JP2966626B2 - punching metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a punching metal used for a door of a cooking device such as a microwave oven.

[0002]

2. Description of the Related Art For example, a door of a microwave oven is provided with a viewing window so that a user can look into a cooking chamber from the outside. The viewing window is configured by, for example, covering a punching metal formed by punching a large number of small holes in a central portion of a thin iron plate with a glass plate. This punched metal not only provides a radio wave shield but also reinforces the door.

As shown in FIGS. 12 to 14, this punching metal 1 has a rectangular shape as a whole, and has a see-through window 3 in which a large number of small holes 2 are formed in a central rectangular area. The outer peripheral portion has a frame portion 4 including a rising portion 4a and a flange portion 4b continuous therewith.

[0004] Such a punching metal 1 is manufactured by first punching out a large number of small holes 2 from a rectangular plate material 5 and then forming the frame portion 4 by drawing. ing. In this case, the plate thickness t of the plate member 5 is, for example, 0.6 mm, and
The bending radius R of the corner formed by the frame portion 4 and the frame portion 4 is set to be at least five times the plate thickness t which is an appropriate value for general drawing.

In this case, by integrally forming the see-through window portion 3 and the frame portion 4 from a single plate material 5, material waste can be suppressed, and the processing steps can be relatively simple. It can be manufactured at low cost.

[0006]

However, it is desired that the inside of a door of a microwave oven or the like has a good visibility so that the food inside can be easily seen. In this case, in order to improve the visibility, for example, the small holes 2 of the punched metal 1 are used.
The hole diameter d is increased while maintaining the pitch p shown in FIG. 14 as it is, and the aperture ratio (the small hole 2 with respect to the entire area of the
It is conceivable to increase the area occupied by the area.

However, when the hole diameter d of the small holes 2 is increased in this manner, the width x of the so-called bridging portion between the small holes 2 is increased.
Becomes smaller. On the other hand, when the frame portion 4 is drawn as described above, the material of the inner portion (the see-through window portion 3) of the plate member 5 may be subjected to a tensile force to the outside. If too much, as shown in FIG. 15, there is a problem that the outermost portion of the small hole 2 forming region of the see-through window 3 is broken at the time of drawing.

For this reason, in the prior art, the frame portion 4
In order to prevent the see-through window portion 3 from being broken by the tensile force at the time of drawing, the diameter d of the small holes 2 cannot be so large. 6
mm, the hole diameter d was 1.2 mm, and the aperture ratio was only about 50%.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to reliably prevent breakage of a see-through window at the time of drawing forming of a frame portion. An object of the present invention is to provide a punching metal capable of improving the performance.

[0010]

According to the punching metal of the present invention, a plurality of small holes are formed in an inner area of a plate material to form a see-through window, and an outer peripheral portion of the see-through window is formed by drawing. The frame portion is formed so as to rise, and a feature is that a bending radius of a corner formed between the see-through window portion and the frame portion is set to be approximately twice or less a plate thickness of the plate material.

[0011]

In general, it is considered appropriate that the roundness of the corners in the drawing process be set to a bending radius of about 5 to 10 times the sheet thickness from the viewpoint of the working force and the uniformity of the sheet thickness. .

However, in the case where the frame portion is formed upright by drawing on the outer peripheral portion of the see-through window having a large number of small holes, if a relatively large bending radius as described above is employed, it is difficult to form the frame at the time of drawing. Due to the tensile force, the spread of the material from the portion corresponding to the see-through window portion of the plate material to the frame portion increases, and there is a possibility that the small hole forming portion is broken.

In view of such circumstances unique to punching metal, the present inventor focused on the bending radius of the corner formed by the see-through window and the frame, and conducted various experiments and studies.
Bending radius that is generally appropriate (more than 5 times the plate thickness)
By deviating from the range and reducing the bending radius,
It was confirmed that the outward tensile force acting during the drawing of the frame portion was cut off at the corners, and the influence on the see-through window could be reduced. Further, as a result of further research, they found that if the bending radius was set to be approximately twice or less the thickness of the plate material, the influence of the tensile force on the see-through window could be extremely reduced, and the present invention was completed. It is.

That is, as shown in FIG. 7, in the process of drawing the plate material a to form the frame portion b, first,
For example, when the peripheral portion of the rectangular upper surface portion c is bent so as to be bent in a right angle direction in a state where the tensile force is small, that is, with little elongation deformation, so-called bending processing is performed. A drawing process for forming a sheet while stretching it by a large tensile force is performed.

On the other hand, the working force P required for drawing the plate material a
As shown in FIG. 8, (kg) can be approximately calculated by the following equation, where t is the thickness of the plate material a, R is the bending radius, and L is the bending length (the unit is mm).

[0016]

(Equation 1) Here, K is a coefficient (1-2, which approaches 1 when R / t increases, approaches 2 when R / t decreases), and σ is the tensile strength (kg / mm 2) of the plate material a.

Therefore, the required working force P is substantially proportional to the square of the plate thickness t, and substantially inversely proportional to the bending radius R of the corner. Further, from this result, the relationship between R / t and the required working force P is as shown in FIG.

