JPH07308975A - Resin molding with boss, molds for molding the same and molding method therefor - Google Patents

Abstract

PURPOSE:To embody a resin molding having a boss by providing a round part at the root of the boss, suppressing a shrink without generating a weld, molds for molding the form and a method for molding the same. CONSTITUTION:Molds are so slidably supported that boss molds 3 are separable from cavity 2 for forming a board. When molten resin is cast by using molds energized toward the cavity 2 by elastic means, a resin molding having no weld line and no shrink upon fluidizing of the resin is obtained while gradually retracting the boss molds by molten resin pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic molded product with a boss, which has an R portion at the base of the boss, a molding die for manufacturing the same, and a molding method.

[0002]

2. Description of the Related Art A characteristic of resin molding technology is that it is possible to produce a product having a complicated shape having irregularities in a short cycle by injecting resin into a cavity of a mold. The injection molding method of injecting into is widely applied.

Taking advantage of the above characteristics, a resin product may be provided with a projection-like thickened portion around its periphery for reinforcing inserts, screws, holes, notches, etc. I call it a boss. The thickness of this boss is generally 2 / of the thickness of the molded product in order to prevent sink marks on the surface.
Within 3 is considered appropriate. Since this boss shape is engraved in the molding die in advance, there are the following problems.

[0004]

The required level of tapping torque for the boss differs depending on the home electric appliances and automobile parts, etc., but is generally required to be 3 to 15 kgf / cm or more. The magnitude of the torque is determined by the screw diameter and the boss hole diameter if the resin is the same, and the torque increases as the boss hole diameter is smaller than the screw diameter. Therefore, if the boss hole diameter is designed so that the required torque can be obtained by reducing the thickness of the boss, there arises a problem that the boss portion is broken during tapping.

This is not simply a problem of stress concentration, but a decrease in strength due to welds. FIG. 5 is a schematic diagram showing the state of generation of a weld line in the boss portion. The arrow a indicates the flow direction of the resin, and the weld line 10 is generated on the downstream side of the resin flow of the boss 9.
The appearance of the weld line differs depending on the size of the boss, but in the injection molding in which the resin is filled from the upstream side of the resin flow, it is essentially unavoidable that a weld is generated in the hole. Although this weld causes the strength of the boss portion 9 to decline, it is a major obstacle to product design because it is difficult to quantitatively grasp and predict the weld.

[0006] Usually, a weld occurs at a point where two or more resin flows meet, but there is a weld in the boss portion which is not a weld in a strict sense. However, that makes it difficult to predict the occurrence of welds at the boss. FIG. 6 is a view of a state in the middle of flow viewed from a direction perpendicular to the flow direction of the resin, and the arrow indicates the flow direction of the resin. As shown in the figure, the boss portion 9
A factor that causes welds is that there is a time difference in the amount of resin injected into the boss on the upstream side and the downstream side.

In order to make up for the decrease in the strength of the boss portion, it is conceivable to increase the thickness of the boss portion. However, if the thickness exceeds ⅔ of the thickness of the portion to be the substrate, the thickness shown in FIG. As shown in the drawing, the sink mark 11 appears prominently on the product appearance. There was a limit to the design of the boss that satisfies both the sink mark and the strength in the ordinary injection molding. Further, if the thickness of the boss is increased, the weld appears more strongly, so the strength is not simply improved.

On the other hand, when the boss portion is designed to have a long length, in addition to tapping characteristics, strength against falling is required. In order to increase the strength against the collapse of the boss, generally, ribs are often provided between the side surface of the boss and the substrate. However, if the thickness of the ribs is made thicker than a certain value, sink marks will appear remarkably on the product appearance, as in the case where the thickness of the boss portion is made thicker. Further, from the standpoint of mold releasability, it is necessary to provide a draft taper also on the side surface of the rib, and if the flow length is lengthened, filling becomes difficult, so a rib that is too high cannot be provided.

In order to improve the falling strength of the boss, it is conceivable to increase the thickness of the boss or to provide an R portion at the base of the boss. However, the method of increasing the thickness of the boss is not preferable because it causes welds and sink marks as described above. Further, the method of providing the R portion at the base of the boss is not preferable because a sink mark appears more noticeably in the product appearance as compared with a boss having no R portion and having an equal thickness.

