In the molding process of medical plastic parts, inserts play a crucial role. Inserts, namely metal or non-metal parts embedded in medical injection molds, become an integral and non-detachable part of the medical plastic component. Typically, these inserts are made of metallic materials. In different medical plastic parts, inserts serve various functions; they can enhance the local strength, hardness, wear resistance, electrical conductivity, and magnetic permeability of the medical plastic parts, as well as improve the dimensional stability of the parts and reduce material consumption.

However, the use of inserts is not without drawbacks. Incorporating inserts often increases the cost of medical plastic parts, complicates the mold structure, and may reduce production efficiency. Therefore, multiple factors need to be considered when designing inserts for medical plastic parts.

Among these, the secure connection between the insert and the medical plastic part, the reliability of insert positioning during the molding process, the stability of insert fixation, and the strength of the medical plastic part are all aspects that require special attention during the design process. The key to addressing these issues lies in the fit between the insert structure and the medical plastic part.

Due to the significant difference in thermal contraction rates between metal inserts and medical plastic parts during cooling, metal inserts exhibit minimal shrinkage during the molding process, while plastics show noticeable shrinkage. This difference in shrinkage leads to internal stress in the plastic around the insert. Improper design can cause deformation or even cracking of the medical plastic part.

The magnitude of internal stress is closely related to factors such as the insert material, plastic properties, differences in plastic shrinkage rates, and the insert structure. Therefore, in the design of medical plastic parts with inserts, material selection and design are particularly important.

In terms of material selection, we should prioritize plastics with high elasticity and low shrinkage rates or choose metal inserts with shrinkage rates similar to those of the plastic to minimize the generation of internal stress. In terms of design, it is necessary to ensure that the plastic layer around the insert is sufficiently thick to effectively prevent cracking of the medical plastic part. At the same time, the design of the insert should avoid sharp corners, and changes in shape should be in the form of bevels or rounded corners to reduce stress concentration. Additionally, through-holes should be avoided on the insert to prevent plastic from being squeezed into the holes during the molding process, which could affect the performance and appearance of the part.