JP2586550B2 - How to bend a plastic sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for folding a plastic sheet.

(Prior Art) Conventionally, when bending a bent portion of a plastic sheet, a heating plate 5 provided with an electric heater 51 is pressed against a bent portion 13 of the plastic sheet 1 as shown in a sectional view of FIG. Thus, the bent portion is heated, the heating plate is removed, and then the plate is cooled to fix the bent shape.

(Problems to be Solved by the Invention) In the above-mentioned conventional method for bending a plastic sheet, the heating plate itself is thermally deformed, or another bending jig is deformed by receiving heat from the heating plate. It was difficult to bend with high precision. In addition, when the temperature of the heating plate is lowered or the air is blown to bend while cooling, the accuracy of the bending is increased, but the processing speed is extremely reduced. Furthermore, when bending is performed in several stages,
There has been a problem that the heat of the subsequent processing affects the bent portion at the front and lowers the accuracy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for precisely and rapidly bending a folded portion of a plastic sheet by heat-treating the folded portion by ultrasonic vibration.

(Means for Solving the Problems) The present invention has been made to achieve the above object, and the gist of the present invention is to fold a plastic sheet, heat the bent portion by ultrasonic vibration, and then cool. Wherein the heat treatment is performed on the bent portion.

Further, a bending groove having a V-shaped cross section is provided in advance in a bending portion of the plastic sheet, and the plastic sheet is bent from the bending groove. Heating for up to 3 seconds is effective in terms of bending accuracy.

As the plastic sheet 1, a hard sheet such as polyvinyl chloride, polypropylene, or the like can be used. Usually, the thickness can be about 0.1 to 1.0 mm.

[Operation] The operation will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an example of an apparatus for carrying out folding of a plastic sheet in the present invention, FIG. 2 is an enlarged sectional view of the vicinity of a folding groove of the plastic sheet to be folded, and FIG. FIG. 4 is a sectional view showing another embodiment of FIG. 3, FIG. 5 is an enlarged sectional view showing another embodiment of the bent groove portion, and FIG. 6 is a conventional device. FIG.

As described above, the plastic sheet is subjected to a heat treatment process of heating and cooling the bent portion of the plastic sheet by ultrasonic vibration, whereby the strain generated when the bent portion is bent is immediately reduced, and the elasticity of the plastic sheet causes the bent portion to return to the original angle. The so-called spring-back phenomenon that attempts to return to normal is prevented, and accurate bending can be performed.

In addition, if the bending groove 12 is formed in advance, it can be bent accurately and quickly along the bending groove, and the bent portion is heated for a very short time of 0.05 to 3 seconds above the softening temperature or melting point of the plastic sheet to bend. The part is distorted at high speed.

In the case where the bending groove 12 is formed by pressing the plastic sheet at a low temperature, the shape of the groove 12 is recovered by this heat treatment, the thickness is recovered, and the strength is improved.

Even if the bent groove 12 is formed by cutting, injection molding, high-temperature pressing, etc., and the shape is not easily recovered by heat, the walls abutting the bent groove 12 are fused and integrated, and in this case, the bent portion is reinforced. Shape fixation is ensured.

In the case where the bent groove is formed by injection molding or the like, if the ridges 14 are provided on both sides of the fold groove 12 as shown in FIG. 5, the ridges 14 are fused by heat treatment, so that the reinforcing effect is further enhanced. .

[Embodiment] In order to carry out the method for folding a plastic sheet of the present invention, for example, as shown in FIG. 1, a female mold 3 having a concave portion 31 corresponding to a shape to be folded, and almost fitting with this female mold A male mold 2 having a shape and fitted to the female mold 3 and capable of pressing the plastic sheet 1 is prepared. First, the plastic sheet 1 is cold-cut (20 ° C.) along the fold line 11 at a blade edge angle of 90 as shown in FIG.
Pressing is performed with a mold blade to form a bent groove 12. Next, as shown in FIG. 1, if the plastic sheet is placed on the female die 3 and pressed with the male die 2 in a cold state, the plastic sheet is accurately bent along the V-shaped apex of the bending groove 12. A hard polyvinyl chloride sheet having a thickness of 0.3 mm was used as the plastic sheet 1, and the bent groove 12 having a depth of up to half of the thickness was formed.

