WO2003008813A2

WO2003008813A2 - Element for connecting two objects, especially parts of appliances

Info

Publication number: WO2003008813A2
Application number: PCT/DE2002/002475
Authority: WO
Inventors: Stefan Kautz; Heinz Zeininger
Original assignee: Siemens Aktiengesellschaft
Priority date: 2001-07-17
Filing date: 2002-07-05
Publication date: 2003-01-30
Also published as: DE10134832A1; WO2003008813A3

Abstract

The invention relates to a connection element (2h) for mechanically connecting two objects (8, 9). Said element consists at least partially of a memory metal and has, as a first form of embodiment (2t), an open clamp comprising two limbs (2b, 2c) having free ends and being interconnected by means of an intermediate part (2a). In the assembled state, said limbs are introduced into corresponding openings (10a, 10b) in the two objects (8, 9). In the mounted state, said limbs (2b', 2c') ensure the connection between the two objects (8, 9) with a second embodiment (2h), due to a deformation, using the memory properties thereof.

Description

description

Element for connecting two objects, in particular device parts

The invention relates to a connecting element for mechanically connecting two objects, in particular two parts of the device.

In almost all areas of technology, it is often necessary to mechanically firmly connect two objects. These objects can be made of similar materials such as metal or plastic; but connections between objects made of different materials are also common. An example is the area of electronic or electrotechnical devices, where different components often have to be connected to one another or to housing parts either in a device or housing. Devices or housing parts can sometimes also be mechanically connected to one another. Screws are known as connecting elements, which are screwed into the objects to be connected. Such a connection technology is complex in several respects. On the one hand, screwing in is relatively cumbersome, time and cost intensive. Furthermore, the objects to be connected generally have to be dimensioned sufficiently for a secure mounting of the screws, so as to avoid that the screw does not grip or tear out if the wall thickness is too small. The problem is the considerable space required as a result of the screws used, which is not available, in particular in the case of highly integrated electrical or electronic devices, or can only be created if the devices are dimensioned larger than desired. Another difficulty often lies in the relatively complex disassembly, which is due to the laborious unscrewing of the screws, if such disassembly is possible at all or the effort involved is pedalable. However, disassembly is often required in the event of maintenance or repair of a device or as part of recycling.

Snap closures, which can also consist of plastic material, are also known as closure systems for the non-positive connection of housings, housing parts or plug-in parts of electronic assemblies. Plastic lugs, for example, are known as corresponding snap locks, which snap into recesses and, by pushing back or pulling out, enable the connected objects to be opened or dismantled. With frequent operation, however, such connecting elements are prone to breakage. Opening the connection, be it for repair or recycling reasons such as in the case of cell phones or corresponding combinations of housing and assemblies must generally be done by hand. Apart from the time involved, the connected housing parts are often damaged. There is also a risk of internal components being destroyed. Corresponding internal components such as electronic assemblies or shielding surfaces are generally connected to a housing via elaborately detachable connecting elements. Such a connection / locking technique, however, limits the design of the components, the housing and / or the corresponding complete system. In the coming years, regulations will also come into force that require the complete disassembly and separation of such electronic assemblies and their housings according to material types.

The object of the present invention is to provide a connecting element which, on the one hand, allows a simple mechanical connection to be created between two objects or device parts and, on the other hand, enables the connection to be opened or dismantled easily. This object is achieved with the measures specified in claim 1. Accordingly, the connecting element should at least partially consist of a memory metal, - have a first shape in an assembled state and have a second shape in an assembled state, which was impressed on the element prior to assembly using its memory properties. The first shape is intended to be that of an open clamp, which has two freely ending leg pieces which are connected to one another by an intermediate piece and which are to be introduced into corresponding openings in the two objects in the assembled state and which are assembled in the assembled state due to their use Memory properties ensure the connection between the two objects.

