GB2578591A

GB2578591A - Method and component

Info

Publication number: GB2578591A
Application number: GB1817776.6A
Authority: GB
Inventors: Rizvi Nadeem; Drysdale James; Burt Julian; Goater Andrew
Original assignee: Laser Micromachining Ltd
Current assignee: Laser Micromachining Ltd
Priority date: 2018-10-31
Filing date: 2018-10-31
Publication date: 2020-05-20
Anticipated expiration: 2038-10-31
Also published as: GB2578591B; GB201817776D0

Abstract

A method of processing a body 20 of a shape memory material by bending or folding the body 20 and locally heat-treating the bent or folded region of the body 20 while the body is held by clamping means 132 & 134 in its bent or folded position. The localized heat treatment raises the temperature of the bent or folded region to above its martensitic to austenitic phase transformation temperature so that the body 20 retains its bent or folded shape after it has been released. The body 20 can be a sheet that can be used as an actuator in a fluid control valve (Fig. 3). Heat treatment can be performed using a laser beam which can be scanned along the bent or folded region of the body 20. The laser beam can also be used to cut the body 20 either before or after it is bent or folded. Suitable materials are nitinol alloys.

Description

METHOD AND COMPONENT

TECHNICAL FIELD

The present invention relates to a method of processing a material, a method of fabricating a component, apparatus for processing a material, apparatus for fabricating a component, to a material processed by a method, and a component fabricated by the method.

BACKGROUND

It is known to employ shape memory materials such as shape memory alloys in the fabrication of components, including actuators. Shape memory materials are characterised by an ability to 'memorise' a particular shape by subjecting the material to a heat treatment whilst in that shape.

It is an aim of the present invention to address disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

In an aspect of the invention for which protection is sought there is provided a method of processing a shape memory material having a first shape, comprising: performing a bending operation whereby a region of the material is bent into a second shape, thereby forming a bend region along a bend line, the bend region having a curvature formed by the bending operation, and held in the second shape; locally heating the bend region of the material, the bend region being heated sufficiently to cause the material to substantially retain the second shape when the sheet is no longer held in the second shape.

The material may be in the form of or comprise a sheet of material.

The curvature may be defined by a radius of curvature; the radius of curvature may be substantially constant over substantially the whole bend region. Alternatively the radius of curvature may vary over the bend region.

It is to be understood that the bend region is a region of the material in which a non-zero curvature is introduced into the material by the bending operation.

It is to be understood that by shape memory material is meant a material that is capable of exhibiting a shape memory effect.

Optionally, holding the material in the second shape comprises holding the material in the second shape by means of clamping means.

The clamping means may include a basal former to which the material is clamped in the second shape by means of clamping elements.

Optionally, the step of locally heating the bend region comprises causing heat to be applied from an external source substantially only in the bend region.

It is to be understood that, whilst heat may be applied substantially only in the bend region, regions of the material away from the bend region, and potentially the entire material, may experience an increase in temperature due to conduction, convention or radiation.

Optionally, the step of locally heating the bend region comprises heating the bend region by means of a laser beam.

Optionally, the laser beam is configured to irradiate the material substantially only in the bend region.

The method may comprise scanning the laser beam along the bend region.

The method may comprise scanning the laser beam along the bend region whereby the material is heated to substantially the same maximum temperature along substantially the entire bend line.

Optionally, the first shape is a substantially flat, planar shape.

Optionally, the shape memory material is a shape memory alloy material.

Optionally, the shape memory alloy is an alloy of Ni and Ti.

Optionally, the amount of Ni is in the range from around 35 to around 65 atomic percent, the balance being Ti.

Optionally, the amount of Ni is substantially 55%.

Optionally, the amount of Ni is substantially 60%.

Optionally, the shape memory material is nitinol.

Optionally, locally heating the bend region of the material comprises heating to a temperature in excess of a phase transition temperature. Optionally, the phase transition temperature is a temperature at which a transition from a martensitic phase to an austenitic phase occurs.

Optionally, locally heating the bend region of the material comprises heating to a temperature in the range from around 50C to 800C, optionally in the range from around 150C to around 750C, optionally in the range from around 200C to around 650C, optionally in the range from around 500C to around 600C. Other temperatures may be useful.

