JP7750267B2 - Joining structure for panel components and method for attaching panel components - Google Patents

Description

The present invention relates to a panel component joining structure and a panel component mounting method that use a mastic adhesive to join a panel component to a reinforcing component or other metal component. The present invention is particularly suitable for automotive panel components (especially outer panels) from the viewpoint of suppressing poor appearance.
Surface sinks are one of the appearance defects of outer panels of automotive panel parts, such as door panels and roof panels. These surface sinks are caused by localized out-of-plane deformation of the outer panel due to the shrinkage of the mastic adhesive. The present invention is a suitable technology for simply and easily avoiding these surface sinks.

Automotive panel parts include exterior panel parts called outer panels and interior panel parts such as floors and dash lowers. These panel parts have a large projected area. Therefore, among the components of an automobile, panel parts have a much greater effect on weight reduction through reduction in plate thickness than other structural parts.
Panel components are generally made up of outer panels with gently curved, wide surfaces. Reinforcement components that reinforce the panel component are placed on the back (inside) of the panel component. The panel component is then bonded (joined) to the reinforcing components with an adhesive called mastic adhesive, resulting in a reinforced structure.

Mastic adhesive is a semi-solid substance before application. However, after bonding the panel components and reinforcing components, the mastic adhesive foams (expands) during subsequent heating processes, such as baking heat in the painting line, and then hardens (shrinks) during cooling. Through this process, the mastic adhesive ultimately acquires rubber-like properties. The mastic adhesive used for bonding serves as a support point for the panel components when they are subjected to external forces, and also plays an important role in suppressing vibration of the panel components.
Here, outer panel parts (outer panels) are exposed to the eyes of users, and therefore a high level of surface appearance quality is required.

However, when outer panels are made thinner to reduce vehicle weight, the surface rigidity of the panel components, known as tensile rigidity, decreases. The lower the surface rigidity of the panel components, the more susceptible they are to out-of-plane deformation due to the shrinkage force of the mastic adhesive that occurs during the cooling process after painting.
The area where this out-of-plane deformation occurs is easily noticeable because it results in a steeper change in surface compared to the surrounding gently curved surfaces. This appearance defect is called surface sink, as mentioned above, and is one of the challenges in making thinner outer panels.

Conventionally, there are techniques described in Patent Documents 1 to 3 as countermeasures against surface sinking of panel parts of automobiles.
Patent Document 1 describes providing a cavity inside the mastic adhesive to be bonded. Patent Document 2 describes including a plurality of two types of hollow resin bodies with different average particle sizes in the mastic adhesive to be used. Patent Document 3 describes including a plurality of thermally expandable fillers in the mastic adhesive.
The techniques described in these patent documents are intended to relieve internal stress when the mastic adhesive and structural adhesive harden and shrink, thereby suppressing sink marks in the outer panel.

WO2018-193706 JP 2012-067191 A Japanese Patent Application Publication No. 6-57224

In order to prevent the occurrence of surface sinks, it is necessary to reduce the stress that occurs on the panel adhesive surface when the mastic adhesive shrinks.
However, with the method described in Patent Document 1, it is extremely difficult to stably form cavities inside the mastic adhesive as it hardens and shrinks. This can lead to problems such as variations in the quality of the mastic adhesive during mass production. Another problem is the cost involved in forming cavities inside the mastic adhesive.

Furthermore, the technology described in Patent Document 2 requires mixing a large number of resin spheres into the mastic adhesive, which increases the cost of the material and may result in a loss of stable effectiveness if the balance between the properties of the mastic adhesive material and the resin that makes up the spheres changes.
Furthermore, the technology described in Patent Document 3 increases costs by adding a thermally expandable filler to the structural adhesive. Furthermore, the filler's high temperature sensitivity means that it is likely to be significantly affected by temperature fluctuations during mass production. This requires strict temperature control, which is likely to increase costs.

The present invention was developed with the above points in mind, and aims to provide a means for easily and stably reducing the stress on the panel adhesive surface that occurs when the mastic adhesive shrinks, thereby preventing surface sinking of panel components.

The inventors conducted extensive research into ways to reduce the stress that occurs on the panel adhesive surface when the mastic adhesive shrinks. They then discovered that by incorporating a metal plate into the mastic adhesive, tensile stress could be generated across the entire surface of the metal plate within the mastic adhesive as the mastic adhesive shrinks. They then discovered that this reduces the tensile stress acting on the panel components and prevents surface sinking. The present invention is based on these findings.

To solve the problem, one aspect of the present invention is a joining structure for panel components, in which the back surfaces of metal panel components facing each other with a gap are joined to another metal component using mastic adhesive, and a metal plate is embedded in the mastic adhesive.
The other metal parts are, for example, reinforcement parts.