Here, when the bending radius R is large (for example, R / t = 5), as shown in FIG. 10, a corner formed between the point B0 and the point C0 by the overhanging process, As the drawing process proceeds, a relatively small processing force P
However, the material of the upper surface portion c extends outward and deforms, and the bending point moves. That is, the initial points A0, B0, C0 move to points A1, B1, C1, respectively, and the points A1-B1
The space between the points B1 and C1 is reversed while the space between the points B1 and C1 is reversed.

On the other hand, as shown in FIG. 11, in the overhanging process, the bending radius R is small (for example, R / t =
1) If a corner portion (between point B and point C) is formed, the processing force P required to move the bending point during drawing becomes enormous, and therefore, an outward tensile force acting on the plate material a. Is stopped by the corners and does not act on the upper surface portion c, so that even if the points A, B, and C move, the movement is very small.

As a result, according to the punching metal of the present invention, since the bending radius of the corner formed by the see-through window and the frame is reduced, the outward tensile force generated when the frame is drawn is reduced. It does not act on the see-through window part inside it, and, even if the diameter of the small hole of the see-through window part is increased, there is no danger of breakage.

According to the study of the present inventor, the specific value of the bending radius at this time is about twice as large as the thickness of the plate material, and the effect of preventing adverse effects on the see-through window becomes remarkable. It has been found that criticality exists. Therefore, by setting the bending radius to be approximately twice or less the plate thickness, it is possible to reliably prevent an adverse effect on the see-through window.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which the present invention is applied to a microwave oven will be described below with reference to FIGS. First,
As shown in FIG. 3, the microwave oven is configured to have a rectangular door 13 for opening and closing the cooking chamber 11 on a front surface of a rectangular box-shaped main body 12 having a cooking chamber 11 having an open front surface. ing. The configuration of the door 13 will be briefly described with reference to FIG.

That is, 14 is a door body having a rectangular shape.
This is composed of an outer plate 15 made of a punched metal according to the present embodiment, which will be described in detail later, and an inner plate 16 made of, for example, an iron plate in a rectangular frame shape. Of these, the inner plate 16
Is attached, for example, by welding to the back side of a peripheral portion (a frame portion described later) of the outer plate 15.

A frame-shaped sash 17 is attached to the outer periphery of the door body 14, and a transparent outer barrier 18 made of, for example, a glass plate covers the front surface of the outer plate 15. Mounted on Further, a transparent inner barrier 19 also made of a glass plate is attached to the back side of the door main body 14 with a sealing material 20 so as to cover the inside of the opening of the inner plate 16.

Although not shown in detail, the door 13 constructed as described above is pivotally supported at the left edge of the front portion of the main body 12, thereby opening and closing the front opening of the cooking chamber 11. ing. Also, at this time, two hooks 21 are provided vertically on the back side of the right edge of the door 13, and when the door 13 is closed, the hooks 21 are locked to the main body 12.

The door 13 has a viewing window 22 so that a user can look inside the cooking chamber 11 from outside.
Is provided. The viewing window 22 is provided on the outer plate 15 with both sides sandwiched between the outer barrier 18 and the inner barrier 19.
In addition, a rectangular see-through window portion 23 is formed at a central portion thereof. Less than,
The outer plate 15 will be described in detail with reference to FIGS.

The outer plate 15 is made of, for example, an iron plate having a thickness t of 0.6 mm, and has a rectangular shape as a whole. The outer plate 15 has the see-through window 23 in the central portion as described above, and has a rising portion 24a rising on the back surface side of the door 13 and a flange-like portion 24 expanding outward on the outer peripheral portion.
(b) is integrally formed.

Of these, the see-through window 23 is formed by forming a large number of small holes 25 in a rectangular region in the center portion of the outer plate 15 so as to be aligned over the whole. Further, as described later, the frame portion 24 is formed by drawing. And in this embodiment,
The bending radius R of the corner formed by the see-through window 23 and the frame portion 24 is set to be approximately equal to the plate thickness t (R / t = 1), which is not more than twice the plate thickness t of the outer plate 15. ing.

Further, in this embodiment, as shown in FIG. 5, the formation pitch p of the small holes 25 is 1.6 mm, and the diameter d is 1.4 mm, so that the aperture ratio of the see-through window 23 (see FIG. The ratio of the area of the small holes 25 to the entire area of the window 23) is 69%. The small holes 25 allow the inside of the cooking chamber 11 to be visually recognized from the viewing window 22 while the function of the radio wave shield by the outer plate 15 is secured.

Next, a procedure for manufacturing the outer plate 15 configured as described above will be described. In the manufacture of the outer plate 15, a working process described below is performed by a press device (not shown). Here, a plate material 26 made of an iron plate having a predetermined thickness and a shape having a size slightly larger than the outer shape of the outer plate 15 is prepared in advance as a material of the outer plate 15.

