Injection Compression Molding Process parameters selection

[riad.ashraf]

Dear Altrusit,

I am working on my project in Injection Compression Molding. I have been using Moldflow to simulate two different materials with three different press compression speed in the compression settings to determine various qualities between these two materials. I have been facing some problems. Please help me out.

1. At first, I set the Fill+Pack setting as the automatic. Then I tried to change the parameters. For three different compression speed I got three different filling time in the automatic section. For the highest velocity profile the filling time is the least and the lowest velocity profile the filling time is the highest. Now I wanted to change the filling paramaters so that I want to get exactly same filling time for each profile. I took the highest filling time as reference and put the value in the Highest velocity profile as Injection time. Then I got the problem Short shot. What is the problem! Is not the filling time means the injection time in filling settings? Or do I assume it wrong or do I put the highest value which will not work here where i got the elast filling time as automatic one.

I want same filling time for all velocity profile. What should I do?

2. I found out that the percentage vollume filled during velocity pressure switch over is 125 percentage from the automatic parameters set. How can this be possible? Is it alright ? I put this value manually and it worked fine. Can you explain how this things happen?

3. There is no packing in Injection compression molding. In that regard, what should I do regarding the packing parametes?

4. In the compression setting switch to press force controll options, should I put from the start of compression? or any other option?

5. I have set all the parameters automatic and it worked fine. Now facing problems while changing the parameters manually. Specially in the filling and packing phase. Please help me out in this filling and packing phase problem. If I want same parameters specially same filling time and other aspects like 100 percent frozen layer fraction, what should I do in the filling and packing phase? How could I get the manual values from the preset data. Which values I need to consider.

These problems need to be solved. Please help me out. Specially @bernor_mf , I am really looking for your help as you helped me earlier. I am sending some screenshots for your consideration.

Best regards.

Riad

[bernor_mf]

Hi,

quite a bunch of questions you have.
I will provide some replies, one at a time or so, due to other commitments.

1) Setting up the process for thermoplastic injection compression is a bit more complicated
compared to traditional thermoplastic injection molding.
What is really controlling the process here?
How does the intended machine to use work?

For the process you have to decide:
Should there be any pack/holding control or not?
Often it is set to 0, and packed by the compression phase.
"Press compression starts : At the end of packing"

Filling: the set fill time and volume gives a flow rate
You then fill the volume, and start compression, after pack/holding phase .
If compression speed is too slow, the pressure affects flow rate, and flow rate goes down
takes longer to fill, and if too less pressure you will end up with short shot.
So you ramp down the press compression speed, which could drop the flow rate too much to
cause a short shot.

Then: when to switch to press force control?
By this I mean, you need to decide if controlling by press compression speed initially or not?
Decide from how you want to control the process
By default 99% of nodes filled.
Maybe you want to control the compression by force from the start of compression?
Or when the press force reaches compression force cap?
Review the settings of "Switch to press force control" to decide suitable control.

2) If you look at PVT you see the specific volume change from one temperature to another.
If you review the 0 MPa curve, you see the change from melt to solid, and down to room temperature.
Depending on material the volume change could be even up to 30%.
The generic PP changes from 1.12 cm3/g at room temperature (25C) to 1.36 cm3/g at 220C, about 21%.
More material injected will affect the final volumetric shrinkage - so this affects how part is packed out.

To be continued.
Hope this helps, and you understand what I explain.
Regards,
Berndt

[bernor_mf]

Hi @riad.ashraf ,
reply to question...:

3) There is packing in injection compression, if you need it for the process.
It means you could have pack/holding phase.
Often it is set to 0s, and packed by the compression phase, but no more melt entering cavity.
"Press compression starts : At the end of packing"

But you could pack and start compression if the process is that way.

So if you fill the melt volume and packing is in compression phase with no additional of melt volume,
then the setting is 0s in pack/holding phase and "Press compression starts : At the end of packing"

At the end of packing also injection location is closed.
This to avoid backflow when compressing.

To have control of melt volume and packing, you set pack/holding phase to 0s,
and then it is packed by the compression phase, but no more melt entering cavity.

Hope this helps.
Regards,
Berndt

[bernor_mf]

Hi @riad.ashraf 
reply to question...:

4) The settings of "Switch to press force control"

"From the start of compression. "
Press force control begins when the compression stage begins.
If the compression stage starts before the injection packing profile has finished,
the switch to force control will be delayed until the packing profile has finished and the injection location is closed.

