DE102018128438B4 - Process for the production of one-piece joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems made of shape memory material as well as one-piece joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems made of shape memory material - Google Patents

Abstract

Method for producing one-piece joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems from at least one shape memory material, in which a first layer of a shape memory material in powder form is formed and solidified by means of an additive manufacturing process, the first layer is subsequently pseudoplastically deformed, a second layer of a shape memory material in powder form is then arranged on the first layer, and the first and second layers are subsequently melted at least in the region of the mutually arranged interfaces of the layers and the first and second layers are bonded in a materially bonded manner essentially without interfaces, wherein further layers can be applied by means of an additive manufacturing process, wherein at least one local region of the second layer of the shape memory material is thermally treated below the liquidus temperature by means of a heat source, wherein the thermal treatment in the local region deactivates the shape memory properties by forming martensite or austenite with phase precipitations.

Description

The invention relates to the fields of materials science, electrical engineering, medical engineering and process engineering and relates to a method for producing one-piece components made of shape memory material as well as one-piece components made of shape memory material. The one-piece components made of shape memory material can be used, for example, as joints, actuators, sensors or as spring elements in damping systems.

Shape memory materials consist of specific metallic alloys that can exist in two different crystal structures. Shape memory materials can therefore return to their previous shape after significant deformation. This effect of the shape memory material is based on the reversible martensitic phase transformation of the material structure and can be induced thermally or mechanically.

If a shape memory alloy is cooled from a high temperature, the austenitic high-temperature phase changes to the martensitic low-temperature phase reversibly and without diffusion. The formation of martensite begins when the martensite start temperature M _s of the shape memory material is reached. Its formation is complete below the martensite end temperature M _f . The martensitic phase transformation is reversible. Therefore, the martensite changes to austenite when the temperature is increased accordingly. When the austenite start temperature A _s is reached, austenite begins to form. The structure is then completely austenitic above the austenite end temperature A _f .

The martensitic structure of a shape memory alloy usually has a high density of twin grain boundaries, whose interfaces are highly mobile. If a shape memory alloy in the martensitic state is deformed above the elastic yield point up to a maximum of 8% elongation, the martensitic structure is reoriented and detwinned. The resulting deformation of the martensitic structure is referred to as "pseudoplastic" and is permanent.

However, if a pseudoplastically deformed structure is heated above the A _s temperature and further up to the A _f temperature, the original crystal orientation of the austenite and consequently the original shape of the material are restored. Subsequent cooling of the austenitic structure to temperatures below the M _f temperature in the stress-free state leads to the formation of a fully martensitic structure without any change in shape. This shape memory effect is called the one-way effect (EWE) and is characterized by the one-time change in shape of a material structure that is pseudoplastically deformed in the martensitic state while it is being heated.

However, if a force is applied during cooling of the austenite, which then exists completely as martensite below M _f , so that it is pseudoplastically deformed, a change in shape also occurs during cooling.

During the deformation, a spring can be prestressed by a phase transformation into austenite when heated. The shape memory effect can occur in both the high-temperature and the low-temperature phase. This effect, which is based on the one-way effect with additional deforming force, is called the two-way effect (TWE).

Furthermore, the transformation of austenite into martensite can be stress-induced, i.e. caused by mechanical forces. If the stress remains constant, the austenite turns into martensite and the latter is first elastically deformed. The martensite then detwins. This so-called "pseudo-elastic" expansion range of up to a maximum of 8% is located downstream of the elastic deformation. After complete unloading, the detwinned martensite transforms back into austenite and changes shape. The pseudo-elastic expansion behavior is completely reversible and can exceed the elasticity of metals many times over.

Joints are movable connections between two components, which usually consist of several components/parts. Joints are classified based on the relative movement and the number of degrees of freedom and are used in robotics, for example. Joints and actuators used to date are assembled from prefabricated components to form structural elements.

Springs made of shape memory alloys are also well known. Such springs in damping systems have the task of absorbing vibrations and oscillations in order to, for example, minimize noise or dampen irregular movements. They can be based on either a spring-loaded, pneumatic, hydraulic or electromagnetic operating principle.

