JPH082568B2 - How to set holding pressure switching point of injection molding machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a holding pressure switching point setting method capable of setting a holding pressure switching point to an optimum value in an inline screw type injection molding machine.

[Prior Art] In an in-line screw type injection molding machine, as is well known, by advancing a screw retracted to a measuring point to a holding pressure switching point, the molten resin measured and stored on the tip side of the screw is stored. The injection process of injecting and filling into the cavity of the mold is executed, and after the injection is completed, a holding pressure (secondary injection pressure) is continuously applied to the molten resin in the cavity by a screw, and this is maintained for a certain period of time. It is designed to carry out a pressure stroke.

By the way, the setting position of the holding pressure switching point is an important factor that influences the quality of the molded product because it is closely related to the molten resin pressure and the filling amount in the cavity. For example, if the holding pressure switching position is set closer to the nozzle tip than the proper position, overpacking will occur, and the pressure of the molten resin filled in the cavity will rise above the proper value, and the mold release This causes problems such as difficulty or damage to the mold, and also tends to cause cracks in the molded product. On the other hand, if the holding pressure switching position is set in a direction farther from the nozzle tip than the proper position, it will be a show shot, resulting in insufficient filling weight and holding pressure, resulting in dimensional variations and sink marks in the molded product. I have a problem.

As described above, the setting of the holding pressure switching point, which is the operating condition setting value that is closely related to the quality of the molded product, has hitherto been performed based on the experience and intuition of a skilled worker. That is, in the trial shot, while changing the holding pressure switching point toward the nozzle tip or away from the nozzle tip, the operator confirms the quality of the molded product, and the human experience makes a so-called groping experience. Therefore, the holding pressure switching point was set to a value that seems to be a proper value.

[Problems to be Solved by the Invention] As described above, since the conventional holding pressure switching point setting method relies on experience and intuition, an operator (worker) who has little experience has an appropriate holding pressure switching point. It was difficult to set. Also, even an operator with a wealth of experience, the work of setting the holding pressure switching point is a complicated and time-consuming task, and it is impossible to confirm whether it is a truly appropriate holding pressure switching point. There was a problem that the actual condition is that the holding pressure switching point is set with some variation.

Therefore, the technical problem to be solved by the present invention is to solve the problems with the above-mentioned conventional technology, and the purpose thereof is to set the optimum holding pressure switching point even for an innocent operator. An object of the present invention is to provide a method for setting a holding pressure switching point of an injection molding machine, which can be easily and reliably performed almost automatically and can shorten the time required for setting the holding pressure switching point.

[Means for Solving the Problems] The above-mentioned object of the present invention is to provide an in-line screw type injection molding machine whose operating conditions are controlled by a microcomputer (hereinafter referred to as a microcomputer). After setting a temporary holding pressure switching point that can sufficiently guarantee and a temporary weighing point that can sufficiently guarantee that the filling amount is insufficient, the microcomputer can change the weighing point while fixing the temporary holding pressure switching point. Repeat the test shot by gradually shifting by a predetermined value in the direction in which the filling amount increases from the tentative weighing point, b. Next, when the filling amount reaches a weighing point that is less than the proper amount by a predetermined amount, This measurement point is confirmed as the set measurement point of the operating conditions controlled by the microcomputer, c. Next, the microcomputer keeps the set measurement point fixed,
Repeat the test shot by gradually shifting the holding pressure switching point from the temporary holding pressure switching point by a predetermined value in the direction in which the filling amount increases, and set the holding pressure in the holding stroke of each trial shot to zero. During this period, measure and create the holding pressure switching point vs. peak injection pressure characteristic line, d. Next, when the bending point appears on the holding pressure switching point vs. peak injection pressure characteristic line, the microcomputer This is achieved by the holding pressure switching point setting method, in which the holding pressure switching point in the first test shot that appears is set and set as the operating pressure setting holding pressure switching point.

