JPH01264821A - Method of cutting gate - Google Patents

Abstract

PURPOSE:To omit a post finishing process without leaving a gate mark behind, by a method wherein after gate sealing, minute vibration are imparted to a constituent member of a gate part of a die, the vicinity of a gate is softened with this vibration energy and cut off. CONSTITUTION:A core plate 4, a composite bearing 7 fitted to a receiving plate 24 and a gate cutting shaft 6 supported turnably with a radial bearing 8 are arranged on the center of a movable side mold and the shaft 6 performs a rotary motion according to a movement of a servocylinder 14 with a pinion 9 and rack 10. The surface facing on a cavity plate 3 of the gate cutting shaft 6 is provided with a runner 16, the outward tip of the same constitutes a gate 17. Injection is begun and gate seal is performed through dwelling and cooling. Then when a servovalve 19 is driven with fixed frequency, the servocylinder 14 repeats microscopic vibration reciprocation and oscillates microscopically the gate cutting shaft 6 through the rack 10 and pinion 9. Resin at interfaces of the cavity 18 and gate 17 is heated and softened with the vibration energy. Then the gate cutting shaft 6 is turned and displaced forcibly and the gate 17 is cut off.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for injection molding plastics, and in particular, in injection molding of plastics, the gate that is the injection port into the cavity may include a side gate, pin gate, or fan gate. , film gates, etc., except for pin gates, the product part and runner are usually removed from the molding die while being connected at the gate part, and the gate is cut in a later process to complete the product, but the present invention This invention relates to a gate cutting method in which the gate is cut in an ideal state within a mold during molding, and the product part and runner are taken out in a separated state.

(Prior art) Methods for cutting the gate within the mold during molding include a tear cutting method that utilizes mechanical movement of the constituent members of the mold (for example, Japanese Patent Application Laid-Open No. 60-73826), Mochi cutting method (
Japanese Unexamined Patent Publication No. 159203/1983, Japanese Unexamined Patent Publication No. 13751/1983
However, since the former method causes variations in the cutting position, it may not be possible to produce a good product as is. Although the latter method is effective for gates with relatively small cross-sectional areas, fine powder is generated during cutting, and this fine powder may get mixed in or adhere to the product during the next cycle, so it is not perfect and is difficult to generate fine powder. Effective for olefin materials such as polyethylene and polypropylene. In general, no matter what method you use to cut the gate in the mold, it is mechanically cut after the gate has been sealed after injection and filling, in other words, after the molding material has cooled, leaving gate marks on the product. In particular, the value of exterior parts as a product is significantly reduced.

(Problems to be Solved by the Invention) Since the conventional cutting method described above is cold cutting, there are problems such as generation of fine powder during cutting, wear of mold members, and leaving gate marks, that is, cut marks. It was inevitable that there would remain.

The object of the present invention is to make it possible to obtain a product with an extremely good appearance without leaving any gate marks or cutting marks in injection molding, to omit the conventional post-finishing process, and to reduce the molding time. The purpose is to provide a gate cutting method that does not extend the length of the gate.

(Means for Solving the Problems) Therefore, the present invention has solved the above-mentioned problems of the prior art by providing a gate cutting method as set forth in the claims. That is, the first gate cutting method according to the present invention is as follows:
Immediately before cutting, vibration energy generates internal heat in the plastic near the cutting (gate) position, allowing high-speed cutting in a softened state, and cooling of the softened part at the same time as cutting reduces wear on mold members. The cut surface has a uniform and smooth surface, and a product with an extremely good appearance without leaving any gate marks or cut marks can be obtained.

Furthermore, since the gate cutting is performed during the cooling process during the injection molding process, there is no drawback that the cycle is longer than the conventional molding cycle. Furthermore, in the second gate cutting method according to the present invention, the gate is cut by sliding a member constituting the mold gate part during the pressure holding process after injection and filling, and furthermore, the gate is cut by microvibrating or gently reciprocating the member. The first gate cutting method involves bringing the polished surface of the mold into contact with the cut surface of the cut gate while applying motion to transfer the polished surface of the mold to the still soft cut surface of the gate to obtain a clean cut surface. Almost the same effect can be obtained.

(Example) Next, an example of the present invention will be described with reference to the drawings.
FIG. 1 shows a sectional view of a mold used in the gate cutting method of the embodiment, and a gate cutting device is mounted on the movable mold, that is, on the core plate 4 side.

The left half of FIG. 2 from the center line shows a front view of the core plate 4 seen from the direction of arrow A along line A-A of FIG. 1, and the right half of FIG. A cross section of the gate cutting device as seen from the direction of arrow B along the line is shown. Figure 3 is the first
The gate part shown in the figure, namely the spool 15 and the cavity 18
FIG. 4 is a partially enlarged view of the connecting portion of the servo cylinder 14 shown in FIG.
is located adjacent to the servo cylinder 14 shown in FIG. The mold is fixed to a fixed side consisting of a fixed mounting plate 2 that fixedly supports a cavity plate 3, a rocket ring 1 fixed to the fixed mounting plate 2, and a movable side mounting plate 23 via a support part 25. The supporting plate 24 and the core plate 4 are supported, the ejector plate 22 is supported so as to be movable toward the receiving plate 24 by a device not shown with respect to the movable mounting plate 22, and the receiving plate 24 is fixed to the ejector plate 22, respectively. A product eject turbine 11 extends through the core plate 4 and faces the cavity 18, and a runner eject turbine 12 extends through the receiving plate 24 and the gate cant shaft 6, which will be described later, to near the surface of the gate cut shaft 6. The movable side is configured as a pair.

