Fill time result is almost double compared to set injection time

[Anonymous]

Hello,

I am working on a 2 cavity analysis.

Gate type: Cashew

Number of Gates: 12 (6 each part)

Process settings:

This is the fill time I see:

Please let me know what I am doing wrong here.

I am also attaching analysis log here.

Any help is appreciated.

[franco.costa]

Hello Sonakshi,

I don't think you are doing anything wrong.

I think you have a very large hot runner volume compared to the cavity volume which is causing this. The analysis log reports that the volume initially filled by melt (the hot runner) is ten time more than the volume to be filled (cold runner/gates and cavities).

Based on the injection time you set, a flow rate is determined which is required to fill the cavity in that time, but as the pressure rises, the mass flow reaching the cavity will be less than the mass flow coming from the injection molding barrel because of compressibility of the melt in the hot runner system which will be taking up some of the mass flow. Usually this compressibility effect is relatively small, but if the hot runner volume is so large compared to the volume to be injected, then the magnitude of compressibility effect increases.

[vgrover]

Hello Sonakshi Soni,

Just go through your log file, it seems, there is short shot in simulation. The flow front froze before the part could be filled. Due to this reason it shows fill time is too high. Reason could be gate size or material hesitations. 

Quick questions :

• Size of cashew gate 
• Shape of gate (Circular or Rectangular)
• No of beam layers for the gate

Suggestions:

Check the input CAD model if there is material hesitation due to part thickness.

Simultaneously, increase the gate size with rectangular shape with 1.25-1.30mm in width (Depend upon the size and shape of parts) and re-run it.

I believe, it will help you to get better results.

Regards,

Mohit UPPAL

[alois.neumaier]

the incomplete filling is the cause ....

** WARNING 128271 ** Short shot detected.  The flow front froze before

                     the part could be filled.

[bernor_mf]

Hi,

Sarlink 4775 B-40 : Teknor Apex Company is a TPV-material.

TPV normally has short injection time, maybe 0.5 - 1.5s
It is a shear-dependent polymer, and small gates used to promote higher shear rates and improve material flow within cavity.

From Analysis Log at V/P switchover:
| 4.202 | 95.55 | 23.84 | 19.43 | 33.97 | V |
| 4.280 | 97.00 | 24.53 | 20.65 | 31.76 | V/P |
| 4.291 | 97.15 | 19.63 | 20.42 | -201.78 | P |
| 4.351 | 97.58 | 19.63 | 19.34 | -2.40 | P |
| 4.500 | 97.94 | 19.63 | 19.47 | 2.21 | P |

Negative flow rate shows a backflow.
So flow rate drops and flow hesitates and stops, which for TPV is sensitive.
Hence a longer fill time and short shot.

Shorter injection time will improve the situation.
I think you should reduce set fill time, from what you use 3s, to try 0.5 to 1.5s.
The material melt is compressed in runner system, so it might also take longer than expected to actual fill of cavity starts, also as explained by @franco.costa 
Another option is to switch over later. Could result in a pressure spike though.

Hope this helps.

Regards,

Berndt