Precision injection molds are core equipment for the production of high-precision plastic products. Their design and manufacturing directly determine product quality and production efficiency. Compared to conventional injection molds, precision injection molds have more stringent requirements in terms of dimensional accuracy, surface roughness, and structural stability. For example, for precision plastic parts used in electronic connectors, medical devices, and other fields, the mold cavity dimensional tolerance must be controlled within ±0.005mm, and the surface roughness must be below Ra0.02μm. This requires the mold material to have extremely high hardness and wear resistance. Pre-hardened alloy structural steel or powder high-speed steel is usually selected, and multiple heat treatments are performed to enhance the material properties.
The structural design of the mold is a key step in precision injection molds, and factors such as melt flow, cooling uniformity, and smooth demolding must be fully considered. In terms of cavity layout, a symmetrical design is often used to ensure consistent filling speed and pressure distribution of the melt in each cavity, reducing dimensional deviations in the plastic parts. At the same time, the mold’s guide mechanism must utilize high-precision ball guide pins and guide bushings, with a clearance controlled between 0.001-0.003mm to avoid wear on the cavity due to misalignment during mold closing. Furthermore, the design of the exhaust system is particularly important. Precision molds typically feature 0.01-0.02mm exhaust grooves at the parting surface, core, and cavity to ensure timely discharge of gas from the cavity and prevent defects such as bubbles and burning in the plastic parts.
The processing technology used in precision injection molds has a decisive influence on their accuracy. From blank to finished product, multiple processes are required, including CNC milling, EDM, wire cutting, and grinding. Each process requires strict control of machining errors. For example, during EDM of the mold cavity, a high-precision servo system and pulse power supply are required to ensure surface roughness and dimensional accuracy, while multiple electrode corrections are performed to eliminate machining errors. Grinding requires the use of high-precision surface and cylindrical grinders, equipped with diamond grinding wheels, to control the flatness and cylindricity of mold parts to within 0.001mm/m. Furthermore, the mold assembly process must be carried out in a constant temperature workshop to prevent thermal expansion and contraction of parts caused by temperature fluctuations from affecting assembly accuracy.
The design of the mold’s cooling system is crucial for ensuring the dimensional stability of precision plastic parts. Due to the thin walls and complex shapes of precision plastic parts, uneven cooling can easily lead to inconsistent shrinkage, resulting in warping, deformation, and other problems. Therefore, the cooling channels of precision injection molds must be in close contact with the cavity surface, with spacing controlled between 15-25mm. The channel diameter should be adjusted based on the thickness of the part, typically 8-12mm. Furthermore, the cooling channels must be connected in series or parallel to ensure consistent cooling water flow and temperature across all parts. For uniquely shaped cavities, custom-shaped cooling channels can be created using custom-shaped channels or 3D printing technology to further improve cooling efficiency and uniformity.
The maintenance and care of precision injection molds are crucial to extending their service life and ensuring production stability. During daily use, the molds need to be cleaned regularly to remove residual plastic and oil from the cavity and prevent corrosion on the mold surface. Also, the mold’s guide mechanism, ejector mechanism, and other moving parts should be inspected, and lubricant should be added promptly to prevent loss of precision due to wear. Mold consumable parts, such as sprue bushings and ejector pins, should be replaced regularly to ensure their performance meets requirements. Furthermore, molds should be rust-proofed during storage and placed in a dry, ventilated environment to prevent moisture, high temperatures, and other factors from affecting mold precision. Only by properly maintaining and servicing the molds can we ensure that precision injection molds consistently produce high-quality parts.
