FR2720675A1 - Injection molding mold of a cylindrical product with internal gear. - Google Patents

Abstract

Cylindrical product with inner gear, injection molded, mold and manufacturing process for the product. The molded product (12) includes a cylindrical base member, an inner spiral gear, and a release groove next to the inner gear, the release groove having a diameter and width larger than that of the inner gear. . The method includes introducing a first cylindrical mold (36) into a second cylindrical mold (37), engaging a toothed portion of the first mold in a groove of the second (37) to form a lower mold (41) ), the mounting of an upper mold (40), the injection of a resin, the retraction of the second mold (37) to open it and the axial displacement of the first mold (36) to introduce the toothed part into the product release groove, and the rotation of the first mold to extract it.

Description

I Injection molding mold of a cylindrical product with gear

  The present invention relates to a cylindrical product with an internal gear formed by injection molding, to a mold for the

  cylindrical product, and a process for making them.

  A zoom lens barrel is often provided with several types of rotation cylinders for the plan change and focus operations. In the zoom lens barrel that the present applicant has developed, a rotation cylinder is used to move in the direction of the optical axis of the first and second cylindrical elements housed therein and to transmit the rotation to the first and second cylindrical elements . The rotation cylinder moves the first cylindrical element back and forth in the direction of the optical axis, and the rotation is transmitted to the second cylindrical element by an internal gear formed on its internal peripheral surface by means of gears, and the like, which move in the direction of the optical axis at the same time as the first

cylindrical element.

  However, in the above-mentioned structure, if the inner gear is formed over the entire inner peripheral surface of the rotation cylinder, cam grooves, and the like, cannot be formed on the same inner peripheral surface. Consequently, a suitable form of rotation cylinder was then keenly sought with a more suitable form of internal gear. In addition, there is a demand for a mold, the manufacture of which would be easy, to form the rotation cylinder with such an internal gear from a material based on

  resin, and for a method of manufacturing the cylinder and the mold.

  Generally, a metal mold of an injection molding device for a cylindrical object with undercuts, such as an inner gear, is provided at its inner periphery with sliding inner cores which are divided into four elements, six

  elements, or even more elements.

  However, in the case where the undercuts have the shape of an internal gear, the tips of the teeth of the sliding cores are liable to interfere with the internal gear formed and with other elementary internal cores, therefore it is necessary to phase-shift the implementation during the driving of adjacent inner cores or to modify the speeds at which the inner cores are driven when the metal mold is opened. For the above-mentioned purpose, it is necessary to provide several drive mechanisms and means for controlling the synchronism and the speed of the drive, which results in a complicated overall structure for the molding machine.

by injection.

  There is a problem with the positions of the dividing lines of the inner sliding core. To increase the thickness of the mold, it is preferable to avoid using the tooth crown surface as a dividing line and to choose the bottom of the teeth to place the dividing lines. However, it is difficult to place all the dividing lines at the

  bottom of the mold in relation to the pitch of the interior teeth.

  In addition, when retracting the inner cores in the radial direction of the inner gear (towards the axis of the inner gear) and when the inner gear has developing teeth, for example, the shoulders of the inner cores interfere with the swollen parts of the teeth. The present invention has been made taking into consideration the problems described above, and its first objective is to provide a cylindrical product with a more suitable internal gear shape, a mold for forming the cylindrical product, and a manufacturing method. of

cylindrical product and mold.

  The second objective of the present invention is to provide a

  injection molding machine for a product with counter

  spoils like an internal gear without using a means of

special order.

  The third objective of the present invention is to provide an internal gear and a metal mold of an injection molding machine for the internal gear, in which the mold structure for the injection molding machine, the drive mechanism and the

  drive controls are simplified.

  The fourth objective of the present invention is to provide an internal gear which can be produced by injection molding even if

  the internal gear has undercuts.

  The present invention provides a mold for forming the product according to the present invention, which comprises: an upper mold for forming the outer surface of the product and a lower mold for forming the inner surface of the product, wherein the lower mold comprises a first cylindrical mold with a spiral toothed part for the internal gear; and a second cylindrical mold with a flat spiral part

for the release groove.

  A further aspect the molded product according to the present invention further comprises a spiral drive groove formed on the inner peripheral surface of the cylindrical base member of

  so as to be parallel to the internal gear.

  In this case, the present invention may further comprise: a mold for forming a cylindrical product, comprising an upper mold for forming the external surface of the product and a lower mold for forming the internal surface of the product, in which the lower mold comprises: a first cylindrical mold with a spiral toothed portion for the internal gear; and a second cylindrical mold with a flat spiral part for the clearance groove and with a spiral projection

for the drive groove.

  The first cylindrical mold may also comprise a cylindrical part of small diameter; and a spiral part of a diameter larger than that of the cylindrical part of small diameter, the toothed part being formed on the outer periphery of said spiral part, and in which said second cylindrical mold comprises: a hole in its center to engage the cylindrical part of small diameter, and a spiral groove

  to accommodate the spiral toothed part.

  An injection molding mold according to the present invention, to achieve the second objective described above, comprises several sets of first and second inner sliding cores, inner molds with undercuts forming parts of the first and second inner sliding cores adjacent to each other constituting a set of first and second inner sliding cores, the first and second inner sliding cores moving in a direction perpendicular to the axis of the inner cores at different speeds from each other to open and close the inner cores, in which the following formula is verified

OF <B <OA (1)

  o OB is the angle between a pair of partition surfaces and a sliding line of the first interior sliding core in a position o the first and second interior sliding cores close the interior molds; OF is the smallest angle so that the pair of partition surfaces of the first and second inner sliding cores do not interfere with each other in positions other than the closed position and partially closed positions; and 0A is the largest angle which makes the undercut parts of the second inner sliding core not interfere with the first inner sliding core when the first and second inner sliding cores are

  move during their opening or closing.

  In one embodiment, the product formed by said inner molds is a cam ring with an inner gear having undercuts; the partition surfaces of the first and second inner sliding cores are formed in the tooth feet of an inner gear part; and the largest angle 0A is the largest angle which allows the tips of the second inner sliding core not to interfere with the first inner sliding core when the surface dividing lines of the first and second inner sliding cores

  are formed on the tooth feet.

  In another embodiment, the first and second inner sliding cores are supported so as to be able to slide in order to approach and move away from a fixed plate at a predetermined angle OC in a direction perpendicular to the axis, the molds interiors being closed when the first and second cores

  sliding doors reach an outermost position.

  In another case, the product formed by the interior molds is a

  cam ring with an internal gear comprising counter

  drafts, and wherein the number of teeth of the inner gear is determined based on a number of first and second

  elementary interior sliding cores.

  In yet another case, the product formed by the interior molds

  is a cam ring with an internal gear comprising counter

  undercuts, in which the tooth shape of the inner gear is formed by involute lines, and in which, furthermore, the inner molds do not interfere with each other when the

  inner cores are driven for their opening and closing.

  The injection molding mold may further include: a locking core slidably guided in a direction parallel to the axis to a space closed by the interior peripheral surfaces of the first and second interior sliding cores, in which , when introduced into the space, the locking core presses and maintains each of the first and second inner sliding cores in a closed position where the contact surfaces of the first and second inner sliding cores are in contact with each other the others, and when the locking core is retracted, the locking core allows the

  first and second interior sliding cores to open.

