Long Cycle Time
Causes, Solutions & Prevention in Injection Molding
Cycle time is the total time for one complete injection molding cycle. Extended cycle time reduces productivity and increases cost.
Below you will find general information about this defect. To get a pinpoint solution tailored to your specific machine, material, and process parameters using the world’s most comprehensive injection molding troubleshooting database — sign up and access AI-powered troubleshooting, 7 engineering calculators, and detailed project tracking.
🔍Symptoms & Visual Identification
⚠️Root Causes by Category
🧪 Material
- Regrind granule size too large and unsuitable
🏭 Machine
- Mold open/close times too long
🗂 Mold Design
- Hot runner nozzle design issue
🔧 Mold Condition
- Mold underwent modification
✅Solutions & Corrective Actions
🧪 Material
- Granulators have 3 screen types. If the largest screen is selected, regrind particle size can reach 8-10 mm vs original 3 mm granule size. This causes bulk density differences and affects parameters. The smallest screen hole size should be selected to minimize variation.
🏭 Machine
- Machine open/close unit speed is important for cycle time reduction. This time is longer on hydraulic machines.
🗂 Mold Design
- When selecting hot runner nozzle design, cooling systems should be chosen. For visual concerns, only point marks are acceptable on the part surface. The correct choice is a cooled-tip hot runner. The hot runner area heats up significantly during production and extends cycle time. An alternative solution is to route a circular cooling channel around the hot runner in the mold body with an independent circuit.
🔧 Mold Condition
- Mold modifications invalidate the original cooling analysis. The modification area sometimes cuts through water channels or changes the distance of channels to the surface. A mold that maintains its cycle time and flow profile after modification is virtually nonexistent.
🛠Step-by-Step Troubleshooting
Verify Material Condition
Granulators have 3 screen types. If the largest screen is selected, regrind particle size can reach 8-10 mm vs original 3 mm granule size. This causes bulk density differences and affects parameters. The smallest screen hole size should be selected to minimize variation.
Check Machine Settings
Machine open/close unit speed is important for cycle time reduction. This time is longer on hydraulic machines.
❓Frequently Asked Questions
What causes long cycle time in injection molding?
Long Cycle Time is caused by several factors including: Regrind granule size too large and unsuitable; Mold open/close times too long; Hot runner nozzle design issue; Mold underwent modification.
How do you fix long cycle time in injection molding?
Start by checking key parameters: Cooling time, Mold temperature, Injection speed, Ejection sequence. Granulators have 3 screen types. If the largest screen is selected, regrind particle size can reach 8-10 mm vs original 3 mm granule size. This causes bulk density differences and affects parameters. The smallest screen hole size should be selected to minimize variation.
Which plastics are most affected by long cycle time?
Common materials include: PP, PA6, PE, ABS, PC. Pay special attention to drying, shrinkage and mold temperature for each grade.
How do I prevent long cycle time in future production runs?
Prevention relies on three pillars: (1) process optimisation — verify Cooling time, Mold temperature; (2) mold maintenance — check gates, vents and cooling channels; (3) material control — ensure correct drying and virgin/regrind ratio.
What is the difference between long cycle time and similar defects?
Cycle time cannot be reduced. Production output lower than calculated. This distinguishes it from related surface defects during visual inspection.
📐Related Calculators
Run these engineering calculators to verify your process parameters and prevent this defect.
🔗Related Defects
About MBPlastiPro
Built by injection molding engineers, for injection molding engineers. MBPlastiPro combines decades of hands-on production floor experience with AI technology to help you solve defects faster, optimize processes, and deliver better parts.