JPH04292925A - Estimating method of dwell end position of injection molder - Google Patents

Abstract

PURPOSE:To make it possible to maintain resin injection amount at a constant level without skill by a method wherein the specific gravity and compression factor of resin at dwell end position are calculated and the dwell end position after the change of injection conditions is determined on the basis of various data and the like before and after the change of the injection conditions. CONSTITUTION:In the injection molder concerned, the resin in a heating cylinder 10 is injected in the cavity of a mold 12 by moving a screw 11 under rotation to the injection direction with a screw rotating motor 25. In this case, the output signals of the detection sensor 17 of the position of the screw, of the pressure sensor 19 of the resin in the heating cylinder, of a temperature sensor 27 and of the input device 23 of molding conditions are inputted to a controlling computer 24. Thus, when injection conditions are changed, the specific gravity and the compression factor of resin at dwell end position are calculated on the basis of the temperatures and pressures of the resin so as to determine the dwell end position after the change of injection conditions on the basis of the resin pressures before and after the change of injection conditions, the resin compression factor, the resin specific gravity, the volume of the resin in the heating cylinder and the dwell end position before the change of injection conditions.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a pressure holding end position prediction method for predicting the holding pressure end position of an injection molding machine after a change in injection conditions. The present invention relates to a method of predicting the end position of holding pressure by taking into account changes in resin specific gravity and resin pressure coefficient.

0002

2. Description of the Related Art In an injection molding machine, molten resin injected into a mold is solidified and shrunk. Therefore, in normal injection molding machines, in order to maintain the pressure inside the cavity in the mold, holding pressure is applied from the end of injection to compensate for the lack of resin due to shrinkage and prevent the formation of cavities in the resin. I have to.

0003

[Problems to be Solved by the Invention] However, in conventional equipment, when injection conditions such as resin type, resin measurement, heated cylinder cross-sectional area, injection pressure, preload force, back pressure, cylinder temperature, resin temperature, etc. are changed, The above-mentioned pressure holding control, especially the pressure holding end position, was not corrected in response to this change, so even though there was no problem before the injection conditions were changed,
There is a problem that defects occur in molded products after changing injection conditions. Therefore, conventionally, when changing the above injection conditions,
The amount of correction for the holding pressure conditions, especially the holding pressure end position, was determined through trial and error. For this reason, there has been a problem in the past in that only skilled workers can carry out the above-mentioned correction work. For example, when changing the type of resin in the injection conditions, the specific gravity of the resin changes, when changing the resin measurement, the injection screw position changes, and when changing the heating cylinder cross-sectional area, the injection screw position changes. When the cylinder temperature or resin temperature changes, the resin specific gravity changes, and due to these changes, the injection weight changes before and after changing the injection conditions. In addition, injection pressure, preload,
Even if the back pressure changes, these changes will cause a difference in the injection weight.

FIGS. 8(a) and 8(b) are for explaining the phenomenon that the injection weight changes depending on the resin temperature. In this plunger type injection molding machine, 1 is a heating cylinder, and 2 is a plunger. jar piston, 3 is melted resin, 4
is the injection nozzle.

In these FIGS. 8(a) and 8(b), the plungers are of the same type and volume, but
The resin temperatures inside the heating cylinder 1 are different from T1 and T2, respectively. That is, in FIG. 8, the resin temperature is different from T1 in (a) and T2 in (b), so that the heating cylinder 1
The specific gravity of the resin inside changes before and after the plunger piston 2 moves. This is because the resin specific gravity has temperature characteristics. In this case, plunger piston 2 in FIG. 8(a)
Let ρ11 be the resin specific gravity in the heating cylinder 1 before starting the movement, and let ρ12 be the resin specific gravity after the piston 2 has been moved by a distance d in FIG. 8(a). Similarly, FIG. 8(b)
The resin specific gravity before and after the piston movement is ρ21, respectively.
, ρ22.

When the cross-sectional area of the heating cylinder 1 is S, the weight of the injected resin is ρ11SL−ρ12S(L−d) in the case of FIG. 8(a), and ρ21SL−ρ22S(L−d) in the case of FIG. 8(b). L-d).

[0007] Therefore, the difference in weight between these is
SL(ρ11-ρ21)-S(L-d)
(ρ21−ρ22) …(1), and this (1
) is not necessarily 0. That is, if the temperature of the resin in the cylinder is different, the injection weight will be different even if other injection conditions are the same, which may cause defects in the injection molded product.

