EP1027177B1 - Method for producing hollow nickel titanium profiles - Google Patents

Abstract

The invention relates to a method for producing hollow nickel titanium profiles with a small external diameter and/or small wall thickness by means of deformation, especially extrusion. According to the inventive method, a composite block is formed, comprising a solid core and one or several hollow blocks surrounding said core. The core and the hollow blocks are made of nickel titanium. The parts of the composite block are separated after deformation to obtain a wire (3a), a tube (1a) with a small diameter and a tube (5a) with a larger diameter.

Description

The invention relates to a method for producing Hollow profiles, especially pipes, with a small outside diameter and / or small wall thickness made of a nickel-titanium alloy by reshaping a composite block according to the preamble of claim 1 (see e.g. WO-A-95 31298).

For alloys that have approximately the same number of titanium and Containing nickel atoms, special effects can be observed, due to which such alloys also shape memory alloys to be named. The effects are based on a thermoelastic martensitic phase transformation, i.e. a temperature-dependent change in the crystal structure: at high temperatures is the alloy austenitic, but martensitic at low temperatures. After T. W. Duerig and H. R. Pelton, ("TI-NI Shape Memory Alloys ", in: Materials Properties Handbook: Titanium Alloys, 1994, pp. 1035-1048, ASM International 1994) have two properties in shape memory alloys to distinguish. Alloys with a titanium content between 49.7 to 50.7 atom% show a thermal Shape memory, also called shape memory, alloys a mechanical one with a titanium content of 49.0 to 49.4 atomic% Shape memory, also called super elasticity.

Not only binary nickel-titanium alloys can do the above Have properties. A shape memory alloy can contain ternary components (e.g. iron, chromium or Aluminum) included. The ratio of nickel and titanium as well as the presence of ternary admixtures have large Influence on the expression of the thermal and mechanical Shape memory; even small changes in concentration have big changes in material properties result.

In order to use the thermal shape memory for components, becomes an alloy with a suitable composition by cooling without diffusion from the austenitic structure in transformed the martensitic structure. A subsequent one Deformation of a component made from this alloy can be achieved by thermal treatment of the component (Heating to temperatures above a certain Transformation temperature) can be reversed again. The original austenitic structure is restored set, and the component takes its original Shape. The transition temperature is generally denotes the temperature at which the martensite is completely is converted to austenite. The transformation temperature is strong on the composition of the alloy and depending on the stresses prevailing in the component. components, which can show a thermal shape memory Generate movements and / or exert forces.

The mechanical shape memory effect occurs in a component made of a suitable alloy with austenitic Microstructure if the component is in a certain temperature range is deformed. It is for the austenitic The structure is more energetically favorable, it is stress-induced convert to martensite, taking elastic strains of up to ten percent can be achieved.

When the load is released, the structure returns to the austenitic Phase back. Components made from such an alloy can therefore store deformation energy.

Alloys which show the properties described above are known under the terms nickel-titanium, titanium-nickel, tea-nee, Memorite ^R , Nitinol, Tinel ^R , Flexon ^R and shape memory alloys. These terms do not refer to a single alloy with a specific composition, but to a family of alloys that show the properties described.

In many technical fields, e.g. medical technology and precision engineering, exists due to the special properties of nickel-titanium alloys of great interest Components made from shape memory alloys use. In mechanics, for example used for switching, adjusting elements or valves become. Shape memory alloys are also used in medical technology increasingly used since Components made of such alloys are compatible with the body and are fatigue-proof and in the case of super-elastic alloys also show a high kink resistance.

Examples of the use of nickel-titanium alloys in medical technology, where the primary product is a nickel-titanium tube is stents, catheters as well as endoscopic and laparoscopic instruments for the minimally invasive diagnosis and therapy. Even in the other fields of application are intermediate products in the form of Pipes, especially those with a small outside diameter, are required.

A wide application of nickel-titanium tubes and instruments stands among other things their currently high price, which is due to the manufacturing processes previously used in manufacturing is due to tubular precursors, opposite.

According to the state of the art, nickel-titanium tubes made by drilling forged bars. The pipes typically have outside diameters between 12 and 25 mm. Due to the poor machinability of Nickel-titanium alloys are the process of deep hole drilling very complex, resulting in short downtimes Tools, long processing times and high manufacturing costs leads for the pipes. Further occurs, in particular in the manufacture of thin-walled pipes, a high one Loss of material. Those that arise when drilling or turning Chips represent lost material.

The production is described in European patent specification 0459909 a seamless tube made of a corrosion-resistant, alloy consisting almost entirely of titanium described by means of a pipe extrusion process. In the process, a perforated press block is used Stamp pressure by a between a mandrel and a gap remaining pressed through a die. The Pipes produced in this way serve for subsequent Forming work, for example for heating Brines in seawater desalination plants and as heat exchanger tubes in chemical production plants.