Optionally, locally heating the bend region of the material comprises locally heating to a temperature above a temperature in the range from around 25C to around 130C. Further optionally, locally heating the bend region comprises locally heating to a temperature in the range from around 500C to around 800C.

Optionally, locally heating the bend region of the material comprises heating to a temperature of at least 200C. Optionally, a width of the bend region that is heated to a temperature in excess of 200C may be no more than substantially 200um. Other widths may be useful.

The method may comprise performing a cutting operation on the material by means of a laser beam.

The method may comprise using the same laser to performing the cutting operation on the material and heating of the material.

The cutting operation may be performed whilst the material is held in the second shape.

Optionally, the cutting operation is performed before the material is held in the second shape.

Alternatively, the cutting operation may be performed with the material in the second shape, after the material has been released, following local heating of the bend region.

In a further aspect of the invention for which protection is sought there is provided an actuator comprising a shape memory material processed according to the method of another aspect.

In an aspect of the invention for which protection is sought there is provided a fluid flow control valve comprising an actuator according to a preceding aspect.

In another aspect of the invention for which protection is sought there is provided a method of processing a shape memory material having a first shape, comprising: performing a folding operation whereby a region of the material is folded into and held in a second shape, the step of folding of the material into the second shape comprising forming a fold region defining a fold line; locally heating the material along the fold line, the material being heated sufficiently to cause the material to substantially retain the second shape when no longer held in that 15 shape.

The material may comprise or be in the form of a sheet of material.

The fold region may have a bend radius; the radius may be substantially constant over the fold region. Alternatively the radius may vary over the fold region.

The material may be held in the second shape by clamping means.

It is be understood that reference to a 'fold region' is reference to a portion of the material defining the fold that has a non-zero curvature introduced by the fold.

Optionally, the step of locally heating the material along the fold line comprises heating the material substantially only in the fold region by means of a laser beam, the laser beam being configured to irradiate the material substantially only in the fold region.

Optionally, the method may comprise scanning the laser beam along the fold line of the bend region.

The method may comprise scanning the laser beam along the bend line whereby the material is heated to substantially the same maximum temperature along substantially the entire bend line.

Optionally, the shape memory alloy is nitinol.

In an aspect of the invention for which protection is sought there is provided an actuator comprising a shape memory material, optionally a shape memory alloy, processed according to the method of a preceding aspect.

In a further aspect of the invention for which protection is sought there is provided a method of processing a shape memory material having a first shape, comprising: performing a bending operation whereby a region of the material is bent into a second shape and held in the second shape by clamping means, the material returning substantially to the first shape upon release; with the material held in the second shape, locally heating the region of the material that has been bent by means of a laser beam, the region being heated sufficiently to induce a shape memory effect whereby, upon release from the clamping means, the material tends to retain the second shape, the material tending to return to the second shape following subsequent bending back to the first shape.

Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination. For example features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

For the avoidance of doubt, it is to be understood that features described with respect to one aspect of the invention may be included within any other aspect of the invention, alone or in appropriate combination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which: FIGURE 1 is a schematic illustration of (a) a substantially flat sheet of shape memory material in plan view, (b) the sheet shown in (a) in plan view following bending along fold line A-A, being a line midway between and parallel to lateral long sides of the sheet, and (c) the sheet as shown in (b) viewed in a direction parallel to the fold line A-A; FIGURE 2 is a schematic illustration of a sheet of shape memory material held by clamping means during laser annealing of the material along a fold line, as viewed (a) in front view and (b) in plan view; and FIGURE 3 is a schematic illustration of the use of a shape memory alloy component in a valve member in (a) cross-sectional and (b) plan views.

DETAILED DESCRIPTION

FIG. 1(a) is a plan view of a sheet of nitinol' shape memory alloy foil 20. The sheet shown is 25um (0.025mm) in thickness, and of lateral dimensions 6mm x 10mm.

