JPH0813486B2 - Control method of mold clamping force of injection molding machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine, in which the mold clamping force of the mold clamping device is filled with pressure or holding pressure, that is, an injection plunger (inline screw type injection molding machine). In the machine, the screw, the same shall apply hereinafter) relates to a device for controlling the resin pressure during advancement and the resin pressure after filling.

<Prior art> The simplest method to control the mold clamping force of the mold clamping device of an injection molding machine is a little larger than the value obtained by multiplying the maximum resin pressure through the filling process and the pressure holding process by the projected area of the mold cavity. The mold clamping force is used to clamp the mold from the start to the end of molding.

In this method, the mold is clamped with a high pressure so that the mold does not open (do not overpack) even if some abnormality occurs during injection and the peak pressure acts, and then the injection process is started. At this time, the molten resin is rapidly filled in the cavity of the mold, whereby the air in the mold is adiabatically compressed to a high temperature, which may cause resin burning. Therefore, in order to avoid this, an air vent is provided along the parting surface of the mold so that the air inside the mold escapes.

However, air vent processing has a subtle know-how in groove width and groove depth, which complicates the design and manufacture of molds. In addition, even though the peak pressure acts on the mold cavity only at the moment, the mold is clamped with a large force from the beginning to the end of the molding process, so the mold is distorted or excessively deformed. The mold clamping force causes stress corrosion cracking on the parting surface of the mold, which accelerates damage to the mold, and wastes energy for maintaining high hydraulic pressure.

Therefore, in order to avoid this, a mold clamping device has been proposed in which the hydraulic chamber of the mold clamping cylinder and the hydraulic chamber of the injection cylinder are connected to make the mold clamping force proportional to the injection pressure.

<Problems to be solved by the invention> However, in the structure in which the hydraulic chamber of the mold clamping cylinder and the hydraulic chamber of the injection cylinder are communicated with each other, the piston diameters of the mold clamping cylinder and the injection cylinder are constant values determined by the capacity of the machine. Therefore, the mold clamping force generated by the mold clamping cylinder is a force proportional to the pressure of the injection cylinder, that is, the resin filling pressure determined thereby, and has no relation to the projected area of the cavity of the mold. Therefore, when the projected area of the cavity is small, the mold clamping force becomes excessive, and the same problem as in the above-described mold clamping in preparation for the peak pressure occurs, and when the projected area of the cavity is large, the hydraulic pressure source is provided only on the mold clamping side. Since the maximum hydraulic pressure cannot be applied, the mold clamping force is insufficient and overpacking easily occurs. So this structure is
It is only effective when the projected area of the mold cavity is within a certain range. Further, the mold clamping device having such a structure has a drawback that extra piping is required.

Therefore, in the present invention, by obtaining a mold clamping force control method for generating a mold clamping force that is approximately proportional to the force obtained by multiplying the resin pressure (filling pressure and holding pressure) acting on the cavity of the mold by the projected area of the cavity, An object of the present invention is to obtain an injection molding machine that clamps a mold with an optimum force in proportion to the size of the mold cavity and the fluctuation of the injection pressure, and therefore does not cause problems such as damage to the mold and overpack.

<< Means for Solving the Problem >> The mold clamping force control method according to the present invention comprises a pressure detecting means 19 for detecting the oil pressure Pi of the injection cylinder 1 and a pressure for controlling the oil pressure Pc supplied to the mold clamping cylinder 7. The controller 12, the calculating means 24 for calculating the pressure command value Q proportional to the detected pressure Pi of the pressure detecting means 19 and the projected area Sm of the mold cavity 5, and the pressure controller according to the pressure command value Q. In the mold clamping force control method of the injection molding machine including the driver 17 for controlling 12, the calculating means 24, the area of the injection cylinder is Si, the area of the injection plunger is Sp, the area of the mold clamping cylinder is Sc, Using the proportional constant C given by C = Si / SpSc, when the projected area Sm of the mold cavity 5 and the detected pressure Pi of the pressure detection means 19 are input, the pressure command value Q is calculated as Q = CSmPi. It is characterized by that.

In this case, the pressure command value Q calculated by the above method
It is possible to control the pressure controller 12 by multiplying with a correction coefficient α greater than 1.