Next, FIGS. 9A and 9B show the case where the resin temperature T and the like are the same, but only the injection pressure P is different. That is, the filling length L of the molten resin 3 in the heating cylinder 1 other than the injection pressure
, firing speed V, piston movement distance d, etc. are all common. The injection pressure in FIG. 9(a) is assumed to be P1, and the injection pressure in FIG. 9(b) is assumed to be P2.

Since the resin specific gravity also changes depending on the resin pressure, the resin specific gravity before injection in FIG. 9 is ρ11 and ρ2, respectively.
1, and the resin specific gravity after injection is ρ12 and ρ22, respectively.

When the cross-sectional area of both cylinders is S, the weight of the injected resin is ρ11SL−ρ in the case of FIG. 9(a).
12S(L-d) In the case of FIG. 9(b), ρ21SL−ρ22S(L-d).

[0011] Therefore, the difference in these weights is
SL(ρ11-ρ21)-S(L-
d) (ρ12−ρ22) (2). here,
In the above equation (2), if the resin pressure before injection is also the same, then ρ11=ρ21, so the above equation (2) becomes the following equation.

-S(L-d)(ρ1
2-ρ22)
...(3) Both equations (2) and (3) do not become 0, and even if only the injection pressure differs, the injection weight will differ.

In FIGS. 10(a) and 10(b), the plungers are of the same type and volume, but the filling length of the molten resin 3 in the heating cylinder 1, that is, the plunger piston position, Then, the resin volume) is L1, respectively.
It is different from L2. In this case, it is assumed that the injection speeds are both set to V, and the plunger pistons 2 are both moved by a distance l at this injection speed V to inject the resin. In addition, the specific gravity of the resin in the heating cylinder 1 before the plunger piston 2 starts moving is ρ0 in both FIGS. 10(a) and 10(b), and the resin after the plunger piston 2 is moved at the same injection pressure P. Let the specific gravity of both be ρ1. When the cross-sectional area of the heating tube 1 is S, the weight of the injected resin is ρ0SL1-ρ1S (L1-l) in the case of Fig. 10(a), and ρ0SL2-ρ1S (L2-l) in the case of Fig. 10(b). becomes.

[0014] Therefore, the difference in these weights is ρ0S(L1
-L2)-ρ1S(L1-L2)=(ρ0-ρ1)S(
L1-L2)...(4).

Considering the compression of the resin, ρ0<ρ1 and L1>L2, so the above equation (4) becomes a negative value,
Therefore, the injection weight in FIG. 10(a) is smaller than the injection weight in FIG. 10(b). That is, in the case of molten resin, if the resin volume before injection differs, even if other injection conditions are the same, the injection weight will differ, causing defects in the injection molded product.

[0016] In this way, when changing the injection conditions,
If no measures are taken, the injection weight will differ, leading to problems with the molded product. For this reason, in the past, the holding pressure end position was changed as appropriate through trial and error in order to prevent problems from occurring, but this type of work can only be done by experts and is inefficient. There's a problem.

The present invention was made in view of the above circumstances, and allows even inexperienced workers to easily and efficiently perform maintenance by automatically calculating the end position of holding pressure when injection conditions are changed. It is an object of the present invention to provide a method for predicting the pressure end position of an injection molding machine that can determine the pressure end position.

[0018]

[Means and effects for solving the problem] In this invention,
In an injection molding machine that performs injection molding by applying holding pressure from the end of injection to a predetermined screw position, when changing the injection conditions, the volume of resin in the heated cylinder is determined before changing the injection conditions, and the holding pressure before changing the injection conditions is determined. The resin temperature and resin pressure at the end position are measured, and from these resin temperature and resin pressure, the resin specific gravity and resin compression coefficient at the pressure-holding end position are determined, and after changing the injection conditions, the resin volume in the heating cylinder is determined, and the resin volume in the heating cylinder is determined. Measure the resin temperature and resin pressure at the holding pressure end position or a predetermined position near the holding pressure end position before changing the injection conditions, and calculate the resin specific gravity and resin compression coefficient after changing the injection conditions from these resin temperatures and resin pressures. , determining the pressure holding end position after changing the injection conditions based on the resin pressure, the resin compression coefficient, the resin specific gravity, and the resin volume in the heating cylinder before and after changing the injection conditions, and the holding pressure ending position before changing the injection conditions. It is characterized by

According to the configuration of the present invention, the resin specific gravity and resin compression coefficient at the pressure-holding end position are determined from the resin temperature and resin pressure, and the resin pressure, resin compression coefficient, and resin before and after changing the injection conditions are determined. The holding pressure end position after changing the injection conditions is determined based on the specific gravity, the resin volume in the heating cylinder, and the holding pressure ending position before changing the injection conditions.

