KR20220101222A - Molding method for having boss structure with high dimensional accuracy - Google Patents

Abstract

The present invention relates to a method for injection-molding a product having a boss structure with high dimensional accuracy, which comprises the following steps of: preparing a first mold (10) having a first molded surface (11) in any shape and an auxiliary air flow path (12) communicating with the first molded surface (11), and a second mold (20) having a second molded surface (21) in any shape, which has a boss-molded surface (22) to combine the two molds; inserting a movable pin (30) into a central portion of the boss-molded surface (22) of the second mold (20) and tightly attaching a top end portion of the air flow path (31) in the movable pin (30) to the auxiliary air flow path (12) of the first mold (10) to communicate therewith; forcibly discharging air remaining respectively in a space between the first and second molded surfaces (11, 21) of the first and second molds (10, 20) combined and a space between the boss-molded surface (22) and an outer surface (33) at a top portion of the movable pin (30) to fill the space between the first and second molded surfaces (11, 21) and the space between the boss-molded surface (22) and the outer surface (33) at the top portion of the movable pin (30) with melted resin (P); cooling the resin (P) for a predetermined time while forcible discharge of air through any one of the auxiliary air flow path (12) or the air flow path (31) is stopped; forcibly infusing and discharging air with constant pressure; and spraying air with predetermined pressure on a boss inner surface (3) of a molded product (1) to prevent the resin (P) inserted into the space between the boss-molded surface (22) and the outer surface (33) of the top portion of the movable pin (30) from invading a boundary portion of the boss inner surface (3) of the molded product (1) while making the movable pin (30) move backward.

Description

Injection method of a molding having a boss structure with excellent dimensional accuracy {Molding method for having boss structure with high dimensional accuracy}

The present invention relates to an injection method of a molded article having a boss structure, and more specifically, injecting a molten resin into a molding space while forcibly discharging air remaining in the molding space, and cooling the movable pin at a certain pressure in the retreating process. of air to the boss, it fundamentally prevents the incomplete filling of the molten resin in the molding space, and at the same time makes the resin structure filled in the molding space more dense, and furthermore, the dimensional accuracy of the boss It relates to an injection method of a molding that can improve the

In injection molding, a boss generally refers to a part that protrudes in the shape of a hollow or solid structure, which protrudes from the surface of the injection molding, and the like. Such a boss is mainly provided for assembly with other molded parts, and in order to maintain a stable bonding state for a long time, the boss part 1 is molded a little thicker than other parts as shown in FIG. 3 .

When designing a mold so that the boss part is thicker than other parts of the injection molded product, there is a problem that sink marks, cavities, weld lines, etc. occur. To this end, in the related industry, as shown in FIG. 4 , the movable pin 3 having the cooling passage 4 formed on the central axis is inserted into the boss molding surface 22 of the mold forming the boss portion in the injection molded product, or FIG. 5 . A method using the hot fin 250 is used as shown.

That is, the space between the first and second forming surfaces 11 and 21 of the combined first and second molds 10 and 20 and the space between the outer surface of the upper part of the movable pin 3 and the boss forming surface 22 are melted, respectively. When the resin is filled, cooling water is supplied to the cooling passages 4 of the movable fins 3 as well as the main cooling passages 14 and 24 of each of the first and second molds 10 and 20 or heat transfer of the hot fins 250 . Through this, the resin filled in the space between the outer surface of the upper portion of the movable pin 3 and the boss molding surface 22 is induced to cool in the shape of the space.

However, as can be seen from each of FIGS. 4 and 5 , the cooling water normally supplied to the movable pin 3 is only supplied to the lower portion of the movable pin 3 and does not enter the vicinity of the boss forming surface 22 . , it is impossible to cool the resin filled in the space between the outer surface of the upper part of the movable pin 3 and the boss molding surface 22 in a stable state.

