Solution to long injection molding cycle
The injection molding cycle refers to the time required to complete the entire injection molding process, including mold closing, injection, pressure holding, cooling, mold opening, and ejection. Excessively long cycles directly reduce production efficiency and increase production costs. In large-scale production, every 1-second reduction in the molding cycle can increase the output of dozens to hundreds of products per shift (8 hours). Therefore, optimizing the molding cycle is crucial to improving economic efficiency. The reasons for a long molding cycle are usually related to factors such as cooling time, injection speed, pressure holding time, and mold design. For example, cooling time accounts for 50%-70% of the entire molding cycle. If the cooling system is not designed properly, it will lead to excessive cooling time, becoming a bottleneck restricting production efficiency.
Optimizing the cooling system is crucial for shortening the molding cycle. The mold cooling system must be designed to ensure uniform and efficient cooling. First, cooling channels should be arranged appropriately based on the product shape, ensuring a uniform distance from the cavity surface (typically 15-25 mm). Channel diameters should generally range from 8-12 mm. For products with thicker walls, contoured channels or conformal cooling can be used to improve cooling efficiency. Controlling the flow and temperature of the cooling medium is also crucial. It is recommended to use a chiller to provide constant-temperature water at 5-15°C, with a flow rate of 5-10 L/min. This ensures turbulent flow within the channels (Reynolds number > 4000) to enhance heat transfer. For complex cavities, beryllium copper inserts can be placed in difficult-to-cool areas. This utilizes beryllium copper’s high thermal conductivity (approximately 200 W/(m · K) , 3-5 times that of ordinary mold steel ) to accelerate heat transfer. In addition, the cooling time can be reduced by increasing the number of cooling water channels, adopting series or parallel water channel design, etc. For example, shortening the cooling time from the original 30 seconds to 20 seconds can reduce the entire molding cycle by 10 seconds.
Optimizing injection and holding pressure parameters can effectively shorten filling and holding times. Slow injection speeds can increase melt filling time. Adjust the injection speed based on part thickness and flow length. For thin-walled parts, high-speed injection (50-100 mm/s) can reduce filling time. For thick-walled parts, use staged injection, initially filling the cavity to 70%-80% at a low speed, then filling to full capacity at a high speed to avoid bubbles and burning. The injection pressure should be determined based on melt flowability and part complexity. While ensuring full filling, minimize injection pressure and reduce pressure transfer time. Excessive holding time can increase molding cycle time. Experimentation can be used to determine the minimum holding time, which is the time at which part weight no longer changes with increasing holding time. Typically, the holding time is 1/3-1/2 of the cooling time. For example, if the cooling time is 20 seconds, the holding time can be set to 7-10 seconds. Furthermore, the holding pressure can be decreased in a stepwise manner, starting high and then decreasing. This ensures both dimensional stability and shortens the holding time.
Improvements in mold structure and equipment performance play an important role in shortening the molding cycle. The opening and closing speed of the mold directly affects the auxiliary time. The speed can be increased by optimizing the mold guide mechanism and adopting a quick mold change system. For example, the opening and closing time can be shortened from the original 5 seconds to 3 seconds. The design of the ejection system must ensure smooth demolding of the product, and adopt efficient ejection mechanisms (such as ejector plate ejection and inclined ejection) to reduce ejection and reset time. In terms of equipment, a servo injection molding machine with a fast response speed is selected. Its pressure and speed control accuracy during the injection and holding stages is higher, and the response time is shorter (usually <0.1 seconds). Compared with traditional hydraulic injection molding machines, it can shorten the molding cycle by 5%-10%. In addition, a mold temperature controller is used to accurately control the mold temperature to avoid unstable cooling time caused by temperature fluctuations. For example, controlling the mold temperature fluctuation within ±1°C can ensure the consistency of the cooling time.
The application of automation and auxiliary systems can reduce non-productive time. Using a robotic arm to automatically remove parts can reduce the time it takes to remove a part to 2-3 seconds, significantly reducing the 5-10 seconds required for manual removal. This also allows for fully automated production and reduces human intervention. Cavity pressure sensors installed on the mold monitor the melt filling and holding process in real time. Closed-loop control adjusts process parameters to avoid cycle times extended by improper parameter settings. For multi-cavity molds, sequential valve gate (SVG) technology can be used to control the filling order of each cavity, ensuring simultaneous filling and holding, reducing overall molding time. Furthermore, management measures such as optimizing production plans, reducing mold change times, and implementing rapid mold change technology (such as a 3-minute mold change) can improve equipment utilization and indirectly shorten the molding cycle per unit product. For example , one company reduced its molding cycle from 45 seconds to 30 seconds by comprehensively optimizing its cooling system, injection parameters, and automated part removal, resulting in a 33% increase in production efficiency and millions of yuan in additional annual output value.