According to this aspect of the present invention, the tensile stress acting on the panel component when the mastic adhesive shrinks can be reduced by the simple means of incorporating a metal plate into the mastic adhesive. As a result, this aspect of the present invention provides a means for easily and stably reducing the stress on the panel bonding surface that occurs when the mastic adhesive shrinks, thereby preventing surface sinking of the panel component.
For example, according to the present invention, by changing the bonding method of the mastic adhesive without changing the automobile production line, it is possible to suppress surface sinks in panel components and achieve stable production quality. It also leads to solving the problem of surface sinks occurring due to the thinning of panel components, and can contribute to weight reduction of automobile bodies.

1A and 1B are diagrams illustrating an example of a joining structure for a panel component according to an embodiment of the present invention, in which (a) is a cross-sectional view cut in the thickness direction, and (b) is a cross-sectional view taken along line X-X in (a). 10A and 10B are diagrams showing another example of a joining structure for panel components, in which (a) is a cross-sectional view cut in the thickness direction, and (b) is a cross-sectional view taken along line XX in (a). 10A and 10B are diagrams showing another example of a joining structure for panel components, in which (a) is a cross-sectional view cut in the thickness direction, and (b) is a cross-sectional view taken along line XX in (a). 10 is a cross-sectional view showing another example of the arrangement of metal plates embedded in mastic adhesive. FIG. FIG. 1 is a diagram illustrating a test jig in an example. FIG. 2 is a diagram showing the structure of each mastic adhesive in the examples. FIG. 10 is a diagram showing the measurement results of the panel surface after heat treatment in an example of the invention. FIG. 10 is a diagram showing the measurement results of the panel surface after heat treatment in Comparative Example 1. FIG. 10 is a diagram showing the measurement results of the panel surface after heat treatment in Comparative Example 2.

Next, an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, application to automobiles is considered, and a reinforcing part will be described as an example of another metal part.

(composition)
1, the joining structure for a panel component of this embodiment is a joining structure for joining a reinforcing component 2 and a rear surface 1a of a panel component 1, which are arranged facing each other with a predetermined gap between them. A mastic adhesive 3 is used to join (adhere) the reinforcing component 2 and the panel component 1. The reinforcing component 2 and the panel component 1 are made of metal, such as steel.
Here, this embodiment is a technology suitable for a joining structure in which automotive panel parts, such as exterior panel parts (door panels, roof panels, etc.) called outer panels of an automobile, and interior panel parts such as floors and dash lowers, are bonded to reinforcing parts using a mastic adhesive. However, the structure of the panel part joining portion of this embodiment can also be applied to cases in which panel parts for other uses are joined to other metal plates using a mastic adhesive.

Here, automotive panel components 1 are often formed in a plate shape with a wide curved surface with a gentle curvature, and tend to have relatively low rigidity in the out-of-plane direction. For this reason, a reinforcing component 2 is disposed on the back side (inner side) of the panel component 1 to reinforce the panel component 1.
At this time, a gap is formed between the back surface 1a of the panel component 1 and the surface 2a of the reinforcing component 2. Therefore, a mastic adhesive 3 is partially interposed in the gap, and the panel component 1 and the reinforcing component 2 are bonded by the mastic adhesive 3. The panel component 1 is then restrained by the reinforcing component 2 through bonding by the mastic adhesive 3. It is preferable that the outer peripheral contour shape of the adhesive surface of the panel component 1 bonded to the back surface 1a be formed by a series of arcs. FIG. 1 illustrates a circular shape. If the contour shape of the adhesive surface of the panel component 1 has corners, such as a rectangular cross section, the corners may retract more severely locally during shrinkage, which may result in behavior different from the actual state.

In general, the joining of the panel part 1 and the reinforcing part 2 with the mastic adhesive 3 is often carried out by applying the mastic adhesive 3 in dots.
In contrast to this, in this embodiment, as shown in Figure 1, a metal plate 4 is embedded in the mastic adhesive 3 that is interposed between the panel component 1 and the reinforcing component 2. Note that simply embedding the metal plate 4 is much easier than uniformly dispersing and blending a large number of particles.

Here, the metal plate 4 does not have to be embedded so that it is completely covered with the mastic adhesive 3. That is, a portion of the embedded metal plate 4 may be exposed from the mastic adhesive 3. However, as shown in Figure 1, it is preferable that the outer periphery of the metal plate 4 is completely covered with the mastic adhesive 3. That is, as shown in Figures 1(a) and 1(b), it is preferable that the mastic adhesive 3 is present around the entire periphery of the metal plate 4. This prevents the exposed outer periphery of the metal plate 4 from directly contacting the panel component 1 or reinforcing member when the vehicle body vibrates.

