CN116175914A - A control method and device for back pressure exhaust of injection molding machine - Google Patents

Abstract

The invention discloses a control method and device for back pressure exhaust of an injection molding machine, relates to the field of injection molding machines, and mainly includes the steps of: pressing a slidable side plate with a thimble and making it slide to an initial position; using a proportional back pressure with a thimble The valve control top presses against the slidable side plate, and under the joint pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference; through the control of the back pressure, the slidable Before the side plate retracts to the maximum displacement position, the cavity pressure in the mold cavity is controlled to be within the safe cavity pressure range. The invention controls the retraction speed of the ejector rod through the adjustment of the back pressure, so that the pressure in the cavity is higher than that during normal injection without increasing the injection pressure, so that the gas in the injection melt is Compared with the injection molding melt, the fluid properties are better discharged through the safety gap under high pressure, realizing molding while injection molding.

Description

A control method and device for back pressure exhaust of injection molding machine

technical field

The invention relates to the field of injection molding machines, in particular to a control method and device for back pressure exhaust of an injection molding machine.

Background technique

During the injection molding process of the injection molding machine, gas will be generated in the barrel, in the mold cavity, or after the raw material is heated. If the air cannot be effectively discharged, the gas will infiltrate into the raw material, or the product will not be fully injected, or the air will penetrate into the product after compression. Internally, quality defects such as porosity and silver streaks are caused. For the exhaust in the mold cavity, we can usually solve it by adding exhaust grooves or using insert exhaust. However, for some raw materials with strong viscosity and poor fluidity, especially some products used to produce long column hydraulic seals, due to their deep mold cavity and good sealing performance, the exhaust requirements are more demanding High, the traditional exhaust method cannot squeeze the air in the raw material as much as possible, and poor exhaust can easily cause defects such as pores in the product, which greatly reduces the qualified rate of the product.

In view of the lack of corresponding injection molding process for such hydraulic sealing products, in order to ensure that the plastic raw materials are fully exhausted, uniformly compacted, and eliminate internal stress problems, and ensure that the product has uniform wall thickness and no air bubbles, it is urgently necessary to exhaust the exhaust during the injection molding process. method for optimization.

Contents of the invention

In order to better discharge the gas in the melt and avoid the impact on the quality of the finished product when performing injection molding of high-viscosity injection molding melt, the present invention proposes a control method for back pressure exhaust of injection molding machine, which is installed on the ejector pin There is a slidable side plate that can slide with the ejector pin. The slidable side plate can control the sliding position in the mold cavity under the action of the ejector pin. The contact surface between the slidable side plate and the mold remains There is a safety gap, which specifically includes steps:

S1: After obtaining the confirmation signal that the injection molding machine has closed the mold to the bottom, press the slidable side plate through the thimble and make it slide to the initial position, and record the screw position in the initial state;

S2: Control the injection molding melt to be injected into the mold cavity at a constant speed through the injection port, and obtain the retraction amount of the ejector pin caused by the push back of the slidable side plate under the action of the material pressure;

S3: Control the top pressure of the slidable side plate through the thimble proportional back pressure valve, and under the joint pressure of the back pressure and the material pressure, the gas in the injection molding melt is discharged through the safety gap under the action of the pressure difference;

S4: Control the cavity pressure in the mold cavity within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement through the control of the back pressure, and record the screw position at the maximum displacement;

S5: Control the injection molding melt to be injected into the mold cavity through the injection port with a preset holding pressure.

Further, in the step S3, the cavity pressure is under the safety cavity pressure, and the injection melt cannot be discharged through the safety gap under the action of the melt viscosity.

Further, in the step S4, the position of the screw at the maximum displacement is the switch point for holding pressure.

Further, in the step S4, in the constant-velocity injection stage, the retraction speed of the slidable side plate is adjusted by decreasing the back pressure in several stages, and the arrival judgment of each stage is performed according to the retraction amount of the ejector pin.