  In this case, the locking core is fixed to a movable plate; inclined pins which are slidably inserted into guide holes of the first and second inner sliding cores are fixed to the movable plate; when the movable plate moves, the inclined pins, which are fixed at predetermined angles OD, OE with respect to the axis, move the first and second inner sliding cores in a direction which opens and closes the first and second cores interior sliding doors at different speeds relative to each other; and the following two formulas are checked simultaneously 8D 0 <E (3); and tan OD <tan 0E. cos OC (4) o, OC is the angle between the sliding lines of the first and

  second interior sliding cores.

  In this case, the smallest angle (F satisfies the following formula OF = tan-1 (sin OC. Tan OE / (tan 0E. Cos OC -tan OD)) o, Oc is the angle between the lines of sliding of the first and second inner sliding cores; OD is the angle between the inclined spindle of the first inner sliding core and the axis; and 0E is the angle

  between the inclined spindle of the second inner sliding core and the axis.

  An internal gear according to the present invention, to achieve the third objective described above, is formed by a mold for injection molding with several internal sliding cores moving radially to open and close the internal molds, and the number of teeth of the internal gear is determined based on the number of

  elementary interior sliding cores.

  In one case, the interior sliding cores comprise a plurality of sets of first and second interior sliding cores, and wherein a set of said plurality of sets of first and second interior sliding cores comprises first and second interior sliding cores which are adjacent to each other. and move radially at different speeds from each other

  to open and close the interior molds.

  Preferably, the number of teeth of the internal gear is determined by the following formula Z = (S / 2). N (2) o, S is the number of elementary internal sliding cores; Z is the number of teeth of the internal gear; and n is a positive integer which is chosen from even numbers depending on the conditions

  meshing with the internal gears as will be discussed below

after.

  In the embodiment if n is less than 14, the shape of the gear will not be an involute. If n was greater than 18, the interior molds would be too small. Consequently, n is chosen according to the

  special design considerations.

  According to a further aspect of the present invention, an injection molding mold according to the present invention has several inner sliding cores moving radially to open and close inner molds and the number of teeth of the inner gear is determined based on the number of interior sliding cores

elementary.

  In one case, the interior sliding cores comprise a plurality of sets of first and second interior sliding cores, and wherein a set of said plurality of sets of first and second interior sliding cores comprises first and second interior sliding cores which are adjacent to each other. and move radially at different speeds from each other

  to open and close the interior molds.

  To achieve the fourth objective described above, an internal gear according to the present invention is formed by a mold with several internal sliding cores moving radially to open and close internal molds and the tooth shape of the internal gear is formed. so that the interior molds do not interfere with each other when they are driven to open and close. In this case, it is possible to conform the tooth shape of the gear

  interior so that it looks like an involute.

  Preferably, the tooth shape of the inner gear is formed by lines resembling an involute. In one case, the teeth of the internal gear extend in a direction parallel to the axis of the internal gear, and the surfaces of the teeth

are substantially flat.

  The characteristics and advantages of the invention will also emerge

  of the description which will follow by way of example with reference to the drawings

  attached, in which Figure 1 is an isometric exploded view of a zoom lens barrel according to an embodiment of the present invention; Figure 2 is an enlarged isometric view of the rear portion of the zoom lens barrel shown in Figure 1; Figure 3 is an enlarged isometric view of the intermediate portion of the zoom lens barrel shown in Figure 1; Figure 4 is an enlarged isometric view of the front part of the zoom lens barrel shown in Figure 1; FIG. 5 is an isometric view of a support mechanism for the drive system of the zoom lens barrel; Figure 6 is an isometric view of gears of the drive system shown in Figure 5; Figure 7 is a side sectional view of the upper half of the zoom lens barrel of the present invention in the retracted position; FIG. 8 is a side view in section of the upper half of the zoom lens barrel of the present invention in the extended position; FIG. 9 is an isometric of a rotation cylinder corresponding to a cylindrical product of the present invention. 10 to 15 are isometric views showing a manufacturing process for manufacturing the cylindrical product using molds; FIG. 16 is a front view of a cam ring with an internal gear according to an embodiment of the present invention; FIG. 17 is an enlarged front view of a main part of the cam ring and the interior molds according to an embodiment to which the interior gear of the present invention is applied; FIG. 18 is a front view of a mold of an injection molding device comprising several pairs of first and second inner sliding cores according to an embodiment of the present invention; Figure 19 is an enlarged front view to explain in detail the structure of the first and second interior sliding cores shown in Figure 18; FIG. 20 is an isometric view of the first and second inner sliding cores according to the embodiment, in the closed state; FIG. 21 is an isometric view of the first and second internal sliding cores according to the embodiment, in the open state; FIG. 22 is a front view of the first and second internal sliding cores according to the embodiment, in the closed state; Figure 23 is a front view of the first and second inner sliding cores according to the embodiment, in the open state; Figure 24 is a sectional view of the first and second inner sliding cores, according to the embodiment, in the closed state which are cut by a plane in the direction in which the first and second inner sliding cores slide, o the first sliding core is shown below the optical axis 0 and the second inner sliding core above the optical axis 0; Figure 25 is a front view of the first and second interior sliding cores to explain the positional relationship between the two, in the closed state; Figure 26 is a sectional view of the first and second inner sliding cores, according to the embodiment, in an intermediate state which is between the closed state and the open state, which are shown cut by a plane in the direction in which slide the first and second inner sliding cores, o the first sliding core is shown below the optical axis O and the second inner sliding core above the optical axis O; Figure 27 is a front view of the first and second inner sliding cores to explain the positional relationship between the first and second inner sliding cores when in the intermediate state which is between the closed and open states shown in the figure 26; Figure 28 is a sectional view of the first and second inner sliding cores, according to the embodiment, in the open state which are cut by a plane in the direction in which the two inner sliding cores slide, o the first sliding core is represented

  below the optical axis O and the second inner sliding core below

  above the optical axis O; and Figure 29 is a front view of the first and second inner sliding cores to explain their positional relationship to each other

  to each other when in the open state shown in Figure 28.

  We will now explain embodiments of the present invention with reference to the drawings. In cameras according to this embodiment, a zoom lens barrel is provided with a zoom lens system comprising a group of front lenses L1 and a group of rear lenses L2. The focus operation is carried out by the group

of front lenses L1.

  Referring to Figures 7 and 8, a fixed lens barrel 11 of the zoom lens barrel 9 attached to a camera housing 10, to which the present invention is applied, is provided with an inner cylinder 11a and of an outer cylinder 1 1 b. The rear ends of the inner cylinder 11a and the outer cylinder 11b, in the direction of the optical axis X of the zoom lens system, are connected to each other by means of the connecting wall 11c, and the front ends of the cylinders 1a and 11b are open. A rotation cylinder (i.e., a cylindrical product) 12, which is introduced from the open end of the cylinders 11a, 11b is rotatably mounted on the outer periphery of the interior cylinder 1 the. Three rectilinear guide grooves 11c, each extending in a direction parallel to the optical axis X are formed on the interior wall 11a. Only one of

  three rectilinear guide grooves 1c is visible in FIG. 8.