At the center of the movable mold are a core plate 4 and a receiving plate 24.
Composite bearing 7 and radial bearing 8 installed in
A gate cutting shaft 6, which is a gate cutting device, is rotatably supported by a gate cutting shaft 6, and the gate cutting shaft 6 is rotated by a pinion 9 and a rack 10 according to the movement of a servo cylinder 14. It is being done. As shown in FIGS. 2 and 3, on the surface of the gate cut shaft 6 facing the cavity plate 3, a runner 16 is provided which forms a gate portion that is a communication path between the spool 15 and the cavity 18 in the radial direction of the surface. The outer end of the runner 16 is connected to the cavity 18 and forms a gate 17 (FIG. 3).

First, a first gate cutting method according to the present invention will be explained. When injection starts into the spool 15 from the nozzle tip of an injection molding machine (not shown), the molten resin flows into the spool 15.
, through the runner 16 and the gate 17 into the cavity 18
is filled with. When filling is completed, the cooling process begins while maintaining the pressure (plastic contracts as it cools, so the filling pressure is maintained to compensate for the shrinkage), and the gate 17 is cooled and solidified to seal the gate. . In general, the cross-sectional area of the gate 17 is smaller than any other part of the cavity 18, so the cooling of the gate 17 is faster than that of the product, and the holding pressure effect disappears after the gate is sealed. is not affected in any way. When the gate sealing is completed, as shown in FIG. 4, the high pressure hydraulic oil generated in the hydraulic unit 20 and the servo valve 19 are driven at the frequency programmed by the servo controller 21, and the servo cylinder 14 shown in FIG. repeats micro-vibration reciprocating motion. This reciprocating movement of the servo cylinder 14 is carried out via the rack 10 and the pinion 9 on the gate cut shaft 6.
This vibration energy causes the resin at the interface between the cavity 18 and the gate 17 to generate heat and soften.

The degree of softening can be freely changed by programming the vibration frequency and vibration time of the servo controller 21.

When the resin of the gate 17 softens, the gate cutting shaft 6 is forcibly rotated by a desired amount to cut the gate 17. The amount of displacement at this time can be appropriately set by a program using the servo controller 21 as described above.

Note that heat generation due to vibration energy occurs only in the resin part.
Since the amount of heat generated on the cut surface of the gate cut shaft 6 is negligible, the softened portion is rapidly cooled down at the same time as the gate is cut.

Since the softening and cutting process of the resin is completed in just a few seconds, it can be performed at the same time as cooling the product, and does not impede productivity compared to conventional molding.

After gate cutting and cooling are completed, the mold is opened in the same way as in normal injection molding, and the product and runner are taken out to complete the molding process.

Furthermore, the gate cut shaft 6 is rotated by a desired amount, and the gate 1
After cutting the gate 7, the mold surface of the gate cut shaft 6 is brought into contact with the cut surface of the gate for a short period of time while the gate cut shaft 6 is slightly vibrated by the servo cylinder 14 via the rack 10 and the pinion 9. You can further clean the cut surface of the gate by touching it, pressing it, and licking it. The vibration of the gate cut shaft 6 may provide a gentle reciprocating motion for a short period of time.

Next, the second gate cutting method according to the present invention will be described. The same mold as in the first gate cutting method shown in FIGS. 1 to 4 is used. When injection into the spool 15 is started from the nozzle tip of an injection molding machine (not shown), the molten resin passes through the spool 15, the runner 16, and the gate 17 and fills the cavity 18. When the filling is completed, the cooling process begins while maintaining pressure, and when the gate 17 begins to cool and solidify (before the gate 17 is cooled and solidified and sealed), the viscosity of the resin in the gate 17 becomes extremely high (
Therefore, it is impossible to fill the shrinkage due to holding pressure, but there is a state in which the material is soft enough to be cut. That is, in the injection cycle, in the pressure holding step after completion of injection 7, the gate 17 usually has the smallest cross-sectional area and tends to be cooled and solidified first.

Therefore, after a certain period of time has elapsed after entering the holding pressure step, there is a time period in which the resin becomes too hard to feed into the cavity 18 due to holding pressure, but is soft enough to be cut. During this time period, servo cylinder 14
The gate cut shaft 6 is rotated to cut the gate 17, and after the gate cutting is completed, the servo cylinder 14 is driven via the servo valve 19 according to the frequency programmed by the servo controller 21 to rotate the gate cut shaft 6 for a short time. Makes a slight reciprocating vibration. At the time when the gate 17 is cut, the cut surface of the gate still remains soft, and the polished surface of the mold of the gate cut shaft 6 is brought into contact with the cut surface of the gate and rubbed, thereby adding a lapping effect. The cut surface of the gate will be finished with a glossy finish. Since the cutting and subsequent abutting steps of 17 are completed within a few seconds, productivity is not hindered compared to conventional injection molding methods. Further, since gate cutting is performed when the holding pressure is no longer effective, there is no adverse effect on the molded product.