In one example of processing a material according to an embodiment of the present invention, a bending operation is performed on the foil sheet shown in FIG. 1(a), in which the foil 20 is bent through an angle of substantially 90 degrees along a fold line A-A, being a line midway between longitudinal edges of the foil 20. The foil is shown in plan view in FIG. 1(b) following the bending operation. FIG. 1(c) shows the foil parallel to line A-A following the bending operation. A bend region 20B is therefore formed in the foil. It is to be understood that in the present example, the bend region 20B is arranged to have a radius of curvature rather than being defined by a substantially abrupt right-angular corner. If the foil is subsequently released without heat treatment, the foil 20 returns to the substantially flat shapeform.

The foil 20 is held in the configuration of FIG. 1(b) by a clamping means as shown in FIG. 2. FIG. 2 is a schematic illustration showing the sheet 20 of shape memory material held by clamping means during laser annealing of the material along a fold line, as viewed (a) in front view and (b) in plan view.

The clamping means is in the form of a metal base 130 (or 'former') of square section and clamp elements 132 that press the foil 20 against orthogonal sides of the bar 130. The base 130 and clamping means are formed from a metal, in the present example aluminium, although other materials may be useful in some embodiments. As may be seen from FIG. 2(a), the base 130 has a notch at one corner, being the corner facing the bend region 20B of the foil 20. The arrangement is such that the bend region 20B of the foil is not in contact with the base 130, i.e. the bend region 20B is exposed to air (or other gas in which the annealing operation is performed) during the annealing operation.

Following clamping, the foil 20 is subject to a laser annealing treatment. A laser beam is directed at the bend region 20B of the foil and scanned along the bend region 20B, i.e. along the fold-line A-A (or 'bend line') of the foil 20. The laser power is set to a value sufficient to cause local heating of the bend region (or 'fold region') 20B as the laser is scanned along the bend region 20B, such that a region substantially 200um wide is heated to a temperature sufficient to cause the foil 20 to substantially retain the shape in which it is held during the annealing operation.

It is to be understood that the laser power and scan rate may be considered to be interdependent, in that the higher the laser power, the higher the scan rate may be set in order to achieve a given local foil temperature as the laser is scanned along the bend region 20B.

In the present example, the foil 20 is heated to a temperature sufficiently high to cause the foil 20 to substantially retain the shape in which it is held by the clamping means when it is released, although it is to be understood that the angle through which the foil 20 remains bent about the fold line A-A upon release may change slightly due to 'spring-back'. That is, the foil 20 may 'spring back', upon release, towards the substantially flat configuration in which it existed prior to being bent through substantially 90 degrees, for example to a configuration in which angle Z of FIG. 1(c) is substantially 95 or 100 degrees rather than 90 degrees. In some embodiments, in order that the angle Z is substantially 90 degrees upon release of the foil 20 from the clamping means following an annealing treatment, the clamping elements and bar 130 may be arranged to hold the foil 20 such that angle Z is less than 90 degrees, for example substantially 85 degrees or substantially 80 degrees.

It is to be understood that, when the laser beam first begins to heat the foil 20, the foil 20 is typically at room temperature. However, as the beam passes along the bend line 20B the nitinol material exposed to the laser beam at a given moment in time has already been partially heated by conduction at least from the area previously exposed to the beam. As a result, higher laser power may be required at the start of the annealing process (to heat the nitinol at the start from room-temperature to the annealing temperature sufficiently quickly) than is needed once the process is underway.

In one example, the rate of scanning of the laser beam along the bend line 20B may be varied in order to control the amount of heating. Thus, with the laser power substantially constant, the speed of travel of the laser beam over the surface of the foil may be relatively low at the start of the annealing operation, and increased once the laser 140 has scanned a certain distance along the bend line 20B. In one example, the speed of travel of the beam as the beam is scanned over the first 1mm of the bend line 20B is approximately 10mm/s. Once the beam has scanned the first 1mm, the rate of scanning of the beam is increased to substantially 50mm/s, thereafter remaining at 50mm/s for the remainder of the annealing process. It is to be understood that, in some embodiments the laser beam is scanned over a substantially stationary foil 20 whilst in some alternative embodiments the base 130 (and therefore also the foil 20) is scanned beneath a substantially static laser beam.