As shown in Fig. 1(b), the shape of the metal plate 4 may be different from the outer peripheral contour shape of the mastic adhesive 3. In Fig. 1, the metal plate 4 and the mastic adhesive 3 are arranged so that their centers of gravity coincide or nearly coincide with each other when viewed in the thickness direction (plan view).
Furthermore, the ratio of the area of the metal plate 4 to the area defined by the outer peripheral contour shape of the mastic adhesive 3 in a plan view is not particularly limited, but is set to, for example, 0.3 to 0.9. If this ratio is too small, the tensile stress generated on the surface of the metal plate 4 will be correspondingly small. If this ratio is too large, the outer peripheral portion of the metal plate 4 will be more likely to be exposed from the mastic adhesive 3.

Furthermore, the thickness of the metal plate 4 need only be thinner than the gap between the panel component 1 and the reinforcing component 2 at the position where they are bonded with the mastic adhesive 3, i.e., the thickness of the mastic adhesive 3. The thickness of the metal plate 4 is, for example, 0.1 to 0.9 times the gap. If the thickness is less than 0.1 times, the desired effect may not be obtained. On the other hand, if the thickness exceeds 0.9 parts, the damping and adhesive properties required of the mastic adhesive may not be sufficiently obtained.
Here, when the mastic adhesive 3 shrinks, tensile stress is generated over the entire surface of the metal plate 4 within the mastic adhesive 3. For this reason, it is preferable that the thickness of the metal plate 4 be thick enough to provide sufficient strength to prevent the metal plate 4 from bending under the above-mentioned tensile stress.

1(a) illustrates an example in which the metal plate 4 is embedded without contacting the panel component 1 or the reinforcing component 2, but this is not limiting. For example, as shown in Figures 2 and 3, the metal plate 4 may be disposed so as to be in contact with either the panel component 1 or the reinforcing component 2. Note that the metal plate 4 may be disposed so that only the edges of the metal plate 4 come into contact with the panel component 1 or the reinforcing component 2.
The metal plate 4 may also be disposed at an angle relative to the surface of the opposing panel component 1 or reinforcing component 2. However, it is preferable that the metal plate 4 be disposed in a position parallel or approximately parallel to the surface of the opposing panel component 1 or reinforcing component 2. When the metal plate 4 is tilted, it is preferable that the angle be less than 30 degrees relative to the above-mentioned parallel surface.

4, the metal plate 4 may be divided into a plurality of pieces in plan view. The divided metal plates 4 do not need to have the same shape, but the mastic adhesive 3 should be interposed in the gaps between the divided metal plates 4. If the number of divisions is too large, the effect of the present invention will be reduced and installation will become more tedious, so if the metal plate 4 is divided into two or more pieces and no more than four pieces, it is preferable.
In this embodiment, the metal plate 4 has a flat plate shape, but the metal plate 4 may be curved or have an uneven surface. The surface of the metal plate 4 may also be roughened to improve adhesion with the mastic adhesive.
Furthermore, when the surface area of the metal plate 4 is converted into a square shape, the length of the sides of the square shape is longer than the thickness.

(Example of joining method)
[First construction example]
When forming a joint by applying the mastic adhesive 3 to the parts, for example, the metal plate 4 is placed in advance at the bonding portion of the mastic adhesive 3, and then the mastic adhesive 3 is applied.
In this case, the metal plate 4 is arranged as shown in FIG. 2 or FIG.
[Second construction example]
After applying half of the mastic adhesive 3 to the surface of one of the components, the metal plate 4 is placed in place. Further, half of the mastic adhesive 3 is applied so as to cover the metal plate 4. This application results in the metal plate 4 being embedded in the mastic adhesive 3. In this case, the metal plate 4 is arranged as shown in Figure 1.

Here, when forming the joint, the metal plate 4 can be positioned manually. However, considering the takt time, it is preferable to position the metal plate 4 using a robot. If scrap material remaining after trimming of a press blank is used as the metal plate 4, it is possible to reduce costs. However, the metal plate 4 may also be prepared from a new material.
There is no particular limitation on the type of metal used for the metal plate 4. However, in consideration of availability and cost, iron is desirable as the metal type for the metal plate 4. The metal plate 4 may also be made of a metal material such as an aluminum alloy.
When the joining structure of this embodiment is adopted, the assembly and painting processes can be performed using the same specifications as existing equipment. Therefore, although there is a cost for arranging the metal plate 4, with only a minimum investment, it is possible to reduce vehicle defects due to surface sinks and achieve vehicle weight reduction.

