射出成形におけるサイクルタイムはどのように計算しますか？

Injection molding is a cyclic process — every part is born from a repeating sequence of injection, packing, cooling, and ejection. The total time for one complete loop is the サイクルタイム¹, and it directly controls your production rate and per-part cost. In our Shanghai factory, we have spent over 20 years fine-tuning cycle times across thousands of molds. This guide breaks down the calculation method so you can estimate, measure, and optimize cycle time on your own projects.

What Is Cycle Time in Injection Molding?

Cycle time is the total elapsed time from the start of one injection shot to the start of the next. It measures how fast your machine can produce parts — and it’s the single most important metric for 射出成形金型ing productivity.

Think of it this way: if you’re running a 4-cavity mold with a 30-second cycle, that’s roughly 480 parts per hour. Shrink that to 25 seconds, and you jump to 576 — a 20% production boost with zero additional capital investment. That’s why experienced engineers obsess over every second.

The formula is straightforward in concept: t_cycle = t_inject + t_pack + t_cool + t_open + t_eject + t_close. In practice, some phases overlap. Screw recovery² (plasticizing the next shot) happens during cooling, so you take the longer of t_cool and t_screw_recovery rather than adding both.

Cycle time isn’t a fixed property — it changes with material, part geometry, mold design, and machine settings. A thin-wall PP cap might cycle in 5–8 seconds, while a thick-wall polycarbonate housing could take 60 seconds or more. Engineers often talk about “optimal cycle time” — the fastest repeatable cycle that still produces parts meeting all quality specs. Push too fast, and you get short shots, sink marks, or dimensional drift. Push too slow, and you’re bleeding money on machine time.

How Do You Calculate Cycle Time Step by Step?

The cycle time formula is the sum of injection, packing, cooling, and mold operation times. Some phases overlap — for example, screw recovery happens during cooling — so you take the longer duration rather than adding both.

Injection Time (t_inject)

This is how long it takes to fill the cavity with molten plastic. For most parts, it’s 0.5–5 seconds. You can estimate it as: t_inject = Part weight (g) ÷ Injection rate (g/s). For example, a 50g part on a machine delivering 100 g/s takes about 0.5 seconds to fill. But real injection profiles use multi-stage speeds (slow-fast-slow), so actual time is slightly longer than the theoretical minimum.

Packing/Holding Time (t_pack)

After the cavity fills, you maintain pressure to compensate for material shrinkage. This typically runs 1–10 seconds depending on wall thickness and gate freeze-off time. Thin parts freeze fast; thick parts need longer hold. The packing phase ends when the gate solidifies, sealing the cavity.

Cooling Time (t_cool)

This is where most of your cycle lives. For semi-crystalline materials, 冷却時間³ is roughly proportional to the square of wall thickness: t_cool ≈ C × (wall thickness)², where C depends on material thermal diffusivity and the temperature difference between melt and mold. For a 3mm wall in ABS, expect 15–25 seconds. For a 5mm wall, it jumps to 40–60 seconds.

Mold Open/Close and Ejection

Mold open and close typically takes 2–10 seconds depending on mold size and press tonnage. Small molds on 80–200T presses run 2–4 seconds; large molds on 500–1000T presses take 6–12 seconds. Ejection time adds 0.5–3 seconds, with automated pickers being faster than manual removal.

Putting It All Together

Here’s a sample calculation for a mid-size ABS housing (3mm wall, 80g, 4-cavity mold on a 200T press): t_inject ≈ 1.5s, t_pack ≈ 3s, t_cool ≈ 20s, t_open + t_eject + t_close ≈ 5s. Total cycle time: approximately 29.5 seconds. In production, we’ve seen cycles range from 5 seconds for thin-wall packaging to over 90 seconds for thick technical parts.

What Are the Four Phases of an Injection Molding Cycle?

The four phases are injection (filling), packing (holding), cooling, and ejection/reset. Each has a distinct role in part quality and cycle efficiency.

Phase 1 — Injection (Filling)

The screw pushes forward, forcing molten plastic through the runner and gate into the cavity. Speed is critical — too slow and the melt freezes before filling; too fast and you get jetting or flash. Injection time is typically the shortest phase, but it sets the foundation for part quality.

Phase 2 — Packing (Holding)

Once the cavity is volumetrically full, the machine switches to holding pressure. This extra pressure packs in additional material to compensate for thermal shrinkage as the part cools. Packing continues until the gate freezes off, sealing the cavity. Getting packing time wrong is a common source of sink marks and voids.

Phase 3 — Cooling

The mold maintains a controlled temperature (usually 20–80°C depending on material), pulling heat out of the part until it’s rigid enough to eject without deformation. This phase runs the longest — often 60–70% of total cycle time. Meanwhile, the screw retracts and plasticizes the next shot, so cooling and screw recovery overlap.

Phase 4 — Ejection and Reset

The mold opens, the part is ejected (mechanically or by robot), and the mold closes for the next shot. Ejection can be a bottleneck if parts stick or if manual inspection is required. Well-designed ejector systems and proper draft angles keep this phase predictable.

Why Does Cooling Time Dominate the Cycle?

