JPH1076570A - Vacuum molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the uneven section of a molded form by a method wherein a sheet is clamped by a clamp to heat and soften the same, subsequently, the clamp is moved to the central part of the sheet to loosen the sheet while mold is applied to the softened and loosened sheet to effect vacuum molding. SOLUTION: Four sides of peripheral part of a sheet 11 are clamped and fixed by the clamps 12, 12,... of a vacuum molding machine to heat the same to the softened condition of the same. The clamps 12, 12,... are moved toward the central part of the sheet 11 so as to be approached to each other whereby the sheet 11 is not extended and is loosened downwardly. The whole surface of the sheet 11 is contacted with the cavity surface 14a of a mold 14 and the inside of the mold 14 is evacuated under this condition whereby the sheet 11 is configured so as to have a surface configuration same as that engraved on the cavity surface 14a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vacuum-forming a thermoplastic resin sheet to obtain a molded product, and more particularly to a method for molding a large-sized and irregularly-shaped molded product with a uniform thickness with little uneven thickness. It is.

[0002]

2. Description of the Related Art FIG. 9 shows a preferred example of a molded product to be molded in the present invention. This molded product A has a three-dimensional shape in which a part of a ceiling and a wall of an elongated rectangular box is cut out, and a rectangular bottom plate 1 and two rectangular plates 2 are set up at right angles to both short sides of the bottom plate 1. It has an irregular shape composed of two side plates 2, 2 and two narrow overhanging plates 3, 3 projecting at right angles from both sides of the bottom plate 1 and the side plates 2, 2. Specific examples of such a shaped article include a front air spoiler and a bumper of a passenger car.

FIG. 10 to FIG. 12 show a method of forming such an irregularly shaped article by a conventional vacuum forming method. First, as shown in FIG.
m, polypropylene with a width of about 300 mm and a thickness of about 5 mm,
A rectangular thermoplastic resin sheet (hereinafter, abbreviated as a sheet) 4, such as a modified polyphenylene ether, is prepared, and four sides thereof are gripped and supported by clamps 5, 5,.

The clamps 5, 5,... Are movably attached to a vacuum forming machine (not shown). Next, the sheet 4 in this state is heated from one side or both sides by a heater (not shown) and is sufficiently softened. Next, as shown in FIG. 11, a vacuum forming die (hereinafter, abbreviated as a die) 6 provided below the softened sheet 4 is raised and clamps 5,
5 and the upper end of the mold 6 are brought into airtight contact.

[0005] The mold 6 is a female mold, in which the surface of the molded article is shaped and a number of vacuum holes having a diameter of about 0.5 to 1 mm are formed on the inner surface of the cavity. . These vacuum holes communicate with the cavity inside the mold 6, and the air in the cavity can be exhausted through these vacuum holes. Then, by exhausting air between the softened sheet 4 and the mold 6, the softened sheet 4 receives atmospheric pressure and is pressed against the cavity surface of the mold 6 to be formed.

Subsequently, when the sheet 4 has cooled, the mold 6 is lowered and the clamps 5, 5,.
Is obtained. Next, this molded product 7
Is cut and trimmed along the broken line in FIG. 12, and the clamp margins 8 and 8 are cut off to obtain a molded article having a target of an irregular shape shown in FIG.

However, in this vacuum forming method, the developed area of the molded product is essentially about five times larger than the area of the sheet 4, and the thickness of the four corners of the molded product is extremely small. It may be about 1/10 of the thickness of the first sheet 4. For this reason, the mechanical strength of the molded product is not sufficient, and a remarkable decrease in strength occurs at the four corners. In addition, since a considerable portion of the molded product is trimmed into a final product, there is a disadvantage that the material is wasted and the cost is increased.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent uneven thickness of a molded article obtained when a molded article having an irregular shape as shown in FIG. 9 is molded by a vacuum molding method. The object of the present invention is to prevent the corners from becoming thinner and to further reduce waste of material.

[0009]

The object of the present invention is to heat and soften a sheet by gripping the sheet at least at two opposing peripheral portions thereof, and then move the clamp toward a central portion of the sheet. This is essentially eliminated by sagging, applying a mold to the softened and sagged sheet, and vacuum forming. Also,
By forming the sheet in a rectangular shape and setting the two places to be gripped by the clamp to have both short sides, it is possible to manufacture the above-mentioned molded article having an irregular shape in particular by solving the above problems.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIGS. 1 to 5 show a first example of the vacuum forming method of the present invention in the order of steps, which is an embodiment of the third aspect. In these figures, reference numeral 11 denotes a sheet having a rectangular planar shape made of polypropylene, modified polyphenylene ether, polyethylene, ABS resin or the like. The sheet 11 is gripped and fixed at its four sides by clamps 12, 12... Of a vacuum forming machine (not shown), and is heated from both sides or one side by a heater (not shown) to be in a softened state.

