Manufacturing method of insert molded article

Abstract

The present invention is intended to provide a manufacturing method of an insert molded article that makes it possible to manufacture efficiently the insert molded article including a metallic insert, an inside member made of a synthetic resin and covering a portion of the insert, and an outside member made of a synthetic resin different from the material of the inside member and covering a portion of the inside member using general molding machines, not a dedicated two-color molding machine. General molding machines are used to manufacture the insert molded article formed by injection molding of a resin part in twice. An insert core 7 is used in common in primary molding using a primary molding die C1 and in a secondary molding using a secondary molding die. A round shaft 7C of the insert core 7 is fitted into an internal hole 2C of an insert 2 to form a coupled body 10 in which the insert 2 and the insert core 7 are coupled together. The coupled body 10 is used in common at the primary molding step and the secondary molding step.

Claims

1. A manufacturing method of an insert molded resin gear including: a metallic insert; an inside member made of a first synthetic resin and covering a portion of the insert; and an outside member made of a second synthetic resin different from the material of the inside member and covering a portion of the inside member, the manufacturing method comprising the steps of: fitting an insert core into the insert to obtain a coupled body in which the insert and the insert core are coupled together; performing a primary molding operation by positioning a base body of the insert core in a primary molding die so as to set the coupled body in place in the primary molding die, closing the primary molding die around the coupled body, and injecting the first synthetic resin into a cavity of the primary molding die extending around the coupled body so as to form the inside member, thereby manufacturing a primary molded article in which the inside member is integrated with the insert and extends partly between the outer peripheral surface of the insert and axially projecting convex portions of the insert core; opening the primary molding die and removing the coupled insert core and the primary molded article therefrom; performing a secondary molding operation by positioning the base body of the insert core in a secondary molding die so as to set the coupled insert core and the primary molded article in place in the secondary molding die, closing the secondary molding die, and injecting the second synthetic resin into a cavity of the secondary molding die extending around each of the primary molded article and the coupled insert core so as to form the outside member, thereby manufacturing a secondary molded article in which the outside member is integrated with the primary molded article; opening the secondary molding die and removing the coupled insert core and the secondary molded article therefrom; and separating the insert core from the secondary molded article.

2. The manufacturing method of the insert molded resin gear according to claim 1, wherein: the insert is an annular sleeve, the inside member is an annular internal member, the outside member is an annular external member, the insert molded resin gear has a metallic core as the insert and having teeth formed on an outer peripheral surface of the annular external member, and the base body of the insert core is disc-shaped, and a round shaft in a radially central portion of the base body is fitted into an internal hole of the annular sleeve to form the coupled body.

3. The manufacturing method of the insert molded resin gear according to claim 2, wherein the convex portions of the insert core provide thinned inner portions to the inside member.

4. The manufacturing method of the insert molded resin gear according to claim 1, wherein the convex portions of the insert core provide thinned inner portions to the inside member.

5. The manufacturing method of the insert molded resin gear according to claim 1, wherein the cavity of the secondary molding die extends between a portion of the inside member and a cavity surface of the secondary molding die so that the injected second synthetic material around and into contact with a portion of the insert core.

6. The manufacturing method of the insert molded resin gear according to claim 1, wherein the insert comprises tooth-shaped projections against which the inner member is formed and integrated with the insert.

7. The manufacturing method of the insert molded resin gear according to claim 1, wherein the insert core comprises a round shaft fitted into an internal hole of the insert to form the coupled body, with the axially projecting convex portions extending peripherally around and spaced from the shaft.

8. The manufacturing method of the insert molded resin gear according to claim 1, wherein the outside member has teeth configured to engage with a gear distinct from the resin gear.

9. The manufacturing method of the insert molded resin gear according to claim 8, wherein the outside member teeth are formed by the secondary molding operation.

10. The manufacturing method of the insert molded resin gear according to claim 8, wherein the teeth are formed by a tooth cutting process performed on the outer peripheral surface of the outside member.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view of a resin gear with metallic core manufactured by a manufacturing method of an insert molded article according to an embodiment of the present invention;

(2) FIG. 2(a) is a perspective view of the resin gear with metallic core before formation of teeth to engage with another gear on the outer peripheral surface as a secondary molded article manufactured at a secondary molding step, and FIG. 2(b) is a vertical cross-sectional view of the same;

(3) FIG. 3(a) is a perspective view of a metallic core as an insert, FIG. 3(b) is a perspective view of an insert core, and FIG. 3(c) is a perspective view of a coupled body in which the insert core is fitted into the metallic core;

