JPS59127740A - Plastic injection molding apparatus - Google Patents

Abstract

PURPOSE:To provide the titled apparatus for mechanically preventing the sink mark of a thick part such as a boss or rib part, constituted by providing a space adjusting body which is moved in a cavity to increase or decrease the sapace thereof and an elastomer for energizing elastic force corresponding to the injection or contraction of resin to said space adjusting body. CONSTITUTION:The cavity 3 formed by a fixed side mold plate 1 and a movable side mold plate 2 shows an example for molding a molded product to which a plate part 41, a rib 42 extending from the plate part at right angles and a boss 43 provided at a spaced apart position are integrally formed. A frame body 5 is provided so as to be embedded in the movable side mold plate 2 in close vicinity to the rib 42 and the boss 43 and an operation block 6 is provided in said frame body 5. The operation block 6 is moved upwardly and downwardly in the inlay orifice 5a thereof to adjust the volume of the cavity 3. A spring 7 for pressing the operation block 6 is provided to the rear surface side of the operation block 6 and energizes pressing force to the direction moving the operation block 6 to the side of the cavity but the other end side thereof is limited by a snap ring 8.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a plastic injection molding device, and particularly to a boss,
The present invention relates to an injection molding device that mechanically prevents sink marks in thick parts such as rib parts.

<Prior art> Plastic molding can produce molded products with a wide variety of colors and designs, and the weight of the resulting molded products is light, so it has become extremely popular as the chemical and physical properties of plastic materials improve. It has come to be used in a wide range of products. This kind of plastic molding usually uses a mold that combines a stationary mold plate and a movable mold plate, and resin is injected into the cavity f created between the two mold plates while applying considerable pressure, and after injection, the resin is poured into a liquid state. The resin is solidified and molded.

When the resin solidifies inside the cavity, the volume decreases. This volume reduction causes sink marks, which have a particularly large effect on thick parts where solidification is delayed, resulting in deformation and abnormal shapes in the molded product.

Conventionally, the following methods have been used to prevent sink marks during the molding process as described above: (1) increasing the injection molding pressure; (2) providing a thinning hole near thick parts such as bosses and ribs. However, in the case of the former method (2), the pressure applied to the molded product, such as the pressure during resin injection and the holding pressure applied during the solidification process, will not be the optimal molding pressure, resulting in distortion of the product or insufficient dimensions. The drawback was that accuracy could not be obtained. Also, even if you try to apply injection molding pressure, the resin will solidify first near the resin injection port, which has a relatively small cross-sectional area, making it difficult to transmit pressure and making it impossible to achieve the intended purpose. There is a problem. If the latter method (■) is used, the template must be specially processed, which increases the number of processing steps and is not as effective as it should be.Also, depending on the type of resin, the pattern of the fleshy part may be visible from the surface of the product. and significantly reduce the value of quality. Furthermore, the wall thickness at the base of the boss rib becomes thinner due to the thickened portion, which has the disadvantage of impairing mechanical strength.

As mentioned above, there is no suitable method to avoid the sink marks that occur in resin, so conventionally it has not been possible to easily provide bosses, ribs, etc. on the back side of the visible part of products, which has caused a great deal of trouble in product design.

<Object of the Invention> The present invention eliminates the drawbacks of the conventional plastic injection molding equipment described above, and provides a plastic injection molding system that can prevent sink marks that occur in thick resin parts during molding process by simply adding a simple configuration. The present invention provides a molding device.

<Example 1> In Fig. 1, fixed 11111 template 1 and movable template 2
A cavity 3 for injecting resin and molding is provided between the two and the same as in the conventional apparatus. In this embodiment, the molded product of the cavity 3 is the plate portion 41.゛Ribs 42 extending perpendicularly from the plate portion 41 and the ribs 4
The shape is designed such that a boss 43 and the like can be integrally formed at a position apart from 2. The frame body 5 is embedded in the movable template 2 in close proximity to the portion where the ribs 42 and bosses 43 are provided.
An operating block 6 is provided inside the frame 5. The actuation block 6 is provided so as to be movable, albeit by a small distance, with respect to the frame 5, and moves in the vertical direction in the figure in the fitting hole 5a formed in the frame 5 to increase the volume of the cavity 3. Adjust. The back side of the actuation block 6 (
On the side not facing the cavity 3, there is an actuation block 6.
A spring 7 is provided to press the actuating block 6 toward the cavity 3. In the figure, a snap ring 8 is attached to the other end of the operating protrusion 6, and the upward movement of the operating protrusion 6 is restricted at a position where the snap ring 8 contacts the wall surface of the frame 5. Further, the bottle 9 provided in the boss portion 43 is provided from the viewpoint of machinability of the template.