Further, after the step S5, the step also includes:

S51: Obtain the screw position after the pressure holding and the actual screw stroke of the current injection mold;

S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value, if yes, go to step S53, if not, go to the next injection mold after opening the mold according to the decreasing adjustment of the current back pressure and return S1 step;

S53: Adjust the retraction speed of the ejector rod under the action of adjusting the retraction distance ratio of each stage by adjusting the back pressure of each stage in the next injection molding cycle, enter the next injection molding cycle after mold opening and return to step S1.

Further, in the S52 step, the actual screw stroke is expressed as the following formula:

s=s1-s0

In the formula, s is the actual screw stroke, s0 is the screw position in the initial state, and s1 is the screw position after the end of pressure holding;

The ideal screw stroke is expressed as the following formula:

s ^′ =(4000M)/(kρπd ² )

In the formula, s' is the ideal screw stroke, M is the total mass of the target injection molded part, k is the coefficient, ρ is the room temperature density of the injection material, and d is the screw diameter.

Further, in the step S53, the adjustment of the back pressure at each stage is expressed as the following formula:

Pn _m ＝(A _n -A _n+1 )/(A ₀ -A _N )*(s/s ^′ )*Pn _m-1

In the formula, n is a constant from 0 to N, m is the number of modes, N is the total number of stages, Pn _m is the back pressure value of the nth stage in the mth mode, _An is the screw position of the nth stage, A _{n +1} is the screw position of the n+1st stage, A ₀ is the screw position when the slidable side plate starts to displace under the action of material pressure, A _N is the screw position of the last stage of the current mold, Pn _m-1 is the first The back pressure value of the nth stage of the m-1 model.

The present invention also proposes a control device for back pressure exhaust of an injection molding machine, including:

The slidable side plate is set on the ejector rod, which can slide with the ejector rod, and controls the sliding position in the mold cavity under the action of the ejector pin;

A safety gap is left on the contact surface between the slidable side plate and the mould;

The main control chip is used to control the thimble to press the slidable side plate and make it slide to the initial position after obtaining the confirmation signal that the injection molding machine is closed to the bottom;

The injection module is used to control the injection of the injection melt into the mold cavity at a constant speed through the injection port when the slidable side plate is slid to the initial position, and to control the injection of the injection melt into the mold through the injection port at a preset holding pressure after entering the holding pressure stage Cavity;

The thimble proportional back pressure valve is used to control the top pressure of the slidable side plate on the thimble. Control the cavity pressure in the mold cavity to be within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement position;

The displacement sensor is used to obtain the retraction amount of the ejector pin during the injection molding process.

Further, when the cavity pressure of the thimble proportional back pressure valve is under the pressure of the safety cavity, the injection melt cannot be discharged through the safety gap under the action of the melt viscosity.

Further, during the process of the thimble proportional valve controlling the thimble, the position of the screw at the maximum displacement of the slidable side plate is the pressure maintaining switching point.

Compared with the prior art, the present invention at least contains the following beneficial effects:

(1) A method and device for controlling the back pressure exhaust of an injection molding machine according to the present invention controls the retraction speed of the ejector rod by adjusting the size of the back pressure, thereby making the cavity The pressure inside is higher than the cavity pressure during normal injection molding, so that the gas in the injection melt can be discharged through the safety gap under high pressure with the help of better fluid properties than the injection melt, realizing molding while injection molding;

(2) By adjusting the retraction speed, the actual stroke of the screw is adjusted, so as to better control the quality of the finished product and reduce the scrap rate caused by unstable weight.

Description of drawings

Fig. 1 is a step diagram of a control method for back pressure exhaust of an injection molding machine;

Fig. 2 is a block diagram of a control device for back pressure exhaust of an injection molding machine;

Fig. 3 is a schematic diagram of the position of the slidable side plate structure.

