DEVICE AND METHOD FOR THE AUTOFRETTAGE OF A WORKPIECE

Abstract

A method for the autofrettage of a workpiece may involve arranging the workpiece between a first securing means and a second securing means, and applying high-pressure fluid to an internal volume of the workpiece that is formed between the first and second securing means. A die or ram may be driven into the internal volume through an inlet in the first securing means. Consequently, as a result of the ram being advanced, not only is a fluid pressure generated in the internal volume, but also the workpiece is mechanically autofrettaged by way of the ram. A device may be employed to perform such hydromechanical autofrettage of the workpiece.

Claims

1.-17. (canceled)

18. A method of autofrettage comprising: positioning a workpiece between a first securing means and a second securing means; applying high-pressure fluid to an internal volume of the workpiece formed between the first and second securing means; driving a die into the internal volume through an opening in the first securing means; and by movement of the die, generating a fluid pressure in the internal volume and mechanically autofrettaging the workpiece.

19. The method of claim 18 wherein the die is driven into the internal volume such that high-pressure fluid is pressed between a head of the die and the workpiece and flows along the die in a direction of the first securing means.

20. The method of claim 18 wherein the die is driven until the die enters a high-pressure proof recess in the second securing means.

21. The method of claim 18 comprising filling the internal volume pressurelessly with high-pressure fluid before the die is driven into the internal volume.

22. The method of claim 18 wherein a pressure-induced widening of the workpiece depends on a size of the die, wherein the pressure-induced widening of the workpiece is independent of a rate at which the die is driven.

23. The method of claim 18 comprising controlling the movement of the die such that a strain of the workpiece causes high-pressure fluid to flow from the internal volume past a head of the die.

24. The method of claim 18 comprising at least one of: building up the fluid pressure in the internal volume from an outside at the first and second securing means after introducing the die into the workpiece; or adjusting the fluid pressure in the internal volume to a defined value, which is below a pressure level that results due to the movement of the die, by way of a pressure limiter connected to the second securing means.

25. The method of claim 18 wherein the fluid pressure for hydraulic autofrettage is generated by way of the die, wherein the workpiece is mechanically autofrettaged by way of a head of the die that is oversized relative to an internal dimension of the workpiece.

26. An autofrettage tool apparatus for autofrettage of a workpiece, the autofrettage tool apparatus comprising: a first securing means that includes an opening; a second securing means, wherein an internal volume of the workpiece is positionable between the first and second securing means, wherein the internal volume of the workpiece is configured to receive high-pressure fluid; and a die configured for mechanical autofrettage of the workpiece, wherein the die is configured to be positioned in the opening of the first securing means, wherein the autofrettage tool apparatus is configured for hydromechanical autofrettage of the workpiece by way of high-pressure fluid and the die.

27. The autofrettage tool apparatus of claim 26 wherein at least one of: the opening of the first securing means is flush with a longitudinal axis of the workpiece; or the second securing means comprises a recess that is flush with a longitudinal axis of the workpiece, the recess being configured as a high-pressure proof recess for high-pressure fluid or for a head of the die.

28. The autofrettage tool apparatus of claim 26 wherein at least one of: a head is detachably fastened on the die or is mounted on an end side in front of the die; or a head of the die comprises a front-side chamfer and a rear-side chamfer, wherein between the front- and rear-side chamfers a lateral surface that is cylindrical or becomes conically wider toward the rear-side chamfer is formed.

29. The autofrettage tool apparatus of claim 26 wherein the second securing means is solid or wherein the second securing means comprises a lower side configured to support the autofrettage tool apparatus and for transmission of die forces.

30. The autofrettage tool apparatus of claim 26 comprising an intermediate element disposed geometrically with respect to the die in the first securing means.

31. The autofrettage tool apparatus of claim 26 wherein the die comprises a head that is oversized relative to an internal dimension of the workpiece, the head being configured for mechanical autofrettage of the workpiece.

32. A control device comprising: a logic unit configured to control the autofrettage tool apparatus of claim 26; a drive; and a measuring device comprises a sensor, wherein the drive is drivable as a function of measurement values recorded by the measuring device.

