6 Major Benefits of Injection Moulding Simulation in Polymer Part Design and Material Selection

Hello and welcome to a new blog post. Today we have a closer look at how injection molding simulations support us in part design, polymer material selection and processing.

1. Injection point and gate placement

Finding the optimal injection point and gating is key to fulfill certain aesthetics or warpage requirements. Also, it helps to prevent flow line situations and as a consequence lower mechanical performance of your part. Nowadays most polymer injection molding simulations have gate placement tools integrated which can recommend you the optimal injection point. 

2. Placement and balancing of runners

Bringing the molten polymers towards the cavity, runners (thin channels) are needed. Aim is to ensure an even filling of your cavity. Runner analysis is hand in hand with the gating analysis from the previous point and most simulation software have a runner balance tool too. 

3. Warpage and shrinkage situation 

Analyzing the shrinkage and warpage situation is in particular needed when you use fiber-reinforced polymers which have an effect on the shrinkage and warpage of your part. Filling simulation can use the information of the velocity vectors to predict fiber behavior in the final part. And over this route, calculate the effect on shrinkage and warpage. 

4. Packing situation 

Analyzing the packing situation allows you to set the packing pressure and time for your part. There are several factors such as the material and mould shape which are influencing the packing. Packing analysis covers the prediction of the gate freeze time, clamping force needed in this phase, and predict areas where high volumetric shrinkage may appear. 

5. Cooling - mold 

There are injection moulding simulation tools which allow a design and optimization of the cooling channel layout of your moving and fixed moulding half. However, most tools simulate a uniform mould cooling at a set temperature.

6. Processing - identify critical shear rates

In case you work with polymers which are sensitive to mechanical stresses like shear rates then it is worth to have a plan of action how to locate critical areas and solve them by using simulation or in a simple way with analytic methods.

In the video I made you can see the perforated plate in the version of side gating and central gating. This applied method of shear rate tracer release is possible in the virtual molding package Sigmasoft.

In the following are the four steps of my procedure I use in the post-processing after I have done a process simulation:

1) Watch the shear rate contour plot to get the "big picture"

2) Activate the shear rate tracer

3) Analyze the release places and where the sheared material will end up in the part (to predict if there will be a decrease in the mechanical properties of the part)

4) Make geometry changes or process changes (melt temperature; inlet velocity profile)

The shear rate tracer method helps you to locate the punctual critical areas. So far, those are the advantages of such an approach. Another aspect is that the allover simulation will take more time and more memory as well as more working space.

In detail you can read here about my shear rate analysis. 

What are some of the most used injection moulding simulations?

There are several suppliers and often used are Autodesk Moldflow, SIGMASOFT Virtual Molding, Moldex3D, Vero VISI Flow, Simcon CadMould, and Solidworks Plastics.

Thanks for reading and till next time!

Greetings,

Herwig 

#findoutaboutplastics

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Literature: 

[1] https://www.findoutaboutplastics.com/2015/04/injection-molding-filling-simulation-my.html

[2] https://www.findoutaboutplastics.com/2018/01/data-is-new-plastic-data-algorithms-in.html

[3] https://www.findoutaboutplastics.com/2021/03/the-future-of-plastics-manufacturing.html

[4]https://www.3erp.com/blog/how-injection-molding-simulation-software-helps-you-design-better-parts/

[5] https://www.downloadcloud.com/injection-molding-software.html

Injection molding filling simulation - My method for clear identification of regions with high shear rates

For showing you a method for a clear identification of high shear rate areas , I want to use again the perforated plate as a demonstration part.

We put lots of emphasis on parameters like filling pressure needed, gating position and temperature raise during filling.

But when you work with polymers which are sensitive to mechanical stresses like shear rates then it is worth to have a plan of action how to locate critical areas and solve them by using simulation or in a simple way with analytic methods.

In this post I show you a way of using CFD- based filling simulations, not only with contour plots but  also with shear rates tracers.

First, let's have a look at the video I made to have a better insight:

In the video you can see the perforated plate in the version of side gating and central gating. This applied method of shear rate tracer release is possible in the virtual molding package Sigmasoft.
For sure, the other suppliers like Moldflow or Moldex3d have similar options, which you can use in the following way.

