Development Process and Compliance Key Points of Injection Molds for Medical Device Housings
1. DFM Review and Locking of Compliance Baseline in the Early Stage
Medical device housings are different from ordinary plastic parts. Some products may contact liquid medicine or human skin, so strict constraints are imposed on material cleanliness, precipitation risk, biocompatibility and batch consistency. Mold development should embed compliance requirements into every development node, forming a traceable control chain from preliminary scheme, processing and assembly, trial mold verification to mass production delivery. At the project initiation stage, it is necessary to clarify the risk level of the device, applicable standards and customer registration requirements, distinguish the control intensity corresponding to Class I, Class II and Class III medical devices, and confirm whether ISO13485 system, FDA, GB4806 and other relevant specifications need to be met.
Commonly used materials for housings include PC, PC/ABS, PP, PEEK and PPSU. The additive system and disinfection resistance of different grades are different, so it is necessary to confirm the subsequent disinfection methods such as ethylene oxide, high-temperature steam, alcohol or hydrogen peroxide. DFM review not only evaluates conventional wall thickness, draft angle, gate and weld line, but also focuses on avoiding dead corners, narrow slits and blind holes that are easy to accumulate dirt, so as to reduce cleaning difficulty and microbial breeding risks. All drawing tolerances, surface roughness and assembly gaps should be sorted out and recorded as the baseline for subsequent mold acceptance.
2. Compliance Considerations in Mold Design Stage
The mold structure shall be designed for easy cleaning and no dead corners. The parting surface, insert joints, ejector pins and sliders shall be simplified as much as possible to reduce tiny gaps that may trap plastic debris and cleaning residues. Hot runner systems are preferred for gating systems to reduce cold runners, waste generation and material degradation caused by long residence in runners. If cold runners are adopted, the runners shall be smooth and easy to disassemble and clean. Corrosion-resistant and easy-to-polish mirror steel such as S136 and STAVAX is selected for mold steel. The surface of the mold shall not adopt easily peelable coatings to prevent coating debris from mixing into products. The cooling water channel shall be arranged evenly to control the internal stress of products, because housings with high internal stress are prone to cracking and excessive precipitation in disinfection environment. All molding parts in contact with plastic shall be equipped with material certificates, part numbers and traceability marks.
3. Processing, Assembly and Cleaning Control
The processing of medical molds shall be isolated from ordinary civil molds to avoid cross-contamination of dust, oil stains and different-color materials. After CNC, EDM and wire cutting, tool marks and carbon deposits shall be removed. The cavity surface shall be polished to high mirror or uniform matte texture without micropores and pits, which may adsorb additives and residues and affect extractables and leachables test results. Clean tools shall be used during assembly, and oil and cutting fluid shall be prevented from contacting the cavity. After assembly, complete degreasing, cleaning and air drying shall be carried out, and dust protection shall be done. The fit clearance of inserts, sliders and ejector pins shall be strictly controlled. Too large clearance will cause flash and debris, while too small clearance will cause jamming and unstable production. All sealing rings of the mold shall be made of materials resistant to disinfection media to avoid aging and precipitation.
4. Trial Mold, Sample Verification and Traceability of Records
Trial molding shall be carried out in a clean workshop or independent clean area. Raw materials shall be dried in accordance with specifications, and the barrel and runner shall be thoroughly purged with special purging materials to avoid residual contamination of other materials. Process parameters shall be fixed during trial molding, and parameters such as melt temperature, mold temperature, injection speed, packing pressure and cooling time shall be completely recorded. All samples shall be marked and isolated by batches. In addition to conventional dimension, appearance and assembly tests, samples shall be sent for extractables, leachables, biocompatibility and disinfection resistance tests according to compliance requirements. If the test fails, it is necessary to evaluate whether the mold surface, joints and steel affect precipitation, and re-sample for verification after rectification. All rectification contents and test reports shall be filed for retention.
5. Mold Identification, Document System and Acceptance Delivery
The complete document package includes mold drawings, material certificates of parts, heat treatment reports, polishing records, cleaning records, trial mold process parameters, sample test reports, cleaning SOP and maintenance specifications. Permanent marks shall be made on the mold body to mark the mold number, product name and cavity quantity for full-life traceability. Acceptance includes hardware acceptance and compliance document acceptance. After acceptance, a mold cleaning procedure shall be formulated to clarify the cleaning method, cleaning agent type and wiping tools before and after each production.
6. Mass Production Maintenance and Continuous Compliance Control
During mass production, the cavity shall be regularly inspected for corrosion, scratches and wear. Thorough purging and cavity cleaning must be carried out before material change, shutdown and production transfer. After mold repair, welding or modification, the mold shall be cleaned again, and re-verification of leachables shall be carried out if necessary. Mold modification records shall be managed in accordance with ISO13485 change process. The mold storage environment shall be dry and clean, equipped with dust covers. Compliance requirements such as cleanliness, traceability and low precipitation shall run through the whole life cycle of medical molds. Only the mutual support of mold design, steel selection, cleaning management and document traceability can stably produce plastic housings that meet medical regulations and registration requirements.