The connecting element according to the invention advantageously consists at least partially of a memory metal known per se, which is also referred to as a shape memory alloy. Such a material has the property that it can change its shape depending on the temperature. For the intended use according to the invention, this means that the clamp-shaped connecting element, which in the assembled state has a first shape with open leg pieces, with these openings or other recesses such as bores in the objects to be connected, e.g. two housing shells is inserted. The clamp element is then heated. Above a phase transition temperature, the structure of the memory metal changes from one

Low-temperature phase in a high-temperature phase (of "Marten- sit ^Λ to" austenite ") around. The high temperature phase is above a second figure, the memory properties exploiting been impressed. Appropriate metals and their memory properties are known (see. Eg, for example, Book by D. Stöckel [Ed.]: "Alloys with shape memory", Expert-Verlag, Ehningen (DE), 1988, especially pages 64 to 79). With the phase change, at least the shape of the leg pieces of the clamp element changes in such a way that they hold the two objects to be connected behind or clasped together.

The invention therefore allows a connection by simply inserting the connecting element into openings provided for this purpose in the two objects and a corresponding temperature increase. This connection is done very quickly, easily and with little effort, since the parts to be connected only have to be heated. To heat these parts, this can be transported, for example, through a heating furnace; the heating can also be achieved by means of a heat finger or by energization. This also means that assembly can be automated thanks to the self-adjusting properties of the memory metal clamp elements after the temperature has increased, e.g. around 50 ° C possible. Furthermore, the connecting element according to the invention requires considerably less space than a connecting screw, which is often of considerable length. It can therefore be used in particular for objects that have small dimensions. Also, the requirements regarding the dimensioning of the connection areas are not the same as for a screw connection; rather, material can be saved in these areas for the connection technology. This is associated with a corresponding cost saving in terms of material costs, manufacturing and recycling costs.

Finally, a simple opening of the connection or a simple disassembly is possible, since the memory metal shows a renewed phase change when it cools sufficiently and changes from the high-temperature phase to the low-temperature phase. It should be exploited that the high temperature phase is significantly harder than the low temperature phase.

For example, martensite is about 5 times softer than austenite. This enables the clamp elements in the easy to remove soft condition. For example, a clip element made of a memory metal with a two-way effect can be self-disassembling without mechanical intervention, for example at temperatures below -40 ° C., so that connected objects, such as housing parts, can be disassembled without damage. The connected objects can thus be easily dismantled by cooling, since this makes the mechanical connections easily detachable. In addition to the clamp elements, valuable components and unloaded components such as plastic housings, yokes, anchors, components of semiconductor technology or precious metal contacts can be easily removed and used again for the same or different purposes. Correspondingly, defective components can also be replaced.

Another advantage is the increased security in the operation of the connected objects. A connection created according to the invention can hardly loosen due to vibrations or other handling-related forces. Rather, the clamp elements can be used to achieve a non-positive connection that is under tension. In addition, in contrast to pre-stressed plastics, such a connection shows good aging resistance even at elevated temperatures.

Advantageous embodiments of the connecting element according to the invention emerge from the dependent claims.

Thus, in particular, the connecting element can at least partially consist of a memory metal which has a first transition temperature at which a high temperature phase forms due to a temperature increase and the second shape takes on, and one of at least 30 ° C, in particular at least 50 ° C below the first transition temperature, further transition temperature, at which the transformation into the low-temperature phase takes place when cooling. Preferably the first conversion temperature for the transition to the high-temperature phase above 40 ° C, in particular above 50 ° C, and the further transition temperature for the transition to the low-temperature phase is below 0 ° C, in particular below -40 ° C. The different transition temperatures are therefore as far apart as possible. This should prevent any temperature fluctuations from affecting the strength of the connection in any way.

The memory metal can also show a one-way effect (see e.g. the book by D. Stöckel, pages 64 to 71). In this embodiment, the clamp element takes on the second shape when the temperature rises. When the temperature drops below the second phase formation temperature, only a phase change occurs in the low-temperature phase; however, the second form remains. The material therefore only becomes soft, but retains its shape-related shape. An easy disassembly is still possible due to the softness of the material.

