5 Factors That Impact Injection Molded Plastic Part Cycle Time

Posted by Al Timm on May 9, 2017 9:18:00 AM
Al Timm

Plastic-Part-Cycle-Time.jpgCycle time directly influences part cost and capacities, so keeping it as low as possible is generally the overarching goal of engineers and project managers. In getting quotes from various injection molders they may be confronted with divergent cycle time estimates, calling accuracy and the molder’s capabilities into question.

The truth is, there is no “magic formula” that an injection molder can simply plug numbers into and pinpoint cycle time. However, an injection molding partner with wide-ranging expertise, and depth of knowledge in scientific molding and mold filling analysis can more realistically quote projects. They have practical experience with a variety of parts and, therefore, can more precisely weigh in on designs and recommend possible cost-cutting measures.

Moreover, an experienced injection molder can anticipate factors that potentially increase cycle time — like thin steel and hot spots — and proactively prevent them by offering design change options. Calculating cycle time takes many factors into consideration:

Wall thickness

The thickest point of the plastic part takes the longest to go from a molten state to being rigid enough to eject. Therefore, the thicker the wall the longer the cycle time. If a wall can be thinned without affecting part integrity, costs can likely be cut since there is less required machine time per part in addition to possibly producing more parts per run.

Plastic type

The chemistry behind the construction of a plastic also underlies cycle time calculation in important ways. Certain polymers may, for example, cool more slowly than others. If chosen for constructing a certain injection molded part, that extra time translates to longer times in the mold, slower ejection and thus extended cycle times.

Part design

If an injection molder is looped into the design phase, chances are greatly improved that cycle time missteps will be avoided. Understanding that certain design parameters like wrapping plastic entirely around mold steel or other non-flat configuration, designing a mold that cannot accommodate cooling lines or including unduly thick walls not only drive up cooling times, they also introduce failure-inducers like thin steel and hot spots. An injection molder that’s previously been through and resolved these struggles will offer invaluable guidance during the design phase.

Mold material

Like plastics selection and part design, mold material influences outcomes. Steel is the most common mold material, but there are occasions where heat must be pulled out of the molded plastic faster than steel allows, known as thermoconductivity. In these instances, aluminum or other highly-conductive metals may be inserted within the steel tooling so it comes into strategic contact with the plastic to address potential hot spots without interrupting molding or delaying cycle times.

Mold cooling design

If containing cooling cannot be adequately accomplished by adjusting mold material, designing the mold to include cooling lines that run through the steel to cool the molded plastic may be an efficient solution. Injection molders that conduct mold fill simulation to estimate of how long it will take that part to reach ejection temperature may encourage the use of cooling lines — or changes to cooling design systems, water temperatures or flow rates — to optimize cycle times and overall molding process. 

Taken in total, molders that pay attention to how each of these factors are addressed will keep cycle times low, meaning you can realize increased capacity at decreased costs. What’s more, accurate estimation of cycle times gives manufacturers the confidence they need in production timelines, from part cost accuracy in planning stages and sales forecasting to part availability for meeting order fulfillment demands.

When it comes to accurately determining production cycle time, an experienced injection molder with deep knowledge of plastic part design, moldflow analysis and ancillary factors impacting production is key. Learn more about how Kaysun contributes to successful outcomes and drives faster time to market in our whitepaper, Mold Design and Tooling for Injection Molding. Click the button below to download your free copy.

Mold Design and Tooling

Topics: Plastic Part Design