[0020] Furthermore, in this invention, in an injection molding machine that performs injection molding by applying holding pressure from the end of injection to a predetermined screw position, when changing injection conditions, the resin volume in the heating cylinder is determined before changing the injection conditions. At the same time, measure the resin temperature and resin pressure at the holding pressure end position before changing the injection conditions, calculate the resin specific gravity and resin compression coefficient at the holding pressure end position from these resin temperatures and resin pressure, and then heat the resin after changing the injection conditions. While determining the resin volume in the cylinder, a test injection is performed with pressure holding before changing the injection conditions, and during the pressure holding of the test injection, the correspondence relationship between the injection screw position, resin temperature, and tree finger pressure is measured,
The resin specific gravity and resin compression coefficient at each injection screw position are determined from the measured resin temperature and resin pressure, and the resin pressure, resin volume in the heating cylinder, resin specific gravity, resin compression coefficient, and holding pressure are determined at each injection screw position. The end position, the resin volume in the heated cylinder after changing the injection conditions, and the measured resin pressure, resin specific gravity, and resin compression coefficient at each injection screw position after changing the injection conditions are calculated as the end position of holding pressure after changing the injection conditions. is substituted into a predetermined arithmetic expression to calculate the relationship between the resin temperature and resin pressure and the injection screw position, and further, the measured value and the calculated value of the injection screw position corresponding to the same resin temperature and resin pressure value are calculated. are sequentially compared, and the calculated value of the injection screw position with the smallest difference between the measured value and the calculated value is determined as the pressure holding end position after changing the injection conditions.

[0021] According to this configuration, the correspondence (calculated values) between the resin temperature and the resin pressure obtained by the calculation formula for calculating the holding pressure end position and the injection screw position, and the resin temperature and resin pressure obtained by the test injection. Compare the correspondence relationship (measured value) between do.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below according to embodiments shown in the accompanying drawings.

FIG. 4 shows the configuration of an embodiment of the present invention, in which 10 is a heating cylinder, 11 is an injection screw, 12 is a mold,
13 is a valve opening/closing machine, 14 is a valve, 15 is an injection cylinder, 16 is a resin inlet, 17 is a screw position detection sensor, 18 is a screw position detection device, 19 is a heating cylinder resin pressure sensor, 20 is a valve opening/closing feedback system , 21
2 is a valve opening/closing drive command generator; 22 is a flow rate control unit;
3 is a molding condition input device, 24 is a control computer, 2
5 is a screw rotation motor, 26 is a piston, and 27 is a temperature sensor for detecting resin temperature. Note that the conditions may be input to the molding condition input device by an operator, or may be input online from each sensor.

In the above configuration, the resin is supplied through the resin inlet 16.
The mixture is filled into the heating cylinder 10 through the screw 11 and injected into the cavity of the mold 12 by the screw 11. The screw 11 is connected to a piston 26 of the injection cylinder 15, and the rotation shaft of a screw rotation motor 25 is connected to the piston 26, and the rotation of the screw rotation motor 25 rotates the screw 11 and moves it in the injection direction. Further, oil from a pump (not shown) is supplied to the injection cylinder 15 via a flow rate control section 22, and the computer 24 variably controls the oil flow rate supplied to the injection cylinder 15 by controlling the flow rate control section 22. to control the injection speed.

[0025] The nozzle section is provided with a nozzle valve 14 for controlling its opening area, and the nozzle valve 14 is connected to a valve opening/closing machine 13 via a link mechanism, and a computer 24 feedback-controls the valve opening degree. This controls the opening area of the nozzle portion. Further, the screw position is detected by a screw position sensor 17 and a screw position detection device 18 and is input to the computer 24 . Further, during injection, the tree finger pressure and resin temperature are detected by the pressure sensor 19 and the temperature sensor 27, respectively, and are input into the computer 24. The computer 24 stores the input resin pressure and resin temperature in a memory within the computer 24 in correspondence with the screw position. The computer 24 inputs a flow rate command corresponding to the injection speed command as shown in FIG. Executes firing speed control. Further, the computer 24 controls the flow rate control section 22 according to the commanded injection pressure to control the injection pressure and holding pressure.