The pressure controller 12 may be, for example, a proportional electromagnetic relief valve or a proportional electromagnetic pressure reducing valve. Further, for example, a variable displacement pump may be equipped with a proportional electromagnetic pressure control valve.

In any case, the hydraulic pressure source 14 on the mold clamping side is controlled by the pressure Pi on the injection side.
If it is affected by the fluctuation of, the control will be hindered. In other words, even in the circuit using the pressure reducing valve, the discharge pressure Pio of the injection-side hydraulic power source 13 does not decrease unless the injection-side pressure Pi is not abnormally reduced and the oil amount is excessively consumed. Therefore, with the same hydraulic source as the injection side, the hydraulic pressure Pc on the mold clamping side
Can also be supplied.

The pressure command value Q given to such a pressure controller 12
Is a value that determines the magnitude of the secondary pressure Pc of the pressure controller 12. The value of the proportional constant C is a constant that is determined for each injection molding machine, and the projected area Sm of the cavity is a constant value that is determined by the mold. Therefore, when the mold is mounted on the injection molding machine, Pi to Q are changed. The proportionality constant SmC for calculation is uniquely determined. The memory 25 stores the proportional constant or a parameter for calculating the proportional constant.

The pressure Pi of the injection cylinder 1 is a pressure determined by the flow path resistance of the resin such as the nozzle 3, the spool 6 and the cavity 5 when the resin is filled in the mold, and is the set pressure when the pressure is maintained.

The resin pressure in the mold can produce a peak pressure when the filling process is complete. This peak pressure includes a pressure increase due to the inertia of the resin and the plunger. Due to this peak pressure, the parting surface of the mold may be opened and overpacked, and burrs may occur in the product. Therefore, in consideration of such a safety factor against excessive pressure, the value of Q may be multiplied by a correction coefficient α larger than 1 to control the pressure controller 12.

The internal pressure of the mold cavity during injection is always lower than the internal pressure of the injection cylinder, and there is a time delay in the internal pressure of the cavity. Therefore, after detecting the pressure Pi on the injection side, the pressure controller 12
Even if there is a slight time delay before the control of, there is little possibility of overpacking, and control that does not multiply by the correction coefficient α usually causes no problem.

Set the maximum value of the filling pressure and holding pressure Pimax set on the injection side to P
Qmax calculated as i is the discharge pressure Pco of the hydraulic pressure source 14 on the mold clamping side.
When the value kmax divided by is called the pressure conversion rate, kmax = Qmax / Pco = CSmPimax / Pco. Substituting C = Si / SpSc into the above equation gives kmax = SiSmPimax / SpScPco.

Therefore, when the pressure conversion ratio kmax is 1 or more, it means that the mold clamping force is insufficient even when the discharge pressure Pco of the hydraulic pressure source 14 is supplied to the mold clamping cylinder 7 when the pressure on the injection side becomes Pimax. To do. In the device provided with the above-mentioned Q value calculating means 24, the value of kmax can be easily calculated from the value of Qmax, so an alarm is issued when the calculated value of kmax is 1 or more. It is also easy to do so that it is possible to prevent an excessively large mold from being mounted and an excessively high filling pressure or holding pressure from being set.

When controlling the pressure controller 12 by multiplying the value of Q by the correction coefficient α, if the value of kmax is also multiplied by the correction coefficient α to issue the above-mentioned alarm, a consistent safety factor can be obtained. Control can be performed.

<Operation> The hydraulic pressure Pc applied to the mold clamping cylinder 7 by the above method
By controlling, the clamping force of the mold becomes proportional to the product of the projected area Sm of the cavity and the oil pressure Pi of the injection cylinder 1, and even if the pressure of the injection cylinder 1 is the same, the projection of the cavity When the area Sm is large, a large mold clamping force is obtained, and when the cavity is small, the mold clamping force is also small, so the mold can be clamped with a clamping force proportional to the magnitude of the force to open the mold, To obtain an injection molding machine that prevents both the problem of energy loss due to excessive mold clamping force, the problem of mold damage, and the problem of overpack due to too small mold clamping force. You can

By setting the correction value α appropriately and checking the molding conditions with the value of the pressure conversion rate kmax in advance, it is possible to obtain an injection molding machine that is safe against peak pressure and setting error.

