Stack mold / Family mold
Stack mold / Family mold
(OP)
We have a 64 cavity stack mold. It is a family mold so 32 cavities in the first stack make part A and 32 cavities in the second stack make part B. Parts A and B are the two sides of an electrical switch housing. Therefore parts A and B have very similar geometries. The differences are primarily in the interior of the parts where there are additional features on part B for holding electrical connectors. The tool utilizes a hot runner system. The material is polystyrene. The problem - of course - is that Part A and Part B fill out differently and production was constantly fighting the tool to get it to run properly. After a long period of sorting out defects related to this problem, a decision was made to run each side of the tool independently because less scrap was generated. This of course has doubled the amount of time required to produce the parts and significantly increased the cost so now the pressure has come back to engineering to get both sides of the tool running simultaneously again. I've previously had some experience with cold runner family molds and with putting flow inhibitors in some of the runners to balance out the flow. This met with a limited degree of success but now is not possible due to the hot runner system. What other options exist for balancing out a family mold?






RE: Stack mold / Family mold
Mike
RE: Stack mold / Family mold
Tip temperature.
In my opinion, family moulds are the work of the devil.
I can understand them for low volume, with a single cavity for each part, but once multiple cavities for each part are required, two moulds should be made and run in smaller machines to keep costs down. In the example above if two stack moulds were made with 2 X 16 cavity of part a and 2 X 16 cavity of part b, I expect very high yields could be produced and although 2 small machines costs more than one big one, good mouldings produce more income than does scrap.
The quicker you produce scrap, the more you lose.
True cycle times are number of parts that the customer accepts per hour, not the number of parts made per hour.
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RE: Stack mold / Family mold
Mike Halloran
Pembroke Pines, FL, USA
RE: Stack mold / Family mold
RE: Stack mold / Family mold
RE: Stack mold / Family mold
To learn more about the root cause, I suggest visiting http://www.meltflipper.com/p&s/mf/hot/hot.html. Figure 1 shows a stack mold and the development of shear biased flow to parting line 1.
Who manufactured the hot runner system?
dhuffy
RE: Stack mold / Family mold
Well, as for the surface runner molds that you look at in the future, use a Melt Flipper. This will solve the problems of balancing a poorly laid out surface runner molds. Never try to gauge primary to secondary runner and increase or decrease diameters to accomodate a filling imbalance.
The stack mold that you have described has two problems.
1). It uses a common manifold system to fill both parts "A" and "B".
2). Its a family mold.
If it is a valve gated mold then I suggest looking into weather or not the valve gates can be driven from seperate energizing sources. This will allow you to sequence the valve gates to the desired filling rates. i.e.. make one part "A" then the other "B" allow for cooling, open and repeat.
If this is a hot drop mold, meaning no valve gate. Then I suggest you look at the cooling and venting scheme of the mold. Make adjustments to one part "A" or "B" to create the fill desired.
RE: Stack mold / Family mold