By the way, the memory in the computer 24 stores data on resin specific gravity ρ and resin compression coefficient V of various resins as functions of resin temperature T and resin pressure P in the form of a function table.

That is, Spencer Gilmor
According to the state equation of e, the resin specific gravity ρ can be expressed as a function of the resin temperature T and the resin pressure P, as shown in the following equation (5).

(P+πi)(Q−n・ω)=n・R′・
T...(5) holds true.

##EQU1## where Q is the resin volume, n is the number of moles of the resin, and πi, ω, and R' are constants specific to the resin.

Further, the change in volume of the resin is defined by the compressibility β of the resin as shown in the following equation.

[0031]

Therefore, from the above equations (5) and (6),

00
33]

[0034]

Further, if the resin compression ratio at a certain pressure P0 and temperature T0 is β0, and the resin specific gravity in that state is ρL0, then the resin specific gravity ρL in any state is ρL=β・ρL0/β0
...(8).

Therefore, in β of the above equation (8), the above (7
), resin specific gravity ρL can be expressed as a function of resin temperature T and resin pressure P.

Although the resin compression coefficient V will be described later, it is actually an approximate value of the resin compression ratio β, so the relationship between the resin compression coefficient V, the resin temperature T, and the resin pressure P is determined by the above equation (6). .

That is, polystyrene, GP styrene,
For various resins such as polymethyl methacrylate, ethyl cellulose, polypropylene, polyacetal, and nylon 610, the above constants πi, ω, and R' are determined in advance, and the various resin temperatures T and various resins are used in equations (7) and (8) above. By substituting the finger pressure P with the constants πi, ω, and R' to find the resin specific gravity ρL, the correspondence between various resin temperatures T and various tree finger pressures P and the resin specific gravity ρL is obtained, and this is stored in the memory in the computer 24. Remember it.

As for the resin compression coefficient V, the resin compression coefficient V is obtained by substituting various resin temperatures T and various resin pressures P together with the above constants πi, ω, and R' into the above equation (6) as described above.
By determining the various resin temperatures T and various tree finger pressures P
and the resin compression coefficient V, and store this in the memory in the computer 24.

Table 1 below shows examples of the constants πi, ω, and R' for various resins.

[0041]

FIG. 5(a) shows the relationship between the position of the injection screw 11 (or piston position) and the holding pressure during holding pressure in the heating cylinder 10. In this case, holding pressure is maintained at position Xs. It started and ended holding pressure at position XA. Note that the pressure holding start position coincides with the injection end position. Here, it is assumed that one or more of the injection conditions shown below are changed while pressure holding control is being performed at the holding pressure shown in FIG. 5(a). (1) Change in resin type (2) Change in resin metering (3) Change in heating cylinder cross-sectional area (4) Change in injection pressure (5) Change in preload force (6) Change in back pressure (7) Change in cylinder temperature or Changes in Resin Temperature Even after changing these injection conditions, it is necessary to change the holding pressure end position in order to prevent underfilling or overfilling of the resin into the mold. Figure 5 (
b) shows the holding pressure after changing the injection conditions, and the holding pressure end position is XB. Note that this device only changes the pressure-holding end position, but does not change the pressure-holding start position or the holding pressure value itself. FIG. 1 is a flowchart showing a first embodiment of calculation for deriving a new holding pressure end position after changing injection conditions.

[0043] A description will be given below according to this flowchart. In this flowchart, the subscript "A" means before the injection conditions are changed, the subscript "B" means after the injection conditions are changed, and the subscript "L" of ρ indicates that the resin is liquid. The subscript "S" of ρ means that the resin is solid.

First, before explaining the flowchart in FIG. 1, the meaning of the resin compression coefficient V and the principle for deriving the relational expression for deriving the injection speed switching position after changing the injection conditions will be explained using FIGS. 6 and 7. Each will be explained.

FIG. 6 is for explaining the resin compression coefficient V. First, two identical plunger cylinders 1 and 1' are prepared as shown in FIGS. 6(a) and 6(b), and these injection cylinders are Assume that the same volume of resin used in molding is measured and filled. Therefore, the positions of these plunger pistons 2 are the same position XE. In this state, the piston 2 is moved by the distances XE-S1 and XE-S2 without performing injection (that is, with the injection nozzle closed) and then stopped. Letting the resin pressures at that time be P1 and P2, respectively, the resin compression coefficient V is given by the following formula.