Because of the unfavorable forming behavior of nickel-titanium alloys can with the help of such a procedure only pipes with a large outside diameter (above 40 mm) can be pressed economically. The pressing of pipes with a smaller diameter is associated with high costs, because none due to lack of cooling sufficient tool life in the through the material predetermined temperature range can be achieved. In addition, the mandrels break off easily when squeezing what leads to a high committee. Because of the very high Resistance to deformation of nickel-titanium alloys at very high forming temperatures is the production of small, thin pipes is not possible because the mandrel of the high thermal and mechanical tensile load cannot withstand. According to the state of the art therefore first of all through pipes with a large outside diameter Pipe extrusion presses prefabricated and then in others complex work steps, e.g. Pull and Rolls to tubes with the desired small diameter reshaped. Because of the advantages of nickel-titanium alloys, especially shape memory alloys the associated with the complex manufacture Cost disadvantages in the state of the art in purchase taken.

From document WO 96/17698 a method of Extrusion of composite blocks with a lost core known without press mandrel. A hollow block is included filled a steel core and then pressed together once. The geometry of the hollow molded product is depending on the geometry of the press die and the core. The larger the core in relation to the press die, the thinner the tube becomes. When manufacturing thin-walled Pipes therefore carry out this type of block preparation to a considerable waste of material, that of nickel-titanium alloys represents a significant disadvantage. In addition, this method has the disadvantage that through the forming process the metal core an intimate metal connection with the nickel-titanium material forms in the pressed product, so that to remove the Core material to obtain a hollow molded product, an additional processing step is required for example by drilling out and / or chemical triggering of the core material. Furthermore, is not in all cases the one-time extrusion of the composite block is a desired, small profile dimensions achievable.

The invention has for its object a method to provide with the hollow profiles or tubes from a Nickel-titanium alloy with a small outside diameter and / or a small wall thickness inexpensively and efficiently can be produced. The hollow profiles or Pipes can have any cross-sectional shape. Under a tube is also any profile tube or hollow profile understood.

In the prior art (WO-A-95 31298) a method for the production of hollow profiles with a small outside diameter and / or Small wall thickness made of a nickel-titanium alloy proposed by reshaping a composite block in which in a first step, a composite block is formed, which has a solid core made of a nickel-titanium alloy, a first hollow block surrounding the core from a Nickel-titanium alloy and a separating layer between the first hollow block and the core. In a second Step is the composite block by means of a forming process reshaped, and in a third step the first hollow block formed into a first hollow profile and the formed core from the formed composite block away.

The invention is based on the idea of both the processing effort as well as the amount of waste lost Nickel-Titanium by reducing the hollow block is stabilized during forming with a core, the Core itself is reshaped and both in terms of its Material as well as its shape for further use suitable is. The core consists of according to the invention a nickel-titanium alloy. The one to a massive full profile reshaped core can be used as wire, for example further used or as a semi-finished product in further processing steps to be used. In this way it is created less waste of the raw material, which is expensive to manufacture.

In the method known from the prior art, a Nickel-titanium raw material zoned, and the spaces are covered with a separation layer, for example a non-metallic powder material that does not combine with nickel-titanium. The Dimensions of the formed products depend on the geometry and the zone division in the composite block and the selected one Forming process. According to the invention, the number and the diameter the individual zones can be designed variably and depends on the desired formed products.

The material forming the separating layer has the task a touch of the individual zones before, during and after prevent reshaping of the composite block to achieve that the individual parts of the formed composite block can be easily separated from each other after forming can.

Different variants are available for the forming process Consideration. A first advantageous embodiment can be found therein exist that the composite block by means of an extrusion process is formed in which the composite block as a heated press block in a block receiver Press used and by pressing a ram is pressed through the opening of a die. Doing so the hollow block, which are extruded into a tube during extrusion with one inserted in it Core stabilized. The core can be extruded be removed. The method according to the invention is so far with one step from a multiple composite extrusion process comparable, but in contrast to the classic, repeatedly repeated composite extrusion presses a single extrusion can suffice and further the components of the composite strand obtained after Extrusion presses to extract a pipe are isolated.

In contrast to pipe extrusion, the invention can Squeeze procedure with a lower one Pressure to be worked, reducing the wear of the Press tools is reduced. Because of the small outside diameter of the pipe manufactured according to the invention in any subsequent forming work, for example when cold drawing, with a smaller outside diameter be started, which saves processing steps become.

Another advantageous embodiment of a forming process can consist in that the composite block by means of a warm drawing, cold drawing, rolling, round hammer or pilger process is reshaped.

In the forming according to the invention, the result is Tube stabilized by the core during forming. In the context of the invention it has been found that in this way despite the unfavorable forming behavior of nickel-titanium alloys, which is usually a forming ratio with extrusion of a maximum of 20: 1, is possible to use pipes with a small outside diameter and / or small wall thickness by forming and thus effectively and inexpensive to manufacture.

For the production of a composite block to be formed there are various possibilities according to the invention Available. In the first possibility according to the invention, the composite block with one or more further Hollow blocks formed around the first hollow block are arranged and each have a separation layer have between adjacent hollow blocks, in which second step comprising several hollow blocks and the core Composite block is formed. This is special advantageous to have several thin-walled hollow profiles in one To produce the forming step.

It can also be advantageous if the composite block by pushing together several hollow blocks, in particular of hollow profiles, preferably of tubes becomes. In this respect, the above and following description applies equally for hollow blocks, hollow profiles and Tube.

