JP3782980B2 - Electric injection molding machine injection control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injection control method for an electric injection molding machine in which a molten material in a cylinder is driven by driving an electric motor to advance a screw and injected into a cavity of a mold to form a molded product.
[0002]
[Prior art]
Injection molding in an electric injection molding machine is generally connected to a screw with an electric motor, a mold closing process for closing a mold, a mold clamping process for clamping the mold, a nozzle touch process for pressing the nozzle against the sprue of the mold, and the electric motor. The ball screw is rotated to advance the screw in the cylinder and inject the molten material accumulated in front of the screw into the mold cavity, and then hold pressure to suppress the generation of bubbles and sink marks For the next cycle between the pressure holding process for a while and the molten material filled in the mold cavity is cooled and solidified, the screw is rotated to melt the resin in front of the cylinder. In order to remove the solidified molded product from the mold, the mold is opened and the molded product is pushed out by a protruding pin provided on the mold. Consisting of an open-molded article ejection process.
[0003]
FIG. 5 is a graph showing the relationship between the injection speed V and the injection pressure P with respect to the injection hold time t from the injection process to the pressure holding process.
[0004]
In general, in injection control in injection molding, the screw is advanced at a set speed, and as the filling amount of the molten material into the mold cavity increases with the injection time, the injection pressure P rises, and the mold cavity A method is adopted in which the pressure control is switched from the speed control to the pressure control at the holding pressure switching position just before the molten material filled therein becomes a full pack, and then the holding pressure is applied for a while. Further, the operator generally sets the injection speed and the injection limit pressure so that the injection pressure P does not exceed the injection limit pressure Pa during the speed-controlled injection process.
[0005]
However, abnormal conditions during injection, such as when injection is performed under wrong molding conditions that maintain high speed without reaching the holding pressure switching position even when the mold cavity is fully packed, When clogging of the molten material occurs in the narrowed flow path portion such as a mold gate, the pressure suddenly rises and the injection pressure P reaches the injection limit pressure Pa as shown in FIG. possible.
[0006]
In such a case, in the conventional control method, when the injection pressure P reaches the injection limit pressure Pa, the injection speed V is braked to limit the rise of the injection pressure P, and the injection limit pressure Pa is maintained. Pressure control is commonly applied.
[0007]
[Problems to be solved by the invention]
However, in the electric injection molding machine, when the pressure P during injection approaches the injection limit pressure Pa, the above-described abnormal state occurs, and the injection pressure P rapidly increases to reach the injection limit pressure Pa. If a situation occurs, the electric motor's rotor and screw are rotated around its axis even if the electric motor is suddenly braked and the injection speed V is suddenly decelerated by the above-described control to stop the pressure increase. Because of the inertia of the drive system such as the bearing part that supports the bearing, the ball screw mechanism part that is assembled to the bearing part, and the timing belt, pulley, and screw that transmit the power of the electric motor to the ball screw mechanism part, the screw is slightly Cannot move forward, that is, inertial flow cannot be avoided. The amount of inertia flow of the screw is generally injection speed × deceleration time / 2. At this time, for example, when nozzle clogging occurs, the molten material from the screw tip to the nozzle tip is compressed, causing a pressure increase and injection. The pressure P exceeds the injection limit pressure Pa, and further exceeds the limit pressure P _L that does not damage the injection device and the mold, and reaches the abnormal pressure Pb. Further, the pressure increase at the time of deceleration from a certain speed to the speed 0 is generally expressed by the pressure increase at the maximum injection speed × (injection speed / maximum injection speed) ² . That is, when the injection speed is low, the pressure increase due to the inertia flow is small, so this is not a problem. However, when the speed approaches the maximum injection speed, the pressure increase becomes extremely large pressure. There was a risk of damaging the mold. It should be noted that the injection limit pressure Pa, a limit pressure on the molding quality of such limitations do not damage the mold pressure or size of the molded article, is the pressure to repeatedly acting out of the allowable dimension, a threshold pressure P _L Is a single limit pressure that does not damage the injection device or mold in the event of an abnormality.
[0008]
Accordingly, the present invention provides a safe injection control method for an electric injection molding machine in which an injection pressure does not exceed a limit pressure due to an erroneous molding condition or an abnormal pressure increase caused by clogging of a molten material. With the goal.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the injection control method of the electric injection molding machine according to the present invention controls the rotation speed of the injection servo motor that moves the screw via the ball screw based on the forward speed of the screw in the cylinder and the injection pressure. In the injection control method of the electric injection molding machine that controls the injection of the molten material into the cavity of the mold, the deceleration until the screw speed becomes zero after the braking signal is transmitted from the controller to the injection servo motor. The pressure increase ΔP during inertia flow, which is the pressure that rises at times, is obtained in advance, and the value and the limit pressure P _L are stored in the storage unit of the controller, and are constantly measured by the load cell during injection at the comparison unit of the controller. and the sum of the injection pressure and the inertial flow at boosting [Delta] P of the molten material in the cylinder which is being is, compared with the threshold pressure P _L, the case of P + ΔP ≧ P _L, Sunawa , (And Pm the injection pressure at this time) when it reaches the P ≧ P _L -ΔP, and characterized in that sending the sudden braking signal to the injection servomotor comprising the step of decelerating the forward speed of the screw until 0 To do.
