KR100259368B1 - A single body injection piston having a velocity-control pin and velocity-control device therefor - Google Patents

Abstract

PURPOSE: An integrated injection piston and a speed controller are provided to mechanically control a speed of the injection piston with a control pin. CONSTITUTION: A speed controller comprises an injection piston moved by hydraulic pressure for injecting melted metal into a mold; a speed control pin changed a speed by corresponding to a change of a size inside the mold; an orifice inserted the speed control pin; a set side induced fluid from an accumulator; and a rod side induced fluid having smaller pressure than the fluid of the set side. The injection piston is moved by the hydraulic pressure of the rod side by flowing out the fluid from the set side and filling the fluid in the rod side. A flux into the injection piston is decided through an interval between the orifice and the speed control pin by separating the speed control pin from the orifice. Thereby, a speed of the piston is controlled.

Description

Integral injection piston with speed control pin and speed control device

The present invention relates to the start of an injection piston used in an injection molding machine, and more particularly, to an injection piston having a speed control pin that can mechanically control the speed of the injection piston.

An injection casting machine is a machine that injects molten metal into a mold to form a shape of a desired product. A die casting machine, a molten metal forging machine, and the like are representative examples thereof.

The molding process using the injection casting machine can be explained by dividing it into three stages as shown in FIG. Firstly, the molten molten metal 9 is filled with about 70% of the sleeve 6 volume (Fig. 1A). The second step is to fill the molten metal (9) filled in the sleeve (6) to the molten metal inlet (gate) 5, the piston (7) is gradually advanced to prevent the rapid flow of the molten metal to mold the molten metal (9) Push it to the entrance of (1,4) (FIG. 2B). The final step is a process of filling the molten metal 9 into the mold space 3 formed by the stationary mold 1, the mill pin 2 and the moving mold 4 before the molten metal 9 solidifies. 7) advances at a high speed to fill the molten metal 9 into the mold and maintain the pressure until solidification is completed (Fig. 1C). The residual water 10 is discharged through the residual water outlet 8.

Considering the series of processes shown in FIG. 1 in terms of the movement of the piston, it can be represented as shown in FIG. 2. There is. Most of the hydraulic circuits of the injection molding machine adopting the two-stage injection method are operated by direct pressure from the pump in the low speed injection section, and the high speed injection section is operated by applying pressure from the accumulator.

First, the problems of the piston motion generated in the low speed section of the injection device using such an injection method are as follows. At low speeds, the speed of the pistons is about 0.2-0.4m / sec. It is almost unchanged even in actual casting. 3a to 3e schematically show the behavior of the molten metal in the sleeve as the injection piston advances in the low speed section, and shows a process in which bubbles generated by the rapid speed change of the piston flow into the mold. This phenomenon is particularly dangerous when the filling rate is low in the sleeve (less than 50% of the hot water level). In addition, even though the filling rate is large, it is difficult to avoid the air curling due to the fluctuation of the melt due to the low-speed injection, so Swiss Buhrer's para-shot injection method that changes the speed smoothly with constant acceleration from low speed to high speed Developed.

4 shows a hypothetical product shape in which the cross-sectional area, i. If the speed of the piston is kept constant in the high speed section to fill the mold space, the filling speed of the molten metal in the mold becomes constant so that the amount of molten metal filled does not correspond to the shape change of the product, that is, the volume change in the mold. As a result, the flow of the molten metal suddenly acts as a cause of product defects such as an air trap.

Efforts to control the speed of pistons in mass production injection machines, such as die casting machines, have been carried out in several ways.

The injection piston currently in use is mainly composed of a simple two-stage speed change at low and high speeds, and the change in the speed of the injection piston is attributable to the change in flow rate as the compressed oil in the cylinder exits the orifice. As a conventional method for controlling the speed of the injection piston through such a change in flow rate, there is a method using a servo valve or an electromagnetic proportional valve.

However, servo valves are generally used to control low speeds of less than 1 kW because they are not easy to control when they require injection conditions that require large-capacity injection machines, that is, large flow rate changes in a short time. have. On the other hand, the use of an electron proportional valve can control a large flow rate, but this method also has a problem in accurate flow rate control when the fluid velocity is high.

