Hi Sayan
I spent some time one this as well, and had a look and some comments from me.
For the provided example and the specific questions:
A reason that filling time is longer in machine, could be that it probably need to slow down flow or switch over and fill by pressure due to a pressure spike/unbalanced flow.
Fill pattern shows unbalanced filling : ends of part fills earlier than centre (where gate is plugged), this will cause pressure spike.
Filling by pressure will cause a longer fill time.
The unbalanced fill might cause a flash. Hence reducing flow and longer fill time.
Pressure in reality vs. simulation
Moldflow cannot consider frictional losses in IMM, and can be around something like 15-25% of injection pressure.
A difference between simulation and real injection pressure expected.
This is what is seen in the sheet as well.
And some more (extensive) comments:
Basically I think the flow balance and gate positioning could be improved. Maybe some minor design changes on part to help manufacturing.
Further analysis to be done to investigate and improve.
The gate on thin thickness area - will freeze off earlier than overall general part thickness, causing packing problem , warpage problem, dimensional issues?
Runner design, time to freeze is long compared to part, probably controlling the cycle time.
(Looking at time to reach ejection temperature result plot.)
The starting point of plugging a gate, means something is not working well in filling the mold.
Plugging a gate gives unbalanced fill. Maybe it was issues already with 3 gates on part?
The gate is diameter 1mm in opening. Quite small. (nominal thickness is 2.8mm, thickness at rib at gate 1.5mm)
Quality prediction shows Red in gate, high shear rate and shear stress.
High shear rate can cause the material to degrade, become brittle, and have a poor surface finish.
High shear stress can cause cracks in the plastic, which can make the part degrade and fail.
Injection pressure required over the gate only is some 30 MPa.
Part weight
Measure real part thickness and compare.
Packing pressure and packing time affects weight.
Mesh, tab Accuracy
To always use Level 3 might not necessarily gives a better result.
In general, it is recommended to use the default settings for most models and analyses, which provides the best combination of analysis speed and resolution.
Higher resolution produces a more detailed model that takes more time and resources to analyze.
Change this option to ensure a high analysis resolution for models with a high proportion of small features such as fillets and radii, or if you want to examine highly detailed results such as hot spots in a cooling analysis result.
So start at Level 0 or Level 1, and when really needed increase the level.
1) Moldflow Design Principles
Use the basic rules to start with (Moldflow Design Principles)
Balanced filling - fill the extremes of part at same time and pressure.
2) Investigate thickness
Use Adviser Design Adviser.
Gate positioning by using basic recommendations.
Change design if needed to improve for manufacturing.
Design part for application and manufacturing.
3) What is controlling cycle time.
Careful with estimated cycle time, as it is estimated.
Review result plot, time to reach ejection temperature
For better accuracy a Cool simulation might be needed.
Comments referring to Moldflow Design Principles and the mold layout.
1) There is unbalanced fill
2) The gate is on thin area, compared to overall thickness. The basic rule is to gate on thick area.
A thin area will freeze off too early causing issues to pack the part and further warp issues.
3) Cooling time / cycle time
Runners should freeze relative to the part freeze
No less than 80% - To prevent packing problems
No more than 200% - To prevent controlling the cycle time
I example part freeze at 25 s, runner generally 111 s, and 180 s in sprue (200% of 25 s would be 75 s).
So cold runners controls the cycle time.
Recommended books:
Moldflow Design Guide
Successful Injection Molding: Process, Design, and Simulation
Runner and Gating Design Handbook
Hope this helps.
Regards,
Berndt
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