  The rotation cylinder 12, as a cylindrical product to which the present invention is applied, is made of a synthetic resin, and a spur gear 12a is integrally formed with the cylinder 12 on its outer periphery, as shown Figure 9. A fine thread 12b is formed integrally with the cylinder 12 at one end of its outer peripheral part. On the inner wall of the rotation cylinder 12, are formed: three spiral drive grooves 12c which are parallel to each other and each inclined with respect to the circumferential direction of the cylinder 12; an inclined spiral inner gear 12d parallel to the drive grooves 12c; and a spiral release groove 12e. The spiral release groove 12e is formed in the vicinity of the gear 12d and has a larger diameter than that of the base circle of the inclined inner gear 12d and a

  width greater than the tooth width of the internal gear 12d.

  A support ring 13 is fixed to the front end opening of the inner cylinder 1a and of the outer cylinder 1b of the fixed lens barrel 11. The support ring 13 comprises a part 13a contacting the inner face of the outer cylinder 1 lb ; a threaded part 13b engaged with the fine thread 12b; a portion 13c contacting an outer face of the inner cylinder 11a, and an outer flange 13e. The support ring 13 is pressed against the fixed lens barrel 1 1 by a spring means (not shown) and it is held in a predetermined position. The reference number 13d is a gear formed on the outer periphery of the support ring 13 for a rotary operation. The support ring 13 also serves to reinforce the edge of the inner cylinder 11a and the cylinder

exterior 1 b.

  A notch 1 d to allow the pinion 11 f to engage with the spur gear 12a is formed on the outer cylinder 1 lb of the fixed lens barrel 11, and other notches similar to the notch 11d are formed on the inner cylinder 11a to reveal the drive groove 12c and the inclined inner gear 12d shown in

Figures 1 and 2.

  A first cylinder 14 which moves in the direction of the optical axis X mounts in the inner cylinder 1a of the fixed objective barrel 1 1. Three rectilinear guide projections 14a are formed integrally with the outer periphery of the first cylinder 14 and are in engagement with the guide grooves 1 the of the fixed objective barrel 1 1. Only one of the three rectilinear guide projections 14a is visible in FIG. 8. A lug 14b engaging in the corresponding driving groove 12c of the rotation cylinder 12 is formed on each of the guide projections 14a. In addition, a female helicoid 14c and three rectilinear guide grooves 14d parallel to the optical axis are formed on the inner wall of the first cylinder 14. In FIG. 3, only one of the three rectilinear guide grooves 14d can be seen. . With the structure described above, the rotation of the rotation cylinder 12 causes the displacement of the first cylinder 14 in the direction of the optical axis X, without rotation, by means of the grooves

  guide 1 1 and drive grooves 12c.

  A second cylinder 15 is housed in the first cylinder 14, and at the rear part of the outer periphery of the second cylinder 15 is formed a male helicoid 15a in engagement with the female helicoid 14c of the first cylinder 14. A rectilinear guide element 14 is introduced into the second cylinder 15, and a rectilinear guide plate 17, which serves as a support, is fixed by fixing screws 19 to the rear part of the guide element 16. An inner flange 1 5b is formed of in one piece with the second cylinder 15 between the guide element 16 and the guide plate 17 so as to rotate in relation to the guide element 16 and the guide plate 17, as shown in FIGS. 7 and 8. Three rectilinear guide keys 17a formed on the periphery of the guide plate 17 engage in a guide groove 14d. As a result, the guide element 16 and the guide plate 17 rotate in relation to the second cylinder 15 and that they move in one piece in the direction of the optical axis X. In others terms, the second cylinder 15 is mobile in rotation and mobile, at the same time, in the direction of the optical axis X by means of the male and female helicoid 15a and 15c on the one hand, and that on the other hand, the guide element 16 and guide plate 17 are movable at the same time as the second cylinder 15 in the direction of the axis

optical X without turning.

  As shown in FIG. 1, the guide element 16 is provided with three rectilinear keys 16b each extending in a direction parallel to the optical axis X. A guide element 18 for rectilinearly guiding the group of front lenses L1 is provided with three rectilinear keys 18a in engagement with the three keys 16b and each extending in a direction parallel to the optical axis X. A shutter block 20 is fixed to the guide element of the lens group before 18 by means of fixing screws 21 and it is further fixed to the front lens group support cylinder 22. As a result, the shutter block 20 and the front lens group support cylinder 22 cannot rotate and can only move in the direction of the optical axis X. As shown in FIGS. 1 and 4, the shutter block 20 is provided with a female helicoid 20a extending parallel to the optical axis X, and a male helix 23a of the lens support ring 23 fixing the group of front lenses L1 is in engagement with the female helix 20a. The lens support ring 23 and the lens fixing ring 40, in engagement with the ring 23 at the front end part of the ring 23, constitute a front lens frame 45. A male helicoid 22a, for moving the support ring lens 23 in the direction of the optical axis X during a plan change operation, is formed at the rear part of the outer periphery of the front lens group support cylinder 22. The shutter block 20 is provided with shutter blades 20c, and control signals are delivered to the shutter block 20 via a

  flexible printed circuit board (FPC card) 20d.

  A rear lens group guide slot 18b is formed on each of the rectilinear keys 18a of the front lens group guide member 18 for rectilinear movement of the rear lens group L2 in the direction of the optical axis X. The rear lens group L2 is fixed to the rear lens frame 24. Three rectilinear keys 24a engaged with the rear lens group guide slots 18b are formed on the rear lens frame 24. A cam lug 24b is formed on each of the keys 24a so as to project therefrom in a

radial direction.

  A female helicoid 15c and three cam grooves 15d are formed on the inner periphery of the second cylinder 15. The female helicoid 15c is engaged with a male helicoid 22a of the front lens group support cylinder 22, and the cam grooves 15d are engaged with the cam lugs 24d of the rear lens frame 24. The cam grooves 15d meet the female helicoid 15c in the same position in the circumferential direction of the second cylinder 15 so that part of the helicoid female 15c is eliminated. In the assembled state, the cam pins 24b of the rear lens frame 24 engage in open grooves 22b of the front lens group support cylinder 22, and in this state, the cam pins 24b are engaged in the grooves cam 15d, and the male helicoid 22a is in engagement with the female helicoid 15c. Under these conditions, the rotation of the second cylinder 15 causes the rectilinear displacement of the front lens group support cylinder 22 (of the front lens group L1) in the direction of the optical axis, due to the relationships between the female helicopter 15c. and the male helicopter 22a and between the keys 16b of the guide element 16 and the keys 18a of the front lens guide element 18. In addition, the rotation of the second cylinder 15 causes the rear lens frame to move. 24 (from the rear lens group L2) along a predetermined path in the direction of the optical axis X, due to the relationships between the cam grooves 15d and the cam pins 24b and between the keys 24a of the rear lens frame 24 and the rear lens group guide slots 18b of the guide member

  front lens 18, thereby effecting the change of plane.

  As explained above, when the rotation cylinder 12 is driven, the first cylinder 14 moves rectilinearly in the direction of the optical axis, and when the second cylinder 15 is rotated in relation to the first cylinder 14 , the second cylinder 15 moves in the direction of the optical axis X, while rotating. As a result, the group of front lenses L1 and the group of rear lenses L2 move in a straight line while the distance between the two

  lens groups varies to make the change of plan as well.