Cooling is the dominant phase, consuming 60–70% of total cycle time because heat extraction from thick polymer walls takes longer than any other step.

The polymer melt enters the cavity at 200–300°C, and you need to pull it down to 40–80°C before it’s safe to eject. The heat transfer rate depends on several factors.

Wall Thickness — The Big One

Cooling time scales roughly with the square of the thickest section. A part that’s 4mm thick needs about 1.8× the cooling time of a 3mm part. This is why DFM reviews always push for minimum uniform wall thickness.

Material Thermal Conductivity

Amorphous materials like PC and ABS cool differently than semi-crystalline ones like PA and POM. Crystalline materials release latent heat during solidification, which adds to cooling time. Material choice isn’t just about part performance — it directly impacts production economics.

Mold Temperature and Cooling Channel Design

Lower mold temperature pulls heat faster, but too cold causes residual stress, warpage, or poor surface finish. Well-placed baffle circuits, heat pipes, or conformal cooling channels can cut cooling time by 20–40% compared to basic drilled channels. This is where mold engineering pays for itself.

The practical implication: if you want to reduce cycle time, attack cooling first. Uniform wall thickness (keep variations under 25%), optimized cooling channel layout, and proper water flow rates give you the biggest returns.

What Factors Impact Cycle Time Most?

The biggest factors are wall thickness, material thermal properties, mold cooling design, and machine capability — roughly in that order.

Part geometry is the top driver. Thicker walls mean exponentially longer cooling. Complex part geometries with deep ribs, bosses, or varying thickness sections create hot spots that force you to extend the whole cycle for the slowest-cooling area.

Material selection matters because different polymers have different thermal properties. PP and PE cool relatively fast. PC, PPSU, and reinforced nylons need more time. If cycle time is critical and performance allows, switching from PC to ABS can cut cooling by 30–40%.

Mold design is where you win or lose. Key factors include cooling channel placement and flow rate, gate type and location, ejection system reliability, and mold material selection. Beryllium copper inserts conduct heat 3–5× faster than steel and are excellent for hot-spot areas. Machine settings give you incremental gains — higher injection velocity, optimized holding profiles, and faster mold open/close speeds all help, but these are fine-tuning compared to design and mold engineering.

How Can You Optimize Cycle Time Without Sacrificing Quality?

Focus on cooling optimization first, then wall thickness reduction, then machine tuning — in that order of impact. Here are the most effective strategies we use in production.

Redesign Cooling Channels

This is the single highest-ROI change. If your mold has basic straight-drilled channels, switching to baffles, bubblers, or spiral channels can reduce cooling time by 15–30%. For high-volume molds, conformal cooling (made possible by metal 3D printing) can achieve 40%+ reductions.

Minimize and Uniformize Wall Thickness

Every 0.5mm reduction in maximum wall thickness can cut cooling time by 10–20%. Keep wall thickness variation under 25% across the part. Work with your design team early — DFM changes are cheap before the mold is cut, expensive after.

Optimize Gate Location and Type

Better gate placement ensures even filling and reduces the need for extended packing time. Hot runner systems with valve gates allow faster cycling because they seal independently of the cooling phase.

Automate Ejection

Robotic pickers or automatic drop systems eliminate the variability of manual part removal. This is especially impactful for cycles under 15 seconds where human response time becomes a bottleneck.

The caveat: any cycle time optimization must be validated with quality data. If you see sink marks, dimensional drift, or warpage after reducing cycle time, you’ve gone too far. Always run a capability study (Cpk) before locking in a new cycle. For guidance on choosing the right manufacturing partner for optimized production, see our injection molding sourcing guide.

What Are Typical Cycle Times for Common Materials?

Cycle times vary widely, but here are typical ranges based on real production data for a mid-complexity part with 2–3mm walls. These ranges assume a standard mold with adequate cooling.

With optimized conformal cooling channels, you can often run 20–30% faster than these ranges. The takeaway: material choice isn’t just about part performance — it directly impacts your production economics through cycle time.

How Do You Measure and Monitor Cycle Time in Production?

Cycle time measurement is performed by the machine’s built-in timer, then tracked with SPC software to catch process drift early.

Machine-Level Monitoring

Every modern press displays real-time cycle time. Most can log cycle-by-cycle data and alert operators when a cycle exceeds the set limit. This is your first line of defense — if the machine says 32 seconds and you’ve set a 30-second target, something needs attention.

SPC Trending and Drift Detection

Track cycle time over hundreds or thousands of shots. A gradual upward trend often indicates a developing problem: fouled cooling channels, worn ejector pins, or material viscosity changes. Catching these early prevents quality issues and unplanned downtime.

Common Causes of Cycle Time Drift

The usual suspects include cooling channel scale buildup (reduces heat transfer), worn hot runner nozzles (slower fill, longer packing), material lot-to-lot variation, hydraulic system degradation on older machines, and ambient temperature changes between seasons.

Our recommendation: set a cycle time upper control limit (UCL) at 5% above your optimized cycle. Any shot exceeding UCL should trigger an investigation. This simple rule catches 80% of developing problems before they produce defective parts. For serious operations, MES (Manufacturing Execution Systems) integrate cycle time data with quality inspection results, letting you correlate cycle variations with part quality in real time.