33. The control device of claim 32 wherein the measurement values concern pressure, force, and/or distance.

Description

DESCRIPTION OF THE FIGURES

[0049] Further features and advantages of the invention may be found in the description of at least one exemplary embodiment with the aid of drawings, and from the drawings themselves, in which

[0050] FIG. 1 shows in sectional view an arrangement of a workpiece in a tool according to previously known purely hydraulic autofrettage;

[0051] FIG. 2 shows in sectional view an arrangement of a workpiece in a tool according to previously known purely mechanical autofrettage;

[0052] FIG. 3 shows in sectional view an arrangement of a workpiece in a hydromechanical autofrettage tool apparatus according to one exemplary embodiment of the invention;

[0053] FIG. 4 shows in schematic representation further components of a hydromechanical autofrettage tool apparatus according to one exemplary embodiment of the invention;

[0054] FIG. 5 shows in schematic representation individual steps of a method according to embodiments of the invention;

[0055] FIG. 6 shows in sectional view an arrangement of a workpiece in a hydromechanical autofrettage tool apparatus according to one exemplary embodiment of the invention; and

[0056] FIGS. 7A, 7B respectively show in sectional view in detail a first flange of a hydromechanical autofrettage tool apparatus according to one exemplary embodiment of the invention.

[0057] For references which are not explicitly described in relation to an individual figure, reference is made to the other figures.

DETAILED DESCRIPTION OF THE FIGURES

[0058] FIG. 1 shows a workpiece 1 which is clamped in a tool 2 for hydraulic autofrettage between a bottom-side flange 2.1 and a top-side flange 2.2, respectively on internal end sides 2.11, 2.21 by means of clamping screws 2.3. A supply line 2.22 for high-pressure fluid HF is coupled by means of a high-pressure proof coupling 2.5 to the upper side of the top-side flange 2.2. Through a pressure connection 2.4, high-pressure fluid HF can be introduced via an opening, formed in particular as a relatively thin small bore, in the top-side flange 2.2 into an internal volume Vi bounded by the workpiece 1.

[0059] The functionality of this tool 2 may be described as follows: the workpiece 1 is placed in the tool 2 and clamped therein. In this case, or in a separate step, the high-pressure supply 2.4, 2.5 needs to be set up. The workpiece 1 is thereupon exposed to a hydraulic autofrettage pressure Ph, which is to be defined specifically for each workpiece. Very high pressures of up to around 14000 bar are conventional. Such high pressures necessitate relatively short maintenance intervals, and it is necessary to comply with stringent safety requirements. The hydraulic components (in particular pumps, pipelines, valves) are cost-intensive special parts.

[0060] In order to achieve high geometrical accuracies, or narrow dimensional tolerances, in many cases finishing is carried out. The manufacturing tolerances may also be improved by monitoring the deformation during the pressure buildup, in particular by means of strain gauges.

[0061] FIG. 2 shows a workpiece 1 which is arranged in a tool 3 for mechanical autofrettage between a support section 3.11 of a baseplate 3.1 and a die 3.5. An internal volume Vi bounded laterally/radially by the workpiece 1 is arranged flush, or coaxially, with a recess 3.12 in the baseplate 3.1. The die comprises a free end 3.51, particularly in the manner of a head, which is defined in the longitudinal direction/forward movement direction of the die by a front-side chamfer 3.52 and a rear-side chamfer 3.54, between which chamfers a lateral surface 3.53 is formed.

[0062] The functionality of this tool 3 may be described as follows: the die 3.5 is driven with a force F1 through the internal volume Vi of the workpiece 1 arranged stably on the baseplate 3.1, until the free end 3.51 reaches the recess 3.12. After this, the workpiece 1 has an internal geometry at least approximately corresponding to that of the free end 3.51, in particular a cylindrical internal geometry.

