Appropriate Pressure Control Method For Injection Molding Machine

Proper control of the required pressure can produce quality and reasonable finished products.

The rotational motion is pformed into linear motion through the ball bearing screw used in the machine tool industry.

The efficiency of the whole process depends partly on the plasticizing process. Screw plays a key role.

In the process of producing the full motor type, the newest solution of Mitsubishi Co includes a screw rod (second screw holding roller) and a screw tip tip with mixing elements.

In this way, the plasticizing capacity and mixing effect can be maximized, the screw length can be shortened, and the high speed operation can be realized.

This process can be controlled by backpressure adjustment to avoid overheating.

Mixing elements can not produce excessive flow rate, otherwise, the polymer will be degraded.

Each polymer has different maximum flow rates. If this limit exceeds, the molecules will stretch and the main chain break will occur.

However, the emphasis is still on controlling the forward axial movement of the screw during injection and packing.

Subsequent cooling processes, including internal stress, tolerance and warpage, are important for ensuring product quality.

All of this is determined by the quality of the die, especially when optimizing the cooling duct and ensuring effective closed loop temperature regulation.

The system is completely independent and will not interfere with mechanical adjustment.

Die movement such as closing and ejection must be precise and efficient.

Speed distribution curves are usually used to ensure that the moving parts are accurately approached.

The contact maintenance force can be adjusted.

Therefore, it can be concluded that without considering energy consumption and mechanical reliability and the same conditions (such as mold quality), the quality of the product is mainly determined by the system in which the control screw moves forward.

In an oil injection molding machine, this regulation is achieved by detecting oil pressure.

Specifically, the oil pressure activates a set of valves through the control panel. The fluid acts through the manipulator and is adjusted and released.

The open loop system relies on a proportional valve.

The proportional tension is applied to the required ratio of fluid so that the pressure is generated in the injection barrel and the injection screw moves at a certain forward speed.

The closed loop proportional valve is adopted in the semi closed loop system.

The loop closes at the location of the closed port, and the closed port controls the flow rate of the oil through the movement of the valve.

The closed-loop system closes at the screw plation speed.

The speed sensor (usually potentiometer type) is adopted in the closed loop system, and the tension drop is detected at regular intervals.

Proportional valve outflow of oil can be adjusted to compensate for the speed deviation.

Close loop control relies on special electronic components integrated with machine.

Closed loop pressure control ensures uniform pressure at injection and holding stages, and ensures uniform backpressure in all cycles.

The pressure value is adjusted to compare with the example valve, and the deviation compensation is made according to the set pressure value.

Generally, hydraulic pressure can be monitored. However, it is another effective method to detect melt pressure in nozzle or mold cavity.

A more reliable solution is to manage the valve by reading the nozzle or the pressure reading of the mold cavity.

Increasing temperature detection on the basis of pressure detection is especially advantageous for process management.

Knowing the actual pressure of material can also help predict the actual weight and size of moulded parts according to the set pressure and temperature conditions.

In fact, by changing the holding pressure value, more materials can be introduced into the mold cavity to reduce the shrinkage of parts and meet the design tolerances (including preset injection shrinkage).

Near the melting condition, the semi crystalline polymer shows a great change in specific capacitance.

Overcharging will not impede the ejection of components.

In other stages of the cycle, the requirements are significantly lower, except for specific situations requiring rapid plasticization (for example, PET injection injection blow molding one-step injection molding machine).

The fixed displacement pump moves the same amount of oil at each rotation. Therefore, the selection of the oil pump depends on the amount of oil needed to move in a specified time.

The speed of the three phase motor is usually 1440 revolutions / points.

Only in the plasticizing process (power up to 100%) can the utilization rate of the oil pump reach the maximum.

In the pause process, machinery does not need energy consumption, and even if necessary, it is also a power loss.

Two or more proportional valves are installed on the injection press to control the following aspects:

Screw rotation speed (level 3-5).

The auxiliary motor sends the amplified signal (output signal) to the valve through a weak input signal, so that the servo valve performs adjustment function.

In servo valves, weak input electrical signals are converted into hydraulic output signals, which are improved according to the required discharge requirements in the form of pressure drop.

Valves must be fast, repeatable and low delay discharge response to tension or general instructions.

In fact, the purpose of the current research is to improve the frequency response, so that the power equipment (hydraulic side) running at several thousand Hz (kHz) frequencies and electronic devices can be dialoged.

Because the effective discharge depends on the degree of polymerization (DP) on the valve, the oil temperature in the hydraulic circuit must be kept within 45-55 C (usually closed loop regulation system), depending on the fluid viscosity and the geometry of the crossing.

There is no proper adjustment system in the valve. The temperature rise will lead to the decrease of viscosity of the solution. If the balanced opening threshold is fitted, the discharge volume can be increased.

Increasing the oil output of the pmission system means that the injection speed will accelerate.

Accurate control of high tech servo drive valve can basically eliminate hysteresis and enhance repeatability of all functions.

Therefore, load sensors are usually used to measure elastic deformation by extensometer, so as to directly measure their strength.

All electric injection molding machine manufacturers have developed various elastic parts and assembled corresponding extensometer.

Another difference is that the back pressure and its control can be achieved by increasing the resistance to axial movement generated by the injection motor, while the other motor causes screw rotation and subsequent material plasticization.

In the past, some mechanical manufacturers used the measuring system installed in the nozzle pducer, and later abandoned the system because of the lack of functionality and reliability.

Therefore, the accuracy and repeatability of pressure detection is a key factor.

In closed loop system, pressure detection is very important. Only by ensuring accurate pressure detection can the regulator make the actual pressure close to or equal to the set value.

In open loop systems, the accuracy and repeatability of pressure detection are more important because they are directly connected to the pmission system.

Now, the open loop system is still in use, and it is more widely used in high tonnage models.

Generally speaking, the speed control based on the set value is carried out in the injection process (that is, the speed change is measured by potentiometer or magnetic contraction sensor), and then converted to pressure regulation.

Access can be initiated on the basis of quotas (quota access) or pressure.

In any case, when the pressure start path is also used as a "cutting edge" to limit mold filling pressure, prevent overflow formation and mold damage, pressure starting path must be used.

Once the pathway is formed, the subsequent pressure holding process is regulated by pressure (profiles are no exception).

The pressure of the hydraulic press is usually detected in the hydraulic circuit, seldom in the die mouth.

For injection molding, the probe must be close to the mold cavity as far as possible.

Therefore, the mold pressure measurement is preferably carried out at the nozzle. Even if it is not too direct, pressure measurement can be carried out in the hydraulic circuit.

When the pressure near the injection reaches the set point and keeps the pressure in the time needed for injection, the die pressure detection can be converted.

The measurement can be carried out directly or through a probe (e.g. piezoelectric sensor).

Direct detection in moulds is very effective, and the only limitation is that traces will be left on the moulded parts.

Indirect detection is often affected by the structure and clearance of the probe. For example, the excessive tolerance leads to material dumping and the detection accuracy is not enough.

However, nozzle pressure detection has some advantages, mainly including: detection is carried out on materials; there is no need to remold the mold; no trace is left on the molded part.

The melt pressure control (preferably in the die cavity) avoids the risk of excessive mold filling (subsequent spillage) at initial pressure.

Thus, the effectiveness of the control can be enhanced, the material scorch can be avoided, the mold filling insufficiency can be prevented, the cycle time can be shortened, and the repeatability can be enhanced.