Sunday 15 March 2015

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.

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

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