V=(S2-S1)/(S2P1-S1P2)...(
9) The above equation (9) defines the resin compression coefficient V, but in this configuration, the resin compression ratio β shown in the above equation (6) is used instead of the resin compression coefficient.

FIG. 7 explains the principle of determining the firing speed switching position. First, as shown in FIG. 7(a), the nozzle 4
The weight of the resin 3 is M0 in the closed plunger cylinder 1.
Weigh only. At this time, the piston 2 is pressing the resin 3 with an initial pressure BP (back pressure), and the piston position at this time is assumed to be XE (resin metering position). After this,
As shown in FIG. 7(b), the piston 2 is pushed with a preload force Ppc to move the piston 2 to position Xpc (preload position). Even in this state of FIG. 7(b), the nozzle 4 is closed and no injection is performed. After this, Figure 7 (
As shown in c), open the nozzle 4, press the piston 2 with an injection pressure of P, and move the piston 2 to position S (
The moving distance is X) Injection and holding pressure are performed. Since the weight of the injected resin at this time is M, the weight of the residual resin is M0' (=M0
-M). At this time, the cross-sectional area of cylinder 1; D resin specific gravity; ρs (solid), ρL (liquid) resin compression coefficient;
V Holding pressure end position before injection condition change; XA Holding pressure end position after injection condition change; XB Resin pressure at holding pressure end position before injection condition change; Shiatsu: PB, BP≒
If it is 0, M0=D・XE・ρL
…(
10) M0=D・XPC・ρL/(1−V・P
pc) …(11)
M0'=D・S・ρL/(1−V・P)
...(12). However, S=Xpc−X=(1−V·Ppc)XEX−X.

Therefore, M=DρL{[V(Ppc-P)XE+X]/(1
-V・P)} ...(13).

Now, assume that all of the injection conditions in (1) to (7) above have been changed, and A is used before the conditions are changed, and B is used after the conditions are changed.
If we add a subscript to each parameter, then MA=
DAρLA {[VA(PpcA-PA)XEA+XA]
/(1-VA・PA)}

…(14
) MB=DBρLB{[VB(PpcB-PB)X
EB+XB]/(1-VB・PB)}


...(15) holds true. Here, since the injection volume before and after changing the injection conditions needs to be the same, the following formula holds true.

MA/ρSA=MB/ρSB

...(16) Therefore, the above formulas (14), (15
) and (16), the following equation (17) holds true.

[0051]XB=f(XA,PA,PB,VA,VB
, ρLA, ρLB, ρSA, ρSB, DA, DB, XE
A, PPCA, XEB, PPCB)

[0052]

Next, a first embodiment of a procedure for deriving a new holding pressure end position after changing injection conditions will be described with reference to FIG. In this first embodiment, since the injection speed or the injection pressure is set low, it is assumed that the injection pressure and the resin pressure are equal.

When performing injection molding, after adjusting the equipment to a state where no defects occur, the injection screw 11
Alternatively, the resin temperature TA and resin pressure PA when the piston 26 is located at the pressure holding end position XA are measured from the outputs of the temperature sensor 27 and the pressure sensor 19, respectively, and these are stored in the memory in the computer 24. Furthermore, the computer 24 measures the resin volume QA filled in the heating cylinder. This resin volume QA is determined in the subsequent step 17.
It is one of the parameters used when calculating the holding pressure end position of 0 (formula (17) above), and specifically, it is the heating cylinder internal cross-sectional area DA (which is input and set in the computer as one of the molding conditions). The resin measurement position XEA (determined from the output of the screw position detection sensor 18 at the injection cylinder position or piston position when resin measurement is completed) is determined and used as a substitute. Further, for the preload force PPCA used in the above equation (17), a command value from the computer 24 to the flow rate control section 22 is stored (step 100).

Then, the computer 24 reads the resin specific gravity ρLA, ρSA and resin compression coefficient VAi corresponding to the measured resin temperature TA and resin pressure PA from the storage table in the memory described above, and stores these (step 110).

After that, the seven injection conditions (1) shown above are applied.
Assume that one or more of (7) is to be changed (step 120).

[0057] The above seven injection conditions (1) to (7)
are changed or changed due to the following reasons.

(1) Change of resin type Changing the resin material of the same molded product.

(2) Change in resin measurement Even if the same amount of resin is measured, the piston position changes each time because the reproducibility of the machine is not perfect.