For making a hollow block with one for insertion The core provided hole can be the hole in a block or drilled or milled through a block. There this inevitably leads to a loss of material, too if the hole, except for the separation gap, is covered by a solid Profile is populated according to a preferred Feature of the invention proposed that the composite block, a hollow block or the core by lowering or Wire EDM of a massive nickel-titanium block, one Nickel-titanium hollow blocks or another nickel-titanium workpiece is formed.

In the context of the invention, it has surprisingly been shown that by means of a spark erosion process, in particular using EDM or wire EDM, nickel-titanium workpieces can be processed advantageously, in particular when removing or separating a part, in particular a solid core or a hollow profile, from one Block. The use of a tubular one is preferred Electrode made of copper or a copper alloy.

The method according to the invention relates to the production pipes made of a nickel-titanium alloy, in particular a shape memory alloy described above. The alloys used can be binary be or contain ternary additions. Preferably is the process used to manufacture pipes a nickel-titanium alloy with super elastic properties. Even the one that was formed into a solid full profile Core preferably has super-elastic properties.

When extruding, the outer diameter of the pressed depends Compound blocks and thus the outer tube of the diameter of the opening of the die, which is not arbitrary is selectable small. The smaller it is, the bigger is the pressure to be applied and the less is the service life of the press tools. Around the outside diameter of a pipe is further reduced formed composite block in a second possibility according to the invention to manufacture the composite output block before removing the reduced core into a second one Hole made in another hollow block made of a nickel-titanium alloy was incorporated to form a Multiple composite block, the further, perforated hollow block and the first, formed composite block with the reduced core, used, the one thus formed second composite block a separation layer between the serving as the core first composite block and the second Has composite block. The multiple composite block becomes then a multiple composite rod using extrusion pressed out, the diameter of the further, perforated hollow block, the first hollow block and of the core can be reduced. This also applies accordingly for composite blocks with several layers and for others Forming processes.

The reshaped composite block comprises one of those second, reduced hollow block formed second tube, the first, further reduced pipe and the further reduced Core. After forming, the pipes are separated and the reduced core removed. With this two-stage Forming, for example extrusion, can be done with a larger die opening, what advantageous to the applied pressure and affects the service life of the pressing tools. After separating the tubes and the core removal stand two extruded tubes with different diameters available for further processing.

If even smaller dimensions, especially for the innermost, smallest tube, if desired, it can be advantageous be, the forming or extrusion on or Repeat several times until a given outer diameter for the smallest pipe. For this, the reshaped multiple composite trestle before the pipes are isolated and the core will be removed, into another hole, which was worked into another hollow block and the further multiple composite block thus formed formed to produce another tube. The insertion and reshaping can be repeated with each tube forming another tube becomes. After completing this multi-stage forming or

Extrusion (multiple composite extrusion) all the pipes formed and the reduced one Core removed.

When repeating the invention one or more times The procedure can also be carried out in such a way that the one or more reduced core and the first, innermost Pipe can be removed from the reduced block (if necessary together with one or more to the first pipe adjacent further pipes), then in the remaining block is another core made of nickel titanium or another material used, the so formed Block is reshaped and further reduced, namely either as is or inserted into one another hollow block. In this way it is possible To produce pipes with a uniform, small diameter, with fewer pipes of larger diameter.

Before forming, the block to be formed or the required hollow blocks each have a hole, whose diameter is preferably between 10 mm and 60 mm, is preferably between 20 mm and 40 mm. The hole will preferably eroded, but can also be on another Way into the material. It has a through hole opposite a blind hole the advantage that during forming, especially pressing, not a solid piece, i.e. a section of the squeezed Rod without a core, which is used to create a tube must first be separated and represents lost material.

In a preferred variant of the method, the Composite block reshaped to a diameter that is essentially the diameter of the first hole in the core before forming. In this way, the reshaped Compound block in another hollow block with same core diameter as the previous hollow block for Formation of a multiple composite block can be used.

The multiple composite block can also advantageously be on a diameter to be formed, which is essentially the diameter of the composite block serving as the core corresponds to the forming. In this way, the reshaped Multiple composite block in another hollow block with the same core diameter to form another Multiple composite blocks can be used.

The required diameter of the formed composite block or multiple composite blocks is replaced by a corresponding Dimensioning of the forming tools obtained. These process variants include the advantage that in the required hollow blocks holes with a uniform diameter can be incorporated, what the effort for block preparation reduced.

The outer diameter of the first is advantageously Hollow blocks or tube after the first forming step less than 40 mm, preferably less than 25 mm. The smaller the outer diameter of the tube or produced pipes, the more the pipes are reduced Costs for the subsequent forming work. The wall thickness a thin-walled tube is usually between 2% and 10% of the outside diameter.