Electrical energy is converted into mechanical energy, whereby the shape memory material is briefly heated above the A _F temperature by current pulses. The resulting change in shape leads to the movement of the spring.

Various methods for producing components made of shape memory material are known from the state of the art.

Out of Gustmann, T. et al.: Properties of Cu-Based Shape-Memory Alloys Prepared by Selective Laser Melting"; Mem. Superelasticity (2017) 3, pp. 24-36 , an additive process for the layer-by-layer production of a component from a shape memory alloy is known, whereby the shape memory properties are deactivated by thermal treatment.

It is also clear from the WO 2016/ 008 043 A1 A method for producing a multiple memory material is known, comprising determining the process parameters for the shape memory material via a controller; receiving the shape memory material at a feed unit; feeding the shape memory material via the feed unit to a processing station; supplying inert gas to the processing station via an inert gas supplier; and supplying the shape memory material with energy via at least one energy source based on the process parameters to produce the multiple memory material.

From the DE 296 06 249 U1 A spiral spring made of a shape memory alloy with at least a first and a second fastening surface, a connecting piece, at least two spring arms bent in the form of turns of a spiral is known, wherein the turns of the spring arms are spaced apart from one another and each spring arm is arranged between the turns of the other spring arm and the spring arms have two ends, wherein the first end is connected to the fastening surface and the second end is connected to the connecting piece.

From the DE 3 910 839 A1 A device for controlling a device for opening and closing a ventilation opening in a room is known, the device being connected to at least one actuator made of a shape memory alloy, by means of which the device is set in the open or closed position when the actuator is in a first shape. The actuator is arranged in a control circuit containing an electrochemical sensor. The sensor, which is acted upon by the air of the external atmosphere, triggers a current flow through the actuator depending on the pollutant concentration in the atmosphere, which causes a change in the shape of the actuator by heating, by means of which the device is set in the closed or open position.

From the WO 2009 / 137 767 A2 an overheat protection system is known which is designed for use with an actuator which includes at least one shape memory alloy element coupled to a source to selectively receive an activation signal therefrom, the actuator element forming a first configuration to be activated by the source for a first period of time and drivingly coupled to a load, the system comprising at least one shape memory alloy switching element selectively coupled to the source and/or the actuator element and forming a second configuration to be activated by the source and/or by the actuator element for a second period of time which is longer than the first, the actuator element, the source and the switching element being cooperatively configured such that the switching element is operable to prevent the actuator element from receiving the signal when the switching element is activated.

From the EN 10 2017 106 158 A1 A thermostat for flow regulation is known, which comprises a thermostat housing with a valve chamber and an inlet and an outlet that are connected to the valve chamber. The thermostat is also provided with an activatable actuator with a shape memory working element, which is designed to increase a gradual opening position of the valve closing body, independently of a setting of the passive actuator, depending on a thermal activation by an electrical power source, or to adjust a closing and opening of a valve in a bypass to the valve chamber formed on the thermostat body.

And also known from the EN 10 2005 059 605 A1 is a device for adjusting a motor vehicle component, with at least one actuator element which has a shape memory material, and with at least one power supply device which can be controlled to supply current to the at least one actuator element depending on a desired change in shape of the same.

A disadvantage of the state of the art is that known joints, actuators and damping systems with or without shape memory alloys consist of several components that have to be assembled into a single component with great effort and expense.

Another disadvantage is that assembled components can have functional errors due to their multi-part structure, making the entire assembly more susceptible to failure. In addition, multi-part components cannot be miniaturized at will.

The object of the present invention is to provide a component and a method for producing a component with which the disadvantages of the prior art are eliminated.

The object is achieved by the invention specified in the patent claims. Advantageous embodiments are the subject of the subclaims, whereby the invention also includes combinations of the individual dependent patent claims in the sense of an AND connection, as long as they do not exclude each other.