In the present embodiment, the laser 140 is a continuous-wave (CVV) laser with a wavelength in the infra-red region of the spectrum centered around 1064nm. In the present example, a laser beam having a power level of approximately 4W was focused onto the nitinol foil 20 using a lens of focal length 420mm, yielding an average power density of around 60kW/cm2 at the foil 20. In the present example a beam of substantially circular cross-section was employed, however it is to be understood that beam shapes other than substantially circular may be useful such as elongated beam shapes. A single pass of the laser beam across the nitinol was used to impart the bend into the foil 20. No external cooling was used during the process and all processing was carried out in ambient air.

It was verified that only the laser annealing process caused the foil 20 to retain its substantially as-bent shape following release from the clamping means. This was achieved by following the bending and clamping procedure, i.e. clamping the foil 20 in the configuration shown in FIG. 2 for a period corresponding to that required to anneal the foil 20, but without the laser 140 being turned on. It was found that in the case the laser 140 was not used, the nitinol foil 20 returned to being completely flat (unbent) when it was released from the clamping means. In the case where the laser process was used then the nitinol foil substantially retained the right-angled bend region 20B once it was released from the clamping means.

It is to be understood that other lasers generating radiation in the infra-red wavelength region may be useful in order to perform the annealing process.

It is to be understood that foils may be caused, following laser annealing, to retain bend angles in bend regions 20B in which they are held during laser annealing that are other than ninety degrees, such as bend angles of 30 degrees, 45 degrees, 120 degrees or any other suitable bend angles.

It is to be understood that foil sizes other than 6mm x 10mm may be employed, such as narrower, wider, longer or shorter foils. The foil 20 employed in the present example was 25 micrometres (urn) in thickness, i.e. 2.5x10E-6 metres in thickness. Sheets in the form of foils or plates of other thickness (greater or thinner) may be useful in some applications.

It is to be understood that embodiments of the present invention are useful in laser processing of shape memory materials such as shape memory alloys. Relatively small foil sizes such as those described herein are of interest since nitinol may be required to be employed in ultra-compact devices where some micro-motion is required. An example of this would be if the nitinol part forms a flap which normally is closed. If air or liquid pressure builds up on one side, establishing a pressure differential across the flap, then the flap may open (in some configurations the nitinol may be forced to bend by the rising pressure), thereby releasing the pressure. Once the pressure difference has reduced, or substantially equalized, the nitinol flap reverts to its original position, thereby closing the flap. Thus, in the present example, the shape of the foil (with a right-angled bend region 20B) shown in FIG. 1(c) may correspond to the 'closed' position of the flap. When sufficient pressure is applied to the foil, tending to cause the foil to revert towards the substantially flat shape of FIG. 1(a) the flap may do so. However, once the pressure is removed, the foil 20 may revert to the shape in which it was annealed, i.e. that of FIG. 1(c), with the bend region 20B reverting to the substantially right-angled configuration. A sheet of nitinol material (e.g. a foil or plate) may itself form the closure flap. Alternatively, the nitinol material may be directly coupled to a closure flap thereby to move the closure flap. In some embodiments the nitinol material may be coupled to a closure flap by means of a mechanical linkage.

The process of annealing the foil 20 may be preceding by a process of cutting the foil, for example in its substantially flat shapeform, to a required shape, before or after placing the foil 20 in the clamping means.

An example of an application of a foil 20 in a micro-motion device is shown in FIG. 3. FIG. 3(a) is a cross-sectional view showing a reservoir 230 in which a quantity of liquid 230F is being stored. A liquid outlet pipe 240 is coupled to a basal surface of the reservoir 230 to allow outflow of liquid from the reservoir 230.

As shown in FIG. 3(a) and FIG. 3(b), the outlet pipe 240, which is of substantially square cross-section in the present embodiment, is provided with a valve arrangement having a valve member 220 and sealing lip 242 around three sides of the pipe 240. The valve member 220 is in the form of a plate of shape memory alloy, in the present embodiment nitinol, that has been bent to form a substantially L' shaped cross-section and locally annealed in a bend region 220B thereof so that is retains the substantially 'L' shaped cross-section without requiring physical constraint (e.g. by being held in a clamp). As shown in FIG. 3(a), a first portion 221 of the valve member 220 has been coupled to an internal wall of the outlet pipe 240 by means of fixing elements 220F whilst a second portion 222 of the valve member 220 at right angles to the first 221 underlies the sealing lip 242, in contact therewith, to form a fluid-tight seal (position P1).

