Method for overmolding a sensitive element

Abstract

The invention relates to a method for overmolding a sensitive element, the sensitive element being provided with a sensitive capsule and two electrical conductors, the method comprising the execution of the following steps: a) a first injection of a first material into a first impression of a mold in which the sensitive element is arranged in order to form a first overmolding of the sensitive element, the first overmolding comprising, in an elongation direction, a hollow section and a solid section, the hollow section defining a cavity provided with an opening leading out through one end of the first overmolding; b) a second injection of a second material into the cavity through the opening, the second injection being carried out while the solid section is arranged in a second impression of the mold; the overmolding method being characterized in that step a) is executed so as to form at least one passage in the hollow section, the at least one passage allowing, during the execution of step b), the second material to flow in a space delimited by the solid section and the second impression so as to form an overmolding, referred to as the second overmolding, of the solid section.

Description

overmolding process of a sensitive element FIELD OF INVENTION

[0001] The invention relates to the field of sensors, and in particular overmolded sensors. Specifically, the invention concerns a method for overmolding a sensing element, and in particular an overmolding method comprising a reduced number of injection steps. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In current temperature sensor manufacturing technologies, multiple overmolding steps are often required to integrate sensitive components and electrical connections while ensuring their protection. Typically, producing such sensors involves at least three separate overmolding operations. This demanding process not only increases manufacturing costs but also lengthens lead times and adds complexity to assembly.

[0003] Furthermore, the precise alignment and positioning of sensitive components and electrical connectors require careful attention during each overmolding phase. Each step carries a risk of misalignment or defect, compromising the reliability of the final sensor.

[0004] Consequently, these processes require careful adjustments and rigorous quality control to ensure the structural and functional integrity of the sensors.

[0005] The proposed invention aims to simplify this process by reducing the number of overmolding operations required, while ensuring precise positioning and optimal protection of the components. BRIEF DESCRIPTION OF THE INVENTION

[0006] The object of the invention is achieved by a process of overmolding a sensitive element, the sensitive element being provided with a sensitive capsule and two electrical conductors, the process comprising the execution of the following steps:

[0007] a) a first injection of a first material into a first cavity of a mold in which the sensitive element is arranged to form a first overmolding of the sensitive element, the first overmolding comprising, along a direction of elongation, a hollow section and a solid section, the hollow section defining a cavity provided with an opening leading out through one end of said first overmolding;

[0008] b) a second injection of a second material into the cavity through the opening, and during which the solid section is placed in a second mold cavity;

[0009] the overmolding process being characterized in that step a) is carried out so as to form at least one passage in the hollow section, and allowing, during the execution of step b), a flow of the second material into a space, delimited by the solid section and the second cavity, to form an overmolding, called second overmolding, of the solid section.

[0010] According to one implementation method, the second overmolding obtained at the end of step b) is formed exclusively by the flow of the second material in the passage.

[0011] According to one implementation method, step b) is also performed to inject the second material into the cavity.

[0012] According to one implementation method, during the execution of step b), a portion of the hollow section, referred to as the upstream portion, separated from the solid section by a downstream portion of the hollow section, is also overmolded with the second material.

[0013] According to one implementation method, during the execution of step b), the upstream portion is placed in a third cavity of the mold delimiting the overmolding of said upstream portion.

[0014] According to one embodiment, step b) is performed by injecting the second material into the third impression, the third impression being configured so that, during the second injection, the second material spreads into a space delimited by the upstream portion and the third impression, into the cavity and into the space delimited by the full section and the second impression via the passage.

[0015] According to one implementation, during the execution of step b), an insert is placed in the cavity, said insert being extracted from the cavity after execution of step b).

[0016] According to one implementation method, the insert is configured so that the material forms ribs in the cavity.

[0017] According to one implementation method, during the execution of step a), the capsule is located at a free end of the solid section.

[0018] According to one method of implementation, the first material and the second material are of the same nature.

[0019] According to one method of implementation, the first material and the second material are of different natures.

[0020] According to one implementation method, the execution of step a) is preceded by a step a0) each electrical conductor is brought into contact with a longitudinal electrical connector intended to be partially overmolded at the end of step a), and whose free ends are intended to be projected relative to the hollow section and in a direction opposite to the elongation direction of the first overmolding.