When the heating is completed, the heaters are retracted, and as shown in FIG. 2, the clamps 12 holding the long sides are opened, and these are retracted. Next, the clamp 1 gripping both short sides of the sheet 11
2 and 12 are moved toward the center of the sheet 11 so as to approach each other. As for the movement of the clamps 12, 12, only one of them may be moved toward the central portion.

By the movement of the clamps 12, 12, as shown in FIG. 3, the sheet 11 in the softened state does not elongate from itself, but sags downward. The amount of sagging of the sheet 11 is determined by the expansion area ratio of the molded article, the distance between the initial clamp 12, 12 and l _0, the distance between the clamps 12 and 12 after the movement When l _1, l ₁ = it is desirable to 0.9～0.5L ₀ about the type of the sheet 11, the shape of the molded article, since it is also affected by the molding conditions, etc., by performing the previously preformed, determine the suitable value It is practical.

At this time, the sheet 1 in a softened and sagged state
As shown in FIG. 4, a box-shaped support frame 13 is provided below 1. The support frame 13 has a rectangular box shape without an upper surface and a bottom surface. Then, by lowering the clamps 12, 12 or raising the support frame 13, the clamp 1
2 and 12 are brought into contact with the upper end of the support frame 13.

Next, as shown in FIG. 5, the mold 14 descends from above the softened and loosened sheet 11 and is pressed against the sheet 11. The mold 14 is a male mold, and its convex outer surface is a cavity surface 14a, and a surface shape to be formed on a target molded product is engraved on the cavity surface. By pressing the mold 14 against the sheet 11, the sheet 11 slightly elongates and comes into contact with the cavity surface 14 a of the mold 14. It is sandwiched and bent upward, and this portion also comes into contact with the cavity surface 14 a of the mold 14. As a result, almost the entire surface of the sheet 11 becomes the cavity surface 1 of the mold 14.
4a.

By evacuating the interior of the mold 14 in this state, the sheet 11 is pressed against the cavity surface 14a of the mold 14 by atmospheric pressure, and the sheet 11 is
It is shaped into the surface shape engraved on a. Then, after the sheet 11 is cooled, the mold 14 is retracted upward and the molded product is taken out, so that a molded product B having an irregular shape as shown in FIG.
Is obtained, and a desired molded product can be obtained by cutting off the clamp margins 19, 19 thereof.

In such a molding method, the clamps 12 on the long sides of the sheet 11 after the heat softening are released, and the clamps 12 on the short sides are moved toward the center of the sheet 11 so that the sheet 11 can be moved. Since the mold 11 is applied to the sheet 11 after being slackened, and the sheet 11 is vacuum formed, the amount of elongation of the sheet 11 itself during vacuum forming does not increase so much. For this reason, uneven thickness of the molded product is reduced, and the thickness of the corner is not particularly reduced. In addition, since the trimming portion of the molded product is only a small portion with only the clamp margins 19, 19, the loss of the sheet 11 is small.

FIGS. 7 and 8 show a second example of the vacuum forming method of the present invention in the order of steps, and are an embodiment of the present invention. In this second example, the sheet 11 is heated and softened, the long side clamps 12 and 12 are released, and the short side clamps 12 and 12 are moved toward the center of the sheet 11, and the sheet 11 is heated. Are the same as in the first example.

In this example, with the sheet 11 softened and sagged, the mold 15 is arranged below the sheet 11 as shown in FIG. The mold 15 here is a female mold, and a surface shape to be formed into a molded product is formed on the cavity surface 15a of the concave inner surface. Next, as shown in FIG. 8, a pressing plate 16 for pressing the sheet 11 against the mold 15 and bending the long side portion of the sheet 11 upward is located above the sheet 11.

The pressing plate 16 has a shape substantially similar to the shape of a molded product, and has a U-shaped pressing portion 17 having both sides in the longitudinal direction of a rectangular plate bent upward. Folded piece 1 formed by bending both side edges inward
8 and 18, the long side of the sheet 11 is bent upward by sandwiching the bent pieces 18 and 18 and the cavity surface 15a of the mold 15 so as to be attached to the cavity surface 15a of the mold 15. ing.