<Actions and other>
According to this embodiment, the metal plate 4 is contained in the mastic adhesive 3. As a result, according to this embodiment, when the mastic adhesive 3 shrinks, tensile stress is generated on the entire surface of the metal plate 4 within the mastic adhesive 3. As a result, according to this embodiment, the tensile stress acting on the panel component 1 is reduced, and surface sinking can be suppressed.
In this way, in this embodiment, a joint can be formed using the simple method of embedding the metal plate 4 in the mastic adhesive 3. This makes it possible to easily and inexpensively relieve the stress applied to the surface of the panel component 1 when the mastic adhesive 3 shrinks. As a result, in this embodiment, it is possible to easily prevent the occurrence of surface sinks caused by bonding the panel component 1 with the mastic adhesive 3.

As will be described later in the Examples, it was found that surface sinks could be suppressed more effectively than in the past for panel components 1 of the same thickness. In other words, when the joint structure of this embodiment is designed to have the same quality as joints made with solid or hollow mastic adhesive, it becomes possible to further reduce the thickness of the panel component 1.
The reason why the plate material embedded in the mastic adhesive 3 is made of a metal plate is as follows. By using a metal plate material, the linear expansion coefficient is smaller than that of the mastic adhesive 3, and the difference in expansion can generate a larger tensile stress. Furthermore, metal plate material is stable and does not change in quality (dissolve, volatilize, etc.) in the temperature range of paint baking. Furthermore, because metal plate is a material that is easily available, material costs can be kept low.

When the present invention is applied to, for example, automotive panel components, surface sinking of the panel component 1 can be suppressed by changing the bonding method of the mastic adhesive 3 without changing the automobile production line. As a result, it becomes possible to produce components with a consistent appearance and quality. It also solves the problem of surface sinking caused by thinner panel components 1, contributing to weight reduction of automobile bodies.

(others)
The present disclosure may also have the following configuration.
(1) A joining structure for panel components, in which the back surfaces of metal panel components facing each other with a gap are joined to another metal component with a mastic adhesive,
A metal plate is embedded in the mastic adhesive.
(2) The metal plate is in contact with the rear surface of the panel component or the other metal component.
(3) The number of embedded metal plates is two or more, and the metal plates do not overlap each other when viewed from the opposing direction of the panel component and the other upper metal component, i.e., in a plan view.
(4) The panel part is an automobile panel part.
(5) A method for attaching a panel component, in which the back surface of a metal panel component is joined to another metal component facing the panel component with a gap therebetween by mastic adhesive,
A metal plate is embedded in the mastic adhesive.
(6) The metal plate is embedded in the mastic adhesive while being in contact with the rear surface of the panel component or the other metal component.

Next, an example based on this embodiment will be described.
(Experimental conditions)
FIG. 5 shows a conceptual diagram of the test jig used in this example.
As shown in FIG. 5, the test jig of this example includes a panel part a, a fixing frame b, a reinforcing part c, and a joining part that joins the panel part a and the reinforcing part c.
Panel component a is a rectangular panel component measuring 300 mm x 310 mm, curved by press forming from a flat steel plate with a tensile strength of 270 MPa. This panel component a is intended for use as an automobile roof panel component (outer panel component). Panel component a is manufactured so that it has a curvature (curvature) with a radius of curvature of 5000 mm along one direction (short side direction) and a flat surface in the direction perpendicular to the curvature (long side direction). The thickness of panel component a is 0.7 mm. A rectangular support frame is attached to the outer periphery of panel component a.

The fixing frame b faces the support frame provided on the outer periphery of the panel component a and is a frame component for fixing the entire outer periphery of the panel component a. The outer periphery of the panel component a is attached to the fixing frame b with screws. The fixing frame b in this example is made of a thick plate with a thickness of 12 mm and is a rectangular frame-shaped component that has the required rigidity to restrain the reinforcing component c and the panel component a.
The reinforcing part c is a part simulating a reinforcing part for an outer panel part, and is a rectangular parallelepiped part measuring 50 mm in width, 310 mm in length, and 1.8 mm in thickness, made of steel plate with a tensile strength of 590 MPa. Both longitudinal ends of the reinforcing part 2 are fixed to the fixing frame b. The extending direction of the reinforcing part c is perpendicular to the curvature direction of the panel part a, and is located at the center of the curvature of the panel part a in a plan view.

