JPS6211654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermoforming method and a thermoforming apparatus for auxiliary heating of a smooth plastic sheet to a moldable temperature and performing vacuum or pressure forming.

Generally, in this type of thermoforming method, the entire area of the heated sheet that is supplied to the molding machine does not become the product; for example, gripping allowance for conveyance, mating surface of the mold, etc. are necessary. , these parts are leftover materials (hereinafter referred to as scrap).

1 to 3 show examples of products molded by conventional thermoforming methods. For example, the first
In a box-shaped product P as shown in the figure, the gripping margin and the peripheral edge S, which is the mating surface of the mold, are scrapped.
In this case, a relatively small amount of scrap is required compared to the product P. However, as shown in Figs. 2 and 3, bridge-shaped products P _a , P _b
In the case of obtaining the above, in addition to the scrap of the peripheral portions S _a and S _b , the side portions S _c and S _d are also scrapped. Therefore, in such cases, there is a disadvantage that the scraps account for more than half of the product.

However, in conventional thermoforming of general plastic sheets to obtain the above-mentioned products, a molding machine as shown in FIGS. 4 and 5 is used. That is, in FIGS. 4 and 5, reference number 10 indicates a mold, and this mold 10 is composed of an upper vacuum mold 12 and a lower pressure box 14,
The vacuum mold 12 is held on an upper table 16, and the compressed air box 14 is held on a lower table 18, so that they can be opened and closed in the vertical direction. A preheated plastic sheet 20 is supplied in a predetermined direction to a joining line (parting line) A of the mold 10 configured as described above. in this case,
Longitudinal side edges 20 of plastic sheet 20
a, 20b as a pair of chain conveyors 22a, 2
It is held by a large number of clips 24a, 24b fixed to 2b and is transported intermittently and continuously to a predetermined position (see FIG. 5). In this manner, when the plastic sheet 20 is supplied to the joining line A of the mold 10, the mold 10 approaches from above and below, as shown in FIG. 4, and enters the mold closed state. The vacuum mold 12 is a female mold that has an inner surface in the shape of a product and has a large number of suction holes 26 on the inner surface to perform a vacuum suction action. Further, the compressed air box 14 is a male mold whose outer peripheral portion 28 is connected to the vacuum mold 12 and has the same plane with the plastic sheet 20 sandwiched therebetween, so that compressed air can be pressed.

Therefore, in the mold 10, the preheated plastic sheet 20 is molded into a predetermined shape by the pressing action of compressed air and the suction action of a vacuum, with the entire peripheral edge thereof being clamped. In this manner, the conventional molding machine molds the products P, P _a , and P _b shown in FIGS. 1 to 3 described above.

In the method of thermoforming plastic sheets using the conventional molding machine described above, when molding products P _a and P _b as shown in FIGS. Sometimes, in order to prevent the sheet in the mold from tearing and to allow the product to be easily removed from the mold, it cannot be made vertical, and a draft angle of, for example, 3 to 10 degrees is required. For this reason, as the height of the product increases, the proportion occupied by the side wall surface increases, increasing the incidence of scrap and lowering the yield. Therefore, the plan view of the sheet required to obtain the product P shown in FIG. 3 is as shown in FIG. ₁ and the part S ₂ that is held between the molds
This results in a side surface _S3 having a draft angle. Moreover,
The side surface _S3 having the draft angle increases as the product P becomes medium and tall.

As mentioned above, in order to overcome the problem of the plastic sheet thermoforming method that generates a large amount of scrap, for example, the width of the sheet is set approximately equal to the width of the product, and when the sheet is fed and transported, both longitudinal ends of the sheet are A molding method has been proposed in which the holding member holding the sheet is released from its holding state during mold molding, and the sheet is displaced integrally with the mold, thereby reducing the occurrence of scrap. In addition, in the above-mentioned forming method, it has been proposed to improve the formability by aligning the sheet holding member in advance and then releasing the holding state of the sheet, thereby allowing the sheet to slacken to fit the mold. ing.

However, the previously proposed molding method simply releases the holding state of both side edges of the plastic sheet when the mold is clamped, so if the mold is a drawing type, for example, the molding process is relatively slow. However, when using a mold consisting of a vacuum mold and a compression box as shown in Figures 4 and 5, for example, the position of the sheet relative to the mold surface may deviate, causing air leakage, etc. However, there is a drawback that the defective rate of the product increases. In addition, in this case, the sheet can move freely in the transport direction, so when the mold is closed, the sheet before molding is held by the clips, so there is no problem, but the sheet after molding is pulled back to the mold side. ,
If the linkage with the trimming machine is not sufficiently considered, there will be many problems such as an increase in the number of defective products as described above.

Therefore, as a result of various studies to overcome all the problems of the conventional molding methods mentioned above, the present inventors developed an upper vacuum mold and a lower pressure box with parting lines along both sides of the product. In the mold consisting of, a sheet locking tool is provided at the edge of both side plates forming the parting line of the compressed air box, and the plastic sheet is supplied and transferred to the mold by holding both side edges with clips, When the sheet is moved upward from the conveying surface by the compressed air box, the holding state of the clip is automatically released at the same time as the sheet locking device locks both side edges of the sheet. It has been found that mold clamping can be achieved while the parts are always held, and that the above problems can be solved at once.

Therefore, an object of the present invention is to provide a method for thermoforming a plastic sheet to obtain a medium-high three-dimensional product from which at least one side is removed, using a mold with parting lines set along both side edges of the product, When the mold is clamped, the edges of both side plates of one of the molds, which have a parting line that is displaced from the conveyance surface of the sheet, are held at the edges of both sides of the sheet, and the holding state of the conveyance clips is automatically released, and the molding is carried out. An object of the present invention is to provide a method and apparatus for thermoforming plastic sheets with improved performance.

In order to achieve the above object, the first invention involves preheating a plastic sheet while holding both side edges thereof with clips fixed to a chain conveyor, and transferring the plastic sheet to a forming mold that is opened and closed by moving vertically. A method for thermoforming a product using a mold consisting of a female mold and a pressure box having parting lines along both side edges of the product to be thermoformed,
When clamping the mold, both edges of the plastic sheet are locked to locking tools provided on the female mold or the air pressure box of the mold, which has a parting line located above the conveying surface of the plastic sheet;
At the same time, the holding state of the clips holding both side edges of the plastic sheet located above the conveying surface is released.

In the above-mentioned thermoforming method, as the clip for holding the plastic sheet, a clip holder is fixed to a chain conveyor, and a clip piece that elastically holds or releases the plastic sheet is pivotally attached to the clip holder. It is preferable that the holding state is automatically released by displacement of the plastic sheet.

A second invention provides an apparatus for carrying out the thermoforming method, which includes a chain conveyor for conveying a plastic sheet, a clip fixed to the chain conveyor for holding both side edges of the plastic sheet, and a clip attached to the upper side of the plastic sheet. The plastic sheet is equipped with a female mold that performs vacuum suction, a pressure box that applies compressed air to the lower surface of the plastic sheet, and a heating device that heats the plastic sheet prior to mold clamping using the female mold and the pressure box. The female mold and the air pressure box are configured to have a parting line located above the conveying surface of the plastic sheet along both side edges of the product to be thermoformed, and the parting line is formed on both sides of the female mold or air pressure box, respectively. The invention is characterized in that a sheet locking device for locking the plastic sheet is provided protruding along the running line.

The seat anchor described above may be comprised of a plurality of pins. It can also be constructed of serrated pieces.

Next, an embodiment of the method for thermoforming a plastic sheet according to the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 7 to 9 show one embodiment of a mold and a means for transporting a plastic sheet of a molding apparatus for carrying out the thermoforming method of the present invention.
For convenience of explanation, the same reference numerals will be used to describe the same components as those of the molding machine shown in FIGS. 4 and 5. That is, the mold 10 and its peripheral technical means for carrying out the thermoforming method of the present invention are basically the same as the conventional mold shown in FIGS. 4 and 5. The mold 10 is used to mold a medium-high bridge-shaped product, and is composed of an upper vacuum mold 12 and a lower pressure box 14. The vacuum mold 12 is held on an upper table 16, and the pressure box 14 is They are held on a table 18 and are configured to be openable and closable in the vertical direction.

However, in this embodiment, both sides of the vacuum mold 12 and the pressure box 14 have shapes that are compatible with a medium-high bridge-shaped product. That is, in this embodiment, the parting line A matches the side shape of the product. Note that the vacuum mold 12 is
The pressurized air box 14 is a female mold having an inner surface in the shape of the product and has a large number of suction holes 26 on the inner surface to perform a vacuum suction action, and the pressurized air box 14 is joined to the vacuum mold 12 at its outer peripheral portion 28. It has the same structure as the conventional one in that it is a male type with a plastic sheet 20 held between them and compressed air is applied. Further, a preheated plastic sheet 20 is placed in the mold 10, and its longitudinal side edges 20a, 20b are connected to a pair of chain conveyors 2.
A large number of clips 24a fixed to 2a, 22b,
It is exactly the same as the conventional one in that it is held by 24b and transported intermittently and continuously to a predetermined position.
However, in this embodiment, as shown in FIGS. 7 to 9, when clamping the mold, the parting line A of the front and rear ends of the mold 10 is aligned with the conveying surface of the sheet 20. Accordingly, the sheet 20 in this portion is held at both side edges 20a, 20b with clips 24a, 24b (see FIG. 8). On the other hand, the sheet 2 at a portion along the parting line A that is displaced above the conveying surface of the sheet 20
0, clip 2 its both side edges 20a, 20b.
4a and 24b are released from the hold (see Fig. 9).

In this way, in this embodiment, the sheet 20
When displacing the side edges 20a, 20b of the sheet 20 to the parting line A that matches the side shape of the product, it is necessary to release the holding by the clips 24a, 24b, but in this case, the position of the sheet 20 is prevented from shifting. This is extremely important for thermoforming. Therefore, in the present invention, both side plates 14 of the compressed air box 14 are
A feature is that a sheet locking device 30 made of a pin or the like is appropriately protruded from the edge portion forming the parting line A of the sheets a and 14b. That is, as shown in FIGS. 10 and 11, the seat locking tool 30 is capable of attaching a large number of pins to both side plates 14 of the compressed air box 14.
a, 14b (see FIGS. 8 and 9) protrudingly spaced apart from each other by a predetermined distance. Alternatively, a seat catch 30 consisting of serrations may be utilized, as shown in FIG.

As mentioned above, one side of the mold 10 (pressure box 1
4) When a sheet locking tool 30 is provided to lock both side edges 20a and 20b of the sheet 20 when mold-clamping, at the same time, the clips that have been holding both side edges 20a and 20b of the sheet 20 are removed. 24a,
24b must be released in a timely manner. Therefore, in the present invention, FIGS.
A clip with an automatic release mechanism as shown in the figure can be preferably used. That is, the first
The clip 24 shown in Figure 3 is attached to the chain conveyor 2.
A clip receiver 32 is fixed to the clip receiver 2, and a clip piece 38 is attached to the clip receiver 32 via a support rod 36 which is elastically and pivotably pivoted under the action of a spring 34. A slider 40 is provided at the upper end of the support rod 36, and an opening/closing operation rod 42 for tilting the slider 40 against the elasticity of the spring 34 is placed in contact with the slider 40. The clip 24 configured in this manner can be clamped by the clip piece 38 by moving the opening/closing operation rod 42 in the direction of the arrow in synchronization with the upward displacement of the compressed air box 14 when the mold 10 is clamped. The held state of the sheet 20 can be released.

Further, the clip 24 shown in FIG. 14 includes a clip receiver 44 fixed to the chain conveyor 22, and a clip piece 46 can be elastically and swung left and right with respect to the clip receiver 44 under the action of a spring 48. It is based on The clip 24 configured in this manner can move the pressurized air box 14 upwardly when the mold 10 is clamped.
By forcibly pushing up the seat 20 while locking the side edge of the seat 20 through the seat locking device 30 provided in the seat, the clip piece 46 swings to the left against the elasticity of the spring 48. However, as a result, the holding state of the sheet 20 held by the clip receiver 44 and the clip piece 46 can be automatically released without any external operation.

A plastic sheet 20 is thermoformed in the same manner as in the conventional method using a molding machine having the above-described configuration, to easily produce a product similar to that shown in FIG. 3 (according to the present invention, both sides are removed). can be obtained. Particularly, the thermoforming method of the present invention allows product NP
FIG. 15 shows a plan view of the required sheet for obtaining the above-mentioned sheet in comparison with that of the conventional product shown in FIG. As is clear from FIG. 15, according to the thermoforming method of the present invention, the product NP (shaded area)
On the other hand, the part to be scrapped is clip 24.
It consists only of a holding part S ₁ and a part S ₂ which is held by the mold 10, and the side part having a draft angle is excluded. Incidentally, as a result of trial production of the product NP shown in FIG. 15, the yield rate of the product NP for the required sheet was approximately 74%. Incidentally, according to the conventional method shown in FIG. 6, the yield rate of product P was about 56%, and according to the thermoforming method of the present invention, the yield rate could be improved by about 18%.

