After flow, pressure, and process limits are defined, the final step is dialing in time. Cooling and gate seal determine how long the material needs to stabilize before the part can be ejected without risk.
At this stage, the question shifts from “can we make a good part?” to “how fast can we make it without losing control?”
This study defines how long packing remains effective before the gate freezes and how much cooling time is required for the part to hold its shape after ejection.
It also establishes the shortest cycle time that still produces consistent, in-spec parts.
This step follows the process window study, once flow behavior, cavity balance, and pressure efficiency are already confirmed.
With those variables locked in, the focus moves entirely to time-based performance and thermal stability.
The study identifies the minimum gate seal time needed to maintain consistent part weight and the minimum cooling time required to prevent shrinkage, warpage, or ejection issues.
From there, the total cycle time is reduced to its most efficient form without compromising part quality.
During packing, material continues to flow through the gate into the cavity. As the gate cools, it solidifies and blocks any further flow.
Once that happens, additional hold time no longer affects the part. You end up with unnecessary cycle time if the hold phase runs longer than needed.
On the other hand, stopping too early prevents full packing, leading to sinks, voids, or weight variation.
The process starts at nominal conditions established in the process window study. Hold time is then increased incrementally across a series of shots.
Each part is weighed, and the results are plotted against hold time. Early in the curve, part weight increases as more material packs into the cavity. Eventually, the curve flattens, indicating that the gate has sealed.
The first point where weight stabilizes consistently marks the optimal gate seal time.
A smooth transition into a plateau shows stable behavior and a clear seal point. If no plateau appears, the gate may not be freezing properly, or cooling conditions may need adjustment.
Sudden drops or inconsistent weights often point to instability in flow, venting, or material conditions.
When the seal point is clearly defined, hold time can be set with confidence, eliminating wasted time without risking underpack.
Cooling time determines how well the part holds its shape after ejection. If it’s too short, parts may warp, shrink unevenly, or stick in the mold.
If it’s longer than necessary, cycle time increases without improving quality.
Starting from the current cycle, cooling time is reduced step by step. At each level, parts are measured for dimensional stability and checked for visual defects.
The point where issues begin to appear defines the lower limit. The optimal cooling time sits just above that threshold, where parts remain stable but no extra time is added.
Temperature data, part measurements over time, and cycle consistency all help confirm the result.
Once gate seal and cooling limits are established, the full cycle is defined as the shortest combination of fill, pack, cool, and eject that still produces stable parts.
This often leads to meaningful reductions in cycle time while maintaining consistency in weight, dimensions, and appearance.
The study produces a hold time versus part weight curve, a cooling time matrix with dimensional results, and a recommended cycle time.
These results tie directly back to the process window centerline and feed into validation, ensuring the process performs consistently under production conditions.
Cycle time isn’t just about speed. It’s about making sure every second contributes to part quality.
When packing ends at the right moment and cooling is dialed in precisely, the process runs efficiently without sacrificing stability, giving you consistent results across every cycle.