[0021] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying figures in which:

[0022] This is a schematic representation of a temperature sensor that can be considered as a sensitive element for the implementation of the overmolding process according to the present invention;

[0023] Laest is a schematic representation of the temperature sensor of laet and therefore each electrical conductor is connected with a longitudinal electrical connector;

[0024] This is a schematic representation of the first overmolding obtained after execution of step a) of the present invention;

[0025] This is a schematic representation of the first overmolding, according to a longitudinal cutting plane, obtained after execution of step a) of the present invention;

[0026] This is a schematic representation of the overmolding obtained after execution of step b) of the present invention;

[0027] Laest schematic representation of the overmolding, according to a longitudinal cutting plane, obtained after execution of step b) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention relates to a method for overmolding a sensitive element, in particular a sensor, and by way of example, a temperature sensor. However, the invention is not limited to this single aspect, and a person skilled in the art, when implementing it, may consider any other type of sensor, for example, a humidity sensor, a dust sensor, a shock sensor, etc.

[0029] Overmolding sensitive components, particularly those with electrical connections, presents several challenges. It is necessary to effectively protect the component while maintaining the functionality of external connections, which requires creating complex shapes in multiple stages. The objective of this invention is to provide a process enabling multi-layer overmolding while minimizing the number of injection molding stages.

[0030] Thus, the invention relates to a method for overmolding a sensitive element, comprising a sensitive capsule and two electrical conductors. The method includes the successive execution of several plastic injection stages to form a multilayer overmolding around the sensitive element, ensuring mechanical and environmental protection while maintaining the integrity of the electrical connections.

[0031] In the rest of the statement, the terms "mold" and "imprint" are used regularly.

[0032] The mold's function of "shaping the material" is performed by the cavity. The cavity is a mold cavity that gives its useful shape to a molten polymer and thus generates the usable injected part, that is, the technical object produced by polymer injection.

[0033] The process takes place in two main injections, as follows: Step a): First injection

[0034] In the first cavity of a mold, the sensitive element is positioned to allow the injection of a first material. This injection forms a first overmolding of the sensitive element, composed of two distinct sections along a direction of elongation:

[0035] Hollow section: It includes a cavity that opens through an opening at the end of the first overmolding. This cavity is intended to receive the second material later.

[0036] Solid section: Massive part of the overmolded element, it provides a certain rigidity and mechanical protection, while serving as a base for the next overmolding step. Step b): Second injection

[0037] This step involves injecting a second material into the cavity of the hollow section. The solid section is then placed in a second mold cavity, allowing a second overmolding to be formed around the solid section.

[0038] The process is distinguished by the creation of a passage in the hollow section during step a), which allows the flow of the second material into a space delimited by the solid section and the second cavity. This feature makes it possible to obtain a homogeneous overmolding around the solid section, while ensuring a uniform distribution of the second material.

[0039] Considering the passage allows for the injection of the second material into the cavity and the overmolding of the solid section in a single step. Thus, the passage reduces the number of injection steps compared to known prior art processes.

[0040] Thus, the second overmolding obtained at the end of step b) is formed exclusively by the flow of the second material through the passage in the cavity.

[0041] According to one variant, the second material is also injected directly into the cavity, allowing it to be filled to add extra protection or adjust the mechanical properties of the overmolding.

[0042] A portion of the hollow section, called the upstream portion, can also be overmolded during step b). This portion is separated from the solid section by a downstream portion and is positioned in a third cavity of the mold for the execution of step b). This third cavity is specifically configured to allow the injection of the second material into the space delimited by the upstream portion and the third cavity.

[0043] During the execution of step b), the third impression helps to guide the injected material so that it spreads simultaneously in the space around the upstream portion, in the cavity of the hollow section and in the space around the solid section via the passage formed in step a).

[0044] An insert can be placed in the cavity before the injection of the second material. This insert is then removed after overmolding, leaving ribs or other specific internal shapes within the cavity, improving mechanical strength or facilitating the integration of other components. The inclusion of ribs also ensures a uniform flow of injected material, thus providing optimal quality to the resulting overmolding.

