JP2609557B2 - Method for ejecting an injection product when opening a mold in an injection molding apparatus - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a casting using an injection molding device such as a die casting machine, and more particularly, to removing a product in the operation of the injection molding device. For ejecting an injection product at the time of opening the mold to retract the movable mold.

2. Description of the Related Art In general, in the production of a cast product by injection molding, first, a predetermined amount of molten metal is poured into an injection sleeve 21 using an injection molding apparatus as shown in FIG. A mold composed of a fixed mold 12 and a movable mold 13
After press-fitting into the cavity 15 molded during the 11 and cooling and solidifying the molten metal filled in the cavity 15 to form a product 27, the movable mold 13 is retracted together with the movable plate 17 to open the mold, After that, the product 27 formed from the movable mold 13 is taken out, the mold 11 is cleaned, a release agent is applied, and the mold is tightened so that the movable mold 13 and the fixed mold 12 are brought together. Then, the molten metal is again press-fitted into the cavity 15, and the injection molding is repeated.

By the way, in order to enhance the mass productivity in the injection molding, various attempts have been made to shorten the cycle time from press-fitting of the molten metal to mold clamping which is the next press-fitting preparation.

In order to shorten the cycle time, in order to shorten the chill time, which is a process of cooling and solidifying the molten metal, the shapes of the fixed mold 12, the movable mold 13, and the cavity 15 are devised.
Further, the efficiency of opening the mold, taking out the product, cleaning the mold 11, applying the release agent, and the like is achieved.

[Problems to be Solved by the Invention] As described above, in order to shorten the cycle time, it is attempted to shorten the chill time, which is the cooling period of the molten metal, and to shorten the time in each step such as mold opening, cleaning, and mold clamping. However, in shortening the chill time, if the chill time is too short, the cooling and solidification of the molten metal will be insufficient, and the movable mold
There is a disadvantage that the product is deformed in the step of taking out the product from the product 13 and further in the cooling and processing steps after taking out the product. In opening the mold, the plunger tip 22 moves forward with the retreat of the movable mold 13 as shown in FIG. Then, the biscuit 29 in which the remaining molten metal in the injection sleeve 21 is solidified is pushed out from the injection sleeve 21, but at this time, the biscuit 29 is broken, and the molten metal inside is scattered.
And has a drawback that the subsequent casting becomes difficult.

In many cases, it takes a long time to cool the remaining hot water which is filled into the cavity 15 in the mold 11 and forms the biscuit 29 which is a thicker or larger lump than the molten metal forming the product 27. In order to prevent the biscuit 29 from being broken when the mold is opened, it is necessary to increase the chill time until the molten metal in the biscuit 29 is completely solidified, resulting in a longer cycle time.

The present invention is a method of removing such disadvantages and opening the mold without breaking the unsolidified biscuit 29 at the time of opening the mold.When the outer peripheral portion of the biscuit 29 is solidified, the mold is opened, and the chill time is reduced. As a result, a mold opening method that can shorten the casting cycle time and improve mass productivity is as follows.

[Means for Solving the Problem] In injection molding, after a required time for injecting a molten metal into a cavity and cooling a casting in a mold has elapsed, when the mold is opened to take out the casting, injection is performed. The injection pressure in the cylinder is detected, the detected pressure is compared with a set low pressure set pressure, and when the detected pressure reaches the upper limit set value of the set pressure, the opening of the injection speed control valve is reduced to reduce the set pressure. When the lower limit value is reached, the opening of the injection speed control valve is increased, and the displacement of the injection cylinder that projects the biscuit in the fixed mold, that is, the forward speed of the plunger tip and the retreat speed of the movable mold, are equal. While maintaining the speed, the pressing force on the biscuit by the plunger tip is maintained at a value lower than the upper limit set value and lower than the lower limit set value.