  We will now explain a drive mechanism for the second cylinder 15. The drive mechanism transmits the rotation of the rotation cylinder 12 to the second cylinder 15. The rear end of the first cylinder 14 is fixed to a pair of support plates d 'gears 26 and 27 by means of fixing screws 29. A pinion 30, in engagement with the inclined inner pinion 12d of the rotation cylinder 12, is fixed movably in rotation to the gear support plate 26, as shown Figures 5 and 6. Between two of the three rectilinear keys 14a is formed a rectilinear guide projection 14a 'having a space 14e to accommodate a pinion 30, as shown in Figure 3. A part of the teeth of the pinion 3, housed in the space 14e, protrudes from the outer periphery of the first cylinder 14. The inclined inner gear 12d of the rotation cylinder 12 is parallel to the drive grooves 1 2c, as shown in Figure 2, so that the mesh ment between the pinion 30 and the inclined inner pinion 12d is retained even when the first cylinder 14 moves in the direction of the optical axis X due to the rotation of the rotation cylinder 12. A gear train 31 receiving the rotation the pinion 30 is supported between the gear support plates 26 and 27, and a shaft transmitting the rotation 32, which extends forward along the optical axis, is formed in one piece with a final gear 31a . Tree 32 has a

  uniform cross-section which is not round.

  A pinion 33 is supported on the guide plate 17 fixed to the rear end surface of the guide element 16. The pinion 33 is mounted on the shaft 32 in such a way that the pinion 33 can slide on the shaft 32 in its axial direction but cannot rotate relative to the shaft 32. In other words, the pinion 33 is movable relative to the shaft 32 in the axial direction thereof and movable in rotation at the same time as the shaft 32. Thus, the pinion 33 moves along the shaft 32 at the same time as the guide plate 17, (and the second cylinder 15) when the second cylinder 15 moves in the direction of the optical axis X. The pinion 33 is engaged with a circumferential inner gear 15e which is formed on the inner surface of the second cylinder 15. Therefore, the rotation of the rotation cylinder 12 is transmitted to the second cylinder 15 by the intermediate inclined internal gear 12d, pinion 30, gear train gears 31, of the shaft transmitting the rotation 32, of the pinion 33 and of the circumferential internal gear 15e, whatever the position of the first cylinder 14 in the direction of the optical axis X. In the lens barrel zoom having the above structure according to the present invention, when the rotation cylinder 12 is rotated in the forward or reverse direction by the zoom motor 40, the first cylinder 14 moves in the direction of the optical axis and the second cylinder 15 rotates. The rotation of the second cylinder 15 allows the second cylinder 15 itself to move in the direction of the optical axis X, and the group of front lenses L1 and the group of rear lenses L2 to move in a rectilinear fashion by modifying the distance between the two groups of lenses to effect the change of plane. As described above, the front lens group L1 and the rear lens group L2 are movable between the retracted state of the lens barrel block

  zoom shown in figure 7 and the fully extended position of figure 8.

  In addition, in the retracted state, the first cylinder 14, the second cylinder 15 and the cylinder supporting the group of front lenses 22 do not protrude from the outer periphery of the main housing (the camera housing 10), this

  which results in a very small extent in the axial direction.

  We will now describe, with reference to FIGS. 9 to 15, a mold for forming the above-mentioned rotation cylinder (that is to say, the cylindrical product) 12 and a manufacturing process for obtaining the characteristics of mold of the present invention. The rotation cylinder 12 shown in Figure 9 is manufactured using a mold 35 shown in Figure 10. The mold 35 is provided with an upper mold 40 forming the upper surface of the rotation cylinder 12 and a lower mold 41 to form the inner surface of the cylinder 12. The lower mold 41 comprises a first cylindrical mold 36 with spiral teeth 36a for the inclined inner gear 12d of the rotation cylinder 12, and a second cylindrical mold 37 with a flat spiral part 37a for the clearance groove 12e. The second cylindrical mold 37 is further provided with three spiral projections 37b corresponding to the grooves

12c.

  The first cylindrical mold 36 is provided with a small cylindrical part 36b which has a smaller diameter than that of the second cylindrical mold 37, and with a spiral part 36c which has a larger diameter

  than that of the small cylindrical part 36b. The teeth 36a mentioned above

  above are formed on the outer periphery of the spiral portion 36c.

  The second cylindrical mold 37 is provided with an insertion hole 37 in its center, and the first cylindrical mold 36 is slidably introduced into the hole 37c. The second cylindrical mold 37 is provided with an engagement groove 37d between the projections 37b of the plate part 37a, as shown in FIG. 15. The groove 37d is shaped to have a spiral in the same direction as the spiral part 36c. When the second cylindrical mold 37 is rotated in the direction indicated by the arrow A in FIG. 10, provided that the spiral part 36c is engaged in the groove 37d, the second cylindrical mold 37 separates from the rotation cylinder 12 in such a way that the spiral part 36c (the teeth 36a) is gradually moved away from the engagement groove 37d, and that the teeth 36a engaged with the inclined internal gear 12d are left as they are in the rotation cylinder. The upper mold is divided into two elements (not shown) at the right position, for example, to remove the rotation cylinder from the mold,

as a product.

  We will now explain the manufacturing process of the rotation cylinder 12 using the mold 35 having the structure mentioned above. First, the upper mold 40, the first cylindrical mold 36 and the second cylindrical mold 37 are combined in a predetermined state to create a space for the formation of the rotation cylinder 12. In this state, a synthetic resin material is poured in space, and after the hardening of the synthetic resin material, the second cylindrical mold 37 is rotated in the direction indicated by the arrow A in Figure 10 to gradually separate the mold from the mold of the upper mold 40, as shown in FIGS. 11 and 12. In this case, the second cylindrical mold 37 causes, by turning, the separation of the small cylindrical part 36b from its insertion hole 37c and it is separated from the rotation cylinder 12 while the teeth 36a engaged with the inclined internal gear 12d are left as they are in the cylinder

of rotation 12.

  After which, as shown in Figure 13, the first cylindrical mold 36 is moved in a direction away from the upper mold 40, and the teeth 36a separate from the inclined inner gear 12d so as to be located in the groove 12th clearance. In this situation, the first cylindrical mold 36 is rotated in the direction in which the second cylindrical mold 37 rotates, whereby the spiral part 36c with the teeth 36a is separated from the rotation cylinder 12, with

  from its interior, along the spiral of the clearance groove 12e.

  By the procedures mentioned above, the rotation cylinder 12, as a product, remains in the upper mold 40, but it is possible to extract the cylinder 12 if the upper mold 40 is divided into elements

appropriate.

  As described above, according to the embodiment mentioned above

  Above the invention, it is possible to produce a cylindrical product in which an internal gear is not formed over its entire internal surface and other cam grooves are formed there. The cylindrical product is made with a relief groove on it so that this relief groove is used effectively to separate the mold from the internal gear after the internal gear has been formed. The above-mentioned mold for the cylindrical product according to the above-mentioned embodiment of the present invention comprises an upper mold for forming the upper surface of the cylindrical product and a lower mold for forming the inner surface of the cylindrical product, and the lower mold comprises a first cylindrical mold with a spiral toothed part for the internal gear and the second cylindrical mold with a flat spiral part for the release groove. As a result, a cylindrical product can easily be formed with an internal spiral gear inclined relative to its circumferential direction and a release groove adjacent to

the internal gear.

