Clamp Tonnage predicted VS actual tonnage

[anoopvvravi]

Hello Friends,

I have a part for correlation, in this the predicted clamp force by moldflow is 1800 tonne. But in actual the clamp force goes to 2700 tonnes. what could be the possible reason. Nozzle & manifold dimension is the same as that in mold.

Its a two cavity mold with 3 direct nozzle per cavity. Part thickness is 4mm.

I have used 3D mesh with cooling channels.

Even the maximum pressure predicted by moldflow is not matching. Then how can we rely on the clamp force result ?

Thanks & Regards,

Anoop v Ravi

[mayur_dhumal]

Hi Anoop,

I have found a solution once in this forum only as:

Use custom results Clamping Force on Plane and use a plane perpendicular to the gating,
or parallel to the split line. This custom results gives the correct clamping force.

The normal Clamp force XY counts area's behind each other double, so it is only valid for flat parts.

http://forums.autodesk.com/t5/Simulation-Moldflow-Insight/Clamp-tonnage-over-prediction/m-p/2990426#...

Why don't you try this.

Regards,
Mayur

[mayur_dhumal]

Hi Anoop,

Also can you do a quick test on Projected (Cavity) Area?
You will get this value in 'Logs', after running a Flow analysis. Just cross-check this value is similar to your value from Mold Drawing or else you can always manually calculate it.

If this value is not nearly similar then you can use Custom Plot.

Hope this helps.

Regards,
Mayur

[madhukeshwart]

Anoop,

You cross check,

1. Melt temperature by taking air shot.

2. cross check the part thickness of prodction sample, may be some programing error during core /cavity machining.

3. check the material viscosity being used in moldflow and viscosity of raw material batch.

4. Imbalance in flow compared to moldlfow results, which might be shooting up pressure and tonnage.

Hope it solves..

[JayMuller]

Doesn't Moldflow always uses the Z-Axis for this?

Or have they changed that in the meantime? When I read custom plot, then not.

As I always simulate parts in final mounting position - I always had to translate my demolding direction into local MF Z-Axis.

But I don't need clamp force very often.

Regards,

Jay

[mayur_dhumal]

Hi Jay,

You stated correctly that MF uses Z-Axis as machine draw direction, but in some cases where surfaces overlap, so MF may calculate those surfaces as double. (I am really not sure if over the time period Autodesk may have changed this) So in this case you have to select those elements & say 'Exclude these elements from Clamp Force Calculation'.
In this way MF will calculate correct values of Clamp force.

Whereas 'Custom Plot' works on this principle, resulting in more accurate practical result.

I think Hanno Or Nordh should answer this, as what to do in such conditions where Clamp force is over predicting or less predicting.

Thanks,
Mayur

[yannick.moret]

A few things to look at.

Clamp force depend on pressure.

Pressure depends from :
- Material data

- Geometry

- Process conditions

So the points you need to check :
- Quality indicator is Gold for filling and packing

- Accuracy of thickness and runner (Is the mold really matching the simulation model ?)

- Parameter in Moldflow are matching machine injection parameter. For example, switch over point might be the key there.

[JayMuller]

Dear Yannick,

"Accuracy of thickness" (of the part) is a very good point - we measure cavity and core side by CAT scan.

But nobody measures the wall between. And if you measure a produced part  (3D Scan) you have the problem to fit CAD and Scan together.

(For this we use GOM Software)

But I think - better use a saw.

Regards,

Jay

[JayMuller]

Just an experience I made:

If pressure result vs reality difference is very high in the first place, then check or enter correct machine screw diameter.

Had that once...tried hard to find, then it came out they used wrong screw or screw diameter.

Regards,

Jay

[anoopvvravi]

Hello Yannick,

thanks you all for your comments.

- The quality indicator of the material is silver with no CRIMS data.

- Thickness of the molded part as well as that of CAD geometry is matching.

- Feed system (nozzle, manifold) dimensions are same as in mold.

- Process settings is same. I checked the short filled part with simulation at V/P switchover. its matching.

One thing i forgot to mention earlier was, the hot runner system has Flexflow system installed from HRS.

Can this be the factor in increasing the clamp tonnage ? almost 1000 tonne difference from simulation to actual.

Maximum injection pressure as per simulation is 38 MPa but in reality it goes to 132MPa.

Best Regards,

Anoop v Ravi

Plastal

[yannick.moret]

Such a difference in pressure is suspicious.

And remember the clamp tonnage just depend on pressure.

The material :

CRIMS is just for warp.

If Material is silver, it is worth to check further how it has been characterized (Moldflow or cappilary rheometer, etc...)

Regarding the flex gate, yes, it cas as it influence the gate diameter of the hot runner.

[JayMuller]

Dear Anoop v Ravi,

just for my personal interest:

Are you using the NEW actuator driven flex system?

Many thanks in advance!

Regards,

Jay

[anoopvvravi]

Hello Jay,

Please see the attached file.

[JayMuller]

OK THANKS!

You are using it as I suggested - we had a look at it, but it is more for huge parts with weld line quality issues where you need sequential filling.

Maybe the problem occurs because this system is brand new.

But owner of HRS (Mr Bazzo) is a personal friend of my father - will ask him.

Regards,

Jay

[mtrujil1]

Hello anoopvvravi

Wich version are you using? with the version 2014 and using a PC Material the result are not accurate, why??? i dont know, maybe  by the rehological properties

Plase try with other version 2013 or 2012 and with the same parameters, and let me your results!!!

regards.

[mayur_dhumal]

Hi,

Currently we are dealing with whatever version we are using, it may not have to be version specific. we need a solution here in this very version on which issue been observed.

Thanks,
Mayur

[mayur_dhumal]

Hi Anoop,

IT may have been overlooked.
Have you used the exact same injection machine as used for simulation or it is not.

Have you used all the same process parameters as seen in 'Injection Molding Machine' dialog, which is find at 'Process Settings Wizard>Advanced Options>Injection Molding Machine>Edit>Injection Unit.'

Regards,
Mayur

[raalteh]

Hi Mayur,

Are the injection pressure trace and the clamp force traces off over the entire filling cycle (e.g. consistently a factor 2 off between simulation or machine) or do you see a spike at the end of fill, the exact matching of the spike can be hard.

Are you using a profiled injection profile or a straight injection time based filling?

Hanno

[tim.vanast]

Hello Anoop,

Unforunately, I've also had simulations that showed significantly less pressure and tonnage that reality.  The software typically does a reasonable job, but I've two examples recently where the injection pressure is less than half of reality.  I've looked into the many possible causes and have yet to come up with anything that made a significant different.

Best regards,

Tim