Injection compression molding node analysis

[riad.ashraf]

Dear Altruist,

I have been working on an Injection Compression moulding process. My part is 150 mm in length. Right now, I have been extracting the nodal analysis of shear rate. I selected a time frame of 2.8 sec. I have three different velocity profile selected for this project. For the initial length from the injection point like 10 mm 20 mm the 2.8 sec gives value for all three velocity profiles but for the later phase like after 80 mm there is no data for 2.8 sec for low velocity profile. I know there could be a lot of reasons but what is the main reasons of it?? Why not data started from 1?? Rather than starting from 3 or other data???

Best regards

Riad

[riad.ashraf]

@bernor_mf  you know this project. Could you help me again? 

Thanks in advance 🙂 

[bernor_mf]

@riad.ashraf 

Hi Riad,

thank you for letting me know.

Now, I am not sure I fully understand what is causing what you see.

A reason could be the intermediate output, when intermediate results are written.

This is set in Advanced options and solver parameters, Intermediate results.

You might need to set more intervals or specify times to write the results.

If shear rate is 0 in plot, the flow has stopped.

Maybe this is true for the 3rd velocity profile, at the node where result is collected?

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf  Thanks so much for the reply. You know the project very well. I used two different materials, and I am trying to get some results from the Injection point at specific time and specific node. I am sending you the screenshot so that it will be easier for you to understand. 

For 60 mm from the injection point the time of 2.8 gives me result for all the three velocity profile but for 80 mm from the injection point I did not find the 2.8 sec for the lowest velocity profile.

What could be the reason for it? And also how do I explain these graphs as for 60 mm there are two peaks which is OK but for 80 mm the graph looks different. Could you help me out? 

Thanks in advance.  

[bernor_mf]

@riad.ashraf 

Hi Riad,

if you do not find result at 2.8 s for the lowest velocity profile at 80mm, you need to check if results are written at all.
Could the lowest velocity profile cause a short shot?

The lowest velocity profile at 60 mm shows a much lower shear rate, indicating a lower velocity.
The pressure might then be to low to maintain the velocity of melt, it stalls, freezes, short short, hence no result.

So, animate the Velocity plot (or Shear Rate plot) to see at which time there is result.
Velocity plot might be giving a better information of if melt is still moving.
It might be so that the result is at different time step than 2.8s.

Hope you find the cause of this to resolve the issue.
Regards,
Berndt

[riad.ashraf]

Dear @bernor_mf  I can not express how much thankful I am to you. You are my savoir. 

Please help me one more time. 

Regarding the  2.8 s for the lowest velocity profile at 80 mm I got some results for shear rate but It started from 3.6 s and as a result I do not have any data related to 2.8s 

What could be the reason that the data started from 3.6s rather than lower values? I am attaching the node analysis results for your help so that you can understand it better. 

I have got some more to explain. I am attaching here.

I am asking the particular questions also. 

1.  Regarding velocity vs. position BS and SS, all Velocity Profile, at position 10 mm, how to describe this graph properly? I can see that the highest rate is at centre position and then it gradually decreases, is it the rheological properties of Injection compression moulding? And then  for all velocity profile the SS shows higher value what are the disadvantages over BS due to this higher rate?

2. Regarding shear rate vs. position SS and BS, all Velocity Profile,10 mm again I got confused with the graph. There are two peaks. Is it OK? How to describe it please let me know. What be my conclusions after seeing this graph specially comparing two different materials of BS and SS? 

3. Regarding shear rate vs. position from the injection point The Highest Velocity Profile, it is clearly visible that when the position is increased for all cases the shear rate increases. Is there anything special which I do not see? Is there any concluding remark for that? 

4. Regarding  Shear rate vs Velocity at specific time, I tried to put the shear rate vs velocity profile and tried to understand the process. It is quite obvious that Highest profile will give the highest results. Still is there any concluding remark?  

5. after analysing all these, what do you think, is BS glass a better mould material than SS in ICM? Just say your opinion and the reasons behind it. 

I know it is a lot. But I am highly relying on you as you are the only one who could help me out. Please help me with your valuable time. Many thanks in advance. 

[bernor_mf]

@riad.ashraf 

Hi Riad,

well, quite a bunch of detailed questions.😊
Pushing this a bit, to be a community discussions.
More of questions for your mentor or Autodesk tech support.
Anyway, I will reply to your questions. 😊

"What could be the reason that the data started from 3.6s rather than lower values?"
The lower velocity makes the flow front travel slower, hence arrives to the node later.