[Operation] The trial shot process of a and b described above, that is, with the temporary holding pressure switching point fixed, the measuring point is gradually shifted from the temporary measuring point by a predetermined value in the direction of increasing the filling amount. The test shot is repeated and the filling amount reaches a weighing point that is less than the appropriate amount by a predetermined amount (for example, it is confirmed in the molded product by the trial shot that the filling amount is about 90% of the planned filling amount). Then, the measuring point is set as the setting measuring point for the operating condition controlled by the microcomputer. This fixed setting of the weighing point is performed by the operator instructing the microcomputer by key operation.

As described above, at the time when only the weighing points are first fixed and set, the filling amount is always insufficient.
In the trial shot process of the above-mentioned c, the microcomputer performs the trial shot by gradually shifting the holding pressure switching point from the temporary holding pressure switching point in the direction of increasing the filling amount by a predetermined value while the set weighing point is fixed. Repeating the above, the holding pressure in the holding stroke of each test shot is set to zero, and the holding pressure switching point-peak injection pressure characteristic line during this period is measured and created.
In this way, if the holding pressure is set to zero and a test shot is performed, the screw tip is kept immobile at each holding pressure switching point that is variably set in increments of 1 mm for each test shot, and the peak injection pressure becomes accurate. It becomes possible to measure.

By the way, in the above-mentioned holding pressure switching point vs. peak injection pressure characteristic line, when the filling amount of the molten resin in the cavity exceeds the appropriate amount (when the filling amount exceeds 100%), this characteristic line clearly shows It has been confirmed by experiments conducted by the inventors of the present application that an inflection point appears, and the slope of the characteristic line increases sharply after this inflection point. When a bending point appears on the peak injection pressure characteristic line, the microcomputer sets the holding pressure switching point in the test shot before the bending point appears as the operating condition setting compensating pressure switching point.

Therefore, even an inexperienced operator can easily, reliably, and in a short time without trial and error by using a test shot executed according to a program for searching and setting the holding pressure switching point written in advance in the microcomputer. It is possible to set the optimum holding pressure switching point.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is an explanatory diagram showing a schematic configuration of a main part of an in-line screw type injection molding machine. The upper left part of the figure shows the mold opening / closing mechanism system. In the illustrated part, 1 is a base, 2 is a fixed die plate fixedly mounted on the base 1, and 3 is a slide base extended on the base 1.
Support plates 4 installed on the la 1 are a plurality of tie bars installed between the fixed die plate 2 and the support plate 3. A mold clamping cylinder (hydraulic cylinder) 5 serving as a mold opening / closing drive source is fixedly mounted on the support board 3, and a known toggle link mechanism 6 is provided at the tip of the piston rod 5a of the mold clamping cylinder 5. The movable die plate 7 inserted through the tie bar 4 is connected. Then, by moving the piston rod 5a forward and backward, the movable die plate 7 is moved toward or away from the fixed die plate 2.

Further, on the surfaces of the fixed die plate 2 and the movable die plate 7 which face each other, a fixed side die 8 and a movable side die 9 are provided.
And are installed. Then, during the mold closing process during the molding cycle, the toggle link mechanism 6 is extended by the advancement of the piston rod 5a to advance the movable die plate 7, and the two dies 8 and 9 are brought into close contact with each other. As described above, the toggle link mechanism 6 is stretched to give a predetermined mold clamping force. On the other hand, during the mold opening stroke during the molding cycle, the toggle link mechanism 6 is moved by the retraction of the piston rod 5a.
And retract the movable die plate 7 to move both molds 8,
9 are separated from each other, and the molded product is taken out by a known eject mechanism (not shown) and an automatic take-out machine for the molded product.