Explanation of reference numerals: 1 - ejector pin, 2 - slidable side plate, 3 - thimble, 4 - cavity.

Detailed ways

The following are specific embodiments of the present invention and in conjunction with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

Embodiment one

Aiming at the problem in the prior art that when the raw materials with high viscosity and poor fluidity are used for injection molding of long cylindrical injection molding parts, the bubbles are not easy to discharge and cause defects in the finished product. Method, as shown in FIG. 3 , in the cavity 4 , firstly, a slidable side plate 2 is provided on the mandrel that can expand and slide with the mandrel 1 . One side of the slidable side plate is a mold cavity, and the other side is in contact with the thimble 3, so that the slidable side plate can control the sliding position in the mold cavity under the pressure of the thimble (or constraint). At the same time, there is still a safety gap on the contact surface between the slidable side plate and the mold. Keep a certain safety gap during the process. In the present invention, the sliding position of the slidable side plate is controlled during the injection molding process, and the gas in the high-viscosity injection molding melt is discharged by utilizing the safety gap. Specifically as shown in Figure 1, including steps:

S1: After obtaining the confirmation signal that the injection molding machine has closed the mold to the bottom, press the slidable side plate through the thimble and make it slide to the initial position, and record the screw position (s0) in the initial state;

S2: Control the injection molding melt to be injected into the mold cavity at a constant speed through the injection port, and obtain the retraction amount of the ejector pin caused by the push back of the slidable side plate under the action of the material pressure;

S3: Control the top pressure of the slidable side plate through the thimble proportional back pressure valve, and under the joint pressure of the back pressure and the material pressure, the gas in the injection molding melt is discharged through the safety gap under the action of the pressure difference;

S4: Control the cavity pressure in the mold cavity within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement through the control of the back pressure, and record the screw position at the maximum displacement;

S5: Control the injection molding melt to be injected into the mold cavity through the injection port with a preset holding pressure.

After the injection molding motorized template and the fixed template are closed to the end, the movable template and the fixed template are tightly closed at this time, so as to ensure the stability of the mold during the injection molding process. At the same time, different from the traditional injection molding process, the traditional injection molding process will reserve a complete cavity during the injection molding process, while the present invention will push the slidable side plate towards the injection port through the thimble when the injection molding starts, until When the initial position is reached (set according to the thickness of the actual injection part or the reserved margin), that is to say, the cavity will be compressed first. In addition, it is also necessary to record the position of the screw in the initial state at this time, as a reference for the cost and quality of the later injection molding.

Then start the injection molding machine to inject the injection molding melt into the mold cavity at a constant speed through the injection port. At this time, due to the existence of material pressure in the mold cavity, the ejector pin and the slidable side plate will be pressed back. In the process of pressing back, in order to better discharge the gas in the injection molding melt, the present invention controls the retraction speed of the ejector pin through the back pressure of the ejector pin proportional back pressure valve. In this way, in addition to the material pressure in the cavity, there will be additional pressure from the slidable side plate. At this time, the injection melt will compress the air in the material due to the high pressure in the cavity, and the melt will The gas inside will be discharged through the safety gap or the original exhaust groove under the action of pressure difference. The reason why the gas can be discharged but the injection melt is not discharged is because of the high viscosity and poor fluidity of the injection melt, which requires a higher pressure to be discharged from such small gaps than gas. . Therefore, when setting the safety gap, it is necessary to consider that it can ensure that the injection melt cannot be discharged from the gap under the pressure of the safety chamber. At the same time, under this injection molding process, it is possible to realize molding while injection molding (injection molding part by part), without the need to fill up the injection molding melt before the overall molding, as in the traditional process.