  Furthermore, the mold for a cylindrical product with a spiral release groove parallel to an inner gear comprises an upper mold to form the upper surface of the cylindrical product and an inner mold to form its inner surface, and the lower mold comprises a first cylindrical mold with a spiral toothed part for the internal gear and the second cylindrical mold with a flat spiral part for the clearance groove, and furthermore the second cylindrical mold comprises a spiral projection for the clearance groove, so that the cylindrical product can easily be formed with the internal spiral gear inclined with respect to its circumferential direction and the release groove adjacent to the internal gear, and the spiral drive groove parallel to the internal gear . Still further, the method of manufacturing a cylindrical product according to the above-mentioned embodiment of the present invention comprises the steps: the first step in which the first cylindrical mold is combined with a spiral toothed part for a gear inside, the second cylindrical mold with a flat spiral part for a clearance groove, and a lower mold to form the lower surface of the cylindrical product; the second step in which a resin-based material is poured into the space formed by the upper and lower molds; the third step in which the second cylindrical mold is rotated so as to be separated from the upper mold after the resin material in the space has hardened; the fourth step in which the first cylindrical mold is moved axially to cause the toothed part to separate from the upper mold; and the fifth step in which the first cylindrical mold is rotated so as to separate from the upper mold, so that the cylindrical product can be easily produced with the internal spiral gear inclined with respect to its circumferential direction and the

  release groove adjacent to the internal gear.

  We will now describe, with reference to the drawings, a mold for a product of cylindrical shape according to another embodiment of the present invention. The metal mold of an injection molding machine is formed of sliding cores which are obtained by dividing the metal mold into several elements, and each of the sliding cores moves radially to open and close the mold. In the embodiment shown in FIGS. 16 and 29, the internal gear produced by injection molding according to the present invention is applied to an internal toothed part of a camera cam 1 1 1 ring. However, it goes without saying that the present invention can be applied to the same rotation cylinder as the previous embodiment. First, we will explain the structure of the cam ring 1 1 1 and the outline of the mold

  metal to make the cam ring 1 1 1 by injection molding.

  As shown in Figure 16, which is a front view of the cam ring 1 1 1, the cam ring 1 1 1 is provided with internal teeth 1 13 on its inner surface. The inner surface of the cam ring 1 1 1, including the inner teeth 1 13, is formed by several sets of interior molds 132, 142 each constituting an elementary interior mold, as shown in Figures 20 to 23. Each of the parts of the internal mold 132, 142 moves radially, with respect to the axis 0 of the mold which coincides with the axis of rotation of the cam ring 111, at different speeds, to open and close the internal mold. Figures 20 and 22 show the inner mold in the closed state and Figures 21 and 23

  represent the mold in the open state.

  The inner teeth 113 of the cam ring 111 extend parallel to the axis of the cam ring 111, and the end faces of the inner teeth 113 follow each other along a spiral shape. The internal teeth are formed substantially on half of the internal periphery of the cam ring 111. In this embodiment, dividing lines of the internal molds 132, 142 are formed in line with the feet of the external teeth (toothed product) 135 , 145 to form the internal gear 113. The dividing lines in this embodiment pass through corners 135a, 145a where the internal molds 132, 142 are in contact with each other

  with others when closed.

  In this embodiment, the following formula is verified Z = (S / 2). n, (2) where Z is the number of teeth for one revolution of the internal gear 113, S is the total number of internal molds 132, 142; and n is a positive integer which is chosen from even numbers as a function of the engagement conditions with the internal gears 113, as

discussed below.

  As described above, if the number Z of the inner teeth 113 and the total number of the inner molds 132, 142 are chosen to satisfy the above formula, the dividing lines of the inner molds 132, 142 can be formed on the feet outer teeth 135, 145. In this embodiment, S and n are fixed, respectively at 12 and 18, so that Z is 108. In the embodiment, if n was less than 14, the shape of the gear would not correspond to an involute. If n was greater than 18, the interior molds 132, 142 would be too small. Therefore, n

  is chosen according to the specific design conditions.

  The cam ring 111 according to this embodiment is not provided with internal teeth 113 over its entire inner periphery but only over about half of the inner periphery. Consequently, it goes without saying that the interior molds 132, 142 are not always provided with the exterior teeth 135, 145 but that only the interior molds at

  right of the desired parts are provided with external teeth.

  We will now explain in detail, with reference to FIG. 17, the characteristics of the internal gear according to the present invention. FIG. 17 is an enlarged front view of a tooth shape and of the part adjacent to the contact part (the dividing line) of the inner molds 132 and 142 for forming the tooth. This figure shows the state in which the inner molds 132 and 142 are closed, i.e., the state in which a tooth of the inner teeth 113 is formed in the space which is closed by the outer teeth 135 of the mold 132 and the external toothing of the mold 142. The reference number 113i designates part of a shape

of an ordinary involute tooth.

  The internal mold 132 moves rectilinearly in the direction parallel to the sliding line 01 during the opening and closing of the mold, which causes the corner 135e of the added part of the external toothing 135 to move on the sliding line 01 which passes through the corner 135c. The sliding line 01 partially covers the involute tooth shape 113i, that is to say that the corner 135c

  interferes with the developing tooth shape 113i.

  Therefore, in this embodiment, if the tooth shape 113a for the inner teeth 113 is formed in such a way that the outer teeth 135 do not interfere with the tooth shape 113a when the inner molds 132 and 142 move radially when they are opened or closed. In other words, in FIG. 17, the tooth 113a is formed so as not to contact the sliding line 01 nor to cut the line 01. The shape of the tooth is chosen freely if the condition mentioned above is satisfied . However, in this embodiment, the conformation of the tooth shape 113a is based on the involute tooth shape 113i, and lines resembling the tooth shape are adopted so as not to lose the regular rotation of the tooth. internal gear 113 when engaged with other gears. We

  can adopt cycloid teeth as standard tooth shape.

  The condition that the trajectory of the teeth 135 and 145 does not contact or cut the internal gear 113 must be satisfied for all the teeth and 145. However, in this embodiment, if this condition is satisfied for the teeth 135 at one end of the inner mold 132, the other teeth 135, 145 will always satisfy the condition since the circumferential length of the inner mold 132 is longer than that of the mold

interior 142.

  The first and second sliding cores 131, 141 of each assembly, according to this embodiment, have basically the same shape as those of the other assemblies, but the outer peripheral surfaces of the interior molds 132, 142 are shaped according to

  inside the final molded product.

  We will now explain, with reference to FIGS. 20 to 23, the main lines of the injection molding machine mold for the cam ring 111 with the internal teeth 113. FIGS. 20 and 21 are isometric views of a part main of the internal sliding cores (the internal molds 132, 142) according to one embodiment of the metal mold of an injection molding machine for the cam ring 111, respectively, in the closed state and in the open state, and Figures 22 and 23

  are front views of the main part in these same states.