The upper right portion of FIG. 1 shows the injection mechanism system, in which 12 is a heating cylinder, 13 is a screw arranged in the heating cylinder 12 so as to be rotatable and forward and backward, and 14 is a heating cylinder 12. Nozzle attached to the tip of the, 15 is a band heater wound around the outer periphery of the heating cylinder 12, 16 is a hopper for supplying the resin material to the rear part of the screw 13, and 17 is a motor (rotational drive source of the screw 13). In this embodiment, for example, an electromagnetic motor is used,
It can be replaced with a hydraulic motor, etc.), 18 is a screw
It is an injection cylinder (hydraulic cylinder) for controlling the forward and backward movement of 13. As is known, the resin material supplied from the hopper 16 is transferred to the tip side of the screw 13 and melted while being kneaded and plasticized by the rotation of the screw 13.
As the molten resin is stored on the tip side of the screw 13, the screw 13 moves backward while controlling the back pressure, and when one shot of the molten resin is stored on the tip side of the screw 13 (at the time when the measuring point is reached). The rotation of the screw 13 is stopped. Then, after a lapse of a predetermined time, when the injection start timing is reached, the screw 13 is driven forward to the holding pressure switching point, and the molten resin is injected into the cavity between the molds 8 and 9 that have been clamped, Subsequently, a holding pressure is applied to the molten resin in the cavity for a predetermined time by the screw 13. In this embodiment, the forward and backward movement of the screw 13 and the application of pressure to the screw 13 are performed by the injection cylinder (hydraulic cylinder 18), which is achieved by combining a hydraulic motor or an electric motor with a rotary-linear motion conversion mechanism. It can be replaced by one.

20 is an injection pressure detection sensor composed of a hydraulic measuring head, etc.
21 is an injection stroke detection sensor including an encoder,
22 is a screw rotation detection sensor including a rotary encoder, 23 is a temperature detection sensor that detects the temperature of the heating cylinder 12, 24 is a pressure detection sensor that is a pressure measurement head that detects the molten resin pressure at the tip of the nozzle 14, and 25 is A mold opening / closing stroke detection sensor composed of an encoder, etc., 26 is a mold clamping pressure detection sensor composed of a hydraulic pressure measuring head, etc., and measurement information signals S1 to S7 of these respective sensors 20 to 26, and measurement from other sensors not shown. The information signal is sent to the microcomputer 30 to be described later with appropriate input conversion processing if necessary. In addition,
In the present embodiment, since the oil pressure of the injection cylinder 18 is measured by the injection pressure detection sensor 20, it is possible to obtain the measurement value of the pressure detection sensor 24 by converting the measurement value of this sensor 20. It is not necessary to intentionally install the pressure detection sensor 24 when adopting such a hydraulic drive system, but in the case of electromagnetic servo drive, it is necessary to measure the molten resin pressure, so such a pressure detection sensor is necessary. (So,
It should be understood that the pressure detection sensor 24 is shown for reference in this embodiment).

30 is a microcomputer that controls the operation of the entire machine,
Control of the entire molding process such as mold opening / closing operation, charging operation, injection operation, non-defective / defective product determination processing, calculation of measurement data, and various calculation processing such as graphic processing are executed. The microcomputer 30 is actually a ROM that stores various I / O interfaces, main control programs and various fixed data, and RA that reads and writes various flags and measurement data.
M, a CPU (central processor unit) for controlling the whole, etc. are provided and various processes are executed in accordance with various programs created in advance. However, in this embodiment, the molding condition setting memory is stored for convenience of explanation. Unit 31, molding process control unit 32, measured value storage unit 33, characteristic line creation unit 34,
The following description will be given on the assumption that the bending point determination unit 35, the holding pressure switching point search operation control unit 36, and other functional units are provided.

The molding condition setting storage unit 31 stores various molding condition values input by the key input means 40 or other appropriate input means in a rewritable form after being subjected to arithmetic processing as necessary. The molding conditions include, for example, the relationship between the screw position and the screw rotation speed and the back pressure during the charging process, suck back control conditions, and the injection speed subdivided from the measuring point (injection start point) to the holding pressure switching point. Conditions, subdivided secondary injection pressure (holding pressure) conditions from the holding pressure switching time to the holding pressure end time, band heater temperature of each part, mold closing stroke and speed, mold closing force, mold opening stroke and speed, Examples include eject control conditions and product take-out machine control conditions.