Next, the operation of the injection molding apparatus with the above structure will be explained.

Before the resin is injected, the actuating block 6 is pressed toward the cavity 3 by the pressing force of the spring 7. Next, when resin is injected into the cavity 3, the resin pressure applied during injection, which reaches several hundred kg/cnj, is applied to the spring 7.
Overcoming the force of zero force, the actuating block is pushed down into the fitting hole 5a, and the actuating pro-tsuku 6 has its back side 6a aligned with the fitting hole wall 5b.
move back to a position where it makes contact with the When the filling of the resin into the cavity 3 is completed and the template begins to cool, the resin begins to shrink.

In this process, the plate 41 is cooled slowly at portions such as the ribs 42 or the bosses 43 that are relatively thick.
A sink mark IO is about to occur on the surface side as shown by the two-dot chain line. The resin filled in the cavity 3 has not yet completely solidified in this state and is in a semi-molten state, resulting in sink marks of 100
By supplementing the area with resin from other areas, sink marks can be eliminated or their effects can be significantly reduced. As mentioned above, in this embodiment, since the back of the actuating block 6 is constantly pressed by the spring 7, this spring pressing force resists the injection molding pressure applied to the resin and causes the resin to contract. The actuating block 6 is moved toward the cavity 3 by acting on the resin contained therein.

Due to the movement of the actuating block 6, the semi-molten resin is removed from the sink lO.
This prevents the occurrence of sink marks.

The position where the actuating block 6 is provided is at the rib 42. It is desirable to provide it close to a position where sink marks are likely to occur, such as the boss 43, and it can be provided correspondingly to each rib or boss, but it can also be provided in common to a plurality of peripheral thick parts. .

By configuring the cavity volume adjustment mechanism including the actuating block as a unit, it can be used for each scale molding template.

<Example 2> In this example, in the movable mold plate forming a cavity with the fixed mold plate, a pressing force was applied to the core bushing body itself provided on the movable mold plate. This is to adjust the cavity volume.

In FIG. 2, the movable template 11 is compared to the fixed template IK.
A core bushing body J3 is movably provided in the fitting hole of the core plate 12 with respect to the core plate 12, and the core bushing body 13 is attached with screws 15 inserted through the core plate 12, and the core bushing body 13 and the fixed side A cavity 3 for resin molding is formed between the mold plate 1 and the mold plate 1. The core bushing body 13 has ribs 42. A space shape for integrally molding the boss 43 and the like is integrally processed. The core bushing body I3 is movably provided in the fitting hole 14 provided in the core plate 12, and the core bushing body The core bushing body 13 moves in the direction of narrowing the cavity 3 by the elastic force of the spring 7 provided on the back surface of I3.
The buckle provided on the screw 15 moves in a minute range until it comes into contact with the core play 412.

In the figure, the core bushing body 13 is pushed up by the elastic force of the spring 7 before being filled with resin. However, the amount of movement due to pushing up is illustrated in an enlarged model, and the screw 15 stops when it comes into contact with the core plate 12. Next, when resin is injected, the core bushing body 13 is subjected to injection molding pressure, and the back surface 13a of the core bushing body 13 is
It then retreats to a position where it contacts the bottom wall 14 of the fitting hole. When the resin filling is finished and the template is cooled, the ribs 4 are formed as in the previous embodiment.
2. There is a sink mark 1 on the surface side of the plate where boss 43 etc. are provided.
0 is about to occur. At this time, the core bushing body 13
The elastic force of the spring 7 pressing the core bushing body 13 overcomes the injection molding pressure applied to the resin due to the volume reduction caused by the resin contraction, and moves the core bushing body 13 toward the cavity. The movement of the core bushing body 13 forces the resin, which is still in a semi-molten state, into the area 10 where sink marks are likely to occur, and as a result, the occurrence of sink marks is stopped.

The mechanism for moving the core bushing body as in the above embodiment can also be applied to a structure in which the core bushing body is further screwed inside the core bluff foot body. Instead of the structure in which the core bushing body is screwed, it is also possible to adjust the cavity volume by providing an elastic body that presses the back surface of the inner core bushing body, as in the above example, and applying force to push the resin away. can.

<Embodiment 3> Embodiment 1t': i A mechanism section is configured that adjusts the cavity volume using an ejector turbine for extruding a molded product.