[0063] FIG. 3 shows a workpiece 1, for example a cylindrical pressure vessel or high-pressure pipe, which is clamped in a hydromechanical autofrettage tool apparatus 10 between a bottom-side base flange 12 and a top-side flange 13, respectively on internal end sides by means of a flange screw connection 14 comprising clamping screws or the like. The base flange 12 comprises a foundation 12.1 and a shoulder 12.2. An internal volume Vi bounded laterally/radially by the workpiece 1 is arranged flush, or coaxially, with a high-pressure proof recess 12.3 in the base flange 12. The recess 12.3 is, in particular, configured as a blind hole (blind-hole bore). The recess 12.3 has internal dimensions, or an internal diameter, which is/are somewhat greater than the external dimensions, or an external diameter, of the die 11. At the bottom, the base flange 12 is solid and not open. The base flange 12 may for example comprise a circular lower side 12.12, which is adapted in particular as a support surface for the tool apparatus 10 as a whole, i.e. in order to absorb and transmit die forces.

[0064] The top-side flange 13 comprises an opening 13.1, the internal lateral surface 13.11 of which may be configured geometrically correspondingly to a die 11 of the tool apparatus 10, in particular cylindrically. The opening 13.1 has internal dimensions, or an internal diameter, which is/are somewhat greater than the external dimensions, or an external diameter, of the die 11. The die 11 comprises a free end 11.1, particularly in the manner of a head, which is defined in the longitudinal direction/forward movement direction of the die by a front-side chamfer 11.2 and a rear-side chamfer 11.4, between which chamfers a lateral surface 11.3 is formed.

[0065] The tool apparatus 10 extends in the forward movement direction of the die along a longitudinal midaxis M, in particular a symmetry axis. High-pressure fluid HF can be introduced into the internal volume Vi, which is in particular cylindrical.

[0066] The functionality according to the invention of this tool apparatus 10 according to the invention may now be described in detail as follows, in which case three successive steps may be highlighted:

[0067] The workpiece 1 is arranged in a first step S1 on the base flange 12, flush or coaxially with the blind-hole bore or depression 12.3, while being closed or sealed in a pressure-tight fashion, in particular both at a circumferential sealing means 12.4, for example a sealing ring or a circumferential elevation or a circumferential web on an internal end side 12.11 of the base flange 12, and on an internal end side 13.21 of the top-side flange 13. This may be carried out by clamping the base flange 12 with the top-side flange 13. In this case, the tool 1 is arranged in the tool apparatus 10 in such a way that the internal volume Vi bounded by the workpiece 1 respectively continues in the opening 13.1 and in the recess 12.3. The opening 13.1, the recess 12.3 and the internal volume Vi bounded by the workpiece 1 this case form three internal volumes arranged flush, in particular coaxially in a row.

[0068] The sealing system or sealing means 12.4 is schematically represented by way of example for seals or sealing systems allowed or suitable for high-pressure technology.

[0069] Then, in a second step S2, the internal volume Vi bounded by the workpiece 1 and the flanges 12, 13 is filled with high-pressure fluid HF. In this case, it is not yet necessary to build up a high-pressure. A high-pressure connection may be obviated.

[0070] The filling with high-pressure fluid HF may be carried out in such a way that high-pressure fluid HF is present not only in the recess 12.3 and in the internal volume Vi but also in the internal volume defined by the opening 13.1. The volume of high-pressure fluid HF used may thus be significantly greater than the internal volume Vi bounded by the workpiece 1.

[0071] In a subsequent third step S3, the die 11, or the head 11.1, is driven through the internal volume Vi of the workpiece 1, particularly in such a way that the following effect is then generated: the high-pressure fluid HF escapes upward, or towards the rear of the head 11.1 on the rear side behind the head 11.1, between the head 11.1 and the internal wall or internal lateral surface 1.1 of the workpiece 1. High-pressure fluid HF can flow past the head 11.1 as soon as a certain internal pressure has been built up. This may take place as a function of a predetermined forward movement rate. The die 11 is in this case moved forward with a die force F2 which is predefined for hydromechanical autofrettage or continuously adjusted, and a hydromechanical autofrettage pressure Phm which is predefined for hydromechanical autofrettage or continuously adjusted is set up in the internal volume Vi. The die 11 can be moved forward as far as the recess 12.3, in particular until the rear-side chamfer 11.4 is moved into the recess 12.3.