[0045] In step a), the sensitive capsule is positioned at a free end of the solid section.

[0046] The method according to the present invention may include, prior to step a), a step a0). Step a0 may, in particular, include arranging the electrical conductors in contact with a longitudinal electrical connector. This connector is partially overmolded during the first injection, while its free ends are left protruding from the hollow section in a direction opposite to the elongation axis of the first overmolding, thus allowing them to be connected to other devices.

[0047] The remainder of this statement describes a particular embodiment of the overmolding process according to the present invention. In particular, the sensing element used comprises a temperature sensor.

[0048] Thus, at Laon we can see a temperature sensor 1. The temperature sensor 1 includes a sensitive capsule 2 and two electrical conductors 3a and 3b which extend from the sensitive capsule 2.

[0049] The overmolding process according to the present invention may first include carrying out a step a0) in which each electrical conductor is brought into contact with a longitudinal electrical connector 4a and 4b. Each electrical conductor 3a, 3b forms with a longitudinal electrical connector 4a, 4b a connection plug 5a, 5b and which each terminates in a pluggable end 6a, 6b.

[0050] In particular, step a0) can be implemented by considering longitudinal electrical connectors 4a and 4b formed by punching a metal plate and held parallel to each other by a metal frame.

[0051] The process according to the present invention includes carrying out a step a) of first injection. In particular, the first injection includes injecting a first material into a first cavity of a mold in which the sensitive element 2 is arranged to form a first overmolding 10 (illustrated in the figure) of the sensitive element.

[0052] The first overmolding 10 comprises, along an elongation direction XX', a hollow section 11 and a solid section 12, the hollow section 11 defining a cavity 13 provided with an opening 14 opening through one end of said first overmolding 10.

[0053] In general, it is accepted, without needing to specify it, that the assembly formed by the sensitive element and the longitudinal electrical connectors also extends along the elongation direction XX'.

[0054] Furthermore, the first injection can be implemented so that the capsule 2 and the electrical conductors are overmolded by the solid section 12, while the longitudinal electrical connectors extend into the hollow section.

[0055] The first overmolding 10 formed at the end of step a) along a cutting plane, said cutting plane including the elongation direction XX', can also be observed on this, at least one passage, and in particular two passages 15a and 15b formed at one end of the hollow section 11 opposite its opening 14. These two passages 15a and 15b each form an open channel leading to the beginning of the solid section 12.

[0056] The structure of the cavity as well as the passage(s) 15a and 15b can be defined by a first insert cooperating with a first impression of a mold implemented during the execution of step a). In particular, the first insert can be implemented to occupy a space intended to be free of the first material.

[0057] The overmolding process also includes a second injection step b).

[0058] Specifically, the second injection involves injecting a second material into the cavity through the opening, and during which the solid section is placed in a second mold cavity. In this respect, the second cavity is arranged so that passages 15a and 15b open into the space between the solid section and said second cavity.

[0059] Thus, the injection of second material into the hollow section allows on the one hand to partially fill said hollow section with second material, but also to overmold the solid section by flow of second material, via passages 15a and 15b, in the space delimited by the solid section and the second cavity, to form an overmold, called second overmold 16, of the solid section (, and).

[0060] Advantageously, the second overmolding 16 obtained at the end of step b) is formed exclusively by the flow of the second material in the passage 15a and 15b.

[0061] According to a particularly advantageous variant, it can be considered, during the execution of step b), that only a portion of the hollow section, referred to as the upstream portion 11a, separated from the solid section 12 by a downstream portion 11b of the hollow section, is also overmolded with the second material. In other words, this involves forming a third overmolding on the upstream portion 11a.

[0062] In this regard, during the execution of step b), the upstream portion 11a can be placed in a third cavity of the mold delimiting the overmolding of said upstream portion 11a. Thus, the downstream portion 11b, at the end of step b), remains exposed to the external environment.

[0063] Advantageously, step b) can be carried out by injecting the second material into the third cavity of the mold, the third cavity being configured so that, during the second injection, the second material spreads into a space delimited by the upstream portion and the third cavity, into the cavity and into the space delimited by the solid section and the second cavity via passages 15a and 15b.