(4) FIG. 4(a) is a perspective view of the state in which a primary molded article manufactured at a primary molding step is removed together with the insert core from a primary molding die, and FIG. 4(b) is a perspective view of the state in which a secondary molded article manufactured at a secondary molding step is removed together with the insert core from a secondary molding die;

(5) FIG. 5(a) is a vertical cross-sectional view of the metallic core and the insert core in the separated state, and FIG. 5(b) is a vertical cross-sectional view of the coupled body in which the insert core is fitted into the insert core;

(6) FIG. 6(a) is a vertical cross-sectional view of the state in which the coupled body illustrated in FIG. 5(b) is set in the primary molding die and the molding die is closed, FIG. 6(b) is a vertical cross-sectional view of the state in which a molten resin for primary molding is injected into the primary molding die, and FIG. 6(c) is a vertical cross-sectional view of the primary molded article and the insert core removed from the opened primary molding die;

(7) FIG. 7(a) is a vertical cross-sectional view of the state in which the primary molded article and the insert core illustrated in FIG. 6(c) are set in the secondary molding die and the molding die is closed, FIG. 7(b) is a vertical cross-sectional view of the state in which a molten resin for secondary molding is injected into the secondary molding die, and FIG. 7(c) is a vertical cross-sectional view of the secondary molded article and the insert core removed from the opened secondary molding die; and

(8) FIG. 8 is a vertical cross-sectional view illustrating the state in which the secondary molded article and the insert core illustrated in FIG. 7(c) are separated from each other.

DESCRIPTION OF EMBODIMENTS

(9) Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments illustrated in the accompanying drawings but includes all embodiments satisfying the requirements described in the claims.

(10) The direction of a rotation axis of a resin gear with metallic core 1 here refers to axial direction, and radial direction and peripheral direction are defined with respect to an axial core of the rotation axis.

(11) The resin gear with metallic core 1 as an insert molded article manufactured by a manufacturing method of an insert molded article according to an embodiment of the present invention illustrated in the perspective view of FIG. 1 is used as a worm wheel of a worm gear for use in electric power steering, for example. The resin gear with metallic core 1 includes an annular sleeve 2 as a metallic insert, an annular internal member 4 as a synthetic resin inside member that covers a portion of the annular sleeve 2, and an annular external member 5 as a synthetic resin outside member that covers a portion of the annular internal member 4.

(12) The annular internal member 4 and the annular external member 5 constitute an annular tooth part 3 that covers the outer peripheral surface of the annular sleeve 2 as a metallic core, and the annular tooth part 3 (the annular external member 5) has teeth 6 on the outer peripheral surface to engage with another gear.

(13) The resin gear with metallic core 1 has the annular tooth part 3 made of a synthetic resin and can be significantly reduced in weight on the whole than metallic gears.

(14) The internal member 4 is made of a synthetic resin fortified with a reinforcing material such as glass fiber or the like, the external member 5 is made of a synthetic resin not fortified with the reinforcing material, for example, and the internal member 4 and the external member 5 are different in material from each other.

(15) A secondary molded article B manufactured by the manufacturing method of an insert molded article according to an embodiment illustrated in the perspective view of FIG. 2(a) and the vertical cross-sectional view of FIG. 2(b) is a resin gear with metallic core 1A before formation of the teeth 6 on the outer peripheral surface. The resin part of the secondary molded article B is an annular tooth part 3A before formation of the teeth 6 on the outer peripheral surface.

(16) The teeth 6 illustrated in FIG. 1 are formed on the outer peripheral surface of the annular tooth part 3A (the external member 5) by mechanical processing such as tooth cut processing. The teeth 6 may be formed in the process of forming the secondary molded article B by injection molding.

(17) As illustrated in the perspective view of FIG. 3(a), the annular sleeve 2 includes tooth-shaped projections (concaves and convexes) 2B on the outer peripheral surface of a base body 2A and has an internal hole 2C as a fit concave portion.

(18) As illustrated in the perspective view of FIG. 3(b), an insert core 7 has a disc-shaped base body 7A, and axially projecting convex portions 7B are peripherally aligned on the outer side of the base body 7A, and the base body 7A has at a radially central part a round shaft 7C as a fitting convex part to fit into the internal hole 2C of the annular sleeve 2.

(19) Accordingly, the round shaft 7C of the insert core 7 can be inserted and fitted into the internal hole 2C of the annular sleeve 2 to obtain a coupled body 10 in which the annular sleeve 2 and the insert core 7 are coupled together as illustrated in the perspective view of FIG. 3(c).