Therefore, indirect flow control using a control pin is widely used as a method for controlling the speed of the injection piston moving at high speed (4-10 kPa) using a large amount of oil as in a die casting machine. Fig. 5 is a schematic diagram of a piston speed control method currently adopted by Toshiba, Japan.

First, in the injection preparation time, when the oil of low pressure (P ₀ ) is filled to the set side from the accumulator, the control pin 30 is reversed to block the orifice, and again the high pressure (P) from the accumulator. The oil of ₁ ) is filled to the load side. At this time, since the low pressure side cross-sectional area D _{0 of} the control pin 30 is larger than the high pressure side cross-sectional area D ₁ , the control pin 30 is balanced without being pushed to the set side, which is the low pressure side. In addition, by turning the handle 20 mounted on the "A" portion before the injection is adjusted to adjust the distance Δd from which the control pin is pushed out.

Next, at the time of injection, the compressed oil on the rod side is blocked by the control pin 30, and when the valve is opened with an external signal P ₂ at the "B" part, the control pin 30 moves to the left side. When pressed, oil having a pressure of P ₁ exits through the orifice, where the oil having a pressure of P ₁ is discharged toward the injection piston 40 at a flow rate corresponding to the cross-sectional shape of the pin. The released oil pressurizes the piston 40 inside the injection cylinder to advance the injection piston 40 toward the mold.

The problem with the above-described method is that the speed of the piston is controlled only at two speeds, low speed and high speed, as pointed out above, and adopts an indirect flow control method for the control of this speed. In addition, it does not provide a way to specifically calculate the proper shape and injection conditions of the control pin for generating a change in the speed of the piston over time.

In the present invention, in the process of filling the molten metal into the mold space, the speed of the injection piston is controlled mechanically over the entire stroke section of the injection piston using a control pin so that the filling speed of the melt corresponds 1: 1 to the volume change in the mold. The purpose is to control.

Figures 1a to 1b shows the product forming process by the general melt injection.

Figure 2 shows the low and high speed motion of the injection piston used in a conventional injection casting machine.

Figures 3a to 3e shows the change behavior of the melt in accordance with the movement of the injection piston occurring in the low speed section of the conventional injection device.

Fig. 4 schematically shows that when the speed of the injection piston is constant in the conventional injection apparatus, if there is a volume change in the mold space, the melt filling speed in the mold space does not correspond to the volume change in the change.

Fig. 5 schematically shows a method for injection piston control of Toshiba, Japan, as a method according to the prior art for injection piston control.

Figure 6 schematically shows the structure of an injection piston comprising a speed control pin for the speed control of the injection piston according to the present invention.

7a and 7b show injection piston speed control pins according to the prior art and injection piston speed control pins according to the invention, respectively.

Figure 8 shows several variables for obtaining a mathematical solution used in the shape design of the control pin for variably obtaining the injection piston speed according to the present invention.

9 shows the case where the speed of the injection piston is controlled using the speed control pin according to the present invention (actually) and the case where the speed is not controlled like the conventional injection piston (dotted line).

10A and 10B are transfer simulations when the injection speed is not controlled when the mold space is filled with molten metal (FIG. 10A) and when the injection speed is controlled using the injection piston speed control pin according to the present invention (FIG. 10B). Show results.

* Explanation of symbols for main parts of the drawings

1: fixed mold 2: mill pin

3: mold space 4: moving mold

5: molten metal inlet (gate) 6: sleeve (sleeve)

7: piston 8: residual water outlet

9: molten metal 10: molten metal

20: handle 30: control pin

40: injection piston

The present invention relates to an injection piston that is moved by hydraulic pressure for injecting molten metal into a metal mold, the end portion of which the molten metal of the injection piston is in contact with so that the moving speed of the injection piston can be shifted in response to a volume change in the mold. Speed control pin is installed on the opposite end having a shape that can correspond to the volume change in the mold; An orifice having a larger diameter than the maximum diameter portion of the speed control pin, into which the speed control pin is inserted, between the orifice and the speed control pin generated while the speed control pin exits the orifice. The flow rate applied to the injection piston is determined by the interval, thereby providing an injection piston having a speed control pin in which the speed of the piston is controlled.

