JPS61172320A - Magnetic field injection-molding method - Google Patents

Abstract

PURPOSE:To improve the rate of orientation of magnetic grains as well as to contrive improvement in the magnetic characteristics of a plastic magnet by a method wherein the cubic volume of a metal mold cavity is varied by periodically changing clamping force, and the orientation of magnetic grains is performed sufficiently. CONSTITUTION:The pushing force of a clamping cylinder 28, namely mold clamping force, is controlled in accordance with the quantity of current applied to a solenoid 34a. A stationary mold 18 and a movable mold 20 are elastically deformed by said clamping force, and the cubic volume of a metal mold cavity is varied. Accordingly, the cubic volume of the metal mold 22 also changes during the prescribed period in which the clamping force is varied. On the other hand, the prescribed current is applied to a magnetic field generating coil 26 by a power source device from the time when a mold-closing process is completed, and the prescribed magnetic field is generated on the metal mold cavity 22. After the magnetic field is stabilized, a fused material containing magnetic grains is injected into the metal mold cavity 22 from an injection cylinder 24. The magnetic grains in the fused material injected into the metal mold cavity 22 are orientated in the direction of magnetic field.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a magnetic field injection molding method.

(b) Conventional technology Magnetic field injection molding is a method for molding plastic magnets and the like by mixing magnetic particles into a molten material. That is, a molten material mixed with magnetic particles is injected into the mold cavity while a current is passed through a magnetic field generating coil to generate a magnetic field in the mold cavity, the magnetic particles are oriented in the direction of the magnetic field, and the material is cooled and solidified. Thereby, a plastic magnet can be obtained.

(c) Problems that Haimei attempts to solve However, the conventional magnetic field injection molding method has the problem that the magnetic properties of plastic magnets cannot be improved beyond a certain level. That is, when the magnetic particles are the same, the magnetic properties of a plastic magnet generally improve as the mixing ratio of the magnetic particles increases and as the orientation rate of the magnetic particles increases. Therefore, increasing the mixing ratio of magnetic particles should improve the magnetic properties, but in reality, even if the mixing ratio of magnetic particles is increased beyond a certain level, the orientation rate decreases accordingly, so the magnetic properties do not improve. There was no improvement, and there was a limit to the mixing ratio of magnetic particles. That is, magnetic particles attempting to align in a magnetic field mechanically contact each other, and the alignment of the magnetic particles is hindered by mutual interference. This state is conceptually shown in FIG. 4. Each magnetic particle 52 in the molten material 50 has an axis of easy magnetization 54, and when a magnetic field is applied, the axis of easy magnetization 54 is aligned with the direction of the magnetic field 56. It tries to rotate, but as shown in Figure 4, the magnetic particles 5
The two comrades interfere with each other, and the easy magnetization axes 54 of all the magnetic particles do not coincide with the magnetic field direction 56. In other words, there is a limit to the orientation rate. The present invention aims to solve the above problems.

(d) Means for Solving the Problems The present invention solves the above problems by periodically varying the mold clamping force at the initial stage of mold clamping. That is, in the magnetic field injection molding method according to the present invention, a mold clamping force that periodically fluctuates between a predetermined upper limit value and a lower limit value is applied for a predetermined time after the completion of mold closing, and then a constant mold clamping force is applied after a predetermined time elapses. It is characterized by applying a tightening force.

(E) Effect By doing the above, the mold clamping force changes periodically at the first stage of the injection process of the molten material containing magnetic particles into the mold cavity, and the mold cavity changes accordingly. The volume fluctuates periodically. This variation in the volume of the mold cavity acts on the magnetic particles in the molten material, causing the magnetic particles to make minute movements. As a result, each magnetic particle secures a predetermined location and is arranged without colliding with adjacent magnetic particles due to the applied magnetic field. Therefore, the phenomenon in which magnetic particles interfere with each other during orientation is prevented from occurring, and the orientation rate of the magnetic particles is improved. Since the orientation rate is improved, sufficient orientation can be achieved even if the mixing ratio of the magnetic particles is increased, and both the mixing ratio and the orientation ratio of the magnetic particles are increased.
The magnetic properties of plastic magnets can be significantly improved.

(F) Embodiments Hereinafter, embodiments of the present invention will be described based on FIGS. 1 to 3 of the accompanying drawings.

FIG. 2 shows an example of a magnetic field injection molding machine, in which a fixed platen 10 and a mold clamping housing 12 are connected by tie bars 14, and a movable platen 16 is guided by the tie bars 14 and is movable. A fixed die 18 is attached to the fixed platen 10, a movable die 20 is attached to the movable platen 16, and the fixed die 18 is attached to the movable platen 16.
A mold cavity 22 is formed by the movable mold 20 and the movable mold 20 .