Fig. 1

einen Längsschnitt durch einen Verbundblock,

Fig. 2

einen Längsschnitt durch einen Kern-Preßblock,

Fig. 3

einen Längsschnitt durch einen Kern,

Fig. 4

eine schematische Darstellung einer Vorrichtung zum direkten Strangpressen,

Fig. 5

eine schematische Darstellung einer Vorrichtung zum indirekten Strangpressen,

Fig. 6

einen ausschnittsweisen Längsschnitt durch einen umgeformten Verbundblock,

Fig. 7

einen Längsschnitt durch einen Mehrfachverbundblock,

Fig. 8

einen ausschnittsweisen Längsschnitt durch einen umgeformten Mehrfachverbundblock,

Fig. 9

einen Querschnitt eines in drei Zonen geteilten, drahterodierten Blocks,

Fig. 10

einen Längsschnitt zu Fig. 9,

Fig. 11

einen Querschnitt eines in drei Zonen geteilten, senkerodierten Blocks,

Fig. 12

einen Längsschnitt zu Fig. 11,

Fig. 13

den zum Strangpressen vorbereiteten Block gemäß Fig. 9,

Fig. 14

einen Längsschnitt zu Fig. 13,

Fig. 15

dem zum Strangpressen vorbereiteten Block gemäß Fig. 11,

Fig. 16

einen Längsschnitt zu Fig. 15,

Fig. 17

einen Längsschnitt des Verbundblocks aus Fig. 14 oder 16 beim Strangpressen,

Fig. 18

das Vereinzeln des umgeformten Verbundblocks aus Fig. 17,

Fig. 19

einen Querschnitt entsprechend Fig. 11 und

Fig. 20

den Querschnitt der Fig. 19 nach dem Umformen.

The invention is explained in more detail below on the basis of exemplary embodiments schematically illustrated in the figures. Show it:

Fig. 1

a longitudinal section through a composite block,

Fig. 2

a longitudinal section through a core press block,

Fig. 3

a longitudinal section through a core,

Fig. 4

1 shows a schematic representation of a device for direct extrusion,

Fig. 5

1 shows a schematic representation of a device for indirect extrusion,

Fig. 6

a partial longitudinal section through a formed composite block,

Fig. 7

a longitudinal section through a multiple composite block,

Fig. 8

a partial longitudinal section through a formed multiple composite block,

Fig. 9

a cross section of a wire-eroded block divided into three zones,

Fig. 10

9 shows a longitudinal section to FIG. 9,

Fig. 11

a cross section of a die-cut block divided into three zones,

Fig. 12

11 shows a longitudinal section to FIG. 11,

Fig. 13

9 the block prepared for extrusion,

Fig. 14

13 shows a longitudinal section to FIG. 13,

Fig. 15

the block prepared for extrusion according to FIG. 11,

Fig. 16

15 shows a longitudinal section to FIG. 15,

Fig. 17

14 shows a longitudinal section of the composite block from FIG. 14 or 16 during extrusion,

Fig. 18

the separation of the formed composite block from FIG. 17,

Fig. 19

a cross section corresponding to Fig. 11 and

Fig. 20

the cross section of Fig. 19 after the forming.

The first hollow block 1 shown in Figure 1 is made of a Shape memory alloy with super elastic properties manufactured, for example forged. In the first hollow block 1, which has a diameter d2 of approx. 100 mm, a continuous first hole 7 is worked, e.g. drilled. The diameter d1 of the first Hole 7 is approximately 30 mm.

To improve the flow behavior and to reduce it tool wear during forming, e.g. Extrusion, is on the surface of the first before forming Hollow block 1 a sliding layer 2 made of a friction reducing Material applied. In the shown Embodiment comprises the sliding layer 2 copper and was applied in that the first hollow block 1 in a copper tube with a corresponding diameter is inserted has been. A copper layer can, for example can also be applied by plasma or flame spraying.

The sliding layer 2 can also be made of glass or another Material. Copper has one at Extrusion frequently used sliding layer made of glass the advantage that in a subsequent cold forming process, for example pulling, also as a sliding layer can serve. A glass sliding layer, however, must be removed beforehand in order to protect the forming tools. However, the sliding layer 2 can also use other materials, especially graphite or a paste applied include ceramic substance applied as sludge.

The total diameter d2 of the first hollow block 1 inclusive applied sliding layer 2 (in the following referred to as the press block diameter) in the shown Embodiment in about 110 mm. On a sliding layer 2 could be omitted if for the forming tools (e.g. extrusion) a material is used which the nickel-titanium alloy has essentially no inclination shows for welding, or selected a forming process where there is no welding.

In the first hole 7 of the first hollow block 1 is under Formation of a composite block 10 a core 3 is used, whose diameter d3 including one applied Separating layer 4 (hereinafter referred to as core diameter) essentially the diameter d1 of the first hole 7 corresponds. The core 3 also comprises a nickel-titanium alloy. It therefore shows the same when pressed Flow behavior like the first hollow block 1. According to an advantageous development for the core 3 a Alloy composition chosen that has a higher martensite-austenite transition temperature than the alloy of the first hollow block 1. This is beneficial for the removal of the core 3 described below the forming.

