Is it better to have a higher glass fiber content? Analysis of mold life problems caused by excessiv

In the selection of engineering plastics, glass fiber reinforced nylon is generally considered to have higher strength, lower deformation, and higher reliability. At the beginning of the project, the design team often believed that increasing the glass fiber content was a simple solution: if GF30 was not enough, they considered using GF40 or higher grade steel. However, actual production experience increasingly shows that excessive reinforcement can introduce underestimated systemic risks, especially those related to mold wear, unstable processing, and long-term production cost increases. . In an automotive electronic casing project, PA66 GF30 material was initially selected. Due to the risk of deformation under high temperature vibration, the glass fiber content is increased to GF40. Although the bending modulus increased by about 25% and the coefficient of thermal expansion further decreased, the mold suffered severe wear after six months of mass production. The rapid deterioration of the gate and cavity surfaces resulted in surface defects and premature mold refurbishment, ultimately delaying the delivery schedule.

From the perspective of material mechanics, the advantages of glass fiber do not necessarily manifest linearly beyond a certain threshold. When the fiber content exceeds a certain threshold, this advantage will disappear. The interaction between 30-40% fibers is significantly enhanced. During high shear injection molding, the fiber ends with insufficient resin coating will repeatedly contact the surface of the mold steel, resulting in micro cutting wear. This type of wear will gradually accumulate and concentrate in the sprue, runner, and thin-walled areas.
Processing data shows that under the same mold and processing conditions, the mold wear rate of PA66 GF40 is 1.6-1.8 times higher than that of GF30, especially in high flow areas. In addition, high glass fiber systems require higher injection pressure and speed, further exacerbating the wear effect.

In addition to mechanical wear, excessive reinforcement can also accelerate the thermal fatigue of the mold. The decrease in thermal uniformity can lead to an increase in temperature gradient within each forming cycle, thereby increasing the risk of microcrack initiation, especially in standard H13 or P20 tool steels.

Industrial experience has shown that many failures are not caused by insufficient material strength, but by excessive reliance on high glass fiber content. In a connector application, increasing the fiber content from PA66 GF35 to PA66 GF50 shortened the mold life from the expected 800000 cycles to less than 300000 cycles, resulting in an increase of over 20% in implicit manufacturing costs. Ultimately, the selection of glass fiber content should strike a balance between structural performance, processing stability, and manufacturing economy, rather than blindly pursuing the maximum degree of reinforcement effect.