JP2007307840A - Mold assembly and method for producing plastic molded object using this mold assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold assembly which efficiently cools a cast release pin for molding a boss part in injection molding. <P>SOLUTION: The mold assembly has: an air pressure inlet; and an ejection sleeve with an inside diameter cut out apart as specified from an apex projection part. When the ejection sleeve advances, compressed air which is normally used in a factory, is flowed between the cast release pin and the ejection sleeve from a compressed air passage of a movable half of a mold, and thereby, the cast release pin is cooled so as to form the hole of the boss part smoothly. A method for producing the plastic object, which adopts the mold assembly and a gas assist molding process, is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a mold apparatus for cooling a core pin with compressed air in injection molding and a boss portion molding method using the same.

Plastic molded products are used in many fields such as transportation equipment, home appliances, and so on. Plastic molded products are mainly manufactured by injection molding. FIGS. 1 and 7 show a process of injection molding of a plastic molded product and a schematic view thereof. Plastic injection molding is the process of heating and melting a plastic material (hereinafter sometimes referred to as resin) into a fluidized state, and injecting it into a cavity (cavity) 7 of a closed mold to solidify it. It refers to a method of making a shape corresponding to a mold cavity. This injection molding is performed by an injection molding machine having a function of melting a resin, opening and closing a mold, a mold clamping mechanism, and the like. After the mold is closed and tightened, the resin 8 melted in the heating cylinder (cylinder) 5 is pressed into the mold through a cylinder nozzle 6 (hereinafter referred to as a nozzle) by a screw in the cylinder. The resin press-fitted into the mold is molded into a shape corresponding to the cavity and cooled and solidified by the mold. Next, the nozzle is retracted, the mold is opened, and the plastic molded product is released from the mold by the ejecting device. As described above, the mold has a function of cooling and solidifying the molten resin as well as molding the molten resin. Therefore, the mold is always cooled by providing cooling water holes. The mold is composed of a fixed mold 2 and a movable mold 4. The movable mold 4 has a core 10 that is a protrusion for forming the inner surface of the molded product. The fixed side mold has a space partial cavity corresponding to the molded product and forms the outer surface of the molded product. When the mold is opened and closed, the movable mold is retracted, and when the mold is opened, the molded product is always left on the movable mold 4 side, and then the mold is released with an ejection pin (eject pin or eject sleeve). An apparatus including such a movable mold, a fixed mold, a cooling water hole, an eject pin, and the like is referred to as a mold apparatus. In order to increase the strength of the plastic molded product, a plate-like rib is attached, or a cylindrical or cylindrical polygonal boss having a hole into which a screw or the like is screwed to be joined as a part to another part is provided. These ribs and bosses are also integrally formed by a mold. The hole 115 of the boss 11 is formed by a core pin integrated with the movable side mold as shown in FIGS. Although the core pin is sometimes called a core pin, the name of the core pin is used here. The boss has a cylindrical or polygonal cylindrical shape, and even if it is not joined to other parts, it is expressed as a boss if it is such a shape. Moreover, the part which comprises the boss | hub of a molded article is expressed as a boss | hub part.

However, the diameter of the core pin is small and it is considerably difficult to provide a cooling water hole inside the core pin from the viewpoint of processing and strength of the core pin. For this reason, when a molded product having a boss portion is continuously injection-molded, the core pin is heated by the molten resin, and the natural cooling when the mold is opened alone is insufficient to dissipate heat and stores heat. As a result, when the mold is opened and the molded product is released, the hole of the boss that is in contact with the core pin is not sufficiently cooled and solidified, and is attached to the surface of the core pin as shown in FIG. It becomes the state of.