Also, depending on the type of resin, instead of applying minute vibrations during the contact process after cutting the gate to the gate cutting shaft 6, for example, the fifth
A reciprocating member 31 is connected to the crank wheel 29 shown in the figure via a connecting link 30, and the rack 10 shown in FIG. A gate cut surface with a good gloss can also be obtained by gently rotating the gate cut surface in a reciprocating manner so that the polished surface of the mold of the gate cut shaft comes into contact with the gate cut surface and rubs against it. After the gate cutting and the subsequent abutting process, the mold is opened in the same manner as in normal injection molding, and the molded product and runner filled with the resin filled in the cavity 18 are taken out, and the molding process is completed.

FIG. 6 is a block diagram showing a drive system for the servo cylinder 14, which is different from that in FIG.
The servo cylinder 1 is almost similar to the drive system of FIG.
4 drives can be obtained.

In addition, in FIGS. 1 to 3, the members constituting the mold gate are rotatably supported in the mold by a gate cut shaft 6 (
7(a) and (d)), but as shown in FIG. 7[
]) As shown in (C), a gate cut member 6' is supported in a reciprocating manner by a device not shown in the mold.
, 6'. In Figure 7, 33.33',
33', 33" is the product, 16.16', 16', 16"
is the runner (gate part). Gate cut member 6'
, 6' can be connected to a servo cylinder 14 or a reciprocating member 31 for reciprocating movement.

(Effects of the Invention) As explained above, the molded product formed by the gate cutting method according to the present invention does not leave any gate marks and can be obtained with an extremely good appearance, and can be finished in a post-finishing process that is conventionally performed. In addition, the softening of the resin and gate cutting are completed in just a few seconds, so they can be performed simultaneously with cooling of the product, without extending the conventional molding time. In addition, in order to make gate cutting easier and to mold products with a beautiful appearance, it was necessary to reduce the gate cross-sectional area as much as possible, but the present invention has the advantage that the gate size can be freely designed. By enlarging the gate, sufficient holding pressure can be applied, which has the great effect of improving dimensional accuracy compared to conventional products. Furthermore, since a portion of the runner can be taken out at the same time as the product, a portion of the runner can be immediately crushed into pellets. For this reason, the time it takes to crush the material is significantly shorter than when it is cut in a subsequent process, so the amount of moisture absorbed during this time is small, which also has the advantage of greatly shortening the drying time of the material.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the main part of a mold used in the gate cutting method according to the embodiment of the present invention, and the left half of Fig. 2 is a front view of the core plate taken along line A-A in Fig. 1 in the direction of arrow A. , the right hand side of Fig. 2 shows a cross-sectional view taken along line B-B in Fig. 1 in the direction of the arrow, Fig. 3 is a partially enlarged view of the gate section in Fig. 1, and Figs. 4 and 6 are cross-sectional views. 2 is a block diagram illustrating drive systems for different servo cylinders located adjacent to the servo cylinder of FIG. 1; FIG. FIG. 5 is a schematic diagram of a device for driving members constituting another mold gate, and FIG. 7 is a partial plan view showing the members constituting different mold gate sections. 5...Core, 6,6''...Gate cut shaft (member that constitutes the mold gate part), 6', 6''...Gate cut member (member that constitutes the mold gate part), 16 .16”
, 16", 16#... runner (gate section), 17.
...Gate, 18...Cavity. Agent Patent Attorney Jun Kawauchi Figure 1 Figure 3 Figure 4 Whistle 5th Mouth 6th Mouth

Claims (4)

[Claims] (1) The member constituting the mold gate section is made slidable relative to the mold cavity or core, and after the gate sealing after injection and filling is completed, minute vibrations are applied to the member to generate this vibration energy. 1. A method for cutting a gate, which comprises softening plastic near the gate, and, when the plastic is sufficiently softened, forcibly displacing the member to cut the gate. (2) The gate cutting method according to claim 1, wherein after forcibly displacing the member, the member is brought into contact with the cut surface of the cut gate for at least a short period of time while applying minute vibrations to the member. (3) The gate cutting method according to claim 1, wherein after forcibly displacing the member, the member is brought into contact with the cut surface of the cut gate for at least a short period of time while giving a gentle reciprocating motion to the member. . (4) A member constituting the mold gate portion is made slidable relative to the mold cavity or core, and during the pressure holding process after injection and filling, the gate is cut by sliding the member,
Furthermore, the gate cutting method further comprises finishing the gate cut surface by bringing the member into contact with the cut gate cut surface for at least a short period of time while applying minute vibrations or gentle reciprocating motion to the member.