According to an alternative, a memory metal with a two-way effect can be provided, so that the embossed first shape takes on when it is converted into a low-temperature phase. In this alternative, the clip element changes between the two embossed shapes. In other words, in the event of cooling for dismantling, the clamp element returns to its original open form of assembly. The mechanical connection can then be released very easily.

Suitable memory metals are preferably TiNi or TiPd or NiMn or NiAl or CuAl or CuZn or FeNi or FeMn alloys, which may also contain at least one further alloy partner.

Further advantageous embodiments of the invention

Connecting element emerge from the subclaims not mentioned above. Details of connecting elements according to the invention result from the exemplary embodiments described below with reference to the drawing. 1 shows in diagrams temperature-dependent properties of a memory metal, FIGS. 2 and 3 show a low-temperature form and a high-temperature form of a clip element, FIGS. 4 to 6 show further embodiments of clip elements and FIG. 7 shows a clip element according to FIG

Condition for connecting two housing halves. Corresponding parts are provided with the same reference symbols in the figures.

With a connecting element according to the invention, two objects or device parts, for example two housing halves, can be mechanically connected. The connecting elements should have a first shape in the unassembled state, the so-called assembly state. In order for these elements to be recyclable, self-adjusting, self-dismantling, easy to assemble, wear-resistant, corrosion-resistant, a memory metal alloy known per se must be provided for this purpose. Alloys suitable for this purpose are in particular TiNi, TiPd, NiMn, NiAl, CuAl, or CuZn, FeNi or FeMn alloys, which may also contain at least one further alloy partner (see also the book by D. Stöckel, pages 15 and 75). The alloy NiTiNbl3 is selected as a concrete exemplary embodiment.

Properties of this alloy or of a connecting element made with this alloy can be seen from the diagrams in FIG. In the diagrams in the ordinate direction, the mechanical stress σ, the mechanical elongation ε and the martensite component A in dependence on the applied Temperature T plotted direction. The lower part of the diagram shows the course of the internal mechanical stresses in a connecting element according to the invention over the temperature. The course is shown for a connecting element with a memory metal, which has a first transition temperature T _A of 50 ° C, at which the formation of the austenite phase (high temperature phase) begins when the temperature rises, and a second transition temperature (T _M ) of approx. -40 ° C, at which the formation of the martensite phase (= low-temperature phase) begins. The inherent stress clearly increases with the onset of austenite phase formation. Is now cooled. the tension remains largely unchanged up to the second transition temperature T _M of approximately -40 ° C. and only then breaks off relatively quickly, since then the formation of martensite sets in to an increased extent and the material becomes softer, whereby tension is reduced.

A corresponding hysteresis curve is shown in the diagram by the upper curve of the martensite component A. If the connecting element is used at room temperature and then heated above 50 ° C, a strong formation of austenite is evident, the martensite component decreasing accordingly. The material becomes very hard overall and the transition to the second curved shape (= high temperature shape) begins. This hard state and thus the high austenite content with a minimum martensite content is retained in a subsequent cooling until the second phase formation temperature T _M of -40 ° C. is reached or fallen below. The martensite component then increases due to a decrease in the austenite component, ie the material becomes soft. If an alloy with a two-way effect is used, a new shape change begins at the same time.

The middle curve between that of the inherent stresses σ and that of the martensite component A gives the corresponding temperature rature-dependent expansion behavior ε of the connecting element again.

As can be seen from the course of the three curves shown, there is a hysteresis-like behavior which enables a connecting element according to the invention to be used as often as desired, since the hysteresis is carried out as often as required by means of temperature changes without any adverse effects on the mechanical connection can be. So the material is very wide

Hysteresis. Depending on the manufacturing process, other hysteresis ranges can be made possible, for example between -150 ° C and + 150 ° C.

