Parallelism Control Specification for Parting Surfaces of Stack Molds
Stack molds adopt double-layer parting surfaces to realize multi-cavity synchronous injection and boost productivity. Their precision requirement for parting surface parallelism, flatness and uniform mold closing is stricter than conventional molds. Excessive parallelism deviation causes uneven clamping stress, local mold opening, mass flash, part indentation, guide pin scratching and template deformation, damaging production yield and mold service life. Standardized full-lifecycle control rules covering machining, assembly, mold trial, mass production and maintenance are formulated to regulate precision management of stack molds.
1. Parallelism Control During Mold Machining Stage
All core plates of stack molds including cavity plates, middle plates and moving plates must undergo precision surface grinding on six sides. Parallelism of each single plate is strictly controlled within 0.002 mm, laying basic precision for individual plates. After machining all plates, stacking re-inspection is carried out and overall parallel error of combined plates shall not exceed 0.005 mm to eliminate height step differences fundamentally. Equal-height cutting is adopted for CNC finishing of parting surfaces with reasonable finishing allowance reserved to avoid uneven plane error caused by local over-cutting and tool marks. Integral grain-direction polishing is applied on parting surfaces with gradually changing abrasive grits, prohibiting local heavy grinding and concave formation which break plane precision. Guide pin holes are bored once to guarantee perpendicularity between guiding holes and parting surfaces, preventing mold closing offset and non-parallel parting surfaces induced by tilted guiding structures.
2. Parallelism Control During Mold Assembly & Fitting Stage
Stack molds are assembled and inspected layer by layer. After assembling each layer, eight-point measurement with dial indicators is performed on precision platforms to test parting surface parallelism. Qualified standard for single-layer parting surface parallelism is ≤0.003 mm, and overall parallelism of double-layer closed molds is controlled within 0.006 mm; rework adjustment is required once tolerance is exceeded. Red lead coloring fitting is adopted to verify fitting degree, requiring effective fitting ratio above 98% on parting surfaces, with slight non-fitting areas only allowed at vent positions. Fine grinding is only permitted on local bright gaps during fitting, and large-area polishing of parting surfaces is forbidden to avoid destruction of overall plane precision. Hammering and forced mold closing are prohibited during assembly to prevent invisible parallelism deviation caused by twisted templates. After installing clamping structures, feeler gauges are used to check stress uniformity at four corners to ensure synchronous fitting and uniform stress distribution of double-layer parting surfaces.
3. Parallelism Control During Mold Trial & Machine Installation Stage
Horizontal level of injection molding machine platen must be calibrated before mounting molds, and mold locking bolts are tightened diagonally in batches to prevent plate tilting caused by unilateral stress. Low-speed slow mold closing is executed first after installation to verify parallelism data of two parting surfaces, and formal mold trial can start only after passing inspection. Clamping force rises stepwise during trial runs, mold deformation status under different pressures is recorded, and safe clamping pressure range is confirmed to prevent parting surface tilt induced by high-pressure deformation. Product status is observed closely during trial molding: continuous unilateral flash, local incomplete filling and uneven indentation act as warning signs, and mold shall be shut down immediately to recheck parallelism deviation. Parallelism test data after qualified trial runs are archived as reference benchmark for subsequent mass production and maintenance inspection.
4. Parallelism Control During Mass Production Stage
Periodic precision inspection is arranged during continuous production: stop production to check fitting status and parallelism value of parting surfaces every 2000 molding cycles. Uniform mold temperature control is enforced to keep temperature difference of the entire mold below 5℃, avoiding plane offset caused by thermal deformation from uneven temperature distribution. Once abnormal phenomena including persistent unilateral flash, overheated guide pins and abnormal mold clamping noise occur in production, halt operation to inspect parallelism of parting surfaces. Clamping pressure must be released during standby downtime, and long-term high-pressure locked mold state is forbidden to prevent plastic deformation of templates and deterioration of parallel precision gradually. Overloaded production and ultra-high clamping force are banned permanently, as long-term overload degrades parting surface precision continuously.
5. Parallelism Repair Rules During Maintenance & Refurbishment Stage
When molds are taken offline for maintenance, carbon deposits, plastic residues, oil stains and rust on parting surfaces are cleaned thoroughly, followed by parallelism measurement and data recording in ledgers. If parallelism deviation ranges from 0.004 mm to 0.008 mm, overall surface grinding is conducted to remove deformed layers slightly and restore plane precision. Plates with deviation over 0.008 mm or structural deformation and concave areas must be replaced directly, and leveling with copper sheets or gaskets is strictly forbidden, which causes uneven stress and accelerated precision degradation. Worn guide pins and guide sleeves shall be replaced in complete sets, and mixed use of new and old accessories leads to guiding offset and secondary misalignment of parting surfaces. After mold refurbishment and re-fitting, multi-point inspection and low-speed mold opening/closing verification must be repeated, and molds can be put back into mass production only after all precision indicators reach standards. Long-term stored stack molds are kept half-clamped inside constant-temperature dry warehouses instead of unilateral stressed placement to prevent plate deformation, and all parallelism inspection data are filed to track precision variation trend of molds.
Conclusion
Parallelism management for parting surfaces of stack molds covers the full lifecycle of machining, assembly, trial molding, mass production and maintenance. Basic plane precision of individual plates and stacked molds is guaranteed during machining, uniform fitting of double-layer parting surfaces is realized via eight-point inspection and red lead fitting in assembly phase, safe clamping parameters are locked during trial molding to avoid deformation risks after installation, periodic inspection, temperature control and standardized operation maintain stable mold precision during mass production, and standardized repair instead of illegal gasket leveling preserves long-term precision in maintenance stage. Strict implementation of this control specification eliminates defects including flash, part indentation and guide pin scratching for stack molds effectively, improves finished product yield, extends mold service life and gives full play to high-efficiency multi-cavity production advantages of stack molds.
