JPH0745099B2 - Pressure casting method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a casting method for injecting a molten metal into a cavity of a die of a die casting machine to form a molded article, and particularly,
The present invention relates to a computer-controlled pressure casting method in which the step of pressurizing the molten metal in the mold is improved in the latter half of the injection step.

[Prior Art] FIG. 2 and FIG. 3 are longitudinal sectional views showing a main part of a die-casting machine for molding a disc wheel, and FIG.
~ (E) is a diagram showing a molding process, and Fig. 2 (f) is a second diagram.
FIG. 3D is an enlarged view of part A of FIG. 3D, and FIG. 3 is a block diagram showing the overall configuration. As shown in the figure, the upper mold 33, the lower mold 35 that can be opened and closed in the vertical direction, and the four cores 34 that can move in the horizontal direction are combined and clamped from the vertical direction in the drawing by a mold clamping mechanism (not shown). Then, in the cavity 38 formed thereby, the molten metal 37 in the injection sleeve 39 is injected by the action of an injection cylinder (not shown) into the injection plunger 36 and the plunger tip 36 that integrally operates with the injection plunger 36.
Fill with the ascending action of a.

FIG. 2 (a) shows a state in which the injection sleeve 39 containing the molten metal 37 is brought into contact with the lower mold 35 and the runners of the injection sleeve 39 and the cavity 38 are connected, and FIG. 2 (b) shows The injection plunger 36 is lifted so that the molten metal 37 becomes the gate portion 38 of the cavity 38.
indicates a state of reaching a, and generally, for example, JP-A-63
As shown in Japanese Patent Publication No. 40659, thereafter, the rising speed of the injection plunger 36 is reduced so that the molten metal 37 is gently injected into the cavity 38 without scattering. Normal,
This timing is detected by detecting the position of the injection plunger 36 with a limit switch (not shown) or the like, and at the same time, the cooling timer starts timing. FIG. 2 (c) shows a cavity
It is in a state where the molten metal 37 has been completely filled into the inside of the 38, and when the working pressure of the injection cylinder (not shown) has exceeded a predetermined pressure value After a lapse of time (pressurization time lag), the pressurizing plunger 40 attached to the cylinder piston 32 of the pressurizing cylinder 31 is excited by exciting the solenoid 23a of the direction switching valve 23 shown in FIG. ), The molten metal 37 in the cavity 38 is pressed to pressurize the molten metal 37 so that the molten metal 37 performs a presser action corresponding to the shrinkage allowance (solidification shrinkage) accompanying cooling. In addition, in FIG.
Reference numeral 5 is a pump, 4 is a motor for driving the pump 5, and 7 is a tank, which constitutes a pressure source for driving the pressurizing cylinder 31. As shown in FIGS. 2D and 2F, in the final stage of pressurization, the pressurizing plunger 40 is lowered to the position of the gate portion 38a of the cavity 38 (gate seal position). That is, the pressure plunger 40 having a diameter slightly smaller than that of the gate portion 38a and having a narrow gap d between the inner peripheral surface of the gate portion 38a is lowered to the gate seal position to form a thin molten metal solidified product 41. Then, when the cooling timer described above is completed, the clamp by the mold clamping mechanism and the pressurization by the injection plunger 36 are released, and as shown in FIG. A mold opening operation is performed between the mold 33 and the core 34 and the lower mold 35 so that the thin portion 41 formed between the molded product 42 and the biscuit 43 can be easily cut.

[Problems to be Solved by the Present Invention] At this time, the operation of the pressure plunger 40 is, for example, as disclosed by the present applicants in Japanese Patent Application No. 63-244552 (Japanese Patent Application Laid-Open No. 2-92446). Further, it is best to control the history of the protrusion stroke amount into the cavity 38 so as to follow a predetermined target locus with the lapse of time from the start of operation. The reason is that the amount of heat from the molten metal 37 causes the pressurizing plunger 40 and the upper mold 33 to change in dimension, but the states are not uniform due to the difference in the thermal expansion coefficient and the cooling state of the two, so the pressurizing plunger 40 If the operating pressure, that is, the feeder force is controlled, the stroke of the pressurizing plunger 40 will not be uniform due to external factors such as changes in frictional resistance and insertion of molten metal. Because it is not stable.