[0010]
As described above, the injection control method of the electric injection molding machine according to the present invention is such that when an abnormal state that makes injection impossible occurs during injection, the injection pressure of the inertia flow when sudden braking is performed from the injection speed at that time. An increase, that is, a pressure increase ΔP during inertia flow is obtained in advance, and the sum of the pressure increase ΔP during inertia flow and the injection pressure P of the molten material in the cylinder, which is constantly measured by the load cell, is compared with the limit pressure P _L. While injecting. In other words, the injection control method of the electric injection molding machine according to the present invention is a pressure increase during the inertia flow of the screw that occurs when the injection servo motor is braked even when an abnormal state occurs during injection. Since the speed of the injection servo motor is controlled in anticipation of the pressure increase ΔP during inertia flow, even if an abnormal condition that prevents injection occurs, the pressure exceeding the limit pressure P _L is applied to the injection molding machine or mold. There is no such thing.
[0011]
Further, in the injection control method of the electric injection molding machine of the present invention, when the maximum injection speed is Vmax and the pressure increase at the maximum injection speed is ΔPmax, the pressure increase ΔP at an arbitrary injection speed Vd is A step of obtaining as ΔP = ΔPmax × (Vd / Vmax) ² may be included.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0014]
In FIG. 1, the schematic block diagram of the injection device of the electric injection molding machine which is one Embodiment of this invention is shown.
[0015]
An injection device of an electric injection molding machine is inserted into a cylinder 1, a screw 3 that is inserted into the cylinder 1 so as to be able to rotate and move forward and backward, and has a screw head 2 at the tip, and one end of a screw 3 opposite to the screw head 2. A load cell 7 that measures the distortion due to the reaction force of the screw 3 at the time of injection as an injection pressure, a ball screw 6 that moves the screw 3 in the axial direction, an injection servomotor 8 that rotates the ball screw 6 via a timing belt 12, And a controller 10 that controls the injection servomotor 8 based on a signal from the load cell 7 and a signal from an encoder 9 provided in the injection servomotor 8. Further, the injection device of the electric injection molding machine rotates the screw 3 while melting the resin supplied into the cylinder 1 and rotates the screw 3 toward the front (left direction in FIG. 1) to plasticize the tachometer 5. The rotary servo motor 4 is provided.
[0016]
The controller 10 includes a setting unit 10a for setting a speed setting value of the moving speed in the axial direction of the screw 3 serving as an injection speed, a pressure limit value of the injection pressure, a holding pressure, and the like. A storage unit 10b for storing pressure P _{L and the} like (pressure increase ΔP during inertia flow and limit pressure P _L will be described later), a comparison unit that compares a speed set value with a detected speed or an injection pressure limit value and a detected pressure value 10c and the like. The injection pressure detected by the load cell 7 is amplified by an amplifier (not shown) and input to the controller 10. The rotation speed of the injection servo motor 8 is detected by the encoder 9 and input to the controller 10 as the detection speed of the screw 3 and is controlled based on this input value.
[0017]
The storage unit 10b of the controller 10 has an abnormal state during injection, for example, an incorrect molding condition that maintains a high speed without reaching the holding pressure switching position even if the mold cavity (not shown) is fully packed. Inertia at the time of sudden braking from the speed at the time of injection or when a state in which the melted material is clogged in the narrowed flow path portion such as the nozzle 1a and the mold gate during filling The pressure increase ΔP during the inertial flow of the injection pressure due to the flow is stored. The storage unit 10b also stores a limit pressure P _L (see FIG. 2) or α when the limit pressure P _L = injection limit pressure Pa + α as a limit value that does not damage the injection device or the mold. .
[0018]
In this embodiment, the injection pressure is detected by the load cell 7 and the speed of the screw 3 is detected by the encoder 9. However, the present invention is not limited to this. It may be attached and detected, or the speed of the screw 3 may be directly measured.
[0019]
Next, an injection control method when an abnormal state occurs during injection in the electric injection molding machine of the present embodiment configured as described above will be described.
[0020]
First, a signal is transmitted from the controller 10 to the injection servo motor 8 so that the screw 3 moves forward at a set speed, and the molten material is injected into the mold cavity. At this time, injection is performed while constantly measuring the injection speed and injection pressure P (step S1).