Accordingly, when the movable pin 3 is retracted after a certain cooling time has elapsed, the resin filled in the space between the outer surface of the upper portion of the movable pin 3 and the boss molding surface 22 is not properly cooled, and some fluidity is reduced. There was a problem in that the resin of the branches swelled in the direction of the center of the hole of the boss, and finally, a molded product with poor dimensional accuracy of the boss was made, which made it difficult to combine the parts with each other.

Republic of Korea Patent No. 1409771

The present invention has been proposed to improve the problems of the prior art, and an object of the present invention is to provide a molding method of an injection molding having a boss structure that can ensure high dimensional accuracy through air discharge and injection.

In order to achieve this object, the present invention provides a first mold 10 in which an auxiliary air passage 12 communicating with the first molding surface 11 and the first molding surface 11 of an arbitrary shape is formed, and a boss molding preparing a second mold 20 in which a second molding surface 21 having an arbitrary shape having a surface 22 is formed; Molding the first and second molds (10, 20); The movable pin 30 having the air flow path 31 formed along the central axis is inserted through the central portion of the boss forming surface 22 of the second mold 20, so that the upper portion of the air flow path 31 of the movable pin 30 is adhering to communicate with the auxiliary air passage 12 of the first mold 10; The space between the first and second molding surfaces 11 and 21 of the first and second molds 10 and 20 combined through any one of the auxiliary air passage 12 or the air passage 31 and the boss molding surface 22 The air remaining in each space between and the outer surface 33 of the upper part of the movable pin 30 is forcibly discharged, and the space between the first and second molding surfaces 11 and 21 and the boss molding surface 22 and the movable pin ( 30) Filling the molten resin (P) into each space between the outer surface 33 of the upper part: the space between the first and second molding surfaces 11 and 21 and the boss molding surface 22 and the movable pin 30 When the resin (P) is filled in each space between the upper surface of the outer surface (33) of the resin (P) for a certain period of time while the forced discharge of air through either the auxiliary air passage (12) or the air passage (31) is stopped. ) cooling; A step of forcibly injecting air at a certain pressure through any one of the air flow path 31 or the auxiliary air flow path 12 and discharging the injected air through any one of the auxiliary air flow path 12 or the air flow path 31 ; The movable pin 30 is slowly retracted and the resin P filled in the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30 is located at the boundary of the boss inner surface 3 of the molding 1 . It is characterized in that it comprises; spraying air of a certain pressure to the boss inner surface 3 of the molding 1 so as not to invade.

At least one injection nozzle 32 communicating with the air flow path 31 may be formed on the movable pin 30 .

At this time, it is preferable that the diameter Φ2 of the injection nozzle 32 is smaller than the diameter Φ1 of the air passage 31 .

In the step of filling the space between the first and second molding surfaces 11 and 21 and the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30, respectively, the molten resin P is filled, The space between the first and second molding surfaces 11 and 21 of the first and second molds 10 and 20 combined through any one of the air passage 31 or the auxiliary air passage 12 and the boss molding surface 22 Forcibly discharging the air remaining in each space between the outer surface 33 of the upper part of the movable pin 30 and the air at a certain pressure through either the air flow path 31 or the auxiliary air flow path 12 . The step of discharging the injected air through any one of the auxiliary air flow path 12 or the air flow path 31 may be repeated a predetermined number of times.

The present invention proposes a method of injecting molten resin into the molding space while forcibly discharging the air remaining in the molding space, thereby fundamentally preventing the molten resin from being incompletely filled in the molding space and filling the molding space. can make the resin structure more dense.

In addition, the present invention is to prevent in advance the phenomenon that the center of the boss part that is in the softened state swells up and the dimensional accuracy decreases by supplying air at a certain pressure to the boss part in the process of retreating the movable pin after cooling the injected resin. be able to

1A-1G are each a schematic step diagram of the present invention.
Figure 2 is a schematic configuration diagram of the movable pin in the present invention.
3 is a schematic configuration diagram of a boss in an injection-molded product;
Figure 4 is a schematic configuration diagram of a movable pin for forming a conventional boss portion.
Figure 5 is a schematic view of another configuration of a movable pin for forming a conventional boss portion.

A preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings as follows. In the description of the embodiments of the present invention, there is no direct relation to the technical features of the present invention, or is common in the technical field to which the present invention pertains. For matters that are obvious to those with the knowledge of

The present invention relates to a method of injecting a molded article having a boss, and a step of preparing a mold and a molding step, an inserting step of a movable pin 30, a resin injection step and a cooling step, and a retreating step of the movable pin (30) It has features that include Let's look at each of these steps in detail.

First, a mold is prepared. The mold may include first and second molds on which first and second molding surfaces and a boss molding surface are formed. 1A, an example of the first mold 10 in which the first molding surface 11 is formed, and the second mold 20 in which the second molding surface 21 is formed are disclosed. Reference numeral 22 denotes a boss forming surface 22 .

Although an example in which two boss forming surfaces are formed is disclosed in the drawings, this is only an example, and of course, one boss forming surface or a plurality of boss forming surfaces may be formed, and the boss forming surface is not the second mold but the first mold. It may be formed on the first molding surface of the mold.

At this time, the auxiliary air flow path 12 is formed in the first mold 10 as shown in the drawing, and the auxiliary air flow path 12 is configured to communicate with the first molding surface 11 . The auxiliary air passage 12 is a passage through which air remaining in the space formed of the first and second molding surfaces 11 and 21 is discharged or air having a predetermined pressure is injected.

Reference numeral 23 denotes an insertion space for a movable pin to be described later, and reference numerals 14 and 24 denote cooling water passages provided in the first and second molds 10 and 20, respectively. Cooling water flows through each of the cooling water passages 14 and 24 .

When the molds are ready, they are molded together. When the mold is molded, a molding space is formed inside the mold including the first and second molding surfaces 11 and 21 and the boss molding surface 22 as shown in FIG. 1A .

When the mold is molded, insert the movable pin. The movable pin is a means for forming the boss portion, more specifically the hole 3 portion disclosed in FIG. 3 . An air flow path 31 is formed on the central axis of the movable pin 30 as shown in FIG. 2 in which an example is disclosed. The movable pin may be advanced or retracted by a movable plate or hydraulic cylinder (not shown).

The insertion of the movable pin is inserted into the central portion of the boss forming surface 22 through the insertion space 23 of the second mold 20, as shown in FIG. 1b, and the upper portion of the air passage 31 of the movable pin 30 moves forward so as to be in close contact with the auxiliary air flow path 12 of the first mold 10 . Accordingly, the outer surface 33 of the upper portion of the movable pin 30 faces the boss molding surface 22 and forms a molding space.

At this time, at least one or more injection nozzles communicating with the air flow path may be formed on the movable pin. The injection nozzle is a part through which the air remaining in the molding space is discharged or air at a predetermined pressure is injected. 2 shows an example in which two injection nozzles 32 are formed on the upper portion of the movable pin 30 .

When the movable pin is provided with an injection nozzle communicating with the air passage, the present invention proposes a case in which the diameter Φ2 of the injection nozzle 32 is smaller than the diameter Φ1 of the air passage 31 as shown in FIG. 1B . This is to prevent a phenomenon in which the molten resin is pushed in through one end of the injection nozzle and the air flow path is blocked. The size of the spray nozzle should be decided in consideration of the type of resin and the temperature of the mold.

When the movable pin is inserted into the combined mold, the space between the first and second molding surfaces 11 and 21 forming the molding space of the combined first and second molds 10 and 20 and the boss molding surface 22 as shown in FIG. 1C ) and the air remaining in each space between the outer surface 33 of the upper part of the movable pin 30 is forcibly discharged, the space between the first and second molding surfaces 11 and 21 and the boss molding surface 22 and the movable pin A molten resin (P) is filled in each of the spaces between the outer surfaces (33) of the upper side of (30).

