In injection molding, there is one variable that has a greater impact on cost than almost anything else:
Cycle time.
While many OEMs focus on material costs or tooling investment, the reality is that cycle time is often the single biggest driver of piece price in plastics manufacturing.
Understanding how cycle time works—and how to reduce it—can unlock significant cost savings and improve overall production efficiency.
At Montrose Molders Corp, we work with customers to optimize cycle time across their programs, often identifying opportunities that materially reduce long-term cost.
What Is Injection Molding Cycle Time?
Injection molding cycle time refers to the total time required to produce one part (or one shot) from start to finish.
A typical cycle includes:
- Injection (filling the mold with molten plastic)
- Packing and holding pressure
- Cooling (the longest portion of the cycle)
- Mold opening
- Part ejection
- Mold closing
👉 The entire process repeats continuously during production.
Example:
If a cycle time is 30 seconds, the machine produces:
- 120 parts per hour (single cavity)
- More with multi-cavity tooling
Why Cycle Time Drives Cost in Injection Molding
Cycle time directly determines how many parts can be produced in a given period.
The Relationship Is Simple:
- Shorter cycle time = more parts per hour = lower cost per part
- Longer cycle time = fewer parts per hour = higher cost per part
Why This Matters
Injection molding machines are typically priced by:
- Machine time (hourly rate)
- Labor and overhead
If your cycle time is reduced by even a few seconds, the cost savings compound over thousands—or millions—of parts.
What Affects Injection Molding Cycle Time?
Several key factors influence cycle time in plastics manufacturing.
1. Cooling Time (The Biggest Factor)
Cooling is often 60–80% of total cycle time.
Why it matters:
- The part must fully solidify before ejection
- Thicker sections take longer to cool
What drives cooling time:
- Part wall thickness
- Material thermal properties
- Injection mold cooling design
👉 Injection mold cooling is the single biggest lever for reducing cycle time
2. Part Design
Design decisions made early in development have a major impact on cycle time.
Key design factors:
- Wall thickness (thicker = slower cooling)
- Uniformity of wall sections
- Part geometry and complexity
Reducing wall thickness—even slightly—can significantly shorten cycle time.
3. Material Selection
Different materials process differently.
Examples:
- High-temperature materials → longer cooling cycles
- High-flow materials → faster filling
Material selection impacts:
- Cooling time
- Injection speed
- Overall process efficiency
4. Injection Mold Design
The design of the injection mold directly impacts cycle efficiency.
Key elements:
- Cooling channel layout
- Gate design
- Venting
- Mold material (aluminum vs steel)
A well-designed mold enables:
- Faster heat transfer
- More consistent cooling
- Reduced cycle variability
5. Machine and Process Optimization
Process settings and machine capability also influence cycle time.
Factors include:
- Injection speed
- Clamp force
- Automation (part removal, etc.)
Optimizing the process ensures that the cycle runs efficiently without sacrificing quality.
Real-World Example: How Small Changes Reduce Cost
Consider a part with the following:
- Cycle time: 30 seconds
- Production volume: 1,000,000 parts
If cycle time is reduced to 27 seconds (a 10% improvement):
- Output increases significantly
- Machine time decreases
- Cost per part drops
👉 Over large volumes, this can result in substantial cost savings
And importantly:
These savings are permanent over the life of the program.
How to Reduce Cycle Time in Injection Molding
Reducing cycle time requires a combination of design, tooling, and process improvements.
1. Optimize Injection Mold Cooling
- Improve cooling channel design
- Use advanced cooling techniques where appropriate
- Ensure uniform heat removal
This is often the highest-impact improvement.
2. Reduce Wall Thickness
- Eliminate unnecessary material
- Maintain structural integrity with ribs instead of thickness
3. Select the Right Material
- Consider materials with better processing characteristics
- Avoid over-specifying high-temperature resins when unnecessary
4. Improve Tool Design
- Simplify part geometry
- Minimize unnecessary complexity
- Ensure efficient mold layout
5. Optimize the Process
- Fine-tune injection parameters
- Reduce unnecessary delays in the cycle
- Implement automation where appropriate
The Balance: Speed vs Quality
While reducing cycle time is important, it must be done carefully.
Pushing cycle time too aggressively can lead to:
- Warpage
- Sink marks
- Incomplete filling
- Increased scrap rates
The goal is to find the optimal balance between speed and part quality.
Why Cycle Time Is Often Overlooked
Many OEMs focus on:
- Material cost
- Tooling cost
But overlook:
- Long-term production efficiency
In reality, cycle time often has a greater impact on total cost of ownership than either of these factors.
Why This Matters in Today’s Manufacturing Environment
In today’s competitive landscape, manufacturers need to:
- Reduce cost
- Improve efficiency
- Maintain quality
Cycle time optimization directly supports all three.
At Montrose Molders Corp, we work with customers to evaluate cycle time early in the quoting and design process—ensuring that parts are optimized for efficient production.
Final Thoughts
Cycle time is one of the most powerful—and most underutilized—levers in injection molding.
- It directly impacts cost per part
- It is driven by design, tooling, and material decisions
- Small improvements create large long-term savings
Understanding and optimizing cycle time is essential for successful plastics manufacturing programs.
Ready to Reduce Your Part Costs?
If you’re looking to improve efficiency or reduce cost in your injection molding program, cycle time is often the best place to start.
We’re happy to review your part design, tooling strategy, or current production process and identify opportunities to improve cycle time and reduce cost.