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Roll Forming Auxiliary Equipment Stable And Highly Reproducible

Jun 05, 2017

Roll Forming Auxiliary Equipment refers to the molding machinery for the production of precision plastic products. For a Roll Forming Auxiliary Equipment, how to measure or judge it?

Usually Roll Forming Auxiliary Equipment has two indicators: First, the product size of the repeated bias; the other is the product of repeated weight deviation. The former because of the size and thickness of the product is difficult to compare; and the latter represents the integrated level of injection molding machine.

General ordinary injection molding machine weight repeat error of about 1%, better machine can reach 0.8%, less than 0.5% for the precision machine, less than 0.3% for ultra precision machine. As mentioned above, Roll Forming Auxiliary Equipment products require dimensional accuracy is generally 0.01 ~ 0.001mm or less.

Many precision injection also requires injection molding machine with:

① high injection pressure, high injection speed;

The clamping system has a large enough rigidity and clamping accuracy. The so-called clamping accuracy refers to the uniformity of clamping force, adjustable, stable and high repeatability, open and close the mold position accuracy;

③ on the pressure, flow, temperature, measurement and so can control the accuracy to the appropriate precision, multi-level injection can be used to ensure the reproduction of the molding process and repeat the accuracy of products.

What are the requirements for precision injection molding on injection molding machines?

1, the technical parameters of the characteristics:

① injection pressure:

Ordinary injection molding machine: 147 ~ 177Mpa; Roll Forming Auxiliary Equipment: 216 ~ 243 Mpa; ultra-high pressure injection molding machine: 243MPa or more, usually between 243 ~ 392 MPa.

Roll Forming Auxiliary Equipment can achieve the benefits of high pressure molding is:

A, to improve the accuracy and quality of precision products.

Injection pressure on the product shrinkage of the most obvious impact, when the injection pressure reached 392 MPa, the product molding shrinkage is almost zero. And then the accuracy of the product only by the mold control or environmental impact. Experiments show that: injection pressure from 98 ~ 392 MPa, the mechanical strength of parts can be increased by 3 to 33%.

B, can reduce the thickness of precision products and improve the molding length.

To PC, for example, the general machine injection pressure of 177 Mpa, can be molded 0.8mm wall thickness of the product, and precision machine injection pressure at 392 MPa can be molded thickness of 0.45mm or more products. Ultra-high pressure injection machine can obtain products with longer flow length.

C, to improve the injection pressure can be full of fat injection rate of efficacy.

In order to achieve the rated injection rate, there are two ways: First, to improve the system maximum injection pressure; the second is to modify the injection device or injection system parameters, including screw parameters;

② injection rate:

Precision injection machine injection speed requirements. Precision hydraulic injection molding machine injection speed requirements to reach more than 200mm / s, all-electric injection molding machine injection rate can reach 300mm / above.

2, precision injection machine in the control of the characteristics:

① the injection molding parameters of the repeat accuracy (reproducibility) requirements, should adopt multi-stage injection feedback control.

1, multi-level position control;

2, multi-level speed control;

3, multi-level pressure control;

4, multi-level back pressure control;

5, multi-level screw speed control.    

Displacement sensor accuracy of at least 0.1mm, so you can strictly control the measurement stroke, injection stroke and the thickness of the remaining pad (injection monitoring point). To ensure that each injection volume is accurate, improve product molding accuracy.

② barrel and nozzle temperature control to be accurate

Temperature control system heating up when the overshoot is small, the temperature fluctuations to be small. Precision injection using PID ratio, integral, differential temperature control, the temperature accuracy of ± 1 ℃ between the ultra-Roll Forming Auxiliary Equipment temperature control accuracy of ± 0.1 ℃, the temperature deviation can be stable control between ± 0.2 ℃.

③ injection molding machine hydraulic oil temperature needs to be controlled

Injection molding machine oil temperature changes lead to fluctuations in injection pressure, hydraulic oil must be used cooling device, the oil temperature stable at 50 ~ 55 ℃ is appropriate.

④ control of the mold temperature requirements

Mold temperature on the latter part of the heat shrinkage has a considerable impact, will also affect the apparent quality of the workpiece and crystallinity, but also affect the mechanical properties of parts. If the cooling time is the same, the thickness of the product having a low mold cavity temperature is larger than the thickness of the product having a high temperature.

3, Roll Forming Auxiliary Equipment hydraulic system

① oil system needs to use proportional pressure valve, proportional flow valve or closed-loop variable pump system.

