if i want to add an extra cavity in my mold with two cavity already…which risks i need to take account and someone did this before…which results did you had (good or not)?

I would recommend adding two more cavities instead of 1. you need a geometrically balanced system if you want decent molding conditions.

Everything is possible . We need just to have more informations. Which kind of part ? Which kind of raw material ? How old is the existing tool ? So many criterias to take in account before to give you the right answer .

1: whether there's enough space for the additional cavity.
2: whether the press tonage is enough.

if there 2 are ok, all other issues can be fixed.

I agree with Kevin R. But you must also consider the fill time for the tool now. If you want to make the same dimensional parts you have to be sure that the machine can fill the additional cavities in the same fill time. Also does the machine have enough pressure to achieve the extra cavities.

Another thought to consider, is the mold running good now? Sometimes adding more cavities to a poorly designed mold is throwing good money after bad situation, it only gets worse...

Jorge Santos-
After analysis of the mold and mold design may be possible.
It is an operation that is done infrequently but is not a problem. Should be taken into consideration some points.
Points to consider:
* is space in the mold for good cooling of the new piece?

* is space for the new part and extraction?

* a balanced fill-it is recommended that the length of the injection channel has the same perimeter in three parts. Is it possible?

* may need to put more Kos to balance the extraction, it is possible?

* one more piece in the mold may force a change in injection molding machine. Analyze capacity and injection molding machine projected area of three parts.

I recommend showing mold or mold design or both to a project designer.

Before going down that path, I would determine the actual costs of adding an additional cavity instead of making a new mold. Not just the costs of physically adding the new cavity, which is obviously cheaper than a new mold, but man-hours in design, troubleshooting the new layout in processing (which is much more likely to have problems than a new mold which has been designed from the start to accommodate the extra cavities), cooling, venting as well as downtime of the currently running mold when you add the additional cavity.

Additionally, you're taking a risk. Not just that you may not get the extra cavity to work properly, but that the two cavities that are already working won't fill properly anymore either. Depending on how old the current mold is, uneven wear may become an issue as well. You could end up wasting all that time and money you're dumping into it only to discover that you need to make a new mold anyways.

I don't know your specific situation, but if you're talking about adding extra cavities, you obviously have more demand than you expected, so I would recommend just making a new mold. Then you'll have the 2 cavity mold for backup if something happens with the new one.

Something to keep in mind is the additional cavities will require additional plastic which relates to a larger shot size. Does your present press have the additional capacity for the shot size. With the additional shot size how will this affect your overall fill time and then your cooling time. Based on all of the great comments above the overall result may not be to your advantage. Can you possibly look at operating at a faster cycle with better cooling and possibly faster injection times, thus potentially reducing your overall cycle and producing more parts with a minimum investment.

Adding a new cavity isn't particularly a problem physically if you have the space. If the machine can accept the increase clamp pressure and shot size you're OK. Do you have enough cooling? You can use a dam that shuts off and fill only that cavity if you choose. If you are filling all the cavities at the same time you must balance the mold's filling capabilities.

You should be looking at the balance by adding 2 instead of 1 cavities. But i do presume that you would have limited space. Cooling and additional depth to your runner are some considerations you might want to take in.

fellows, i am sure it´s better to make a good project to avoid any rework over the tooling!!! But I am considering a hypothetic scenario, when we could due volume increase, check the possibility to add a extra cavity instead built a new mold.

Premisses:
1) I have enough space in my Mold
2) I can guarantee good balance
3) The Mold is New (less than 20% of use)

According your know-how what do you suggest (recommend):
1) Finally to build a new mold (only extra cavities needs) - more expensive, but less risk, also part cost increase
2) To build a new mold (all cavities required) - much more expensive, but less risk
3) Planning a extra cavity to soak up the volume increase - less expensive, but with risks. Also possibility to decrease price/cost by part.