よくある質問

射出成形サイクルタイムの公式は何ですか？

基本式は、t_cycle = t_inject + t_pack + t_cool + t_open + t_eject + t_closeです。ただし、一部の工程は重複します――特に冷却とスクリュー回復です。両方を加算するのではなく、長い方の時間を採用します。簡易見積もりでは、冷却時間は通常全体の60–70％を占めるため、冷却時間を計測し1.4–1.6を乗算することで妥当な概算値が得られます。実際のサイクル時間は製品形状、材料、金型設計に依存するため、常に実機データで検証してください。

典型的な射出成形サイクルは何秒ですか？

Most injection molding cycles fall between 10 and 60 seconds. Thin-wall packaging parts like bottle caps can cycle in 5-8 seconds on optimized high-speed machines. Standard technical parts with 2-3mm walls typically run 15-30 seconds on conventional presses. Thick-wall or high-performance materials like polycarbonate can push to 45-90 seconds due to extended cooling requirements. The specific cycle depends heavily on wall thickness, material thermal properties, mold cooling capacity, and part complexity. If you are consistently running over 60 seconds, investigate cooling optimization.

射出成形における最も長い工程は何ですか？

Cooling is almost always the longest phase, consuming 60-70% of total cycle time across most production scenarios. This is because you must extract enough heat from the molten polymer to make the part rigid enough for ejection without deformation. The thermodynamics are unavoidable: cooling time scales roughly with the square of the wall thickness, meaning even small increases in part thickness dramatically extend the total cycle. On thin-wall packaging parts, injection time can be significant, but cooling still dominates the vast majority of production runs.

壁の厚さはサイクルタイムにどのように影響しますか？

Wall thickness is the single biggest driver of cycle time because cooling time scales approximately with the square of the wall thickness. Doubling the wall thickness roughly quadruples the cooling time required. For example, a part with a 2mm wall might need 8 seconds of cooling, while the same geometry at 4mm requires 25-30 seconds. This exponential relationship is why design-for-manufacturing reviews always push for minimum uniform wall thickness. Any sections significantly thicker than the rest become the bottleneck for the entire cycle, forcing extended cooling for all cavities.

金型を変更せずにサイクルタイムを短縮できますか？

Yes, you can reduce cycle time without mold changes, but gains are smaller compared to mold-level modifications. Machine-side optimizations include increasing injection velocity, adjusting holding pressure profiles, ensuring optimal cooling water flow rate and temperature, and switching to a faster-cycling material grade. These adjustments typically yield 5-15% improvements in cycle time. For larger gains of 20-40% or more, you generally need mold modifications such as improved cooling channels, beryllium copper inserts in hot-spot areas, or gate redesign for more efficient filling.

射出成形におけるサイクルタイムとリードタイムの違いは何ですか？

Cycle time measures production speed — the time for one machine cycle from shot to shot. Lead time is the total time from order placement to delivery, including tooling fabrication, material procurement, production scheduling, quality inspection, and shipping. A part with a 20-second cycle time might have a 4–6 week lead time for a new mold, or 3–5 days for a repeat production run. Understanding both metrics is essential for project planning — fast cycle times don’t help if the mold isn’t ready.

射出成形における冷却時間はどのように計算しますか？

A simplified cooling time estimate uses the formula t_cool = (thickness squared times thermal_factor) divided by thermal_diffusivity, where the thermal factor depends on the temperature difference between melt temperature and mold temperature. In practice, most engineers rely on empirical production data or mold simulation software like Moldflow because real part geometries are too complex for accurate hand calculations. As a practical rule of thumb, for a 3mm wall in amorphous material like ABS, expect 15-25 seconds. For the same thickness in semi-crystalline nylon, add 20-30% more cooling time.

なぜサイクルタイムはショットごとに変動するのですか？

Minor cycle time variation of plus or minus 0.5-1 second is completely normal and results from slight differences in material feeding consistency, screw position repeatability, and hydraulic system response. Larger variations exceeding 2 seconds usually indicate a real problem: inconsistent material drying, clogged or scaled cooling channels, a worn check ring causing shot-size variation, or faulty temperature sensors. If you observe a gradual upward trend over hundreds of shots, check cooling water flow rate first because mineral scale buildup inside channels is the most common cause of slow cycle time drift.

Ready to Optimize Your Injection Molding Cycle Time?

ZetarMold’s engineering team has over 20 years of experience optimizing production cycles across 400+ materials. For a detailed overview of capabilities, see our complete guide to injection molding. From mold design review to production tuning, we help you achieve the fastest cycle without compromising quality. Request a free quote for your next project.

1. Cycle time: Cycle time refers to the total elapsed time from the start of one production cycle to the start of the next in a repeating manufacturing process. ↩

2. Screw recovery: Screw recovery refers to the phase where the injection screw rotates to plasticize and accumulate the next shot of material while the previous part cools in the mold. ↩

3. 冷却時間： Cooling time refers to the duration required to reduce the temperature of a molded polymer from its melt temperature to a safe ejection temperature within the mold cavity. ↩