JPH0564577B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a thermoforming method for plastics, for example, an auxiliary plug forming method (plug assist method) used in vacuum forming using a female mold or compressed air pressure forming. Regarding improvements.

(Prior Art) When obtaining a deep-drawn molded product by vacuum forming or compressed air pressure forming using a female mold, there is generally a problem that the thickness of the molded product tends to be uneven. Conventionally,
As a means of solving this problem, as shown in FIG. 3, an auxiliary plug molding method is known in which a thermoplastic resin material sheet 2 is once pre-stretched by an auxiliary plug 3 and then molded.

(Problems to be Solved by the Invention) According to the conventional auxiliary plug molding method, it is possible to obtain a molded product 4 with a relatively uniform wall thickness. However, when examined in more detail, as shown in FIG.
It is unavoidable that the wall thickness will be slightly larger than the wall thickness of other parts. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to improve moldability in auxiliary plug molding by eliminating the uneven thickness of a molded product between the area where the auxiliary plug contacts and the other areas.

(Means for Solving the Problems) The present invention was devised to achieve the above object, and is characterized in that the auxiliary plug is rotated during the pre-stretching process of the material sheet using the auxiliary plug. .

(Function) In the molded product 4 obtained by the conventional auxiliary plug molding method, the portion 4a that contacts the auxiliary plug 3
The reason why the wall thickness of the material sheet 2 is slightly larger than that of other parts is that the part of the material sheet 2 that contacts the auxiliary plug 3 creates friction due to its close contact during pre-tensioning, making it difficult to slip and stretch. The main reason is that it is possible to suppress Therefore, by reducing the friction at the contact area between the auxiliary plug 3 and the material sheet 2 during pre-tensioning and improving the sliding of the material sheet 2, it is possible to obtain a molded product with uniform wall thickness without suppressing elongation. . According to the present invention, since the auxiliary plug rotates when the material sheet is pretensioned, the auxiliary plug and the material sheet do not come into close contact with each other, and therefore the friction between the auxiliary plug and the material sheet is reduced.

(Example) An example will be described with reference to FIGS. 1 and 2. First, a thermoplastic resin material sheet 2 is placed in a clamped state on top of the female mold 1 and heated and softened, and then, as shown in FIG. 1, the auxiliary plug 3 is lowered into the inside of the female mold 1. Pretension the material sheet 2. In this pre-tensioning step, the auxiliary plug 3 is rotated about its central axis at an appropriate number of revolutions. After this pre-stretching process is completed, the space 5 between the material sheet 2 and the female mold 1 is evacuated and the material sheet 2 is pressed onto the female mold 1 by atmospheric pressure to form the material, and then it is cooled and hardened. By tightening the vacuum and removing the mold from the female mold 1, a molded product 4 having a uniform wall thickness can be obtained, as shown in FIG.

Although the above embodiments are applied to vacuum forming, it is of course applicable to compressed air forming.

(Effects of the Invention) Since the present invention is configured as described above, even when the material sheet is pre-stretched by the auxiliary plug, the thickness of the part of the molded product that comes into contact with the auxiliary plug is the same as that of other parts, as in the conventional case. The thickness of the molded product does not become slightly larger than that of the molded product, and the thickness of the entire molded product becomes uniform, resulting in improved moldability.

[Brief explanation of the drawing]

Figure 1 is a cross section showing the pre-stretching process of a material sheet according to an example of the present invention, Figure 2 is a cross-sectional view of a molded product obtained in an example of the present invention, and Figure 3 is a pre-stretching process of a material sheet of a conventional example. FIG. 4 is a cross-sectional view of a molded product obtained in a conventional example. 1... Female mold, 2... Material sheet, 3... Auxiliary plug, 4... Molded product, 5... Space.

Claims (1)

[Claims] 1. An auxiliary plug forming method characterized by rotating the auxiliary plug during the pre-stretching process of the material sheet using the auxiliary plug.