JPH0310828A - Method for folding and working plastic sheet - Google Patents

Abstract

PURPOSE:To fold a plastic sheet into an accurate shape without recovering the angle of a folded part by resiliency of the plastic sheet by folding the plastic sheet and heating the folded part and thereafter cooling it. CONSTITUTION:When a plastic sheet 1 is placed on a female mold 2 and cold- pressed by a male mold 3, the plastic sheet is accurately folded along the folding line to obtain a folded body 11. Then when ultrasonic vibration is imparted to the male mold 3, the folded part 12 is regulated to the high temp. not lower than the softening temp. by the frictional heat due to ultrasonic energy in a short time and softened. At this time, the folded end part 13 of the plastic sheet is inhibited by an extrusion preventing member 4 from being moved. Therefore the plastic sheet is molded into an accurate shape. Furthermore when to the ultrasonic vibration is stopped, the folded part 12 is rapidly cooled to the temp. of the female mold 2 and the male mold 3 themselves and the folded shape is fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of folding a plastic sheet.

(Prior Art) Conventionally, when bending a bent portion of a plastic sheet, a heating plate equipped with an electric heater is pressed against the bent portion of the plastic sheet to heat the bent portion, and the heating plate is removed. It was then cooled down to fix the bent shape.

However, the heating plate itself undergoes thermal deformation, and other bending jigs receive heat from the heating plate and deform, making it difficult to bend with high precision.

In order to solve this problem, the present inventor has constructed a plastic sheet 1 with a male mold 3 and a female mold 2, as shown in a perspective view in FIG.
The inventors have invented a method in which the bent portion is heated by ultrasonic vibration while the bent portion is pressed between the two.

(Problems to be Solved by the Invention) In the above-mentioned bending method, errors may occur in the settings of the pressing force and gap between the male and female dies, and the ultrasonic heating time and the thickness of the plastic sheet to be bent may vary. If excessive heating and pressure are applied due to errors or other reasons, as shown in the perspective view in FIG. The problem was that there was no.

An object of the present invention is to provide a method of bending a plastic sheet while maintaining high precision at the bent end when heat treating the bent portion of the plastic sheet using ultrasonic vibration.

(Means for Solving the Problems) The present invention has been made to achieve the above object, and its gist is to fit a plastic sheet of a predetermined shape into a female mold having a recess. The plastic sheet is placed between the plastic sheet and the male mold, and the male mold is pushed into the female mold to bend the plastic sheet, and the bent portion is heat-treated by ultrasonic vibration while a protrusion prevention member is brought into contact with the bent end. This is a unique method for bending plastic sheets.

As the plastic sheet 1, a hard sheet made of polyvinyl chloride, polypropylene, etc. can be used. The thickness can usually be about 0.1 to i, on+i.

As mentioned above, the bending part of the plastic sheet is heated by ultrasonic vibration and then cooled through a heat treatment process, which quickly relieves the distortion that occurs when the plastic sheet is bent, and the elasticity of the plastic sheet allows the bending part to return to its original angle. This prevents the so-called springback phenomenon in which the sheet tries to return to its normal position, allowing for accurate bending.

Furthermore, even if the plastic sheet softens during heat treatment, the bent end portion is in contact with the extrusion prevention member, so that it is molded into that shape, and there is no risk of it extruding into an irregular shape.

This will be explained below with reference to the drawings.

FIG. 1 is a perspective view showing an example of an apparatus for folding a plastic sheet in the present invention, FIG. 2 is a front view, FIG. 3 is a side view, and FIG. 4 is a device for folding a plastic sheet. FIG. 5 is a side view, FIG. 6 is a cross-sectional front view of a plastic sheet folded by the method of the present invention, and FIG. 7 is a cross-sectional side view of another example of an apparatus for , FIG. 8 is a perspective view showing an example in which the folded body is used as a shutter for a disk cassette, FIG. 9 is a cross-sectional view showing a conventional device, and FIG. 10 is a plastic sheet bent by the device shown in FIG. FIG. 2 is a perspective view showing an example of a sheet.

In order to carry out the method of folding a plastic sheet of the present invention, for example, as shown in FIG. A male die 3 that can fit into the female die 2 and press the plastic sheet 1 is prepared.

In the example shown in FIGS. 1 to 3, both ends of the male mold 3 are made to protrude downward according to the width of the plastic sheet 1, and are used as the extrusion prevention member 4, and both ends of the bottom of the recessed part 21 of the female mold 2 are used as the extrusion prevention member 4. It is formed to a size that fits.

Portion 41 that comes into contact with the bent end of the extrusion prevention member 4
It is preferable to chamfer the edges.

First, a plastic sheet 1 is placed on a female die 2 as shown in FIG. 1, and then cold pressed with a male die 3.
The plastic sheet is folded precisely along the fold line to obtain the folded body 11 shown in FIG. 6.7.

Next, when ultrasonic vibration is applied to the male die 3, the bending portion 12 becomes heated to a temperature higher than the soft temperature in a very short time of about 0.1 seconds due to the frictional heat generated by the ultrasonic energy, and becomes soft.