Injection molding machine hydraulic system need to use proportional pressure valve, proportional flow valve, the system to achieve different working pressure and flow. Whether it is quantitative pump hydraulic system, or variable pump hydraulic system, there are proportional valves to control the pump output pressure and working flow, and to achieve proportional linear adjustment.

② In the direct pressure clamping mechanism, the mold part of the oil and injection part of the oil circuit separately. 

This requirement for direct pressure injection molding machine, because the direct injection molding machine is in the mold after the high pressure from the moment, began to inject the melt, fill the mold cavity. At the same time, there must be oil filling mold clamping cylinder, forming a high pressure clamping.

Otherwise the plate will be due to the filling pressure and expansion of the role of force and back, it is not allowed to happen. This requires the separation of the mold and the oil injection path, otherwise it will occur due to oil filling the mold cylinder and injection cylinder fuel pump overload problem occurs, and will affect the injection speed and system stability.

③ Because of the high speed of Roll Forming Auxiliary Equipment, it is necessary to emphasize the response speed of hydraulic system.

Most of the precision injection molding is done at high ejection and high speed (the connector or the phone key), the filling time is very short, usually only zero seconds, which requires the system to have high response performance, otherwise the response hysteresis, eventually lead to The system output signal and the input signal requirements of the larger deviation of the molding process debugging difficult, the production will also directly affect the size of the workpiece or weight stability.

The high responsiveness of the injection molding machine depends on the scanner's scanning time, the pump's response time, and the oil valve's response time. For the installation of servo valve hydraulic system, in terms of response and repeat the accuracy of a considerable advantage.

For the variable pump injection molding machine, because the pump pressure and flow output, is through the pump swashplate swing angle adjustment, so with high responsiveness and high responsiveness, the pump repeatability can reach 0.2% or less.

④ Roll Forming Auxiliary Equipment hydraulic system, to fully reflect the machine - electric - liquid - instrument integration project.

The current injection molding machine generally use the whole computer control, the function gradually improved, with "man-machine dialogue", fault self-diagnosis, forming status monitoring, SPC quality monitoring and other intelligent functions. Injection molding machine hydraulic system is the action of the injection molding machine dynamic components, the controller is the hydraulic system control center, all kinds of instruments is the machine running status of the auxiliary monitoring part. Injection molding machine is actually machine, electricity, liquid, instrument organic combination of agents.

4, the structural characteristics of Roll Forming Auxiliary Equipment

(1) Due to the high injection pressure of precision injection machine. This requires a high rigidity of the mold clamping system. The parallelism of the movable template is controlled within the range of 0.08 to 0.10 mm.

(2) the need for low-voltage mold protection and clamping force size control accuracy. Because the size of the mold to affect the degree of deformation of the mold, and ultimately to affect the dimensional tolerance of parts.

(3) Kai, closing speed faster, generally about 60mm / s.

(4) plastic parts: screw, screw head, reverse ring, barrel, etc., to design a strong plasticizing ability, a good degree of homogenization, high injection efficiency of the structure; screw drive torque to large, and can be stepless Variable speed.

Injection molding machine to achieve the performance of precision injection molding

As mentioned above, injection molded products have been applied to various fields, widely used to replace the high precision metal parts, which the injection of the dimensional accuracy, quality accuracy, apparent quality and mechanical properties put forward stringent requirements. At the same time, the impact of the quality of injection molding process factors also put forward higher requirements.    

The ideal state of the injection molding machine to control the product is to be able to directly control the product size, quality, apparent quality, mechanical properties of the variable feedback signal feedback control. But for now, these non-electric quantity directly measured and converted into electrical signals have not yet been resolved, so only by controlling the quality of the above-mentioned products can be controlled variable injection molding machine to solve, there are:

(1) screw melt cylinder sections of the temperature, non-periodic signal, generally at least 4-stage heating;

(2) hydraulic oil temperature, aperiodic signal, with conventional thermocouple detection;

(3) screw pre-plastic displacement, with the displacement of electronic scale detection of periodic signals, which leads to the speed signal;

(4) injection system pressure, with strain sensor installed in the injection cylinder, the detection of periodic signals, the determination of injection pressure, pressure and back pressure signal pressure;

(5) screw speed, with the speed sensor to detect screw speed, keep the back pressure constant;

(6) screw back stop position, used to measure the amount of injection, with electronic scale detection;

(7) injection pressure at least 4 set curve and feedback signal detection, the feedback control;

(8) injection speed at least 4 set curve and feedback signal detection, the displacement variable conversion speed feedback, and feedback control.