JP2001138373A - Injection molding method and injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a weld mark from being generated in the vicinities of a fitting holes in the case of forming comparatively thin-wall and large-sized moldings having the fitting holes near to a gate. SOLUTION: Until reaching the end of molding, a resin flowing thick-wall channel 13 is formed in the inside of one side wall part F, in which fitting holes H are formed. Resin material is injected and filled in a cavity 5 through the resin flowing channel 13 having little flowing resistance from a gate 8. When molding reaches the end, the resin flowing channel 13 is allowed to disappear so as to be crushed and resin existing in the resin flowing channel 13 is filled in the cavity 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method and a structure of an injection mold for molding a thermoplastic resin molded article, and for example, a relatively large and thin molded article such as an automobile bumper. In forming, when a molded product has a plurality of mounting holes penetrating in the thickness direction, the generation of weld lines (weld marks) near the mounting holes is effectively suppressed. The present invention relates to an injection molding method and a structure of an injection mold.

[0002]

2. Description of the Related Art For example, when a thin and large molded article W as shown in FIG. 8 is molded by an injection molding method, a relatively inconspicuous non-design surface of the molded article W is used. In general, a relatively large gate G such as a film gate is set. FIG. 8 shows a state in which a gate trace G1 and a runner trace R1 are attached to the molded product W after demolding, and the gate trace G1 and the runner R1 trace are cut and removed from the molded product W in a later process. Is done.

On the other hand, in a molded product W shown in FIG. 8, a plurality of mounting holes H penetrating in a thickness direction as shown in FIG. 6 may be provided in a product portion region close to a gate G (gate trace G1). is there. In such a case, the plurality of mounting holes H are formed only when the pin-shaped portions (not shown) corresponding to the respective mounting holes H are present in the cavity. Since the pin-shaped portion comes close to the gate G, the resin material injected and filled from the gate G is once divided at the pin-shaped portion and then merges and fuses again. A molding defect called a weld line or a weld mark occurs in a portion near the mounting hole H on the front surface side, and the quality of the molded product W cannot be improved. This molding defect called a weld line or a weld mark is not only unfavorable in terms of the appearance quality of the product, but also in some cases, it is easy to be mistaken for a crack and may cause a problem in terms of the strength of the product. Many.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in particular, the occurrence of molding defects called weld lines or weld marks when molding large and thin molded products as described above. It is an object of the present invention to provide an injection molding method and a structure of an injection molding die capable of effectively suppressing the injection molding.

[0005]

The invention according to claim 1 is a method for molding a resin molded product having a plurality of holes penetrating in a thickness direction by an injection molding method, wherein at the time of injection of the resin material, A thick resin flow channel communicating with the gate portion is formed in a portion of the cavity that is close to the plurality of holes and that corresponds to a back surface side that does not become a design surface of the molded product, and is formed through the resin flow channel. While the resin material is filled in the cavity serving as the product area, when the end of injection is reached, the cavity is filled with the resin material in which the resin flow channel has been formed by crushing and eliminating the resin flow channel. It is characterized by:

According to a second aspect of the present invention, there is provided an injection molding die for molding a resin molded product having a plurality of holes penetrating in a thickness direction by an injection molding method. By providing a slide block that can move forward and backward in the thickness direction of the molded product at a position close to the plurality of holes in a certain cavity block or core block, and by holding the slide block at the retracted position when injecting a resin material. Forming a thick resin flow channel communicating with the gate portion in a portion of the cavity that is close to the plurality of holes and that corresponds to a back surface side that is not a design surface of the molded product; The resin block is filled with a resin material while the slide block is held at the forward position at the end of the injection. By disappear crushed channel, it is characterized in that the resin material forming the resin flow channel and configured to fill in the cavity before.

Therefore, according to the first and second aspects of the present invention, the resin flow channel is formed as a thick portion of the product area (cavity) from the initial stage of injection to the end of the initial stage, that is, the flow resistance of the resin material is the smallest and the flow is minimized. Since the resin material functions as an easy part, the resin material injected and filled from the gate part first flows into the resin flow channel, and thereafter flows through the entire cavity including the part that should be a plurality of holes. Therefore, unlike the conventional case, the flow of the resin material injected and filled from the gate portion does not immediately break at the portion that should become the hole portion, and a molding defect called a weld line or a weld mark occurs. Is suppressed.

Thereafter, when the required amount of the resin material is injected and filled in the resin flow channel until the end of injection, the resin flow channel is erased as if crushed by a slide block. As a result, even the resin material that previously formed the resin flow channel is filled in the cavity, and the resin flow channel loses its shape and function. In other words, as the resin flow channel remaining as a thick part of the product disappears until the end of injection, the compressive force accompanying the disappearance of the resin flow channel spreads over the entire product, and a portion corresponding to the resin flow channel. It is also possible to prevent the occurrence of secondary inconveniences such as “sink” and warpage.