Further, in order to better control the quality of the injection molded product, in the process of pushing back the ejector pin (the injection port is pressed into the injection molding melt at a constant speed), the present invention divides it into multiple stages (according to the return of the ejector pin). The amount of retraction is determined by the arrival of each stage) and the back pressure is gradually adjusted, so as to realize the retraction speed control of the slidable side plate when it reaches the maximum displacement. The position of the screw corresponding to the maximum displacement is the pressure holding switching point, that is, the V/P switching point. Therefore, after step S5, the steps are also included:

S51: Obtain the screw position (s1) after the pressure holding and the actual screw stroke of the current injection mold;

S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value, if yes, go to step S53, if not, go to the next injection mold after opening the mold according to the decreasing adjustment of the current back pressure and return S1 step;

S53: Adjust the retraction speed of the ejector rod under the action of adjusting the retraction distance ratio of each stage by adjusting the back pressure of each stage in the next injection molding cycle, enter the next injection molding cycle after mold opening and return to step S1.

In consideration of control cost and program stability, this embodiment takes three-stage back pressure (N=3) as an example for illustration. When the melt is injected into the cavity and reaches a certain pressure, it starts to press back the ejector rod, record the screw position A ₀ at this time, and then perform the first stage of retreat according to the first preset back pressure value, when returning to the second stage At the initial position, it will retreat according to the second preset back pressure value. At this time, record the screw position A ₁ . When it returns to the starting position of the third stage, it will retreat according to the third preset back pressure value. Record the screw position A ₂ at this time, and record the screw position A ₃ when it returns to the maximum displacement of the ejector rod. At this time, it also means that the melt injection phase at a constant speed is over, and it is necessary to enter the pressure holding phase.

When the pressure holding phase is over, the screw position s1 is obtained, then the actual stroke s of the current mode screw = s1-s0. In order to control the weight of injection molded products, the ideal injection screw stroke s' for the weight of qualified plastic products is generally preset. However, since the ideal injection screw stroke for the first trial mold cannot be accurately determined, the density calculation formula can be used:

ρ=M/V

V＝πd ² /(400*s ^′ /10)

Available,

s ^′ =(4000M)/(kρπd ² )

In the formula, M is the total mass of the target injection molded part, k is the coefficient, ρ is the room temperature density of the injection material, and d is the screw diameter.

By comparing the ratio of the actual screw stroke and the ideal screw stroke to the ideal screw stroke, it is considered that an adjustment is required when the preset value is exceeded. At this time, if s>s', the back pressure value of each stage should be appropriately increased according to the preset formula to slow down the final retraction speed of the ejector pin, and if s<s', the value of each stage should be appropriately reduced according to the preset formula The value of the back pressure to increase the final retraction speed of the ejector pin. The preset formula is as follows:

Pn _m ＝(A _n -A _n+1 )/(A ₀ -A _N )*(s/s ^′ )*Pn _m-1

In the formula, n is a constant from 0 to N, m is the number of modes, N is the total number of stages, Pn _m is the back pressure value of the nth stage in the mth mode, _An is the screw position of the nth stage, A _{n +1} is the screw position of the n+1st stage, A ₀ is the screw position when the slidable side plate starts to displace under the action of material pressure, A _N is the screw position of the last stage of the current mold, Pn _m-1 is the first The back pressure value of the nth stage of the m-1 model.

Through the preset formula, the ejector pin back pressure value at each stage is automatically adjusted mold by mold until the weight of the injection molded product is qualified, and then the actual screw stroke of the qualified injection molded product is formally replaced with a fixed ideal injection screw stroke. After that, the actual screw stroke of each mold continues to be compared with the fixed ideal screw stroke, and the thimble back pressure value is continuously fine-tuned to ensure sufficient exhaust of plastic products, and at the same time make the quality and quality more stable.