In order to avoid sink marks and voids, the thickness of the ribs and bosses is ideally ½, preferably ３ or less of the thickness of the surrounding plate in terms of product design. The thickness means the thickness of the boss or rib and does not mean the height of the rib or boss. However, in some cases, the thickness may be 1/2 or more of the plate thickness in product design. Sink marks and voids are generated by the shrinkage of the resin. As a result of the shrinkage, sink marks appear on the surface of the molded product, and voids appear inside. In order to avoid such sinks and voids, the box-shaped boss 111 of FIG. 11 (hereinafter referred to as a box boss) is used by using a slide core 113 or an oblique core (not shown). Since attaching a slide core or the like is expensive and time-consuming to manufacture a mold, a gas-assisted injection molding method (hereinafter referred to as a gas-assist method or a gas-assist molding method) is used for molding a boss that tends to cause sink marks on the surface of the molded product. It is considered. In the gas assist molding method, a molten resin is pressed into the cavity, and then high-pressure nitrogen gas is injected into the molten resin to hold the gas pressure inside the cavity. It prevents warping. As shown in FIG. 12, the boss portion is formed with a cavity at the bottom of the boss by a gas assist molding method to prevent sink marks and the like. The bottom of the boss refers to the portion where the boss protrudes from the thick plate, and the portion where the screw or the like enters is the tip of the boss. Since the boss is directly formed into a thick plate without using a slide core or the like, this is hereinafter referred to as a straight boss 112. In other words, the boss has a box boss and a straight boss, and the box boss is a boss formed using a slide core or a slanted core, and the direct boss is a slide core or the like regardless of whether or not the gas assist molding method is used. It shall be a boss formed without using. When a straight boss is formed by the gas assist molding method, the overheating of the cast pin not only causes the boss portion to be sufficiently cooled and solidified, but also causes unevenness of the hole, as shown in FIG. In some cases, the wall between the hole and the gas-assisted cavity is broken and both are short-circuited to cause gas leakage.

As described above, cooling of the core pin that forms the boss portion is an important issue. As an improvement measure, there is a method (Non-Patent Document 1) in which a material having a good thermal conductivity such as beryllium copper is used for a cast pin. In addition, it is impossible to provide a cooling water hole in the casting pin, and a method of cooling the casting pin by providing an air circulation hole having a diameter smaller than that of the cooling water hole (Patent Document 1) or after casting the mold in a cylindrical molded product. A method of supplying a cooling medium to the medium passage of the extraction pin to forcibly cool the inner peripheral surface (Patent Document 2) has been filed.
Hirohiro Arikata "Plastic molding processing basics and practice" Nikkan Kogyo Shimbun, 2005 Patent Publication 10-6367 Patent Publication 2003-71842

However, the use of materials such as beryllium copper increases the production cost of the mold. Further, the cooling effect is not sufficient. Providing an air circulation hole in a core pin has a limit due to the strength of the core pin and difficulty in machining, and it is difficult to provide a core pin having a small diameter. Further, the method of cooling the molded product with the low-temperature refrigerant through the coolant passage of the movable mold after the mold is opened makes the machining of the mold complicated and increases the production cost. Accordingly, it is an object of the present invention to develop a mold apparatus that efficiently cools a core pin for forming a boss having a small hole diameter.

The present invention is characterized in that after the mold is opened, compressed air is allowed to flow between the eject sleeve and the core pin to cool the core pin.

That is, the invention of claim 1 includes a movable mold for forming one molding surface and a fixed mold for forming the other molding surface, and the movable mold and the fixed mold are provided. In a mold apparatus for forming a molded product by filling a molding material between cavities formed therebetween, after the molded product is released from the movable mold by a protruding device, the boss portion of the molded product is It is a mold apparatus characterized in that a core pin forming a part of the movable mold for forming a hole is cooled by compressed air. The cast pin is a central pin for forming the hole of the boss and forms a part of the movable side mold. Making a part of the movable die for the core pin means that it is included as a part of the movable die, and it does not matter whether it is integrated with the movable die. The compressed air refers to room temperature air compressed by a compressor generally used in factories or the like, and it is sufficient if it is about 4 to 6 atmospheres, and this is blown onto a core pin for a predetermined time.