(3) Change in the cross-sectional area of the heating cylinder When a molding condition that does not cause molded product defects is found for a certain mold, and an order is placed for production using that mold and molding conditions, the molding machine of the ordering company is The heating cylinder may not be the same as the one from the ordering source.

(4) Changes in injection pressure The injection pressure changes depending on conditions such as imperfect reproducibility of the machine and outside temperature.

(5) Change in preload force It changes depending on conditions such as the imperfect reproducibility of the machine and the outside temperature.

(6) Changes in back pressure Changes occur due to conditions such as imperfect reproducibility of the machine and outside temperature.

(7) Change of cylinder temperature or resin temperature This parameter is changed as appropriate depending on the molding state.

When these injection conditions are changed, after actually changing the injection conditions, the injection screw or piston is moved to the holding pressure end position XA before the change in injection conditions or a predetermined position near the holding pressure end position XA. The resin temperature TB and resin pressure PB at the respective positions are measured from the outputs of the temperature sensor 27 and the pressure sensor 19, and these are stored in the memory in the computer 24. Further, when measuring the resin or changing the cross-sectional area of the heating cylinder, measure the resin volume QB filled in the heating cylinder. As above, this resin volume QB is determined by the heating cylinder internal cross-sectional area DB (inputted into the computer as one of the molding conditions) and the resin metering position XEB (the injection cylinder position or piston position when resin metering is completed). (obtained from the output of the position detection sensor 18) (step 140
). Further, as the preload force PPCB, a command value from the computer 24 to the flow rate control section 22 is stored.

Then, the computer 24 reads out the resin specific gravity ρLB, ρSB and resin compression coefficient VBi corresponding to the measured resin temperature TB and resin pressure PB from the storage table in the memory described above, and stores these (step 150).

When step 150 is completed, all of the 15 parameters in equation (17) are known except for the resin pressure PBi after changing the injection conditions.

Therefore, in step 160, the resin pressure PB at the pressure holding end position after changing the injection conditions is determined, but in this first embodiment, as described above, the injection pressure is low due to the low injection speed or low injection pressure. It is assumed that and the resin pressure are equal.

Therefore, in this first embodiment, the resin pressure PB at the pressure-holding end position after the change is made equal to the resin pressure PA at the pressure-holding end position before the change (PB=PA). By substituting into the formula, the holding pressure end position XB after changing the injection conditions
(Step 170).

When a new pressure-holding end position is determined in this way, the computer 24 calculates the thus-obtained pressure-holding end position X.
By controlling the flow rate control unit 22 according to B, injection molding is executed up to a new pressure holding end position XB (steps 180, 130). That is, the screw position is detected by the position detection sensor 17 during injection, and the computer 24 controls the flow rate control section 22 while referring to the detected screw position, so that after the injection is completed,
The pressure holding control is executed from the pressure holding start position to the pressure holding end position.

FIG. 2 shows a second embodiment of the present invention, which differs from the first embodiment only in that step 160 is omitted, and is otherwise completely the same.

That is, this second embodiment assumes that the resin pressure is less than the injection pressure, and when calculating the holding pressure end position XB after changing the injection conditions in step 170, the holding pressure end position XB after changing the injection conditions is The resin pressure at the holding pressure end position XA before the injection condition change measured and stored in step 140 or at a predetermined position near the holding pressure end position XA is used as the resin pressure PB at the position.

In other words, the idea behind the first and second embodiments is that the resin pressure PB needs to be accurately measured at the new holding pressure end position XB, but since this is actually impossible, The measurement position is approximated to the holding pressure end position or a position near it before the injection conditions were changed.

FIG. 3 shows a third embodiment of the present invention, in which steps 140 to 170 of the second embodiment are replaced with steps 125, 141, 151, 161 and 171, and the injection The processing before changing the conditions is the same as in the first and second embodiments. This third embodiment also assumes a case where the tree finger pressure is less than the injection pressure.

That is, in this third embodiment, when changing the injection conditions, after actually changing the injection conditions, a trial injection is performed at the same injection speed and injection speed switching position as before the injection conditions were changed (step 125). While performing this trial injection, check the positions of each piston or screw in the heating cylinder 1 (especially the holding pressure end position XA before changing the injection conditions).
(in the vicinity of Find each correspondence.

