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Injection Molding is a highly efficient manufacturing process where molten plastic is forced into a mold cavity, cools and solidifies, and then the finished part is ejected for the next cycle. The total time for one full cycle—commonly referred to as the “cycle time”—is critical for production planning, cost estimation, and process optimization. Cycle time essentially determines the quantity of parts that can be produced per hour, per shift, and per day.
Cycle time in injection molding is the sum of several distinct phases. According to technical sources, the relationship can be expressed as:
t = td + ti + tc Here:
td = time for mold closing, part ejection, and preparation for the next shot (sometimes called the “dry cycle” or intermediate time)
ti = injection time (filling the cavity and holding pressure)
tc = cooling time (allowing the molten plastic to solidify sufficiently for ejection)
Each phase contributes differently to the total. Notably, cooling time is often the largest portion of cycle time and is heavily influenced by part thickness, material properties, mold design, and temperature control systems.
Because every part, material, and mold is different, there is no one “normal” cycle time. However, industry sources give useful ranges and guidelines to help estimate.
For many standard thermoplastic parts with moderate wall thickness, cycle times can range from a few seconds up to tens of seconds. One source states typical cycles range from 1 to 5 seconds for “very small” thin-walled parts.
Another discussion suggests cycles might last from two seconds up to two minutes, but parts with thicker walls may require five to ten minutes or longer.
A technical explanation emphasises that cooling often accounts for about 80 % of the cycle time in many cases.
Thus, when planning a project, one might see typical cycle times of, say, 10–30 seconds for moderate parts, but significantly longer for large, thick, or complex components.
Several parameters play a role in how long an injection molding cycle takes. Understanding these helps in both planning and optimization efforts.
Part geometry and wall thickness: Thicker walls cool more slowly, extending the cooling phase substantially.
Material selection: Different polymers have different thermal and flow characteristics (melt temperature, thermal conductivity, specific heat). These affect fill time, packing behaviour, cooling time.
Mold design and cooling system: Efficient mold cooling channels, mold materials, even surface treatments influence how quickly heat can be removed and the part can be ejected.
Machine settings and automation: Faster clamp movements, efficient part ejection, minimal delays between cycles all help reduce td. Optimising injection speed and packing also reduces ti.
Process stability and quality requirements: If high precision or special surface finish are needed, more conservative cooling or slower transitions may be required, increasing cycle time.
For a rough estimation of cycle time for a given part, you can follow a simplified method:
Estimate the injection time (fill plus pack/hold) based on cavity volume and machine injection rate.
Estimate cooling time: a rough formula shows cooling time is proportional to the square of the maximum part thickness and inversely proportional to thermal diffusivity of the material.
Add intermediate/machine handling times (mold open, eject, mold close).
If higher quality is required, add safety margin (e.g., +20 %) to cooling time to account for material variation and machine performance.
By using this method, engineers can forecast cycle times for new parts and evaluate whether tooling changes, material changes or process improvements are needed.
Cycle time has a direct impact on production output, costs, mould lifespan and scheduling. Some of the practical consequences include:
Shorter cycle times mean higher throughput — more parts per hour, which lowers per-part cost.
However, reducing cycle time without considering quality may lead to defects (warpage, sink marks, incomplete fill) or reduced mold durability. For example, cooling too little can cause dimensional instability.
For high volume manufacturing, even a one-second reduction in cycle time across thousands of cycles yields significant savings.
For very large, thick parts or parts requiring long cooling or other treatments, cycle times may become several minutes, reducing hourly output and thus affecting machine selection, cost planning and lead-times.
When selecting a supplier or partner for injection molding or related auxiliary equipment, it's helpful to choose a company with well-designed machines, reliable moulds, and strong process support. For instance, the company Guangzhou Bohang Intelligent Technology Co., Ltd. presents itself as a developer and manufacturer of injection-molding machine peripheral equipment, robot Manipulators, moulds and related services. Their promise of quality assurance, fast delivery and effective after-sales service makes them a candidate to consider when you look to optimise cycle times and production efficiency.
Cycle time in injection molding is a fundamental metric defined as the total time required for one complete part production cycle (closing the mold, injecting material, cooling, opening the mold, ejecting the part, and preparing for the next shot). Cooling time often dominates the cycle, commonly accounting for 70-80 % of the total. Reasonable cycle times for standard parts may be in the range of a few seconds up to tens of seconds; but for large, thick or complex parts they can extend to minutes. Cycle time is influenced by part design, materials, mold engineering, machine settings and process stability. Estimating and optimising cycle time allows better cost control, higher throughput and improved production planning. Partnering with experienced equipment and tooling suppliers can help achieve efficient, stable and reliable production.
