Injection Cycle Time – Engineering Guide 2026

Introduction to Cycle Time Calculation

Cycle time calculation is the cornerstone of injection molding economics. This critical parameter determines your production capacity, manufacturing costs, and equipment utilization. Whether you're a mold designer estimating project feasibility or a plant manager optimizing existing processes, accurate cycle time prediction saves thousands in development costs and ensures profitable production.

In this comprehensive guide, we'll break down the complete engineering formula for injection molding cycle time, covering cooling time equations, fill calculations, and optimization strategies. We'll provide the mathematical foundation to predict production rates before cutting steel, with specific examples and Tederic machine performance data.

The Four Phases of Injection Molding Cycle

Every injection molding cycle consists of four sequential phases, each contributing to total cycle time:

1. Filling Phase (Injection)

The molten plastic is injected into the mold cavity under high pressure and velocity.

2. Packing Phase (Packing/Holding)

Additional material is packed into the mold to compensate for shrinkage as the plastic cools.

3. Cooling Phase

The plastic solidifies in the mold, typically the longest phase (60-80% of total cycle time).

4. Mold Movement Phase

The mold opens, the part is ejected, and the mold closes for the next cycle.

Understanding each phase's contribution is essential for accurate cycle time calculation and optimization.

The Cooling Time Equation

Cooling time is typically the dominant factor in injection molding cycle time, often accounting for 70-80% of total cycle duration. The cooling time equation is derived from heat transfer fundamentals:

t_cooling = (h²/π²α) × ln(const × (T_melt - T_mold)/(T_eject - T_mold))

Where:

• t_cooling = Cooling time (seconds)
• h = Wall thickness (mm)
• α = Thermal diffusivity (mm²/s)
• T_melt = Melt temperature (°C)
• T_mold = Mold temperature (°C)
• T_eject = Ejection temperature (°C)

Simplified Engineering Formula

For practical calculations, engineers often use the simplified form:

t_cooling = (wall thickness)² × material factor × ΔT factor

Where:

• Wall thickness in mm
• Material factor: PP = 0.8-1.0, ABS = 1.0-1.2, PC = 1.5-2.0
• ΔT factor: Based on temperature difference

Example Calculation

For a 2mm thick polypropylene part:

Melt temp: 220°C, Mold temp: 60°C, Eject temp: 100°C

t_cooling = (2)² × 0.9 × 1.2 = 4.32 seconds

Injection Fill Time Calculation

Fill time depends on injection rate, shot volume, and part geometry. The formula is:

t_fill = (Shot Volume)/(Injection Rate)

Where:

• Shot Volume = Part volume + runner volume (cm³)
• Injection Rate = Cross-sectional area × fill speed (cm³/s)

Advanced Fill Time Formula

Considering flow path and viscosity:

t_fill = (L × h × w × ρ)/(Q × η_correction)

Where:

• L = Flow length (cm)
• h, w = Channel dimensions (cm)
• ρ = Density (g/cm³)
• Q = Volumetric flow rate (cm³/s)
• η_correction = Viscosity correction factor

Tederic High-Speed Injection

Tederic DE series machines achieve fill speeds up to 500 mm/s, reducing fill times to 0.5-2 seconds for typical parts.

Packing and Holding Time

Packing time is determined by gate freeze time and pressure requirements:

t_pack = Gate Freeze Time + Safety Margin

Gate Freeze Time Formula

t_freeze = (Gate Thickness)² × k / α

Where:

• k = Thermal conductivity factor
• α = Thermal diffusivity

Packing Pressure Profile

Typical packing profile:

• Initial pack: 80-90% of injection pressure (0.5-2 seconds)
• Secondary pack: 50-70% of injection pressure (2-5 seconds)
• Holding: 20-40% of injection pressure until gate freeze

Mold Opening and Closing Time

Mold movement time depends on mold weight, machine specifications, and stroke distance:

t_open/close = (Stroke Distance)/(Opening Speed) + Acceleration Time

Typical Times

Machine Size	Opening Time	Closing Time	Ejection Time
50-100 ton	0.8-1.2s	0.6-1.0s	0.3-0.5s
100-300 ton	1.0-1.5s	0.8-1.2s	0.4-0.6s
300-1000 ton	1.5-2.5s	1.2-2.0s	0.5-0.8s

Tederic Electric Toggle Advantage

Tederic TT series electric toggles achieve opening/closing times 30-50% faster than hydraulic systems, with precise positioning accuracy within ±0.01mm.

Dry Cycle Time Importance

Dry cycle time is the theoretical minimum cycle time without cooling requirements. It's a critical machine specification:

Dry Cycle = t_fill + t_pack + t_open + t_close + t_eject

Industry Benchmarks

Application	Typical Dry Cycle	Production Cycle	Efficiency
Thin-wall packaging	2-3s	8-12s	25-35%
General purpose	3-5s	15-30s	15-25%
Large technical parts	5-8s	45-90s	8-15%

Machine Selection Based on Dry Cycle

Choose machines where dry cycle time is 20-30% of total production cycle time for optimal efficiency.

