Method for attaching a strain gauge to a component, and component that can be produced by means of a method of this kind

Abstract

The invention relates to a method for attaching a strain gauge (12) to a component (1). According to the invention, at least a region of the component (1) in which the strain gauge (12) is intended to be attached, or a carrier film of the strain gauge (12), is heated at least to a melting temperature, and the strain gauge (12) is pressed against the component (1). Protection is also sought for a component that can be produced by means of a method of this kind.

Description

[0001] Description

[0002] Method for attaching a strain gauge to a component and component producible by such a method

[0003] The invention relates to a method for attaching a strain gauge to a component. The invention also relates to a component that can be produced by such a method.

[0004] Strain gauges (SGs) are typically used to measure strain or compression on the surface of components. This makes it possible to record the loads on a component. A common strain gauge design is a foil strain gauge, in which a measuring grid made of meandering resistance wire is laminated to a thin plastic carrier film, etched, and provided with electrical connections.

[0005] The attachment of strain gauges to a component is usually done manually. For this purpose, an adhesive is used to secure the strain gauge to the component.

[0006] The strain gauge is then covered with a suitable cover to protect the measuring point with the strain gauge from environmental influences.

[0007] Typically, a strain gauge is bonded directly to a component. However, this requires an additional work step and additional material for the bonding. Alternatively, to embed a strain gauge in a component, the strain gauge must be pre-mounted or bonded to a support element. This also represents an additional work step that must be performed manually. Furthermore, additional material is required that differs from the material of the actual structural component. In addition to the additional labor and higher costs, this can also have a negative impact on component strength and service life.

[0008] A leaf spring arrangement for a vehicle wheel suspension is known from DE 102018 123 082 B4. Specifically, the wheel suspension comprises two leaf springs made of fiber-reinforced plastic for resiliently supporting wheel carriers of a vehicle axle. The leaf springs each have a first sensor for detecting a load variable representing the load on the respective leaf spring and for generating a load signal. The first sensor comprises a strain gauge embedded in the leaf spring. For this purpose, the strain gauge is pre-mounted on a support element in the form of a thin plate made of aluminum, steel, or organic sheet. A second sensor serves to detect an inclination variable representing the inclination of the respective leaf spring and to generate an inclination signal.Furthermore, an electronic processing unit is provided which is designed to determine a state variable representing a state of the entire vehicle from the load and inclination signals of the two leaf springs.

[0009] The present invention is based on the object of proposing a method for attaching a strain gauge to a component that can be implemented cost-effectively. Furthermore, the method should enable a reliable connection of a strain gauge to the component. A further object of the invention is to propose a component that can be manufactured using the method according to the invention.

[0010] This object is achieved by a method having the features of patent claim 1 and by a component having the features of patent claim 10. Advantageous embodiments and further developments of the invention can be found in the dependent claims.

[0011] The invention is based on a method for attaching a strain gauge to a component. According to the invention, at least one region of the component in which the strain gauge is to be attached, or a carrier foil of the strain gauge, is heated at least to a melting temperature, and the strain gauge is pressed against the component.

[0012] The component can be made of metal or plastic. A plastic component is also defined as a component made of fiber-reinforced plastic. In this case, the plastic material serving as the matrix for the fiber material is also heated to at least its melting temperature. The strain gauge can then be pressed into the molten plastic matrix.

[0013] The method according to the invention allows the strain gauge to be attached without an additional component. Furthermore, no additional carrier element or adhesive is required. The process can be automated and thus accelerated. Furthermore, by melting the carrier film of the strain gauge or by melting the plastic material of the component, if the component is plastic, better adhesion of the strain gauge to the component or even a material-to-material bond between the strain gauge and the component can be achieved.

