Injection Molding cycle time calculator

This calculator helps you to find out the injection molding cycle time for your custom plastic part. Before contacting any molder or mold maker, get yourself a realistic idea of what the cycle time would be. Try it out, it is for free!

The injection molding cycle time is probably the most important time metric for any plastic manufacturing operation. It is the total time needed to finish one molding cycle, which can be translated into the production of 1 shot of parts. There are several stages that go into the cycle time, more about that in detail under the topic “Cycle time formula and how to prepare”.

online cycle time calculator

Injection molding cycle time

Why do you need to know it?

There are several good reasons why you should know the cycle time of your design/part. The obvious reasons, if you are a molder yourself, are to plan the production and create sufficient capacity to reach the production quantity goal.

However, for all of you who outsource their entire production or even just specific parts, you better know the realistic cycle time of your part before talking to any molder or mold maker.
We all know the saying that time is money, well since cycle time is the most important time regarding plastic manufacturing, you can also say:
Cycle time = Money
When you outsource, do you want to solely rely on the molder to give you an accurate cycle time estimation before starting? Some might even give you higher numbers, just so that they have an easier job or can charge you more for the production. Guessing the cycle time or using a time that fits your planning does not work either. Your planning needs to be focused around the cycle time and not the other way around.

Be it either from experience, through previous, similar, parts, or through calculations tools like advanced CAD software or this website. You need to have an idea of the cycle time. Even though the theory most often can deviate from the real cycle time, you better have an idea. From experience in dealing with the most sophisticated mold flow simulation software, you can never perfectly simulate real circumstances. So don’t argue about 1-2 seconds, before the mold is in an injection machine.

Important factors

The most important factor regarding cycle time is definitely the cooling time, which is the stage of an injection molding cycle where the part has to cool down and solidify. This usually takes more than half of the time. Therefore, optimizing the cooling has always been a top priority when designing and building molds.
There are 2 factors that pretty much dictate the cooling time:
1. Wall thickness
2. Plastic material
Plastic material is always chosen based on its properties and cost, the same goes for wall thickness. Use the smallest wall thickness that satisfies your application, with a safety factor. Use designs that help to improve strength while not needing thicker walls.
3d stl object
This is an example of a not-so-good design. The wall thickness on the bottom is 5mm which is quite big, it would be the bottleneck in trying to optimize the cycle time. There are more advanced ways of designing it, with rips, to have the same strength but to lower the wall thickness down to 2mm. Try it out, you will see that reducing the wall thickness down to 2mm instead of 5mm (which is just aesthetical nature and not fully needed for the application) would improve the manufacturing performance significantly.

Cycle time formula and how to prepare

Not much to prepare, just export as STL.
Think about a few important factors. Additionally, explain that I could have made it more detailed and thus accurate, but many designers don’t know some manufacturing-related details, such as preferred machine size.
The main components of the cycle time formula are:

Injection and filling time - Filling:
This time consists of the screw driving, the plasticizing capacity of your injection machine, and the general filling phase. The molten plastic enters the mold until it is sufficiently filled.

Pressure holding time - Packing:
Extra pressure is applied to force more plastic material into the mold and to hold the pressure for a short moment. It is immediately followed by the cooling period.

Cooling time:
Even though this stage is unspectacular, it takes the longest time. There is no more pressure being applied to the polymer and the mold is just held shut. The plastic needs to cool down to prevent any deforming when ejecting.

Mold ejection & operating time:
This includes opening the mold and ejecting the part as well as closing the mold so that the filling can begin again. Any extra work, such as loading inserts or a substrate for over-molding, can also be accounted for in this stage.
cycle time proportions

Cycle time calculator - needed input

There are plenty of details that contribute to the cycle time, however, it is unlikely that you know all of those right at the beginning of a project. For example, do you already know on which machine the mold goes?

For this reason, we have simplified the input area of this calculator to the bare minimum. All the other components are calculated by algorithms based on your input. Coupled with the machine learning capabilities over time, this calculator can give reasonably accurate estimates. However, there are a few key details that you need to know:

Wall thickness:
Any designed plastic part should be designed with a specific wall thickness in mind, you should not have strongly varying wall thicknesses in your part.

According to the application of the plastic part, if you do not have an idea which plastic is a good fit, take a look at the “Top 15 injection molding plastic materials”.

Cavity Quantity:
This almost only depends on your required volume. If the volume is rather low, or you are just starting out, better go for 1 cavity. This will also result in the cheapest mold possible and might be a good starter option, especially for medium to large-sized parts.

Runner system:
You don’t have to know this right away, but if you do, better to mention it here. There will be a runner (plastic waste basically) if you use a cold runner system. A hot runner system does not have that runner plastic waste but increases the mold costs quite a bit. This is something you could ask your mold maker about. If you don’t know it yet, just start with “cold runner”.

That’s it, enough to estimate the cycle time of your part. With the help of your 3D model, we can now almost instantly calculate the injection cycle time.
inout for cycle time calculator

Cycle time calculator results

cycle time calculator results
The cycle time is a good estimate of what the real cycle time will be. It should fit 90% of regular parts to be injection molding.
In case you have insert molding, over-molding, or anything more complex, this calculator gets more limited but can still work as a guideline.

Don’t pay too much attention to the milliseconds and rather concentrate on the time +/- 2 seconds as this should be enough for the next step, contacting an injection molder or mold maker or even planning your production and quantity. This tool helps you with any theoretical planning in your project. The eventual cycle time on the machine might be similar but can also deviate based on the complexity of the part and the mold design.

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