JPS632690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a plate made of aluminum or an aluminum alloy as at least an outer panel material, and uses a flat hemming process to join the plate to an inner panel. The present invention relates to a method that can effectively reduce surface roughness by preventing the occurrence of such occurrences.

In general, the hemming method is also called the seam-folding method, and involves bending the edge of one plate according to this method, and then mechanically assembling the edge of another plate into the bent part. By further bending,
Conventionally, joining these two plates together has been adopted. Taking car parts as an example,
Engine hoods, doors, trunk lids, etc. are all formed by hemming the outer and inner panels of thin steel plates (approximately 0.7 mm thick), and the edges of these are designed to have a sharp feel. Even after hemming, the edges did not develop cracks or roughness, and there were no particular problems.

However, as people tried to use aluminum outer panels in order to meet the modern demand for lighter automobiles, serious problems began to arise in the hemming process. That is, in the hemming process for joining an outer panel made of a high-yield aluminum alloy plate to an inner panel, cracks or roughness may occur at the edges, making the product difficult to use. for example
SAE (Society of Automotive Engineers) No.780392 (1978)
According to the report, aluminum alloy plates such as 6010-T4 and 2036-T4, which have high yield strength, have rope hems (second
It has been suggested that it is not desirable to adopt the flat hem process shown in FIG. 1.

However, when comparing the advantages and disadvantages of flat hems and roped hems, roped hems (1) have a less sharp feel and are unfavorable in appearance, and (2) have a smaller contact area between the inner and outer panels. There are problems such as a lack of adhesion, and for this reason, it is desired to employ flat hems in the manufacture of the above-mentioned automobile parts. By the way, aluminum alloy 6009-T4, which can be made into a flat hem, has a high yield strength.
131MPa (13.4Kg/mm ² ), 186MPa (19.0Kg/mm ² ) of the aluminum alloy 6010-T4, 2036-
It is significantly lower than the 200 MPa (20.4 Kg/mm ² ) of T4, and therefore has the inherent problem of inferior dentability resistance. It is necessary to use plate materials such as aluminum alloys 6010-T4 and 2036-T4, which have excellent dentability and high yield strength, for automobile doors and hoods, and can be applied to such plate materials without fear of cracking or roughening. The development of a flat hemming processing method that can be used is awaited.

Against this background, the present invention was made with the object of providing a method for flat hemming aluminum alloys, etc., which have high yield strength and excellent dental resistance, without fear of cracking or roughening. The gist of this is flat hemming, in which a high-yield plate made of aluminum or aluminum alloy is used as at least the outer panel material, and the outer panel is bent to join it to a predetermined inner panel. In the processing, the down flange process as one of the processes of edge bending of the outer panel is performed until the bending radius R of the flange corner is 0.8T or more.
After forming a predetermined flange at the end of the outer panel, a pre-hemming operation and a final flat hemming operation are applied. Alternatively, the outer panel and the inner panel are joined by applying a final hemming operation after the down flange process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in more detail below based on the drawings.

FIG. 3 is a cross-sectional view of the main parts of an automobile engine hood, in which 1 is an outer panel, 2 is an inner panel attached to the inside as a reinforcing material,
3 is the hemming processing part of both.

FIGS. 4a to 4e illustrate this hemming process according to the order of the forming steps. FIG. 4a shows a drawing step (first step) performed by a press machine after cutting the material and taking appropriate material. Fig. 4b shows the trimming process (second process) to cut off unnecessary parts around the periphery, and Fig. 4c shows the predetermined bending radius R to form a flange with a width of about 10 to 11 m/m necessary for edge bending. Down flange process (3rd process) to bend at right angle, and pre-hem process (4th process) to bend the flange to about 45 degrees after inserting the inner panel (Fig. 4 d) (However, if the 4th process is omitted) Figure 4e shows the final stage of hem bending, and the final hem process (fifth stage) forms a flat hem with a flat hem shape.
process).

In the present invention, in the down flange process (third process) of the above processes, by setting the bending radius R of the corner to a predetermined size or more, work hardening of the material is suppressed, and the subsequent prehem process (third process) This effectively prevents cracking and roughening of the bent edge portion in the final hem step (step 4) and the final hem step (step 5). In addition, the size of the corner radius in the conventional down flange process was 0.1 to 0.5 mm for all plate thicknesses, and the pre-hem process and final hem process caused cracks and cracks in the edge bending process. There was an underlying cause of skin irritation.

By the way, the above steps 1 to 5 are performed in 2 steps.
Two aluminum alloy materials 6009--T4 and 6010
-The results of flat hem processing using T4 are shown in Figure 5. The plate thickness is 1.2 mm, and the corner radius size in the down flange process (third process) is 0 mm, 1 mm, 2 mm, and 2.4 mm.
Experiments were carried out depending on the type.