The molding process control unit 32 is based on the molding process control program created in advance and the setting condition values stored in the molding condition setting storage unit 31, based on the sensors 20 to 23, 25,
While referring to the measurement information from 26 and the like and the timing information from the clock built in the microcomputer 30, the corresponding drive source is driven and controlled via the driver group 41 to execute a series of molding steps. In FIG. 1, the drive signal D1 of the driver group 41
Drives and controls the mold clamping cylinder 5 via the control valve 42,
The drive signal D2 drives and controls the electric heat source of the band heater 15, the drive signal D3 drives and controls the motor 17, and the drive signal
D4 drives and controls the injection cylinder 18 via the control valve 43, and another drive signal drives and controls an appropriate drive source (not shown).

The measured value storage unit 33 includes the sensors 20 to 23, 2 described above.
Position (distance) data, pressure data, velocity data, temperature data, and time data obtained by appropriately converting measurement information from 5, 26, etc. are stored and held over multiple solution shots. The data stored in the actual measurement value storage unit 33 is used to create a characteristic line for holding pressure switching point vs. peak injection pressure in the processing for searching and setting the holding pressure switching point during the trial shot, which will be described later. The data is used for controlling the shot, or for statistical calculation processing and graphing processing.

In the trial shot process for searching and setting the holding pressure switching point, which will be described later, the characteristic line creating unit 34 stores the holding pressure switching position data that is sequentially changed and the peak injection pressure data at the holding pressure switching position. It is loaded from the measured value storage unit 33, and this is subjected to arithmetic processing, for example, as shown in FIG.
A holding pressure switching point vs. peak injection pressure characteristic line as shown in the figure is created.

The data of the holding pressure switching point vs. peak injection pressure characteristic line created by the characteristic line creating section 34 is sent to the bending point determining section 35, and whether or not there is a bending point on the characteristic line in the bending point determining section 35. It is determined whether or not the result of this determination is sent to the holding pressure switching point search operation control unit 36. When the bending point is determined by the bending point determination unit 35, this data is used as the determined holding pressure switching point data and the molding condition setting storage unit 31
And is set and stored as a holding pressure switching point during continuous molding (during normal operation).

The holding pressure switching point search operation control unit 36 searches for a predetermined holding pressure switching point according to an operator's instruction.
A program for setting is executed, and the molding process control unit is operated by a command from the holding pressure switching point search operation control unit 36.
32 executes a holding pressure switching point search / setting operation (test shot) as described later.

In FIG. 1, reference numeral 44 denotes a display device such as a color CRT display or the like, and reference numeral 45 denotes a printer such as a dot printer. The output devices 44 and 45 output processing results by the microcomputer 30 as necessary. Is done. Reference numeral 46 denotes an external memory such as a magnetic disk device, which exchanges information with the microcomputer 30 as needed.

An operation for searching / setting a holding pressure switching point in the present anion having the above-described configuration will be described below with reference to FIG. FIG. 2 is an explanatory diagram of the search / setting operation of the holding pressure switching point.

Prior to the continuous molding operation for molding the product, after the operator inputs the general conditions by which the test shot can be performed except the holding pressure switching point and the weighing point by the key input means 40, the operator uses the key input means 40 When a trial shot for searching and setting the pressure switching point is instructed, the microcomputer 30 receives this and displays on the display device 44, for example, to input a temporary holding pressure switching point and a temporary weighing point. Then, the operator inputs the position data (distance data) of the temporary holding pressure switching point and the temporary weighing point by this.

The temporary holding pressure switching point and the temporary weighing point are set to values that can guarantee that the filling amount in the cavity is sufficiently insufficient. Since this is an extremely rough value, it is an operator with little experience. However, it is possible to instruct easily. In FIG. 2, P _C0 and P _M0 respectively indicate the temporary holding pressure switching point and the temporary measuring point which are provisionally set in this way, and these are the most advanced position of the screw 13 (in the state without resin). The mechanically most advanced position) S ₀ is represented as a zero reference.
For reference, the normal range of the holding pressure switching point of the machine is, for example, 2 to 10 mm, and the normal range of the weighing point is, for example,
In the case of 70 to 90 mm, the temporary holding pressure switching point P _C0 may be roughly set to 15 mm or more, and the temporary weighing point P _M0 may be roughly set to 60 mm or less, for example, even if the operator is a beginner. It is easy to set the temporary holding pressure switching point P _C0 and the temporary weighing point P _M0 .