[0009]

According to the first and second aspects of the present invention, the gate is formed in a portion of the cavity which is close to the plurality of holes of the molded product and which corresponds to the back surface side which is not a design surface of the molded product. A relatively thick resin flow channel that communicates with the part is formed. During injection, the cavity is filled with resin material through the resin flow channel. The cavity is filled even with the resin material that formed the channel, so that the flow of the resin material does not break at the parts that should be multiple holes as in the past, and the weld line or weld mark In addition to preventing the occurrence of molding defects, which are referred to as "molding defects", the compression force accompanying the disappearance of the resin flow channel acts on the cavity. A "sink" or effect of preventing even the occurrence of secondary defects warp at the portion corresponding to the resin flow channel.

[0010]

1 to 7 are views showing a preferred embodiment of an injection molding method and an injection mold according to the present invention. In particular, FIGS. 1 and 3 are sectional views taken along line AA of FIG. And B
2 and 4 are enlarged views of main parts in FIGS. 1 and 3, respectively, and FIG. 6 is a molded product W which is a final product demolded after molding. FIG. 7 shows a shape in which a molded product W in the middle of molding in a mold is conveniently taken out. As shown in FIGS. 6 and 7, the molded product W has a box shape with a thickness of about several millimeters, and a plurality of mounting holes H penetrating in the thickness direction in one side wall portion F. Have been. However, the gate traces G1 and the runner traces R1 and the like, which are non-product part regions attached to the molded product W in FIG. 7, are cut and removed in a later step. In the present invention, a thick resin flow channel 13 is attached to the molded product W in the middle of the molding, but when the final stage of molding is reached, the resin flow channel 13 is crushed to form the shape shown in FIG. It is characterized by finishing.

1 to 4, reference numeral 2 denotes a core block;
Is a cavity block that forms the mold 1 together with the core block 2, and the core block 2 and the cavity block 3 are clamped on the parting surface 4 to form a cavity 5 as a product space. You.
Then, in the clamped state, a sprue 6
The runner 7 and the gate 8 are formed separately, and a predetermined thermoplastic molten resin material is injected from the nozzle 9 to form the molded product W shown in FIG.

A portion of the cavity block 3 which controls the molding of the one side wall F of the molded product W is provided with a slide core 10 which forms a part of the cavity block 3 so as to face the parting surface 4. The slide core 10 has a pin-shaped portion 11 for forming the plurality of mounting holes H.
Are formed to protrude. That is, the plurality of mounting holes H
Since the part that controls the molding of the mold has a so-called undercut relationship with respect to the mold clamping and mold opening directions of the mold 1, a slide core structure is employed to avoid this undercut. The core 10 slides according to the expansion and contraction operation of a hydraulic or pneumatic type cylinder 12 attached to the cavity block 3.

On the other hand, a portion of the core block 2 which is responsible for molding the back surface of the one side wall F of the molded product W, that is, a portion which is adjacent to a plurality of mounting holes H and which is responsible for molding on the back side thereof, A long slide block 14 for separating and forming the resin flow channel 13 shown in FIG. 7 is arranged. The slide block 14 forms a part of the core block 2 and is capable of moving forward and backward within the range of the stroke S in accordance with the expansion / contraction operation of the hydraulic or pneumatic type cylinder 15, as shown in FIGS. When the slide block 14 is retracted, the thick resin flow channel 13 having a rectangular cross section as shown in FIG. 7 is formed so as to communicate with the gate 8.

Accordingly, in order to perform the injection molding of the molded article W under such a mold structure, the mold is in a clamped state as shown in FIGS. While the core 10 is held in the forward position, the slide block 14 for separating the resin flow channel 13 described above is held in the retracted position. In this state, the cavity 5 is formed in the mold 1 as a product shape part that reflects the shape of the molded product W with the resin flow channel 13 in FIG.

When the resin material is injected from the nozzle 9 shown in FIG. 1, the resin material passes through the runner 7 and the gate 8 from the sprue 6 shown in FIGS.
Flows preferentially to the resin flow channel 13 side which is thicker than the general thick portion and has a lower flow resistance,
When the space 3 is filled with the resin material, a lot of the resin material flows from the resin flow channel 13 into the other cavities 5 from this point. At this time, as is clear from FIG. 7, the resin material flows from the gate 8 to the resin flow channel 13 first.
The resin material flows almost all at once from the resin flow channel 13 around the plurality of mounting holes H, and the occurrence of molding defects such as a weld line or a weld mark due to the separation of the resin flow as in the related art. Can be prevented beforehand.