Embodiment two

In order to better understand the technical content of the present invention, this embodiment illustrates the present invention in the form of a system structure, as shown in Figure 2, a control device for back pressure exhaust of an injection molding machine, including:

The slidable side plate is set on the ejector rod, which can slide with the ejector rod, and controls the sliding position in the mold cavity under the action of the ejector pin;

A safety gap is left on the contact surface between the slidable side plate and the mould;

The main control chip is used to control the thimble to press the slidable side plate and make it slide to the initial position after obtaining the confirmation signal that the injection molding machine is closed to the bottom;

The injection module is used to control the injection of the injection melt into the mold cavity at a constant speed through the injection port when the slidable side plate is slid to the initial position, and to control the injection of the injection melt into the mold through the injection port at a preset holding pressure after entering the holding pressure stage Cavity;

The thimble proportional back pressure valve is used to control the top pressure of the slidable side plate on the thimble. Control the cavity pressure in the mold cavity to be within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement position;

The displacement sensor is used to obtain the retraction amount of the ejector pin during the injection molding process.

Furthermore, when the pressure of the thimble proportional back pressure valve is under the pressure of the safety chamber, the injection melt cannot be discharged through the safety gap under the action of the melt viscosity.

Further, in the process of controlling the thimble by the thimble proportional valve, the position of the screw at the maximum displacement of the slidable side plate is the pressure-holding switching point.

To sum up, the method and device for controlling the back pressure exhaust of an injection molding machine according to the present invention control the retraction speed of the ejector rod through the regulation of the back pressure, so that the injection pressure can be increased without increasing the injection pressure. The pressure in the cavity is higher than the cavity pressure during normal injection molding, so that the gas in the injection melt can be discharged through the safety gap under high pressure with the help of better fluid properties than the injection melt, realizing molding while injection molding.

By adjusting the retraction speed, the actual stroke of the screw is adjusted, so as to better control the quality of the finished product and reduce the scrap rate caused by unstable weight.

It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relationship between the components in a certain posture (as shown in the accompanying drawings). Relative positional relationship, movement conditions, etc., if the specific posture changes, the directional indication will also change accordingly.

In addition, in the present invention, descriptions such as "first", "second", "one" and so on are used for descriptive purposes only, and should not be understood as indicating or implying their relative importance or implicitly indicating the indicated technical features quantity. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In the present invention, unless otherwise specified and limited, the terms "connection" and "fixation" should be understood in a broad sense, for example, "fixation" can be a fixed connection, a detachable connection, or an integral body; It can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediary, and it can be an internal communication between two elements or an interaction relationship between two elements, unless otherwise clearly defined. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

In addition, the technical solutions of the various embodiments of the present invention can be combined with each other, but it must be based on the realization of those skilled in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered as a combination of technical solutions. Does not exist, nor is it within the scope of protection required by the present invention.

Claims (10)