[0014] According to a first advantageous development of the invention, it is proposed that a stamp-like tool is heated at least to the melting temperature of the component or to a melting temperature of the carrier film of the strain gauge and then pressed onto the component, wherein the strain gauge is arranged between the component and the stamp-like tool. Before the stamp-like tool is pressed on, the strain gauge must therefore be aligned on the component or on the stamp-like tool. When the heated, stamp-like tool is pressed on, if the component is a plastic component, the plastic material or the plastic matrix is ​​partially melted on the surface, allowing the strain gauge to bond firmly to the plastic component. If the component is made of metal, the carrier film of the strain gauge is partially melted, which also leads to improved adhesion of the strain gauge to the component.

[0015] To protect the strain gauge, it is conceivable that a protective film is placed over the strain gauge before the stamp-like tool is pressed onto the component.

[0016] According to another development of the invention, it is also conceivable for the component to be a plastic component, and for the entire component to be heated to at least the melting temperature of the plastic, the strain gauge being inserted into a part of a tool and positioned. Subsequently, the heated plastic component is placed into the part of the tool containing the strain gauge, and finally, the tool is closed. This also creates a material bond between the strain gauge and the heated, surface-melted plastic component, thus reliably bonding it.

[0017] In a further development, the component is heated by a heat source, preferably infrared (IR) radiation. This allows for very uniform and rapid heating of the component. Another possible heating option is placing the component in an oven. This list is not intended to be exhaustive.

[0018] To protect the strain gauge, a further development would be conceivable: before the entire, heated component is inserted into the part of the tool containing the strain gauge and the tool is closed, a protective film is placed under the strain gauge. The protective film is then heated and melted, creating a bond between the protective film and the plastic component.

[0019] In a further development of the inventive concept, it is proposed that the strain gauge attached to the component be subsequently overmolded with a plastic material. This provides effective protection for the strain gauge against environmental influences. In a further development, it is also conceivable that—if the component is a plastic component—the overmolded plastic material is the same material as the plastic component. This can contribute to a good bond between the protective coating and the plastic component.

[0020] According to another development of the method, if the component is a plastic component, it is further proposed that the component be joined to another component formed as a plastic component. In this case, the components are heated to at least a melting temperature of the plastic, at least in the area where the strain gauge is to be applied. The heated plastic components are then brought together, sandwiching the strain gauge between them.

[0021] As already stated, the invention also aims to protect a component that can be manufactured using the method according to the invention. Such a component, to which a strain gauge is attached, is characterized by the presence of molten material in the area of ​​the strain gauge, which is either molten material from the component or molten material from a carrier foil of the strain gauge.

[0022] Preferred embodiments of the invention are illustrated in the figures and are explained in more detail in the following description with reference to the figures. This also makes further features and advantages of the invention clear. The same reference symbols, even in different figures, refer to the same, comparable, or functionally identical components. Corresponding or comparable properties and advantages are achieved even if a repeated description or reference to them is not made. The figures are not, or at least not always, to scale. In some figures, proportions or distances may be exaggerated in order to emphasize features of an embodiment more clearly.

[0023] They show, schematically

[0024] Fig. 1 is a flow chart of a conceivable process sequence according to a first

[0025] embodiment,

[0026] Fig. 2 is a flow chart of a conceivable process sequence according to a second

[0027] embodiment,

[0028] Fig. 3 shows the process sequence according to Fig. 2 with representation of the components involved and

[0029] Fig. 4 is a flow chart of a conceivable process sequence according to a third

[0030] Embodiment.

[0031] Fig. 1 shows a flow diagram of a conceivable process sequence of the method according to the invention.

[0032] After the process has started, a plastic component is removed from a container in process step S1. The component can, for example, be a fiber-reinforced plastic component, preferably with glass or carbon fibers incorporated into a plastic matrix for reinforcement. The component is then moved to a heating area.

[0033] In a process step S2, the component is then heated in the heating area. The heating can preferably be carried out using infrared radiation. The heating takes place at least to the melting temperature of the plastic or the plastic matrix of the component. Thus, the heating temperature can preferably be several hundred degrees.

