25 years of plastic simulation - sigmasoft virtual molding

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25 Years of Plastic simulation

IntroductionPlastic injection moulding simulation is coming on age; arbitrarily one can put the initial industry adoption of plastic simulation at the K’83 which makes that it is celebrating its 25th anniversary this year. All though prior to the K’83 plastic simulation was also used, on a not so a wide spread and more academic scale by a couple of innovative polymer producers through dial-up services. Over these 25 years plastic simulation has evolved steadily, through the formation years to the second generation with shrinkage warpage functionality becoming available in 1990 to the current third generation providing 3D simulation.

3D simulation is the current buzz word and the plastic professionals know that 3D is about the three dimensional flow of the polymer into the cavity. The 3D filling simulation is of course necessary for accurately simulating voluminous geometries, which was a short coming of the previous software generations. However equally important is the 3D simulation of the thermal flow. Thinking, exercising and conceptualizing the thermal flows in moulds and the polymer is not yet so developed as thinking, exercising and conceptualizing the polymer flow. This is because the filling of cavities is quite visible and imaginable, moulded shorts shots help to understand how polymer flows. Also having a moulded product will provide insight into how polymer flows. One can easily discuss polymer flow with one and another because of the short shots and the end product. This is not so with the thermal flows, it is a challenge to discuss thermal flows in moulds, because we do not have an actual example of the thermal flow, a sort of a snap shot which we can hold. For sure professionals do discuss thermal flows however because of the transient nature and lacking the proof of the pudding their thermal flow models are often still simple and basic. A nice example of this is the current fashion of discussing cavity contour following cooling channels; advocates of these systems do instil, directly or indirectly state that it is imperative to take the heat away as quickly as possible. The other side of the coin, any other ‘negative’ phenomena coming with such a cooling are not discussed. Undesirable effects induced by this type of cooling could be a disadvantageous thermal distribution which could return a highly warped product. For semi crystalline products with a contour cooling (conformal cooling) the polymer will not have fully crystallized which will mean that during its service life it will continue to crystallize which means it will continue to shrink.


SIGMA Engineering from Aachen Germany, developer of the three dimensional polymer system simulation product suite SIGMASOFT has used their Frontier optimization module to provide an insight in the impact of the transient thermal distribution in moulds. Frontier can fully automatically step wise move the position of cooling channels between user specified limits. For instance the three cooling channels found in a typical mobile telephone housing mould can be varied as show in Fig. 1. The two cooling channels in the ejector side, one contour following channel and one regular channel can be moved independently from each other closer and further away from the cavity.

The contour following channel has been specified to be able to get as close as 10 mm towards the cavity wall. On the fixed side the cooling channel is specified to ‘narrow and broaden’ itself. Variant # 53 in Fig. 2 shows the cooling channels in their outer positions. The target is to find a cooling channel configuration which provides minimal shrinkage between two mounting bosses, as depicted in Fig. 3. And at the same time to find the quickest cycle time in this case specified as the smallest melt volume at the end of the filling phase. The melt volume is the volume of polymer which is still above a specified temperature.

Fig.1. Variation limits for the three cooling channels.


SIGMASOFT Frontier was started with the cooling channel configuration in their outer limits, variant # 53. Figure 4 depicts the number of simulations performed by Frontier. In the Pareto-plot, on the x-axes the cooling time is depicted for each configuration and on the y-axes the shrinkage is given between the two posts. Variant # 53 with the cooling channels in the outer positions returns a high shrinkage and it returns a long cycle time. All though it is interesting to see that 10 cooling channel configurations return even worse cooling times while their cooling channels are closer to the mould wall cavity! Variant # 41 is the cooing channel configuration which returns the best cycle times however it also returns the highest shrinkage. Variant # 16 returns a quite low shrinkage and returns a quick cycle.

Interesting to note between variant # 41 and variant # 16 is however that the contour following cooling channel is only moved 5 mm more outward. The other channels have the same positions. In a way it is scary to note that by just moving one cooling channel 5 mm does make such a distinct impact on the shrinkage between the posts.

Fig. 2 Outer positions of the cooling channels

Fig. 3. Optimization target is minimal shrinkage between the posts.


A famous saying under plastic professionals comes strongly to mind; ‘in-engineered problems can not always be processed out’. Meaning that in the plastic value chain decisions are made which are not so easily reversible. The cutting of the cavity and the drilling of the cooling channels are prime examples. And if during the moulding trials problems occur these can sometimes be corrected by varying the process settings like melt temperature, mould temperature, injection time, packing profile and the like. However the saying points out that sometimes an unfortunate series of non reversible mould decisions are made which produce an undesirable part quality which can not be corrected by the remaining process or material freedom.

