multi cavity moulds 4

[evapi]

We have a new product consisting of 20 different components of various sizes. We wanted to produce individual moulds with 4 cavities but it turns out they are more expensive than we though. We have a quote for making 2 family moulds but we are afraid it will not work irrespectively of the toolmaker assurance. Any good ideas of how to bypass this problem and test all components effectively handling also low production demands?

 

[MikeHalloran]

Any money 'invested' in a family mold might as well be burned.

Consider starting with single- cavity soft molds, e.g., aluminum,

OR with single cavities sunk in mold bases big enough for four cavities. Add cavities as production ramps up, after the part design stabilizes.





Mike Halloran
Pembroke Pines, FL, USA

 

[Pud]

Hi,

How I agree with Mike!!

As a moulder, we do not use "family" moulds - I tell our customers who have these bright ideas that it is more accurately called a "dysfunctional family" tool.

If the customer insists, then they are welcome to find some other moulder who is willing to waste time and money!

btw - never believe a toolmaker!! - talk to the moulder (or should that be "molder"?!)

Rgds

Harry

 

[dhuffy]

I also strongly discourage family molds. I ran them in my previous job and hated every minute of it. But at times they are an evil necessity. They can be done successfully if certain guidelines are followed, especially regarding the amount of non-similarities between the parts being molded. We have helped companies design family molds for success, and have actually cut costs versus individual 4 cavity molds. Here is a link to one such 4+4 family mold you may enjoy reading...

http://www.beaumontinc.com/news/pr/05-03.html

Dave

 

[patprimmer]

Family moulds are sometimes a necessary evil. They do greatly restrict the processing window, sometimes to the extent that a suitable window is not possible for all cavities simultaneously.

Also an excess of rejects on one cavity only gives an excess of other parts.

Family moulds work very well on mirror images where an otherwise identical left and right hand part are required.

They are especially problematic where there is a considerable variation in part weight, flow length or section thickness between the cavities.

10 parts in each family mould sounds like a horror story to me. About 7 moulds with about 3 parts each or 5 moulds with 4 parts each sounds maybe doable, depending on part geometry.

Please discuss this in detail with your moulder and the raw materials supplier rather than a toolmaker or at least in addition to the toolmaker. Toolmaking is a highly skilled profession, but does not necessarily indicate a good understanding of the entire moulding process.

Talk to each together to get a consensus, but also individually to get a more frank opinion of each others input. Remember the others all have overlapping relationships on other projects as well as yours.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evapi]

Many thanks for the replies,

I thought of adding flow restrictors/valves (if there are such things) so that in the worst case senario by which the flow can not be balanced, we can at least produce the parts individually for further tests and sampling. Is this possible, or would the problems still exist?

 

[patprimmer]

The runner can be blocked with a pin that has a grove to match the runner. It can be turned one way to make parts or at 90 deg to block the cavity, but then, you are using a very large mould in a large expensive machine to mould a small part.

There is more than just balancing the flow. That can be done by tuning gate size. For example, different fill speeds, different pack conditions to control size, finish warping etc can also be problems.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[BradJH]

As a molder, I have seen family molds work but it it VERY rare. If you want to save tooling costs for low production volumes I suggest that you look into modular molds like a master unit die.

 

[injectionmolder]

Family tools the devil of the plastics shop. I have found that if possible and done right work better by balance the runner according to the thickness, and gates to be kept the same size. However, still a nightmare to get to a profitable production level.

Regards

 

[ozchevy]

Dare I say it - "I'm a Toolmaker" I agree family dies do not work. It's extremely hard to balance all the components so that the flow of molten plastic through the runners/sprues and or DME Hot runner gate system will mould correctly. Too many variables with components of various sizes, different cooling rates, venting problems, ejection problems.

Bite the bullet, buy multi cavity individual dies.
The days of hit and miss with tooling are gone with the latest Cad/Cam software around these days, you can get very good quality and workable dies requiring little mods if they don't mould exactly right from word go.

Good luck with it anyway.

 

[evapi]

I have finally finished the family molds. They are OK but not excelent... At least I got a chance to test the product and make some pilot runs. Now I am developing tools for high production and I came up with a less costly solution: Make a few sets of moulds with hot runners (6 outlets) and have changeable inserts. In one case I have a total of 16 parts and I am thinking of having 6 inserts of each so that when inserted the mould will balance correctly since all parts wil be the same. My problem is that 16 different designs will need pins at so many different places that only a few will much. How can you handle this ejector pin problem. I also thank all for the replies. They are very helpfull.