The longitudinal center of the top surface of the reinforcing component c was bonded to the back surface (lower surface) of the panel component a, which faced the top surface, with an adhesive. At the joint, the distance between the panel component a and the reinforcing component c (the vertical gap) was 3 mm.
The adhesive used for bonding the joints was a rubber-based foam-hardening mastic adhesive d, applied in an amount of 3 g. After applying the mastic adhesive d to the reinforcing part c, the panel part a and the reinforcing part c were bonded together, and the outer periphery of the panel part a was fixed to the fixing frame b.
In this example, three types of joint structures were used: an example of the invention, a comparative example 1, and a comparative example 3. The amount of mastic adhesive d applied was the same.

<Example of invention>
In the example of the present invention, as shown in Figure 6(a), a metal plate e is embedded in the center of the mastic adhesive d that forms the joint. The metal plate e is a square steel plate with a side length of 1.5 mm (thickness of 1.8 mm) and a tensile strength of 440 MPa.

<Comparative Example 1>
In Comparative Example 1, as shown in Figure 6(b), the mastic adhesive d constituting the joint was applied in a solid cylindrical shape. In other words, it was formed by normal solid application.
<Comparative Example 2>
In Comparative Example 2, as shown in Fig. 6(c), the mastic adhesive d constituting the joint was applied in a doughnut shape, i.e., a cavity was provided in the center of the applied mastic adhesive d.
In addition, under all application conditions, the application work was carried out manually, so the outer periphery of the applied mastic adhesive d was not a smooth, perfectly circular surface, but was slightly uneven.

<Heat treatment>
For each of the above coating conditions, the test jigs were placed in a heating furnace and heated. The heating temperature was 170°C, the paint baking temperature for automobiles. Specifically, in the heating treatment of this embodiment, the temperature was raised from the ambient temperature (approximately 20°C) at a rate of 10°C/min, and the furnace temperature was maintained for 20 minutes after reaching 170°C. Thereafter, each test jig was removed from the furnace and subjected to a cooling treatment. Specifically, in the cooling treatment, a gentle breeze was blown onto each test jig, and cooling was controlled so that the cooling rate was 20°C/min until the temperature reached 80°C. After 80°C, each test jig was allowed to cool naturally by standing.

(evaluation)
<Evaluation of surface sink>
For each test jig, the sink mark (distortion) at the center of panel component a was measured using a distortion measuring device. That is, the inclination of the surface of the measurement target portion was measured using the distortion measuring device. The measured values were then curve-fitted and differentiated to obtain a second-order differential value, which was then quantified.
It is generally known that the larger the fluctuation (amplitude) of the second derivative of the cross section of the sink mark, the larger the sink mark appears to be. This example was also carried out using this evaluation index.

7 to 9 show the evaluation results obtained using a distortion measuring device.
Fig. 7 shows the evaluation results for the example of the present invention. Fig. 8 shows the evaluation results for Comparative Example 1. Fig. 9 shows the evaluation results for Comparative Example 2. Here, (a) in each figure indicates the zebra pattern that occurred on the surface of the panel component 1. The positions of the arrows in Figs. 8 and 9 indicate the positions where surface sinks occurred.
As shown in Fig. 8, under the normal coating conditions of Comparative Example 1, surface sinks occurred in the center of the panel component 1. Moreover, as shown in Fig. 9, under the doughnut-shaped coating conditions of Comparative Example 2, the sinks were even larger than those of Comparative Example 1.
In contrast to this, under the coating conditions of the example of the present invention in which the metal plate e was inserted, no sink marks were observed, as shown in FIG.

As described above, it has been suggested that the present invention can suppress surface sinking more effectively than bonding using only the current solid type mastic adhesive d (equivalent to Comparative Example 1).

1 Panel part 1a Back surface 2 Reinforcing part 3 Mastic adhesive 4 Metal plate

Claims (6)

A joining structure for panel components, in which the back surfaces of metal panel components facing each other with a gap are joined to another metal component using a mastic adhesive,
A metal plate is embedded in the mastic adhesive.
A joining structure for panel components characterized by: The embedded metal plate is in contact with the back surface of the panel component or the other metal component.
2. The joining structure for panel components according to claim 1. The embedded metal plates include two or more metal plates, and the metal plates do not overlap each other when viewed from the opposing direction of the panel component and the other metal component.
3. The joining structure for panel components according to claim 1 or 2. The panel component is an automotive panel component.
2. The joining structure for panel components according to claim 1. A method for attaching a panel component, in which the back surface of a metal panel component is joined to another metal component facing the panel component with a gap therebetween by a mastic adhesive,
Embedding a metal plate in the mastic adhesive.
A method for attaching panel components. The metal plate is embedded in the mastic adhesive while being in contact with the rear surface of the panel component or the other metal component.
6. The method for attaching a panel component according to claim 5.