JPH053813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection holding pressure switching control device using mold parting surface displacement, which can be applied to injection molding machines, die casting machines, etc.

(Prior Art) FIG. 5 shows an overview of a conventional injection molding machine and its control circuit diagram, and FIG. 6 shows a graph of controlled variables by the same control circuit.

In FIG. 5, 1 is a mold clamping cylinder, 2 is a mold clamping ram inside the cylinder 1, 3 is a tie bar connecting the mold clamping cylinder 1 and the fixed mold platen 5, and 4 is the tie bar 3.
This is a movable mold plate which is supported so as to be movable back and forth and connected to the mold clamping ram 2. 6 is a movable side mold attached to the movable die platen 4, 107 is a fixed side die attached to the fixed die platen 5, and 20 is a molded product cavity.

The raw resin is supplied to the right side of the screw 14 in the cylinder 13 from a hopper (not shown), and is melted and plasticized by heating by a heater (not shown) and rotation of the screw 14 driven by a hydraulic motor 18. It is sent forward and stored as molten resin 12.

On the other hand, by sending pressure oil from the hydraulic inflow source 34 through the servo valve 38 to the illustrated side of the injection cylinder, the screw 14 is advanced to the left in the figure via the injection ram 16 and the bearing box 17, and the screw 14
The molten resin 12 at the tip is injected into the molded product cavity 20. In addition, 130 in the figure is a controller, 1
9 is a position sensor, 31 and 32 are oil pressure sensors, 33
35 and 37 are relief valves, and 36 is a switching valve.

Next, in FIG. 6, Po is the injection cylinder 15
This is the detection value of the oil pressure sensor 32 at the injection oil pressure.
V _F is the forward speed of the screw 14 and is generally called the injection speed. t is time and ,,, indicates the injection period. Injection speed as usual
Prevent molding defects and improve quality by changing _VF . In the other section, a constant injection hydraulic pressure is applied to compensate for cooling shrinkage of the molten resin in the molded product cavity 20 during injection holding. In addition,,
, may be set based on the screw position detected by the screw position sensor 19 instead of time.

Target control is performed as shown in the solid line graph in FIG.
The dotted line graph shows the dependent variable value portion of each solid line. Pmax is the set value of the relief valve 37.
In each interval of ~, V _F (constant value part) as shown in the figure
The amount of injected oil is controlled by the servo valve shown in Figure 5 so that Po (constant value) as shown in the figure is maintained in the other sections.

However, in this conventional example, an overshoot of the injection oil pressure as shown by arrow B in Fig. 6 occurs, and even if the injection holding oil pressure Po in the section is constant, the oil temperature, machine temperature, mold temperature, resin temperature, etc. are not constant. ,
The critical resin pressure inside the mold cavity fluctuates. Also, due to condition fluctuations or condition setting errors,
The resin pressure within the cavity overcomes the mold clamping force and pushes the parting surface of the mold open, causing molten resin to spill into the opened gap and causing burrs. In injection molding, once burrs appear, they tend to become habitual and can damage the mold. As mentioned above, in the conventional example,
Since variables directly related to burrs were not detected and controlled, burrs could not be reliably prevented.

(Problems to be Solved by the Invention) As mentioned above, conventional injection control devices often have the problem of burrs forming on the mold parting surface and damaging the mold.The present invention solves this problem. Measures have been taken to solve this problem and reliably prevent the occurrence of burrs.

(Means for Solving the Problem) Therefore, the present invention sets the switching point from injection filling to injection holding pressure by a certain value of mold clamping pressure or mold clamping force, and increases mold clamping pressure in every cycle of injection molding. Automatically detects and stores the mold parting surface displacement δ C when the mold clamping oil pressure or mold clamping force reaches the above set value, and then automatically detects and stores the mold parting surface displacement δ _C when the mold parting surface displacement reaches δ _C during injection filling. This system is designed to switch to injection holding pressure at times, and this is a means to solve problems.