When controlling the protrusion stroke amount of the pressure plunger 40 so as to follow a predetermined target locus, first, the pressure plunger 40 is set with reference to the time t from the operation start time (t = 0) of the pressure plunger 40. The moving stroke amount st of the 40 into the cavity 38 is predetermined in the model unit 9 as a target locus. The deviation amount e (e between the stroke amount st which is the target locus and the actual movement stroke amount stb of the cylinder piston 32 detected by the position detector 3, that is, the pressure plunger 40
= St-stb) is obtained by the deviation detecting unit 10, and this deviation amount e
In response to this, the gain setting unit 8 appropriately processes and outputs a predetermined output signal v corresponding thereto to the driver 12. The driver 12 outputs the output signal p in accordance with the magnitude of the output signal v from the gain setting section 8 to adjust the pressure adjusting valve 6 to control the pressure P of the pressure source. In addition, the model unit 9, the deviation detection unit
The feedback controller 11 is composed of 10 and the gain setting unit 8.

In this way, the pressure plunger 40 is adjusted according to the deviation e between the target trajectory st and the actual movement stroke amount stb of the pressure plunger 40.
By changing the working pressure that drives the pressure plunger 40, the moving stroke amount of the pressure plunger 40 with respect to time is configured to follow and control so as to follow the target trajectory. It is possible to eliminate the factors of unstable operation such as fluctuations in.

Against this technical background, it was possible at the same time to lower the pressurizing plunger 40 to the gate seal position shown in FIGS. 2 (d) and 2 (f) at the final stage of pressurization. ) Due to the structure of the mold, the moving stroke of the pressure plunger 40 before reaching the gate seal position is long, and the molten metal that the pressure plunger 40 removes before reaching the gate seal position.
If the volume of 37 is considerably larger than the volume of the shrinkage allowance (solidification shrinkage) due to the cooling of the molten metal 37, or 2) as the molding is continuously performed, the temperature state of the mold becomes stable. At the stage of filling the molten metal 37 with the injection plunger 36,
When 37 becomes easy to rotate around the cavity 38 and the filling force by the injection plunger 36 acts effectively to increase the filling density relatively, even if the pressurizing cylinder 31 gives the maximum output, it reaches the gate seal position. The pressure plunger 40 may not reach. Especially at the gate seal stage, the biscuit part that is relatively easily cooled
Since the working pressure by the pressure plunger 40 does not act on the injection plunger 36 as pressure propagation because 43 (close to the injection sleeve 39 from the gate 38a of the molten metal 37) has already solidified, even if the working pressure that the pressure plunger 40 can generate is generated. However, even if it is larger than the injection plunger 36, it does not push the injection plunger 36 back.

If the pressure plunger 40 does not finally reach the gate seal position, the cross-sectional area of the molten metal solidified material of the gate portion 38a becomes equal to the gate area, and therefore becomes extremely large compared to the normal time. Therefore, in the operation of cutting the gate shown in FIG. 2 (e), the force required for the cutting becomes very large. As shown in the figure, this gate cutting is performed by opening the mold with a predetermined mold opening force while the core 34 is still inserted. Therefore, a large cutting force means that the hub of the disk wheel is a molded product. Surface (part H shown in FIG. 2 (e))
It is nothing but a large pulling force in the state shown in the figure. As a result, the disc wheel was distorted, resulting in a defective product.

[Means for Solving the Problems] In the present invention, in order to solve such problems,
The molten metal is filled in the mold through the gate by the action of the injection device having the injection plunger, and the inside of the mold is provided by the action of the pressurizing device having the pressure plunger that can advance the tip to the gate part and seal the gate. In the pressure casting method that pressurizes the molten metal after filling, while the molten metal is being pressed by the action of both the injection plunger and the pressure plunger, start pressing the molten metal by the action of the pressure plunger. After a lapse of a predetermined time or when the pressurizing plunger advances by a predetermined moving stroke amount, it is changed to a process of continuously pressurizing the molten metal by the pressurizing plunger while releasing the working pressure to the injection plunger by the action of the injection device, The tip portion of the pressure plunger is advanced to the gate portion to seal the gate.

[Operation] By pressurizing the molten metal by the pressure plunger while releasing the operating pressure on the injection plunger due to the operation of the injection device, the pressure plunger 40 can be surely reached to the gate seal position, and the thin molten metal A solidified product is formed and penetrated. As a result, the molded product and the biscuit portion are easily cut from the thin portion formed by the mold opening operation.