The core 3 has the task of the first hollow block 1 at Forming into a first tube to stabilize. Also determined he, since its diameter also when squeezing is reduced, the inner diameter of the first tube. Therefore, it is advantageous if the core 3 is a material has a similar or the same when reshaping Flow behavior like the alloy of the first hollow block 1 shows. In this way, the composite block diameter d2 and the core diameter d3 evenly during forming reduced, i.e. the ratio of the cross sectional area of the first hollow block 1 including sliding layer 2 to the Cross-sectional area of the core 3 including the separating layer 4 remains essentially before and after the forming equal. Thus, the outside and inside diameter of the resulting pipe for given starting conditions (in particular composite block diameter d2, core diameter d3, diameter of the die opening during extrusion) be calculated.

With a relatively thin-walled resulting pipe, i.e. with smaller cross-sectional area ratios of pipe to core 3, it can be advantageous if core 3 also includes a super elastic alloy.

In an alternative version, especially the repeated one Forming with an exchanged core, can the core 3 comprise a copper-chromium alloy. This shows a similar flow behavior as the nickel-titanium alloy of the first hollow block 1.

To prevent the core 3 and the first hollow block 1 non-detachably when forming, is a temperature-resistant interface on the core 3 4 applied from copper. It can do others Materials, especially graphite, talcum, a mixture with talcum or a ceramic substance such as Have aluminum oxide, magnesium oxide or titanium oxide. The separating layer 4 has the task of diffusing Atoms between core 3 and first press block 1 when pressed to prevent.

In one process variant, one is made by means of a forming process manufactured core 3 used. For the production of the core 3 is, as shown in Figure 2, on a solid core press block 11 made of a shape memory alloy a sliding layer 4a made of copper. By means of a known forming, e.g. one Extrusion process, the core press block 11 becomes one Formed strand. The strand is cut to length, whereby the actual core 3 is formed (Figure 3). The one on the Sliding layer 4a located on the outer surface of the core 3 can serve as a separating layer 4 in the further process. Alternatively, the core 3 by means of the invention Forming or extrusion processes are produced.

The core 3 is, as shown in Figure 1, inserted into the first hole 7 of the first hollow block 1. When the core press block 11 is pressed without a sliding layer 4a has been made on the resulting core a separate separating layer 4 is applied upon insertion.

The shaping by extrusion is based on the figures 4 and 5 explained. The composite block is used for pressing 10 from FIG. 1, which shows the first hollow block 1 and the core 3 includes, heated to about 900 to 950 ° C and in a heatable Block picker 16 of a press 15 used. The temperature depends on the alloys used. For other nickel-titanium alloys, the extrusion temperature can be typically lie between 850 and 950 ° C. In order for a composite block 10 with different Hollow block and core material the even flow of Core 3 and hollow block 1 can improve this before the pressing separately from each other to different Temperatures warmed, then assembled and then pressed together to form a formed composite block 12 become.

When pressing through direct extrusion (Figure 4) are the matrix 17 and the block sensor 16 fixed. On Press ram 19 moves downward in the direction of arrow 21 and exerts pressure on the composite block 10. Thereby this moves relative to the block sensor 16 and is formed through the opening 18 of the die 17 as a Compound block 12 pressed out.

The composite block 10 is preferred by indirect Extrusion (Figure 5) pressed out. The moves die arranged at a tip of a hollow punch 20 17 for pressing out as a result of the pressure of the press ram 19 relative to the block transducer 16 and the one used therein Compound block 10. It penetrates into the compound block 10 a while this through the opening 18 of the die 17 and the hollow punch 20 as a formed composite block 12 is squeezed out. The indirect extrusion has opposite the direct advantage that between near the edge and areas of the composite block 10 located further inside essentially no different when pressed Flow rates occur. This results in a largely homogeneous material flow, that of an undesirable Counteracts wall thickness fluctuation of the resulting pipe. Due to the lower pressing force requirement and better material flow due to the lack of friction the indirect between the transducer and the press block Extrusion preferred.

By direct, indirect or another, for example hydrostatic extrusion or another forming process is made from the first, perforated hollow block 1 as a formed hollow block 1a, a first tube and from the original core 3 a reduced core 3a formed are the components of the formed composite block 12 (Figure 6). A comparison between Figure 1 and Figure 6 shows that both the composite block diameter d2 and the core diameter d3 is reduced by pressing were. It can be seen that the press ratio is chosen in this way that the outer diameter d4 of the formed Compound blocks 12 essentially the core diameter d3 equivalent. The press ratio is in the present Case approx. 14: 1. As a result of the same forming behavior between core 3 and first hollow block 1 results from the Pressing a first tube 1a with an outer diameter of approx. 30 mm and an inner diameter of approx. 8 mm. The ratio of outside to inside diameter remains the same Get extrusion.

