How to master the injection molding machine within 30 days? You need to master the basic operating knowledge of the following injection molding machines.
Knowledge of injection molding machine adjustment:
After the mold tester has finished testing a set of molds, it is necessary to fill in the obtained injection data on the test mold record report so that in the future, the record data on the report can be used to adjust the production conditions of the injection molding machine, but Often due to production pressure, the time that testers can use injection molding machines to try out molds is very short. Therefore, they conduct mold trials under the condition of insufficient time, and the parameters of the cleaning conditions obtained may not be able to provide trouble-free production conditions.
The first task of a successful injection molding machine manufacturer must be to meet its customers' requirements in the most economical and efficient way. The source of his huge profits must also start from the correct setting of the production conditions of the injection molding machine. Because once the production conditions are set, the production will be smooth and the profit will be maintained.
When we analyze any injection cycle, we can find some characteristics. That is, in each injection molding cycle, certain time periods affect productivity, while other time periods affect product quality. In order to distinguish these characteristics, we need to identify and list the constituent elements of an injection molding cycle. Since 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 all related to the injection mold. The elements that make up the injection cycle are: mold closing, mold locking, mold filling, mold holding pressure, mold cooling, mold opening, and mold delay (also known as intermediate time).
Assuming that the injection molding machine is a direct-injection type of screw for producing thermoplastics, and the injection molding machine has just completed a certain cycle at this time, the following is the operation sequence of the injection molding machine:
1. Mold closing-the mold clamping system of the injection molding machine is responsible for closing the mold, and the clamping system can be a direct hydraulic toggle type.
2. Mold locking-after closing the mold, the clamping system of the injection molding machine also provides the force to lock the mold. The force depends on the projected area of the construction plastic and the cavity.
3. Move the injection device or injection table before manufacturing (assuming that the injection table needs to reciprocate once a week to facilitate the main runner to escape from the mold cavity or the main spout wire cover).
4. Mold filling-the screw advances forward to send the melt into the mold cavity. The screw usually does not rotate when advancing. Because there is not much melt in front of the screw, the pressure loss is relatively small. During the entire screw stroke, the screw advancing speed (injection speed) may change several times in order to obtain satisfactory quality.
5. Mold holding pressure-after the screw moves forward for a set distance, it almost stays still under pressure on the back (or the speed of moving forward is very slow, which is not easy to detect at the time, this distance is from the screw injection The front position to the holding pressure conversion position), the injection pressure at this time has been converted to a lower secondary pressure (ie holding pressure); the pressure conversion signal can be generated from the limit system, the induction system, the stroke converter or the pressure conversion Device. The pressure transition point is usually set when the cavity is filled with 95=98%. The use of lower secondary pressure not only reduces the need for operating energy for the injection molding machine, but also reduces the weight and internal stress level of the finished product, and can also make the weight change of the finished product slightly (lower internal stress level makes the finished product stronger). The section of melt in front of the screw during the mold holding stage is called "screw gasket". The length of these screw pads needs to be adjusted appropriately to ensure stable and adequate pressure transfer. Generally, 3mm (0.118in) screw spacers can be used on fewer injection molding machines, and 9mm (0.354in) screw spacers can be used for larger injection moulding machines.
6. Mold cooling-in this stage the following series of things will happen:
a) The screw rotates and pushes the plastic to the front of the screw tip, and generates pressure to push the screw back. At this time, the screw retreats while rotating. The screw retreat stroke provides the amount of glue required to produce the injection parts. When it retreats to a certain point, the screw stops rotating (the stop signal can come from a limit system, an induction system or a stroke converter). We can adjust the pressure acting on the back of the screw (called back pressure) to make the screw retreat a certain degree of difficulty, thereby improving the plasticizing ability of the screw and improving the uniformity of the melt. The rotation speed of the screw and the value of the back pressure depend on the type of plastic to be constructed, but the values of the two should be as low as possible.
b) After stopping the rotation, the screw is pulled back a short distance to relieve the pressure of the previous melt. This action is called "screw reset" or "pressure relief". It prevents the leakage of molten material at the injection nozzle, thereby obtaining a more stable injection volume, and the screw reset method can avoid the use of closed injection nozzles.
c) The injection device (injection table) moves back a certain distance (for example, 6mm/0.236in) to make it easy to detach the main runner.
d) When the above actions are in progress, the heat of the molten material in the cavity is continuously draining away from the mold. The channel for heat dissipation is the cooling pipe of the mold, and the cooling liquid in it is circulated continuously to take away the heat.
7. Mold opening-when the set cooling time is completed, the mold is opened again and the finished product is ejected. At present, most injection molding machines are equipped with hydraulic ejector system, which allows the setting of ejector force, speed and number of times. Can meet the needs of different applications.
8. Mold delay (intermediate time)-the mold remains open, allowing the finished product runner to fall out of the mold range or be taken away by other equipment.
Knowledge of productivity and product quality considerations:
The above-mentioned mold filling, holding pressure and cooling stages are very important to the quality of injection molded products. The speed at which the melt enters the mold cavity and then forms under pressure (new melt enters the mold cavity constantly to compensate for the volume shrinkage of the melt). Finally, the high temperature at the beginning of the melt temperature is reduced at a specific cooling rate to the temperature at which the injection can be ejected from the mold cavity, which determines the degree of distortion of the finished product and other important quality factors. The molten material previously injected into the mold cavity must be prepared again. Therefore, during the mold cooling stage, the screw and the injection cylinder device of the injection molding machine soften the injection molding and transport it to the front end of the screw under a certain set condition for downloading. One cycle use. The parameter values used by the screw and the injection cylinder when storing materials are ultimately reflected in the quality of the finished product.
As for the opening and closing of other molds and the stages of intermediate residence time, they are all related to productivity. The setting of the time of each stage reflects the technical level and proficiency of the mold operator or production staff. The setting of these three periods affects the production time of the whole week and the production quantity of each shift. If we compare how different injection molding operators of a certain company set the production condition parameters of a certain mold, we can find that the most important difference is the speed of the opening and closing distance of the mold. If these time differences severely increase the injection cycle time and make the full cycle time much more than a specified amount, the operator generally reduces the production cycle time to a reasonable level by shortening the cooling phase time-this method is extremely unacceptable Properly, the quality of the product will deteriorate. If we can reasonably analyze and correct these production stages and time, the quality of the products can be ensured.
Lisong Machinery's injection molding machine technology provides a microprocessor and/or computer-controlled injection molding machine. They are equipped with a display to report the time of each actual production stage, such as mold opening time, mold closing time, mold opening stroke, etc. These values are updated once a week, and each control parameter can set upper and lower limits to ensure production Condition parameters can be controlled within the set range, and the quality and stability of the finished product can be guaranteed.