JPH0649311B2 - Injection molding method and electric motor driven injection molding machine implementing the method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a servomotor drive type injection molding method and an improvement of an injection molding machine for carrying out the method.

[Prior art and its problems]

The conventional injection molding machine has a heating cylinder (2
3 ') is provided with two injection servo motors (71') for reciprocating injection molding and screw rotation servo motors (72 ') for rotating the screw (22'), The screw rotation servo motor (7) is used to convey and fill the molten resin to the tip of the heating cylinder (23 ').
2 ') is driven, and when the charging of the molten resin is completed, the injection servomotor (71') is activated to transfer the molten resin from the tip of the heating cylinder (23 ') to the mold cavity (not shown). The method of ejecting was adopted. In this case, simply rotate the screw (22 ') and
The molten resin is conveyed to the tip side of 3 '), and the screw (22') is advanced and the molten resin is injected when the molten resin is charged by the set amount. Therefore, since there is only kneading by rotating the screw (22 ') at the time of charging the molten resin, there is a drawback that the heating cylinder (23') must be long in order to achieve a sufficient degree of kneading. In addition, since separate servo motors (71 ') and (72') had to be used for rotation charging of the screw (22 ') and injection for reciprocating drive, the cost and installation of the control device were also included. There was a drawback that there was a considerable burden on the place.

[Purpose of the present invention]

The present invention has been made to solve the above problems, and the object thereof is to obtain a high kneading degree and to shorten the heating cylinder, and to charge and inject one servo motor. It is an object of the present invention to provide an injection molding method that can be completed by the method and an electric motor driven injection molding machine that implements the method.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides, in the first item, an injection molding screw (22) housed in a heating cylinder (23).
Reciprocating motion of moving forward in forward rotation and backward in reverse rotation is performed by one servo motor, and pulsation is given to the rotation speed of the servo motor during forward movement of the screw, and molten resin is added to the tip of the heating cylinder (23). Is charged, and then the resin is injected from the tip of the heating cylinder (23).

The technical means is adopted, and in the second paragraph, the injection molding screw (22) housed in the heating cylinder (23).
Reciprocating motion of moving backward in forward rotation and moving forward in reverse rotation is performed by one servo motor, and pulsation is given to the rotation speed of the servo motor during forward movement of the screw, and molten resin is added to the tip of the heating cylinder (23). Is charged, and then the resin is injected from the tip of the heating cylinder (23).

The technical means is adopted. In the third item, in the injection molding method of the first item or the second item, the forward stop position of the screw (22) is sequentially shifted rearward each time the reciprocating motion is performed.

In the fourth item, the electric motor driven injection molding machine is used for the resin-filling screw (22) and the rear end of the resin-filling screw (22). A connecting shaft (33) protruding rearward, a reciprocating drive screw cylinder (15) reciprocally moved back and forth together with the connecting shaft (30), which is rotatably inserted onto the connecting shaft (30), and a'servo motor. (7) and a reciprocating drive nut (11) rotatably disposed in the housing (A) and screwed into the reciprocating drive screw cylinder (15) to transmit the rotation of the servo motor (7). ) And a screw for screw rotation provided at the rear end of the connecting shaft (30)
(33) and a stationary nut (35) attached to the housing (A) by being screwed into the screw turning screw (33).

Is adopted as a technical means.

[Operation] When the motor (7) is operated, the forward movement is transmitted to the reciprocating drive screw cylinder (15) via the reciprocating drive nut (11), and the screw (22) is moved forward.

At this time, in the case of the first term, the screw rotating screw (33) is normally rotated by the stationary nut (35) with the forward movement, and the resin in the heating cylinder (23) is sent forward while being kneaded.
(In the case of the second term, the screw (22) reversely reverses.) Then, when the motor (7) reverses, the screw (22) reverses and reverses in the case of the first term, but at this time, the heating cylinder (twenty three)
Due to the difference in the wear coefficient of the inner surface of the screw and the wear coefficient of the outer peripheral surface of the screw (22), the resin in the heating cylinder (23) remains almost in front, and only the screw (22) returns. (In the case of the second term, the screw (22) will reversely rotate in reverse.) Then, the motor (7) is normally rotated again and the screw (22) is moved forward and normally while kneading the resin again. Send it forward.

