Injection molding process for protective cases — 2026 B2B guide

# Injection molding process for protective cases — 2026 B2B guide Injection molding is the dominant production process for plastic protective cases (PP, ABS, HD-PE). This B2B guide covers machine types, mold design, process parameters, cycle time, and quality control for buyers evaluating suppliers. ## Machine types by tonnage ### Small cases (< 400×300×200mm) - Machine: 50-200 ton clamping force - Shot weight: 100-500 g - Cycle time: 25-45 seconds - Kexin uses: Haitian Mars II 90T, 150T, 200T - Cavitation: 1-2 per mold (for low MOQ flexibility) ### Medium cases (400-600mm) - Machine: 250-500 ton - Shot weight: 500-1,500 g - Cycle time: 45-90 seconds - Kexin uses: Haitian 380T, 500T - Cavitation: 1 per mold (large parts) ### Large cases (> 600mm, e.g. 9-series HD trolley) - Machine: 800-1,600 ton - Shot weight: 2,000-5,000 g - Cycle time: 90-180 seconds - Kexin uses: Haitian 1,200T, 1,600T - Special: 2-shot molding for hard-soft combinations ## Mold design basics ### Cavity count trade-off - 1 cavity: lowest mold cost (USD 3,000-5,000), slowest production (5-10 sec per shot, total cycle = single cycle) - 2 cavities: balanced, USD 5,000-8,000, 50% faster than 1-cavity - 4 cavities: USD 10,000-15,000, 75% faster but requires precise flow balance - 8+ cavities: high-volume only (10,000+ pieces), USD 25,000+, requires hot runner system Kexin default: 1 cavity for OEM (low MOQ flexibility), 2 cavities for ODM/White-label ### Mold material - P20 steel: standard, 200,000-500,000 shots lifetime - H13 steel: pre-hardened, 1M+ shots, higher cost - S136 stainless: medical/food grade, corrosion-resistant - Aluminum: prototype only, 5,000-10,000 shots ### Cooling channels - Conformal cooling (3D printed): -30% cycle time, +50% mold cost - Standard drilled channels: baseline - Beryllium copper inserts: for hot spots, +USD 2,000-5,000 per insert ## Process parameters ### Temperature - PP: melt 200-260°C, mold 20-60°C - ABS: melt 220-260°C, mold 40-70°C - HDPE: melt 200-240°C, mold 20-50°C - Mold temperature: critical for surface finish, warpage, cycle time ### Pressure - Injection pressure: 800-1,500 bar (typical) - Holding pressure: 30-60% of injection, 5-15 seconds - Back pressure: 5-30 bar (controls melt homogeneity) ### Speed - Injection speed: 30-100 mm/s (faster = better surface, more flash risk) - Screw speed: 50-150 rpm (plasticizing) ## Cycle time breakdown | Phase | Duration | Variables | |-------|----------|-----------| | Mold close | 2-5 s | Clamp speed | | Injection | 1-3 s | Shot size, pressure | | Holding | 5-15 s | Part thickness | | Cooling | 15-60 s | Wall thickness, mold temp | | Plasticizing | 5-15 s | Screw design, melt temp | | Mold open | 2-3 s | Ejector design | | Part ejection | 1-2 s | Automation | | **Total** | **30-100 s** | | ## Quality control checkpoints ### IPQC (in-process) - Every 50 shots: visual + dimensional check (3-5 key dimensions) - Every 200 shots: full AQL 2.5 sample (50 pieces) - Every shift: Cpk verification on critical dimensions ### Critical dimensions to monitor - Wall thickness: ±0.3mm typical tolerance - Latch force: 8-15 N (depending on series) - Hinge torque: 5-10 N (depending on series) - Color: ΔE ≤ 3.0 vs. Pantone reference - Surface finish: SPI-A2 to SPI-B3 (Ra 0.2-1.6 μm) ## Common defects and solutions ### Sink marks (depressions on thick sections) - Cause: insufficient packing pressure, too short hold time - Solution: increase holding pressure +20%, add cooling time ### Flash (excess material at parting line) - Cause: clamp force too low, worn mold - Solution: reduce injection speed, check clamp tonnage, polish mold surfaces ### Weld lines (visible flow fronts meeting) - Cause: low melt temperature, slow injection - Solution: increase melt temp +10°C, faster injection ### Warpage - Cause: uneven cooling, residual stress - Solution: longer cooling time, balanced mold temperature, annealing ### Short shots (incomplete filling) - Cause: insufficient material, low pressure, blocked gates - Solution: increase shot size, check gate cleanliness ### Burn marks (dark spots) - Cause: trapped air, excessive injection speed - Solution: add venting, reduce speed ## Cycle time optimization Kexin 2026 best practices: - Conformal cooling on high-volume molds: -25% cycle time - Hot runner system: -15% cycle time + no runner waste - Servo-electric machines: -20% energy + faster response - Parallel operations: insert + eject during closing ## Material flow analysis Kexin uses Moldflow simulation for: - Gate location optimization - Weld line prediction - Cooling time estimation - Warpage prediction - Pressure drop calculation ## Recycled material processing - 35% rPP in 6-series: requires melt filtration (60-100 mesh), cycle time +10% - 50% r-aluminum in 8-series: aluminum is machined, no melt processing - Bio-PP: slightly higher melt viscosity, +5°C melt temp ## Industry 4.0 / smart manufacturing - Real-time process monitoring (pressure, temp, position) - Statistical process control (SPC) dashboards - AI defect detection via vision system (5 cameras per line) - Predictive maintenance (vibration analysis on tie bars) - MES (Manufacturing Execution System) integration Kexin: 4 of 6 injection lines have Industry 4.0 monitoring (2026 plan: 6 of 6) ## Capacity calculation example 500 pieces of 8-series 5023 (500×350×230mm, 1.2kg shot weight): - Cycle time: 75 seconds (with conformal cooling) - Available hours: 16h/day × 2 shifts × 30 days = 960h/month = 57,600 min/month - 1-cavity mold: 57,600/75 = 768 shots/month = 768 pieces - 2-cavity mold: 1,536 pieces/month - For 500 pieces delivery: 1-cavity works (less than 1 month) ## B2B buyer checklist When visiting a factory, ask: - [ ] How many injection lines? (5+ for serious factory) - [ ] Machine age? (5-10 years is fine; > 15 years is concerning) - [ ] Clamp tonnage range? (covers all series you need?) - [ ] Hot runner availability? (essential for high-volume) - [ ] In-house mold maintenance? (vs. outsourced) - [ ] Mold storage capacity? (5,000+ molds for serious OEM) - [ ] Cpk data on critical dimensions? (target Cpk ≥ 1.33) - [ ] First pass yield (FPY)? (target ≥ 95%) - [ ] Internal scrap rate? (target < 2%) - [ ] Industry 4.0 monitoring? (best practice but not required) ## Bottom line Injection molding is a mature process; the differentiator for B2B buyers is: 1. **Cycle time** (drives unit cost) 2. **Cpk** (drives quality) 3. **Mold maintenance** (drives delivery reliability) 4. **Capacity** (drives MOQ flexibility) Kexin offers 6 injection lines (90T-1,600T), 95% FPY, 1.8% scrap, in-house mold maintenance, and 4/6 lines with Industry 4.0 monitoring as of 2026.