[0072] The depth of the recess 12.3 is to this end at least as large as the length of the free end 11.1, in particular as the length of an oversize of the free end 11.1.

[0073] Advantages achievable by means of hydromechanical autofrettage may again be summarized as follows:

[0074] The method can be carried out in a self-regulating fashion, since with an increasing internal pressure the amount of high-pressure fluid flowing away can increase. Friction forces between the head and the internal wall can be avoided, in particular since the high-pressure fluid can in this case undertake a lubricant function. In this case, the high-pressure fluid may also be pressed into the surface structure of the workpiece. A rear-side section of the head may finally smooth and compress the surface. It has been found that a high degree of surface quality can be achieved by means of the high-pressure fluid flowing past in combination with a high surface pressure. Grooves can be prevented. In particular, finishing of the internal surface(s) is also no longer necessary because of this. A precise, dimensionally compliant, internal contour can be produced in a very narrow tolerance range. Plasticizing, or internal strain, of the workpiece can also take place to a higher degree than in the case of hydraulic autofrettage, in particular at least approximately as far as full plasticizing. Not least, the tool apparatus, in particular the head, may be operated/used over a longer lifetime or service life, than in the case of mechanical autofrettage.

[0075] FIG. 4 describes a control device 20, by means of which the tool apparatus 10 according to the invention can be operated, in particular through some or all of the method steps according to the invention. The drive 21 delivers a forward-movement or die force F2. The drive 21 may also comprise a pump for introducing or pumping off hydraulic fluid. A measuring device 22, which is in communication with a logic unit 23 of the control device 20, comprises a plurality of sensors, in particular at least one pressure/force sensor 22.1 (which is/are for example on or in the base flange 12), at least one position sensor 22.2 for the (instantaneous) position of the die (which is/are for example on or in the top-side flange 13), at least one measuring unit 22.3 for the forward movement rate, at least one force sensor for the die force 22.4, at least one flow sensor 22.5. All the sensors may record measurement values, and deliver them to the logic unit, during the method according to the invention.

[0076] The components shown in FIG. 4 may, for example, be provided in a tool apparatus according to the exemplary embodiment described in FIG. 3.

[0077] Individual method steps are described in detail in FIG. 5: in the first step S1, the tool is arranged in the tool apparatus. At a first control/regulation point R1, a prestress force, by means of which the workpiece is clamped and thereby sealed in relation to predefinable overpressures, may be monitored or adjusted. In the second step S2, high-pressure fluid is introduced into the internal volume of the workpiece. At a second control/regulation point R2, the amount of high-pressure fluid introduced may be adjusted or monitored, in particular on the basis of measurement values of a flow sensor, which may for example be arranged on a feed line to the internal volume. In the third step S3, a die is driven through the internal volume of the workpiece. At a third control/regulation point R3, in particular the pressure in the internal volume and/or the forward movement rate of the die may be monitored or adjusted.

[0078] In a fourth step S4, the die 11, or the head, may be positioned in a recess 12.3, particularly in such a way that the free end 11.1 is decoupled from the workpiece 1. The tool apparatus 10 may then be dismounted and the workpiece 1 may be removed. Optionally, the high-pressure fluid HF is in this case can be pumped off before the dismounting. In this case, the die without the head may be drawn back through the workpiece. The die may thus initially be moved back again, in particular counter to the forward movement direction/axis (z), in particular fully out from the workpiece 1, before the tool apparatus 10 is dismounted.

[0079] One of the possible configurations of the method will be described again in summary below.

[0080] After the actual autofrettage process is ended, the die without the head is drawn out the workpiece, or out from the corresponding component of the tool apparatus. The head in this case remains in the recess. The workpiece is then taken out of the tool apparatus, which may for example be arranged in a hydraulic press or at least comprises parts thereof. The head is then removed from the recess. The mounting for a further untreated workpiece is then carried out. With a view to large production runs, it may be particularly advantageous to operate a plurality of tool apparatuses or a plurality of heads, in parallel.