When the microcomputer 30 confirms that the temporary holding pressure switching point P _C0 and the temporary weighing point P _M0 are set, the molding process control is performed with reference to the signal from the holding pressure switching point search operation control unit 36. The part 32 controls the molding operation of the entire machine, and in the first trial shot (first trial molding) SH ₁ , after the screw 13 is moved back to the temporary weighing point P _M0 in the charging process (measuring process), The screw 13 is advanced to the temporary pressure holding switching point P _C0 by the set injection speed and pressure, and injection is performed. At this time, after the screw 13 has moved forward to the temporary holding pressure switching point P _C0 , the holding pressure set on the screw 13 is set to zero. Note that the holding pressure is set to zero in the same manner in each of the following test shots. Next, the microcomputer 30 uses the second test shot SH ₂
Then, the measuring point is a predetermined amount in the direction in which the filling amount increases from the tentative measuring point P _M0 (for example, about 0 to several mm, but this pitch can be arbitrarily set by the operator. The screw 13 is retracted to a measuring point P _M1 which is shifted by a certain amount to perform charging, and the screw is advanced from this measuring point P _M1 to the temporary holding pressure switching point P _C0 to perform injection. In the third test shot SH ₃ , the metering point is moved from P _M1 to P _{M2 in the} direction of increasing the filling amount by a predetermined amount, and similarly, the screw is advanced to the temporary holding pressure switching point P _C0 to perform injection.

In this way, with the temporary holding pressure switching point P _C0 initially set temporarily fixed, the trial shot is performed by gradually shifting the weighing point from the temporary weighing point P _M0 by a predetermined amount in the direction in which the filling amount increases. ,
The process is repeated until the filling amount reaches the weighing point P _MN, which is less than the proper amount by the predetermined amount. The metering point P _MN that the filling amount is insufficient by a predetermined amount than a proper amount, for example, the filling amount of 90%
At this point, the operator can easily confirm this by visually observing the test molded product from the test shot.
The operator causes the microcomputer 30 (the holding pressure switching point search operation control unit 36) to recognize this by operating a key or the like.

As described above, in the Nth test shot SH _N , the filling amount is only a predetermined amount than the proper amount (this may be a considerably rough value).
When it is recognized that the insufficient measuring point P _MN is reached, the microcomputer 30 determines this measuring point P _MN as the measuring point data during continuous molding operation, and the data is stored in the molding condition setting storage unit 31. Is stored.

After this, the molding process control unit 32 of the microcomputer 30 continues.
Refers to the command from the holding pressure switching point search operation control section 36 to perform the next test shot. The next test shot
In SH _{N + 1} , after fixing the measuring point P _MN and performing charging, the holding pressure switching point is changed to the temporary holding pressure switching point P during injection.
Holding pressure switching point P shifted from _C0 by a predetermined value in the direction of increasing filling amount (for example, about 1 mm, but this pitch can be set arbitrarily by the operator)
Injection is performed by advancing the screw 13 to _C1 . On this occasion,
At the holding pressure switching point P _C1 , since the holding pressure is set to zero as described above, the injection pressure detection sensor 20 causes the pressure corresponding to the molten resin pressure in the cavity at the holding pressure switching point P _C1 . The detected value is stored in the measured value storage unit 33 together with the data of the pressure holding switching point P _C1 as the peak injection pressure converted into the resin pressure.

Similarly, in this next test shot SH _{N + 2} , the weighing point P
After charging with _MN fixed, at the time of injection, the holding pressure switching point is shifted from the holding pressure switching point P _C1 to the holding pressure switching point P _C2 which is further shifted by a predetermined value in the direction of increasing the filling amount.
, The injection is performed, and in the same manner, the trial shot in which the weighing point P _MN is fixed and the holding pressure switching point is shifted in the direction in which the filling amount gradually increases is the holding pressure switching point peak injection pressure characteristic as described later. Until a bending point appears on the line (For example, in the example shown in the figure, the test shot SH _{N + 4} = SH _{N + K} where the holding pressure switching point is P _CK
Repeated).