In Fig. 5, curve A shows the surface roughness (μ) of the edge when flat hemming is performed on an outer panel using aluminum alloy plate 6010-T4, which has a relatively high yield strength, and the down flange R (mm). )
This is shown in comparison with . This A curve is R
When R = 0 mm, the surface roughness is infinite and fracture is shown, but when R = 1 mm, the surface roughness is about 20 μ (slightly rough surface), and R = 2 mm, 2.4 mm.
In this case, the surface roughness tends to further decrease, and even if R becomes even larger, the surface roughness converges to a substantially constant value. Although not shown, similar results were obtained for the 2036-T4 material. Furthermore, B
The curve shows aluminum alloy plate 6009, which has relatively low yield strength.
-Similar experimental results for the outer panel of T4 are shown, and the surface roughness is large when the R is 0 mm, but as the R increases to 1, 2, and 2.4 mm, the surface roughness gradually decreases. It has been shown that rough skin is significantly improved.

In general, when hemming aluminum-based materials, the product can be used if there are no cracks on the edge surface and the surface roughness is kept to about 20 μm. Therefore, in the A curve, R =
It can be said that it can be used with a thickness of 1 mm or more. In this case, since the plate thickness T = 1.2 mm, R = 1 mm corresponds to approximately 0.8 T. From this fact, in the corner bending radius R = 0.8 T to 1.8 T of the down flange, the prehem process (fourth It is understood that the final hem process (step 5) and final hem process (fifth process) were carried out without any abnormality, no breakage occurred, and the roughness of the skin was within an acceptable level.

Experiments have demonstrated that flat hems can be applied to aluminum alloys with high yield strength such as 6010-T4 and 2036-T4 in the range of R = 0.8T or more.
The above suggests that it is not desirable to adopt flat hem processing for 6010-T4, 2036-T4, etc.
This is completely contrary to the description in the SAE report and the common sense of those skilled in the art, and has made it possible to perform work that was previously considered impossible.

Also, the corner bending radius R of the down flange is
If it is less than 0.8T, use the 6010-T4 material or 2036-
In the case of T4 material, cracks occur at the edge, and even in the case of 6009-T4 material, the surface roughness is 25 to 35μ.
In either case, the product becomes unusable or difficult to use.

On the other hand, the upper limit of the corner bending radius R of such a down flange will be determined as appropriate, taking into account the fact that the larger it is, the larger the spring back will be, which will cause problems when assembling both panels. In general, in order to form sharp edges, improve the appearance, and facilitate the subsequent assembly work, it is desirable that the upper limit of R be approximately 1.8T.

The material of the outer panel is aluminum or its alloy, and especially in the case of automobile doors etc., an aluminum alloy with excellent dentability and high yield strength is used, such as the above-mentioned 6010-T4,
2036-T4 etc. is suitable. On the other hand, the material of the inner panel is not particularly limited since it has nothing to do with the surface roughness of the edge portion, and may be made of steel plate or other plate materials in addition to aluminum material.

As detailed above, according to the method of the present invention,
By performing the down flange process of flat hemming within certain limits, flat hemming can be performed on aluminum or aluminum alloy plates with high yield strength, which was previously considered impossible, without fear of cracking or roughening. You will get
In addition, when the skin cracks are large, the surface roughness can be further reduced, and this has great industrial significance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a flat hem in hemming process, and FIG. 2 is a sectional view similarly showing a rope hem. FIG. 3 is a sectional view of the main parts of the engine hood. Figure 4a shows the drawing process, Figure 4b shows the trim process, Figure 4c shows the down flange process, Figure 4d shows the pre-hem process, and Figure 4e shows the product shape at the end of the final hem flat hem process. FIG. FIG. 5 is a graph showing the relationship between down flange R (mm) and surface roughness (μ) when flat hemming is performed on two types of materials based on the method of the present invention. 1: Outer panel, 2: Inner panel,
3: Hemming processing section.

Claims (1)

[Claims] 1. In flat hemming processing, in which a high-yield plate made of aluminum or aluminum alloy is used as at least the outer panel material, and the outer panel is edge-bent to be joined to a predetermined inner panel, the edge bending of the outer panel is The down flange process is one of the processes in which the bending radius R of the flange corner is 0.8T~
After forming a predetermined flange at the end of the outer panel, a pre-hemming operation and a final flat hemming operation are applied. Alternatively, a method for hemming an aluminum or aluminum alloy plate, characterized in that the outer panel and the inner panel are joined by applying a final flat hemming operation after the down flange step.