In manufacturing the outer plate 15, first,
A perforation process is performed. In this perforating step, the plate 2
Small holes 25 are punched and formed in a rectangular area inside 6.
As described above, the small holes 25 are formed with the diameter dimension d of 1.4 mm and the pitch p of 1.6 mm, and thereby the see-through window 23 is formed.

When the perforating step is completed, a drawing step is performed. In this draw forming step, as shown in FIG. 2, the outer peripheral side of the see-through window 23 of the plate member 26 is drawn and formed in an upright shape, thereby forming the frame portion 24. Thereafter, unnecessary portions around the outer periphery of the plate material 26 are cut, and further, required bending, drilling, and the like are performed, thereby forming the outer plate 15.

In the above-described drawing step, especially when the diameter x of the small hole 25 is increased and the width x of the bridging portion is reduced as in the present embodiment, the drawing process is not performed. When a large tensile force acts on the see-through window 23, there is a possibility that the small hole 25 may be broken.

However, in the present embodiment, the bending radius R of the corner formed by the see-through window 23 and the frame portion 24 is extremely small, which is substantially equal to the thickness t of the outer plate 15. As described in the description, by forming the corners at the stage of the overhanging process with a small tensile force on the see-through window 23 in the early stage of the drawing process,
At the time of drawing, the outward tensile force acting on the plate material 26 is stopped by the corners, and is prevented from acting on the see-through window 23. Therefore, the small hole 2 of the see-through window 23
This eliminates the risk of breakage or deformation of the 5 formed portion.

As described above, according to the outer plate 15 of this embodiment,
Since the bending radius R of the corner formed by the see-through window 23 and the frame portion 24 is set to be approximately twice or less the plate thickness t, the frame portion 24 is formed.
The outward tensile force generated during the drawing process does not act on the see-through window 23.

Therefore, unlike the conventional one shown in FIG. 12, the diameter of the small hole 25 of the see-through window 23 is changed from 1.2 mm to 1.4 mm.
Even if it is increased to mm, it is possible to reliably prevent the see-through window portion 23 from being deformed or broken, and thus to greatly increase the aperture ratio from 50% to 69% as compared with the conventional case. As a result, the visibility of the see-through window 23 can be significantly improved.

FIG. 6 shows a punching metal 31 according to another embodiment of the present invention.
The projection 32 a is formed over the entire outer peripheral edge of the see-through window 32. Here, the see-through window 32
The bending radius R of the corner formed by the (projecting ridge 32a) and the frame 33 is, of course, not more than twice the plate thickness t, and the same effect as in the above embodiment can be obtained. You can do it.

The present invention is not limited to the above embodiment. For example, the dimensions such as the thickness t of the punched metal, the bending radius R of the corners, the pitch p of the small holes, the diameter d, etc. Various changes can be made within a range not departing from the gist, for example, it may be appropriately set according to.

[0039]

As is apparent from the above description, according to the punching metal of the present invention, a plurality of small holes are formed in the inner region of the plate to form a see-through window, and the see-through window is formed. In the case where the frame portion is formed upright by drawing on the outer peripheral portion of the portion, the bending radius of the corner formed by the see-through window portion and the frame portion is set to approximately twice or less the thickness of the plate material. Thus, it is possible to reliably prevent breakage of the see-through window at the time of forming by drawing, and to achieve an excellent practical effect that the visibility of the see-through window can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a punching metal showing one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a punching metal.

FIG. 3 is a perspective view of a microwave oven with an open door.

FIG. 4 is a partial cross-sectional plan view of a microwave oven door.

FIG. 5 is a partially enlarged front view of the see-through window.

FIG. 6 is a sectional view of a punching metal showing another embodiment of the present invention.

FIG. 7 is a view for explaining the operation of the present invention and is a view showing a range of stretching and drawing in a drawing forming step.

FIG. 8 is a perspective view of a plate for explaining a calculation formula of a required processing force.

FIG. 9 is a diagram showing a relationship between a bending radius and a required processing force.

FIG. 10 is a sectional view showing a state of movement of a bending point when a bending radius is large.

FIG. 11 is a diagram corresponding to FIG. 10 when the bending radius is small.

FIG. 12 is a diagram corresponding to FIG. 1 showing a conventional example.

FIG. 13 is a diagram corresponding to FIG. 2;

FIG. 14 is a diagram corresponding to FIG. 5;

FIG. 15 is a perspective view of a punching metal showing how the see-through window is broken.

[Explanation of symbols]

In the drawing, 12 is a microwave oven body, 13 is a door, 14 is a door body, 15 is an outer plate (punched metal), 16 is an inner plate,
7 is a sash, 18 is an outer barrier, 19 is an inner barrier, 22 is a viewing window, 23 and 32 are see-through windows, 24 and 33 are frame parts, 25 is a small hole, 26 is a plate, 31 is punching metal, 32a Indicates a ridge.

Claims (1)

(57) [Claims] 1. A structure in which a plurality of small holes are formed in an inner region of a plate material to form a see-through window portion, and a frame portion is formed upright by drawing on an outer peripheral portion of the see-through window portion. A punching metal, wherein a bending radius of a corner formed by the see-through window and the frame is set to approximately twice or less a thickness of the plate.