[Operation] In the present invention, when a biscuit is extruded from a fixed mold, the hydraulic pressure to an injection cylinder for advancing a plunger tip for pushing the biscuit is detected, and when the hydraulic pressure reaches an upper limit set value of a set pressure, the injection speed is increased. Decrease the opening of the control valve to slow down the forward speed, thereby lowering the pressing force of the plunger tip on the biscuit that can be retracted according to the retracting of the movable mold, and injecting when the set lower limit is reached When the opening of the speed control valve is increased, the forward speed of the plunger tip is advanced in accordance with the retracting speed of the movable mold.When the biscuit is pressed to retract the biscuit in accordance with the retracting of the movable mold, When the hydraulic pressure to the injection cylinder reaches the upper limit set value, the opening of the injection speed control valve is reduced so as not to exceed the set upper limit. The biscuit sandwiched between the plunger tip and the movable mold can be pushed out of the fixed mold without being crushed by the plunger tip.

Therefore, even if the melt inside the biscuit is not solidified,
If the outer periphery of the biscuit is solidified by cooling, of course, if the product in the cabinet is solidified by cooling, the mold can be opened and the chill time can be reduced.

[Embodiment] As an apparatus for carrying out the method of the present invention, for example, a die casting machine as shown in FIG. 1 is used.

In FIG. 1, 11 is a mold comprising a fixed mold 12 and a movable mold 13, 15 is a cavity of the mold 11, 16 is a fixed plate, 17 is a movable plate, 18 is a link housing, 19 is a toggle mechanism, Reference numeral 20 denotes a mold clamping cylinder, 14 denotes a machine base, 9 denotes a column, 10 denotes a column nut, 21 denotes an injection sleeve, 22 denotes a plunger tip, 24 denotes an injection plunger, and 25 denotes an injection cylinder.

In the injection molding apparatus, the retreat of the movable platen 17, that is, the movable mold 13, is often performed by using the mold clamping cylinder 20 and the toggle mechanism.
When the mold 11 is opened and closed by the toggle mechanism 19, the retreat speed of the movable platen 17 is increased with respect to the retreat amount of the mold opening cylinder as shown in FIG. Because it changes from time to time, the movable plate 17, that is, the retreat of the movable mold 13,
The retreat speed changes in a complicated manner depending on the retreat position, and the injection cylinder is synchronized with the retraction of the movable mold 13.
25, that is, it is extremely difficult to advance the plunger tip 22.

Further, the forward speed of the injection plunger 24 at the time of opening the mold is extremely low compared to the high speed forward speed of the injection plunger 24 when filling the cavity 15 with the molten metal,
It was difficult to synchronize the forward speed of the injection plunger 24 and the plunger tip 22 with the backward speed of the movable mold 13.

However, when the injection speed control valve 50 as shown in FIG. 4 developed by the present applicant is used, a single injection speed control valve 50 is used without using a separate flow control valve for an extremely low speed.
Has made speed control possible.

The injection speed control valve 50 has a structure as shown in FIG. 4. In the injection speed control valve 50 shown in FIG. 4, reference numeral 52 denotes a hydraulic oil inlet 53 from the axial direction and a right angle to the axis at the inner peripheral surface. A valve body 55 having an annular groove 54a for hydraulic oil outflow and a hydraulic oil outlet 54, which moves in the axial direction in the valve body 52, and a spool having an axial through hole 55a inside near the outer peripheral surface. Reference numeral 56 denotes a shaft integrally provided on the rear portion of the spool 55, reference numeral 56a denotes a nut shaft integrally provided on the rear end side of the shaft 57, and reference numeral 57 denotes a nut screwed onto the internal shaft portion of the nut shaft 56a by a ball screw 58. Screw shaft, 59 is screw shaft
A joint 60 connects the shaft of the pulse motor 51 to the shaft 57, and a key 60 for preventing the nut shaft 56a from rotating and guiding movement in the axial direction.

The spool 55 moves back and forth in the axial direction in response to the rotation of the pulse motor 51, instantaneously adjusts the opening and closing of the valve and adjusts the opening, and thereby controls the flow rate. As described above, the injection speed control valve 50 is provided with a hydraulic oil inlet 53 at an axial end face and a spool 55 in a cylindrical valve body 52 having a side hydraulic oil outlet 54a which is an annular groove. Is controlled in the axial direction by the action of the pulse motor 51 to control the flow rate.The axial thrust of the spool 55 due to the hydraulic oil is rapidly changed according to the opening amount and the moving speed of the spool 55, and the spool 55 When the valve starts moving from the small opening position to the large opening position, a thrust in the valve opening direction acts to make the valve easy to open, and when the spool 55 moves to the large opening position, it moves in the valve closing direction. The driving force required for high-speed switching of the flow rate is reduced by allowing the valve to stop quickly due to the thrust acting, and the switching time is also extremely short.
The injection speed control valve 50 can further improve the high-speed switching performance of the flow rate and reduce the driving force.

