Acceptance Standard for Clean Machining of Medical Plastic Molds
Most medical plastic products are applied in sterile assembly scenarios or directly contact human body and liquid medicine, which impose strict limits on plastic precipitates, particulate contamination, mold rust and residual oil contamination. Cutting fluid, polishing dust and metal debris generated by conventional mold machining processes may transfer to finished plastic products, leading to excessive particles and precipitation risks. Therefore, independent clean processing and finished mold acceptance standards must be formulated for medical molds, covering full procedures including machining, cleaning, polishing, assembly and inspection.
1. Acceptance Requirements of Raw Materials and Blank Preprocessing
Corrosion-resistant mirror-finish stainless steel is preferred for mold steel, including common grades S136 and STAVAX. Complete material quality certification documents such as material analysis reports shall be provided, and steel grades containing harmful precipitating elements are prohibited. Visual inspection is implemented for blanks after arrival; rust, interlayers, cracks and pinholes are not allowed on surfaces. Degreasing cleaning must be finished before blank cutting to remove rolling anti-rust oil; blanks carrying oil are forbidden to enter CNC finishing procedures. Atmosphere environment shall be controlled during heat treatment to avoid oxide scale formed on cavity surfaces. Stabilization treatment is carried out after heat treatment to release internal stress and prevent surface peeling during long-term service. All molded component blanks are stored in separated zones and isolated from ordinary mold workpieces to avoid cross contamination.
2. Cleanliness Control Acceptance for CNC and EDM Machining
Sulfur-free, chlorine-free and silicon-free special cutting fluid shall be adopted for CNC finishing; ordinary industrial emulsified liquid is prohibited. Uniform polishing allowance is reserved on molded surfaces after finishing, and metal chips must be cleared immediately after machining to prevent long-term adhesion on cavities. High-purity copper electrodes are used for EDM processing, and low-impurity dedicated EDM oil serves as working fluid. Sufficient flushing is conducted on narrow gaps of cavities after machining. Surface white layers must be removed after electric discharge, and carbon residues and erosion debris trapped inside gaps are not permitted. Molded surfaces of workpieces are covered with protective film during transportation, and placed on plastic pallets. Direct contact with iron tooling platforms shall be avoided to prevent rust spots and metal debris. Visual inspection is required for acceptance: molded surfaces are free from collision pits, oil stains and carbon deposits.
3. Cleanliness Environment Acceptance Specifications for Polishing Procedures
Polishing operations shall be conducted in relatively enclosed areas with low dust concentration, and operation environment needs regular cleaning. Silicon-free, low-precipitation oil stones, sandpaper and polishing compound are selected as polishing consumables. Polishing additives containing silicon are forbidden, to prevent silicon residue resulting in foggy spots and precipitation risks on plastic products. Stepwise polishing shall be followed strictly, and dust generated during grinding shall be cleaned timely. Simple cleaning is required for workpieces after each grade of sandpaper replacement. No residual polishing compound shall be embedded in tiny textures on molded surfaces after polishing. Recycled old sandpaper and worn oil stones cannot be used for processing medical mold cavities. Inspection adopts strong light side lighting detection after polishing; molded surfaces are free from scratches, orange peel textures and embedded dust, and no grinding residues are trapped in gaps of parting surfaces and inserts.
4. Acceptance Criteria for Multi-stage Cleaning Procedures
All molded parts, ejector pins, inserts, slides and other accessories shall undergo standardized multi-stage cleaning before assembly. The first stage is ultrasonic alkaline cleaning to remove grease and organic contaminants. The second stage is pure water rinsing to wash away residual cleaning agents. The third stage is low-temperature hot air drying, and water stains left by water evaporation are forbidden. Narrow gaps and ejector pin holes as well as cooling channels are flushed by high-pressure pure water. Cleaning solvent needs regular replacement to avoid secondary adhesion of impurities inside solution. Dried workpieces cool down in clean environment and shall be assembled quickly; exposed placement duration is strictly controlled. Acceptance requirements include no water stains, oil film and white spots on component surfaces, and no solid particles trapped inside gaps. Wiping test is implemented: no visible dirt and metal powder are left on clean white paper after wiping molded surfaces.
5. Clean Assembly and Full Mold Clamping Acceptance Conditions
Anti-static soft rubber mats are laid in assembly zones. Cleanroom wipes, plastic and copper tooling are equipped; steel tools cannot directly strike molded surfaces. Assembly operators keep hands clean and can wear dust-free gloves during operations. Mold cavities, sliding ways and cooling water channels are purged again before assembly to eliminate iron scraps and sandpaper debris. Medical mold dedicated high-temperature grease is used for sliding positions with appropriate dosage; excessive grease easily seeps out and contaminates mold cavities. Repeated mold opening and closing movements are carried out after assembly, followed by disassembly re-inspection to confirm wear debris generated during movement cannot fall into molding zones. The whole mold is purged and cleaned after assembly, and cooling channels are verified for smooth flow. Key acceptance inspection targets narrow gaps between inserts, ejector pin fitting clearances and slide blind areas to confirm no foreign solid impurities exist.
6. Comprehensive Final Inspection and Protection Acceptance
Full-scale inspection is carried out after overall mold cleaning. Mold cavities are checked thoroughly under strong light. If available, blank injection test can be adopted to judge residual contaminants by surface status of plastic components. Silicon-free, low-precipitation dedicated anti-rust agent is used for molded surface rust prevention, sprayed uniformly in thin layers instead of thick accumulation. Protective film covers all molded surfaces; paper materials cannot be stuffed directly inside mold cavities. The whole mold adopts independent clean moisture-proof film for outer packaging. Documentation acceptance is conducted simultaneously, including steel certification, heat treatment reports and cleaning records, which shall be filed and delivered with molds. If oil contamination or embedded particles are detected, the mold must be returned for re-cleaning and can only pass acceptance after re-inspection.
Conclusion
Clean machining acceptance of medical plastic molds differs from dimensional inspection of conventional molds. Its core control target is eliminating oil contamination, metal particles, grinding residues and silicon pollutants, lowering risks of particulate pollution and chemical precipitation of plastic finished products. Every acceptance node from blank preprocessing, machining, polishing, multi-stage cleaning to assembly and protection restricts mutually. Deficient cleanliness management in any procedure will trigger contamination defects on final products. Strict implementation of the complete clean acceptance standard can satisfy specification requirements of medical device production, reduce defects of particles and stains during trial production, and support long-term stable molding of clean-grade plastic components.