<< Example >> Next, the Example shown in drawing is described. In FIG. 1, 1 is an injection cylinder, 2 is an injection plunger, 3 is a nozzle, 4 is a mold, 5 is a mold cavity, 6 is a spool, 7 is a mold clamping cylinder, and 8 is a direction switching valve on the injection cylinder side. , 9 is a direction switching valve on the mold clamping cylinder side, 10 is a flow control valve for controlling the speed of the injection plunger 2 at the time of filling, 11 is an upper limit value Piu of the oil pressure given to the injection cylinder 1 at the time of filling, and a holding pressure Pip are set. Pressure control valve for controlling the mold clamping force, 12 for controlling the mold clamping force, 13 for the hydraulic pressure source on the injection side, 14 for the hydraulic pressure source on the mold clamping side, 15 for the controller, 16 and 17 for the pressure control valve 11 and 12
Is a driver for the flow control valve 10, 19 is a pressure converter for detecting the hydraulic pressure of the injection cylinder 1, 20 is an interface circuit, 21 is an input device such as a keyboard, and 22 is a display device such as a CRT.

The control device 15 includes a CPU 23, a memory 24 storing a calculation program for calculating the hydraulic pressure applied to the mold clamping cylinder 7,
A data memory 25 is provided. In the data memory 25, the area Si of the injection cylinder 1, the area Sp of the injection plunger 2, the area Sc of the mold clamping cylinder 7, the discharge pressure Pco of the hydraulic pressure source 14 and the like are preset as constant values. Further, when performing the molding operation, the projected area Sm of the cavity 5 of the mold attached to the mold clamping device, the filling speed V given as a function of the position of the injection plunger at the time of filling, and the allowable upper limit value Piu of the filling pressure, the holding pressure The holding pressure Pip and the correction coefficient α described later are input from the input device 21 and stored.

The CPU 23 receives the data from the input device 21 and outputs the data memory 25.
Molding conditions (filling speed V and holding pressure Pip) stored in
Based on the above, a control signal is sent to the flow rate control valve driver 18 and the pressure control valve driver 16 to control the injection speed and injection pressure during molding.

Generally, at the time of filling, the filling speed V is set as a function of the position of the injection plunger, and the filling operation is controlled by speed control. The pressure in the injection cylinder 1 at this time is generated as a reaction force of the flow path resistance of the molten resin flowing into the cavity 5 through the nozzle 3 and the spool 6,
The upper limit value Piu of the filling pressure is set in the pressure control valve 11 on the injection cylinder side because it is necessary to release the injection pressure when the pressure rises abnormally due to, for example, a gate clogging. Further, the holding pressure Pip given to the molten resin in the holding pressure step after the filling is set through the pressure control valve 11. Although it depends on the fluidity of the resin, the pressure detected by the pressure converter 19 gradually increases from the start of filling, reaches the maximum immediately before the completion of filling, and then reaches the set holding pressure Pip.

The hydraulic pressure Pc applied to the mold clamping cylinder 7 during the filling and holding process is controlled by a value calculated by a calculation program based on each set value stored in the data memory 25 and the detected pressure Pi of the pressure converter 19. To be done.

The control procedure of the hydraulic pressure Pc applied to the mold clamping cylinder 7 will be described with reference to FIG.

Prior to the start of the molding operation, the filling speed V, the upper limit value Piu of the pressure during filling, the holding pressure Pip, the projected area Sm of the cavity and the correction coefficient α described later are input from the input device 21, and these values are stored in the data memory. Stored in 25. Then, the proportional constant CSm is calculated and stored using the input projected area Sm of the cavity 5 of the mold. Here, C is a constant peculiar to the injection molding machine given by C = Si / SpSc where Si is the area of the injection cylinder 1, Sp is the area of the injection plunger 2, and Sc is the area of the mold clamping cylinder 7.

Next, the upper limit value Piu and the holding pressure P
The pressure conversion rate kmax is calculated with kmax = CSmPimax / Pco, with the maximum value of ip as Pimax. Here, Pco is the discharge pressure of the hydraulic pressure source 14 on the mold clamping side.

Next, the calculated kmax is multiplied by the correction coefficient α, and it is confirmed that this does not exceed 1. The correction coefficient α is a coefficient for performing control on the safe side in consideration of the peak pressure that may occur at the end of the filling process, other pressure fluctuations, and detection delay.