Generally, I think you need to understand the relation of velocity and shear rate for thermoplastics melt.
They are related, and related to melt viscosity.

If you read and understand this, it will shed light over your questions.

You need to dive in to this and understand the relation.

See this link: Melt shear viscosity

"Generally speaking, the faster the adjacent material elements move over each other, the higher the shear rate is.
Therefore, for a typical melt flow velocity profile, shown in (a), it is clear that the shear rate is highest at the mold-melt interface (or at the melt-solid interface if there is a frozen polymer layer).
On the other hand, the shear rate approaches zero at the center line because there is no relative material element movement due to flow symmetry, as shown in Figure 2 (b).
Shear rate is an important flow parameter since it influences the melt viscosity and the amount of shear (viscous) heating"
And see: FIGURE 2. (a) A typical velocity profile with relative flow element movement and (b) the corresponding shear rate distribution in injection molding filling.

1) Highest velocity in center of thickness for thermoplastic injection molding and compression molding.
If higher or lower velocity is better depends on maximum shear rate allowed for material.
And if velocity causes frictional heating and too high for material.
Higher velocity in center will create higher relative movement of layers in plastic melt, hence higher shear rate.
A too high shear rate could cause temperature increase, material degradation. Review material properties for limits.

See this link for relation and basic understanding:
Melt shear viscosity

2) Yes, the two peaks is the shear rate.
See information in Melt shear viscosity

3) Increase of velocity will increase shear rate
See information in Melt shear viscosity
FIGURE 2. (a) A typical velocity profile with relative flow element movement and (b) the corresponding shear rate distribution in injection molding filling.

4) Expected: Increase of velocity will increase shear rate
This is well explained in link:
Melt shear viscosity

5) Seems as both could work, with decent velocity profile: not too slow, and not too fast
Generally:
Too slow, low velocity, low shear rate, higher pressure, higher temperature drop of melt
Too fast, higher velocity, higher shear rate, higher pressure, temperature increase of melt
Yes, pressure could be higher if too low or too high velocity.

You need to compare:
Pressure to fill
Fill balance : is part filled to extremities at same time and pressure
Temperature (decreases or increases?) should be close to set melt temperature. Some difference to be expected though.
Much higher indicate shear heating
Much lower indicate loss of temperature and maybe stall of flow front.

How is material data shear rate meeting the process result.

Over and out for this time. 😊
Hope this helps and that you will be able to complete this now.
Regards,
Berndt

[riad.ashraf]

Dear @bernor_mf ,

I can not express enough gratitude for these help. It means a lot. I am really grateful. I am sending one last pictures for your feedback. For the Comparison of Thermal Properties I found out that the temperature graph for BS tends to 80 °C whereas for SS it is 30°c but all the criteria for the simulation were same for these two different materials. Is there any issue or is it okay? I am sending the screenshot for your help. 

Best regards

Riad 

[bernor_mf]

@riad.ashraf 

Hi Riad,

which material is SS and BS in clear text?

Are they available in Moldflow official database?

In the matter of process conditions, is the mold temperature really set to the same for simulation?

Looking at temperature profile, it seems as mold wall temperature is higher for BS material compared with SS material.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf 

Thanks  for the reply.

Firstly, SS means stainless steel and BS means Borosilicate Glass.

No they are not in the database. I put them manually by changing thermal and electrical properties of material in the settings.

I do not have access of the simulation software right now but as far as I know that I set the temperature to the same. I did no change anything. Could it be due to the position of 80 mm from the injection point where these two materials are behaving differently? What could be the explanation if everything is same. I am a bit confused. From my opinion is it due to the lower thermal coefficient I set for Borosilicate glass(BS) which shows resistance? 

Eagerly waiting for your reply. Thanks in advance. 

[bernor_mf]

@riad.ashraf 

Hello Riad,

thank you for clarification.

So SS and BS are mold material, and then the same thermoplastic material is used in both cases?

Looking and temperature profile in previous posted picture, the outer points (low temperature) seems to be on mold wall, right?
Thermal properties of mold material could have an effect.
But analysis with not using Cool will use set mold temperature, as mold wall temperature.
I would check that first, what set in study file.

Did you run Cool analysis?

(Meaning Cool+Fill+Pack, and with modeled cooling circuits.)

Regards,

Berndt

[riad.ashraf]

Dear,

Thanks a lot for the reply.

Yes, the outer points (low temperature) is on mold wall, the direction is in the thickness portion from the bottom(0) to top(1.5)

I used the cooling options while doing simulation. So it was a Fill+Pack+Cool+Warp analysis.

Same thermoplastic material of Teonex PEN has been used and only the compression surface has been changed. I am sending you one screenshot so that you will understand which I have changed and also the thermoplastic material.

Thanks in advance. 

[bernor_mf]

@riad.ashraf 

Hi Riad,

thanks for the information.

If you ran Cool analysis, with same inlet temperature on cooling circuits for SS and BS, and BS has higher thermal resistance, then mold wall temperature will be higher.

What was inlet temperature for cooling circuits in Cool analysis?

The thermoplastic recommended mold temperature is 80C.

For normal tool steel (P20) the inlet temperature for cooling circuits are normally 10-20C below the aimed

mold wall temperature.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf 

Thanks a lot for the answer.

Regarding What was inlet temperature for cooling circuits in Cool analysis?

It is the default settings. I did not change anything on it but I do not exactly remember what is the default settings as I do not have the access from the lab also.

Thanks for the info about tool steel. Is it is the case then showing resistance is a good sign or bad for BS? At least if I want to compare BS with SS, then what should I focus on? From my opinion BS shows resistance but it also shows sudden huge jump in temperature. Is it good or bad? 

Best regards 

Riad 

[bernor_mf]

@riad.ashraf 

Hello Riad,

the default inlet temperature for cooling circuit is 25C.

The used Thermoplastics material, acc. to picture:
Recommended mold temperature: 80C
Mold temperature range: 20-150C

If using same time for cooling, and the default inlet temperature for cooling circuit 25C.

BS has higher thermal resistance, hence higher mold wall temperature.

Difficult to say what is good or bad in this case without the whole picture.

Recommended mold temperature: 80C, which BS shows to be closer to with the input used for simulation.

But will take longer time to cool and eject.

Is cycle time important?

SS mold wall temperature is within Mold temperature range, but on lower side.

Mold wall temperature variance?  How does temperature vary over mold?

Rule of thumb: within +/- 10C for amorphous material and +/- 5C for semi-crystalline material.

Time to reach ejection temperature? Is cycle time important?

Temperature jump? Not sure I understand what you mean.

The melt temperature could increase if velocity increase, hence a frictional heating of melt.

A sudden increase in temperature could indicate pressure spike, and increased velocity.

Should be avoided.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf 

Thanks a lot for the info. I am really grateful for this help and support. I will try to use it and if something arises I am knocking you. I can not show enough gratitude for these help.

Best regards

Riad 

[bernor_mf · Accepted solution]

@riad.ashraf 

Hi Riad,

thank you for the feedback.

Hope you will complete the project now, and wish you success.

If replies resolves issues, please mark as "Accepted Solution".

Thank you.

Regards,

Berndt

[riad.ashraf]

Dear @bernor_mf Thanks a lot. My project is done, and I am grateful for your support. Just for my better understanding, I am sending one simple image of the PVT diagram which has been taken from the Mold flow. Could you please explain, how could I define and describe the volumetric shrinkage for two different processes of Injection Molding and Injection Compression Molding? How to draw and define that in ICM, the volumetric shrinkage is less than IM? the polymer material is Teonex-8065s. I am eagerly waiting for your reply and will be grateful if you please draw and explain 😄

[bernor_mf]

Hi Riad,

I think you could draw this in the graph yourself with help from following information.

Hank Tsai have an explanation of this for thermoplastic and conventional injection molding process.
Understanding to Plastics P-V-T Relationship on Injection Molding Process

This is a good picture for what happens at different positions near gate and far from gate.

The main difference between Injection Molding (IM) and Injection Compression Molding (ICM) in packing phase
is that applied packing pressure in part varies by distance from gate in IM (hence the aim is often to create a packing profile, but pressure drop also depends on part size and thickness), and in ICM the packing pressure is applied with compression of mold halves, more even pressure over the cavity and part.
So ICM has a more even packing, hence it could be described with one curve trace in PVT-graph.

What you have to keep in mind, is that when using ICM, the cavity is easier to fill, and you might add more melt volume.
This will result in a higher part weight, and less volumetric shrinkage.

Review part weight from your simulations, IM and ICM, to understand the difference.
Review packing pressure from your simulations, IM and ICM, to get an understanding of applied packing pressure difference.
This should help on how to draw and complete a process curve(s) in the PVT-graph.

Hope this helps.
Regards,
Berndt