Avoiding Racetracking through Mold Flow Analysis
During the design for manufacture stage, one important consideration is the ability of the resin to adequately fill the core and cavity of the mold. Extra difficulty in filling can result in either short shots or overpacking, which increases the risk of flash on the molded parts.
Filling difficulties can be caused by variations in wall thicknesses, especially when thin-walled areas are close in proximity to relatively thick-walled areas. A thin-walled section surrounded by thicker walls poses the risk of a gas trap. This happens because the resin is slow to fill the thin wall and flows more quickly on the surrounding features. This effect is referred to as racetracking.
The first step is to know whether the risk is present. Modeling the fill rates with mold flow analysis during the mold design phase will help identify those areas most at risk of racetracking.
Once these areas of risk are identified, the analysis can then be run to assess potential alternatives to address the issue. Adding vents and gates is the common reactive practice when this issue is not identified until after the fact. But this supposedly ‘intuitive’ solution can actually worsen the problem and create multiple gas traps.
Using mold flow analysis to optimize gate designs can sometimes yield non-intuitive solutions. As the likelihood and impact of the risk increases, the benefits of investing the time and resources to perform mold flow analysis also increase.