[0034] In a process step S3, a strain gauge is then placed and positioned in a lower part of a tool.

[0035] In a subsequent process step S4, the component, which has been melted on its surface by heating and is formed as a plastic component, is inserted into the lower part of the tool, covering the strain gauge already located there. The strain gauge can preferably already be provided with electrical connecting lines, for example, in the form of a flexible circuit board.

[0036] Then, in process step S5, the tool is closed by moving the upper part of the tool onto the lower part. The clamping force can be several hundred kN. The resulting pressure presses the strain gauge onto the component and virtually embeds it.

[0037] Finally, in process step S6, the strain gauge is overmolded with a plastic to protect it from environmental influences. The plastic is preferably the same material as the plastic or the plastic matrix of the component designed as a plastic part.

[0038] All process steps S1 to S6 can be automated, for example, using a handling robot. The resulting product is a plastic component with a strain gauge reliably embedded within it, i.e., firmly bonded to it.

[0039] With reference to Fig. 2, a flow diagram of a conceivable, alternative process sequence of the method according to the invention will now be explained.

[0040] In a process step S10, a component designed as a plastic component is first placed on a suitable base and aligned.

[0041] In a process step S20, a strain gauge is then positioned and aligned on the component. Alternatively, positioning and alignment on a punch of a punch-like tool is also conceivable. For this purpose, the strain gauge can be held to the tool by means of negative pressure or a clamping device.

[0042] Subsequently, in a method step S30, a stamp-like tool is heated to at least a melting temperature of the plastic or the plastic matrix of the component.

[0043] Process step S40 then serves to press the stamp-like tool onto the component, with the strain gauge located between the stamp-like tool and the component. The heated, stamp-like tool melts the plastic or plastic matrix of the component in the area of ​​the strain gauge, thereby embedding the strain gauge into the component. The strain gauge can preferably already be provided with electrical connection lines, for example in the form of a flexible circuit board. In a process step S50, the strain gauge is then overmolded with a plastic to protect it from environmental influences. The plastic is preferably the same material as the plastic or plastic matrix of the component.

[0044] However, instead of process step S50, it is also conceivable that the strain gauge is covered by a second plastic component without further overmolding and is thus enclosed between two plastic components.

[0045] Finally, a process step S60 can be used to remove the component with the attached strain gauge and place it in a container.

[0046] The process steps S10 to S60 can all be carried out automatically or with the help of a robot.

[0047] Reference is now made to Fig. 3. This figure depicts the process variant shown in Fig. 2. A component 1 formed as a plastic component is visible, which is also conceptually removed from the process structure for better explanation. In the exemplary embodiment, component 1 is formed as a fiber-reinforced plastic component. Component 1 has a plastic matrix 10 into which reinforcing fibers 11 are embedded. The fibers 11 can preferably be made of carbon or glass.

[0048] The component 1 is placed and aligned on a base 2. Furthermore, a strain gauge 12 is placed and aligned on the component 1. A stamp-like tool 3 with a stamp 3a is also visible. The stamp 3a can be heated via a voltage source 4 to a temperature that corresponds at least to the melting temperature of the plastic matrix 10.

[0049] After heating the stamp 3a to the melting temperature of the plastic matrix 10, the tool 3 is moved in a movement Z toward the base 2 and brought into contact with the component 1 and the strain gauge 12. This locally melts the plastic matrix 10 in the area of ​​the stamp 3a. The strain gauge 12 is pressed into the molten plastic matrix 10 and bonded to it. The strain gauge 12 preferably already contains the necessary cables or electronics 12a.

[0050] After the tool 3 retracts, the strain gauge 12 located on the component 1 can be overmolded with a plastic (not shown). Alternatively, it is conceivable that a protective film 13 is placed over the strain gauge 12 by the tool 3 before the pressing process. As the tool 3 moves down onto the base 2, the protective film 13 is simultaneously heated and bonded to the component 1, with the protective film 13 covering the strain gauge 12.