  The metal mold 120 comprises several sets of inner sliding cores 131 and 141 (6 sets, a total of 12 elements in this embodiment) to form the inner peripheral surface of the cam ring 111, among which a set of sliding cores consists of a first inner sliding core 131 and a second inner sliding core 141; a plate 121 for movably supporting the inner sliding cores 131 and 141 in the radial direction perpendicular to the axis O of the metal mold which coincides with the axis of the cam ring 111; a locking core 123 situated in a space close to the axis which is closed by the interior peripheral surfaces 131a and 141a of the first and second interior sliding cores 131 and 141 for pressing and supporting the first and second interior sliding cores 131, 141 in the closed state when the locking core moves to a front position by a movement parallel to the axis O; a plate 125 for moving the locking core 123; inclined pins 127, 128 fixed to the plate 125 to drive the first and second sliding cores 131, 141 at different speeds in the direction in which the cores are opened and closed when the plate 125 moves. The fixed plate 121 is fixed to a block, or the like, of the injection molding device, and the movable plate 125 is driven by a hydraulic cylinder, a press shaft, or

  analogous, which are not shown in detail in the drawings.

  Each of the first and second inner sliding cores 131, 141 is provided with an inner mold 132, 142, which is, respectively, integrally formed with the front ends of base parts 133, 143, and the inner molds 132, 142 closely contact the other neighboring interior molds 132, 142 in the closed state to form the interior peripheral surface of the cam ring 111. In addition, the base parts 133, 143 are provided with guide parts 134, 144 to guide the first and second inner sliding cores 131, 141 (the inner molds 132, 142) in the direction in which the cores are opened and closed (the radial direction). The first and second inner sliding cores 131, 141 of each assembly are identical to the

  point of view of their basic construction, therefore, we will describe below

  below the other structure relating to the basic construction and the mechanism with reference to a single set of first and second cores

interior sliding doors.

  The guide parts 134, 144 are provided with dovetail cross sections (which are not shown in detail in the drawings). A dovetail guide groove 121b is formed in the fixed plate 121, which extends in the direction perpendicular to the axis O (the axis of the cam ring 111), and the guide parts 134, 144 are slidably engaged in the guide grooves 121b. Each of the interior molds 132, 142 projects forward from a

  opening 121a in the fixed plate 121 in the mounted state mentioned above

  above and moves radially while being guided by the parts of

  guide 134, 144 and the guide groove 121 b.

  The inner molds 132, 142 are separated from each other so as to open by moving in the direction of the axis O. In addition, the inner molds 132, 142 move radially away from the axis O to come into abutment, by its outer peripheral surface, against an edge 121c of the opening 121a, then at the moment when any further movement towards the outside is prohibited, the interior molds 132, 142 are in the closed state. The position and condition of the interior molds 132, 142 at this

  moment are called the closed position and the closed state.

  In the closed state, outer gears 135, 145 for forming the inner teeth 113 are formed on the outer peripheral surface of each of the inner molds 132, 142. The cam ring 111 may be provided with inner teeth 113 as well as grooves, holes, protrusions and bosses. In which case, bosses, protrusions, holes and

  grooves are formed on the interior molds 132, 142.

  The end faces of the cam ring 111 are formed by the front face of the fixed plate 121, the inside diameter of the opening 121a is almost the same as that of the cam ring 111, and the inner peripheral surface of the cam ring 111 is formed by the molds

  interiors 132, 142 protruding from the opening 121a.

  The inner peripheral surfaces 131a, 141a, of the first and second inner sliding cores 131, 141 are formed so as to gradually become smaller in diameter towards the fixed metal mold 151 (in the forward direction) to form a frustoconical part , and the locking core 123 is formed like a truncated cone, the conical part 123a of which contacts the interior peripheral surfaces 131a and 141a. The angle between the conical part 123a or the internal peripheral parts 131a, 141a and the axis O is defined as being qG- The movable plate 125 is provided with inclined pins 127, 128 to transmit, to the internal sliding cores 131, 141, a rectilinear displacement in the directions forward and backward parallel to their axis O, when they move in the direction of opening and closing. The front rod parts 127a, 128a of the pins 127, 128 are housed so that they can slide, respectively, in holes

  guide 136, 146 of the internal sliding cores 131 and 141.

  The inclined pins 127, 128 are fixed to the movable plate 125 at determined angles OD, 0E relative to the axis O to move the first and second inner sliding cores 131, 141 at different speeds. The movable plate 125 is provided with recesses for the screw holes i125a, 125b, where the extensions of their axes intersect the axis O, respectively, along the angles 0D, 0E. Male threaded parts 127c, 128c are formed on the inclined pins 127, 128 in line with their parts adjacent to the heads 127b, 128b. In this structure, the front rod parts 127a, 128a of the inclined pins 127, 128 are introduced into tapped holes 125a, 125b from the rear of the movable plate, and the male threaded parts 127c, 128c are engaged with the holes threaded 125a, 125b, which allows the inclined pins 127, 128 to be fixed to the movable plate 125 according to the angles 0D, OE relative to the axis O. The angles OD and OE are different from one other to allow the first and second inner sliding cores 131 and 141 to be driven at different speeds. In the embodiment, the second inner sliding core 141 contacts the first inner sliding core 131 from the side of the axis O, so that the angles mentioned above are chosen so that we have 0D <OE, for move the second inner sliding core 141 faster than the first sliding core

  inside 131 when the fixed plate 125 moves back and forth.

  The speeds of the first and second inner sliding cores 131, 141 relative to the locking core 123 in the direction in which they are open and closed (the radial direction) are, respectively, tan 0D and

tan OE.

  The means for driving the first and second inner sliding cores 131, 141 at different speeds is not limited to the inclined pins 127, 128, but other structures can be adopted, for example, a surface, inclined on the core of blocking 123 can contact so as to be able to slide an inclined surface on the inner surface of the sliding cores 131, 141, or else a groove on one element and a projection on the other element can engage so as to be able to slide

With each other.

  Furthermore, in this embodiment, the angle of inclination qG of the conical part 123a is fixed so that there is 8D <0E <OG so that the conical part 123a of the locking core 123 abuts against the interior peripheral surfaces 131a, 141a in the closed position or in an almost closed position and does not interfere with their others

retracted positions.

  We will now explain, with reference to FIGS. 18 and 19, the detailed structure of the first and second inner sliding cores 131, 141. FIG. 18 is an enlarged front view of the inner cores 132, 142 (of the first and second sliding cores interiors 131, 141), Figure 19 is a more enlarged front view of the inner cores

132, 142.

  As shown in FIG. 18, the first and second inner sliding cores 131, 141 neighbors move, respectively, along the first and second sliding lines 01 and 02, and their basic conformation is formed so as to be symmetrical with respect to

  to the sliding lines 01, 02 which intersect the axis 0.

  The angle between the first and second sliding lines 01, 02 is defined as Oc. The angle OC is determined by the total number of first and second inner sliding cores 131, 141. In this embodiment, the number of cores 131 and 141 is a total of 12. By

  therefore, OC = 360/12 = 30 degrees.

  To prevent the partition surfaces 131c and 141c from interfering in positions other than the closed position and the positions close to the closed position when the first and second inner sliding cores 131 and 141 move during their opening and closing , the displacement speeds of the inner sliding cores 131, 141 are, respectively, tan 8D, tan OE and the angle OC satisfies the following formula: tan OD <tan OE. cos OC (4) The first and second inner sliding cores 131, 141 contact each other on the two lateral surfaces in their circumferential direction (the partition surfaces 131c, 141c) and the

  internal molds 131, 141 are closed when they are in the closed state.

  When measuring counterclockwise from the sliding line 01 in the figure, the partition surfaces 131c, 141c of the first and second inner sliding cores 131, 141 form the same angle 0E by relative to the first sliding line 01 of the first inner sliding core 131. The angle OB is determined in such a way that the partition surface 141c of the second inner sliding core 141 contacts the partition surface 131c of the first inner sliding core 131 when the partition surface 141c moves along the sliding line 02 with respect to the axis 0. The partition surfaces 131c, 141c of the first and second inner sliding cores are formed by the sliding cores 131, 141 and are symmetrical, respectively , compared to planes formed by extending axially

the sliding lines 01, 02.

  GA designates the largest angle for causing the outer teeth to interfere with the mold 142 or the outer teeth 145 when the first and second inner sliding cores 131, 141 move when they are opened and closed. The largest angle eA is the angle between the line connecting the corner 135a of the first inner sliding core 131 to the outermost upper part (the corner) of the outer teeth 145 and the first sliding line 01 , as shown in the figure. The largest angle qA varies depending on the position of the dividing line (the separation position of the outer teeth 135, 145), but the separation position is preferably taken to be at the foot, and not

  not on the tooth surface, to maximize its strength.

  The smallest angle Op between the partition surfaces 131c, 141c and the first sliding line 01 which allows the partition surfaces 131c, 141c to be movable towards the open and closed positions without interfering with each other is defined by the following formula: OF = tan1 (sin OC. tan OE / (tan 0E. cos Oc - tan OD) (5) In this formula, as indicated above, OC is the angle between the sliding lines 01, 02 first and second inner sliding cores 131, 141; OD is the angle between the inclined spindle 127

  and the axis O; and OE is the angle between the inclined spindle 128 and the axis 0.

  The angle OB between the partition surfaces 131c and 141c of the axis and the sliding line 01 of the first internal sliding core 131 is taken to be greater than the smallest angle OF and smaller than the angle the greater 0A, that is to say to satisfy the following formula, by which they move, when they open and close, in synchronism with the movement of the movable plate 125 without the first and second cores internal slides 131 and 141, that is to say without the internal molds 132, 142, interfering with each other:

OF <OB <OA (6)

  We will now explain, with reference to FIGS. 24 to 29, the opening and closing of the first and second internal sliding cores 131, 141. FIGS. 25, 27 and 29 are front views of the first and second internal sliding cores 131, 141 to explain the relationship between the two, and Figures 24, 26 and 28 are sectional views of the inner sliding cores 131, 141 shown in Figures 25, 27 and 29, which are taken along a plane passing through the lines 01, 02, and the first inner sliding core 131 is shown above the axis and the second inner sliding core 141

below the axis.

  In the closed state, in which the inner cores 132, 142 are in close contact with each other, the locking core 123 moves to bring its conical part 123a into abutment against the inner peripheral surfaces 131a, 141a of the first and second cores internal slides 131, 141 and to press them towards the closed position (towards the outside). The inner sliding cores 131, 141 which are subjected to the pressure are pushed into the closed position (towards the outside) along guide grooves 121 b and the partition surfaces 131, 141c contact each other closely to close the interior molds 132, 142, as shown in FIGS. 20,

22, 24 and 25.

  In the closed state, the exterior metal mold 151 cooperates with the interior molds 132, 142 and a cavity to form the cam ring 111 is created by the exterior peripheral surfaces of the interior molds 132, 142, the peripheral surface of the exterior metal mold 151, and the front faces of the fixed plate 121. Synthetic resin is injected into the cavity by an injection piston or the like, and it is solidified, or

  hardened to form the cam ring 111.

  To extract the cam ring 111 formed, the movable plate 125 is retracted from the closed state, and the locking core 123 and the inclined pins 127, 128 are retracted simultaneously, which allows

  to the first and second internal sliding cores 131, 141, that is to say

  tell the interior molds 132, 142, to disengage from the conical part 123a and to open (to move in the direction towards the axis 0). In addition, the inclined pins 127, 128 are retracted simultaneously so that the inner molds 132, 142 move in the opening direction while being limited by the inclined pins 127, 128. Then, the inner molds 132, 142 are separated from the inner teeth 113 and the inner molds 132, 142 are separated from each other as shown in Figures 27

and 28.

  Referring to Figures 21, 23, 28 and 29, approximately when the movable plate 125 is further retracted and reaches the open position, the outer gear parts 135, 145 of the inner molds 132, 142 are completely removed from the teeth 113 from the cam ring 111 to allow the cam ring to be removed 111. In this open state, the outer molds 151 are separated from each other to remove the cam ring and the cam ring is extracted from the molds external metal 151. In this open state, the planes 131b, 141b connecting the inclined surfaces 131a, 141a and the sharing surfaces 131c, 141c of the first and second internal sliding cores 131, 141 are closest to each other. It goes without saying that the planes 131b and 141b are shaped in such a way that they do not interfere with each other when the first and second inner sliding cores 131, 141 move between the open and closed positions. In the case where the cam ring 111 is provided with undercuts also on its peripheral surface

  exterior, the exterior metal mold 151 is also divided.

  As described above, with the mold used for the injection molding machine according to the embodiment of the present invention, the only movement forward and backward of the movable plate 125 brings the first and second inner sliding cores 131, 141 to move, at different speeds, in the direction in which they are open and closed without interfering with each other. As a result, one can easily form a cylindrical product with undercuts in line with its interior peripheral surfaces, such as the cam ring 1 1 1, by injection molding with a structure and a

simple controls.

  In this embodiment, an explanation has been given relating to

  a cam ring 1 1 1, shaped like a product with counter

  spoils, manufactured by injection molding. It is obvious that the present invention can be applied to products other than the ring to

cams 1 1 1.

  Furthermore, in this embodiment, the number of interior teeth 113 of the cam ring 11 1 is determined based on the number of elementary interior molds, which allows each of the molds to be manufactured as a standard conformation to simplify the construction of the mold as well as that of the drive means for opening and closing the mold. In addition, with the structure mentioned above, the dividing lines are formed in line with the feet of the outer teeth

  135, 145 to easily form the inner teeth 1 13.

  If the number of elementary interior sliding cores 131, 141 is S; and if the number of teeth of the internal gear is Z, Z is determined by the following formula: Z = (S / 2) .n, (n is a positive integer). In general, the coefficient n is taken from among the even numbers taking into account the gears engaged with the internal gear 113

  in this embodiment as discussed above.

  Furthermore, in this embodiment, the number of teeth Z in the formula mentioned above is an integer since several sets of interior molds are adopted as first and second interior sliding cores 131, 141 constituting a set of molds interiors. It is possible to preferentially determine the number of teeth Z, however, in this case the quotient of the above formula is not always a whole number. In such a case, certain sets of first and second inner sliding cores 131, 141 are adjusted

  to conform the mold correctly.

  In this embodiment, the cam ring 1 1 1 has been described, and the metal mold for forming the cam ring 1 1 1 as an example of a

  produced with an internal gear, produced by injection molding.

  However, it goes without saying that the present invention is applicable to products with an internal gear other than the cam ring 111 and to

* a metal mold to form the product by injection molding.

  In addition, in the embodiment described above, the tooth shape 1 13a of the internal gear 113 of the cam ring 111 is shaped in a rectilinear manner so as not to interfere with the path of the external teeth 135, 145 to form the inner gear 113 in the direction in which the outer teeth 135, 145 move, this allows the inner molds 132, 142 to be radially retracted. As a result, it is possible to manufacture by injection molding products with undercuts for which the internal molds 132, 142 cannot be retracted in a direction parallel to the axis O.

  As can be clearly understood from the explanation above

  above, in the present invention, the angle OB between the partition surfaces 131c and 141c and the sliding line of the first inner sliding core 131 is fixed to be greater than the smallest angle OF to prevent the partition surfaces first and second inner sliding cores to interfere with each other in positions other than the closed position and positions close to the closed position, and the angle 0B is set to be smaller than the largest angle OA relative to the direction of movement of the first sliding core to prevent undercuts of the second inner sliding core from interfering with the first inner sliding core when the first and second inner sliding cores move during their opening and their closure, whereby the inner sliding cores are driven during their opening and closing without using a means in special control, this results in a simple control means for the injection molding machine and a structure

of simple drive means.

  In addition, in the present invention, the number of teeth of the inner gear, which are formed by the metal mold of injection molding using several inner sliding cores moving radially for the opening and closing of the molds interior, is determined based on the number of elementary interior sliding cores, which allows that the dividing lines of the interior molds to form the interior teeth are located at the foot of the teeth. This results in a considerably simpler mold structure. In addition, the structure and the control means of the drive means for opening and

  closing the mold are also much simplified.

  Furthermore, in the present invention, the tooth shape of an inner gear, which is formed by an injection molding mold with several inner sliding cores moving radially for the opening and closing of the inner mold, is formed so as not to interfere with the inner sliding cores when the inner sliding cores move during their opening and closing, whereby it is possible to form the inner gear with molds moving radially. What it follows is that a product with,

  at its inner periphery, an inner gear comprising counter

  drafts other than the internal gear, for which the internal molds cannot be retracted in a direction parallel to the axis of the gear, can also be formed by injection molding in

using the present invention.

Claims (11)

  1. Injection molding mold (120) comprising several sets of first and second inner sliding cores (131, 141), said first and second inner sliding cores (131, 141) having inner molds (132, 142) with counter - undercuts forming adjacent parts to each other constituting a set of first and second inner sliding cores (131, 141), characterized in that said first and second inner sliding cores move in a direction perpendicular to the axis of said inner cores at different speeds from each other to open and close said inner cores (131, 141); in that the following formula is verified: OF <OB <OA (1)   o OB is the angle between a pair of partition surfaces (131c, 141c) and a sliding line (01) of said first inner sliding core (131) in a position o said first and second inner sliding cores (131, 141) closing said inner molds (132, 142); OF is the smallest angle so that said partition surfaces (131c, 141c) of said first and second inner sliding cores (131, 141) do not interfere with each other in positions other than the closed position and a partially open position and 0A is the largest angle which causes said undercuts of said second inner sliding core (141) not to interfere with said first inner sliding core (131) when said first and second sliding cores interiors (131, 141) move   during their opening or closing.   2. Mold for injection molding (120) according to the   claims, characterized in that the product formed by said molds   interiors (132, 142) is a cam ring (1 1 1) with an internal gear (113) having undercuts; in that the partition surfaces (131c, 141c) of said first and second inner sliding cores (131, 141) are formed in the tooth feet of an inner gear part (113); and in that the largest angle OA is the largest angle which allows the tips of said second inner sliding core (141) not to interfere with said first inner sliding core (131) when said surface dividing lines first and second inner sliding cores (131, 141) are formed on said tooth feet.   3. Injection molding mold (120) according to claim 1, characterized in that said first and second inner sliding cores (131, 141) are supported so as to be able to slide in order to approach and move away from a plate fixed (121) at a predetermined angle OC in a direction perpendicular to said axis (0), said interior molds (132, 142) being closed when said first (131) and said second (141) sliding cores reach a most distant position 'outside. 4. An injection molding mold (120) according to claim 1, characterized in that it further comprises: a locking core (123) slidingly guided in a direction parallel to said axis (0) up to a space closed by the inner peripheral surfaces of said first (131) and said second (141) inner sliding cores, characterized in that, when it is introduced into said space, said locking core (123) presses and maintains each of said first (131 ) and said second inner sliding cores (141) in a closed position o the contact surfaces of said first (131) and said second inner sliding cores (141) are in contact with each other, and in that during retraction said blocking core (123), said blocking core (123) allows said first (131) and said second   (141) interior sliding cores to open.   5. An injection molding mold (120) according to claim 4, characterized in that said blocking core (123) is fixed to a movable plate (125); in that inclined pins (127, 128) which are slidably inserted into guide holes of said first (131) and said second (141) inner sliding cores are fixed to said movable plate (125); in that when said movable plate (125) moves, said inclined pins (127, 128), which are fixed at predetermined angles OD, 0E with respect to said axis (0), move said first (131) and said second ( 141) inner sliding cores in a direction which opens and closes said first (131) and said second (141) inner sliding cores at different speeds from each other; and in that the following two formulas are verified simultaneously: OD <OE (3); and tan OD _ tan 0E. cos OC (4) o, OC is the angle between the sliding lines (01, 02) of said   first (131) and said second (141) inner sliding cores.   6. Injection molding mold (120) according to claim, characterized in that the smallest angle OF satisfies the following formula: OF = tan-1 (sin OC. Tan OE / (tan 0E. Cos OC -tan OD)) o, OC is the angle between the sliding lines (01, 02) of said first (131) and said second (141) inner sliding cores; One is the angle between said inclined spindle (127) of said first inner sliding core (131) and said axis (0); and eE is the angle between said inclined pin   (128) of said second inner sliding core (141) and said axis (0).   7. Mold for injection molding (120) comprising several internal sliding cores (131, 141) moving radially to open and close internal molds (132, 142), characterized in that the number of teeth of the internal gear is determined based on the   number of said elementary inner sliding cores (131, 141).   8. Mold (120) according to claim 7, characterized in that said interior sliding cores comprise several sets of first and second interior sliding cores (131, 141), and in that a set of said several sets of first and second cores interior sliding includes first and second interior sliding cores (131, 141) which are adjacent to each other and move radially at different speeds relative to each other to open   and closing said interior molds (132, 142).   9. Mold (120) according to claim 7, characterized in that the number of teeth of said inner gear is determined by the following formula: Z = (S / 2) .n (2) o, S is the number of sliding cores elementary interiors (131, 141); Z is the number of teeth of said internal gear; and n is a positive integer.   10. Injection molding mold (120) according to claim 1, characterized in that a product formed by said internal molds (132, 142) is a cam ring (111) with an internal gear comprising -15 of the counter- drafts, and in that the number of teeth of said internal gear is determined based on the number of said first and   said elementary second inner sliding cores (131, 141).   11. injection molding mold (120) according to claim 1, characterized in that a product formed by said internal molds (132, 142) is a cam ring (111) with an internal gear comprising undercuts, and in that the tooth shape of said inner gear is formed by lines resembling an involute, and in that further said inner molds (132, 142) do not interfere with each other when the inner cores ( 131, 141) are trained to their opening and closing.