According to the invention, the object is achieved by a method for producing one-piece joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems from at least one shape memory material, in which a first layer of a shape memory material in powder form is formed and solidified by means of an additive manufacturing process, the first layer is subsequently pseudoplastically deformed, a second layer of a shape memory material is then arranged on the first layer, and the first and second layers are subsequently melted at least in the region of the mutually arranged interfaces of the layers and the first and second layers are bonded in a materially bonded manner essentially without interfaces, wherein further layers can be applied by means of an additive manufacturing process, wherein at least one local region of the second layer of the shape memory material is thermally treated below the liquidus temperature by means of a heat source, wherein the thermal treatment in the local region deactivates the shape memory properties by forming martensite or austenite with phase precipitations.

Advantageously, a thermally, mechanically and/or magnetically excitable shape memory material is used.

Also advantageously, Cu-based alloys, particularly CuNiAl-, CuZnAl- or CuNiAlZr-based alloys, are used as shape memory materials.

It is further advantageous if at least two further layers of one or more shape memory materials are arranged on the first layer of shape memory material by means of an additive manufacturing process.

It is also advantageous if, during the additive manufacturing process, one of the further layers of a shape memory material is completely thermally treated using a heat source.

Laser cladding, electron beam welding and/or laser beam melting are advantageously used as additive manufacturing processes.

In an advantageous embodiment, the thermal treatment is carried out by means of electromagnetic radiation, in particular by means of laser radiation, electron radiation and/or X-rays.

It is particularly advantageous if a non-shape memory material, particularly advantageously one or more insulating materials or electrically conductive materials, are arranged in certain areas.

The object is also achieved with a one-piece component having one or more shape memory materials, wherein the one or more shape memory materials have at least one local region in which the shape memory properties are deactivated.

CuNiAl-, CuZnAl- or CuNiAlZr-based alloys are particularly advantageous as shape memory materials.

In an advantageous embodiment of the one-piece component, a non-shape memory material is present in some areas, wherein the non-shape memory material is particularly advantageously an insulating layer or heating layer.

It is advantageous if the number and/or volumes of the local regions with deactive shape memory properties are graded over the height and/or width of the component.

It is also advantageous if the shape memory material is designed in such a way that several layers with alternating deactive and active shape memory properties are present.

In an advantageous embodiment, the one-piece component is designed as a single or multi-part component.

The present invention provides for the first time components in the form of joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems, which are formed in one piece, consist of one or more shape memory materials and are manufactured in one process step.

This is achieved through an additive manufacturing process in which the component is constructed and manufactured layer by layer from one or more shape memory materials.

In the context of the invention, a component is to be understood as a component that can be integrated into a system, a circuit or a device.

In the context of the invention, a one-piece component is to be understood as a component that is composed of only one component or part, wherein the one-piece component is designed as a single-part or multi-part component.

The additively manufactured component made of one or more shape memory materials is realized in such a way that a powder made of a shape memory alloy is arranged on a construction platform and solidified, the first layer is then pseudoplastically deformed, the construction platform is then lowered by a defined layer thickness and coated again with a layer of a shape memory material.

The interfaces created by the layer structure are melted and the layers lying on top of each other are bonded together in a material-tight manner and essentially without interfaces. This additive and layer-by-layer construction of the component is continued continuously until the desired component with the desired dimensions and contours is completed.

The additive manufacturing process used according to the invention makes it possible, for example, to manufacture entire spring packages in one process step. The subsequent time-consuming and costly assembly of individual components into a component is eliminated, as is the occurrence of interfaces within a component, as is the case, for example, with the ex-situ combination of a shape memory material with a conventional metal.

After each layer arrangement and material bond or after completion of several layers, the shape memory material is thermally treated at least in one local area using a heat source, whereby the thermal treatment deactivates the shape memory properties in the thermally treated local area.

Through the additional thermal treatment of local areas of the shape memory material using a heat source, the structure of the shape memory material is specifically manipulated and adjusted. The thermal treatment with a heat source creates different phases with a special morphology in the structure, in which the shape memory properties are specifically suppressed and deactivated.

It is particularly important that the thermal treatment of the shape memory material using a heat source is always carried out below the liquidus temperature. The thermal treatment of the shape memory materials below the liquidus temperature results in phase precipitations at the grain boundaries of the austenite or martensite, which cause the shape memory properties to be deactivated.