It has to be concluded that the lay-out of cooling channels is a sensitive decision, and that without the support of an accurate true 3D filling simulation with a true 3D thermal solver it is sheer impossible to engineer optimal moulds meeting conflicting criteria first time right.

And looking at the mobile telephone housing once more, one will realize that this is a typical thin shell product, demonstrating that 3D injection moulding should not be seen as only for voluminous geometries.

SIGMASOFT can incorporate the complete mould with all its details, by doing so capturing all the details to simulate accurately the thermal distribution in the mould.

Fig. 4. Pareto-plot, cooling channel variations as function of the cooling time – shrinkage

V 41

V 16 Optimal

V 53


At times a complete multi cavity hot-runner system with all the components and the complete mould with sometimes up to over 2500 geometry entities are read in over direct translators. For this reason SIGMA prefers to call their program a polymer system simulation code instead of just plastic simulation or a mudflow simulation.

Polymer instead of plastics because it will not only simulate thermoplastics but also rubbers, elastomers, thermosets and PIM (powder injection moulding). System simulation because any control system which can be incorporated, like for instance pulse cooling or incorporating the heating-bands of the hot runner complete with thermocouples and the PID controllers. Not a temperature will be assigned to the heater-bands but an electrical power in Watts is fed to the heater-band in the simulation. The amount of Watts fed to the heater bands is controlled by the software PID controller, representing accurately how such a system behaves in real life. The SIGMASOFT heater-band functionality will show the thermal performance for hot-runners. However this functionality is also used to engineer rubber article moulds where often a well targeted thermal flow is required to support the cross linking of otherwise slowly cross linking areas.

Of course it is no requirement that the fully detailed mould and hot-runner are available, the SIGMA workflow does support the engineering of moulds, cavities/geometries and processes in the early stages of development.

SIGMASOFT over time has implemented multiple industry first break-troughs, some of earlier break-troughs were multi-cycle simulation, multi-component simulation, fully coupled simulation with part inserts. A more recent industry first was crystallization functionality and high cooling rate pVT. On the Kunststoffe’ 07 in-mould stress relaxation with automatic shrinkage hindrance assessment and ejector force simulation have been implemented.


In Fig. 6 the part is depicted with the ejector configuration. Figure 7 depicts shape following ejector ends with the associating force vectors displayed. It is obvious that the two inner ejectors do the grunt of the work. This is so due to the way the housing shrinks onto the mould, which is depicted in Fig. 8. However the force plot for the ejectors changes fundamentally once the ejector-ends are made flat instead of contour following. Now the ‘lower outer’ ejectors contribute more and the inner ejectors are less contributing. The four ‘top’ ejectors do not significantly help in either case.

Fig. 5 Plastic part with ejectors, results are strain due to ejection.

Fig. 6. Ejection forces with contour following ejector ends.


SIGMA Engineering proudly continues what the founding fathers of the plastic simulation industry started more 25 years ago, developing software which will serve the polymer injection moulding industry creating better products, better moulds and better processes through capturing plastic phenomena.

Fig.7 Contact pressure at end of packing between part and cavity.

Fig. 8 Ejector forces for flat topped ejector.


SIGMA® (www.sigmasofT.de) is 100% owned by MAGMA® (www.magmasoft.de), the world market leader in casting process simulation technology based in Aachen, Germany. Our SIGMASOFT® Virtual Molding technology optimizes the manufacturing process for injection molded plastic components. SIGMASOFT® Virtual Molding combines the 3D geometry of the parts and runners with the complete mold assembly and temperature control system and incorporates the actual production process to develop a turnkey injection mold with an optimized process.

At SIGMA® and MAGMA®, our goal is to help our customers achieve required part quality during the first trial. The two product lines – injection molded polymers and metal castings – share the same 3D simulation technologies focused on the simultaneous optimization of design and process. SIGMASOFT® Virtual Molding thus includes a variety of process-specific models and 3D simulation methods developed, validated and constantly improved for over 25 years. A process-driven simulation tool, SIGMASOFT® Virtual Molding provides a tremendous benefit to production facilities. Imagine your business when every mold you build produces required quality the first time, every time. That is our goal. This technology cannot be compared to any other simulation approach employed in plastics injection molding.

New product success requires a different communication between designs, materials, and processes that design simulation is not meant for. SIGMASOFT® Virtual Molding provides this communication. SIGMA® support engineers, with 450 years of combined technical education and practical experience, can support your engineering goals with applications specific solutions. SIGMA® offers direct sales, engineering, training, implementation, and support, by plastics engineers worldwide.

25 years of plastic simulation - sigmasoft virtual molding

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