At this time, the bent end portion 13 of the plastic sheet is
Since movement is prevented by the protrusion prevention member 4,
It is molded into the correct shape as shown in FIG. Further, when the ultrasonic vibration is stopped, the bent portion 12 is quickly cooled down to the temperature of the female die 2 and the male die 3 themselves, and the bent shape is fixed.

Although the male die 3 is used as an ultrasonic horn for top stripping, the two may be separate units.After removing the male die 3, a separate ultrasonic horn equipped with an extrusion prevention member is inserted and heat treatment is performed. You may go.

Further, the folded plastic sheet body 11 is held in the male die 3, and the female die 2 is held from the outside of the bent portion 12.
It is also possible to apply ultrasonic vibrations to heat the substrate, and then stop the ultrasonic waves and cool it down.

In the example shown in Fig. 4.5, the extrusion prevention member 4 is formed on both the female mold 2 and the male mold 3, and when both molds are fitted together, It is protruded so that it butts against you.

Furthermore, if a bending groove is formed in advance on the plastic sheet 1 to be folded, the plastic sheet 1 can be folded along the groove accurately and quickly.

In the method of the present invention, a cooling pipe 22 is installed in the female mold 2, and the male mold 3 is air-cooled, thereby making cooling efficient. Further, by cutting off an unnecessary portion of the tip of the male mold 3 (or the female mold recess 21), the bent portion 12 can be locally heated, thereby making heating by ultrasonic vibration more efficient.

In the case where the bending grooves are formed by pressing the plastic sheet at low temperatures, the heat treatment restores the shape of the grooves, restores the thickness, and improves the strength.

In addition, even if the bending groove is formed by cutting, injection molding, high temperature pressurization, etc. and is difficult to recover its shape due to heat, the walls that the bending groove abuts will be fused and integrated, and in this case too, the bent part will be reinforced and the shape will be fixed. becomes certain.

The present invention can be particularly suitably applied to manufacturing the shutter 111 for the disk cassette 5 shown in FIG. This shutter 111 requires very high precision, and if there is any protrusion on the bent end 113, there is a problem that chips are likely to be generated due to the operation, and errors may occur in the stopping position.

In the case of this shutter 111, an example of which will be described below, the width W1 of the opening shown as the folded body 11 in FIG. 7 is smaller than 1/2 of the width W2 of the bottom;
It is preferably greater than 0.

If the disk cassette is larger than 1/2, the shutter built into the disk cassette will expand during use or when the ambient temperature rises, and will tend to get caught when the disk cassette is set in a drive device.

On the other hand, if the opening is closed, the middle part 112 of the shutter will warp inward during storage, and when it is assembled into a disc cassette, it will easily catch on the window 51 of the disc cassette shown in FIG.

In order to obtain such a shutter, as shown in FIGS. 1 to 5, the folded portion 12 sandwiched between the male mold 2 and the male mold 3 is heat-treated by applying ultrasonic vibration, and can be easily manufactured. The reason for this is not clear, but during heat treatment,
It is presumed that this is because the inside of the folded part 12 in contact with the male mold 3 is heated particularly strongly, and the inside contracts during the cooling process, causing the folded part to fall inward.

(Effects of the Invention) The method for folding a plastic sheet of the present invention includes heat-treating the folded portion by folding the plastic sheet, heating the folded portion, and then cooling it. It can be bent into the correct shape without any damage. In addition, only the bent part is quickly heated by ultrasonic vibration, and cooled quickly by stopping the ultrasonic vibration, so there is no heat conduction to parts other than the folded part of the plastic sheet, and the plastic sheet quickly cools and solidifies, making it accurate. Bending can be done at high speed and does not adversely affect other parts of the plastic sheet.

Since the male mold, female mold, etc. themselves are not heated very much, there is no thermal deformation and accurate mold accuracy is maintained, and the plastic sheet does not melt and stick.

Furthermore, even if the plastic sheet softens during heat treatment, the bent end portion is in contact with the extrusion prevention member, so that it is molded into that shape, and there is no risk of it extruding into an irregular shape.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of an apparatus for folding a plastic sheet in the present invention, FIG. 2 is a front view, FIG. 3 is a side view, and FIG. 4 is a device for folding a plastic sheet. FIG. 5 is a side view, FIG. 6 is a cross-sectional front view of a plastic sheet folded by the method of the present invention, and FIG. 7 is a cross-sectional side view of another example of an apparatus for , FIG. 8 is a perspective view showing an example in which the folded body is used as a shutter for a disk cassette, FIG. 9 is a cross-sectional view showing a conventional device, and FIG. 10 is a plastic sheet bent by the device shown in FIG. FIG. 2 is a perspective view showing an example of a sheet. 1...Plastic sheet 12...Folded portion 13...Folded end 2...Female mold 21...Concave portion 3...・・Male type 4・・・・Protrusion prevention member

Claims (1)

[Claims] A plastic sheet of a predetermined shape is placed between a female mold having a recess and a male mold that fits into the female mold, and the male mold is pushed into the female mold to bend the plastic sheet and fold the bent end. A method for bending a plastic sheet, characterized by heat-treating the bent portion by ultrasonic vibration while abutting against an extrusion prevention member.