(Function) In the above configuration, the setting for switching to injection holding is performed by the mold clamping oil pressure or mold clamping force, and the parting surface displacement corresponding to the set value is automatically detected and stored when the mold clamping pressure is increased, and the injection holding is performed. When the parting surface displacement reaches the above memorized value during filling, the injection holding mode is switched.

(Embodiments) Below, embodiments of the present invention will be explained with reference to the drawings. FIGS. 1 to 3 show embodiments of the present invention,
Fig. 1 shows an overview of the injection molding machine and its control circuit, Fig. 2 shows an enlarged cross-sectional view of the part in which the parting surface displacement detection device, which is the main part of the present invention, is installed.
The figures show the main circuits of the controller of the present invention.

In FIG. 1, a mold 7, a parting surface displacement detection device 8, which will be described later, and a lead wire 21, which will also be described later.
Since the components other than a and the controller 30 are the same as the conventional device shown in FIG. 5, the explanation of these same components will be omitted.

Next, A in FIG. 1, which is the main part of the present invention.
To explain in detail the part indicated by A, the details of the part indicated by A are shown in Fig. 2. 6P is the parting surface of the movable mold, 7P is the parting surface of the fixed mold, and 21 is the displacement sensor. It is fitted into the sleeve 22. The outer periphery of the mounting sleeve 22 is divided into a large diameter part and a small diameter part via a shoulder part 22a, and one end of the small diameter part is fixed to the stationary mold 7, and the other end of the mounting sleeve 22 is fixed to the large diameter part.
A rubber pad 23 is attached to prevent the mold from coming off, and the dimensions are such that the rubber pad 23 is slightly compressed when the mold is closed as shown in the figure.

24 is a set screw for preventing the displacement sensor 21 from coming off from the mounting sleeve 22. 21a is a lead wire of the displacement sensor 21, which is guided to the outside of the mold and connected to the controller 30 shown in FIG.

The mounting sleeve 22 is press-fitted into the stationary mold 7, for example, and the shoulder portion 22 of the mounting sleeve 22
a is in tight contact with the mold 7. but,
If the tightness of the shoulder 22a loosens during use, it will cause an error in gap measurement, so to prevent this, when the mold is closed, the mounting sleeve 22 is always attached to the shoulder 22a side by a rubber pad 23. It's starting to feel like pressure.

In Fig. 3, 31 is the same oil pressure sensor as shown in Fig. 1, 21 is the same displacement sensor as shown in Fig. 2, and 40 is a setting device for mold clamping oil pressure P _C to switch from injection filling to injection holding pressure. be.

41 and 42 are amplifiers, 43 and 44 are comparators, 4
7 is a signal line, and in the same figure, a signal is output (ON) from the comparator 43 when the mold clamping oil pressure P≧ _PC . A memory 45 stores the parting surface displacement input δ from the signal line 46 when the signal from the comparator 43 is switched from OFF to ON, and outputs the value δ _C at that time to the signal line 48. The direct line of this δ _C is the signal from signal line 47.
It remains unchanged while ON, and is cleared to 0 when the signal switches from ON to OFF. 49 is a signal that is turned ON only during the injection process, and the comparator 44 operates only when the signal 49 is ON. 50 is a switching signal from injection filling to injection holding pressure, which is output (ON) from the comparator 44 when the signal 49 is ON and δ≧ _δC .

Next, to explain the operation of the above embodiment, in FIG. 1, the switching valve 36 directs the pressure oil from the hydraulic inflow source 33 to the mold closing side (left side in the figure) or the mold opening side (the right side in the figure) of the mold clamping cylinder 1. ) and supply it. That is, when the solenoid a is energized, the pressure oil from the hydraulic inflow source 33 flows to the left side of the mold clamping cylinder 1, and the mold clamping ram 2, and therefore the movable mold platen 4 and the movable side mold 6 connected to it, are Move it to the right to close the mold. Conversely, when solenoid b is energized, the pressure oil from the hydraulic inflow source 33 flows to the right side of the mold clamping cylinder 1, causing the mold clamping ram 2, the movable mold platen 4,
Move the movable mold 6 to the left and perform a mold opening operation. In addition, in the neutral position where neither solenoids a nor b are energized, both the mold closing side and mold opening side oil are released to the tank.

