JPS583824A - Molding by solid phase stamping for thermoplastic synthetic resin sheet - Google Patents

Abstract

PURPOSE:To improve deep drawing property and prevent thinning of a molded product and generation of a wrinkle, etc., by heating and temperaure-controlling the temperature of a blank holder and a peripheral part of the upper mold at a specified temperature and forming it by solid phase stamping. CONSTITUTION:An upper mold 3 and a lower mold 4 provided with a blank holder 5 are respectively attached to an upper mold fixing platen 1 of a press and a lower mold fixing platen 4. A blank holder 5 and a peripheral part 11 of the upper mold are heated and temperature-controlled at 50-100 deg.C, a thermoplastic resin sheet 6 heated and temperature-controlled at a temperature lower by 0-20 deg.C than its melting point is set and stamped. Even though the thermoplastic resin sheet 6 is nipped between the blank holder 5 and the peripheral part 11 of the upper mold in stamping, it does not cause the deterioration of softeness due to quenching and thinning of a product.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solid-phase stamping forming a molded article from a thermoplastic synthetic resin sheet.

Conventionally, automobile parts such as fender liners, tire housings, and splash covers, and home appliance parts such as refrigerator door inner panels, main body inner boxes, and evaporation pans, have been made by injection molding of thermoplastic synthetic resins or vacuum molding of the same resin sheets. It is obtained by molding, air pressure molding, etc.

However, in these molding methods, there is a limit to the thickness of the molded product due to the fluidity of the resin, which is at least 1.5 cm.
1.8fi, and in terms of polyolefin resin, ζ
Rono's melt flow rate (230℃) is also 2.01! '7
It is difficult to use a material with a length of less than 10 m, and materials with excellent physical properties cannot be used. Even in the latter case, the temperature during sheet forming is high. For example, if it is a crystalline polymer, it exceeds the melting point, and due to the nature of drawdown, the temperature range is extremely high. Molded under narrow conditions.

Furthermore, each of the above-mentioned moldings had a problem in that the molding cycle was long.

On the other hand, in solid-phase stamping molding, the temperature range during molding of the resin sheet is 0 to 20°C below the melting point for crystalline polymers, and the VICAT softening point (ASTM152) for non-grade polymers.
5) A pair of male and female molds (MatsuchiDai) are kept in a solid state at 0 to 30°C or higher, and the tension of the material is increased compared to the molten state, and the clearance is in the range of 100 to 110 inches relative to the thickness of the resin sheet. ) using a hydraulic or mechanical press for general sheet metal processing.
The resin sheet is clamped at a mold clamping speed of 5 to 15 kf/eC or less.
This is a method in which the resin sheet is pressure-molded at a pressure of cm2 and cooled from both sides of the resin sheet using male and female molds.

In this molding method, the material is in a solid state, so the thickness after molding is the same as that of the original resin sheet or only slightly reduced.Furthermore, the material itself has a certain degree of tension compared to the molten state, so the sheet It is easy to handle, transport, etc. As for the molding cycle, cooling from both sides by the mold, and the temperature of the original resin sheet, as mentioned above, is below the melting point for crystalline polymers, 0 to 20 degrees Celsius, and for non-grade polymers, it is VTC.
Since the AT softening point is 0 to 30°C lower, it has the advantage of being significantly shorter than vacuum forming, pressure forming, injection molding, etc.

However, this molding method has problems such as thinning (necking) at corners, rounded shoulders, etc. of the molded product, insufficient drawing depth, and wrinkles on the blank on the blank holder.

This invention solves this problem, and its gist is that when a thermoplastic synthetic resin sheet is stamped in a solid state using male and female molds and a blank holder, the peripheral part of the blank holder and the upper mold, i.e. The heating temperature is controlled at the point where the wrinkle holding function is performed to prevent the blank temperature from dropping during blank holding and maintain the flexibility of the blank, as well as between the blank and the blank holder, and between the blank and the clasp.

This is a method for solid-phase stamping molding of resin molded products, which is characterized by performing solid-phase stamping molding while maintaining the slipperiness between the peripheral edges of the mold, improving deep drawability, and maintaining uniformity of plate thickness. .

This will be explained below with reference to the drawings.

An upper die (female die) 3 is attached to an upper die fixing plate 1 of the press, and a lower die (male die) 4 is attached to a lower die fixing plate 2 of the press.

The lower mold 4 is also equipped with a blank holder 5 on which polyethylene, polypropylene, or ABS is heated and kept at a temperature in the range of 0 to 20°C below the melting point.

A thermoplastic resin sheet (hereinafter referred to as blank) 6 such as HIPS or PVC is left still. The blank 6 is nipped by the blank temperature drop 5 and the upper die peripheral portion 11 during stamping molding. Note that the upper mold peripheral portion 11 is the upper mold 3
It may be an integral structure with the main body or a side structure.