By repeating such a reciprocating motion of the screw (22), the tip of the heating cylinder (23) is charged with resin.

In such an injection molding method, the forward stop position of the screw (22) is sequentially shifted rearward each time the reciprocating motion is performed, and the operation of charging the tip of the heating cylinder (23) with the molten resin fat by a set amount is more preferable. The kneading is also high and quick, and in this case, the screw (22) is advanced when the screw is moved forward.
By giving pulsation to (22), the kneading degree of the resin can be further increased.

〔Example〕

 An embodiment of the present invention will be described.

Bracket (2) fixed on the base (1) of the injection molding machine
Headstock on four support bars (3) supported by (2) '
(4) and the boss portion (5a) of the gear box body (5) are mounted so as to be slidable back and forth, and serve as a base body of the injection device. (6) is a cover of the gear box body (5), and the housing (A)
Is composed of the gear box body (5), the lid body (6) and the like.

The motor (7) used in the present invention is, for example, a servo motor, and the motor (7) will be described below as a servo motor.
The servomotor (7) shown in the embodiment is fixed to the gear box body (5) so that the shaft is horizontal, and the shaft end (7a) of the servomotor is fixed to the drive gear (8) by the fixing device (9). ) Is fixed, and the driven gear (10) screwed to the main driving gear (8) is fixed to the reciprocating drive nut (11) by a fixing tool (12). Therefore, when the servo motor (7) rotates, the rotation is transmitted to the reciprocating motion drive nut (11) via the driven gear (10), and the reciprocating motion drive nut (11) rotates forward and backward to reciprocate. The drive screw cylinder (15) is adapted to move forward and backward.

In the first term of this embodiment, the reciprocating drive screw cylinder (15) is set to move forward when the servo motor (7) rotates in the forward direction, and in the second term, the servo motor (7) reversely moves. The screw cylinder (15) retracts when it rotates in the normal direction, and an appropriate method is adopted according to the type of resin and various other conditions.

The reciprocating drive screw cylinder (15) is fixed to the bearing case (18) with a bolt through the receiving plate (16) and the pressure sensor (17) (eg, load cell). A drive shaft (19) is supported in the bearing case (18) by a radial bearing (20) and a thrust bear link (21). Therefore, the forward and backward reciprocating motion of the reciprocating drive screw cylinder (15) is
It is transmitted to 9).

The rear end of the screw (22) is inserted into the front recess of the drive shaft (19) and is fixed by the key (29) and the contact plate (29a). Forward and backward movement is transmitted.

The heating cylinder (23) containing the screw (22) is inserted from the front of the horizontal through hole of the headstock (4) through the cylinder flange (23a) and the heat insulating material (26), and the rear end (23b) is inserted. Headstock by screwing in with fixing nuts (27)
It is fixed to (4).

A hopper (28) is located above the vertical hole (4a) of the headstock (4).
Is installed, and the plastic raw material in the hopper (28) is
It is heated by a heater (not shown) wound around the heating cylinder (23) and is transferred forward while being kneaded by the screw (22). Further, a nozzle (24) is screwed into the front part of the heating cylinder (23), and an exit chamber of the nozzle (24), which is the tip of the heating cylinder (23), is injected into the injection chamber via a screw (22). A nozzle check device (not shown) is provided so that the resin sent to (24a) does not overflow outside the room.

On the other hand, the front end of the connecting shaft (30) is inserted into the rear recess of the drive shaft (19) and is fixed by the key (31). The connecting shaft
The numeral (30) penetrates the hollow portion (15a) of the reciprocating drive screw cylinder (15), is supported by the radial bearing (32a) and the needle bearing (32b), and further extends rearward. That is, the connecting shaft (30) is a rear extension member that is integrated with the drive shaft (19) to perform forward and backward reciprocating motion integrally with the reciprocating drive screw cylinder (15) and to reciprocate the drive screw cylinder (15). ) Is independent of the rotational movement.

The drive source for rotating the connecting shaft (30) is
A screw rotating screw externally inserted to the shaft end (30a) extending rearward integrally with the connecting shaft and fixed by a fixing tool (34).
(33) and a stationary nut (3
5) By screwing.

