JP2892956B2 - Molding method for resin sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a resin sheet which has been softened by heating with a mold.

[0002]

2. Description of the Related Art For example, a molded product obtained by vacuum-forming a heat-softened resin sheet must have a proper thickness or more after molding in order to effectively maintain and improve the appearance quality. Alternatively, it is necessary that the thickness of each part after molding is substantially uniform.

However, the resin sheet tends to be excessively stretched due to the uneven portion of the molded product, so that the thickness of the molded resin sheet cannot be effectively maintained or the resin sheet is damaged. Was. This is because the heat-softened resin sheet has a low strength and is easily cut when stretched.

[0004] Therefore, a device for applying heat softening treatment and drawing to the synthetic resin sheet and for moving a pair of chains holding the synthetic resin sheet inwardly to each other in conjunction with the closing operation of the drawing die (particularly). (See JP-A-56-17219) (hereinafter referred to as Conventional Example 1) and molding in a state where the temperature of a portion where tension occurs in a synthetic resin sheet is set lower than other portions within the moldable temperature range. (Refer to JP-A-59-199207) (hereinafter referred to as Conventional Example 2), and the holding position of at least one holding member holding the skin in accordance with the shape of the convex parting surface in the mold clamping direction. There is known a method in which the surface is brought into contact with the convex mold by changing the shape, and after the mold is clamped, the holding by all the holding members is released to perform vacuum forming (see JP-A-3-224720) (hereinafter referred to as Conventional Example 3). Being That.

[0005]

However, the above-mentioned prior art 1 has a structure in which a pair of chains holding a synthetic resin sheet is shifted inward from each other.
In the above-mentioned conventional example 3, there is a structure in which the holding member holding the skin is changed in the mold clamping direction, and there is a problem that these mechanisms are complicated. Furthermore, in the above-mentioned conventional example 2, it is pointed out that a high-precision, that is, expensive circuit is required to precisely control the heating temperature over the entire synthetic resin sheet, and that the adjustment operation takes time. ing.

The present invention is intended to solve such a problem, and provides a method for forming a resin sheet capable of effectively maintaining the thickness of the formed resin sheet by a simple process. The purpose is to:

[0007]

In order to achieve the above object, the present invention provides a method for forming a heat-softened resin sheet by using a forming die. A step of distinguishing between a portion that is easily stretched and a portion that is not easily stretched by the later uneven shape, and a mold closing speed of the molding die and / or a moving speed of the resin sheet, wherein the portion that is easily stretched is slowed down compared to the portion that is hardly stretched. A step of setting and a step of shaping the resin sheet at the set speed.

[0008]

In the method for molding a resin sheet according to the present invention, first, the resin sheet is divided into an easily stretchable portion and a hardly stretchable portion according to the shape after shaping. The speed and / or the moving speed of the resin sheet are set to be lower than the hardly stretchable portion. This allows
The elongation of the resin sheet in the easily stretchable portion is reduced, and the breakage of the resin sheet is prevented. As a result, the thickness of the resin sheet after shaping is optimized as a whole.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a resin sheet according to the present invention will be described in detail with reference to the accompanying drawings, with reference to the accompanying drawings.

In FIGS. 1 and 2, reference numeral 10
Shows a molding apparatus for performing the molding method according to the present embodiment. The molding apparatus 10 includes a lower platen 12, and an upper platen 16 is fixed to upper ends of guide posts 14 a to 14 d erected on the lower platen 12.

The lower platen 12 holds a male lower die 18 and the upper platen 16 is provided with a mold closing hydraulic cylinder 20 and frame ram hydraulic cylinders 22a and 22b. . A rod 24 extending downward from the hydraulic cylinder 20 is fixed to a mold ram 26.
Can be moved up and down guided by the guide posts 14a to 14d. A female upper mold 28 is fixed to the lower surface of the mold ram 26.

Rods 30a, 30b extending downward from the hydraulic cylinders 22a, 22b pass through the mold ram 26,
It is fixed to a frame ram 32 which is disposed between the mold ram 26 and the lower platen 12 so as to be movable up and down. The frame ram 32 has gripping means 34a, 3g for gripping the end of the resin sheet S.
4b is provided.

As shown in FIG. 2, a heating device 40 is provided in the vicinity of the molding device 10.
Is provided with a plurality of heaters 42 for heating the resin sheet S to a predetermined temperature before shaping.

Next, the molding apparatus 1 configured as described above
The operation of vacuum forming the resin sheet S using No. 0 will be described.

First, the resin sheet S is conveyed into the heating device 40 and heated to near the softening point via the heater 42, and then sent from the heating device 40 to the molding device 10. Then, the resin sheet S is gripped by the gripping means 34a and 34b constituting the molding apparatus 10.

In this case, the resin sheet S is previously classified into a portion that is easily stretched and a portion that is not easily stretched by the uneven shape after shaping, and the descending speed of the frame ram 32 and / or the mold ram 26 along this section. Is set.