This tabbing pressure is optionally adjusted by a hydraulically or pneumatically actuated cylinder 7 or spring 8 (both shown). As mold clamping progresses in the stamping molding process, the blank 6 protrudes from the male mold 4 and undergoes overhang, pushing, etc., and the material molded product design, plate thickness, and temperature of the blank are transferred between the blank holder 5 and the peripheral part of the stopper die. The peripheral part of the blank 6 also partially flows into the projection plane of the molded product as it slides while being subjected to the wrinkle pressing force determined by the following.

In general stamping molding, including metal sheets, the limit of drawing depth is determined by the material and design of the molded product, especially the radius of a corner, the roundness of the shoulder, etc.

If this limit is exceeded, wrinkles will appear in the blank area, and the wrinkle pressing force will be increased to suppress this. This method applies to metal sheets that undergo so-called work hardening.

The drawn metal sheet hardens in that area, improving its elastic modulus and causing continuous flow around the unprocessed blank.

On the other hand, in the case of crystalline thermoplastic synthetic resin sheets, the work hardening that occurs in sheet metal does not occur in the solid state in the temperature range of 0 to 20°C below the melting point, and wrinkles are suppressed to suppress the occurrence of wrinkles. Increasing the force will result in thinning of parts such as corners and rounded shoulders of the molded product.

This is because the tension of the material is extremely weak below the melting point, and due to the effect of the wrinkle pressing force, local thinning occurs at the rounded position of the shoulder of the male die even in areas where the drawing depth is shallow. The same thing can be seen in the solid phase state where the VI CAT softening point of non-quality polymers is 0 to 303 or higher.

In order to prevent this phenomenon and increase the drawing depth, a blank 6 that has been heated and kept warm is placed on a blank holder 5 that has been heated and temperature controlled by a heating temperature control means 10 typified by an electric heater. , perform stamping molding. At this time, remove the periphery of the upper mold. Since the blank holder 5 and the A-type peripheral portion 1+ are heated and temperature controlled, the blank is not nipped between them during stamping molding and is not rapidly cooled, so that the blank does not lose its flexibility. Furthermore, this also reduces springback after molding.

In this heating temperature control, when the temperature of the blank holder 5 and the upper die peripheral portion 11 is below 50°C, when a wrinkle pressing force is applied within a range that does not cause wrinkles or necking, the cooling of the blank is accelerated and the hardening process is accelerated. The degree of elasticity of the material increases compared to other parts of the blank, and the resistance force increases even when subjected to drawing processing, which prevents the molded part around the blank from sliding into the projection plane and reduces formability. It was confirmed that In addition, the blank holder 5 and the nozzle-shaped peripheral portion 11
If the temperature exceeds 100° C., the flange of the molded product after molding, that is, the edge that remains without the above-mentioned sliding movement, will be deformed, which will cause problems for molded products that require seven lunges. Therefore, the appropriate temperature range for the blank holder 5 and the mold peripheral portion 11 varies somewhat depending on the composition of the thermoplastic synthetic resin, but is between 50°C and 100°C.
It is desirable to be within the range of .

The blanks are made by cutting pre-formed thermoplastic synthetic resin sheets of uniform thickness according to the molded product design, and cutting sheets of uniform thickness that are in the process of being cooled immediately after being extruded using a hot plate or hot wire heater. You can also use it.

As described above, the present invention heats a part of the mold to be used, makes it easier to flow the peripheral part of the blank into the projected plane of the molded product, and improves deep drawability, thereby making it possible to use the solid phase stamping method. It eliminates the problem of thinning of the molded product, and compared to vacuum forming, pressure forming, etc., the blank is in a solid state, so it has shape retention and is easy to transport during molding, and the molding cycle can be shortened by 4 times. It has many effects.

[Brief explanation of drawings]

Figure 1 is a sectional view showing a heated blank placed on a blank holder and immediately before being stamped by the closing upper mold, and Figure 2 is a heated blank placed on a blank holder and then cooled after stamping is completed with the upper mold closed. , is a cross-sectional view showing the state in which the pressure holding state is entered. 1...Upper mold fixing plate, 2...Bending lower die fixing plate, 3...Upper die (female), 4...Lower die (male) type), 5...Blank holder,
6... Blank (resin sheet), 7... Curved cylinder 8... Spring, 9... Molded product, 10... Heating temperature control means, 11.
River: Upper mold periphery. Patent applicant Showa Denko K.K. agent Patent attorney Sei Kikuchi

Claims (1)

[Claims] When stamping a thermoplastic synthetic resin sheet in a solid state using male and female molds and a blank holder, the temperature of the blank holder and the upper mold periphery is set to 50 to 100°C.
A solid phase stamping molding method for a thermoplastic synthetic resin sheet, which is characterized by performing solid phase stamping molding by heating and controlling the temperature to ℃.