Smart Molding International 2-2022

42 simulation & software smart_molding international 2/2022 Virtual molding instead of just simu- lation: the mold makes the difference! Not only the behavior of the part but also the thermal behavior of the mold can be analyzed and optimized with SIGMASOFT ®elastomer. The molder can now accelerate the development process and achieve the desired part quality from the very first shot. Fur- thermore, he will be able to start the virtual series production even before his mold is built. Case study After production crack formation could be observed on one side of a suspension bushing which caused a malfunction (Fig. 1). The molder reached out to SIGMA to analyze the possible reasons for this failure. The part was simulated together with the full mold and all process pa- rameters to achieve a realistic rep- resentation and to consider all fac- tors influencing the cracking: rubber part, runner system, metallic insert, contour providing plastic inserts. In this way, the real production could exactly be reproduced over several molding cycles (Fig. 2). The analysis of the current status showed big differences of the tem- peratures within the rubber part. The temperatures of the outer regions were much higher compared to the inner regions, due to the thickness of the metal insert. Additionally, it became evident that the plastic in- sert (PEEK) blocked the heat transfer into the rubber. Thus, it was not pos- sible to reach the necessary curing inside the critical area (circled in Fig. 3, left). Even after a cycle time of 420 s (395 s heating time) there was still significant variation of the cur- ing throughout the part and – even more important – an average curing degree of only 20%, which was dis- tinctly too low (Fig. 4, left). Possible counter measures include a longer cycle time (resulting in high- er production costs) or the optimi- zation of the curing behavior inside the part. It was proposed to preheat the inserts to 100°C. This change was included into the virtual process and a second thermal rheological analysis of the filling, holding and heating phase was performed. The preheated inserts led to a more ho- mogenous temperature distribution inside the part. In the critical area the temperature could be increased by 40°C with this approach (Fig. 3, right). The higher average tempera- ture, the more homogenous temper - ature distribution and the bigger en- ergy amount available (mostly in the metal inserts) led to a higher curing degree of 93% instead of 20% after a cycle time of 420 s (Fig. 4, right). Thus, the warpage induced by curing was also reduced. Besides achieving a higher curing degree in the critical area (which improves the local mechanical strength), the local stresses could also be reduced. Both together pre- vent the cracking of the part. The problem of crack formation in the suspension bushing thus could be avoided by preheating the inserts. A possible additional reduction of the cycle time was not investigated. Figure 1: Cracks in a rubber part (suspension bushing) after injection molding (all pictures: SIGMA) Figure 2: Modelling of all components. Red: elastomer compound; blue: plastic insert (PEEK); green: metal insert (Steel) Elastomer troubleshooting: the influence of insert preheating The problem of crack formation in rubber parts can be avoided by preheating the inserts.