When the molten resin is injected through a gate (not shown), the injected resin fills the molding space sequentially while pushing out the air remaining in the molding space. If the molding space is complicated or the injection pressure is not appropriate, the resin It often occurs that the molding space is incompletely filled because the air cannot be completely pushed out, resulting in defective products being manufactured.

To this end, the present invention proposes a method of injecting a molten resin into the molding space while forcibly discharging the air remaining in the molding space, thereby preventing the phenomenon in which the molten resin is incompletely filled in the molding space due to the conventional residual air. It is possible to prevent fundamentally.

In addition, if air is forcibly discharged while injecting the molten resin into the molding space as in the present invention, it is also possible to remove the air remaining in the form of bubbles in the molten resin that fills the molding space in the process. In this case, the structure of the resin filled in the molding space becomes more dense, so that the hardness of the final molding can be improved.

At this time, the air remaining in the space between the first and second molding surfaces 11 and 21 and the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30 is discharged through the auxiliary air passage 12 . ) or the air passage 31 is preferably made through any one of.

This is to make it easier to forcibly discharge the air remaining in the molding space, and the present invention does not exclude the case of discharging air while maintaining the auxiliary air flow path and the air flow path in communication with each other as needed. FIG. 1C discloses a case in which air is discharged through the auxiliary air passage 12 in a state in which the air passage 31 is closed.

As shown in Fig. 1d, when the resin (P) is completely filled in each of the space between the first and second molding surfaces 11 and 21 and the space between the boss molding surface 22 and the outer surface of the upper part 33 of the movable pin, Fig. As shown in 1e, the resin (P) is cooled for a certain period of time using cooling water in a state where the forced discharge of air is stopped. The cooling time may vary depending on the material of the resin.

After cooling for a predetermined time, air of a predetermined pressure is forcibly injected through any one of the air flow path or the auxiliary air flow path, and the injected air is discharged through any one of the auxiliary air flow path or the air flow path. 1f shows an example in which air of a certain pressure is injected into the air flow path 31 and then discharged into the auxiliary air flow path 12 .

In this state, the movable pin 30 is slowly retracted as shown in FIG. 1G using a hydraulic cylinder (not shown). Since air of a certain pressure is injected into the air flow path 31 , when the movable pin 30 is retracted, the air of a predetermined pressure injected into the air flow path 31 moves to the upper end of the movable pin 30 and the injection nozzle 32 . It is sprayed into the resin portion filled in the space between the boss molding surface 22 and the upper portion outer surface 33 of the movable pin 30 through the .

According to the injection pressure of this air, the resin filled in the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30 does not invade the boundary of the boss inner surface 3 of the molding 1 . and it hardens slowly. In addition, according to the injection pressure of the air, the resin structure of the boss portion is dense and hardness is improved.

As shown in FIG. 3 , the boss portion 1 is formed to be slightly thicker than other portions. Therefore, even after the same cooling time elapses after the resin injection, the center of the boss is not hardened and has a softened state. In this case, there was a problem that the assembling itself between the moldings became impossible.

To this end, when the cooling time for the injected resin has elapsed, the present invention prevents the swelling of the center of the boss part forming a softened state by supplying air at a certain pressure to the boss part during the retreating process of the movable pin. At the same time, it is possible to increase the density of the tissue in the boss area. The pressure of the injected air may vary depending on the cooling time and the material of the resin.

On the other hand, in the present invention, in the step of injecting and filling the molding space of the combined mold with the molten resin, the forced discharge step of the air remaining in the molding space and the forced air injection step of a certain pressure are alternately performed for a certain number of times. suggest

That is, the space between the first and second molding surfaces 11 and 21 of the first and second molds 10 and 20 combined through any one of the air flow path 31 or the auxiliary air flow path 12 as shown in FIG. 1C, and The air remaining in each space between the boss forming surface 22 and the outer surface 33 of the upper part of the movable pin 30 is forcibly discharged, and either the air passage 31 or the auxiliary air passage 12, as shown in FIG. The state of forcibly injecting air of a certain pressure through one of the auxiliary air passages 12 or the air passage 31 and discharging the injected air through one is repeated.