In view of the above-mentioned problems, the present invention has an R at the root of the boss.
It is an object of the present invention to provide a resin molded product having a boss portion which has no welds and which suppresses the occurrence of sink marks, and a molding die and a molding method for molding this resin molded product. .

[0011]

A resin molded product having a boss according to the present invention is a resin molded product having a boss, wherein an R portion is provided at the base of the boss, and the boss portion has a resin flow resistance. It is characterized by having no weld lines and sink marks associated with it.

Further, in the molding die of the present invention, the molding die is for molding a resin molded product having a boss, and the boss metal mold portion 3 can freely come into contact with and separate from the cavity 2 forming the substrate. It is characterized in that it is slidably supported in the mold and is biased toward the cavity 2 by the elastic means. In addition to that, the elastic means for urging the boss die is a coil spring 8.

Further, the molding method of the present invention is a method for molding a resin molded article having a boss, in which when a molten resin is injected into a molding die, a boss die portion which is slidable by the molten resin pressure is provided. It is characterized in that the boss is formed while being pressed and gradually retracted.

By adopting this construction, a resin molded product, a molding die and a molding method having an R portion at the root portion of the boss, a boss portion in which no weld line is generated and shrinkage is suppressed are obtained. To be

[0015]

FIG. 1 is a diagram for explaining the principle of the present invention. In the figure, 1 and 1'are molding dies, 2 are cavities, 3 are boss dies, and 4 are pins for forming pilot holes for tapping screws. The boss mold 3 has a cylindrical shape, is slidable in the mold 1, and is urged toward the cavity 2 by an elastic means (not shown) so that one end thereof is substantially flush with the surface 2a of the cavity 2. There is. Further, one end of the pin 4 is fixed to the molding die 1, and the other end thereof substantially coincides with the surface 2 a of the cavity 2. Further, R is provided at the edge portion of the hole 6 for holding the boss die 3 of the molding die 1 slidably in contact with the cavity 2.

Then, when the molten resin 5 is injected into the cavity 2 as shown in FIG. 1B, the boss die 3 is pressed by the pressure of the molten resin and retracts, and the state shown in FIG. The state becomes 1 (d). During this time, the molten resin 5 presses the boss die 3 and is injected into the boss portion together with the die, so that no weld occurs. Further, even if the resin injected into the boss portion is contracted when it is cooled and solidified, since the boss die 3 presses the resin in the direction of the cavity 2, no sink mark is generated on the back side of the boss of the molded product.

[0017]

EXAMPLE FIG. 2 is a sectional view showing an example of a molding die capable of molding the resin molded product of the present invention. In the figure, 1 and 1'denominate molding dies, and a cavity 2 is formed between the two dies 1, 1 '. A boss die 3 is slidably provided on one of the forming dies 1. The boss die 3 has a cylindrical shape, and has a collar 3a serving as a stopper at one end.

Further, a step 6a is formed in the hole 6 for slidably supporting the boss die 3 of the molding die 1, and the step 6a is engaged with the flange 3a of the boss die 3 to end the boss die 3. The part is made to substantially coincide with the surface of the cavity 2. Further, at the tip of the hole 6 for slidably supporting the boss die 3 of the molding die 1, there is chamfered R connecting to the surface of the cavity 2.

A blind plug 7 is provided on the surface of the molding die 1 opposite to the cavity, which serves as a stopper when the boss die 3 retracts. Further, the blind plug 7 is provided with a pin 4 for forming a screw hole in a boss of a molded product so that its end face is substantially aligned with the surface of the cavity 2. The pin 4 is slidable in the hole of the boss die 3.

A coil spring 8 as an elastic means is inserted between the blind plug 7 and the boss die 3 to constantly urge the boss die 3 toward the cavity 2.

A method of molding a resin molded product using the molding die of this embodiment having the above-described structure will be described with reference to FIG. First, the molten resin 5 is injected into the cavity 2. Cavity 2
The molten resin 5 injected into the boss presses the boss die 3 against the urging force of the coil spring 8 by the injection pressure and gradually retracts the state as shown in FIG. 3 (a), that is, the collar of the boss die 3. 3a enters until it contacts the blind plug 7. Then, the injection of the molten resin is stopped and the mixture is cooled and solidified.