According to a second aspect of the present invention, the ejecting device has an eject sleeve arranged coaxially with the core pin, and the eject sleeve is ejected from the compressed air passage of the movable side mold when the eject sleeve advances when the molded product is released. 2. The mold apparatus according to claim 1, wherein compressed air flows through a gap formed by the core pin and cools the core pin. When the movable mold is retracted and the mold is opened, the molded product is in close contact with the movable mold, and then released from the ejector pin. Since the release resistance is large at the boss portion, the entire tip surface of the boss portion is protruded by the sleeve. Since the boss has a cylindrical or polygonal cylindrical shape, the eject sleeve also has a cylindrical shape along this, and the eject sleeve moves forward to push the tip of the boss portion and remove the molded product from the movable mold. Release. At this time, a gap is formed between the core pin and the eject sleeve, which becomes a passage for compressed air for cooling the core pin and cools the core pin. The gap between the cast pin and the eject sleeve is cut off the inner surface of the eject sleeve, or part of the cast pin that forms the boss hole is tapered to make the tip of the boss taper, It can be formed by adding a draft angle.

According to the invention of claim 3, the eject sleeve is provided with a compressed air inlet and the inner diameter of the eject sleeve is cut at a predetermined distance from the tip of the eject sleeve, and the eject sleeve advances when the molded product is released. When the compressed air passage of the movable mold and the compressed air inlet of the eject sleeve coincide with each other, the compressed air flows through the gap formed by the eject sleeve and the cast pin, and the cast pin is cooled. The mold apparatus according to claim 2. In the present invention, a compressed air inlet is provided in the eject sleeve. Compressed air is sent to the movable mold, a compressed air passage is provided in the movable mold, and the position of the compressed air inlet opened in the eject sleeve and the compressed air flow path of the movable mold in the place where the eject sleeve has advanced Make sure the positions match. Compressed air flows into it and cools the core pin through the gap. It is the same as in claim 2 that a part of the core pin is processed into a taper shape, or the core pin is provided with a draft angle.

The invention of claim 4 is a method for producing a plastic molded product having a boss portion using the mold apparatus of claim 1, claim 2 or claim 3. The mold apparatus according to claim 1, 2 or 3 cools the core pin with compressed air, and invents a plastic molded product produced by a method of injection molding using the mold apparatus. It is intended for. A plastic molded product is defined as a solid that is artificially made into a useful shape by being heated and melted using a polymer material as a main raw material, poured into a closed mold and solidified. High molecular weight materials include thermoplastic resins such as polyethylene, polypropylene, and polyamide, and thermosetting resins such as epoxy resins and polyurethane resins. The present invention can be applied to most thermoplastic resins and part of thermosetting resins. Can be applied.

A fifth aspect of the present invention is a method for producing a plastic molded product having a boss portion in which the mold apparatus according to the first, second or third aspect and the gas assist molding method are used in combination. Claim 4 uses a gas assist molding method in combination. The gas-assisted molding method is to press the molten resin into the cavity and then inject high-pressure gas into the cavity to hold the pressure inside the cavity, thereby making the molded product hollow and preventing sink marks and warpage of the molded product. It is.

The cast pin cooling method of the present invention is such that the boss hole has a smooth surface, and even if the gas assist molding method is used together, the wall between the gas assist cavity and the boss hole is broken and short-circuited by the gas pressure. It can be prevented. As a result, it is possible to reduce the defective rate of the molded product including the boss in the injection molding.
In Claim 1, it is a metal mold | die apparatus which has the effect which can be cooled by spraying normal temperature compressed air of about 4-6 atmospheres used in a factory on a casting pin.
According to a second aspect of the present invention, the die device is capable of cooling the core pin by flowing the compressed air between the core pin and the eject sleeve.
According to a third aspect of the present invention, when the compressed air inlet is provided in the eject sleeve and the mold is opened, the compressed air passage of the movable side mold is matched with the compressed air inlet of the eject sleeve so that the compressed air is cast into the cast sleeve. This is a mold apparatus capable of cooling a cast pin through a gap between punch pins.
A fourth aspect of the present invention is a method of producing a plastic molded product having a boss portion by using a mold device capable of cooling the core pin, and a method of reducing defective molding of the boss hole.
A fifth aspect of the present invention is a method of producing a plastic molded product by using a die apparatus for cooling the core pin and a gas assist molding method, and is a method for reducing the formation failure of the boss hole as described above.