General definitions:

A tracer is nothing else then a velocity vector colored when passing through a defined cell of your part. In case of the shear rate tracer, defining an area of cells is not possible. Furthermore, the definition of a critical shear rate is done.

You know at which level the shear rate can be dangerous regarding degradation of the polymer. This value you can use as a maximum border and a value underneath (25% less) presents as the releasing border of the tracer. So, you still have a safety pillow.  

My procedure:

This is my 4th step procedure I use in the post-processing after I have done a process simulation:

1) Watch the shear rate contour plot to get the "big picture"
2) Activate the shear rate tracer
3) Analyze the release places and where the sheared material will end up in the part (to predict if there will be a decrease in the mechanical properties of the part)
4) Make geometry changes or process changes (melt temperature; inlet velocity profile)

The final aim of every part and mold design should be that the critical areas are located at the gating. Here we use higher shear rates for decreasing viscosity and ensure a final mixing of the polymer, especially if it is colored). There should be no critical shear rate areas in the part itself.

Conclusions:

The shear rate tracer method is helps you to locate the punctual critical areas. So far, those are the advantages of such kind of approach. Another aspect is that the allover simulation will take more time and more memory as well as more working space.

Greetings,
Herwig

Filling simulation in the quoting process: Pareto principal is the solution! (incl. Video)

It is a simple formular you have to memorize:

Filling simulation + Pareto principal = Successful quoting process

What is the background?

Injection molding filling simulations are widely used in the design of molds and products. However, the utilization of this powerful tool for quoting processes is still a hidden-champion.

Well, it doesn’t need to be.

In this Blog post I want to share with you a possible way to go.

What are the most common negative thoughts regarding the use of simulation during the quotation phase?

(you might have already heard of one or another)

I have heard the following statements quiet often:

• It takes very long
• It needs more than one person to figure the results out
• You need to have years of experience to understand simulations and on their basis to take the right decisions

In fact, 80% of the results of the simulation analysis are enough to make a decision on the preplaned mold concept. And here the pareto principal takes its place: with 20% of time consumption you can reach already 80% of your results [1]. The remaining 20% of the results are achieved by using 80% of the time.

The user is able to make a statement if the mold concept is worth to follow or if changes need to be done by analyzing 80% of the filling simulation results. For the remaining 20 % of the results, more detailed program packages of flow simulation are needed. 

It is important to focus on the main results which are:

1. The filling flow fronts and weld lines. Here the user can get an insight into where weak points can occur as well as where air is trapped. For making a statement about the quality of the weld line, you need to look at the temperature of the flow front. If the temperature is too low, a proper welding will be no longer possible. The result is a mechanical weak point.
2. A contour plot of the pressure shows the injection pressure needed to completely fill the part. After obtaining this value, the necessary clamping force can be estimated.
3. Subsequently to the part filling, a first value of the expected cooling time can be seen. More accurate values are only possible by doing a complete cooling analysis. Furthermore, a calculation of the temperature distribution at the stage of the part's ejection can be done. Thus, the user gets a feeling of how complex the cooling system will be by the end.
4. On the basis of knowing flow conditions while filling, holding-pressure, and cooling, the next stage of calculating the shrinkage and warpage is reached. The user will not get an absolute value, but a trend regarding the direction of the part's warpage.
5. Then the position of the gate can be changed to achieve the lowest warpage of the part. Such procedure may be optional; an optimization of the welding line can be done too.

Having these results (Number 1. - 4.) a much more accurate cost calculation of the part and mold, in comparison to simple analytical calculations, can be done. The time consumption is much lower and when keeping the Pareto-principle in your head, success is on the way to come!

By the end I want to show you an example of a filling analysis (Programme: Sigmasoft®) of a perforated plate (filling time: 2 seconds, material: polypropylene). Two different gating systems have been applied. The pressure, shear rate and welding fronts were compared to each other using just a simple filling simulation.

Video link

[1] H. Class: Simulation in der Angebotsphase, Kunststoffe 2/2015