[0051] Finally, another embodiment of the method is described with reference to Fig. 4:

[0052] In a process step S100, a component designed as a metal component is first placed on a suitable base and aligned.

[0053] In process step S200, a strain gauge is then positioned and aligned on the component. Alternatively, positioning and alignment on a punch of a punch-like tool are also conceivable. For this purpose, the strain gauge can be held to the tool by means of vacuum or a clamping device.

[0054] Subsequently, in a method step S300, a stamp-like tool is heated to at least a melting temperature of the plastic from which a carrier film of the strain gauge is made.

[0055] Process step S400 then serves to press the stamp-like tool onto the component, with the strain gauge positioned between the stamp-like tool and the component. The heated stamp-like tool melts the plastic of the strain gauge's carrier film, thereby reliably adhering the strain gauge to the component. The strain gauge can preferably already be equipped with electrical connecting leads, for example, in the form of a flexible circuit board.

[0056] In process step S500, the strain gauge is then overmolded with a plastic to protect it from environmental influences. The plastic is preferably the same material as the plastic used for the strain gauge's carrier film.

[0057] Finally, a process step S600 can be used to remove the component with the attached strain gauge and place it in a container.

[0058] Process steps S100 to S600 can all be automated, for example, using a handling robot.

[0059] 1 component, plastic component, fiber-reinforced plastic component

[0060] 2 base

[0061] 3 stamping tools

[0062] 3a stamp

[0063] 4 Voltage source

[0064] 10 Plastic matrix

[0065] 11 fibers (carbon or glass)

[0066] 12 strain gauges (SGs)

[0067] 12a cable, electronics

[0068] 13 Protective film

[0069] S1-S5 process steps

[0070] S10-S60 process steps

[0071] S100-S600 process steps

[0072] Z movement

Claims

Patent claims 1. Method for attaching a strain gauge (12) to a component (1), characterized in that at least one region of the component (1) in which the strain gauge (12) is to be attached, or a carrier film of the strain gauge (12), is heated at least to a melting temperature and the strain gauge (12) is pressed against the component (1).

2. Method according to claim 1, characterized in that a stamp-like tool (3) is heated at least to the melting temperature of the component (1) or to a melting temperature of the carrier film of the strain gauge (12) and is then pressed onto the component (1), the strain gauge (12) being arranged between the component (1) and the stamp-like tool (3).

3. Method according to claim 2, characterized in that before pressing the stamp-like tool (3) onto the component (1), a protective film (13) is arranged over the strain gauge (12) 4. Method according to claim 1, characterized in that the component (1) is a plastic component and the entire component (1) is heated at least to the melting temperature of the plastic, the strain gauge (12) is inserted and positioned in a part of a tool, then the heated component (1) is placed in the part of the tool containing the strain gauge (12) and finally the tool is closed.

5. Method according to claim 4, characterized in that the component (1) is heated by IR radiation.

6. Method according to claim 4 or 5, characterized in that before inserting the entire heated component (1) into the part of the tool containing the strain gauge (12) and closing the tool, a protective film is arranged under the strain gauge (12).

7. Method according to one of the preceding claims, characterized in that the strain gauge (12) attached to the component (1) is subsequently overmolded with a plastic material.

8. Method according to claim 7, characterized in that the plastic material is a material which also comprises the component (1) designed as a plastic component.

9. Method according to one of claims 4 to 8, characterized in that the component (1) is to be connected to a further component designed as a plastic component, wherein the components are heated at least in such a region in which the strain gauge (12) is to be attached, at least to a melting temperature of the plastic of the components and then the heated plastic components are brought together, embedding the strain gauge between them.

10. Component, producible by a method according to one of the preceding claims, wherein a strain gauge is attached to the component, characterized in that molten material is present in the region of the strain gauge, which is either molten material of the component or molten material of a carrier film of the strain gauge.

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