The present invention also provides an injection piston which is moved by hydraulic pressure for injecting molten metal into a mold; A speed control pin installed to have a shape capable of responding to a volume change in the mold at an end opposite to an end where the molten metal of the injection piston contacts so that the moving speed of the injection piston is shiftable in response to a volume change in the mold; ; An orifice having a diameter larger than the maximum diameter portion of the speed control pin, into which the speed control pin is inserted; One of two regions separated by the orifice, the set side into which a constant pressure fluid is introduced from the accumulator while the piston is in its initial position while the opposite end of the injection piston is kept closed in the initial position; In a region opposite to the set side separated by the orifice, a fluid of a small pressure is introduced relative to the pressure of the fluid introduced from the accumulator to the set side, wherein the speed control pin is positioned past the orifice before injection. The rod side is formed, the fluid is discharged from the set side and the fluid is filled from the accumulator to the rod side, the injection piston is moved by the hydraulic pressure of the rod side, the speed control pin is It provides a speed control device of the injection piston having a speed control pin to control the speed of the piston by determining the flow rate applied to the injection piston between the orifice and the speed control pin generated while exiting the orifice. .

According to the present invention, the shape of the control pin for obtaining the desired melt filling speed or the speed of the injection piston and the condition setting of the injection cylinder before injection are designed through computer simulation, and by using this, the melt rate filled in the mold is varied. To control.

As can be seen in Fig. 6, when the oil of the preset pressure P ₂ is filled on the set side before injection, the control pin shuts off the orifice and locks the valve in this state, and then loads the oil of pressure P ₁ from the accumulator. Filling the side is ready for injection. Injection is achieved by opening the set side oil through the valve and the piston is pushed by the pressure P ₁ on the rod side to move towards the mold. At this time, the pin fixed to the piston moves together to exit the orifice. The speed change of the injection piston occurs as the pin exits the orifice. In other words, when the portion of the pin having a small cross-sectional area is located in the orifice, the gap between the orifice and the pin increases, so that a large flow rate of oil passes, resulting in a high speed of the injection piston. On the contrary, when the large cross-sectional area is located in the orifice, the gap between the orifice and the pin becomes small, so that a small flow rate passes, and the injection piston is slowed down. Therefore, the filling speed of the molten metal filled in the actual mold space can be controlled by integrating a pin having a shape that satisfies the condition for controlling the speed of the injection piston into the injection piston.

7B is a schematic view of the designed injection piston in which the control pin and the injection piston are integrally connected. In addition, in order to be able to control the speed over the entire stroke of the injection piston, the length of the control pin is equal to the stroke distance (300-500 mm) of the piston. On the other hand, in the conventional method, as shown in Fig. 7A, the length of the control pin is 15-30 mm, which is shorter than the stroke distance of the piston, so that it is impossible to control the speed over the entire stroke region of the injection piston. As described above, the shape of the pin is calculated by computer simulation so as to reproduce the desired melt filling speed under a predetermined injection condition. The theoretical background for this is described below. 8 schematically shows the various conditions inside the piston during the injection process.

는 식 (1)과 (2)의 형태로 표현된다.When the valve on the set side is opened in the cylinder that is ready for injection, the oil starts to be discharged by the pressure on the rod side.

Is expressed in the form of equations (1) and (2).

[Equation 1]

[Equation 2]

: 셋 사이드에서 오일의 배출속도,here,

Is the discharge rate of oil on the three sides,

A _out : Outlet cross section of three side,

γ = Pg (P is the density of the fluid, g is the acceleration of gravity),

P ₃ : Oil pressure inside the cylinder when oil is drained from the set side,

V _p : speed of the piston,

A _cyl , A _pistion : Cross section of cylinder and piston.

At the same time oil is discharged to the set side, oil is charged from the accumulator to the rod side.

는 아래식 (3)과 (4)에 의하여 표현된다.Change in fill volume of oil to the rod side

Is expressed by the following equations (3) and (4).