[Example] An explanation will be given according to FIG. Note that the elements having the same functions as those in the above-described description of FIGS. 2 and 3 have the same reference numerals, and detailed description thereof will be omitted here.

The signal v processed and output through the model unit 9, the deviation detection unit 10 and the gain setting unit 8 is output to the driver 12. The decompression command device 14 is programmed, for example, as shown in FIG. 4, receives the time t from the model unit 9 or the moving stroke st, and this is a preset predetermined time.
The pressure reduction command dc is output to the injection pressure control 16 at t ₁ or when the predetermined movement stroke st ₁ is reached.

In the present embodiment, the injection plunger 36 acts to fill the molten metal 37 into the cavities 38 of the molds 33, 35, and the injection plunger 36 continues to pressurize the molten metal 37 as it is. After a lapse of time (pressurizing timing), the pressurizing operation is started by advancing the pressurizing plunger 40, and the time t or the moving stroke st at the pressurizing operation start point by the pressurizing plunger 40 is set to zero. And
From this point of time, in addition to the pressure action of the injection plunger 36, the pressure action of the pressure plunger 40 is performed. The forward movement of the pressure plunger 40 is performed along a preset time-movement stroke curve.

Then, when the predetermined time t ₁ from the start of the pressurizing operation by the pressurizing plunger 40 or the predetermined moving stroke st ₁ from the pressurizing operation starting position by the pressurizing plunger 40 is reached,
While releasing the working pressure on the injection plunger 36, only the pressurization of the molten metal by the pressure plunger 40 is continued. Then, the tip portion of the pressure plunger 40 is securely inserted into the gate portion 38a. Then, the pressure applied by the pressure plunger 40 is stopped.

The injection pressure control 16 adjusts the pressure control valve 17 to control the pressure generated by the pressure source 18, that is, the working pressure of the injection cylinder 19, thereby controlling the filling pressure of the molten metal 37 into the cavity 38 by the injection plunger 36. There is. In addition, the model part 9,
The deviation detection unit 10, the gain setting unit 8 and the mold opening command unit 14 constitute a feedback controller 15.

Now, as in Figs. 2 and 3, the upper mold 33, which can be opened and closed vertically,
The lower mold 35 and the four cores 34 that can move in the horizontal direction are combined, and clamped from the vertical direction in the drawing by a mold clamping mechanism (not shown), and in the cavity 38 formed thereby,
The molten metal 37 in the injection sleeve 39 is lifted and filled by the action of the piston 20 of the injection cylinder 19 and the injection plunger 36 and the plunger tip 36a that operates integrally with the injection plunger 36 (the molten metal in the cavity 38 is shown in the figure). Filled 37).

After a lapse of a predetermined time (pressurization time lag) from the time when the molten metal 37 is completely filled, the pressure plunger 40 attached to the cylinder piston 32 of the pressure cylinder 31 is excited by exciting the solenoid 23a of the direction switching valve 23. The molten metal 37 is projected into the cavity 38 and the molten metal 37 in the cavity 38 is pressurized so that the molten metal 37 has a function of feeding in proportion to the shrinkage allowance (solidification shrinkage) accompanying cooling of the molten metal 37. The operation of the pressurizing plunger 40 is configured so that the feedback controller 15 follows and controls the target locus st as described above. That is, in the operation of the pressure plunger 40, the movement stroke amount of the pressure plunger 40 into the mold cavity 38 is predetermined as a target locus st, and the movement stroke amount of the pressure plunger 40 is set as the target locus st. , By changing the working pressure for driving the pressure plunger 40 according to the deviation amount of the actual movement stroke amount,
The moving stroke amount of the pressure plunger 40 is controlled to follow. At this time, in the feedback controller 15, the time t from the model unit 9 or the movement stroke st is also output to the decompression commander 14, and here, as shown in FIG. It is determined whether t ₁ or the predetermined movement stroke st ₁ is reached. As shown in the model portion 9, the predetermined time t ₁ or the predetermined movement stroke st ₁ reaches the pressure plunger 40 up to the region r ₁ which mainly applies the feeder effect and the gate seal injection stg. The boundary point with r ₂ which is the gate cutting area is set.