(20) Next, the manufacturing method of the resin gear with metallic core 1 according to an embodiment of the present invention will be described.

(21) In the manufacturing method of the resin gear with metallic core 1, a dedicated two-color molding machine is not used but two general molding machines, that is, a first injection molding machine including a primary molding die and a second injection molding machine including a secondary molding machine, are used.

(22) In addition, the insert core 7 is used in common in the primary molding using the primary molding die and in secondary molding using a secondary molding die. That is, when being removed from the primary molding die, the insert core 7 is coupled to the primary molded article A as illustrated in the perspective view of FIG. 4(a), and when being removed from the secondary molding die, the insert core 7 is coupled to the secondary molded article B as illustrated in the perspective view of FIG. 4(b).

(23) In the primary molded article A illustrated in FIG. 4(a), the annular internal member 4 includes the tooth-shaped projections (concaves and convexes) 4B on the outer peripheral surface of the base body 4A.

(24) <Coupling Step>

(25) As illustrated in the perspective views of FIGS. 3(a) and 3(b) and the vertical cross-sectional view of FIG. 5(a), the annular sleeve 2 and the insert core 7 separated from each other are fitted together by inserting the round shaft 7C into the internal hole 2C to form the coupled body 10 illustrated in the perspective view of FIG. 3(c) and the vertical cross-sectional view of FIG. 5(b).

(26) <Primary Molding Step>

(27) As illustrated in the vertical cross-sectional views of FIGS. 6(a) and 6(b), the primary molding die C1 includes a movable die 8A and a fixed die 9A.

(28) As illustrated in FIG. 6(a), the base body 7A of the insert core 7 is positioned in the movable die 8A of the primary molding die C1, the coupled body 10 is set in the primary molding die C1, and the primary molding die C1 is closed.

(29) Next, as illustrated in FIG. 6(b), a molten resin for primary molding is injected from a gate G1 into the cavity of the primary molding die C1 to form the annular internal member 4 by injection molding.

(30) <Primary Molded Article Removal Step>

(31) After cooling the primary molding die C1 illustrated in FIG. 6(b) and hardening the resin, the primary molding die C1 is opened and the insert core 7 and the primary molded article A illustrated in the perspective view of FIG. 4(a) and the vertical cross-sectional view of FIG. 6(c) are removed from the first injection molding machine. The primary molded article A is formed by integrating the annular internal member 4 into the annular sleeve 2.

(32) <Secondary Molding Step>

(33) As illustrated in the vertical cross-sectional views of FIGS. 7(a) and 7(b), the secondary molding die C2 includes a movable die 8B and a fixed die 9B.

(34) As illustrated in FIG. 7(a), the base body 7A of the insert core 7 is positioned in the movable die 8B of the secondary molding die C2, the insert core 7 and the primary molded article A are set in the secondary molding die C2, and the secondary molding die C2 is closed.

(35) Next, as illustrated in FIG. 7(b), a molten resin for secondary molding is injected from a gate G2 into the cavity of the secondary molding die C2 to form the annular external member 5 by injection molding.

(36) <Secondary Molded Article Removal Step>

(37) After cooling the secondary molding die C2 illustrated in FIG. 7(b) and hardening the resin, the secondary molding die C2 is opened and the insert core 7 and the secondary molded article B illustrated in the perspective view of FIG. 4(b) and the vertical cross-sectional view of FIG. 7(c) are removed from the second injection molding machine. The secondary molded article B is formed by integrating the annular external member 5 into the primary molded article A.

(38) <Separation Step>

(39) In the state where the insert core 7 and the secondary molded article B are coupled together as illustrated in the vertical cross-sectional view of FIG. 7(c), the insert core 7 and the secondary molded article B are relatively moved in the axial direction to release the fit between the round shaft 7C of the insert core 7 and the internal hole 2C of the annular sleeve 2 of the secondary molded article B.

(40) Accordingly, as illustrated in the vertical cross-sectional view of FIG. 8, the insert core 7 and the resin gear with metallic core 1A before formation of the teeth on the outer peripheral surface as the secondary molded article to engage with another gear are separated from each other.

(41) The thus separated insert core 7 is reused at the coupling step described above.

(42) In the manufacturing method of the resin gear with metallic core 1 as described above, a two-color molding machine as a special molding machine is not used but the first injection molding machine including the primary molding die C1 and the second injection molding machine including the secondary molding die C2 are used for injection molding of the annular tooth part 3A (the annular internal member 4 and the annular external member 5) as the resin part in twice. Accordingly, the use of the general molding machines suppresses increase in introduction cost and provides high versatility to facilitate the fabrication of the dies.