Next, the control device will be described. Control device (not shown)
Is a computer control system with a built-in microcomputer. Central processing unit (CPU), memory (RAM)
And (ROM), input device (I), output device (O), and setting keyboard (KB). As an input sensor, a position sensor that measures the position of the screw tip, the internal pressure of the plastic molten resin in the injection chamber is measured. The signal from the pressure sensor (17) that operates is input to the input interface. On the other hand, the servo motor from the output interface
Send forward and reverse commands to (7). The position sensor at the tip of the screw is attached to the servo motor (7) and transmits the origin of rotation (corresponding to the screw backward limit position).
For example, an encoder (7b) may be used.

The operation of the first item of the present embodiment configured as above will be described.

When the servomotor (7) rotates in the forward direction, the reciprocating drive nut (11) rotates in the forward direction via the driving gear (8) and the driven gear (10).
The reciprocating drive screw cylinder (15) advances.

The forward movement of the reciprocating drive screw cylinder (15) advances the screw (22) via the drive shaft (19).

When the drive shaft (19) advances, the screw turning screw (33) also advances via the connecting shaft (30). Screw for turning the screw
By screwing the (33) and the stationary nut (35), the screw turning screw (33) rotates and advances. Therefore, the screw (22) also advances while rotating. Screw (2
Select the screwing relationship between the stationary nut (35) and the screw turning screw (33) so that the screw (22) can rotate forward in the direction that the plastic raw material is sent toward the nozzle (24) when 2) moves forward. I'll do it.

After kneading the plastic raw material in this way and sending it out, the servo motor (7) reverses and the reciprocating drive nut (11) reverses, and the reciprocating drive screw cylinder (15).
Retreat. Then, the drive shaft (19) and the screw (22) are also retracted as the reciprocating drive screw cylinder (15) is retracted. On the other hand, the screw turning screw (33) is also retracted via the connecting shaft (30), and the screw (22) is reversely moved backward by screwing the screw turning screw (33) and the stationary nut (33). To do.

As described above, according to the present invention, one servo motor is used.
By the forward and reverse rotations of (7), the screw (22) can move forward, and can rotate forward in the direction in which the plastic raw material is fed to the nozzle (24), and the screw can move backward and rotate in the reverse direction. In the case of the second term, the first
When the servo motor (7) rotates in the
2) will move backward, and when it reverses, it will move forward.

The control action of charging the plastic raw material while the screw (22) of the first term repeatedly moves forward and backward will be described with reference to FIG. Initially, the screw was at the origin of the backward limit
(22) is a forward rotation of the plastic raw material in the direction of feeding the nozzle (24) forward by the normal rotation of the servomotor (7), and is advanced, heating and kneading the plastic raw material, and the injection chamber (24a) on the nozzle side. The charge operation is sent to. Injection chamber
While measuring the internal pressure of (24a) with a pressure sensor (17) such as a load cell, when the set pressure is reached, the screw (22) reversely rotates and retracts. At this time, since the wear coefficient of the inner peripheral surface of the heating cylinder (23) and the wear coefficient of the screw (22) are different, the resin does not return together with the screw (22) and remains at the front position.
When the screw (22) reaches the backward limit, the screw (2
2) becomes forward rotation and moves forward. This forward / backward operation is repeated, and when the resin pressure in the injection chamber (24a) reaches the set value during forward charging and the screw tip 1 reaches the position (S) at which the predetermined charge amount is reached, Stop charging repeatedly. Such repetitive charging by one servo motor (7) is a feature of the first aspect of the device of the present invention. After the charging is completed, the screw (22) is rotated forward and greatly moved forward to inject the resin.

Further, in the method of the present invention, as described above, one servo motor is used.
Using (7), the screw (22) is rotated forward and backward and reciprocally back and forth to gradually charge the resin into the injection chamber. At this time, the pressure of the screw (22) is reciprocated. Each time it is detected and stopped when it reaches a predetermined pressure, the forward stop position is sequentially shifted to the rear so that the resin is smoothly filled and the screw (22) is advanced when the screw (22) is advanced.
It is characteristic that the degree of kneading and the conveyance of the resin are promoted by giving pulsation to the advance of the resin. This is represented by the temporal program of FIG.