If the forced air ejection step and the constant pressure air forced injection step are repeated in this way, the bubbles contained in the molten resin can be more completely removed, and the density of the resin structure can be made higher. do. Of course, the execution time and the number of repetitions of each step may vary depending on the shape or thickness of the molding, the material of the resin, and the like.

In the above description, limited to preferred embodiments of the present invention, this is only an example, the present invention is not limited thereto and can be changed and implemented in various ways, and further, separate technical features are provided based on the disclosed technical idea. It will be obvious that it can be implemented in addition.

10, 20: 1st, 2nd mold 11, 21: 1st, 2nd molding surface
12: auxiliary air flow path 22: boss forming surface
30: movable pin 31: air flow path
32: spray nozzle

Claims (4)

A first mold 10 having an arbitrary shape of a first molding surface 11 and an auxiliary air passage 12 communicating with the first molding surface 11, and a boss molding surface 22 having an arbitrary shape preparing a second mold 20 on which a second molding surface 21 is formed;
Molding the first and second molds (10, 20);
The movable pin 30 having the air flow path 31 formed along the central axis is inserted through the central portion of the boss forming surface 22 of the second mold 20, so that the upper portion of the air flow path 31 of the movable pin 30 is adhering the first mold 10 to communicate with the auxiliary air passage 12;
The space between the first and second molding surfaces 11 and 21 of the first and second molds 10 and 20 combined through any one of the auxiliary air passage 12 or the air passage 31 and the boss molding surface 22 The air remaining in each space between and the outer surface 33 of the upper part of the movable pin 30 is forcibly discharged, and the space between the first and second molding surfaces 11 and 21 and the boss molding surface 22 and the movable pin ( 30) filling each space between the outer surface 33 of the upper part of the molten resin (P):
When the resin (P) is filled in each of the space between the first and second molding surfaces 11 and 21 and the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30, the auxiliary air flow path 12 or cooling the resin (P) for a certain period of time while stopping the forced discharge of air through any one of the air passages (31);
A step of forcibly injecting air at a predetermined pressure through any one of the air passage 31 or the auxiliary air passage 12 and discharging the injected air through any one of the auxiliary air passage 12 or the air passage 31 ;
The movable pin 30 is slowly retracted and the resin P filled in the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30 is the boundary portion of the boss inner surface 3 of the molding 1 . spraying air at a certain pressure to the boss inner surface 3 of the molding 1 so as not to invade the
Injection method of a molding having a boss structure with excellent dimensional accuracy including The method of claim 1,
At least one injection nozzle (32) communicating with the air flow path (31) is formed on the movable pin (30). 3. The method of claim 2,
The injection method of the molding having a boss structure with excellent dimensional accuracy, characterized in that the diameter Φ2 of the injection nozzle (32) is formed smaller than the diameter Φ1 of the air passage (31). The method of claim 1,
In the step of filling the space between the first and second molding surfaces 11 and 21 and the space between the boss molding surface 22 and the outer surface 33 of the upper part of the movable pin 30, respectively, the molten resin (P) is filled, The space between the first and second molding surfaces 11 and 21 of the first and second molds 10 and 20 combined through any one of the air passage 31 or the auxiliary air passage 12 and the boss molding surface 22 Forcibly discharging the air remaining in each space between the upper surface of the movable pin 30 and the outer surface 33 of the movable pin 30 and forcing air at a certain pressure through either the air flow path 31 or the auxiliary air flow path 12 . Injection method of a molded article having a boss structure with excellent dimensional accuracy, characterized in that the step of injecting into a furnace and discharging the injected air through any one of the auxiliary air passage (12) or the air passage (31) is repeated a certain number of times.

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