How to calculate injection moulding cycle time?

Injection moulding cycle time varies based on wall thickness of the part, but some cases due to the profile it takes more time, for example warpage control, it needs rather design change, can perform DOE studies with various cycle time versus part dimensions to confirm suitable cycle time.

At a sprinkler manufacturer we used to have a plot of the existing tools with xy coordinates of wall thickness vs resin. For automotive, a lot of those tools ran slow cycles in the minutes in order to control flatness. Cap & closures used refrigerator water and most walls were about 1/32". Their cycles could be 3-5 seconds. Medical components are probably from 10-40 seconds for small parts. For a new part you need to consider how well the mould cooling can be. Example would be pen barrels w/o core cooling.

There is no generic formula for this and wall thickness is only one of many variables. All of the following and more are other variables that can greatly change the injection moulding cycle time:

• number of cavities in the mould
• type of material
• any slides, core pulls, or unscrewing mechanisms will all add time
• robot for part or runner removal will add time
• geometry of the part
• design of the mould
• type of injection moulding machine that is running it
• runner type
• gate type
• the shop that runs it

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