Subsequently, from the required amount of the resin material for obtaining the molded product W shown in FIGS.
When the amount of the resin material excluding the volume of the resin material of 3 is injected and filled into the cavity 5, the cylinder 15 shown in FIGS. 1 and 3 is extended to move the slide block 14 forward. The forward movement of the slide block 14 is caused by the resin flow channel 1 which has existed as a thick portion until then.
3 means that the slide block 14 gradually fills the space of the resin flow channel 13 and fills the other cavities 5 with a predetermined compressive force while gradually crushing the space of the resin flow channel 13. Then, when the slide block 14 reaches the forward limit position, the resin flow channel 1 existing up to that point
3 completely disappears, and the molding of the molded article W is completed.

After the molded product W is completely solidified, the slide core 10 is first retracted by the reverse operation of the cylinder 12 so that the plurality of mounting holes H and the pin-shaped portions 11 on the slide core 10 are undercut. Is released, the core block 2 and the cavity block 3 are opened, and finally, the molded product W is removed from the mold 1 by an ejector pin (not shown).
Stick out from. As a result, a molded product W with a runner trace R1 and a gate trace G1 as shown in FIG. 6 is obtained, and the runner R1 trace and the gate trace G1 attached to the molded product W are separated from the molded product W in the trace process. It is cut and removed.

As described above, according to this embodiment, the relatively thick resin flow channel 13 communicates with the cavity 5 close to the position where the mounting hole H of the molded product W is to be formed until the end of molding. If the resin material has passed through the resin flow channel 13 to fill the cavity 5 while allowing the resin material to flow from the gate 8 into the resin flow channel 13 at the end of molding, For example, since the resin flow channel 13 is eliminated and the resin material corresponding to the resin flow channel 13 is filled into the cavity 5, the flow of the resin material immediately after passing through the gate 8 is reduced as in the conventional case. H can be prevented from being divided at the portion that should become H. As a result, it is called a weld line or a weld mark due to the joining of the resin material flows after the division. The occurrence of molding failure can be prevented that. In addition, when the partially thick resin flow channel 13 exists as described above, secondary problems such as “sink” and warpage are likely to occur. By filling the portion of the resin material into the cavity 5 with a predetermined compressive force, such a secondary problem does not occur at all.

[Brief description of the drawings]

FIG. 1 is a view showing a preferred embodiment of an injection mold according to the present invention, and is a cross-sectional view taken along line AA of FIG.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a sectional view of the injection mold along the line BB of FIG. 7;

FIG. 4 is an enlarged view of a main part of FIG. 3;

FIG. 5 is a sectional perspective view of the injection mold along the line BB in FIG. 7;

FIG. 6 is a perspective view showing an example of a molded product formed by the injection molding die of the present invention.

FIG. 7 is a perspective view showing a state in which a molded product in the middle of molding is removed from the mold for convenience.

FIG. 8 is a perspective view showing an example of a molded product formed by a conventional injection molding die.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Die 2 ... Core block 3 ... Cavity block 5 ... Cavity 8 ... Gate 13 ... Resin flow channel 14 ... Slide block F ... One side wall H ... Mounting hole W ... Molded product

Claims (2)

[Claims] 1. A method for molding a resin molded product having a plurality of holes penetrating in a thickness direction by an injection molding method, wherein a portion of a cavity is close to the plurality of holes when a resin material is injected. While forming a thick resin flow channel that communicates with the gate portion at a portion corresponding to the back side that does not become the design surface of the molded product, and filling the resin material into the cavity serving as the product area through this resin flow channel, An injection molding method, wherein when the end of injection is reached, the cavity is filled with the resin material in which the resin flow channel has been formed by crushing and eliminating the resin flow channel. 2. An injection molding die for molding a resin molded product having a plurality of holes penetrating in a plate thickness direction by an injection molding method, wherein said mold component is a cavity block or a core block. A slide block that can move forward and backward in the thickness direction of the molded product is provided at a position close to the plurality of holes, and the resin block is held at the retracted position during injection of the resin material, so that A thick resin flow channel communicating with the gate portion is formed in an adjacent portion and on a portion corresponding to a back surface side that does not become a design surface of a molded product, and a resin material is formed in a cavity serving as a product area through the resin flow channel. At the end of injection, the slide block is held at the forward position and the resin flow channel is crushed and disappears. The injection molding die is characterized in that the cavity is filled with the resin material in which the resin flow channel has been formed up to that time.