Benefits from moldflow analysis software and moldflow simulation software.

We have used Autodesk Moldflow Insight almost a decade now and mostly with reactive molding (thermoset) or rubber injection.
Many positive things have happened to Autodesk Moldflow Insight since then.
Development has gone a long way, especially when it comes to meshing.
We always use 3D meshing because most geometries in the moldflow simulations we do must have a 3D mesh for a reliable result.
The 3D mesh uses tetrahedral elements (tetras) that have four nodes to describe a solid element.
A 3D mesh simulation takes longer and sets higher demands on your hardware, but you get a better result.
3D simulation fits thick wall thicknesses or complicated geometries.
To set a target value, we can say that when the wall thickness ratio exceeds 1 to 4, you should use 3D simulation.

Why moldflow analysis?

There are many arguments to why it is good with mold flow simulation or mold flow analysis.
Everything from reducing the number of prototypes, launching new products on the market faster or optimizing injection molded components.
There's nothing to say about it because this is pure fact.
In addition, there are many parameters that are not as visible, clear or easy to measure. Quality is such a thing.
In many cases, you cannot see with your eye that something is wrong or that it only occurs occasionally and you do not understand why.

Stressing the material or the fact that the mold has too little venting are examples of the above mentioned.
Sometimes the limits are exceeded and it becomes clearer that something is wrong.
You may get a burn mark on your part because there is air, which has been trapped in the cavity.
A burn mark is visible and you realize something is wrong. Then you can fix the problem.
If you have problems with stress (shear rate) it is often not that obvious.
You may have too high injection speed or a poor runner system and the stress will cause material degradation.
Your details do not get the right strength for example and you do not know why.
Then it is significantly harder to decide what needs to be done in order to make it work as intended.

One example we encountered when it comes to moldflow simulation is this:
The injection mold design has a cavity and the part looks like a large flat-bottomed drinking glass.
The finished injection molded part should later be further processed and therefore the gate is centered directly on the gable.
The wall thickness is about 5 mm and it is a cylindrical mold. You cannot fail to manufacture this part?
The part is so simple and thus it has the best conditions for being easily manufactured. It is circular with a direct gate or sprue gate in the center.
The part in rubber has in fact been manufactured around the clock 5 days a week for longer than 10 years.
It has never worked really well and the rejection has occasionally suddenly passed 10-15%.
Increased injection speed gives more problems while the problems vary with the material batches.

The geometry of the part is simple and it becomes less than 400,000 tetras which makes simulations go fast.
After about 12 hours of simulation we can safely say what the problem is. Although there is venting around the entire cavity, it is not enough.
About 500cm³ of air will pass out of the cavity through the air venting and the (air) resistance will simply be too great.
It also increases as the injection speed increases.

After doubling the depth of the air venting, the problems disappear.
The quality is getting high and uniform on the parts and the rejections are gone completely.
The injection time can in addition be reduced by 12 seconds.
These are things that we think make moldflow simulation invaluable, but to specify why is harder.

Moldflow and productivity.

One thing that is significantly easier to understand with moldflow simulation is increased productivity.
It is visible and directly measurable. Before we got the opportunity to use moldflow simulation, we did as well as possible.
Often with successful results and sometimes worse ones. This is of course much about experience and competence.
When you want to develop and maybe make even bigger or more advanced parts problems can arise.
You simply cannot handle it because you approach the limit of what is possible.
That is when you can get further forward by using tools such as moldflow simulation.

We can take O-rings as an example because it is just an O-ring is it not?
We will in addition talk about O-ring injection molds that have very shallow film gates and reactive molding.
Not reactive compression molding or reactive injection compression molding.
The problems with O-rings are that the variations in dimensions never seem to end.
If it is a larger O-ring there might only be one cavity in the injection mold but if it is a smaller O-ring there might be 500.
It is however still just an O-ring to be manufactured.
How many cavities there is room for is of course depending on the size of the outer diameter of the cavity and what there physically is room for in the injection molding tool.
At the same time you must take into account the total flow length.
If you are not careful a long flow length with a small cross section might be a very bad combination.
Adding a runner system around the entire cavity is of course a solution.
The customer probably does not want to pay for material waste and you will not get the assignment either.

Often we have had problems with O-rings where the inner diameter approaches or exceeds about 140mm and with a cross-sectional diameter of about 3mm.
The invisible errors - when you do not know why they arise - appear.
It may for example be when the measurement of the finished part varies too much and the quality requirements of cpk are not met or that the injection molding is generally bad and the rejections increase.
In some cases you have to double the number of film gates and thus get a bigger and more expensive runner system.
When the situation is really bad you might be forced to reduce the number of cavities from maybe 4 to 1.
This is not good for profitability.

Today there are answers to the problems that arose. Moldflow simulation was required in order to understand what was happening.
The problem was poor design of the runner system in combination with an excessive injection pressure.
Since the runner system was poorly designed the temperature of the material became very high in certain parts of the mold.
In addition - if a very high injection pressure is required to fill the cavities even more harmful parameters are created.
There was a problem with mold shrinkage because temperatures varied too much.
As the shrinkage was not stable due to temperature variations the measurements of the O-rings turned into a problem.
On top of this the quality requirements of cpk were not met. The high injection pressure resulted in many rejections.
When the injection pressure got too high this resulted in material degradation due to stress (shear rate) in the material.
Without the help of Autodesk Moldflow injection molding simulation software this knowledge would not exist.

What was sometimes a weakness has now turned into full strength.
When the problems with poorly designed runner systems and high injection pressures became known they could be taken care of.
Today a similar O-ring with an inner diameter of 200mm can be manufactured without an excessively large runner system.
The injection pressure is also not a problem. If larger injection molding machines were available the cavities could be expanded to 6 pieces.
When using tools like moldflow simulation you can solve the problems before they occur. You do not need to chance or take unnecessary risks.
Instead you can find out what works and what does not work at a relatively low cost.
If you have the opportunity to increase the size of the mold and fill it with more cavities you can do it.
You know in advance what works and what does not.

Investing in moldflow simulation software whether it is Autodesk Moldflow, Sigmasoft, Moldex3D, SolidWorks Plastics (SolidWorks moldflow) or any other SW can be a big step.
The most important thing is that when the results are experienced in production and they can be trusted then it is also possible to think bigger.
If our experience of moldflow simulation might argue in addition to the default arguments - these could be:

Moldflow and even more productivity.

Do you have parts that are suitable for manufacturing with two daylights, so called 3-plate or double-deck molds?
With moldflow simulation there is no problem balancing your injection molding tool.
We will show the result of an analysis of an O-ring made from FKM with 7+7 cavities in a 3-plate or a double-deck mold.
In this way it is possible to increase productivity further by approximately 50% compared to a regular 2-plate mold.
The approach is to analyze the fixed side first in order to optimize the runner system while keeping the pressure requirements under control.
When the fixed side is analyzed add the moving side and increase the cross sectional area of the runner system until the filling pattern is balanced.
The film gates should be exactly the same and the cavities should be positioned exactly above each other.
The result can look like this: