JPH10217326A - Device and method for vacuum molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum molding device for molding a large and irregular-shaped product and a vacuum molding method using the device for molding with good yield without generating the distortion caused by the bridge phenomenon or residual stress. SOLUTION: In a vacuum molding method, clamps 11a and 11b respectively holding two sides Se, Se facing each other of a thermoplastic resin sheet S are provided, and a central section Sc of the sheet S held by the clamps and heat-softened is hung down and at least one of the clamps 11a and 11b are moved horizontally toward the sheet central section Sc so that the central section of the sheet is placed on a vacuum molding die 20 below. A vacuum molding device 10 provided with servo mechanisms 12a and 12b driven by servo motors 13a and 13b is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum forming apparatus and a vacuum forming method for manufacturing a molded product by vacuum forming a thermoplastic resin sheet. The present invention relates to a vacuum forming apparatus capable of forming at a high yield without generating distortion due to heat or residual stress, and a vacuum forming method using the same.

[0002]

2. Description of the Related Art In many cases, various molded products such as bumpers, aero parts, and interior materials of automobiles are manufactured by a vacuum molding method using a thermoplastic resin sheet. Vacuum forming method is to cover the heat-softened thermoplastic resin sheet on the vacuum forming die, press the sheet against the die by giving a pressure difference between the front and back, and release from the die after cooling and solidification. This is a method for obtaining molded articles.

According to the vacuum forming method, a molded article can be obtained by a relatively simple mold and molding apparatus, so that a large-sized and / or odd-shaped molded article can be produced at a low cost, and a relatively small quantity can be produced. Also has the advantage of being economical.

FIGS. 3 to 6 show an example of a conventional vacuum forming method used for producing a large molded product. This conventional example is for molding a bumper member A having the shape shown in FIG. This bumper member 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 is vertically set on a rectangular bottom plate 1 and two opposite short sides of the bottom plate 1 facing each other. It has an irregular shape comprising two side plates 2 and 2 and two narrow width extension plates 3 and 3 projecting at right angles from both sides of the bottom plate 1 and the side plates 2 and 2.

[0005] 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 “sheet”) 4 made of modified polyphenylene ether or the like is prepared, and the four sides are gripped from above and below by frame-shaped clamps 5 and 5 and supported in a loosely stretched state. I do. The clamps 5, 5 are attached to a vacuum forming machine (not shown). Then, the sheet 4 in this state is heated from one side or both sides by a heater (not shown), and is thermally softened as necessary and sufficiently.

Next, as shown in FIG. 5, a vacuum forming die (hereinafter, referred to as “below”) provided below the heat-softened sheet 4.
Abbreviated as "mold". 6.) 6 is raised to bring the lower clamp 5 and the upper end of the mold 6 into airtight contact. This mold 6
Is a female type, in which the surface of the molded article is shaped and a number of vacuum holes having a diameter of about 0.5 mm to 1 mm are formed on the inner surface of the concave portion. These vacuum holes communicate with the cavity inside the mold 6, and the air in the recess can be exhausted through these vacuum holes. Due to this exhaust, a pressure difference is generated between the front and back of the heat softening sheet 4, and the heat softening sheet 4 is pressed against the concave surface of the mold 6 and formed.

After cooling and solidifying the sheet 4 on the mold, the mold 6 is lowered and the clamps 5 and 5 are removed.
As shown in FIG. 6, a box-shaped molded product 7 having a clamp margin 8 is obtained. The molded product 7 is cut and trimmed along the broken line in FIG. 6 and the clamp margin 8 is cut off to obtain the target large-sized molded product (bumper member A) shown in FIG.

[0008]

However, in the conventional vacuum forming method, when a molded product having the above-mentioned dimensions and shape is formed, the developed area of the molded product is increased to about 5 times the area of the sheet 4, so that the molded product is particularly difficult. The thickness of the four corners is very thin,
In some cases, the thickness may be about 1/10 of the thickness of the original 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.

Further, in the conventional vacuum forming method, when molding a molded article having an undercut (uneven portion) having a complicated shape, the under pressure is generated due to the disorder of the balance between the tension of the heat-softened sheet and the suction force of the mold. The heat-softened sheet does not adhere to the cut mold surface, causing a so-called bridging phenomenon. Also, at the corners of the undercut, distortion due to residual stress occurs and the strength of the molded product is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a large-sized molded article which is free from distortion due to a bridging phenomenon and residual stress, and is made of a material. It is an object of the present invention to provide a vacuum forming apparatus and a vacuum forming method capable of forming at a high yield.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a clamp for gripping two opposing sides of a sheet, and a central portion of a sheet gripped and thermally softened by these clamps. And a servo mechanism for horizontally moving at least one of the clamps toward a central portion of the sheet in response to a command so that the mold is placed in a mold disposed below. . In this vacuum forming apparatus, it is preferable that the servo mechanism is driven by a servomotor.

According to the present invention, two opposite sides of the sheet are gripped by the clamps and softened by heating using the vacuum forming apparatus, and then the servo mechanism is driven to drive at least one of the clamps. Is horizontally moved in a controlled mode toward the central portion of the sheet, the central portion of the sheet is hung down, the hung sheet is laid on a mold disposed below, and vacuum forming is performed. provide.

[0013]

Embodiments of the present invention will be described below with reference to the drawings by way of examples. 1 and 2, reference numeral 10 indicates the entire vacuum forming apparatus (hereinafter, referred to as "the present apparatus") of this embodiment.

The apparatus 10 includes two opposite side portions Se, Se of a sheet (thermoplastic resin sheet) S used for vacuum forming.
And the central portion Sc of the sheet S gripped and thermally softened by the clamps 11a and 11b is suspended as shown in FIG. And a servo mechanism 12a, 12b for horizontally moving at least one of the clamps 11a, 11b toward the center of the sheet S in response to a command.

The servo mechanisms 12a and 12b include servo motors 13a and 13b whose rotation direction, rotation amount and speed are controlled by an external control program, respectively.
Screw rod 14 connected to clamps 11a, 11b
a and 14b, and converters 15a and 15b for converting the rotation mode of the servo motors 13a and 13b into a mode of horizontal movement of the threaded rods 14a and 14b. S is fixed to bases 16a and 16b arranged with a gap over which S is stretched.

The clamps 11a and 11b can be horizontally moved back and forth on the bases 16a and 16b toward the center Sc of the sheet S by being driven by the threaded rods 14a and 14b. Clamps 11a and 11b are seat S
When advancing on the base toward the central portion Sc of the base 16, its tip projects inward beyond the opposing ends of the bases 16 a and 16 b.

The mold 20 shown in FIG. 2 is for vacuum-forming the molded product (bumper member A) shown in FIG. 3, and includes a mold member 22 fixed to a mold base 21 which can move up and down.
Consists of The mold member 22 is a female mold. Although not shown, the surface of the molded product is formed on the inner surface of the concave portion, and a large number of vacuum holes having a diameter of about 0.5 mm to 1 mm are formed. . These vacuum holes communicate with a cavity 23 below the mold member 22, and when the cavity 23 is evacuated, the air in the concave portion of the mold member 22 is exhausted through the vacuum hole. I have.

The following operation is performed to manufacture a molded product using the present apparatus 10 and the mold 20. First, two opposing sides S of a sheet S cut into a rectangular shape as shown in FIG.
e and Se are gripped by the clamps 11a and 11b, respectively. Next, the servo mechanisms 12a and 12b are separately or simultaneously operated based on an external command, and the clamps 11a and 11b are horizontally moved outward to gently stretch the sheet S, and the central portion of the sheet is moved. Sc
Is adjusted to be located substantially at the center of the gap between the bases 16a and 16b.

Next, the sheet S is heated from both sides or one side thereof by a heater (not shown) to be in a thermally softened state. As a result, the sheet S is clamped by the clamps 11a and 11b.
While the both terminals are supported, and the terminal is suspended by its own weight with the central portion Sc as the bottom point. At this time, the mold 20 is raised to an appropriate position, and the servo mechanisms 12a and 12b are operated in controlled modes, respectively, so that the clamps 11a and 11b are operated.
To the inside of each to the appropriate position,
The sheet S hangs down and is placed on the molding surface of the mold 20.

When air is sucked through the cavity 23 of the mold in this state, the thermally softened sheet S is sucked and adheres to the mold surface. Next, the sheet S on the mold is cooled and solidified, the clamps 11a and 11b are loosened, and the sheet S is released from the mold.
Is obtained.

If the apparatus 10 is vacuum formed by the above-described method, the amount of droop of the thermally softened sheet S and the relative position with respect to the mold 20 are appropriately adjusted by mode control of the servo mechanisms 12a and 12b. Therefore, a sheet S having a necessary and sufficient area corresponding to the development area of the mold surface can be supplied on the mold surface. Even if there is an undercut (uneven portion) in the shape, the sheet S having an area corresponding to the portion is supplied, so that a so-called bridge phenomenon or residual distortion is prevented from occurring. As a result, it is possible to manufacture a molded product with less uneven thickness, uniform strength, and high precision that faithfully reproduces the shape of the mold surface with a high yield of the material.