[0081] FIG. 6 shows a hydromechanical autofrettage tool apparatus 10 which, in addition to the components described above, also comprises a high-pressure line 12.5 outward, here configured as a bore in the foundation 12.1. By means of a pressure limiter 24 and an external device for pressure generation, in particular a pump 25, pressure regulation may be carried out from the outside, in particular periodically in addition to the pressure regulation by means of the forward movement of the die. To this end, one or more pressure sensors 22.1 may be provided on the outside.

[0082] FIGS. 7A, 7B show a hydromechanical autofrettage tool apparatus 10 which, in addition to the components described above, also comprises an intermediate element 15, in particular configured as a fitting bush. The intermediate element 15 is arranged in a geometrically corresponding recess in the first flange 13 and bears on the workpiece 1. The intermediate element 15 and the head form a press-fit, with the effect that high pressure can already be built up in the section above the workpiece 1. The accuracy of the method can thereby be improved. The desired high pressure may be built up immediately, i.e. even before the head comes in contact with the workpiece 1.

List of References:

[0083] 1 workpiece, for example cylindrical pressure vessel or high-pressure pipe [0084] 1.1 internal wall, or internal lateral surface [0085] 2 previously known tool for hydraulic autofrettage [0086] 2.1 bottom-side flange [0087] 2.11 internal end side [0088] 2.2 top-side flange [0089] 2.21 internal end side [0090] 2.22 supply line for high-pressure fluid [0091] 2.23 opening for high-pressure fluid [0092] 2.3 clamping screw [0093] 2.4 pressure connection for high-pressure fluid [0094] 2.5 high-pressure proof coupling of the supply line [0095] 3 previously known tool for mechanical autofrettage [0096] 3.1 baseplate [0097] 3.11 support [0098] 3.12 recess [0099] 3.5 die [0100] 3.51 free end of the die, in particular head [0101] 3.52 front-side chamfer [0102] 3.53 lateral surface [0103] 3.54 rear-side chamfer [0104] 10 hydromechanical autofrettage tool apparatus [0105] 11 die, in particular cylindrical [0106] 11.1 free end of the die, in particular head [0107] 11.2 front-side chamfer of the free end [0108] 11.3 lateral surface of the free end [0109] 11.4 rear-side chamfer of the free end [0110] 12 second securing means, in particular bottom-side base flange [0111] 12.1 foundation [0112] 12.11 internal end side [0113] 12.12 lower side, in particular support surface [0114] 12.2 shoulder [0115] 12.3 recess, in particular blind hole (blind-hole bore) [0116] 12.4 sealing system or sealing means [0117] 12.5 high-pressure line outward, in particular bore in the foundation [0118] 13 first securing means, in particular introduction/top-side flange [0119] 13.1 opening geometrically corresponding to the die [0120] 13.11 internal lateral surface of the opening [0121] 13.21 internal end side [0122] 14 fastening of the securing means, in particular flange screw connection [0123] 15 intermediate element, in particular fitting bush [0124] 20 control device [0125] 21 drive [0126] 22 measuring device [0127] 22.1 pressure/force sensor [0128] 22.2 position sensor [0129] 22.3 measuring unit, in particular for speed [0130] 22.4 force sensor for die force [0131] 22.5 flow sensor [0132] 23 logic unit [0133] 24 pressure limiter [0134] 25 external device for pressure generation, in particular pump [0135] F1 die force, purely mechanical [0136] F2 die force, hydromechanical [0137] HF high-pressure fluid [0138] M longitudinal midaxis, in particular symmetry axis [0139] Ph hydraulic autofrettage pressure [0140] Phm hydromechanical autofrettage pressure [0141] R1 control/regulation point relating to a prestress force [0142] R2 control/regulation point relating to the amount of high-pressure fluid introduced [0143] R3 control/regulation point relating to the pressure in the internal volume and/or relating to the forward movement rate of the die [0144] S1 step of arranging the workpiece in the tool apparatus [0145] S2 step of introducing high-pressure fluid into the internal volume of the workpiece [0146] S3 step of driving a die through the internal volume of the workpiece [0147] S4 step of positioning the die [0148] Vi internal volume [0149] x, y, z width direction, depth direction and height direction