If αkmax exceeds 1, it means that the molding condition exceeds the mold clamping capacity of the injection molding machine, and an instruction to change the set value is given. If that is not possible, the molding machine is changed.

If αkmax is 1 or less, it waits until the molding work is started in this state, and when the molding work is started, the pressure Pi of the injection cylinder 1 is read from the detection signal of the pressure converter 19 and the stored proportional constant is stored. The control value Q is calculated by multiplying CSm by Pi. Then, the value of Q is multiplied by the correction coefficient α,
Set the secondary pressure of the pressure control valve 12 to the pressure control valve driver 17 by α
A control signal is output so as to set to Q.

And pressure transducer until the end of one molding cycle
The reading of the detection signal of 19 and the control of the pressure control valve 12 are repeated, and the mold clamping force Pc of the mold clamping cylinder 7 is controlled according to the value of the injection pressure Pi at that time.

When the setting value of the molding condition is changed between one molding cycle and the next molding cycle, the proportional constant CSm is stored and αk
Re-determine max and move to the next molding cycle with similar control.

In the embodiment described above, the pressure of the mold clamping cylinder is controlled by the pressure control valve, but as described above,
It is also possible to control the pressure applied to the mold clamping cylinder 7 by a pressure control valve mounted integrally with the load sensitive pump.

<< Effects of the Invention >> According to the method of the present invention described above, the mold is fastened with a weak force at the time of filling when the resin is rapidly filled in the mold. The air venting of the mold is not necessary, and the air venting process of the mold is not necessary, and the resin burning due to the adiabatic compression of air does not occur. Further, only the minimum required mold clamping force is applied to the mold at all times, so that the life of the mold is prolonged and there is no risk of over-packing the mold clamping force by mistake. Also, because it is electrically controlled,
No piping is required to connect the injection cylinder and the mold clamping cylinder,
Since it can be controlled by software using a microcomputer, it has the feature of being highly flexible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart showing a control procedure. In the figure, 1: Injection cylinder, 4: Mold 5: Mold cavity, 7: Mold clamping cylinder 12: Pressure control valve on mold clamping cylinder side 17: Pressure control valve driver, 19: Pressure converter 24: Program Memory, 25: Data memory

Claims (4)

[Claims] 1. A pressure detection means (19) for detecting an oil pressure Pi of an injection cylinder (1), a pressure controller (12) for controlling an oil pressure Pc supplied to a mold clamping cylinder (7), and a pressure. Calculation means (2) for calculating a pressure command value Q proportional to the detected pressure Pi of the detection means (19) and the projected area Sm of the mold cavity (5).
4) and the pressure controller (1
2) In a mold clamping force control method for an injection molding machine, which comprises a driver (17) for controlling the injection molding machine, the arithmetic means (24) defines the injection cylinder area as Si, the injection plunger area as Sp, and the mold clamping cylinder area as Sp. Using the area Sc as the proportional constant C given by C = Si / SpSc, the mold cavity (5)
When the projected area Sm and the detected pressure Pi of the pressure detection means (19) are input, the pressure command value Q is calculated as Q = CSmPi, and the mold clamping force control method for the injection molding machine is characterized. 2. The mold clamping force control method for an injection molding machine according to claim 1, wherein the pressure command value Q is multiplied by a correction coefficient α larger than 1 to control the pressure controller (12). . 3. The calculation means (24) uses the discharge pressure Pco of the mold clamping side hydraulic power source, the proportional constant C, and the maximum value Pimax of the filling pressure and the holding pressure set during the molding operation to convert the pressure conversion rate kmax. Is calculated as kmax = CSmPimax / Pco, and when the value of kmax becomes 1 or more, an alarm is issued, and the mold clamping force control method for an injection molding machine according to claim 1. 4. The calculation means (24) uses the discharge pressure Pco of the mold clamping side hydraulic power source, the proportional constant C, and the maximum value Pimax of the filling pressure and the holding pressure set during the molding operation to convert the pressure conversion rate kmax. Is calculated as kmax = CSmPimax / Pco, and when the value obtained by multiplying the value of kmax by the correction coefficient α according to claim 2 is 1 or more, an alarm is issued, and the injection molding according to claim 2. Control method for mold clamping force of machine.