It is to be understood that, when a head of fluid pressure in the reservoir 230 is sufficiently high, the second portion 222 of the valve member 220 is deflected under the pressure of fluid, for example from position P1 to position P2, permitting fluid to drain from the reservoir 230. Once the head of fluid pressure has fallen to a sufficiently low level, the second portion 222 of the valve member 220 is able to return to contact with the sealing lip 242 (position Pl) and fluid flow terminates.

It is to be understood that other arrangements may be useful in some embodiments.

Other applications of the method and apparatus may be envisaged.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. A method of processing a sheet (20) of a shape memory material having a first shape, comprising: performing a bending operation whereby a region (20B) of the sheet (20) is bent into a second shape, thereby forming a bend region (20B) along a bend line (A), the bend region (20B) having a curvature formed by the bending operation, and held in the second shape; locally heating the bend region (20B) of the sheet (20), the bend region (20B) being heated sufficiently to cause the sheet (20) to substantially retain the second shape following release of the sheet (20) from the clamping means (130, 132, 134).
2. A method according to claim 1 whereby holding the sheet in the second shape comprises holding the sheet in the second shape by means of clamping means.
3. A method according to claim 1 or claim 2 whereby the step of locally heating the bend region comprises causing heat to be applied from an external source substantially only in the bend region.
4. A method according to any preceding claim whereby the step of locally heating the bend region comprises heating the bend region by means of a laser beam.
5. A method according to claim 4 whereby the laser beam is configured to irradiate the sheet substantially only in the bend region.
6. A method according to claim 4 or claim 5 comprising scanning the laser beam along the bend region.
7. A method according to claim 6 comprising scanning the laser beam along the bend region whereby the sheet is heated to substantially the same maximum temperature along substantially the entire bend line.
8. A method according to any preceding claim wherein the first shape is a substantially flat, planar shape.
9. A method according to any preceding claim wherein the shape memory material is a shape memory alloy material.
10. A method according to claim 9 wherein the shape memory alloy is an alloy of Ni and Ti.
11. A method according to claim 10 wherein the amount of Ni is in the range from around 35 to around 65 atomic percent, the balance being Ti.12. A method according to claim 10 or claim 11 whereby the amount of Ni is substantially 55%, further optionally whereby the amount of Ni is substantially 60%.
12. A method according to any preceding claim wherein the shape memory material is nifinol.
13. A method according to any preceding claim whereby locally heating the bend region of the sheet comprises local heating the bend region to a temperature in excess of a martensitic to austenitic phase transition temperature.
14. A method according to any preceding claim comprising performing a cutting operation on the sheet by means of a laser beam.
15. A method according to claim 14 as depending through claim 4 comprising using the same laser to performing the cutting operation on the sheet and heating of the sheet.
16. A method according to claim 14 or claim 15 wherein the cutting operation is performed whilst the sheet is held in the second shape.
17. A method according to claim 14 or 15 wherein the cutting operation is performed before the sheet is held in the second shape.
18. An actuator comprising a sheet of a shape memory alloy processed according to the method of any preceding claim.
19. A fluid flow control valve comprising an actuator according to claim 18.
20. A method of processing a sheet of a shape memory material having a first shape, 35 comprising: performing a folding operation whereby a region of the sheet is folded into and held in a second shape by clamping means, the step of folding of the sheet into the second shape forming a fold region defining a fold line; locally heating the sheet along the fold line, the sheet being heated sufficiently to cause the sheet to substantially retain the second shape following release of the sheet from the clamping means.
21. A method according to claim 20 whereby the step of locally heating the sheet along the fold line comprises heating the sheet substantially only in the fold region by means of a laser beam, the laser beam being configured to irradiate the sheet substantially only in the fold region.
22. A method according to claim 21 comprising scanning the laser beam along the fold line of the bend region.
23. A method according to claim 22 comprising scanning the laser beam along the bend line whereby the sheet is heated to substantially the same maximum temperature along substantially the entire bend line.
24. A method according to any one of claims 20 to 23 wherein the shape memory alloy is nitinol.
25. An actuator comprising a sheet of a shape memory alloy processed according to the method of any one of claims 20 to 24.