This technical effect and the technical effect of the invention will be explained in more detail using the example of a CuNiAlZr-based shape memory alloy.

A first layer - hereinafter referred to as the first layer component - of a CuNiAlZr-based shape memory alloy is arranged without thermal treatment by a heat source. This first layer component of the CuNiAlZr-based shape memory alloy consists almost exclusively of martensite with dissolved Zr and finely distributed sub-µm-sized Y-phase precipitates. The first layer component of this shape memory alloy can transform into martensitic material during heating. The shape memory material of the first layer component is first pseudoplastically deformed. A second layer - hereinafter referred to as the second layer component - of the same shape memory alloy is then arranged on the first layer component using an additive manufacturing process and the second layer component is thermally treated in local areas of the structure using a heat source. After thermal treatment, the structure of the second layer component consists of either a martensitic or austenitic matrix with coarsened Y-phase precipitations, as a result of which the second layer component of the shape memory alloy does not show any martensitic transformation or no longer has any shape memory properties. A typical phase precipitation when using a CuNiAlZr-based shape memory alloy is a Heusler-Cu ₂ ZrAl phase (Y phase).

Subsequent heating of the component produced in this way above the austenite end temperature A _f , for example by means of a current pulse, leads to a phase transformation of the pseudoplastically deformed martensite into austenite. The first layer component returns to its original shape through deformation due to its active shape memory properties. The second layer component with the coarsened Y-phase precipitates is only elastically deformed during the deformation. Energy is stored and the previously undeformed second layer component is pre-stressed like a spring.

This is followed by cooling to below the M _f temperature. The non-prestressed austenitic second layer component with evenly finely distributed sub-µm-sized Y-phase precipitates changes into martensite from the martensite start temperature M _s temperature. This has a significantly lower yield, compression or bending limit than the elastically prestressed austenite, which does not show any reversible martensitic transformation during cooling due to the coarsely precipitated Y-phase precipitate. As a result, this relieves the load and at the same time pseudoplastically deforms the martensitic component. Reheating this component to temperatures above A _f leads to a change in shape and elastic prestressing of the non-converted component.

The heating and cooling described is referred to as a cycle of a two-way effect and can be repeated as often as desired. The change in shape and thus the extent of movement of, for example, an actuator or a spring assembly made of several layers of active and deactive shape memory material can be precisely controlled, since the volume of the individual local areas of the component made of shape memory material can be precisely adjusted using additive manufacturing. Another advantage is that the extent of movement of the component can be increased by arranging several layers of shape memory material with local areas with a deactivated shape memory effect.

It is particularly advantageous if Cu-based alloys, in particular CuNiAl-, CuZnAl- and/or CuNiAlZr-based alloys, are used as shape memory material. Cu-based shape memory alloys with operating temperatures of over 100 °C are classified as high-temperature shape memory alloys and are more cost-effective than TiNi-based shape memory alloys.

The use of Cu-based shape memory alloys in conjunction with an additive manufacturing process advantageously leads to the formation of fine-grained structures, which prevents brittle failure of the one-piece component. The shape memory alloys that are preferably used also make it possible, in conjunction with the additive manufacturing processes, to control the cooling rate and thus specifically adjust the grain size distribution of the structure in order to obtain the desired material properties of the component.

In a further advantageous embodiment of the method, at least one further layer of the shape memory material is completely thermally treated using a heat source. With a complete thermal treatment of a layer, in particular a single-part actuator or a spring package can be produced that also consists of alternating layers of deactive and active shape memory material.

It is also advantageous if laser deposition welding, electron beam welding and/or laser beam melting are used as additive manufacturing processes. These advantageous manufacturing processes advantageously enable a defined energy input into the respective layer, whereby the structure of the shape memory material can be varied and adjusted in a targeted manner. In addition, these processes can be used to produce particularly small and delicate one-piece components in just one process step, which saves costs and time in the production of the component and enables components to be produced in the µm to cm range.