1. A control method for back pressure exhaust of an injection molding machine, characterized in that the ejector pin is provided with a slidable side plate that can slide with the ejector pin, and the slidable side plate can be pressed by the ejector pin The sliding position is controlled in the mold cavity, and a safety gap is left on the contact surface between the slidable side plate and the mold, which specifically includes the steps of: S1: After obtaining the confirmation signal that the injection molding machine has closed the mold to the bottom, press the slidable side plate through the thimble and make it slide to the initial position, and record the screw position in the initial state; S2: Control the injection molding melt to be injected into the mold cavity at a constant speed through the injection port, and obtain the retraction amount of the ejector pin caused by the push back of the slidable side plate under the action of the material pressure; S3: Control the top pressure of the slidable side plate through the thimble proportional back pressure valve, and under the joint pressure of the back pressure and the material pressure, the gas in the injection molding melt is discharged through the safety gap under the action of the pressure difference; S4: Control the cavity pressure in the mold cavity within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement through the control of the back pressure, and record the screw position at the maximum displacement; S5: Control the injection molding melt to be injected into the mold cavity through the injection port with a preset holding pressure. 2. A control method for injection molding machine back pressure exhaust as claimed in claim 1, characterized in that, in the S3 step, the cavity pressure is under the safe cavity pressure, and the injection molding melt is under the effect of melt viscosity Cannot be discharged through safety clearance. 3. A control method for back pressure exhaust of an injection molding machine according to claim 1, characterized in that, in the step S4, the position of the screw at the maximum displacement is the switch point for maintaining pressure. 4. A control method for back pressure exhaust of injection molding machine as claimed in claim 1, characterized in that, in the step S4, in the stage of uniform injection, the gradual adjustment of the back pressure is slidable through several stages The retraction speed of the side plate is adjusted, and the arrival judgment of each stage is carried out according to the retraction amount of the ejector pin. 5. A kind of control method for injection molding machine back pressure exhaust as claimed in claim 4, is characterized in that, also comprises the step after described S5 step: S51: Obtain the screw position after the pressure holding and the actual screw stroke of the current injection mold; S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value, if yes, go to step S53, if not, go to the next injection mold after opening the mold according to the decreasing adjustment of the current back pressure and return S1 step; S53: Adjust the retraction speed of the ejector rod under the action of adjusting the retraction distance ratio of each stage by adjusting the back pressure of each stage in the next injection molding cycle, enter the next injection molding cycle after mold opening and return to step S1. 6. A kind of control method for injection molding machine back pressure exhaust as claimed in claim 5, is characterized in that, in described S52 step, actual screw stroke is expressed as following formula: s=s1-s0 In the formula, s is the actual screw stroke, s0 is the screw position in the initial state, and s1 is the screw position after the end of pressure holding; The ideal screw stroke is expressed as the following formula: s ^′ =(4000M)/(kρπd ² ) In the formula, s' is the ideal screw stroke, M is the total mass of the target injection molded part, k is the coefficient, ρ is the room temperature density of the injection material, and d is the screw diameter. 7. A control method for injection molding machine back pressure exhaust as claimed in claim 6, characterized in that, in the step S53, the adjustment of the back pressure at each stage is expressed as the following formula: Pn _m ＝(A _n -A _n+1 )/(A ₀ -A _N )*(s/s ^′ )*Pn _m-1 In the formula, n is a constant from 0 to N, m is the number of modes, N is the total number of stages, Pn _m is the back pressure value of the nth stage in the mth mode, _An is the screw position of the nth stage, A _{n +1} is the screw position of the n+1st stage, A ₀ is the screw position when the slidable side plate starts to displace under the action of material pressure, A _N is the screw position of the last stage of the current mold, Pn _m-1 is the first The back pressure value of the nth stage of the m-1 model. 8. A control device for back pressure exhaust of an injection molding machine, characterized in that it comprises: The slidable side plate is set on the ejector rod, which can slide with the ejector rod, and controls the sliding position in the mold cavity under the action of the ejector pin; A safety gap is left on the contact surface between the slidable side plate and the mould; The main control chip is used to control the thimble to press the slidable side plate and make it slide to the initial position after obtaining the confirmation signal that the injection molding machine is closed to the bottom; The injection module is used to control the injection of the injection melt into the mold cavity at a constant speed through the injection port when the slidable side plate is slid to the initial position, and to control the injection of the injection melt into the mold through the injection port at a preset holding pressure after entering the holding pressure stage Cavity; The thimble proportional back pressure valve is used to control the top pressure of the slidable side plate on the thimble. Control the cavity pressure in the mold cavity to be within the safe cavity pressure range before the slidable side plate retracts to the maximum displacement position; The displacement sensor is used to obtain the retraction amount of the ejector pin during the injection molding process. 9. A control device for back pressure exhaust of an injection molding machine as claimed in claim 8, characterized in that, when the pressure of the thimble proportional back pressure valve is under the pressure of the safe cavity, the injection melt is in the melt Due to the viscosity, it cannot be discharged through the safety gap. 10. A control device for back pressure exhaust of injection molding machine according to claim 8, characterized in that, during the process of the thimble proportional valve controlling the thimble, the position of the screw at the maximum displacement of the slidable side plate That is, the switch point of the holding pressure.

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