In the vacuum forming method of the above embodiment, the control mode relating to the horizontal movement of the clamps 11a and 11b is as follows.
It is determined by the moving direction, the moving amount, the moving speed and the moving timing of each clamp. This control mode is determined in advance by experiments in consideration of the requirements of the mold side, such as the shape and dimensions of the mold 20, the development area, the presence or absence of local undercut, and the thickness, area, and physical properties of the sheet to be used. Is input to the servomotors 13a and 13b as a command program from a computer or the like, and the clamps 11a and 11b are controlled by the rotation of the servomotors.

In order to manufacture a molded product having various shapes and dimensions such as deep drawing, shallow drawing, and undercut with less bridging phenomenon and residual strain, less uneven thickness and improved yield, each clamp 11a is required. , 11b
Operate accurately in accordance with the timing, direction, speed, and movement amount programmed for each mold in advance, be able to change the movement speed quickly, start and stop instantly, and have the correct position. , Etc. are required. Although this requirement can be achieved to some extent by, for example, a general-purpose motor or a stepping motor provided with an inverter control mechanism, it is particularly preferable to use a servomotor in terms of accuracy.

As the servomotor, a DC servomotor which has been widely used in a control device can be used. Of course, an AC servomotor which does not require a brush or a commutator and is excellent in maintenance-free property and reliability is used. Is more preferred.

As a conversion mechanism for converting the rotation of the servomotor into a horizontal linear movement of the clamp, any conventionally known mechanism can be used. For example, as shown in FIG. 1, the threaded rod 1 connected to the clamps 11a and 11b
4a, 14b and pulleys 17a, 17b coaxially screwed with the threaded rod and rotated in synchronization with the rotation of the servomotors 13a, 13b, or a so-called rack and pinion mechanism, A crank mechanism, a hydraulic mechanism, or the like may be used.

By the vacuum forming method using the present apparatus, it is possible to manufacture various large-sized and irregularly shaped molded articles with high precision and at low cost, particularly including grills, bumpers, aero parts, and interior materials of automobiles.

[0027]

As described above, the vacuum forming apparatus of the present invention comprises a clamp for gripping two opposing sides of a sheet, and at least one of these clamps is directed horizontally toward the center of the thermally softened sheet. Since it has a servo mechanism for moving, by using this apparatus, it is possible to accurately supply a sheet with a necessary and sufficient area corresponding to the size and shape of the vacuum forming mold and the development area of the mold surface. As a result, the bridging phenomenon during molding is prevented, molding accuracy is improved, distortion and uneven thickness due to residual stress of the molded product are reduced, and a molded product with high mechanical strength can be obtained. Material costs can be reduced by improving the yield.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of a vacuum forming apparatus of the present invention.

FIG. 2 is a side view showing one embodiment of the vacuum forming method of the present invention.

FIG. 3 is a perspective view showing an example of a molded product.

FIG. 4 is a perspective view showing one embodiment of a conventional vacuum forming method.

FIG. 5 is a perspective view showing another embodiment of the conventional vacuum forming method.

FIG. 6 is a perspective view showing another embodiment of the conventional vacuum forming method.

[Explanation of symbols]

 10: Vacuum forming apparatus of the embodiment (this apparatus), 11a, 11b: clamp, 12a, 12b: servo mechanism, 13a, 13b: servomotor, 14a, 14b: threaded rod, 15a, 15b: converter, 16a, 16b: base, 20: mold, S: thermoplastic resin sheet (sheet) Se: sheet side, Sc: sheet center.

Claims (3)

[Claims] 1. A clamp for gripping two opposing sides of a thermoplastic resin sheet, and a central portion of the thermoplastic resin sheet gripped and thermally softened by the clamps is disposed downwardly. A servo mechanism for horizontally moving at least one of the clamps toward a central portion of the thermoplastic resin sheet in accordance with a command so as to be placed in a vacuum forming mold. 2. The vacuum forming apparatus according to claim 1, wherein said servo mechanism is driven by a servomotor. 3. A vacuum forming apparatus according to claim 1,
Two opposite sides of the thermoplastic resin sheet are gripped and thermally softened by the clamps, respectively, and then the servo mechanism is driven to control at least one of these clamps toward the center of the thermoplastic resin sheet. In this mode, the center portion of the thermoplastic resin sheet is suspended by horizontal movement, and the suspended thermoplastic resin sheet is placed on a vacuum molding die provided below, and vacuum-molded. Vacuum forming method.