By taking this out from the molding dies 1, 1 ', a resin molded product having a boss 9 as shown in FIG. 3 (b) can be obtained.
The boss portion 9 of this resin molded product is formed by the resin entering due to the gradual retreat of the boss die, so that no weld is generated, and at the time of cooling and solidification, the coil spring 8 is inserted via the boss die 3.
Since it is pressed by, the occurrence of sink marks is also suppressed.

Next, the results of comparative evaluation of the characteristics of the resin molded product molded by the molding die of the embodiment of the present invention and the resin molded product molded by the conventional molding die will be described. There are two types of sample size, 1.0mm and 2.0mm for the substrate thickness,
The boss wall thickness was 1.8 mm, the boss hole diameter was 2.8 mm, and the boss height was 10 mm.

As the molding material, ABS resin 1001,
PC / ABS Alloy FC-30, ABS / PBT / (G
F20%) alloy resin TB-904GE, (all of which are thermoplastic resins manufactured by Mitsubishi Rayon Co., Ltd.), and an injection molding machine (IS-50EP, Toshiba Machine Co., Ltd.) was used for molding.

JIS1 class φ for the evaluation of tapping characteristics
The maximum tightening torque when the boss was broken was measured using a 3.5 × 10 mm screw, and the average of n = 5 was taken. Further, the evaluation of the amount of sink was measured using a surface roughness meter (Surfcom manufactured by Tokyo Seimitsu Co., Ltd.), and an average of n = 5 was taken. In addition, as shown in FIG. 4, the boss collapse strength is evaluated by setting a pin 12 in the boss 9 and applying a load P to the pin 12 to apply bending and shearing stress to the root of the boss 9 and bending moment when the boss is broken. Was measured and used as an index of the collapse strength. In this case, the average of n = 10 was taken.

The evaluation results are shown in Tables 1 and 2. Table 1 shows the case where the thickness of the substrate is 1 mm, and Table 2 shows the case where the thickness of the substrate is 2 mm. From Tables 1 and 2, the maximum tightening torque,
It is understood that the examples of the present invention are superior to the comparative examples in both the amount of sink mark and the collapse strength.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

According to the present invention, a resin molded product having a boss having an R portion at its root can be molded without sink marks and welds. Further, by providing the R at the base of the boss, the fall strength becomes strong, so that the rib for reinforcing the boss is not required, and the degree of freedom in designing a product or a mold is increased.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a sectional view showing an embodiment of a molding die for molding a resin molded product having a boss according to the present invention.

FIG. 3 is a diagram for explaining a molding method of a resin molded product having a boss according to the present invention.

FIG. 4 is a diagram for explaining a method of measuring the collapse strength of a boss.

FIG. 5 is a diagram showing a weld line generation state in a boss portion.

FIG. 6 is a view showing a state where a molten resin is flowing in a conventional molding die.

FIG. 7 is a diagram showing sink marks of a resin molded product.

[Explanation of symbols]

 1, 1 '... molding die 2 ... cavity 3 ... boss die 4 ... pin 5 ... molten resin 6 ... hole 7 ... blind plug 8 ... coil spring 9 ... boss 10 ... weld line 11 ... sink mark

Claims (4)

[Claims] 1. A resin molded article having a boss, wherein an R portion is provided at the base of the boss, and the boss has no weld line and sink mark associated with resin flow. Resin molded product. 2. A mold for molding a resin molded product having a boss having an R portion at its base, wherein the boss mold part (3) contacts a cavity (2) forming a substrate. A molding die, which is slidably supported in the die so as to be separable, and is biased in the direction of the cavity (2) by elastic means. 3. The molding die according to claim 2, wherein the elastic means for urging the boss die is a coil spring (8). 4. A method for molding a resin molded article having a boss, wherein when a molten resin is injected into a molding die, the slidable boss die portion is pressed by the molten resin pressure to gradually retreat. A molding method characterized by forming a boss portion.