Strict material selection
Material selection of medical injection molding is very strict, because medical injection molding are completed in the clean room. First, mold materials need stainless steel materials and need to do matching surface treatment such as vacuum heat treatment, PVD coating, laser heat treatment and so on. Plastic materials of medical device products often have medical grade PP, PVC, ABS, PSU, POM, PA, etc., which is high-intensive, corrosive, wear-resistant and high transparent, etc. Requirements for injection mold are relatively high. The commonly used mold steels are imported S136, 2316, S136H, NAK80, etc., to meet high corrosion resistance and high polish ability. Because of large quantity of cavities and large batch size of injection molds for medical consumables, requirement for hardness and wear resistance of injection mold materials are very high. Hardness of the commonly used medical device injection molding steel is suitable around HRC48-56. It can ensure strength of mold and good polishing performance.
Different design requirement of mold forming structure
Design requirements of mold forming structure are also different. There are many transparent parts for medical consumable products. So medical device injection molding should select hot runner as much as possible to reduce the trace of fusion; when using cold runner, soft PVC should minimize size of runner as much as possible; For small size and large batch of disposable medical device products and short run injection molding, automatic unloading and shearing gates should be used to ensure production efficiency and quality; Simultaneously as disposable medical device products and short run injection molding have more transparent tubular parts, so pay attention to gate feeding position during design and dynamic model Z fixed model injection molding assembly, to avoid improper selection of gate location and core fixing method, resulting in uneven material flow during injection molding, elastic deformation of core, uneven product or incomplete filling and uneven wall thickness. Extension tube shape product should adopt appropriate exhaust method. Inlet port runner should open overflow well depending on molding condition of product to avoid product molding difficulties due to closed gas. Mold cooling system should adopt multiple sets of separate cooling channels, reasonable control of dynamic mold temperature to control the deformation of product. In addition, many medical device products involve problem of push-to-seal sealing, so core of medical device injection molding should be designed as straight body rather than designed as a draft angle, and it can ensure that mold release is normal without strain. Therefore, cooling of design should be uniform and can provide higher mold temperature. Surface of core needs to be treated, and special requirements are required on the mold release method to ensure quality and precision of product after injection.
Manufacturing precision of medical injection molding is high, because products are in contact with blood and liquid medicine that entering human body. Injection molding products related to medical equipment are definitely not allowed to have presence of burr, and many of them are directly matched by plastic parts to achieve requirement of sealing and pressure resistance effect and multi-cavity product compatibility. The processing precision of mold core is extremely high, and machining precision of some cores is less than 0.005mm. Surface of mold core is required to ensure that Ra value is more than 0.20. These precisions have basically reached high manufacturing precision of imported precision equipment. Protection and special handling are required on the polishing process of mold.
In general, there is not much difference in the structure between medical injection molding and traditional prototype plastic molding, which is mainly reflected in the control of processing technology and processing precision. Use environment of medical injection molding is relatively harsh.
Prospect of medical injection molding
Development of medical injection molding standard parts and injection molding assembly is of great significance for shortening design and manufacturing cycle of medical device injection molding, reducing cost of mold production, and improving quality of molds. If professional production and commercial supply of mold standard parts can be realized, it will greatly promote development of China or the whole mold industry.
Although China mold industry has made great progress, gap is still large compared with foreign countries. The implementation of specialized production of molds is an important part of accelerating industrial development. In many areas of China, regional mold cities have been established, which has played a positive role in the development of mold industry. For example, Chang’an is a famous town in China’s electronic information industry and a famous town of China’s mechanical hardware molds. It is also the single champion of hardware mold industry in Dongguan. The only “national-level mold quality inspection center” in South China has settled in Chang’an Town. Hafo Mould, established in Dongguan in 1998. specialize in the development of plastic molding, die casting molding, parts production and product assembly.