In the injection speed control valve 50, a control pulse train from a control pulse generator built in the injection speed control device 44 is used.
The amount of rotation of the pulse motor 51, that is, the rotation angle
Is determined, the flow rate to the injection cylinder 25 is controlled, and the rate of change of the flow rate, that is, the state of the speed is determined by the magnitude of the rotation speed during the rotation of the pulse motor 51.

In addition, the injection speed control valve having such a structure and operation.
In 50, the time until the spool 55 actually starts to open after receiving the speed change command can be suppressed to a maximum of 1 millisecond or less, and the responsiveness is extremely high compared to the conventional ordinary flow control valve. Also, the operability and operation accuracy of valve opening and closing are extremely improved. A permanent magnet 61 is fixed to a part of the surface of the nut shaft 56a, and a position detector 63 by a magnetic action called a zero-cross sensor is attached to the permanent magnet 61 and a part of the opposing casing 62, for example.
The position detector 63 is constituted by a proximity switch responsive to the movement of the permanent magnet 61, and can accurately detect the axial movement distance of the nut shaft 56a or the spool 55 here and feed it back to the control device. Further, the zero position of the spool 55 is electrically detected by the action of the permanent magnet 61 and the position detector 63, and the position of the spool 55 is controlled by controlling the pulse motor 51 driven by a control pulse generator (not shown). Can be stopped exactly.

Incidentally, as the position detector 63, one having an accuracy of 0.01 mm can be used. Therefore, such an injection speed control valve 50
By using this, it is possible to control not only the injection speed when the molten metal is filled into the cavity 15, but also the accurate advance of the plunger tip 22 at a low speed in accordance with the retreat of the movable mold 13.

Of course, a flow control valve 48 similar to the injection speed control valve 50 can be used in the mold clamping circuit. That is, in FIG. 1, reference numeral 20 denotes a mold clamping cylinder for driving a toggle mechanism attached to the link housing 18, reference numeral 47 denotes a switching valve for opening the mold closing mold, and reference numeral 48 denotes a flow control valve capable of controlling the opening speed of the mold closing mold. is there.

In this embodiment, the flow rate control valve is replaced by an injection speed control valve.
In this method, control is performed based on oil pressure detection so that the oil pressure sent to the injection cylinder 25 is extremely low as shown in FIG.

In this embodiment, the injection pressure in the injection cylinder 25 is detected by the injection pressure detector 45, compared with the set low pressure of the pressing force setter 46 which is set artificially, and controls the injection speed control valve 50, When the retreat speed of the movable mold 13 is lower than the forward speed of the plunger tip 22, the resistance force from the movable mold 13 hinders the advance of the plunger tip 22 via the biscuit 29, and the hydraulic pressure of the injection cylinder 25 increases. When the upper limit set value of the low pressure set by the pressing force setter 46 is reached, the injection speed control valve 50
The opening of the plunger tip 22 is reduced, and the forward movement of the plunger tip 22 is decelerated so that a pressure higher than a predetermined pressure is not applied to the biscuit 29.

Also, if the retreat speed of the movable mold 13 is higher than the forward speed of the plunger tip 22, the forward resistance of the plunger tip 22 received from the biscuit 29 becomes smaller, so that the injection cylinder
When the hydraulic pressure of 25 decreases and the hydraulic pressure reaches the lower limit, the opening of the injection speed control valve 50 is increased to increase the forward speed of the plunger tip 22 so as to follow the retreat speed of the movable mold 13. Then, by applying a pressure between the upper limit set value and the lower limit set value of the set low pressure to the biscuit 29, the forward speed of the plunger tip 22 is synchronized with the retreat speed of the movable mold 13 to advance. An upper limit set value and a lower limit set value are provided for the set low pressure, and when the sending oil pressure reaches the upper limit set value, the opening degree of the injection speed control valve 50 is reduced to reduce the forward speed of the plunger tip 22, and When the feed pressure reaches the lower limit set value, the opening of the injection speed control valve 50 is increased to increase the forward speed of the plunger tip 22, so that a constant pressure between the upper limit set value and the lower limit set value is maintained. Movable mold in pressure range
The forward speed of the injection plunger 24 is synchronized with the retracting speed of the movable mold 13 so that the plunger tip 22 is advanced by following the backward speed of the thirteen and thus the backward speed of the biscuit 29.

