Basic Operation Knowledge Of Injection Molding Machine

I. injection molding machine

When the mold tester completes the test of a set of molds, it is necessary to fill in the injection data recorded in the mold test report so that the production conditions of the injection molding machine can be adjusted according to the recorded data in the report. However, the time for the tester to use the injection molding machine is often very short because of the pressure of production.

Therefore, when they are tested under the condition of lack of time, the parameters of the plasticized products are likely not to provide trouble free production.

The term "trouble free production" means that the reject rate in production is the least (for example, less than 0.5%). The appearance, size and performance of most of the finished products can meet the requirements, and the production capacity index and production performance index required by the household are also achieved.

The first task of a successful injection factory must be to meet the demands of its customers in the most economical and efficient way.

The source of his huge profits must also start with correctly setting the production conditions of injection molding machines.

Since the production conditions have been fixed, production must be smooth and the profits must be maintained.

When we analyze any injection cycle, we can find some special features.

It is in each injection cycle that certain time periods affect productivity, while other time paragraphs affect the quality of the product.

To separate these features, we need to identify and list the components of a plastic injection cycle.

Because the mold used to produce injection parts is called "the heart of the production process" (it can also be considered that the mold is controlling the overall product quality and production stability), the following cycle components are related to the injection mold.

The elements that make up the injection cycle are: mold closure, mold locking, mold filling, mold pressure holding, mold cooling, mold opening and mold delay (also known as intermediate time).

hypothesis

1. mold closure -- the injection molding machine's clamping system is responsible for closing the mold, and the clamping system can be direct hydraulic elbow bar type.

2. mold locking - when the mold is closed, the clamping system of the injection molding machine also provides the force for locking the mold, depending on the projection area of the construction plastic and mold cavity.

3. the injection device or the injection table makes the forward movement (assuming that the injection platform needs to be moved back and forth every week to facilitate the main channel to take out the die cavity or the main injection wire bushing).

4. mold filling screw forward to melt into the mold cavity, screw is usually not rotating when advancing, because the screw front of the melt is not much, so the pressure loss is relatively small.

In the whole screw stroke, there may be several changes in screw propulsion speed (injection speed) to achieve satisfactory product quality.

5. mold pressure keep the screw moving forward for a certain distance, and it is almost stationary when the pressure is behind it. (or the speed of forward movement is very slow, and it is not easy to detect at the time. This distance is from the forward position of screw injection to the position of pressure keeping conversion). At this time, the injection pressure has been changed to a two lower pressure (i.e. pressure keeping pressure); the signal of pressure conversion can produce self limiting system, induction system, stroke converter or pressure pducer.

The pressure switch points are always set when the cavity is filled with 95=98%.

The use of two lower pressures not only reduces the need for the injection molding machine to operate energy, but also reduces the weight and internal stress level of the finished product. It also changes the weight of the finished product slightly (low internal stress level makes the finished product intensity higher). A section of molten material in front of the screw is called the "screw pad" when the mold is in the holding stage.

The length of these screw pads should be appropriately adjusted to ensure stable and sufficient pressure pfer.

Generally in less injection molding machines, 3mm (0.118in) screw padding is available, while larger injection molding machines use 9mm (0.354in) screw padding.

6. mold cooling - the following series of events will take place at this stage:

A) the screw rotates the plastic to the front of the screw tip, produces pressure and pushes the screw back, when the screw is turned back.

The back stroke of the screw provides the amount of glue needed to produce the injection parts. When the point is back to a certain point, the screw will stop (the stop signal can come from the limit system, induction system or stroke converter).

We can adjust the pressure acting on the back of the screw (called back pressure) to make the screw back a certain difficulty, so as to improve the plasticizing ability of the screw and improve the uniformity of the melt.

The rotational speed of the screw and the proper back pressure value depend on the type of plastic used in the construction, but the values of the two are suitable as low as possible.

B) when the screw is stopped, the screw is pulled away for a short distance to remove the pressure of the front melt. This action is called "screw reset" or "pressure relief".

It prevents the phenomenon of melt leakage in the nozzle area, and obtains a stable ejection amount. The use of the screw reset method can avoid the use of the closed nozzle.

C) the injection device (injection platform) moves backward for a distance (e.g. 6mm/0. 236in), making the main road easier to detached.

D) when the above actions are going on, the heat of the melt in the mold cavity is continuously draining away from the mold, and the cooling channel is the cooling pipe of the mould, and the coolant in the mold is circulating the heat continuously.

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7. mold opening - when the set cooling time is completed, the die is opened again and the finished product is ejecting. Most of the injection molding machines are equipped with an oil pressure stick system, allowing the setting of the strength, speed and frequency of the top stick to meet different application needs.

8. mold delay (middle time) - the mold remains open, allowing the finished runner to fall out of the mold area or be removed by other device.

For semi-automatic production cycle (injection molding machine is completed after the production cycle to automatically stop), the middle time timer is still working as usual to ensure the stability of the cycle.

When the die is opened, the intermediate time will start to calculate. After setting the value, the mold will close immediately.

Two. Consideration of productivity and product quality.

The above mentioned mold filling, holding and cooling stages are very important for the quality of injection molding products.

The velocity of the melt entering the mold cavity is then formed under pressure (continuously new melt enters the mold cavity to compensate the volume shrinkage of the melt).

Finally, the high temperature at which the initial temperature of the melt begins to decrease at a specific cooling rate to the temperature that the workpiece can be ejecting from the mold cavity determines the distortion and other important quality factors of the finished product.

The melt that has been injected into the mold cavity must be prepared again. Therefore, during the cooling stage of the mold, the screw and the cylinder of the injection molding machine will soften the injection and deliver it to the front end of the screw under certain conditions, so that it can be used in the next cycle.

The parameter values of the screw and the ejection cylinder are also reflected in the quality of the finished product.

As for the opening and closing of other moulds and the stages of intermediate residence time, they are all related to productivity.

The setting of each stage reflects the technical level and proficiency of the die operator or production personnel.

These three periods of time affect the whole weekly production time and affect the production volume of each class.

If we compare how the different injection operators of a company set the production parameters of a mold, we can find that the most important difference is the speed of opening and closing of the die.

If these time differences seriously increase the injection cycle and make the whole week time exceed a specified number, operators usually reduce the production cycle time to a reasonable level by shortening the cooling time. This method is highly improper and can make the finished product quality worse.

If we can reasonably analyze and correct these production stages, the quality of the products will be ensured.

The most advanced technology of injection molding machine provides microprocessor and / or computer controlled injection molding machine.

They are equipped with a display device to report the actual production stages, such as mold opening time, closing time, and mold opening stroke. These values are updated once a week. Each control parameter can set the upper and lower limit to ensure that the production conditions can be controlled within the set range, and the quality and stability of the finished product can be guaranteed.