If these dimensions for the subsequent forming work are already sufficient, the reduced core 3a can be removed from tube 1a after a single shaping. To remove or loosen the reduced core 3a the formed composite block 12 is treated mechanically. To the reduced core 3a becomes at a temperature below the transition temperature of the core material is stretched. At this temperature, tube 1a remains austenitic and thus elastic state, while the reduced Core 3a plastically deformed in the martensitic area becomes. As a result of the tensile stress, the reduced Core 3a longer (change in length up to 10%) and thinner and can thus be pulled out of the tube 1a. If the core 3 comprises a super-elastic alloy, the stretching is preferably carried out by clamping the reduced Core 3a on one side and the tube 1a on the other side. More options, the reduced To loosen core 3a mechanically especially milling, rolling and hammering the composite block 12th

To remove or loosen the reduced core 3a the composite block 12 also undergoes thermal shock treatment be subjected. As a result of material or composition differences voltages are induced, those for releasing the reduced core 3a in the tube 1a lead, so that they are then pulled out can. When using an alloy core, which is not a nickel-titanium alloy, the composite block 12 can also be chemically treated to the reduced Remove or loosen core 3a. At a The composite block becomes the core of a copper-chromium alloy treated with nitric acid, for example, the reduced core 3a dissolves or dissolves, the nickel-titanium tube but does not attack. Mechanical, chemical or thermal methods to remove or loosen the reduced Kerns 3a can also be used in combination become.

When using suitable materials as separating layer 4 can the parts without complex procedures, for example by simply pulling them apart.

To make even smaller outside and inside diameters for the to come first tube 1a, the composite block 12 before the Removing the reduced core 3a cut to length and in one second hole 8 made in a second hollow block 5 a nickel-titanium alloy was incorporated under Formation of a multiple composite block 13 are used, what Figure 7 shows. The sliding layer 2 on the composite block 12 from the first pressing process can be used as Serve separation layer. Was the composite block 10 without The sliding layer 2 is pressed out onto the composite block 12 a separate one before inserting it into the second hole 8 Separation layer applied. On the outer surface of the second Hollow blocks 5, whose outer diameter including d5 Sliding layer 6 is approximately 110 mm, is also a Slip layer 6 made of copper. The diameter d6 of the second hole 8 corresponds to the diameter d1 of the first hole 7 in the first hollow block 1.

The multiple composite block 13 thus formed, the second Hollow block 5 and the composite block 12 with a reduced core 3a comprises, for example by means of extrusion an outer diameter d7, which is essentially the diameter d6 corresponds to the composite block 12 used, reshaped (Figure 8). The diameter of the second hollow block 5 and the composite block 12 reduced. The reformed multiple composite block 14 includes one of those second hollow block 5 formed second tube 5a, the further reduced, first tube 1a and the further reduced Core 3a. Because the same geometrical pressure ratio when pressing as used in the first pressing step the second tube 5a has an outer diameter of approx. 30 mm and an inner diameter of approx. 8 mm, the first tube 1a, on the other hand, has an outer diameter of approximately 8 mm and an inner diameter of approx. 2.2 mm.

After reshaping, the reduced core 3a becomes as above described, removed. The concentric, nested Pipes 1a, 5a of the multiple composite block 14 are sporadically. The pipes 1a, 5a thus produced stand available for further forming work. The reshaped Core 3a can be used as wire or further processed become.

The second forming stage can be used before separating of tubes 1a, 5a and the removal of the reduced core 3a of the multiple composite block 14 one or more others Connect forming stages to the pipe diameter still further reduce. As explained above, also the reduced core with one or more internal tubes removed and replaced by another Core to be replaced.

Figures 9 to 20 illustrate an inventive Process for the production of thin hollow profiles made of nickel-titanium alloys, in which the starting material divided into three zones and the zones between non-metallic powder materials are filled. The Forming is preferably carried out by extrusion, whereby a strand-shaped pressed product is created in which the zone structure preserved. Due to the powder material in the individual parts do not come into the intermediate zones in contact with each other, so that after the forming in tubular hollow profiles with different diameters and a solid profile can be separated. The figures 9 to 20 show an embodiment with a Core and two tubular hollow blocks arranged around it with spaces in between. Other variants can only have one or more than two Include hollow blocks.

FIGS. 9 to 12 illustrate how a solid, cylindrical nickel-titanium raw material in three zones comprising the core 3, the first hollow block 1 and the second hollow block 5 is divided. The division can preferably be done by spark erosion.

In the exemplary embodiment according to FIGS. 9 and 10 the division by wire EDM. It can be done with a Wire that is thinner than the joint width along the The extent of the joint on both its inside and on its Outside diameter of the starting material can be cut. The process of wire EDM has the advantage that little waste material arises, since a compact, recyclable sleeve with the dimensions of the parting line 23 or 24 arises. There are basically two options the conduct of the procedure. If the EDM wire is along a longitudinal hole in the starting material is closed over its scope, compact pipe detached from the joint 23 or 24. If, on the other hand, the wire is fed radially, this forms pieces separated from the starting material longitudinally carved sleeve, which can also be used is.

During die sinking EDM, which is illustrated in FIGS. 11 and 12 is the cross section of the parting line 23 or 24 eroded out. The electrodes are thin-walled Pipes made of copper or a copper alloy, their diameter corresponds to the diameter of the joints. The Electrodes can erode around their longitudinal axis and / or are moved along their longitudinal axis. At the Die-sinking EDM is the same as the parting lines 23, 24 Material as fine erosion waste. Indeed Die sinking EDM has the advantage that, provided the electrodes not completely through the starting material be a floor at one end of the block remains, which stabilizes the arrangement and in the subsequent Filling the parting lines 23, 24 with a Interface-forming material is advantageous to that To facilitate filling and to prevent falling out. In Fig. 12 the bottom is at the right end of the illustration to recognize.