Furthermore, when the resin measurement or the cross-sectional area of the heating cylinder is changed, the resin volume QB filled in the heating cylinder is measured. As above, this resin volume QB is determined by the heating cylinder internal cross-sectional area D (inputted into the computer as one of the molding conditions) and the resin metering position XE (the injection cylinder position or piston position when resin metering is completed). (obtained from the output of the position detection sensor 18) is used instead (step 141). Further, as the preload force PPCB, a command value from the computer 24 to the flow rate control section 22 is stored.

Then, the computer 24 calculates the resin specific gravity ρLBj, ρSBj corresponding to the measured resin temperature TBj and resin pressure PBj from the storage table in the memory described above.
and VBj, and store them (step 151). In this way, the obtained resin temperature T
Let the combination of the correspondence between Bj and resin pressure PBj and the injection screw position be (TBj, PBj, XBMj).

Next, the holding pressure end position XA before the injection condition change is substituted for XA in the above equation (17), and the holding pressure end position measured and stored in the previous step 100 is substituted for the resin pressure PA before the condition change. Substitute the resin pressure PA1 at the position, substitute the values obtained in the previous step 110 for the resin compression coefficient VA and resin specific gravity ρLA, ρSA before changing the injection conditions, and further substitute the resin pressure PB after changing the injection conditions. Resin pressure values P obtained during the trial injection at multiple locations near the holding pressure end position before changing injection conditions
Substitute Bj sequentially.

In addition, when sequentially substituting the resin pressure value PBj, the resin specific gravity ρLBj, ρSBj and resin compression coefficient V obtained corresponding to each tree finger pressure PBj in the previous step 151 are used.
Bj is substituted into the above equation (17) together with each resin pressure PBj. In addition, the heating cylinder internal cross-sectional areas DA and DB, which are parameters of the resin volume Q before and after changing the injection conditions, the resin measuring positions XEA and XEB, and the preload forces PPCA and PPCB before and after changing the injection conditions are also calculated using the above formula (17). By substituting , the number of XBj corresponding to the plurality of locations is derived. The combination of resin temperature TBj and resin pressure PBj derived in this way and screw position XBj is set as (TBj, PBj, XBCj) (step 161
).

Next, the previously stored combination of measured values (TBj, PBj, XBMj) and the calculated value combination (
TBj, PBj, XBCj), XBCj=X
BMj or XBCj - XBC where XBMj is the minimum
The value of j is set as the holding pressure end position after changing the injection conditions (step 171). That is, the measured value XBMj and the calculated value XBCj associated with the same combination of resin temperature TBj and resin pressure value PBj are compared for each combination of resin temperature TBj and resin pressure value PBj, and the difference is the smallest among them. XBCj is set as the new holding pressure end position.

[0081] In the third embodiment, the measured values (TBj, PBj, XBMj) in the trial injection process are stored, and after the trial injection process is completed, the holding pressure end position after changing the injection conditions is derived. However, the above calculated values (TBj, PBj,
BCj), the holding pressure end position XA before changing the injection conditions, and the resin pressure PA at the holding pressure ending position before changing the injection conditions.
The resin specific gravity ρLA, ρSA before changing the injection conditions, and the resin compression coefficient VA before changing the injection conditions have already been determined before changing the injection conditions, and are also obtained during the trial injection to be substituted into equation (17) above. The resin pressure value PBj, the resin specific gravity ρLBj, ρSBj after changing the injection conditions, and the resin compression coefficient VBj after changing the injection conditions can be determined while performing a trial injection, so the maintenance after changing the injection conditions described above can be performed. The calculation for determining the pressure end position may be executed in parallel with the injection process, that is, in real time.

[0082] In this way, the pressure holding end position after changing the injection conditions is almost automatically calculated by the computer 24, and the computer 24 executes pressure holding control in accordance with the calculated holding pressure end position.

[0083]

[Effects of the Invention] As explained above, according to the present invention,
When changing injection conditions, the holding pressure end position is automatically determined by adding the resin pressure, resin specific gravity, and resin compression coefficient to the calculation parameters, so that no defects will occur in the molded product in response to changes in various injection conditions. Since the accurate holding pressure end position is determined, even inexperienced workers can easily and efficiently find the appropriate holding pressure end position. No defects will occur in the molded product.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a first embodiment of the invention.

FIG. 2 is a flowchart showing a second embodiment of the invention.

FIG. 3 is a flowchart showing a third embodiment of the invention.

FIG. 4 is a diagram showing an injection molding machine to which the method of the invention is applied.

FIG. 5 is a diagram showing the relationship between piston position and holding pressure.