For example, in an injection molding apparatus having a mold clamping force of 1650 t, the injection pressure of the molten metal is usually several tens t to 100 t, whereas the pressure set by the pressing force setting device 46 is extremely small, such as 5 t. While adjusting the forward speed of the tip 22 to the retreat speed of the movable mold 13, the pressing of the plunger tip 22 on the biscuit 29 is extremely small, such as a maximum of 5 t, so that the biscuit 29 is pushed out of the injection sleeve 21 without being crushed. It becomes possible.

Therefore, the injection plunger 24 is advanced by using the injection speed control valve 50 as described above, and at that time, the movable mold 13 is moved as described above.
The injection speed control valve 50 sends a very small amount of pressure oil to the injection cylinder 25 so that the feed oil pressure is extremely low, so that the feed oil pressure is extremely low so that the biscuit 29 has the movable mold 13 and the plunger tip. Biscuit without being overpowered by 22
Even if the inside of 29 is not solidified, if the outer periphery of the biscuit 29 is solidified to some extent, the injection sleeve in which the biscuit 29 is attached to the fixed mold 12 without crushing the biscuit 29
You can extrude from 21.

[Effects of the Invention] As described above, the present invention relates to a method of opening a mold in an injection molding apparatus in which the advance of a plunger tip for pushing out a biscuit at the time of mold opening is advanced at an extremely low pressure in synchronization with the retreat of a movable mold. Because it is a method of protruding the injection product, there is no danger of crushing the biscuit when opening the mold,
Even if the inside of the biscuit is in an unsolidified state, the outer periphery of the biscuit is solidified by cooling, and therefore, the mold can be opened when the outer periphery of the molten metal of the product part filled in the cavity is sufficiently solidified. In addition, it is possible to shorten the chill time in the injection molding and, consequently, the cycle time, and to improve the mass productivity of the product.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an injection molding apparatus, FIG. 2 is a diagram in which a movable mold is slightly retracted, and FIG. 3 is a diagram showing a relationship between a retracting amount of a mold opening cylinder and a retracting speed of a movable mold. FIG. 4 is a diagram showing an example of an injection speed control valve, and FIG. 5 is a block diagram showing an example of a control circuit. 11 = mold, 12 = fixed mold, 13 = movable mold, 15 = cavity, 16 = fixed board, 17 = movable board, 18 = link housing,
19 = toggle mechanism, 20 = mold cylinder, 21 = injection sleeve, 22 = plunger tip, 24 = injection plunger, 25 =
Injection cylinder, 27 = product, 29 = biscuit, 43 = comparator, 44 = injection speed control device, 45 = injection pressure detector, 46
= Pressure setting device, 48 = Flow control valve, 50 = Injection speed control valve.

Claims (1)

(57) [Claims] In injection molding, after a required time for injecting a molten metal into a cavity and cooling a casting in a mold has elapsed, an injection pressure in an ejection cylinder when opening the mold to take out the casting. Is detected, the detected pressure is compared with a set low pressure set pressure, and when the detected pressure reaches the set upper limit value of the set pressure, the opening of the injection speed control valve is reduced, and the detected pressure becomes the lower limit of the set pressure. When the set value is reached, the opening of the injection speed control valve is increased, so that the forward speed of the plunger tip, which projects the biscuit in the fixed mold, and the retreat speed of the movable mold are constant, and the biscuit by the plunger tip is used. A method of ejecting an injection product at the time of opening a mold in an injection molding apparatus, wherein the pressing force to the mold is maintained smaller than an upper limit set value of a set pressure and larger than a lower limit set value.