Both wire and sinker EDM have opposite other processes such as drilling etc. that little waste of nickel-titanium arises, since only the material the parting lines 23, 24 or part of this material as waste.

After dividing the starting material into a core 3, a first hollow block 1 and a second hollow block 5 the parting lines 23, 24 formed are filled with powder, so that a composite block 10 with three nickel-titanium zones and two zone gaps are created.

Figures 13 to 16 show such finished, for pressing prepared composite blocks 10. They are with a sleeve 25 clad in copper to provide a direct extrusion Contact between the nickel titanium of the second To prevent hollow blocks 5 and the die and a Welding between nickel titanium and the tool steel to avoid. Also on the end faces of the composite blocks 10 is for this purpose a disk 26 made of a high-strength Copper alloy attached.

For the escape of the located in the parting lines 23, 24 To prevent powder, the block ends with a second disc 27 made of a high copper alloy Tightness locked. To mechanically arrange the arrangement fix and stabilize, guide pieces 22 are provided, the parting lines 23, 24 or sections in Fill in the area of the block ends. For example, 14 and 16, to which second discs 27 may be formed. 14 also points the disc 26 guide pieces 22, because the parting lines 23, 24 go right through the material. 16 is into the right end of the block through the EDM left webs stabilized.

The powder material used to fill the parting lines 23, 24 consists preferably of hard, temperature-resistant Metal oxides such as aluminum oxide powder, that has the ability during the forming process the change in shape of the nickel-titanium material to slide accordingly without causing plastic deformation the oxide particles take place.

17 shows how the prepared composite block 10 hot formed into an extrusion by extrusion becomes. Both direct and indirect extrusion is also possible. This is preferred indirect extrusion shown in FIG. 17. The composite block 10 is inserted into the block receiver 16 and by the pressing process, in which the block receiver 16 and the ram 19 together with the pressing composite block 10 in the direction of on a Hollow punch 20 lying die 17 moves against the Press die 17 pressed and to a formed composite block 12 formed into a strand.

18 is the singulation in the formed composite block 12 contained items shown by pulling out. This creates the desired formed products, comprising a reduced core 3a as a solid round profile, a formed hollow block 1a as a tube and one formed second hollow block as a second tube 5a. With a single forming process creates two at the same time or more tubular formed products different Dimensions and a solid profile as a by-product. The material waste and the processing effort are small. In addition, there is no complex processing step for separating the individual parts. This in the parting lines 23, 24 introduced powder can usually be reused.

Figures 19 and 20 show a numerical example of a method according to the invention according to Figures 9 to 18, in which a nickel-titanium press block with a three-zone division after hot forming by extrusion, in which the diameter and wall thickness of the individual parts are reduced , is divided into three pressed products. When extruding a composite block 10 with a diameter D ₁ of approx. 110 mm using a block transducer with a diameter of 110 mm and a die with a diameter of approx. 26 mm, a pressing ratio of approx. 18: 1 results. This means that the ratio of the cross-sectional area of the composite block 10 to be pressed, which corresponds to the cross-sectional area of the block receiver, to the cross-sectional area of the strand block 12, which corresponds to the cross-sectional area of the die opening, is 18. When extruding a nickel-titanium press block comprising several zones, the individual zones and zone gaps are also formed with a pressing ratio of 18: 1.

The dimensions of the individual zones in the composite block 10 and in the formed composite block 12 shown in FIGS. 19 and 20 are approximately as follows: D ₁ 110 mm, D ₂ 108 mm, D ₃ 89 mm, D4 76 mm, D ₅ 63 mm, D ₆ 51 mm, D ₁₁ 26 mm, D ₂₂ 25.5 mm, D ₃₃ 21 mm, D ₄₄ 18 mm, D ₅₅ 15 mm and D ₆₆ 12 mm. In this numerical example, a possible further compression of the powder material contained in the parting lines 23, 24 as parting layer is not taken into account during the pressing process, which can lead to a slight deviation in the product dimensions. However, this effect can be compensated for by a corresponding change in the diameter of the individual zones in the composite block 10.

After the formed composite block 12 has been separated into individual parts, the following products are produced: The reduced core 3a is a round, full profile with a diameter D ₆₆ . The formed first hollow block 1a is a tube with an outer diameter D ₄₄ and an inner diameter D ₅₅ . The formed second hollow block 5a is a second tube 5a with an outer diameter D ₂₂ and an inner diameter D ₃₃ . If a sleeve 25 made of copper was used, it is covered with an approximately 0.25 mm thin copper layer (diameter D ₁₁ ).