FIG. 6 is a diagram illustrating a resin compression coefficient.

[Figure 7] Diagram explaining the formula for determining the firing speed after changing the injection conditions

FIG. 8 is a diagram illustrating the difference in injection weight due to the difference in resin temperature.

FIG. 9 is a diagram illustrating a difference in injection weight due to a difference in resin pressure.

FIG. 10 is a diagram illustrating that the injection weight varies depending on the plunger piston position.

[Explanation of symbols]

1...Heating cylinder 2...Plunger piston 3... Melted resin 4... Injection nozzle 10...Heating cylinder 11...Injection screw 12...Mold 13... Valve opening/closing machine 14...Valve 15...Injection cylinder 16...Resin inlet 17...Screw position detection sensor 18...Screw position detection device 19...Heating cylinder resin pressure sensor 20...Valve opening/closing feedback system 21...Valve opening/closing drive command generation device 22...Hydraulic control device 23... Molding condition input device 24...Control computer 25...Screw rotation motor 26...Piston 27...Temperature sensor

Claims (5)

[Claims] Claim 1: In an injection molding machine that performs injection molding by applying holding pressure from the end of injection to a predetermined screw position, when changing injection conditions, the volume of resin in the heated cylinder is determined before changing the injection conditions, and the injection conditions are Measure the resin temperature and resin pressure at the pressure-holding end position before the change, and calculate the resin specific gravity and resin compression coefficient at the pressure-holding end position from these resin temperatures and resin pressure. while determining the volume, measuring the resin temperature and resin pressure at the pressure-holding end position or a predetermined position near the pressure-holding end position before the injection condition change;
The resin specific gravity and resin compression coefficient after changing the injection conditions are determined from these resin temperature and resin pressure, and the resin pressure, resin compression coefficient, resin specific gravity, and resin volume in the heating cylinder before and after changing the injection conditions are calculated. A method for predicting the end position of pressure holding in an injection molding machine, the method comprising determining the end position of pressure holding after changing injection conditions based on the previous end position of holding pressure. 2. A correspondence relationship between resin temperature, resin pressure, and resin specific gravity, and a correspondence relationship between resin temperature, resin pressure, and resin compression coefficient are stored in advance in a table format for various resins, and before the injection conditions are changed, Prediction of the holding pressure end position of an injection molding machine according to claim 1, wherein the resin specific gravity and the resin compression coefficient are determined by inputting the resin temperature and tree finger pressure measured later into the stored table. Method. 3. When the holding pressure and the finger pressure are substantially equal, the resin pressure at the holding pressure end position before the injection condition change is substituted for the resin pressure at the holding pressure end position after the injection condition change. The method for predicting the end position of holding pressure in an injection molding machine as described above. 4. If the tree finger pressure is less than the injection pressure, the tree finger pressure at the holding pressure end position after the injection condition change is the holding pressure end position measured after the injection condition change or the holding pressure end position before the injection condition change. 2. The method for predicting the end position of holding pressure in an injection molding machine according to claim 1, which uses finger pressure in the vicinity of the position. 5. In an injection molding machine that performs injection molding by applying holding pressure from the end of injection to a predetermined screw position, when changing injection conditions, the resin volume in the heating cylinder is determined before changing the injection conditions, and the injection conditions are Measure the resin temperature and resin pressure at the pressure-holding end position before the change, and calculate the resin specific gravity and resin compression coefficient at the pressure-holding end position from these resin temperatures and resin pressure. In addition to determining the volume, a test injection is performed with pressure holding before changing the injection conditions, and during the pressure holding in the test injection, the correspondence relationship between the injection screw position, resin temperature, and tree finger pressure is measured, and the measured resin temperature and resin pressure are measured. The resin specific gravity and resin compression coefficient at each injection screw position are determined from the pressure, and the resin pressure, resin volume in the heated cylinder, resin specific gravity, resin compression coefficient, and pressure holding end position before changing the injection conditions are determined. A predetermined calculation formula for calculating the holding pressure end position after changing the injection conditions from the resin volume in the heated cylinder afterward, and the measured resin pressure, resin specific gravity, and resin compression coefficient at each injection screw position after changing the injection conditions. The correspondence relationship between the resin temperature and resin pressure and the injection screw position is determined by substituting into A method for predicting the end position of pressure holding in an injection molding machine, characterized in that the calculated value of the injection screw position with the smallest difference between the value and the calculated value is determined as the end position of pressure holding after changing injection conditions.