The additional thermal treatment of local areas of the shape memory material using a heat source is best carried out using a laser. The use of a laser as a heat source offers the advantage that only defined local areas of the shape memory material are targeted and thermally treated, thereby achieving a localized deactivation of the shape memory properties. This allows the conversion properties of the shape memory material to be individually adjusted to the respective requirements of the application area and defined local areas of the component to be specifically functionalized in accordance with the application requirements.

According to the invention, one-piece components are provided for the first time that consist of one or more shape memory materials. The one-piece components have at least one local region in the structure in which the shape memory properties are deactivated.

The advantage of the one-piece components according to the invention made of one or more shape memory materials is that the one-piece design of the component made of shape memory material and the functionalized local areas with deactivated shape memory properties result in a significantly improved service life of the component. Joints of several Components such as are necessarily present in multi-part components are not present according to the invention.

Another advantage of the one-piece component is that, for example, in a component consisting of a spring package, the damping capacity can be specifically adjusted for the first time by the number, extent, arrangement and number of pseudo-elastic and purely elastic springs made of shape memory material by forming local areas with deactive shape memory properties. The entire spring package therefore has defined damping properties.

In a particularly advantageous embodiment of the invention, a non-shape memory material can be arranged on the component and/or within the component in some areas using the additive manufacturing method according to the invention. The non-shape memory material can be made of an insulating material and can serve as an insulating layer against thermal ingress into the adjacent shape memory material.

However, it is also possible that the non-shape memory material consists of an electrically conductive material and serves as a heating layer for the adjacent shape memory materials in order, for example, to achieve deactivation of the shape memory properties by thermal treatment only in the boundary area between electrically conductive material and shape memory materials.

In a special version of the one-piece component, actuators and damping systems with a graded structure or sharp interfaces can be produced by intelligently tailoring the structure. The structure can be specifically adjusted to a sub-µm size. The structure can thus be modified and graded in a defined manner with regard to grain size, phase volume fractions and/or phase morphology.

The solution according to the invention makes it possible to produce joints, actuators and damping systems in a wide range of sizes in the µm range to the cm range. This means that for the first time, one-piece miniature joints, actuators and damping systems in µm size, with a complex structure and special geometric design can be provided with high flexibility.

The one-piece components according to the invention can be used, for example, as highly efficient miniature actuators, joints or springs in advanced surgical robots, which are used, for example, for neuromedicine.

• - sehr einfach und kostengünstig durch ein additives Fertigungsverfahren hergestellt werden,
• - in einem Fertigungsprozess herstellbar sind, wodurch ein nachträgliches Zusammenfügen von einzelnen Bauteilen zu einem Bauelement entfällt,
• - besonders filigran und klein ausbildbar sind, sodass Bauelemente im µm-Bereich, bis cm-Bereich bereitgestellt werden können,
• - besonders leicht und leise in der Anwendung sind,
• - einfach konstruiert und modelliert werden können,
• - eine hohe Arbeitsleistung pro Volumen bei hoher Standzeit aufweisen,
• - eine besonders kurze Reaktionszeit aufweisen,
• - durch die thermische Behandlung lokaler Bereiche des Formgedächtnismaterials mit einer Wärmequelle individuell funktionalisiert und auf die zukünftige Anwendung angepasst werden können.

In summary, the technical advantage of the solution according to the invention is that components made of shape memory material are provided which

• - can be manufactured very easily and cost-effectively using an additive manufacturing process,
• - can be manufactured in one production process, which eliminates the need for subsequent assembly of individual components to form a component,
• - can be made particularly delicate and small, so that components in the µm range up to cm range can be provided,
• - are particularly easy and quiet to use,
• - can be easily constructed and modelled,
• - have a high performance per volume with a long service life,
• - have a particularly short reaction time,
• - can be individually functionalized and adapted to future applications by thermally treating local areas of the shape memory material with a heat source.

The invention is explained in more detail below using an embodiment.