When the mold closing operation is performed by energizing the solenoid a as described above, after the mold is closed, the mold clamping pressure rises to the set pressure of the relief valve 35 and is maintained.
Further, the injection operation is performed after the mold clamping pressure has increased sufficiently.

Next, explaining the injection operation, pressure oil is injected into the injection cylinder 15 from the hydraulic inflow source 34 through the servo valve 38.
By feeding the screw 14 to the side shown in the figure, the screw 14 is advanced to the left side in the figure via the injection ram 16 and the bearing box 17, and the molten resin 12 at the tip of the screw 14 is injected into the molded product cavity 20. Note that the relief valve 37 is a safety valve that provides relief when the oil pressure increases too much.

Further, the parting surface displacement detecting device 8 detects the gap δ in FIG. That is, in FIG. 2, the displacement sensor 21 generates an output (voltage or current) proportional to the gap δ through the lead wire 21a. Now, in FIG. 1, the displacement detected by the parting surface displacement detection device 8 (gap δ in FIG. 2) is sent to the controller 30, and the controller 30 performs injection control as shown in FIG. 4 using the circuit shown in FIG. Do this.

Now, to explain Fig. 4, the graphs of mold clamping pressure and parting surface displacement have a common time axis,
In both graphs, points with subscripts 1 and 2 attached to the same alphanumeric symbol represent the same point in time. In the same figure, δ _D is the parting surface displacement immediately after each of the molds 6 and 7 is closed, and when no clamping force is applied. In addition, in the mold clamping pressure increase section a, the parting surface displacement represented by the gap δ in Fig. 2 decreases due to compressive deformation of the mold due to the increase in parting surface bearing pressure, and the minimum value δ _E
reach. In addition, the curve at _two points in G is
This is because at point _G2 (corresponding to point _G1 on the graph of mold clamping pressure) at which the mold clamping pressure has increased sufficiently, the amount of oil in the hydraulic inflow source 33 is reduced to the amount of oil sufficient to maintain the mold clamping.

Subsequently, in the injection filling section f, the resin pressure in the molded product cavity 20 acts in the direction of opening the mold, so the compressive deformation decreases, and therefore the parting surface displacement begins to increase, and the process switches to the injection holding pressure section h. The maximum displacement δ _C is reached at point C. In section h, the resin pressure decreases as the resin in the cavity 20 cools, so the compressive deformation increases again, and the parting surface displacement (gap δ) decreases again.

If the maximum displacement δ _C is smaller than the initial displacement δ _D ,
Since the parting surface is not open, burrs do not occur. On the other hand, if δ _C is larger than δ _D , the parting surface will open, and there is a risk that the molten resin in the cavity 20 will flow out onto the parting surface and become burrs. Therefore, the parting surface displacement δ _C at the switching point C from the injection filling section to the injection holding section must be set so that δ _C < δ _D.

By the circuit shown in Fig. 3, the mold clamping pressure P _C for injection holding pressure switching shown in Fig. 4 is set, and when the mold clamping pressure P reaches P _C in the mold clamping pressure increase section a (points C ₁ and
C ₂ corresponds), the parting surface displacement at that time is stored as δ _C , and when the parting surface displacement δ reaches δ _C in the injection filling section f (corresponding to point C), it switches to the injection holding pressure section h. That is, instead of setting δ _C , P _C is set and δ _C is automatically calculated from P _C. Also, the maximum mold clamping pressure
P _E is also set with a setting device (not shown) and its value is known, so P _C can be set so that it always satisfies O < P _C < P _E , so the relationship δ _E < δ _C < δ _D is also established. You will be satisfied. In this way, since the relationship δ _C < δ _D is maintained, the parting surface does not open and burrs do not occur. On the other hand, if δ _C is too close to δ _E , there is a risk of switching from injection filling to injection holding pressure before the molded _product cavity is fully filled. Displacement δ _E
Since it corresponds to ~δ _D , mold clamping oil pressure for injection holding pressure switching
P _C can be easily set to be sufficiently smaller than the maximum mold clamping pressure _PE (for example, half of P _E ), and δ _C and δ _E can be prevented from becoming close to each other.