As is clear from the examples described above, according to the method of thermoforming a plastic sheet according to the present invention,
The parting line formed by the mold can be matched to the shape of the side edges of the product, and when the mold is clamped, both side edges of the sheet held by the clips can be locked with the mold and the clips can be held at the same time. By releasing the condition, thermoforming of plastic sheets with excellent workability and economy can be achieved. Therefore, according to the thermoforming method of the present invention, the product is not limited to the above-mentioned simple symmetrical bridge-shaped product, but can also be applied to vehicle fenders (FIG. 16a), for example, as shown in FIGS. 16a to 16e. , vehicle trunk lining (Fig. 16b), single-opening product (Fig. 16c), four-way opening product (Fig. 16d), and double-plying product (Fig. 16d).
It can be suitably applied to molding such as in Figure 6 e).

Further, the thermoforming method of the present invention can be applied not only to in-line molding or combination molding in which plastic sheets are continuously supplied, but also to off-line molding in which plastic sheets are cut into pieces.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

Figures 1 to 3 are perspective views showing conventional thermoformed products made from plastic sheets, Figure 4 is an explanatory side view of a mold, which is the main part of a conventional thermoforming machine, and FIG. 5 is a cross-sectional view of the mold shown in FIG. 4, FIG. 6 is an explanatory plan view of a sheet required to obtain the thermoformed product shown in FIG. 3, and FIG. FIG. 8 is a right side view of the mold shown in FIG. 7, FIG. 9 is a sectional view of the mold shown in FIG. 8, and FIGS. 10 to 12. 13 is an explanatory diagram showing different embodiments of the sheet locking device provided in the mold used in carrying out the method of the present invention, and FIG. An explanatory diagram showing one embodiment of the release mechanism, FIG. 14 is an explanatory diagram showing another embodiment of the release mechanism for the sheet holding clip, and FIG. 15 is a product similar to the product shown in FIG. 3 made by the thermoforming method of the present invention. 16A to 16E are perspective views of products suitably obtained by the thermoforming method of the present invention. 10... Molding mold, 12... Vacuum mold, 14... Pressure box, 16... Upper table, 18... Lower table, 20... Plastic sheet, 22... Chain conveyor, 24... Clip, 26... Suction hole, 28... Outer periphery, 30... Seat locking tool, 3
2...Clip holder, 34...Spring, 36...Support rod, 38...Clip piece, 40...Slider, 42
...Opening/closing operation rod, 44...Clip holder, 46...
Clip piece, 48...spring.

Claims (1)

[Scope of Claims] 1. A plastic sheet is heated in advance while holding both side edges thereof with clips fixed to a chain conveyor, and the product is thermoformed by transferring it to a mold that opens and closes by moving vertically. In this method, a mold consisting of a female mold and a pressure box having parting lines along both side edges of the product to be thermoformed is used, and the mold is positioned above the conveying surface of the plastic sheet when the mold is clamped. Both side edges of the plastic sheet are locked to locking tools provided on the female die of the mold or the pressure box having a parting line, and at the same time, both side edges of the plastic sheet located above the conveyance surface are locked. A method for thermoforming a plastic sheet, characterized by releasing the holding state of a holding clip. 2. As a clip to hold the plastic sheet, a clip holder is fixed to the chain conveyor, and a clip piece that elastically holds or releases the plastic sheet is pivotally attached to the clip holder, and the plastic sheet is held by displacement of the plastic sheet. 2. A method of thermoforming a plastic sheet according to claim 1, wherein the method is configured to automatically release the condition. 3 A chain conveyor that conveys a plastic sheet, a clip fixed to the chain conveyor that holds both side edges of the plastic sheet, a female mold that performs vacuum suction on the upper surface of the plastic sheet, and a compression mold that acts on the lower surface of the plastic sheet. Equipped with a pressure box that applies air pressure, and a heating device that heats the plastic sheet prior to mold clamping with these female molds and the pressure box,
The female mold and the air pressure box are configured to have parting lines located above the conveying surface of the plastic sheet along both side edges of the product to be thermoformed, and the female mold and the air pressure box have parting lines located above the conveying surface of the plastic sheet, respectively. A plastic sheet thermoforming device characterized by having a sheet locking tool protruding along a parting line to lock the plastic sheet. 4. The apparatus for thermoforming plastic sheets according to claim 3, wherein the sheet fastening device comprises a plurality of pins or serrations.