In the rapidly developing era of modern manufacturing, precision injection molds, as the core equipment for the production of plastic products, their structural design directly determines the precision, quality, and production efficiency of the products. From the micro-components of 3C products to the special parts in the aerospace field, every detail of the mold structure undertakes the precision pursuit of industrial manufacturing. The following is an analysis of the basic framework and core components of the mold.
The basic framework of a precision injection mold consists of a moving mold and a fixed mold. The fixed mold is fixed on the fixed template of the injection molding machine, and the moving mold is installed on the moving template. The two achieve precise opening and closing through a guiding system:
When closing the mold, the moving mold and the fixed mold form a closed cavity and a gating system to provide a molding space for the plastic melt;
When opening the mold, the molded product is demolded with the help of an ejection system. This structure needs to meet the micron-level matching accuracy. In the context of intelligent manufacturing in the new era, by simulating the mold opening and closing process with digital twin technology, the contact stress distribution of the moving and fixed molds is optimized to avoid precision attenuation caused by long-term use.
The gating system is a key channel connecting the injection molding machine and the cavity, including:
Main Runner: It closely matches the nozzle of the injection molding machine, and the taper design (usually 1° to 3°) takes into account the fluidity of the melt and the convenience of demolding;
Sub-Runner: It has an equidistant and symmetrical layout to ensure the uniform distribution of the melt to multiple cavities;
Gate: The type is selected according to the characteristics of the product. For example, a pin gate is commonly used for mobile phone casings, and a side gate is used for large household appliance parts to ensure the filling speed.
In the new era, the design of the gating system has achieved "digital twin preview". By simulating the pressure loss and temperature field changes of the melt with CAE software such as Moldflow, the optimization accuracy of the gate position can reach ±0.05mm, so that the wall thickness tolerance of large products such as automobile bumpers can be controlled within 0.02mm.
The molding parts include the cavity (female mold), the core (male mold), and the molding inserts, which determine the shape and size of the product:
For high-precision parts such as mobile phone middle frames, the surface roughness of the cavity needs to reach Ra0.02μm (the arithmetic mean deviation of the profile is 0.02 micrometers). After aging treatment, the deformation after quenching is controlled within 5μm (5 micrometers);
In the new era, 3D printing technology is used for the manufacturing of complex cores. For example, the selective laser melting (SLM) process is used to manufacture conformal cooling cores, which improves the heat dissipation efficiency by 40% and solves the problem of special-shaped water channels that are difficult to achieve with traditional processing.
The temperature regulation system maintains the constant temperature of the mold by means of cooling water channels or heating elements, and the design matches the characteristics of the plastic:
When processing PC materials, the mold temperature is controlled at 80 to 120 degrees Celsius, and for PE materials, it is 40 to 60 degrees Celsius;
The intelligent temperature regulation system in the new era realizes closed-loop control. Optical fiber sensors are implanted in key parts of the mold to monitor temperature fluctuations in real time (with an accuracy of ±0.5 degrees Celsius), and the water flow rate is adjusted by a servo valve to stabilize the shrinkage rate of automobile lampshades within 0.3%.
The venting system avoids defects such as scorching and material shortage of the product due to poor venting. The design points are:
Venting grooves (usually with a depth of 0.01 to 0.03mm) are set on the parting surface and at the root of the core;
Porous steel inserts (with 20 to 30μm micropores) are used for complex parts such as micro gears, reducing the injection defect rate from 5% to 0.1%;
With the application of the vacuum-assisted venting system, the air residue in the cavity is controlled below 0.5%.
The guiding system is composed of guide pillars and guide bushes to ensure the coaxiality of the moving and fixed molds during mold closing (with a tolerance of ≤0.005mm):
For large molds, a composite guiding structure of "guide pillar + precision positioning pin" is adopted, combined with self-lubricating bearings, which can withstand a lateral force of more than 500kN;
The intelligent guiding system in the new era integrates displacement sensors to monitor the position accuracy of mold opening and closing in real time, and an alarm is triggered when the deviation exceeds 0.01mm.
The ejection system balances the contradiction between the demolding force and the deformation of the product:
Elements such as ejector pins, ejector plates, and angle ejectors are arranged according to the "equal force distribution" principle;
For fragile parts such as curved screens, a gas-liquid linkage ejection technology is used. Through progressive pressure control of 0.1MPa, the impact force during demolding is reduced to below 5N;
The visual inspection system at the ejection position can automatically identify the deviation of the product and adjust the stroke of the ejector pin in real time.
With the advancement of Industry 4.0, the structure of precision injection molds is undergoing a transformation of "modularization + intelligence":
The modular design enables the rapid replacement of components such as the cavity and the gating system, reducing the mold change time by 60%;
The built-in sensor network collects data such as temperature, pressure, and vibration in real time, and transmits it to the cloud analysis platform via the industrial Internet to realize predictive maintenance.
The structural design of precision injection molds integrates the precision of mechanical engineering and the innovation of intelligent manufacturing. From the precise cooperation of the basic framework to the efficient coordination of the core systems, it undertakes the mission of product precision and production efficiency. In the wave of Industry 4.0, the trends of modularization and intelligence break through the boundaries of traditional molds, making them evolve into "intelligent manufacturing units". In the future, with the deepening of materials, digital twin and other technologies, molds will evolve towards "more precision, more intelligence, and more environmental protection", providing competitive support for high-end manufacturing, empowering the development of industries such as automobiles, electronics, and aerospace, and interpreting the manufacturing charm of "millimeter-level design, micrometer-level realization".