That is, the speed V at which the resin sheet S is pulled
And the Young's modulus E of the resin sheet S has a relationship shown in FIG. Thereby, the tensile speed V of the resin sheet S is
Becomes faster, the Young's modulus E becomes smaller, and the resin sheet S becomes easier to stretch. Therefore, by setting the descending speed of the frame ram 32 and / or the descending speed of the mold ram 26 in accordance with the uneven shape of the resin sheet S after shaping, the elongation of the entire resin sheet S after shaping is kept constant. Can be secured.

Therefore, the lowering speed of the frame ram 32 corresponding to the shape (molded product shape) of the resin sheet S after shaping is set as shown in FIG. Thereby, as shown in FIG.
In the steeply shaped portion (easily stretchable portion) 50 of the lower die 18, the lowering speed of the frame ram 32 is slowed down, whereas in the gentle shape portion (hardly stretchable portion) 52 of the lower die 18, the lowering of the frame ram 32 is performed. Speed increases.

Next, when the hydraulic cylinders 22a and 22b are driven to extend the rods 30a and 30b downward, the frame ram 32 fixed to the rods 30a and 30b descends under the guide action of the guide posts 14a to 14d. I do. For this reason, after the resin sheet S comes into contact with the lower mold 18, the ends gripped by the gripping means 34 a and 34 b are pulled downward, so that the resin sheet S is spread in a state shown by a two-dot chain line in FIG. 1. Is done.

After the frame ram 32 is lowered and a so-called seat down is performed, the upper die 28 which starts lowering with a drive action of the hydraulic cylinder 20 later than the lowering of the frame ram 32.
Presses the resin sheet S gripped and spread by the frame ram 32, is closed by the lower die 18, and performs vacuum suction, whereby a molded product shaped into a predetermined shape is formed. can get.

In this case, in this embodiment, the resin sheet S
However, it is distinguished into a portion that is easily stretched and a portion that is not easily stretched by the uneven shape after the shaping, and the descending speed of the frame ram 32 is set along this section. That is, in the resin sheet S, by setting the descending speed of the easily stretchable portion to be slow, the Young's modulus E is increased in the stretchable portion (see FIG. 3), and the stretch amount is suppressed. On the other hand, in a portion that is difficult to elongate, the Young's modulus E is reduced (see FIG. 3) by setting the descent speed fast, and the amount of elongation is increased.

Further, the shapes of the lower mold 18 and the upper mold 28 constituting the molding apparatus 10 are variously changed, and the whole of the lower mold 18 and the upper mold 28 may have a steep shape or a gentle shape. In this case, the lowering speed of each resin sheet S may be set so that a mold having a gentle shape is faster than a mold having a steep shape.

For this reason, the thickness of the resin sheet S after shaping can be kept uniform by simple control without being affected by the uneven shape after shaping. This makes it possible to reliably prevent the resin sheet S from being partially stretched too thin and from being damaged, and to reduce the thickness of the resin sheet S after shaping as a whole. ,
The effect that uniformity can be obtained is obtained.

In the present embodiment, the control for changing the descending speed of the frame ram 32 in accordance with the uneven shape after the shaping is performed. However, instead of this, or together with this control,
Control for changing the lowering speed of the mold ram 26 can also be performed. This is because the resin sheet S is spread by the concave and convex shapes of the mold ram 26 and the lower mold 18, and the same phenomenon as when the frame ram 32 descends appears.

[0025]

According to the resin sheet molding method of the present invention, the following effects and advantages can be obtained.

The resin sheet is classified into a portion that is easily stretched and a portion that is not easily stretched according to the shape after the shaping, and the speed at which the mold is closed and / or the speed at which the resin sheet is moved is set according to this division. Thereby, the thickness of the resin sheet after the shaping can be properly adjusted and made uniform by simple control without being affected by the uneven shape after the shaping.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a molding apparatus to which a molding method according to the present invention is applied.

FIG. 2 is a layout diagram of the molding device and a heating device.

FIG. 3 is a diagram showing the relationship between the tensile speed of the resin sheet and the Young's modulus.

FIG. 4 is a diagram showing the relationship between the shape of a molded product and the lowering speed of a frame ram.

FIG. 5 is a diagram illustrating a relationship between a difference in lower mold shape and a resin sheet engaged with the lower mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Molding apparatus 18 ... Lower mold 20 ... Hydraulic cylinder 26 ... Mold ram 28 ... Upper mold 32 ... Frame ram 34a, 34b ... Grasping means S ... Resin sheet

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-246039 (JP, A) JP-A-8-174654 (JP, A) JP-A-3-150125 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B29C 51/00-51/46

Claims (1)

(57) [Claims] 1. A method for forming a resin sheet, which is formed by shaping a heat-softened resin sheet with a molding die, wherein the resin sheet is distinguished into a part that is easily stretched and a part that is hardly stretched due to irregularities after the formation. Setting the mold closing speed of the molding die and / or the moving speed of the resin sheet to be slower for the stretchable portion than for the hardly stretchable portion; and shaping the resin sheet by the set speed. A method for molding a resin sheet, comprising: