JP2010221550A - Method of manufacturing eccentric article and eccentric article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an eccentric article capable of manufacturing a precise eccentric article easily by injection molding and an eccentric article. <P>SOLUTION: The method of manufacturing an eccentric article comprises injection-charging an at least cylindrical cavity 4 formed between a fixed mold 2 and a movable mold 3 with a resin during mold closing of a mold 1 so as to obtain an eccentric article having a recessed part on the side opposite to a gate 5 communicating with the cavity 4 with respect to the central axis O of the cavity 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an eccentric body manufacturing method and an eccentric body.

  Conventionally, in injection molding, when a core or a pin is provided in a mold to form a hollow part or the like in a molded product, the molten resin flows so as to branch in the cavity, A weld line is generated in the welded portion where it has joined again after welding.

  Weld line refers to a groove (concave part) that occurs where two or more flow fronts meet, and it is difficult to avoid the occurrence of this weld line in injection molding, increasing the temperature of the molten resin and mold. Although it can be minimized by increasing the injection pressure, it is difficult to eliminate it completely. For this reason, it has been necessary to devise so that the weld line is formed in a conspicuous position in the molded product (Patent Document 1).

JP-A-7-148765

  Further, when a molded product is manufactured by cutting or polishing, it is necessary to perform precise cutting or polishing, which causes problems such as high cost and low productivity. In particular, it is difficult to manufacture a precise eccentric body by cutting or polishing, and a simpler method is desired.

  The present invention has been made in view of the above-mentioned problems of the prior art, and provides an eccentric body manufacturing method and a highly accurate eccentric body that can easily obtain a highly accurate eccentric body with excellent productivity. The purpose is to do.

  In order to solve the above-described problem, the eccentric body manufacturing method of the present invention passes through a gate communicating with the cavity at a position that does not coincide with the central axis of the cavity in a plan view, into the cylindrical cavity of the molding die. It is supposed to supply molten resin.

  According to the present invention, an eccentric body can be easily obtained by utilizing a weld portion generated in injection molding. When molten resin is supplied into the cavity from the gate that is not coincident with the central axis of the cavity, the molten resin branches in the cavity, flows around the central axis, and joins again. Since a weld portion is generated at the welded portion where the molten resin is merged, for example, an eccentric body having the weld portion as a bottom dead center can be obtained. Moreover, since it is injection molding, the accuracy improvement as an eccentric body can be expected, and a precise eccentric body can be mass-produced.

Further, it is preferable that the molten resin is supplied into the cavity through the plurality of gates that are not point-symmetric with respect to the central axis of the cavity.
According to the present invention, by supplying molten resin through a plurality of gates that are not point-symmetric with respect to the central axis of the cavity, a plurality of welds corresponding to the number of gates are formed on the side peripheral surface of the molded product. It becomes. That is, an eccentric body having a desired eccentricity can be obtained by increasing or decreasing the number of gates.

Further, it is preferable that the degree of eccentricity is adjusted by the positions of the plurality of gates.
According to the present invention, an eccentric body having a desired eccentricity can be easily obtained by adjusting the position of the gate in advance.

The eccentric body of the present invention has a cylindrical shape having a hollow portion at the center, has a concave portion extending in parallel with the central axis of the hollow portion on the side peripheral surface, and the concave portion is a molten resin at the time of molding. Is a weld portion formed by joining.
According to the present invention, since it is an eccentric body using a weld portion, it can be mass-produced by injection molding. In addition, a molded product obtained by injection molding has high reproducibility compared to cutting and polishing, and thus becomes a highly accurate eccentric body.

Further, it is preferably a cam that rotates around the central axis.
ADVANTAGE OF THE INVENTION According to this invention, it can be set as the highly accurate eccentric cam using the weld part produced by injection molding.

Sectional drawing which shows the molding die of the multipoint gate used for the manufacturing method of the eccentric body of this embodiment. The top view which shows the position of a gate. Sectional drawing which shows a mode that resin is filled into a cavity from each gate. The top view which shows the flow state of resin in a cavity. Sectional drawing which shows a mold opening process. The perspective view of the eccentric body obtained by the manufacturing method of the eccentric body of this invention. The perspective view which shows the eccentric body of 2nd Embodiment. The top view which shows the flow state of resin in a cavity.

  Embodiments of the present invention will be described below with reference to the drawings. In each drawing used for the following description, the scale of each member is appropriately changed to make each member a recognizable size.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a molding die used in the method for manufacturing an eccentric body of the present invention, and FIG. 2 is a plan view showing the position of the gate with respect to the cavity.

  First, the molding die 1 used for the manufacturing method of this embodiment is described. As shown in FIGS. 1 and 2, the molding die 1 includes a fixed mold part 2 and a movable mold part 3 that engages with the fixed mold part 2, and the fixed mold part 2 and the movable mold part 3 when closed. A cylindrical cavity 4 is formed between the two.

  In the present embodiment, the fixed mold portion 2 is provided with a plurality of gates 5 (5a, 5b, 5c), and each gate 5a, 5b, 5c has a so-called multi-point gate configuration that leads to the cavity 4. . In the present embodiment, as shown in FIG. 2, the plurality of gates 5 a, 5 b, 5 c are arranged at positions that are not point-symmetric with respect to the central axis O of the cavity 4, and what is the central axis of the cavity 4 in plan view? Each communicates with the cavity 4 at a position that does not match.

The fixed mold part 2 has a cylindrical cavity forming part 21 that opens to the joint surface 2b, and forms the above-described cavity 4 by being closed with the movable mold part 3. .
On the other hand, the movable mold part 3 is provided with a shaft part 31 that projects into the cavity forming part 21 when the mold is closed, and the cavity 4 has a cylindrical shape. The tip 31a of the shaft part 31 is in contact with the upper part 21a of the cavity forming part 21 as shown in FIG.

  The structure of the molding die 1 is not limited to that described above, and can be appropriately changed depending on the shape of the target molded product. In this embodiment, the shaft portion 31 is provided on the movable mold portion 3 side. However, the shaft part 31 may be provided on the fixed mold part 2 side, or a structure using a pin or the like of another member instead of the shaft part 31 may be used.

The manufacturing method of the eccentric body of the present invention includes a resin filling step S1, a pressure holding step S2, a cooling step S3, and a mold opening step S4.
In the resin filling step S1, molten resin 6 melted in the cavity 4 is supplied through the gates 5a, 5b, and 5c. The molten resin 6 supplied from the gates 5a, 5b, 5c into the cavity 4 flows around the central axis of the cavity 4 between the cavity forming portion 21 and the shaft portion 31, and the molten resin 6 flows. The front end portion 6a merges with the flow front end portion 6a of the molten resin 6 filled from the adjacent gate 5 around the central axis. Then, a groove called a weld line (hereinafter referred to as a weld portion 7) is formed in a portion where the molten resin 6 has joined. In the present embodiment, since the molten resin 6 is simultaneously supplied from the three gates 5 a, 5 b, 5 c into the cavity 4, a plurality of welds 7 (concave portions) are formed around the central axis of the cavity 4.

  Since the weld portion 7 is formed at a portion where the molten resin 6 flowing in the cavity 4 joins, the position where the weld portion 7 is formed can be adjusted by changing the position of the gate 5 communicating with the cavity 4. It is.

  In addition, at the time of resin supply, it is preferable to heat the molding die 1 together with the resin material. In addition, the filling pressure of the molten resin 6 in each gate 5 is appropriately adjusted according to the type of the molten resin 6 and the shape of the molded product, and in this step, the filling pressure of the molten resin 6 supplied through each gate 5 is equal. ing.

  As the resin filled in the cavity 4, a thermoplastic resin is used. For example, injection of polyolefin such as polyamide, ABS, polycarbonate, acrylic resin, PPE, PP, polyester, thermoplastic urethane elastomer, polyvinyl chloride, PEEK, etc. Resins that can be molded are listed. In order to increase the rigidity of the molded product, a reinforcing material such as carbon fiber or glass fiber may be mixed in the resin.

  In the pressure holding step S <b> 2, a predetermined pressure is applied to the molten resin 6 filled in the cavity 4 to replenish the molten resin 6 against sink marks (shrinkage) of the molten resin 6 filled in the cavity 4. Do. The replenishment operation of the pressure load and the molten resin 6 may be alternately repeated.

In the cooling step S <b> 3, cooling is performed until the molten resin 6 in the cavity 4 is cured while being allowed to stand for a predetermined period of time so as to familiarize the molten resin 6. The temperature adjustment of the molding die 1 is performed by filling the cavity 4 by flowing a cooling medium such as temperature-controlled cooling water or oil in a temperature control medium flow path (not shown) provided around the cavity 4. The molten resin 6 can be cooled evenly.
The cooling time varies depending on the type of the molten resin 6 to be used and the like, and a certain time sufficient to obtain a desired accuracy of the molded product is set.

  In the mold opening step S4, the movable mold part 3 is moved and released from the fixed mold part 2, and the cooled and solidified eccentric body 8 is taken out from the inside.

According to the above manufacturing method, it is possible to obtain a molded product having a plurality of welds 7 formed according to the number of gates 5, that is, an eccentric body 8 utilizing a weld line generated by injection molding.
In addition, since the plurality of gates 5a, 5b, and 5c are arranged so as not to be point-symmetric with respect to the central axis O of the cavity 4, the degree of eccentricity is adjusted according to the number and position of the gates 5. The eccentric body 8 having an eccentric structure (eccentricity) can be formed with high accuracy.

  Since the accuracy of the molded product depends on the molding conditions including the dimensional accuracy of the molding die 1, if this is set appropriately first, high-precision eccentric bodies 8 can be easily mass-produced in subsequent manufacturing. Can do. Further, the fact that the molding method is injection molding is advantageous in improving accuracy.

  A plurality of gates 5 a, 5 b, 5 c communicate with the upper part of the cavity 4 in the molding die 1 used in the present manufacturing method, and open to the side peripheral surface of the cavity 4 where the weld portion 7 is formed. Since there is no problem, there is no problem in accuracy and the like, and the processing of the gate trace becomes easy.

(Eccentric body)
The structure of the eccentric body (molded product) obtained by the manufacturing method described above will be described with reference to FIG.
The eccentric body 8 has a cylindrical shape having a hollow portion 81 at the center, and a plurality of welds 7 (concave portions) formed by the molten resin 6 joining at the time of molding are formed on the side peripheral surface 8A. Yes. The plurality of welds 7 are concave weld lines extending from the upper end 8a to the lower end 8b in parallel with the axis O, and the dimensional shape of each line such as the groove depth is the same.

  The plurality of welds 7 are not point-symmetric with respect to the axis O. And the thickness of the weld part 7 is made thin compared with another part, and the eccentricity degree is adjusted by arrangement | positioning distribution of the weld part 7 in 8 A of side peripheral surfaces.

  Conventionally, various attempts have been made to eliminate the weld portion 7, but since there is no effective solution yet, there is a method of minimizing the occurrence of the weld portion 7 or moving to a portion that does not require accuracy. It was taken.

  In this embodiment, the eccentric body 8 uses the weld portion 7 that is always formed during injection molding. In other words, a highly accurate eccentric body 8 can be obtained by using the weld portion 7 that is difficult to be eliminated. Since the eccentric body 8 obtained by injection molding has higher reproducibility than the conventional molded product in which the eccentric structure is formed by cutting or polishing, the desired highly accurate eccentric body 8 can be obtained. Become.

  In the present embodiment, the plurality of welds 7 that are not point-symmetrical with respect to the axis O have a desired eccentricity.

(Second Embodiment)
Next, the manufacturing method of the eccentric body of 2nd Embodiment which concerns on this invention is described. FIG. 7 is a perspective view showing an eccentric body obtained in the manufacturing method of the present embodiment, and FIG. 8 is a plan view showing a flow state of the resin in the cavity.
The eccentric body 9 of the present embodiment is formed by using a molding die having only one gate communicating with the cavity. One eccentric body 9 extends along the axis O on the side peripheral surface 9A. A weld portion 7 is provided.

  As shown in FIG. 8, the molten resin 6 supplied from the gate 5 of the molding die 1 flows so as to branch in the cavity 4, and then circulates around the shaft portion 31 in the branch portion, and then merges again. And join. A weld portion is formed at a portion where the flow fronts of the molten resin 6 merge and join, but in this embodiment, the gate 5 provided in the molding die 1 is one, so the gate The molten resin 6 joins at a position farthest from 5, that is, at a position opposite to the gate 5 via the central axis O, and a weld portion 7 is formed at this portion.

  According to this embodiment, it is also possible to mold the eccentric body 8 using a molding die that has been conventionally used when obtaining a cylindrical shaped product. As a result, the cost of manufacturing a molding die having a multipoint gate structure can be reduced, so that an accurate eccentric body can be obtained at low cost.

  As described above, the preferred embodiments according to the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the examples. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  In the first embodiment, injection molding using a multipoint gate has been described. However, the number of gates is not limited to three, and it is of course possible to provide three or more gates according to the shape of the target molded product.

  Further, for example, the eccentric body 8 according to the present invention is applied to various cam mechanisms by setting the end point of the stroke with the weld portion 7 as the bottom dead center and the side peripheral surface other than the weld portion as the top dead center. It is also possible.

DESCRIPTION OF SYMBOLS 1 ... Molding die, 2 ... Movable mold part, 3 ... Fixed mold, 4 ... Cavity, 5 (5a, 5b, 5c) ... Gate, 6 ... Molten resin, 7 ... Cavity, 8 ... Eccentric body, molded article, O ... Center axis

Claims (6)

A manufacturing method of an eccentric body, characterized in that molten resin is supplied into a cylindrical cavity of a molding die through a gate communicating with the cavity at a position that does not coincide with the central axis of the cavity in plan view. 2. The method of manufacturing an eccentric body according to claim 1, wherein the molten resin is supplied into the cavity through the plurality of gates arranged to be not point-symmetric with respect to the central axis of the cavity. 3. The method of manufacturing an eccentric body according to claim 2, wherein the degree of eccentricity is adjusted by the positions of the plurality of gates. Presenting a cylindrical shape with a hollow in the center,
Having a recess extending in parallel to the axial center of the cavity on the side peripheral surface;
An eccentric body, wherein the concave portion is a weld portion formed by joining molten resin during molding. The eccentric body according to claim 4, wherein a plurality of concave portions arranged so as not to be symmetric with respect to the axis are provided. 6. The eccentric body according to claim 4, wherein the eccentric body is a cam that rotates around the axis.

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