Designing effective cold runner systems is as important as designing a molded part. After optimizing the gate location for a new part design, the next step is to determine the best cold runner size. Cold runner size will influence overall part quality, molding cycle time, and overall profits.
Identifying critical material process characterizations that will influence sizing the cold runner include shear sensitivity of the polymer, viscosity, and cooling behavior. Additionally, such factors as overall size of the part, maximum wall thickness, gate shape and locations, cycle time requirements, and the molding machines’ available injection pressure and clamp tonnage capabilities must all be considered.
Establishing the optimal volume, injection pressures, and clamp tonnages for different sized runner systems is essential – these factors will have significant impact on overall profitability.
Although a small difference in volume may not seem significant, the impact of this reduction over the course of multiple cycles can have a significant impact. Let’s use an example of a 7.5-gram difference in weight between two different cold runner designs. This reduction in weight with a cycle time of 20 seconds would save 22.5 grams per minute, 1,350 grams per hour, and 32 kilograms per day.
Bringing material cost into this evaluation, assuming the material is $3 per kilogram, the savings would be around $100 per day, $3,000 per month, and $36,000 per year. And this does not even consider the reduced cycle time that would create even more savings!
Understanding how to optimize runner sizes for parts will enhance the molding process and reduce the cycle time. By using the correct runner sizes, material waste can be minimized, costs can be reduced, and cycle times can be optimized for higher profitability.