In FIG. 3, the structure in which a cavity 3 is formed by a fixed mold plate 1 and a movable mold plate 2 is the same as that of the first embodiment. An eject turbine I6 is provided passing through the movable mold plate 2, and the eject turbine I
The other end of 6 passes through return plate +7 and is held by return plate 17 and ejector plate 18. A stopper 19 is fixed to the tip of the return plate 17, and the stopper I9
The ejector turbine 16 moves within a very small range within the +7 fitting hole 2o to adjust the volume of the cavity 3. A spring 7 is provided on the back surface of the stopper 19 for pushing up the tip of the eject turbine 16 toward the cavity.

In the injection molding apparatus having the above structure, when the resin is first injected, the stopper 19 is pressed against the bottom wall 20b of the fitting hole 20 by the injection molding pressure.
The ejector pin 16 is pushed down when it comes into contact with the ejector pin 16. Next, when the resin contracts, the pressing force of the spring 7 overcomes the injection molding pressure and pushes up the ejector turbine 16, forcing the semi-molten resin into the area 10 where the sink is occurring, as in the previous embodiment, resulting in Prevents sink marks from occurring.

<Embodiment 4> This embodiment is constructed with a mechanism that adjusts the cavity volume by applying a pressing force directly to thick parts such as ribs and bosses where sink marks are likely to occur.

FIG. 4 shows an example of application to a boss part, in which a sleeve 21 having approximately the same cross-sectional area as the bottom surface of the boss is provided in the portion of the movable template 2 where the boss 43 is formed, and the sleeve 21 is provided with a cross-sectional area that is approximately the same as the bottom surface of the boss. A pin 22 that moves in the coaxial direction is provided, and the tip of the pin 22 is placed so as to reach the hollow portion 43aK of the boss. The other end of the pin 22 is a return plate 17. It passes through the ejector plate 18 to reach the holding plate 23, and a stopper 24 is attached to the tip to prevent insertion and removal. Clasp 2
A spring is provided on the back side of the pin 22 to press the tip of the pin 22 toward the cavity.

In the injection molding apparatus having the above structure, the pin 22 is retracted by the pressure during resin injection to a position where the bottom surface 24a of the stopper 24 contacts the wall 26b of the fitting hole 26, as in the previous embodiment, and then the pin 22 is cooled. In the process, the pin 22 is pushed up by the pressing force of the spring 7, and force is forcibly applied to the semi-molten resin to force the resin to flow into the area 10 where the volume decreases, thereby preventing the occurrence of sink marks.

In the above structure, the pin 22 is configured to be movable, but the pin 22
A spring 7 is attached to the other end of the sleeve 21 through which the spring 7 is inserted.
The same configuration can be achieved by arranging the sleeve 2I and pressing the resin of the post 43 itself by moving the sleeve 2I to adjust the cavity volume.

In each embodiment, the elastic body that applies the elastic force is not limited to a spring, and various elastic bodies such as a disc spring can be used.

Effects> As described above, according to the present invention, it is possible to prevent sink marks that tend to occur in thick parts such as bosses and ribs, prevent deformation during processing of molded products, and increase yield. It becomes possible to provide bosses, ribs, etc. with considerable freedom, increasing the degree of freedom in product design, and also making it possible to increase the mechanical strength without impairing the design aspect of the product.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing one embodiment according to the present invention, and FIGS. 2 to 4 are sectional views of main parts showing other embodiments according to the invention. 1: Fixed side template 2: Movable side template 3: Cavity 4
1 Nibble part 42: Rib 43: Boss 6: Movable block 7: Spring lo: Sink 13° core bushing body 5a, +4.20.26: Fitting hole 16:
Ejector pin 21 sleeve 22: pin

Claims (1)

[Scope of Claims] 1. A device for injecting resin into a cavity of a template for molding, including a space adjustment body that moves within the cavity to increase or decrease the space, and a space adjustment body that is capable of injecting and contracting the resin. 1. A plastic injection molding device, comprising: an elastic body that applies an elastic force to the plastic injection molding device. 2. Plastic injection molding apparatus 03 according to claim 1, wherein the space adjustment body is located near a thick part of the resin. 2. The plastic injection molding apparatus according to claim 1, wherein the plastic injection molding apparatus also serves as a core bushing body provided on a side mold plate. 4 The space adjustment body is a 5gt machine for extruding the molded product.
The plastic injection molding apparatus 0 according to claim 1, wherein the elastic force id of the elastic body J is selected to a magnitude that applies a pressing force to the semi-molten resin to compensate for sink marks caused by resin contraction.