In FIG. 4, when the servomotor (7) rotates in the normal direction, that is,
When the screw (22) moves forward, it pulsates the forward rotation speed of the servomotor (7), and when the servomotor (7) reverses, that is, when the screw (22) moves backward, the servomotor (7) The reversal speed of is uniform.

Now, when the screw (22) moves forward, the screw (22) is rotated by the pulsating forward rotation of the servo motor (7) while rotating forward in the direction of feeding the plastic raw material toward the nozzle.
Is also pulsating. The plastic raw materials have friction coefficients μ ₁ and μ ₂ between the surface of the screw (22) and the inner surface of the heating cylinder (23), respectively. Normally, the surface finish of the screw (22) is improved and μ ₁ <μ ₂ By making the relationship, the resin can be forwardly transferred with heating, and at the time of reverse rotation, the resin is accumulated at the forward conveyance position and only the screw (22) is reversely retracted.

In the present invention, since the screw (22) is pulsatingly rotated forward as the screw (22) advances, μ ₁ becomes extremely small, and the plastic material is more efficiently transferred to the nozzle (24) to perform the charging operation. Moreover, since the charge is controlled to be completed when the resin pressure in the injection chamber (24a) reaches the set value, the raw material resin accumulated in the injection chamber (24a) always has a uniform property, Leads to stabilization.

While charging in this way, the resin injected into the cavity is cooled, the mold is opened, the molded product is ejected, and the mold is clamped in the next cycle, and then the molten resin that has been charged is advanced by the screw (22). Is injected into the cavity by. At this time, the screw (22) also performs injection while rotating forward.

In the second item, the rotation direction is opposite to that in the first item, as described above.

〔The invention's effect〕

According to the first aspect of the present invention, as described above, the screw for injection molding housed in the heating cylinder is caused to reciprocate by advancing during forward rotation and retracting during reverse rotation, thereby causing melting at the tip of the heating cylinder. Since the resin is filled and then the resin is injected, a reciprocating reciprocating movement of the screw is newly added in the resin filling work, and as a result, the kneading degree of the resin is increased more than ever and the quality of the injection molded product is improved. Since the kneading degree increases as soon as they are connected, there is an advantage that the heating cylinder with a smaller L / d is used for feeding, and in the second term, the injection molding screw housed in the heating cylinder is retracted at the time of normal rotation to reverse rotation. At some point, the reciprocating motion of advancing is performed to charge the molten resin at the tip of the heating cylinder, and then the resin is injected, so when the entire molten resin is conveyed forward by the screw. The rotation of the clew acts in the direction to pull the resin back, and conversely, when the screw is retracted and the entire resin is pulled back, the rotation of the screw acts in the direction to convey the resin to the front. Strong kneading is added, and the heating cylinder can be shortened accordingly.

In the third item, the resin kneaded in order to shift the forward and backward stop positions of the screw to the rear after each reciprocating motion is intermittently supplied to the tip portion of the heating cylinder, and the resin previously supplied by the movement of this cylinder. This means that the resin supplied later is mixed in the tip portion, and the resin in the tip portion is in a sufficiently kneaded state at the time of injection, which is also useful for improving the quality of the molded product. Further, in the fourth term, since pulsation is given to the advance of the screw when the screw advances, there is an advantage that a smooth advance can be achieved when heating and melting by exerting a vibration effect.