Examples and results of the present invention will be described below.

An embodiment of claim 2 will be described with reference to FIGS. 1, 2, 3 and 4. 2 and 3 show a structure in which a compressed air passage is provided in the ejecting device and compressed air flows between the eject sleeve and the core pin. FIG. 2 shows a state where the mold is closed. The inner diameter was cut by 0.2 mm at a predetermined distance from the tip of the eject sleeve. The reason why “a predetermined distance from the tip of the eject sleeve” is set in order to prevent the molten pin from flowing into the gap in the injection holding pressure process in the injection process shown in FIG. It is. That is, the mold is clamped in FIG. 1, and the molten resin is injected and held in the cavity. At this time, the molten resin must be fitted with the core pin at the tip of the eject sleeve so that the molten resin does not flow into the gap between the core pin and the eject sleeve, and must withstand the pressure of the molten resin. Therefore, the inner diameter of the eject sleeve must not be cut to a predetermined distance from the tip. The mold opens and the molded product is pushed out by the eject sleeve. Then, as shown in FIG. 4 (1), the tip of the eject sleeve protrudes forward from the tip of the core pin, the molded product is released, and the gap formed by the core pin and the eject sleeve is the tip of the core pin. Come out ahead of the part. From that time, compressed air (broken arrows) flows to cool the core pin. Details of the circular broken line portion of FIG. 2 are shown in FIG. Compressed air is sent to the compressed air passage 17 of the ejector having an eject sleeve by a pressure hose not shown. The compressed air flows between the eject sleeve whose inner diameter is cut and the core pin, and cools the core pin. The compressed air is controlled by a controller (not shown) and supplied into the eject sleeve during the compressed air blowing time shown in FIG. Then, the movable side mold is retracted, the mold is opened (mold open), and the ejection sleeve is advanced to compress the predetermined time from when the molded product is released from the movable side mold until the movable side mold is closed again. The core pin is cooled by air. Further, in order to make it easier to screw a screw or the like into the hole of the boss and further reduce the punching resistance, the cast pin may be processed into a tapered shape 123 (FIG. 4 (2)). In this case, since the tapered step forms a gap through which the compressed air passes, it is not necessary to push the eject sleeve to the front of the core pin.

An embodiment of claim 3 will be described with reference to FIGS. In FIG. 5, the eject sleeve 13 is provided with a compressed air inlet 14. Further, the inner diameter is cut by 0.2 mm at a predetermined distance from the tip of the eject sleeve. While the mold is closed, the compressed air passage of the movable mold is closed by the eject sleeve, and the compressed air does not flow. When the mold is opened and the eject sleeve is advanced, the pneumatic inlet 14 provided in the eject sleeve is also moved forward to coincide with the position of the compressed air passage 16 of the movable mold. The compressed air flows from the compressed air inlet of the eject sleeve into the air passage formed by the eject sleeve and the cast pin, and cools the cast pin. Furthermore, in this embodiment, the tip of the boss is tapered to facilitate screwing in. Then, the tapered step also forms a gap between the cast pin and the eject sleeve, and the compressed air easily flows by that amount. In order to reduce the mold release resistance, a draft angle may be given to the core pin. If a draft angle is given to the core pin, the gap between the eject sleeve and the core pin becomes large correspondingly, and the compressed air easily flows. The compressed air stopper 22 is a stopper for preventing compressed air from flowing in the direction of the ejecting device, and a fluorine-based resin having a low frictional resistance is used.

FIG. 6 shows a plastic molded product made by a gas assist molding method using the mold apparatus of claim 3. The heights of A, B, and C of the straight boss 112 are 75 mm, 35 mm, and 35 mm, respectively. The thickness (wall thickness) of the inner cylinder of the straight boss is 5 mm. The rib 20 is integrally formed to increase the strength of the straight boss 112. The lower part of FIG. 1 shows an injection process by a gas assist molding method. As shown in FIGS. 5 and 11, the high-pressure nitrogen gas enters the molten resin through the gas injection port 211, passes through the gas channel 21, reaches the bottom of the straight boss 112, and forms a gas-assisted cavity 114. Maintaining this gas pressure prevents the occurrence of sink marks and voids. If the gas assist molding method is used in combination, the holding pressure is short, but the resin is held at the inner wall surface of the mold by the high-pressure nitrogen gas that forms a cavity in the resin. Next, nitrogen gas is released, and during that time, the molten resin is cooled and solidified by a mold. It takes about 7 seconds for the mold to open and close again, during which compressed air is blown onto the core pin. In 100 plastic molded articles by this method, the hole of the straight boss was smooth, and it was not found that the hole of the boss and the cavity by gas assist were short-circuited.

The degree to which the core pin was cooled by compressed air was examined. First, the core pin was heated with a burner, and immediately after that, compressed air was blown onto the core pin to measure the surface temperature of the core pin. The results are shown in Table 1. According to this result, the blowing time of compressed air is about 5 seconds and the surface temperature of the core pin is 50 ° C. or less, and if the compressed air is blown within the open time of the mold, there is a cooling effect. Is shown.

There are many plastic molded products that require bosses in motorcycles, automobiles, home appliances, and the like. In particular, many plastic molded products require bosses that are thicker than the plate thickness for assembly. The present invention can prevent the boss hole from being defective in response to such a demand, and is expected to be used in the future in the operation of injection molding.

Injection molding process Eject sleeve, core pin and gap Compressed air passage and core pin Blowing compressed air onto core pins Compressed air inlet and passage Schematic diagram of prototype Schematic diagram of injection molding process Straight boss and core pin Boss hole condition (1) Boss hole state (2) Short circuit due to gas pressure Box boss and slide core Direct boss by gas assist molding method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed side mounting plate 2 Fixed side metal mold 3 Movable side mounting plate 4 Movable side metal mold 5 Cylinder 6 Nozzle 7 Cavity 8 Molten resin 9 Molded article 10 Core
DESCRIPTION OF SYMBOLS 11 Boss 111 Box-shaped boss 112 Direct boss 113 Slide core 114 Cavity by gas assist 115 Boss hole 12 Casting pin 121 Casting pin base part 122 Casting pin tip part 123 Casting pin taper part 13 Eject sleeve 131 Eject pin 132 Eject sleeve tip 14 Compressed air inlet 15 Clearance (between eject sleeve and cast pin)
16 Compressed air passage of movable mold
17 Extruding device compressed air passage 18 Factory compressed air 19 Extruding device 20 Rib 21 (gas assist method) gas channel 211 Gas inlet (by gas assist molding method) 212 Short-circuit portion by gas pressure 22 Compressed air stopper

Claims (5)

A movable side mold for forming one molding surface and a fixed side mold for forming the other molding surface, and a space between the movable side mold and the cavity formed between the fixed side molds In a mold apparatus for forming a molded product by filling a molding material into the mold, the movable side mold for forming a hole in a boss portion of the molded product after releasing the molded product from the movable side mold by a protruding device A mold apparatus, wherein a core pin forming a part of a mold is cooled by compressed air. The ejecting device has an eject sleeve arranged coaxially with the core pin, and is formed by the eject sleeve and the core pin from the compressed air passage of the movable mold when the eject sleeve advances when the molded product is released. 2. The mold apparatus according to claim 1, wherein compressed air flows in the gap to cool the casting pin. The eject sleeve is provided with a compressed air inlet, and the inner diameter of the eject sleeve is cut at a predetermined distance from the tip of the eject sleeve, and the movable side mold is compressed when the eject sleeve advances when the molded product is released. 3. The mold apparatus according to claim 2, wherein the positions of the compressed air inlets of the air passage and the eject sleeve coincide with each other and the compressed air flows through a gap formed by the eject sleeve and the cast pin to cool the cast pin. . A method for producing a plastic molded article having a boss portion using the mold apparatus according to claim 1, 2 or 3. A method for producing a plastic molded article having a boss portion using the mold apparatus according to claim 1, 2 or 3 and a gas assist molding method in combination.

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