Next, the holding plate 16 is lowered, and the sheet 11 in a softened and sagged state is pushed down and pressed against the mold 15, and in this state, the inside of the mold 15 is evacuated and the sheet 11 is sucked into the cavity surface 15a. Then, the surface shape of the cavity surface 15a is shaped. After the sheet 11 has cooled, the holding plate 16 is retracted upward to take out the molded product B having the shape shown in FIG.
The desired product can be obtained by cutting off.

According to the second molding method, similarly to the previous example, the corners of the molded product are not thinned, the trimming amount is reduced, and the material loss is reduced.

In the first and second molding examples,
Although it is suitable for manufacturing the irregularly shaped article shown in FIG. 9 using the rectangular sheet 11, the present invention is not limited to these examples, and the sheet has a square shape as described in claim 1. , A circle, an ellipse, a polygon, etc., and the molded product is not limited to the one shown in FIG. For example, a circular sheet is clamped at four points on its circumference at equal intervals, heated and softened, and the four clamps are simultaneously moved to the central part of the sheet to sink the central part of the circular sheet into a bowl shape. In this state, the hollow cylindrical deep drawing female mold is applied from below the sheet in this state, and vacuum forming is performed to obtain a hollow cylindrical deep drawn product with less uneven thickness. At this time, a plug assistant method of lowering the plug from above the seat may be used together.

Hereinafter, specific examples will be described. (Example) Length 2370 mm, width 260 mm, thickness 5 m
The m-shaped polypropylene sheet having the shape and the dimensions shown in FIG. As a result, the thickness of the four corners of the molded product is 2.0 to
The thickness was 2.6 mm, the average thickness was 2.4 to 2.6 mm, and the thickness deviation was extremely small.

(Comparative example) Length 1830 mm, width 260 m
Using a polypropylene sheet having a thickness of 5 mm and a thickness of 5 mm, a similar shaped article was produced by a conventional method. As a result, the thickness of the four corners of the molded product was 0.5 to 0.7 mm, and the average thickness was 1.0 to 1.1 mm.

[0025]

As described above, according to the vacuum forming method of the present invention, when forming a deep drawn product having a large development area, uneven thickness is reduced, and particularly, the thickness of the corner of the formed product is reduced. Can be increased, and a molded product having high mechanical strength can be obtained. Further, when a rectangular sheet is used, a high-strength deformed product suitable for an air spoiler or the like can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first example of a vacuum forming method of the present invention.

FIG. 2 is a perspective view showing a first example of the vacuum forming method of the present invention.

FIG. 3 is a perspective view showing a first example of the vacuum forming method of the present invention.

FIG. 4 is a perspective view showing a first example of the vacuum forming method of the present invention.

FIG. 5 is a perspective view showing a first example of the vacuum forming method of the present invention.

FIG. 6 is a perspective view showing a molded product obtained by the first example of the vacuum molding method of the present invention.

FIG. 7 is a perspective view showing a second example of the vacuum forming method of the present invention.

FIG. 8 is a perspective view showing a second example of the vacuum forming method of the present invention.

FIG. 9 is a perspective view showing an example of a molded product to be molded by the vacuum molding method of the present invention.

FIG. 10 is a perspective view showing an example of a conventional vacuum forming method.

FIG. 11 is a perspective view showing an example of a conventional vacuum forming method.

FIG. 12 is a perspective view showing an example of a conventional vacuum forming method.

[Explanation of symbols]

 11 Sheet 12 Clamp 14, 15 Vacuum forming mold

Claims (4)

[Claims] 1. A thermoplastic resin sheet is gripped by a clamp at at least two opposing peripheral portions thereof to be softened by heating, and then the clamp is moved toward a central portion of the sheet to thereby remove the sheet. A vacuum forming method, wherein a vacuum forming die is applied to the softened and sagged sheet to form a vacuum. 2. The vacuum forming method according to claim 1, wherein the planar shape of the thermoplastic resin sheet is rectangular, and the two places gripped by the clamp are both short sides. 3. The vacuum forming method according to claim 1, wherein the vacuum forming die is a male type, and is applied from above the softened and sagged sheet. 4. The vacuum forming method according to claim 1, wherein the vacuum forming die is a female mold, and is applied to the sheet from below the softened and sagged sheet.