FIG. 2 shows a low-temperature form of a clamp element 2t — index “t” indicates the low-temperature form — made of a corresponding material. The element is shown in its open, first form. It has two free-ended legs or sides that are connected to one another by an intermediate piece 2a - Tent parts 2b and 2c If the temperature T _M falls below -40 ° C for a short time, a martensite transformation occurs and the open brackets shown result, which then remains intact up to + 50 ° C If this temperature T _{a is} exceeded, at least one of the leg pieces 2b and 2c is curved, assuming the high-temperature shape shown in Figure 3 (somewhat schematically), namely if the temperature T _{A is} briefly exceeded, the austenite transformation occurs. This shape then remains the temperature T _{M of} the martensite transformation is obtained, and the maximum temperature to which the element can be exposed is eg at about 350 ° C. In the figure, the clamp element in its high-temperature form is denoted by 2 _h - index “h ^λ indicates the high-temperature form - and its curved leg pieces are denoted by 2b ^λ or 2c ^Λ .

If the memory metal clamp element with the above properties is heated above 50 ° C, it will forth imprinted high temperature shape, preferably the bracket shape. If the material has the so-called two-way effect (cf. the book by D. Stöckel, pages 64 to 71), the clip will bend again if the temperature falls below -40 ° C, because at these temperatures it has another low-temperature shape that is imprinted on it 2 with the elongated shape of its leg pieces 2b and 2c. If the memory metal has only a one-way effect, the material will only take on the shape of the clip that is stamped on it when the upper temperature mark is exceeded, but not another shape if the martensite start temperature is undershot. However, the mechanical behavior of the memory metal clamp element at different temperatures represents an essential special feature. While a very solid state is assumed after the austenite temperature is exceeded, the so-called austenite phase, T _M of -40 ° with the martensite phase, a mechanical state is set that is significantly softer, for example by a factor of 3 to 5, softer than the high-temperature phase. As a result, the clip element, which does not obey the two-way effect, is nevertheless very easy to remove in the martensite state and can be converted back to the very solid state by increasing the temperature. The high-temperature mold maintains its mechanical properties up to very high temperatures of, for example, 350 ° C. This results, for example, in the possibility of decentralized assembly in so-called active zones at high temperatures, without the fear of creep deformations of the safety locks of the parts to be connected. Corresponding clamp elements enable a very high number of aging-free deformation cycles in the order of magnitude of, for example, 10,000.

Corresponding clamp elements using memory metal show excellent corrosion resistance and are therefore also of interest to the automotive industry, for example. In addition, they are given the opportunity to construction and the shape of the bracket vary depending on the intended use. Figures 4 to 6 show such possible variations. Figure 4 shows a composite structure of a clamp element 3 _h in its high temperature form. Its intermediate piece 3a consists of inexpensive steel — indicated in the figure by greater blackening — and thus essentially shows no temperature-dependent deformation. Its two side parts 3b and 3c, on the other hand, are made of memory metal and, depending on the temperature application, show an austenite or martensite transformation.

In contrast to the embodiments of clamp elements 2 _t or 2 _h or 3 _h according to FIGS. 2 to 4, in which a closing high-temperature shape has been assumed, according to FIG. 5 there is of course also an opening shape of a clamp element 4 _h opening outwards possible. The shape shown is again the embossed high-temperature form, which is taken after the austenite transition temperature has been exceeded for a short time.

The clamp element 5 _h shown in FIG. 6 is composed of a plurality of limbs and intermediate pieces which, in their high-temperature form, can also include angles other than 90 °.