In this way, the raw material plastic is transferred forward by the pulsating screw, and when the molten resin is charged in the injection chamber, the screw retreats and the pulsating rotation advances again to inject the molten resin. Since the cylinder is repeatedly charged by reciprocating back and forth, the kneading effect is much stronger in the present invention than in the conventional in-line screw machine. As a result, the heat history of the resin is small because the heating cylinder having a small L / d is sufficient. Therefore, there is an advantage that the quality of the molded product is improved. Further, as described in the fifth item, the electric motor driven injection molding machine according to the present invention includes a resin filling screw, a connecting shaft projecting rearward from the rear end of the resin filling screw, and a rotatable connecting shaft. A reciprocating drive screw cylinder that is externally inserted and reciprocates back and forth together with the connecting shaft,
A reciprocating drive nut that is rotatably disposed in the housing and that is screwed into a reciprocating drive screw cylinder to transmit the rotation of the motor, a screw rotating screw and a screw screw provided at the rear end of the connecting shaft. Since it is composed of a stationary nut that is screwed into a dynamic screw and attached to the housing, both charging and injection operations can be performed with only one servo motor, which reduces costs.
There is an advantage that a positive solution is made at the mounting location and the advantages of the electric motor drive type injection molding machine are weighted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 ... Front view showing the outline of an injection device of the present invention FIG. 2 ... Cross-sectional view of an embodiment of the injection device of the present invention FIG. 3 ... Screw part of the present invention 4 is a graph showing the rotational speed versus time characteristic of the servo motor according to the present invention. FIG. 5 is a graph showing the screw forward position versus time characteristic of the present invention. FIG. 6 is a conventional electric motor driven injection. It is a waist cross-sectional view of the molding machine. (A) …… Housing, (1) …… Base, (2) …… Bracket, (3) …… Support bar, (4) …… Headstock, (4a) …… Raw material outlet, (5) ...... Gear box, (5a) …… Bracket, (6) …… Lid, (7) (71) (72) …… Motor, (7a) …… Motor shaft, (7b) …… Encoder, (8 ) …… Main drive gear, (9) …… Fastener, (10) …… Driven gear, (11) …… Reciprocating drive nut, (12) …… Fastener, (13) …… Radial bearing, ( 14) ...... Thrust bearing, (15) ...... Reciprocating drive screw cylinder, (15a) ...... Hollow part, (16) ...... Retaining plate, (17) ...... Load cell, (18) ...... Bearing case, (19) …… Drive shaft, (20) …… Radial bearing, (21) …… Thrust bearing, (22) …… Screw, (23) …… Heating tube, (23a) …… Cylinder flange, (24) ...... Nozzle, (24a) …… Injection chamber, (26) …… Insulation material, (27) …… Heating cylinder fixing nut , (28) …… hopper, (29) …… key, (30) …… connecting shaft, (30a) …… shaft end, (31) …… key, (32a) …… radial bearing, (32b)… … Needle bearing, (33) …… Screw for screw rotation, (34) …… Fixing device, (35) …… Stationary nut.

Claims (4)

[Claims] 1. An injection molding screw housed in a heating cylinder is provided with a reciprocating drive means for converting a rotational motion into a reciprocating motion, and the screw rotates forward and backward in response to the reciprocating motion. A screw rotation means is provided at the rear end of the screw, and the rotation of the servomotor is transmitted to the screw through the reciprocating drive means to move the screw forward during normal rotation and backward when reverse rotation. Motion and screw rotation motion are performed by one servo motor, and the rotation speed of the servo motor during forward movement of the screw is pulsated to charge the molten resin at the tip of the heating cylinder. An injection molding method characterized by injecting. 2. An injection molding screw housed in a heating cylinder is provided with a reciprocating motion drive means for converting a rotational motion into a reciprocating motion, and the screw is rotated in reverse or forward in response to the reciprocating motion. A screw rotating means is provided at the rear end of the screw, and by transmitting the reciprocating motion of the rotation of the servo motor to the screw through the reciprocating motion driving means, the screw is retracted in forward rotation and forward in reverse rotation. Motion and screw rotation motion are performed by one servo motor, and the rotation speed of the servo motor during forward movement of the screw is pulsated to charge the molten resin at the tip of the heating cylinder. An injection molding method characterized by injecting. 3. The injection molding method according to claim 1 or 2, wherein the forward stop position of the screw is sequentially shifted to the rear after each reciprocating motion. 4. A resin filling screw, a connecting shaft protruding rearward from a rear end of the resin filling screw, and a reciprocating drive screw rotatably externally inserted to the connecting shaft and reciprocatingly driven back and forth together with the connecting shaft. A cylinder, a servo motor, a reciprocating drive nut that is rotatably disposed in the housing, and is screwed into the reciprocating drive screw cylinder to transmit the rotation of the servo motor, and is provided at the rear end of the connecting shaft. It is characterized by comprising a screw turning screw, a stationary nut screwed into the screw turning screw and attached to the housing, and a control device for causing pulsating rotation of the servo motor when the screw advances. Motor driven injection molding machine.