Based on the variable holding pressure switching point data measured in each of the trial shots SH _{N + 1 to} SH _{N + K} and stored in the measured value storage unit 33 and the peak injection pressure data related thereto, the characteristic line The creating unit 34 creates and updates the holding pressure switching point vs. peak injection pressure characteristic line as shown in FIG. 3 each time the latest data is input. The holding pressure switching point vs. peak injection pressure characteristic line data is transferred to the bending point determination unit 35, and the presence or absence of the bending point X is determined from the degree of inclination of the characteristic line per unit area. .
That is, in the example shown in FIG. 3, since there is a bending point X between the holding pressure switching point 4 mm and the holding pressure switching point 3 mm, immediately after the trial shot SH _{N + K with} the holding pressure switching point P _CK = 3 mm. Bending point X
Is detected by the bending point determination unit 35, and a signal indicating this is sent to the holding pressure switching point position search control unit 36.

In the present embodiment, after this, the molding process control unit 32 of the microcomputer 30 further refers to the command from the holding pressure switching point search operation control unit 36 to perform the next test shot. In the next test shot SH _{N + K + 1} , after the measurement point P _MN is fixed and charging is performed, the holding pressure switching point during injection is set to the test shot SH _{N + K} immediately before the bending point appears. _-1 = S _{N + 3} holding pressure switching point (In the present embodiment, as shown in FIG.
P _C3 ) In the direction of increasing the filling amount, a predetermined pitch finer than before (for example, about 0.1 mm, but this pitch can be set arbitrarily by the operator). Screw 13 up to P _{C3 + 0.1}
Is advanced to perform injection. Similarly, weigh points P _MN
The test shots in which the holding pressure switching point is fixed and the holding pressure switching point is shifted at a fine pitch in the direction in which the filling amount is gradually increased until the bending point X appears on the characteristic curve of the holding pressure switching point versus the peak injection pressure (for example, in the example shown in the figure, Test shot SH where the pressure switching point is P _{C3 + L
N + K + 2} = SH _{N + K + L} ) Repeated.

Therefore, in the example shown in FIG. 2, the holding pressure switching point P _{C3 + L}
= P _{C3 + 0.2} = Trial shot with 3.8mm SH _{N + K + L} = SH _{N + K + 2}
Immediately after, the bending point X is detected by the bending point determination unit 35, and a signal indicating this is sent to the holding pressure switching position search control unit 36, which causes the holding pressure switching position search control unit 36 to detect it. The shot program for searching and setting the holding pressure switching point is ended. At the same time, the bending point determination unit 35 determines that the pressure holding switching point P _{C3 + 1} = at the test shot SH _{N + K + L-1} = SH _{N + K + 1} before (just before) the bending point X appears.
3.9 mm is fixed as the holding pressure switching point data during the continuous molding operation, and the data is stored in the molding condition setting storage unit 31.

In the above-described embodiment, in order to determine the holding pressure switching point accurately and in detail, the bending point X is searched by a test shot in which the holding pressure switching point is changed in 1 mm steps and a trial shot in which the holding pressure change points are changed in 0.1 mm steps. Although it is divided into
Even if the bending point X is detected only in the trial shot process in which the bending point X is varied in 1 mm increments, the holding pressure switching point in the trial shot immediately before (immediately before) where the bending point X appears can be determined as the holding pressure switching point data during continuous molding operation. Of course, there may be cases where there is no practical problem.

Here, the holding pressure switching point vs. peak injection pressure characteristic line of FIG. 3 described above corresponds to the operation explanatory diagram of FIG. 2, and is a molded disk formed of impact-resistant polystyrene resin. However, the characteristic curve of the holding pressure switching point vs. peak injection pressure changes variously depending on the shape of the molded product, the resin material, etc. For example, when the lens is molded with acrylic resin as the molded product, it is shown in Fig. 4. The above-mentioned holding pressure switching point vs. peak injection pressure characteristic line is obtained. In addition, in FIGS. 3 and 4,
The characteristic line part shown by the two-dot chain line shows the peak injection pressure part of the high pressure after the bending point X obtained by the experiment for reference, and in the two-dot chain line part, the mold is damaged due to excessive pressure. Therefore, it is necessary to make a trial shot from the two-dot chain line part and change the holding pressure switching point in the direction in which the filling amount decreases to search the bending point X, because it may cause mold opening failure. It is essential to search the bending point X by changing the holding pressure switching point in the direction in which the peak injection pressure increases.