In addition, in the detection of the parting surface displacement δ, errors occur due to the influence of temperature and other environments, but in this device, the parting surface displacement corresponding to the set mold clamping pressure P _C for injection holding pressure switching is detected in each cycle of injection molding. Since the surface displacement δ _C is detected and used, the error affects only within one cycle, and the injection holding pressure switching control based on the parting surface displacement has good accuracy. Incidentally, since the mold clamping oil pressure and the mold clamping force are in a proportional relationship, it is possible to easily change the above example to use the mold clamping force in place of the mold clamping oil pressure by incorporating a conversion circuit therefor.

(Effects of the Invention) As described above in detail, according to the present invention, O
~ Set the mold clamping hydraulic pressure (or mold clamping force) for switching from injection filling to injection holding pressure within the range of the maximum mold clamping hydraulic pressure (or maximum mold clamping force), and change the mold parting surface displacement at that setting value. Since the injection holding pressure is switched, the mold parting surface does not open when switching to the injection holding pressure, and burrs can be reliably prevented.
In addition, by automatically detecting the displacement of the mold parting surface corresponding to the mold clamping oil pressure (or mold clamping force) set above for each cycle of injection molding, the influence of errors in the detection of displacement of the mold parting surface can be fully suppressed. The accuracy of injection and holding pressure switching control can be ensured.

As described above, the setting items for switching from injection filling to injection holding pressure in the present invention are mold clamping oil pressure or mold clamping force, but these item values can be set without a molding trial. According to the present invention, setting is facilitated by setting the value of an item different from the detected variable of the mold parting surface. On the other hand, in the present invention, since the mold parting surface does not open when the mold parting surface is displaced in a state where the mold parting surface is sealed, it is possible to reliably prevent the occurrence of burrs. Furthermore, since the present invention automatically corrects the actual switching point from injection filling to injection holding pressure in each molding cycle, the mold parting surface corresponding to the set value of the mold clamping oil pressure or mold clamping force is adjusted for each cycle. Automatically detect and rememorize displacement. By performing automatic correction in this manner, errors caused by environmental influences such as temperature can be removed, and the accuracy of injection and holding pressure switching control can be maintained at its best.

[Brief explanation of the drawing]

Fig. 1 is a side view of an injection molding machine showing an embodiment of the present invention and a schematic diagram of its control circuit, Fig. 2 is an enlarged view of part A in Fig. 1, and Fig. 3 is the main circuit of the controller of the present invention. Figure 4 is a diagram showing the relationship between mold clamping pressure increase and elapsed time during injection, mold clamping oil pressure, and parting surface displacement. Figure 5 is a side view of a conventional injection molding machine and a schematic diagram of its control circuit. , FIG. 6 is a diagram showing changes in injection control variables in the prior art. Explanation of main parts of the figure, 6, 7... Mold, 8... Parting surface displacement detection device, 21... Displacement sensor, 3
0... Controller, 31... Oil pressure sensor, 40... Setting device, 43, 44... Comparator, 45... Memory device.

Claims (1)

[Claims] 1 The switching point from injection filling to injection holding pressure is set by a certain value of mold clamping oil pressure or mold clamping force, and in every cycle of injection molding, when the mold clamping pressure increases, the mold clamping oil pressure or mold clamping force reaches the above set value. An injection method characterized by automatically detecting and storing the mold parting surface displacement δ _C at the time of injection filling, and then switching to injection holding pressure when the mold parting surface displacement reaches δ _C during injection filling. Control device.