pressure, must overcome. Because this frictional resistance is reliable Forming due to the thinning of the material runs on the hollow profile 2, it is the intention of Invention to reduce friction and thus process reliability increase in the forming. Here you can also the process limits of internal high pressure forming be extended without damage.

For this purpose, the device 1 contains at least one body vibration exciter, at least during the forming process vibrates a friction partner in such a way that a radial relative movement of the friction partners to each other reveals that their placement between the maxima 22nd the body vibration is canceled (Fig. 3 and 4). For this there are several possibilities in the device 1 as required given. The tool parts 11, 12, 13 and 18 oscillating together or independently of one another Vibration frequency in the Hertz or Kilohertz range, but preferably in the range of 0 <ν ≤ 200 Hz mechanically by means of a reciprocating piston as vibration exciter, which can be moved back and forth via an eccentric drive is to be moved. The body vibration is thereby in the form of a longitudinal wave directed towards the hollow profile 2 is initiated. The vibration exciter can too a piezo element or a pulsed electromagnet. The vibration exciter can save space in the forming tool 3 be integrated. An acoustic is also conceivable Excitation of the tool parts 11, 12, 13 and 18. Des the counter-stamp 9 can also be equipped with such Vibration exciter is provided, where the system of Cap 24 of the neck 10 on the end face 21 of the counter-punch 9 is reduced by the vibration. includes the device 1 additionally punch for punching of holes on the circumference of the hollow profile 2 or shaping Stamps, for example, when forming blanks, can these can also be coupled with a vibration exciter. The Depending on the progress of the process, vibration can be damped by means of of a spring-damper system 25, which are in the lower tool 5 on the one hand on the floor 26 of its receiving space 17 and on the other hand on the side facing the bottom 26 27 of the tool part 18 supports. In the upper tool 4 supports this system 25 on the ceiling wall 28 of the receiving space 14 on the one hand and on the other hand on the facing sides 29.30 of the tool parts 12 and 13. The locking force the tool parts 11, 12, 13 and 18 swing into their respective Normal position back during the forming process. in this connection it is conceivable that the locking force increases until the end of the process (Fig. 3) or throughout the process remains constant (Fig. 4). The vibration can be a pure sine wave 23 run with flat amplitudes (FIG. 3) or as a sawtooth 31 (Fig. 4) or as a result of Rectangular pulses can be designed. The sawtooth shape and the Rectangular pulses are advantageous for the process in that that due to the very steep flanks of the Vibration patterns periodically a spontaneous complete cancellation the system of the two friction partners can be achieved, which reduces the overall friction particularly strongly becomes. It is also conceivable that the entire upper tool 4 or / and the entire lower tool 5 for swinging is excited.

Another way of getting a vibration to the friction partner to be applied, the excitation of the hollow profile 2 himself. This can be achieved via the sealing stamp 19, the one with the vibration exciter on the one hand and in sealing Use position with the workpiece, i.e. with the hollow profile 2 is coupled. 1 serves as a vibration exciter a reciprocating piston 32 with eccentric drive 33, the Reciprocating piston 32 in the radial direction with the sealing plunger 19 vibrationally coupled. When stimulated spreads thereby a transverse wave in the hollow profile 2 along its Shape course, which also radially oscillating Relative movements of the hollow profile 2 to the surrounding one Tool 3 arise. With this possibility is also one Combination of the introduction of transverse waves into the Hollow profile 2 and longitudinal waves in one tool part 12, 13 and 18 for a particularly strong lifting of the hollow profile 2 conceivable from the adjacent forming tool 3.

The vibration excitation can also be rotary by initiation of a torsional vibration if - as in FIG. 2 is shown - the friction partner, the hollow profile 2 and a the engraving 6 includes two half-shells Tool part 34 of the forming tool 3, rotationally symmetrical are trained. The half shells are in the upper tool 4 or in the lower tool 5 in short circumferential grooves held. While the tool part 34 directly in Circumferential direction by a few degrees of angle or even only fractions of which can be driven back and forth quickly, the torsional vibration must be introduced into the hollow section 2 be conveyed by the sealing stamp 19, the one the rotary actuator forming the vibration exciter accordingly the direction of the arrow is driven. The suggestion of Tool part 34 favored by a torsional vibration in tool-technically simple way of feeding Hollow profile material from the end region of the hollow profile 2, since the end area of the remaining hollow profile 2 of the excitation point is closest and therefore most intensely recorded becomes. It is due to the relatively small size too actuating mass of the tool part no high travel and Bearing forces required. It is also an education of the tool part 34 possible as a closed sleeve, which in corresponding recesses of the lower tool 5 in front of the Forming is inserted and then by the not yet formed, straight hollow profile 2 is passed through. Then the upper tool 4 is on the lower tool 5 is lowered and thus the forming tool 3 closed to the sequence of the forming.