Next, the male mold 2 was removed, and the ultrasonic vibration horn 21 was placed on the plastic sheet as shown in FIG.
When the ultrasonic vibration horn 21 is fitted to the ultrasonic vibration horn 21 and the ultrasonic vibration is applied to the ultrasonic vibration horn 21, the bent portion 13 is heated to a temperature higher than the softening temperature in a very short time of about 0.1 second due to frictional heat generated by the ultrasonic energy, and softens. As shown in the figure, the shape of the groove 13 is reduced by the shape recovery, that is, the bent portion 13 recovers its thickness and is reinforced. When the ultrasonic vibration is further stopped, the bent portion 13 is quickly cooled to the temperature of the female mold and the ultrasonic vibration horn itself, and the bent shape is fixed.

Here, the cooling pipe 32 can be installed in the female die 3 or the harmonic vibration horn 21 can be air-cooled to make the cooling more efficient. Further, the ultrasonic vibration horn 21 can also be used as the male mold 2. Further, as shown in FIG. 3, unnecessary portions of the tip of the ultrasonic horn 21 (or the female concave portion 31) are shaved so that the bent portion 13 can be locally heated, so that the heating by the ultrasonic vibration is efficiently performed. You can also.

Also, as shown in FIG. 4, the folded plastic sheet is held in the male mold 2 and an ultrasonic vibration horn 21 is pressed from the outside of the bent portion 13 and heated by ultrasonic vibration to stop the ultrasonic wave as it is. Cooling.

(Effect of the Invention) According to the method for bending a plastic sheet of the present invention, the plastic sheet is bent, and the bent portion is heated and then cooled to heat-treat the bent portion. Can be bent to an accurate shape without recovery. In addition, since only the bent portion is quickly heated by the ultrasonic vibration and quickly cooled by stopping the ultrasonic vibration, there is no heat conduction in the portion other than the bent portion of the plastic sheet, and the plastic sheet immediately cools and solidifies, so accurate. Folding can be performed at high speed, and there is no adverse effect on other parts of the plastic sheet.

Since the ultrasonic vibration horn, the female mold and the like are not heated very much, there is no thermal deformation, accurate mold accuracy is maintained, and the plastic sheet does not melt and adhere.

Further, a bending groove is provided in advance in a portion of the plastic sheet to be bent, and the plastic sheet is bent from the bending groove, and the bent portion is heated at a temperature not lower than the softening temperature or melting point of the plastic sheet for 0.05 to 3 seconds. In this way, accurate bending can be performed, and the bent grooves return to the shape in the bent state and are fused to each other, so that the shape can be fixed securely.

And so on.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an apparatus for carrying out folding of a plastic sheet in the present invention, FIG. 2 is an enlarged sectional view of the vicinity of a folding groove of the plastic sheet to be folded, and FIG. FIG. 4 is a sectional view showing another embodiment of FIG. 3, FIG. 5 is an enlarged sectional view showing another embodiment of the bent groove portion, and FIG. 6 is a conventional device. FIG. 1 ... plastic sheet 11 ... bending line, 12 ... bending groove 13 ... bending part

Claims (2)

(57) [Claims] 1. A method for bending a plastic sheet, comprising bending a plastic sheet, heating the bent part by ultrasonic vibration, and then cooling the bent part. 2. A plastic sheet is provided with a bending groove in advance at a portion to be bent, and the plastic sheet is bent from the bending groove. The method for bending a plastic sheet according to claim 1, wherein heating is performed for 3 seconds.