[Equation 3]

[Equation 4]

: 로드 사이드로의 오일의 유입 속도,here,

Is the flow rate of oil into the rod side,

A _orf : inlet cross section of rod side,

A _pin : cross section of the pin,

A _cyl : the inner diameter of the cylinder,

P ₁ : oil pressure on the rod side,

P ₂ : Oil pressure between orifice and piston.

Equations (5) and (6) can be obtained using equations (1)-(4).

[Equation 5]

[Equation 6]

으로부터 아래 식 (7)을 구한다.Also equilibrium of force

From Eq. (7) is obtained.

[Equation 7]

Where F _cavity is the repulsive force when the melt is filled into the mold,

m: mass of the piston,

P ₃ : Oil pressure inside the cylinder when oil is drained from the set side,

x _p : position (or displacement) of the piston,

t is time.

에 상응되는 핀의 형상(P₂)을 계산할 수 있다.F _cavity can be found experimentally, and assuming that P ₁ is a constant, three equations (Eq. (5)-(7)) are given for three unknowns (P ₁ , P ₂ , x _p ) speed

The shape of the pin (P ₂ ) corresponding to can be calculated.

Therefore, according to the present invention, it is possible to provide an injection piston capable of changing the melt injection speed so as to cope with the shape change of the product. In Fig. 9, the speed change waveform (solid line) of the injection piston, which is expected when the present invention achieves the target, is compared with the existing speed waveform (dotted line).

According to the present invention, since the speed of the injection piston is controlled so that the filling of the molten metal is performed at the filling speed corresponding to the volume change of each zone in the mold, it is possible to reduce the product defect rate and improve the quality. 10 is a simulation result showing the effect of the difference in mold filling speed on the air trap in the product. In order to form a healthy product, the molten metal corresponds to the internal shape of the mold during the process of filling the mold. It implies that the filling speed, ie the speed of the injection piston, must be controlled.

Claims (4)

In the injection piston moving by hydraulic pressure for injecting molten metal into the mold, the injection piston is moved to an end opposite to the end where the molten metal of the injection piston touches so that the moving speed of the injection piston can be shifted in response to a volume change in the mold. A speed control pin installed to have a shape capable of responding to a volume change in the mold; An orifice having a larger diameter than the maximum diameter portion of the speed control pin, into which the speed control pin is inserted, between the orifice and the speed control pin generated while the speed control pin exits the orifice. The injection piston having a speed control pin, characterized in that the speed of the piston is controlled by determining the flow rate applied to the injection piston by the interval. The speed of claim 1, wherein the speed control pin has a length that can correspond to the full stroke distance of the injection piston to control the speed of the injection piston over the full stroke distance of the injection piston. Injection piston with control pin. An injection piston moving by hydraulic pressure for injecting molten metal into the mold; The speed control pin is installed while having a shape that can correspond to the volume change in the mold at the end opposite to the end where the molten metal of the injection piston is in contact so that the moving speed of the injection piston can be shifted in response to the volume change in the mold. and; An orifice having a diameter larger than the maximum diameter portion of the speed control pin, into which the speed control pin is inserted; One of the two regions separated by the orifice, the set side into which a constant pressure fluid is introduced from the accumulator while the injection piston is held in its initial position at the opposite end of the injection piston with its orifice closed before injection; ; In a region opposite to the set side separated by the orifice, a fluid of a small pressure is introduced relative to the pressure of the fluid introduced from the accumulator to the set side, wherein the speed control pin is positioned past the orifice before injection. The rod side is formed, the fluid is discharged from the set side and the fluid is filled from the accumulator to the rod side, the injection piston is moved by the hydraulic pressure of the rod side, the speed control pin is Speed control of the injection piston having a speed control pin is controlled by determining the flow rate applied to the injection piston by the interval between the orifice and the speed control pin generated while exiting the orifice. Device. The speed of claim 3, wherein the speed control pin has a length that can correspond to the full stroke of the injection piston, thereby controlling the speed of the injection piston over the full stroke of the injection piston. Speed control device of injection piston with control pin.

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