Mold Simulations and faster cycles.

Everyone wants faster cycles but (because of the two generic excuses “we always did it that way” or “It's convenient”) most mold makers and engineers allow a common mistake to happen: the gates are too small and the runners too big.  Thick cross sections will always make for slower cycle times.  There is an easy solution to improve cycle times that is often overlooked: Most companies are doing fill simulations to be sure they cavity can be filled.  Almost any FEA modeling tool will work.  First do the normal simulation on the cavity.  The answer to this simulation will be the minimum pressure required to fill the tool.  Now simulate the gate, runner and sprue system and see if you can deliver this pressure to the cavity.  Keep playing with the diameters of the runner system until you are 10% over the minimum pressure to fill the cavity.  Remember full round runners lend themselves to every gate design, trapezoid or half round runners only work with sub-gates and three plate molds.  The only thing you need to keep in mind is that the cavity must be full and the gate NOT frozen off so you can pack the part out.  Packing can only occur when the gate is open, so calculating the runner/gate freeze-off time is another important variable.

Once the gate and runners are in the tool, they are difficult to change.  Although when you change gate and runner dimensions, you might also change the filling characteristics, this iterative process is well worth it.  You'd be surprised how small the cross sections of your runner systems need to be to still get good parts.  Small diameters mean faster cooling times, mean shorter cycles and less regrind, mean MORE PROFITS.  Keep the money.

Have fun.

Call with questions
Bill Tobin – President WJT Associates
wjtassociates.com
303 604 9592