If the determination condition by the pressure reduction command device 14 is satisfied, the pressure reduction command dc is output to the injection pressure control 16. The injection pressure control 16 receives the decompression command dc and gradually reduces the filling pressure pm of the molten metal 37 into the cavity 38 by the injection plunger 36 as shown in the time t-pressure P diagram of FIG. The pressure control valve 17 is controlled so as to fall to. here
The tc time is determined in consideration of the time required for the pressurizing plunger 40 to finally reach the gate seal position, but it usually takes a relatively long time of several seconds or more to reduce the pressure of the hydraulic oil in the injection device. Then, the filling force of the injection plunger 36 is reduced. Therefore, in the final stage of pressurization, when the pressurizing plunger 40 moves to the gate seal position, the filling force by the injection plunger 36 is simultaneously depressurized, which makes it easier to operate, and the above-mentioned problems have been shown. ),
It is possible to reliably reach the gate seal position without being affected by 2). Moreover, since the effect of the feeder is not impaired, it is possible to effectively apply the feeder to the solidification contraction of the molten metal 37 due to cooling.

[Advantages of the Invention] In the present invention, since it is configured as described above, it is not only effective to prevent so-called cavities that are likely to occur during solidification contraction of the molten metal, but also to ensure reliable gate cutting, which is unnecessary. It is possible to improve the yield rate and the yield rate of molding.

That is, in the present invention, when the molten metal is being pressurized by the actions of both the injection plunger and the pressure plunger, when a predetermined time has elapsed from when the molten metal was started to be pressurized by the action of the pressure plunger, or When the pressurizing plunger advances by a predetermined movement stroke, change to the process of continuously pressurizing the molten metal by the pressurizing plunger while releasing the working pressure to the injection plunger by the action of the injection device, and change the tip of the pressurizing plunger. Since the gate is sealed by advancing to the gate portion, the pressurizing plunger can be sufficiently advanced without being blocked by the working pressure of the injection plunger, and as a result, sufficient feeder action can be performed. As a result, it is possible to obtain a dense molded product having no hot spots and good surface properties and no hollows.

In addition, since the tip of the pressure plunger can be advanced to the gate portion for gate sealing, the molded product and the biscuit part are already almost separated at the end of the feeder operation. The part is reliably and easily cut with a very small force by the mold opening operation. As a result, almost no gate cutting force is required when the mold is opened, a force pulling a portion of the molded product near the gate portion downward does not act, and no distortion occurs in the molded product.

Therefore, it is possible to easily obtain a molded product having good hot water flow and no voids and good mechanical properties.

Further, as a result of the above, since almost no molded product having a molding defect or a casting defect is generated, both the yield rate of the molded product and the yield rate are improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of an apparatus for carrying out the direction of the present invention, and FIGS. 2 (a) to (e) show the operation sequence in one example of a conventional apparatus similar to the present invention. Fig. 2 (f) is a longitudinal sectional view, Fig. 2 (d) is an enlarged view of a part of Fig. 2 (d), Fig. 3 is a block diagram showing an example of the same conventional device as Fig. 2 (a) to (e), FIG. 4 is a flow diagram showing a part of the control state in the present invention, and FIG. 5 is a time-pressure diagram showing the control state in the present invention. 3 ... Position detector, 6 ... Pressure control valve, 8 ... Gain setting section, 9 ... Model section, 10 ... Deviation detection section, 12 ... Driver, 14 ... Pressure reduction commander, 15 ... Feedback Controller, 16 …… Injection pressure control, 17 …… Pressure control valve, 19
...... Injection cylinder, 31 …… Pressurizing cylinder, 33 …… Upper mold,
34 …… core, 35 …… lower mold, 36 …… injection plunger, 37…
… Melt, 38… Cavity, 39… Injection sleeve, 40…
… Pressurized plunger.

Claims (1)

[Claims] 1. A mold is filled with molten metal through a gate by the action of an injection device having an injection plunger, and
In the pressure casting method for pressurizing the molten metal after filling in the mold by the action of the pressurizing device having the pressure plunger whose tip advances to the gate and can perform gate sealing, the injection plunger and the pressure plunger are While pressurizing the molten metal by both actions, when a predetermined time has elapsed after starting the pressurization of the molten metal by the action of the pressure plunger, or when the pressure plunger advances by a predetermined movement stroke amount, the injection device The operation was changed to a process of continuously pressurizing the molten metal by the pressure plunger while releasing the pressure acting on the injection plunger by the action of, and advancing the tip of the pressure plunger to the gate portion to seal the gate. A pressure casting method characterized by the above.