[0064] Advantageously, during the execution of step b), an insert, called the second insert, is placed in the cavity, said second insert being extracted from the cavity after execution of step b).

[0065] The second insert can be configured so that the second material forms ribs within the cavity. The ribbing also ensures a uniform flow of injected material, thus providing optimal quality to the resulting overmolding.

[0066] The process according to the present invention, and in particular the consideration of the passage(s), makes it possible to limit the injection steps required for overmolding the sensitive element. Specifically, the second injection allows for the formation of the second overmolding, the third overmolding, and also the injection of the second material into the cavity, all in a single step.

[0067] Grooves 18, 19 can also be formed on either of the second and third overmoldings to accommodate O-rings considered for final assembly of the structure obtained at the end of the execution of the process according to the present invention.

[0068] Furthermore, considering the first overmolding followed by the second overmolding ensures effective coating of the capsule. Indeed, after the first overmolding, the capsule may not be uniformly coated by the initial material. In particular, some parts of the capsule may be exposed to the air. This problem can be related to various parameters, including...

[0069] - the minimum thickness constraints of the first overmolding

[0070] - the dimensional variation(s) of the capsule

[0071] - the fact that the capsule is not stationary during injection due in particular to the lack of rigidity of the electrical conductors.

[0072] Thus, the use of a second overmolding makes it possible to overcome these problems and in particular to standardize the coating of the capsule.

[0073] According to one variant, the first material and the second material are of the same nature.

[0074] According to another variant, the first material and the second material are of different natures.

[0075] Of course, the invention is not limited to the embodiments described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

A method for overmolding a sensitive element, the sensitive element having a sensitive capsule (2) and two electrical conductors (3a, 3b), the method comprising carrying out the following steps: a) a first injection of a first material into a first cavity of a mold in which the sensitive element is arranged to form a first overmolding (10) of the sensitive element, the first overmolding (10) comprising, along an elongation direction, a hollow section (11) and a solid section (12), the hollow section (11) defining a cavity having an opening (15) opening through one end of said first overmolding (10); b) a second injection of a second material into the cavity through the opening (15), and during which the solid section (12) is arranged in a second cavity of the mold;the overmolding process being characterized in that step a) is carried out so as to form at least one passage (15a, 15b), in the hollow section (11), and allowing, during the execution of step b), a flow of the second material into a space, delimited by the solid section (12) and the second cavity, to form an overmolding, called second overmolding (16), of the solid section (12). Overmolding process according to claim 1, wherein the second overmolding (16) obtained at the end of step b) is formed exclusively by the flow of the second material in the passage (15a, 15b). Overmolding method according to claim 1 or 2, wherein step b) is also performed to inject second material into the cavity. Overmolding process according to any one of claims 1 to 3, wherein during the execution of step b), a portion of the hollow section (11), referred to as the upstream portion (11a), separated from the solid section (12) by a downstream portion (11b) of the hollow section (11), is also overmolded with the second material. Overmolding method according to claim 4, wherein during the execution of step b), the upstream portion (11a) is disposed in a third cavity of the mold delimiting the overmolding of said upstream portion (11a). Overmolding method according to claim 5, wherein step b) is carried out by injecting the second material into the third cavity, the third cavity being configured so that, during the second injection, the second material spreads into a space delimited by the upstream portion (11a) and the third cavity, into the cavity and into the space delimited by the solid section (12) and the second cavity via the passage (15a, 15b). Overmolding method according to any one of claims 4 to 6, wherein during the execution of step b), an insert is disposed in the cavity, said insert being extracted from the cavity after execution of step b). Overmolding method according to claim 7, wherein the insert is configured so that the material forms ribs in the cavity. Overmolding method according to any one of claims 1 to 8, wherein during the execution of step a), the capsule (2) is at a free end of the solid section (12). Overmolding process according to any one of claims 1 to 9, wherein the first material and the second material are of the same nature. Overmolding process according to any one of claims 1 to 9, wherein the first material and the second material are of different natures.

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