FIG. 5 is a flow chart showing an example of a processing flow for searching / setting a holding pressure switching point executed by the microcomputer 30. In the figure, ST1 and ST2 are steps for setting the temporary holding pressure switching point and the temporary measuring point, and the processing proceeds to step ST3 via these steps ST1 and ST2. In step ST3, a trial shot is performed by shifting (backing) the metering point by a predetermined value in the direction of increasing the filling amount while the temporary holding pressure switching point is fixed, and the process proceeds to the next step ST4.
In step ST4, it is asked whether or not the filling amount reaches a weighing point that is less than the proper amount by a predetermined amount (for example, whether or not the filling amount exceeds 90%). If NO, the process returns to step ST3, and YES If (the operator makes this determination), the process proceeds to the next step ST5. In step ST5, for example, the filling amount is 90%
With the weighing point at the time of exceeding the set as the fixed weighing point, with this fixed, this time the holding pressure switching point is shifted (moved forward) by the first pitch (eg 1 mm) in the direction in which the filling amount increases
Perform a test shot and proceed to the next step ST6. In ST6, it is determined whether or not the bending point appears by referring to the holding pressure switching point vs. peak injection pressure characteristic line created as described above. If NO, the process returns to step ST5, and if YES, the process proceeds to the next step ST7. In step ST7, the holding pressure switching point is shifted by a second pitch (for example, 0.1 mm) in the direction of increasing the filling amount from the holding pressure switching point in the previous shot when the bending point appears in step ST6 ( Make a trial shot (by moving it forward) and proceed to the next step ST8. In step ST8,
Similar to step ST6, it is determined whether or not the bending point appears by referring to the holding pressure switching point vs. peak injection pressure characteristic line,
If NO, the process returns to step ST7, and if YES, the next step ST
Go to 9. In step ST9, the holding pressure switching point in the last shot seen when the bending point appears in step ST8 is fixedly set as the holding pressure switching point in continuous operation, and the series of processes ends. The end of this series of processing is notified to the operator by, for example, a buzzer and a CRT screen, and the operator recognizes the end of the holding pressure switching point and the weighing point search / setting operation. After this, the operator executes a test shot for determining other conditions as necessary, confirms all the automatic molding operation conditions, and then starts full-automatic molding.

The present invention has been described above with reference to the illustrated embodiment,
It goes without saying that those skilled in the art can make various modifications without departing from the spirit of the present invention. For example, a stepwise variation of the measuring point and the holding pressure switching point during the search / setting operation of the holding pressure switching point ( Any value can be selected for the pitch).

[Advantages of the Invention] As described above, according to the present invention, even an inexperienced operator can easily and reliably set the optimum holding pressure switching point almost automatically, and injection molding that enables good product molding. It is possible to provide a method for setting the holding pressure switching point of the machine. Moreover, the time required for setting the holding pressure switching point required 30 minutes or more in the conventional method, while in the present invention, this can be shortened to 10 minutes or less and 3/1 or less, and for the condition setting. This type of in-line screw type injection molding machine, which eliminates the anxiety, has a remarkable industrial effect.