Complete Cycle Time Formula

The complete cycle time calculation combines all phases:

Total Cycle Time = t_fill + t_pack + t_cooling + t_open + t_close + t_eject

Comprehensive Formula

Cycle Time = MAX(t_cooling, t_other) + t_machine

Where:

• t_cooling = Cooling time (usually the bottleneck)
• t_other = Sum of fill, pack, and movement times
• t_machine = Machine-dependent times

Production Rate Calculation

Parts per Hour = 3600 / Cycle Time

Daily Production = (Parts per Hour) × (Operating Hours) × (Efficiency)

Example: Complete Calculation

For a 2mm PP part with the following parameters:

• t_fill = 1.5s
• t_pack = 3.0s
• t_cooling = 25.0s
• t_open/close/eject = 2.5s

Total Cycle = 1.5 + 3.0 + 25.0 + 2.5 = 32.0 seconds

Production Rate = 3600/32 = 112.5 parts/hour

Cycle Time Optimization Strategies

Effective cycle time optimization requires systematic approach to each phase:

1. Cooling Time Optimization

• Conformal cooling channels reduce cooling time by 30-50%
• Optimize mold temperature to balance cooling and cycle time
• Use high-conductivity mold materials (copper alloys)
• Implement active cooling systems with temperature control

2. Fill Time Optimization

• Increase injection speed while maintaining quality
• Optimize gate design for better flow
• Use hot runner systems to reduce viscosity
• Implement cascade injection for multi-cavity molds

3. Machine Optimization

• Choose electric machines for faster movements
• Optimize clamp force to reduce closing time
• Use servo-hydraulics for precise control
• Implement parallel movements where possible

4. Part Design Optimization

• Minimize wall thickness variation
• Optimize rib and boss design for uniform cooling
• Design for manufacturability with flow considerations
• Use family molds to amortize cycle time

Tederic Electric Toggle Advantages

Tederic machines are specifically designed for cycle time optimization:

TT Series Electric Toggle Features

• High-speed mold movements: Opening/closing 30% faster than hydraulic
• Precise positioning: ±0.01mm accuracy for consistent cycles
• Energy recovery: Regenerative braking reduces power consumption
• Low maintenance: No hydraulic oil changes or leaks

DE Series All-Electric Advantages

• Ultra-fast injection: Up to 500 mm/s fill speed
• Parallel processing: Mold opening during screw recovery
• Quiet operation: Suitable for clean room environments
• Temperature stability: Better process consistency

Performance Comparison

Parameter	Tederic Electric	Hydraulic Standard	Improvement
Dry cycle time	2.5-4.0s	3.5-6.0s	25-35%
Energy consumption	0.3-0.5 kWh/kg	0.6-0.9 kWh/kg	40-50%
Repeatability	±0.01mm	±0.1mm	10x better

Economic Impact of Cycle Time

Cycle time directly impacts manufacturing economics:

Cost Calculation

Hourly Production Cost = (Labor + Equipment + Material) / Production Rate

ROI of Cycle Time Reduction

A 2-second cycle time reduction on a 30-second cycle:

• Production increase: 6.7% (from 120 to 128 parts/hour)
• Annual savings: Depends on part value and volume
• Typical ROI: 6-12 months for cycle optimization projects

Industry Benchmarks

Industry	Typical Cycle Time	Parts/Hour	World Class
Thin-wall packaging	5-8s	450-720	3-5s cycle
Automotive components	30-60s	60-120	20-40s cycle
Technical parts	45-120s	30-80	30-90s cycle

Capacity Planning

Annual Capacity = (Parts/Hour) × (Hours/Shift) × (Shifts/Day) × (Operating Days) × (Efficiency)

Where efficiency accounts for downtime, setup time, and quality issues.

Summary & Key Formulas

Mastering injection molding cycle time calculation is essential for profitable manufacturing. The key formulas to remember:

Core Formulas

• Cooling Time: t_cooling = (h²/π²α) × ln(const × (T_melt - T_mold)/(T_eject - T_mold))
• Fill Time: t_fill = (Shot Volume)/(Injection Rate)
• Total Cycle: Cycle Time = t_fill + t_pack + t_cooling + t_open + t_close + t_eject
• Production Rate: Parts/Hour = 3600 / Cycle Time

Optimization Priorities

1. Cooling time reduction (usually 70-80% of cycle time)
2. Machine speed optimization (electric vs hydraulic)
3. Part design for manufacturability
4. Process parameter optimization

Tederic Advantages

• Electric toggle systems: 30-50% faster mold movements
• High-speed injection: Up to 500 mm/s fill speeds
• Parallel processing: Multiple operations simultaneously
• Energy efficiency: 40-50% lower consumption

Accurate cycle time calculation enables informed decisions about mold design, machine selection, and process optimization. Use these formulas with mold flow simulation for the most accurate predictions.

For detailed cycle time analysis and Tederic machine recommendations, contact our engineering team. We can help optimize your processes for maximum productivity and profitability.

See also our articles on Injection molding clamping force, Masterbatch dosing – LDR & mixing guide 2026, and AI-powered predictive maintenance.