Injection Molding Machine Injection Unit and Maintenance - Advanced Plastic Processing Technology for Precision Injection Molding
The injection unit is the device that heats and melts the resin material and injects it into the mold. As shown in the figure, the resin is squeezed into the barrel from the hopper, and the melt is transported to the front end of the barrel through the rotation of the screw. During this process, the resin material in the barrel is heated by the heater, and the resin becomes molten under the shear stress of the screw. The molten resin equivalent to the molded product, main runner, and sub-runners is retained at the front end of the barrel (called metering), and the continuous forward movement of the screw injects the material into the mold cavity. When the molten resin flows in the mold, the movement speed of the screw (injection speed) must be controlled, and after the resin fills the mold cavity, it is controlled by pressure (holding pressure). When the screw position and injection pressure reach a certain value, we can switch from speed control to pressure control.
How to maintain injection molds?
1. Processing companies should first equip each mold with a history card, which records and tracks its usage, maintenance (lubrication, cleaning, rust prevention), and damage in detail. This information can be used to identify which parts and components are damaged and the degree of wear, providing information for identifying and solving problems, as well as the molding process parameters and materials used for the product. This shortens mold trial time and improves production efficiency.
2. Processing companies should test the various performance of the mold under normal operation of the injection molding machine and mold, and measure the dimensions of the final
Molded Plastic Parts. This information can be used to determine the current state of the mold and identify damage to the cavity, core, cooling system, and parting surface. Based on the information provided by the plastic parts, the damage status of the mold and repair measures can be determined. 3. Several important components of the mold should be closely monitored and inspected: The function of the ejection and guiding components is to ensure the opening and closing movement of the mold and the ejection of the plastic parts. If any part is jammed due to damage, it will lead to production stoppage. Therefore, the mold ejector pins and guide pins should be kept lubricated at all times (the most suitable lubricant should be selected), and the ejector pins and guide pins should be regularly checked for deformation and surface damage. If any damage is found, they should be replaced promptly; after completing a production cycle, the working surface, moving parts, and guiding components of the mold should be coated with professional anti-rust oil. Special attention should be paid to the protection of the bearing parts of molds with gears and racks, and the spring strength of spring molds, to ensure that they are always in the best working condition; as production time continues, scale, rust, sludge, and algae are easily deposited in the cooling channels, reducing the cross-section of the cooling channels and narrowing the cooling passages, which greatly reduces the heat exchange rate between the coolant and the mold, increasing production costs. Therefore, cleaning of the cooling channels should be given attention; for hot runner molds, the maintenance of the heating and control system is particularly important to prevent production failures. Therefore, after each production cycle, the band heaters, rod heaters, heating probes, and thermocouples on the mold should be measured with an ohmmeter. If any are damaged, they should be replaced promptly, and compared with the mold history record, and records should be kept to identify problems in a timely manner and take corresponding measures.
4. The surface maintenance of the mold should be emphasized, as it directly affects the surface quality of the product. The focus is on preventing rust, so choosing a suitable, high-quality, and professional anti-rust oil is particularly important. After the mold completes its production task, the residual plastic should be carefully removed according to different injection molding methods. Copper rods, copper wires, and professional mold cleaning agents can be used to remove residual plastic and other deposits in the mold, and then air-dried. Hard objects such as iron wires and steel bars should not be used for cleaning to avoid scratching the surface. If there are rust spots caused by corrosive injection molding, a grinding machine should be used for grinding and polishing, and then a professional anti-rust oil should be sprayed on. The mold should then be stored in a dry, cool, and dust-free place. Strategic Approach to Scientific Process Development
Process validation is a critical step in the development cycle; only after validation can the mold and product be considered suitable for production. During this process, scientific molding principles should be applied to determine the nominal operating conditions for a given mold, material, etc.
Scientific injection molding involves a series of steps aimed at determining process parameters such as nominal fill time, injection pressure, gate freeze time, holding pressure, cycle time, and clamping force. Subsequently, key process parameters are typically tested using Design of Experiments (DOE) to find the optimal process window that can be reliably reproduced in each production run.