It is essential for all of these elements that, in an assembled state, they take on a second shape (= high-temperature shape) embossed prior to assembly, using their memory properties, which ensure a clamp function between two objects to be connected and thus ensure a non-positive connection between the two objects. A corresponding embodiment is shown in Figure 7. Here, the clamp element 2 _t or 2 _h according to FIGS. 2 and 3 serves to connect or clamp two housing halves 8 and 9 or other device parts. An opening 10a or 10b is provided in each of these housing halves, into which the free leg pieces 2b or 2c in the first, open Shape (= low-temperature mold 2 _t ) can be inserted. The corresponding form of assembly is indicated by dashed lines in the figure. After the insertion of these leg pieces, indicated by a double arrow 11, there is a brief heating above the temperature T _{A of} the austenite transformation, for example above 50 ° C., the leg pieces 2b and 2c, for example, bending inwards by previously pressing them at substantially Take higher temperature impressed high temperature form 2b ^Λ or 2c ^Λ according to Figure 3. This curvature creates the positive connection between the housing halves 8 and 9. By briefly dropping below the martensite transformation temperature T _M of, for example, -40 ° C., the first shape 2 _{t of} the assembly state can be restored, so that an easy disassembly possibility is created. The disassembly or assembly direction is illustrated in the figure by the double arrow 11.

The illustration of the clamp elements according to FIGS. 2 to 7 is greatly simplified or idealized in the drawing. In general, the free leg pieces 2b and 2c to be inserted into the openings or their corresponding leg pieces according to the embodiments according to FIGS. 5 and 6 will not exactly enclose angles of 90 ° with respect to an intermediate piece connecting them. It is only essential that a curvature of these leg pieces in the high-temperature form ensures that the clamp element is non-positively clamped between the objects to be connected.

Claims

claims

1. connecting element (2 _h to 5 _h ) for mechanically connecting two objects, in particular two device parts (8, 9), which at least partially consists of a memory metal, has a first shape (2t) in an assembled state and in an assembled state has a second shape (2 _h ), which was impressed on the element prior to assembly using its memory properties, the first shape (2 _t ) being that of an open clamp, which has two free ends, via an intermediate piece (2a ) has interconnected leg pieces (2b, 2c) which are to be inserted into corresponding openings (10a, 10b) in the two objects (8, 9) in the assembled state and (2b, 2c) in the assembled state due to a deformation under Utilize their memory properties to ensure the connection between the two objects (8, 9).

2. Connecting element according to claim 1, characterized by a memory metal which has a first transition temperature (T _A ) at which a high temperature phase forms due to a temperature increase and the second shape (2 _h ) is taken, and one by at least 30 ° C, in particular by at least 50 ° C, below the first transition temperature (T _A ) is a further transition temperature (T _M ), at which the conversion into the low-temperature phase takes place during cooling.

3. Connecting element according to claim 2, characterized in that the first transition temperature (T _A ) for the transition to the high temperature phase is above 40 ° C, preferably above 50 ° C, and the further transition temperature (T _M ) for the transition to the low temperature phase is below 0 ° C, preferably below -40 ° C.

4. Connecting element according to one of the preceding claims, characterized in that the memory metal shows a one-way effect or a two-way effect, so that when converted into a low-temperature phase in the impressed first shape (2 _t ) is assumed.

5. Connecting element according to one of the preceding claims, characterized by a memory metal made of a TiNi or TiPd or NiMn or NiMn or NiAl or CuAl or CuZn or FeNi or FeMn alloy, which optionally also has at least one contains another alloy partner.

6. Connecting element according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the

Leg pieces (2b 2c ^λ ; 3b, 3c) in the second shape (2 _h ; 3h) with their free ends extending towards one another (FIGS. 3 and 4).

7. Connecting element according to one of claims 1 to 5, characterized in that the leg pieces in the second shape (4 _h ) extend with their free ends away from each other (Figure 5).

8. Connecting element according to one of the preceding claims, g e k e n n z e i c h n e t by a partial formation of a non-memory metal.

9. Connecting element according to claim 8, so that at least the intermediate piece (3a) consists of the non-memory metal, in particular steel, (FIG. 4).