[Brief description of drawings]

Each of the drawings relates to an embodiment of the present invention, FIG. 1 is an explanatory view showing a schematic structure of an injection molding machine, FIG. 2 is an explanatory view of a search / setting operation of a holding pressure switching point, and FIG. 3 is a holding pressure. Explanatory drawing showing an example of the switching point vs. peak injection pressure characteristic line, FIG. 4 is an explanatory view showing another example of the pressure holding switching point vs. peak injection pressure characteristic line, and FIG. 5 is a holding pressure executed by a microcomputer. It is a flow chart figure showing an example of the processing flow for search and setting processing of a switching point. 1 ... Base, 2 ... Fixed die plate, 3 ... Support board, 4 ... Tie bar, 5 ... Mold clamping cylinder, 6 ... Toggle link mechanism, 7 ... Movable die plate, 8 ... Fixed side metal Mold, 9 ... Movable mold, 12 ... Heating cylinder, 13 ...
Screw, 14 ... Nozzle, 15 ... Band heater, 16 ...
… Hopper, 17 …… Motor, 18 …… Injection cylinder, 20…
... Injection pressure detection sensor, 21 ... Injection stroke detection sensor, 22 ... Screw rotation detection sensor, 23 ... Temperature detection sensor, 24 ... Pressure detection sensor, 25 ... Mold opening and closing stroke detection sensor, 26 ... Mold clamping Pressure detection sensor, 30 ... Microcomputer, 31 ... Molding condition setting storage unit, 32 ... Molding process control unit, 33 ... Actual measurement value storage unit, 34 ... Characteristic line creation unit, 35
...... Bending point judgment unit, 36 ...... Holding pressure switching point search operation control unit, 40 ...... Key input means, 41 ...... Driver group, 42,43 ...
… Control valve, 44 …… Display device, 45 …… Printer, 46 …… External memory.

Claims (2)

[Claims] 1. A heating cylinder is provided with a screw arranged so as to be able to rotate and move forward and backward, and in the measuring process, the raw material supplied from the hopper to the rear part of the screw in the heating cylinder is kneaded and plasticized by the rotation of the screw. It is fed to the tip side of the screw, and as the molten resin is stored on the tip side of the screw, the screw is rotated and retracted to the measuring point, and when the measurement is completed, the rotation of the screw is stopped and the predetermined time after that. At the same time as the injection start timing, the screw is advanced to the holding pressure switching point, the injection process of injecting and filling the molten resin into the cavity of the mold from the nozzle at the tip of the heating cylinder is executed, and then the cavity is passed through the screw. A pressure-holding process is performed to give a pressure-holding pressure to the resin inside, and the operating condition is a microcomputer. In the controlled in-line screw type injection molding machine, a. Temporary holding pressure switching point that can sufficiently guarantee that the filling amount is insufficient and temporary measurement point that can sufficiently guarantee that the filling amount is insufficient are set. After that, the microcomputer repeats the test shot by gradually shifting the measuring point from the temporary measuring point by a predetermined value in the direction of increasing the filling amount while fixing the temporary holding pressure switching point.b. When the filling amount reaches a weighing point that is less than the proper amount by a predetermined amount, the weighing point is confirmed as the setting weighing point of the operating condition controlled by the microcomputer, and c. While holding the set metering point fixed, the holding pressure switching point is gradually shifted from the temporary holding pressure switching point by a predetermined value in the direction in which the filling amount increases, and the trial shots are repeated, and the holding pressure of each trial shot is increased. Set the holding pressure to zero and measure / create the holding pressure switching point vs. peak injection pressure characteristic line during this period.d. Next, the bending point appears on the holding pressure switching point vs. peak injection pressure characteristic line. At that time, the microcomputer sets the holding pressure switching point in the test shot before the bending point appears as the setting holding pressure switching point of the operating condition, so that the holding pressure switching of the injection molding machine is performed. Point setting method. 2. The holding pressure from the holding pressure switching point in the last test shot at which the bending point appears at the time when the bending point appears on the holding pressure switching point vs. peak injection pressure characteristic line. Repeat the test shots by gradually shifting the switching point in the direction of increasing the filling amount at a finer pitch different from the previous one by a predetermined value, and set the holding pressure of each test shot to zero to set the holding pressure switching point in the meantime. Measure and create a characteristic curve for peak injection pressure vs. holding pressure switching point When the bending point appears on the characteristic curve for peak injection pressure vs. peak pressure setting, set the operating pressure at the holding pressure switching point in the last test shot where this bending point appears. A method for setting a holding pressure switching point of an injection molding machine, which is characterized in that the holding pressure switching point is set surely.