Example

A cuboid-shaped component with dimensions of 1.0 mm × 0.5 mm × 1.0 mm (w × h × l) is manufactured from gas-atomized powder (Cu-11.35Al-3.2Ni-3Mn-0.5Zr) with a particle size of 30 µm to 76 µm using a selective laser melting system (SLM 250 ^HL , 400 W:YAG laser). The cuboid-shaped component consists of two layers with the same composition but different microstructures that vary along the height. The volume of the component that can undergo martensitic transformation is manufactured with a powder layer thickness, S _D , of 80 µm, laser power, P, of 300 W, scanning speed, S _V , of 800 mm/s and a hatching distance, S _{A ,} of 50%. After the solidified section is 270 µm high, it is pseudoplastically deformed to an elongation of 8%. Subsequently, further layers of a powder made of (Cu-11.35Al-3.2Ni-3Mn-0.5Zr) are applied until the total height of the component is 500 µm. Each additional solidified layer is additionally post-exposed twice with a laser with the following parameters: P = 150 W, S _V = 800 mm/s and S _A = 50%.

The additively manufactured component in the form of a one-piece actuator is then heated to a temperature above A _F using a current pulse (square wave signal, current of 1 A and pulse duration of 500 ms). This causes a change in shape so that the one-piece actuator is stretched and is present as a straight component. After the current pulse has passed through this one-piece actuator, its temperature decreases and the component bends back to its original shape from the M _S temperature. The bending is complete below M _F. The actuator described can be used in a medical device.

Claims (16)

Method for producing one-piece joints, actuators, sensors, lifting and adjusting elements, actuators in control circuits or spring assemblies in damping systems from at least one shape memory material, in which a first layer of a shape memory material in powder form is formed and solidified by means of an additive manufacturing process, the first layer is subsequently pseudoplastically deformed, a second layer of a shape memory material in powder form is then arranged on the first layer, and the first and second layers are subsequently melted at least in the region of the mutually arranged interfaces of the layers and the first and second layers are bonded in a materially bonded manner essentially without interfaces, wherein further layers can be applied by means of an additive manufacturing process, wherein at least one local region of the second layer of the shape memory material is thermally treated below the liquidus temperature by means of a heat source, wherein the thermal treatment in the local region deactivates the shape memory properties by forming martensite or austenite with phase precipitations. Procedure according to Claim 1 , in which additional layers of shape memory material are applied. Procedure according to Claim 1 or 2 , in which a thermally, mechanically and/or magnetically excitable shape memory material is used. Method according to at least one of the preceding claims, in which Cu-based alloys, particularly advantageously CuNiAl-, CuZnAl- or CuNiAlZr-based alloys, are used as shape memory material. Method according to at least one of the preceding claims, in which at least two further layers of one or more shape memory materials are arranged on the first layer of shape memory material by means of an additive manufacturing process. Method according to at least one of the preceding claims, in which during the additive manufacturing process one of the further layers of a shape memory material is completely thermally treated as a local region by means of a heat source. Method according to at least one of the preceding claims, in which laser cladding, electron beam welding and/or laser beam melting are used as the additive manufacturing method. Method according to at least one of the preceding claims, in which the thermal treatment is carried out by means of electromagnetic radiation, in particular by means of laser radiation, electron radiation and/or X-rays. Method according to at least one of the preceding claims, in which a non-shape memory material, particularly advantageously one or more insulating materials or electrically conductive materials, are arranged in regions. One-piece joint, actuator, sensor, lifting and adjusting element, actuator in control circuits or spring assembly in damping systems manufactured according to the process of at least one of the Claims 1 until 9 , comprising at least a first and a second layer made of a powder of a shape memory material, wherein the first layer is pseudoplastically deformed and the second layer of the shape memory material has at least one local region in which the shape memory properties are deactivated by the martensite or austenite with phase precipitations formed. Component according to Claim 10 in which Cu-based alloys, in particular CuNiAl-, CuZnAl- or CuNiAlZr-based alloys, are present. Component according to at least one of the preceding, wherein a non-shape memory material is present in some regions. Component according to Claim 12 , wherein the non-shape memory material is an insulating layer or heating layer. Component according to at least one of the preceding, in which the number and/or volumes of the local regions with deactive shape memory properties are graduated over the height and/or width of the component. Component according to at least one of the preceding, in which several layers with alternating deactive and active shape memory properties are present. Component according to at least one of the preceding, in which the one-piece component is designed as a single or multi-part component.