"Only when the press force reaches compression force cap. "
This is the default setting.
Press force control begins when the compression force reaches the defined maximum value.

"By press force. "
Specify the press force value, in tons, for the press force control to begin.

So it basically depends on how this is to be set up in machine.
It could initially be a press compression speed.
But if max force cap is reach you switch over to press force control.

Check how this is to be processed in machine to decide.

Hope this clarifies.
Regards,
Berndt

[bernor_mf]

Hi @riad.ashraf 
reply to question...:
5) Not so easy to answer, as I think a lot has been covered in point 1 to 4.

Setting up the process for thermoplastic injection compression is a bit more complicated
compared to traditional thermoplastic injection molding, also when moving from automatic
to manual control, which you experience.

There will be variations in fill time, as how compression is set up.
You have to review press compression speed (maybe not profiled?), and when to switch to press control.

The fill time could/will vary in thermoplastic injection molding too,depending on flow rate, when velocity / pressure switch over happens, and packing level and time.

I think you should fill the melt volume.
To have control of melt volume and packing, you set pack/holding phase to 0s, then "Press compression starts : At the end of packing" as then it is packed by the compression phase, but no more melt entering cavity.
Review compression phase to fill within wished fill time, and the compress to pack out.

Hope this helps.
Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf ,

Thanks a lot for your gracious reply. I have made a small prototype. I am getting errors for short shot. Earlier it was working fine but right now there has been some problems. I am not sure where is the problem. Could you please see and let me know, why short shot is happening?

I am sending you the process parameters, warnings and results screenshot in a power point file. So that it will be helpful for you to understand the problem.

Please let me know. Best regards.

[bernor_mf · Accepted solution]

Hi @riad.ashraf ,

thank you, no worries. 

I think Autodesk should put me on the payroll for doing tech support...🤔 just kidding. 😊 😉

A lot of information in the powerpoint...
Could help if you attach the study file too, the .sdy-file, but has to be zipped first.

Anyway:
The Press displacement is 0.996 mm according to analysis log picture p.19.
Press Open is set to 8.5 mm p.14.
It hardly moves for a long time , hence slow filling, which I think causes the short shot.

Lower flow rate -> higher viscosity, -> higher risk of flow stagnation and short shot.

You switch to press force control from the start of compression.
The compression force after switch to press force control: Relative to the value at switch over :
But what is the relative value, in time and %?

It seems to be too low and too long.

Set to absolute, if you know the press force.
It should be high enough to maintain a decent flow.
And not too long, as it affects flow, and lower flow rate higher viscosity, higher risk of flow stagnation and short shot.

Look at result:
Press Force XY plot : Is it reasonable?
Press Displacement XY plot : Is it reasonable? Has it moved as much as intended?
Press speed XY plot : Is it reasonable?

So, first you need to decide how to run your process.
Is it press force control directly?
Is it a speed first, then a press force control?

Hope this helps.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf ,

Thanks a lot for your reply and suggestion. It worked fine for me in the prototype. It gives me a great relieve. But I need some more assistance. Could you please help me in that regard?

1)In the process setting wizard, In the Injection Compression Advanced option, I set the injection molding parameters, intermideate results time as an 0.1 interval till the end of compression to get an idea of the each step precisely. Still, while I check in the results analysis, in the Fill time section, from 2.013s it suddenly jumps to 2.195s. I do not know the reasons of this jump. I want more steps in the fill time. How could I do that? is this sudden jump normal?

2)There has been probelm with the shear value it seems. It is too high. I do not understand the Shear rate patterns at all. For your consideration I have made a powerpoint file along with all the screenshot. I also provided the Section view. Could you please describe the reasons of Shear rate getting too high and also how there is inhomogenous distribution of shear as shown in the figure.

3) I do not understand the Press Speed results. How to extract knowledge out of it? For your consideraton I have provided the Compression Process Setting Wizard.

I know I am asking a lot but I do not have any other option than this. I am really worried about this results. Only your help could help me out. Thanks in advance. Best regards. I am eagerly waiting for your reply. I am seindg the Powerpoint File to you.

[bernor_mf]

Hi @riad.ashraf ,

would you mind to attacht your Moldflow study file?

It is in project folder, extension .sdy.

Zip it before attaching.