Molten material containing magnetic particles can be injected into the mold cavity 22 from an injection cylinder 24 . A magnetic field generating coil 26 is installed on the outer periphery of the fixed mold 18 and the movable mold 20 in the clamped state.
is placed. The movable platen 16 is connected to a piston 30 of a mold clamping cylinder 28 attached to the mold clamping housing 12, and thereby can be driven in the axial direction. Hydraulic pressure from a hydraulic source 32 acts on the mold clamping cylinder 28,
The oil pressure of the oil pressure source 32 is controlled by an electromagnetic relief valve 34. That is, the electromagnetic relief valve 34 is the solenoid 34
The hydraulic pressure supplied to the mold clamping cylinder 28 is adjusted by discharging a portion of the oil discharged from the hydraulic pressure source 32 according to the operating state of the hydraulic pressure source 32. Current is supplied to the solenoid 34a from an amplifier 38 that operates based on a signal from a control device 36. The control device 36 includes a mold clamping force setting device 39, an angular frequency setting device 40, and an amplitude setting device 42. Control device 3
6 operates as described later by a sequence controller 44 and a timer 46 that control the operation of the injection molding machine.

Operations such as mold clamping, molding, and magnetization by the magnetic field injection molding machine are performed as follows. First, hydraulic pressure is supplied to the mold clamping cylinder 28 of the injection molding machine, which is in the mold open state, to cause it to close. That is, the movable platen 16, which had been moving leftward in FIG. 2, is moved rightward, and the movable mold 20 is brought into contact with the fixed mold 18.

When the contact of the movable mold 20 with the fixed mold 18 is detected by a position detector (not shown) such as a limit switch, the sequence controller 44 gives a command to the control device 36, and the control device 36 sets a predetermined current I = IO+
A command signal is given to the amplifier 38 to energize the solenoid 34a with I 1 ·sin ωt. Here, Io, work 1 and ω are the mold clamping force setter 39 and the amplitude setter 42, respectively.
and the angular frequency setter 40, respectively.

The supply of this current continues for a predetermined time set in the timer 46, and after the predetermined time has elapsed, it is controlled to supply a constant current Io. This supply of electric current 0 is continued until the sequence controller 44 commands the end of the magnetization process. The electromagnetic relief valve 34 controls the pressure of the hydraulic power source 32 according to the current applied to the solenoid 34a, and causes the pressure to act on the mold clamping cylinder 28. Therefore, the pushing force of the mold clamping cylinder 28, that is, the mold clamping force, is controlled according to the amount of current applied to the solenoid 34a. If the mold clamping force corresponding to the current Io is Fo, and the mold clamping force corresponding to the electric current 1 is Fl, the mold clamping force F until the predetermined time elapses is F=Fo+F1.
Indicated by in(I)t. Consequently, the mold clamping force changes as shown in FIG. The fixed mold 18 and the movable mold 20 are elastically deformed by this mold clamping force, and the mold cavity 2
The volume of 2 changes.

Therefore, during the predetermined time period in which the mold clamping force oscillates, the volume of the mold cavity 22 also oscillates. On the other hand, a predetermined current is supplied to the magnetic field generating coil 26 by a power supply device (not shown) from the time the mold closing process is completed, and the mold cavity 2
2, a predetermined magnetic field is generated. After the magnetic field is stabilized, molten material containing magnetic particles is injected into the mold cavity 22 from the injection sill 24. The magnetic particles in the molten material injected into the mold cavity 22 are oriented in the direction of the magnetic field. During the predetermined time set by the timer 46, the volume of the mold cavity 22 changes periodically, so the molten material and the magnetic particles contained therein are also in a vibrating state, and the magnetic particles secure their respective optimal positions due to this vibration. Then, after a predetermined period of time has elapsed, the mold clamping force is kept constant, the volume of the mold cavity 22 stops changing, and the magnetic particles are sufficiently oriented by a constant magnetic field. As a result, the orientation rate of the magnetic particles is greatly improved, and even when the mixing ratio of the magnetic particles is high, the orientation can be ensured. The orientation state of the magnetic particles in this case is conceptually shown in FIG. 3, where the axis of easy magnetization 54 of most of the magnetic particles 52 in the molten material 50 coincides with the magnetic field direction 56. Thereby, the magnetic properties of the plastic magnet can be significantly improved. Note that the supply of electricity to the magnetic field generating coil 26 is stopped after the magnetization is completed, and then the molded product is cooled. During this time, the molded product is demagnetized, the mold clamping force is removed, the mold is opened, and the molded product is taken out.

(G) As described in detail, according to the present invention, the volume of the mold cavity is varied by periodically varying the mold clamping force, and the magnetic particles are sufficiently oriented. , the orientation rate of the magnetic particles is improved, and the magnetic properties of the plastic magnet can be greatly improved.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the characteristics of mold clamping force according to the present invention, Fig. 2 is a diagram showing a magnetic field injection molding machine, and Fig. 3 is a diagram showing the orientation state of magnetic particles according to the present invention. , FIG. 4 is a diagram showing the orientation state of magnetic particles by the conventional magnetic field injection molding method. 18...Fixed type, 20...Movable type,...φ mold cavity, 24 fist...Injection cylinder, 26...Magnetic field generating coil, 28...Mold clamping cylinder, 32-φ-hydraulic source ,
34...Electromagnetic relief valve, 36・φΦ control device, 44
... Meeting sequence controller.

Claims (1)

[Claims] In a magnetic field injection molding method in which a molten material containing magnetic particles is injected into a mold cavity in which a magnetic field is generated, a period between a predetermined upper limit value and a predetermined lower limit value is cycled for a predetermined time from completion of mold closing. A magnetic field injection molding method characterized in that a mold clamping force that fluctuates over time is applied, and a constant mold clamping force is applied after a predetermined period of time has elapsed.