Furthermore, it is also possible to excite the vibrations take place before engaging the hollow profile 2 on the engraving 6 to let, since then the adhesion of the Hollow profile 2 at the engraving reduced or even prevented becomes.

Finally, it should be noted that the vibration excitation the friction partner also through a combination of translational and rotational suggestions can be made.

Claims (16)

1. A process for the internal high-pressure forming of a work piece (2) in a closed internal high-pressure forming tool (3), the work piece (2) being expanded by means of the fluid internal high pressure exerted by a pressure generator and coming into contact with the engraving of the forking tool (3), the work piece (2) and the forming tool (3) forming friction partners (2, 4, 5, 10, 11, 12, 13, 18, 34) in the areas in which they come into contact,
   characterised in that
   during forming at least one of the friction partners (2, 4, 5, 10, 11, 12, 13, 18, 34) is set oscillating (23, 31) directly by an oscillation exciter.
2. A process in accordance with claim 1,
   characterised in that
   the oscillation (23, 31) is introduced into the work piece (2) in the form of a transverse wave which spreads along its length.
3. A process in accordance with claim 1,
   characterised in that
   oscillation is excited mechanically.
4. A process in accordance with claim 1,
   characterised in that
   oscillation is excited by means of a piezo element.
5. A process in accordance with claim 1,
   characterised in that
   oscillation is excited acoustically.
6. A process in accordance with claim 1,
   characterised in that
   oscillation is excited electro-magnetically.
7. A process in accordance with claim 1,
   characterised in that
   the oscillation (23, 31) is introduced into at least one forming tool part (11, 12, 13, 18) in the form of a longitudinal wave directed towards the work piece (2).
8. A process in accordance with claim 1,
   characterised in that
   the oscillation (23, 31) has a frequency in the hertz or kilohertz range, in particular within a range of 0 < υ ≤ 200 Hz.
9. A process in accordance with claim 1,
   characterised in that
   if the friction partners (2, 34) are rotationally symmetrical the oscillation can be excited by the introduction of a rotary oscillation.
10. A device for the internal high-pressure forming of a work piece (2) with an internal high-pressure forming tool (3) split along the length of the work price and connected to a fluid pressure generator, the forming tool (3) and the work piece (2) forming friction partners (2, 4, 5, 10, 11, 12, 13, 18, 34) when the work piece is in the expanded state process, and with at least one sealing die (19) by means of which the work piece can be sealed axially, to carry out the process in accordance with claim 1,
    characterised in that
    that the device (1) contains at least one oscillation exciter which is designed in such a way that is connected to at least one of the friction partners (2, 4, 5, 10, 11, 12, 13, 18, 34) in such a way as to excite oscillation and is able to excite oscillation in it directly during the forming process.
11. A device in accordance with claim 10,
    characterised in that
    the oscillation exciter is a piezo element.
12. A device in accordance with claim 10,
    characterised in that
    the oscillation exciter is an electromagnet.
13. A device in accordance with claim 10,
    characterised in that
    the oscillation exciter is a reciprocating piston (32) which can be moved back and forth by means of an excentric drive unit (33).
14. A device in accordance with claim 10,
    characterised in that
    in the event of oscillation excitation at least one tool part (11, 12, 13, 18, 34) of the oscillation exciter is integrated in the forming tool (3).
15. A device in accordance with claim 10,
    characterised in that
    the oscillation exciter is a rotary actuator which is in active contact with a rotationally symmetrical friction partner (2, 34).
16. A device in accordance with claim 10,
    characterised in that
    the oscillation excitation is linked to the work piece (2) by means of the sealing die (19).

Images