It would help to understand and analyze what you see and describe it ppt.

Thanks.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf ,

I am sending the attachment. Please have a look.

[bernor_mf]

Hi @riad.ashraf ,
just a first feedback on the most recent questions:

1)
This could be related to solver parameters, Filling parameters... Maximum %volume to fill per time step.
or Packing parameters... Maximum packing time step.

As you moved to compression by force, I think you should change Maximum packing time step to 0.1 s to capture the steps.
This will extend analysis time and required disk space.
Review analysis log if, end of line, you have a "P" for Pressure phase.

The part fills really fast from 2.013 to 2.195, so in 0.18 s.
This increase velocity and affects shear rate.

Seems as the compression phase is too fast.

2)
Material data: Tejin Limited : TN-8065S (PEN)
From Material details: Tab Recommended
Maximum shear stress: 0.5 MPa
Maximum shear rate: 100000 1/s

From ppt slides about Shear Rate, Shear Rate maximum, it is below 100000 1/s.

Shear Rate maximum is max over the cycle.
The results shows about 55000 1/s.

When flow rate drops, velocity drops, shear rate drops.
Hence low shear rate when filled and packed.
So it will become 0 at a time in cycle.
Sometimes change plot properties Scaling to Per Frame could help to better understand the results.

The reason you see symmetrical shear rate when scaling to 500 1/s is difficult to say.
Underlying reason is probably a velocity difference.
This could be mesh related, and that one side of part fills before other side, but a very small difference.

Please, provide study file as requested.

Have a good weekend.
Regards,
Berndt

[riad.ashraf]

dear @bernor_mf ,

have you received the model study file? Please let me know.

Best regards.

[bernor_mf]

Hi @riad.ashraf ,

confirm zip files are downloaded.

You could remove zip files from post if you wish.

Which Moldflow release do you use?

Good to know.

Any specific reason to run Cool on this study?

No Cool mesh, and yes, I see mold material is glass.

When setting a mold surface temperature, and no Cool, the surrounding temperature will be the same.

Regards,

Berndt

[riad.ashraf]

dear @bernor_mf ,

Thanks a lot.

I deleted the study file.

the version is 2017.

I do not use cooling for special purpose. Should I trim it off? is it needed?

Can you please explain me the 3rd point which I asked regarding the Press speed. I do not understand the graph. How does it work? Can you explain it after seeing my ppt file. It is in the last two pages.

Can you please explain about the shear rate? For my project is shear rate working fine? is it normal?

Just a qurious question. Should the shear rate be highest in the surface region? I studied that it would be near the surface but when I checked for my analysis, I found the highest shear in the surface part in the thickness direction. Is it okay?

best regards. Thanks again.

[bernor_mf]

Hi @riad.ashraf ,

you could use Cool analysis if wished.
Initially maybe not, just to get Flow to complete sooner to get results for process setup.
You use mold of glass, and probably no cooling circuits, so the way used should be okay.
Just not typical.

I reran your study in 2018.2, but it got a short short.
Cannot recall if you saw this in 2017 for same study.

"in the Fill time section, from 2.013s it suddenly jumps to 2.195s. I do not know the reasons of this jump.

I want more steps in the fill time. How could I do that? is this sudden jump normal?"
It the settings you have write to specified times: 1.9 / 2.0 / 2.2
So you asked solver to output this jump.
Refine the times if needed.

Shear rate maximum is close to mold wall.
See: Melt shear viscosity
http://www.dc.engr.scu.edu/cmdoc/dg_doc/develop/process/physics/b3200002.htm
The shear rate depends on velocity, and if well below maximum it is fine.

Press speed:
You press with a certain force.
As the resistance increase, compressing with same force, the speed goes down.

General comments on model:
There are 6 layers of tetras through thickness.
Recommended is at least 8 layers of tetras through thickness.
Do understand if you wish to have shorted edge length on part sides.
On main surface it could be coarser.
This would bring analysis time down.

Regards,
Berndt

[riad.ashraf]

Dear @bernor_mf ,

Thanks a lot for your reply.

First of all, I ran it in 2017 and did not get short shot.

Should I do something regarding this? What is your suggestion?

secondly, 'Review analysis log if, end of line, you have a "P" for Pressure phase.'

Where to find this option? in the Fill+Pack log? What do I need to check here?

Thirdly, 'The part fills really fast from 2.013 to 2.195, so in 0.18 s.This increase velocity and affects shear rate.Seems as the compression phase is too fast.'

What should I do to minimise it? I know it is well below the Highest Shear rate, still is there any way to minimise he shear rate maximum to lower level? If I want to minimize it then what should I do?

Thanks a lot. You are my saviour right now. I am blessed getting your help. Waiting for your reply.

[bernor_mf]

Hi @riad.ashraf ,

you are welcome. Happy to help, 😊

Regarding release of Moldflow Insight, if 2017 is what you have, use it.

The differences are due to solver development. Latest release is 2019.0.5.

(If you could update, it would be good, but no always possible which is understandable.)

"Review analysis log if, end of line, you have a "P" for Pressure phase."

> Yes, this is the log file . Not an option, a result text line in log file,

The compression force of 8 tonne is used by press immediately, hence a high speed.

I think you should use press speed, not too high, to have decent flow rate.

This will reduce velocity, hence shear rate.

Maybe 5 - 10 mm/s ?

Then limit press force to 8 tonne, as max available (I guess).

I think you should work on a small model in number of elements, to get a faster turn around of the

studies of process parameters.

The setup of injection-compression is more complex as more parameters compared to conventional injection molding, which is clearly seen and demonstrated in your example and our discussion.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf ,

Thanks a lot. I almost solve all the problems. I am working on the small prototype as you suggest.

Reagrding '

I think you should use press speed, not too high, to have decent flow rate.

This will reduce velocity, hence shear rate.

Maybe 5 - 10 mm/s ?

Then limit press force to 8 tonne, as max available (I guess).'

Could you please tell me what should be my press speed. What I did, I am telling you. As I told you I have two different mold materials and three different compression velocity profile. For these 6 models I found that 8 tonnes should be the highest press force. But for BS glass in the highst velocity profile, for automatic selection I found it to be 3.5 tonnes. Is it hampering my simulation as for automatic parameters it was accomplished in 3.5 tonnes but as I set it to 8 tonnes. Is it hampering overall simulation?

Besides that, '

This will reduce velocity, hence shear rate.

Maybe 5 - 10 mm/s ?

Then limit press force to 8 tonne, as max available (I guess).'

What do you exactly suggest? I did not get that point. What should I change in the process setiings? Could you please explain?

Best regards. I think I will be able to solve problems as you are helping me a lot. I am really indebted to you.

[bernor_mf]

Dear @riad.ashraf ,

right, two different mold materials and three different press speed profiles.

With all the information and discussion over time it is a bit difficult to keep up with all details.

I attach a zip file with 2 studies. (Remeshed for faster analysis run time.)
Fill+Pack analysis sequence .
(no Cool to initially avoid effects on process, used general mold temp 40C)

Please, review process settings, and run on your side.

Used the press profile:
2.8 mm 36.02 mm/s
2.8 mm 6.56 mm/s
2.9 mm 1.71 mm/s

Switch to press force control :
Only when the press force reaches compression force cap

Now, then tested for compression force 8 tonne and 3.5 tonne.
Which also is set as Absolute value and for 11 s.

Both studies completes ok.
I think the results are ok.

Note: For the elements, Compression element (3D), property I unchecked option "Frozen check for compression control"
With this option selected, only the selected elements are included in the frozen check. Or all, if set for the property.
For 3D injection compression models, the compression stroke is stopped if a sufficient number of surface elements are frozen.
This will/might cause compression stroke to stop to soon.
So when polymer melt becomes solid at element, no further press displacement will occur and press speed will remains zero.
Analysis will continue, but mold halves might not have closed.
If Cool, and this option on, and areas cool faster the compression stroke could stop to early.
Having this on could be a reason for hampering.

Hope this will wrap up the issue and you could complete the work.
Regards,
Berndt

[riad.ashraf]

Dear @bernor_mf ,

Without you I will not be able to reach so far. I got stuck in another phase. It is about the compression distance,time and speed calculation. As I earlier said, I have predeterminded values of compression speed considering our model then we also know the press open distance and divided it almost equal distance in press distance section but the result is giving is something absured. The press displacement curve is not as I ask. It should be homogenous graph with realtion to distance to time where with increase of time, I will get distance profile. Am i doing wrong while calculating the press distance, speed and time section? Can you explain how should I do that?

I am sending the screenshot. Best regards and thanks in advance.