LIST OF REFERENCE NUMBERS

1

first hollow block

1a

formed hollow block

2

Sliding layer on 1st

3

core

3a

reduced core

4

Interface

4a

Sliding layer on 3rd

5

second hollow block

5a

second pipe

6

Sliding layer on 5

7

first hole

8th

second hole

10

composite block

11

Core press block

12

formed composite block

13

Multiple composite block

14

reshaped multiple composite block

15

Press

16

Billet

17

die

18

Opening the die

19

ram

20

hollow punch

21

arrow

22

guide piece

23

parting line

24

parting line

25

shell

26

disc

27

second disc

d1

Diameter of 7

d2

Diameter of 1 including 2

d3

Diameters of 3 including 4 or 4a

d4

Diameter of 12

d5

Diameter of 5 including 6

d6

Diameter of 8

d7

Diameter of 14

Claims (18)

1. Method of producing hollow profiles having small external diameters and/or a small wall thickness from a nickel titanium alloy by shaping a composite block, wherein
   in a first step, a composite block (10) is formed comprising a solid core (3) of nickel titanium alloy, a first hollow block (1) of nickel titanium alloy surrounding the core (3), and a separating layer (4,23) disposed between the first hollow block (1) and the core (3),
   in a second step, the composite block (10) is shaped by a formation method, and
   in a third step, the first hollow block shaped into a first hollow profile (1a), and the shaped core (3a) are removed from the shaped composite block (12),
   characterized in that
   either the composite block (10) is formed with one or more additional hollow blocks (5) which are placed around the first hollow block (1) and which each comprise a separating layer (4,24) between neighboring hollow blocks (1,5) and, in the second step, the composite block (10) comprising several hollow blocks (1,5) and the core (3) is shaped, or,
   following the second and before the third step, the shaped first composite block (12) is inserted as a core into an additional hollow block (5) of a nickel titanium alloy, wherein the second composite block formed in this fashion comprises a separating layer (4) between the core and the additional hollow block, and, subsequently, the second composite block is shaped by a formation method, and, subsequently, in the third step, the additional hollow block, shaped into a hollow profile, the additional shaped first composite block and the additional shaped core are removed from the shaped second composite block.
2. Method according to claim 1, characterized in that the composite block (10) is shaped by an extrusion method, wherein the composite block (10) is inserted as a heated press block into a block recepticle (16) of a press (15) and is extruded through the opening (18) of a die (17) via the pressure of an extrusion die (19).
3. Method according to claim 2, characterized in that the composite block (10) moves relative to the block recepticle (16) during extrusion (direct extrusion).
4. Method according to claim 2, characterized in that the die (17) is disposed at a tip of a hollow die (20) and moves relative to the block recepticle (16) and the inserted composite block (10) during extrusion of the composite block (10) (indirect extrusion).
5. Method according to any one of the claims 2 through 4, characterized in that the composite block (10) is heated up for extrusion to a temperature between 850 °C and 950 °C, preferably between 900 °C and 950 °C.
6. Method according to claim 1, characterized in that the composite block (10) is formed by warm drawing, cold drawing, rolling, round-hammering or pilger method.
7. Method according to any one of the preceding claims, characterized in that the composite block (10) is formed by inserting the core (3) into the first hollow block (1), in particular into a hollow profile, and preferably into a tube.
8. Method according to claim 1, characterized in that the composite block (10) is formed by sliding several hollow blocks (1,5), in particular hollow profiles and preferably tubes, into one another.
9. Method according to any one of the preceding claims, characterized in that a hole (7) is drilled or milled into a block or through a block to produce a hollow block (10) having a hole (7) for insertion of the core (3).
10. Method according to any one of the preceding claims, characterized in that the composite block (10), a hollow block (1,5), or the core (3) are formed by cavity sink EDM or wire EDM of a solid nickel titanium block, a nickel titanium hollow block or another nickel titanium workpiece.
11. Method according to claim 1, characterized in that prior to separation of the shaped hollow blocks and the core, the insertion of a resulting shaped composite block into an additional hollow block of a nickel titanium alloy and the shaping of the composite block formed in this fashion are repeated once or a plurality of times.
12. Method according to claim 1 or 11, characterized in that in the second step, the composite block is shaped to a diameter (d4) which corresponds essentially to the diameter (d1) of the core prior to the second step, such that the shaped composite block can be inserted as a core into an additional hollow block having the same core diameter as the first composite block.
13. Method according to any one of the preceding claims, characterized in that the shaped composite block (12) is mechanically treated, subjected to a thermal shock treatment or chemically treated for removing a hollow profile (1a, 5a) or the core (3a).
14. Method according to any one of the preceding claims, characterized in that, prior to formation, a core in a composite block has a diameter between 10 mm and 60 mm, preferably between 20 mm and 40 mm.
15. Method according to any one of the preceding claims, characterized in that, following a shaping step, a composite block has an external diameter less than 40 mm, preferably less than 25 mm.
16. Method according to any one of the preceding claims, characterized in that a hollow block and/or the core are made from a nickel titanium alloy having superelastic properties or from a shape memory alloy.
17. Method according to any one of the preceding claims, characterized in that the core is made from a nickel titanium alloy having a higher martensite-austenite-transition temperature than the alloy of the hollow block.
18. Method according to any one of the preceding claims, characterized in that the nickel titanium workpiece is treated with a spark erosion method, in particular by means of cavity sink EDM or wire EDM, for removing or separating a core or a hollow profile from a block.

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