(43) According to the manufacturing method of the resin gear with metallic core 1 as described above, the coupled body 10 formed by concave-convex fitting the insert core 7 into the annular metallic sleeve 2 and coupling the two is used in common at the primary molding step using the primary molding die C1 of the first injection molding machine and at the secondary molding step using the secondary molding die C2 of the second injection molding machine, it is possible to suppress the deformation of the primary molded article A removed from the first injection molding machine after the primary molding step under influence of mold shrinkage and the like.

(44) In addition, since the base body 7A of the insert core 7 used in common at the primary molding step and the secondary molding step is positioned in the primary molding die C1 and the secondary molding die C2, the positioning of the annular sleeve 2 in the primary molding die C1 and the positioning of the primary molded article A in the secondary molding die C2 become easy and reliable.

(45) Accordingly, at the manufacture of the resin gear with metallic core 1 by injection molding of the resin part in twice, it is possible to stabilize mass-production quality and improve yield while suppressing a rise in manufacturing costs partly because the dies can be fabricated without using a special molding machine and the deformation of the primary molded article A under the influence of mold shrinkage and the like can be suppressed.

(46) Further, the annular internal member 4 can be easily provided with thinned portions D as illustrated in FIG. 8 by the axially projecting convex portions 7B in the insert core 7 (see FIGS. 3(c) and 5(b)). The provision of the thinned portions D reduces the weight of the resin gear with metallic core 1. In addition, the molded article becomes smaller in volume to bring about a shorter hardening time. As a result, it is possible to shorten the molding cycle and decrease the amount of shrinkage to suppress sink marks, voids, and others.

(47) Moreover, the convex portions 7B of the insert core 7 are inserted in the thinned portions D formed in the annular internal member 4 at the primary molding step, and the convex portions 7B remain in the thinned portions D until the separation step after the secondary molding step.

(48) Accordingly, it is possible to suppress the deformation of the thinned portions D in the primary molded article A removed from the first injection molding machine after the primary molding step under the influence of mold shrinkage and the like.

(49) The manufacturing method by which the insert core 7 is used in common in the primary molding using the primary molding die C1 and the secondary molding using the secondary molding die C2 is not limited to the manufacture of the resin gear with metallic core 1. The foregoing manufacturing method is also applicable to the manufacturing method of an insert molded article that includes a metallic insert, an inside member made of synthetic resin and covering a portion of the insert, and an outside member made of a synthetic resin different from the material of the inside member and covering a portion of the inside member.

(50) Specifically, the base body of the insert core is provided with a fitting convex portion projecting in a direction toward a portion of the insert not covered by the inside member, the insert is provided with a fitting concave portion to fit to the fitting convex portion at a portion not covered by the inside member, so that the insert core and the insert can be concave-convex fitted to each other to obtain the coupled body. Alternatively, the insert may be provided with a fitting convex portion projecting in a direction toward the base body of the insert core at a portion not covered by the inside member, the base body of the insert core may be provided with a fitting concave portion to fit to the fitting convex portion, so that the insert core and the insert can be concave-convex fitted to each other to obtain the coupled body.

(51) In the foregoing description, two general molding machines, that is, the first injection molding machine including the primary molding die C1 and the second injection molding machine including the secondary molding die C2 are used. However, the present invention is not limited to this configuration. That is, in the case of small-lot production, one injection molding machine may be used to perform the primary molding using the primary molding die C1 and the secondary molding using the secondary molding die C2 while exchanging the dies and the resin materials.

REFERENCE SIGNS LIST

(52) 1 Resin gear with metallic core (insert molded article) 1A Resin gear with metallic core before formation of teeth on the outer peripheral surface to engage with another gear 2 Annular sleeve (insert) 2A Base body 2B Tooth-shaped projection 2C Internal hole (fitting concave portion) 3 Annular tooth part 3A Annular tooth part before formation of teeth on the outer peripheral surface to engage with another gear 4 Annular internal member (inside member) 4A Base body 4B Tooth-shaped projection 5 Annular external member (outside member) 6 Teeth 7 Insert core 7A Base body 7B Convex portion 7C Round shaft (fitting convex portion) 8A and 8B Movable die 9A and 9B Fixed die 10 Coupled body A Primary molded article B Secondary molded article C1 Primary molding die C2 Secondary molding die D Thinned portion G1 and G2 Gate