[0021]
At this time, the comparison unit 10c compares and calculates whether or not the sum of the injection pressure P and the inertia flow pressure increase ΔP is larger than the limit pressure P _L (step S2). When P + ΔP ≧ P _L (the injection pressure at this time is shown as Pm in FIG. 2), a sudden braking signal is transmitted from the controller 10 to the injection servo motor 8 to suddenly brake the injection servo motor 8, and the injection pressure P is prevented from increasing beyond the limit pressure P _L (step S3). Thereafter, pressure control is executed at the injection limiting pressure Pa (step S4). Further, after that, it is determined whether or not the screw position has advanced to the holding pressure switching position (step S5). If the screw 3 has not advanced to the holding pressure switching position, the injection restriction pressure Pa is maintained (in FIG. 2). , Solid line) The machine is stopped (step S6). If the screw 3 moves forward to the holding pressure switching position, the process proceeds to the holding pressure process (broken line in FIG. 2) (step S7). The relationship of the injection pressure P with respect to the injection hold time t in each of the above steps is as shown in FIG.
[0022]
On the other hand, if P + ΔP <P _L in step S2, it is further determined whether P <Pa (step S8), and P <Pa is satisfied, that is, in a normal state, a predetermined speed control in the injection process is performed. If it is executed (step S9) and the screw position advances to the holding pressure switching position, the pressure holding process is started (step S7). In this case, the relationship of the injection pressure P with respect to the injection hold time t is as shown in FIG.
[0023]
In step S8, if P ≧ Pa is satisfied, that is, if P + ΔP <P _L and P ≧ Pa, the process proceeds to step S4, and pressure control is performed at the injection restriction pressure Pa. Then, if the injection limit pressure Pa can be filled, the screw 3 is advanced to determine whether the screw position has advanced to the holding pressure switching position (step S5), and if the screw 3 has not advanced to the holding pressure switching position, The machine is stopped while maintaining the injection limiting pressure Pa (solid line in FIG. 2) (step S6). In this case, the relationship between the injection pressure P and the injection pressure P is as shown in FIG.
[0024]
When the injection servo motor 8 is decelerated at a constant deceleration in step S3, the pressure increase ΔP at an arbitrary speed Vd during deceleration is obtained by ΔP = ΔPmax × (Vd / Vmax) ² . Here, Vmax is the maximum injection speed, and ΔPmax is a pressure increase during inertial flow at the maximum injection speed.
[0025]
【The invention's effect】
As described above, according to the present invention, during the injection, the injection pressure P is always measured, and the injection is performed while determining whether or not P + ΔP ≧ P _L. The sudden braking control of the injection servomotor 8 is performed at the time when the possibility of exceeding the limit pressure P _L occurs. For this reason, even if an abnormal state occurs during injection, pressure exceeding the limit pressure P _L is not applied to the injection molding machine or mold, and damage to the injection molding machine or mold can be prevented. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an electric injection molding machine according to an embodiment of the present invention.
FIG. 2 is a graph showing an example of an injection pressure waveform according to the injection control method of the present invention when an abnormal state occurs during injection.
FIG. 3 is a flowchart for explaining an example of an injection control method of the present invention.
FIG. 4 is a graph showing an example of an injection pressure waveform according to the injection control method of the present invention when P + ΔP ≦ P _L and P ≧ Pa are satisfied during injection.
FIG. 5 is a graph showing an example of a waveform of an injection pressure by a conventional injection control method.
FIG. 6 is a graph showing an example of a waveform of injection pressure according to an injection control method when an abnormal state occurs during injection in the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylinder 1a Nozzle 2 Screw head 3 Screw 3 Timing belt 4 Rotation servo motor 5 Tachometer 6 Ball screw 7 Load cell 8 Injection servo motor 9 Encoder 10 Controller 10a Setting part 10b Storage part 10c Comparison part 11 Bearing part 12 Timing belt

Claims (2)

Electric injection molding that controls the injection of molten material into the mold cavity by controlling the rotation speed of the injection servo motor that moves the screw through the ball screw based on the forward speed of the screw in the cylinder and the injection pressure In the injection control method of the machine,
Inertia flow boost ΔP, which is the pressure that rises during deceleration from when the braking signal is transmitted from the controller (10) to the injection servo motor (8) until the speed of the screw (3) becomes zero, and during injection molding The limit pressure P _L is stored, and the sum of the injection pressure P of the molten material in the cylinder (1), which is constantly measured at the time of injection, and the pressure increase ΔP during the inertia flow, and the limit pressure P _L are determined. In comparison, when P + ΔP ≧ P _L is satisfied, it includes a step of transmitting a sudden braking signal to the injection servo motor (8) to reduce the forward speed of the screw (3) to zero. Injection control method of injection molding machine. When the maximum injection speed is Vmax and the pressure increase at the maximum injection speed is ΔPmax, the pressure increase ΔP during inertia flow when the screw (3) is decelerated from an arbitrary speed Vd is expressed as follows: ΔP = ΔPmax × (Vd / Vmax) comprising the step of obtaining a ² injection control method for an electric injection molding machine according to claim 1.

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