Help me please. I always thought that if cooling time is not enough then dimensions will be bigger. So if I have any problem with cooling need to increase cooling time. Is that right?

Dear Alexey, the cooling time is not enough, the dimension of the products is not stable.
firstly is to check the mold cooling channel is reasonable or not.
as per my experience, one, increase cooling time by adjust the injection machine,
increasing the cooling water temperature by water chiller.
Can you tell me your problems more detailed? maybe i can offer some help , if i can't answer you, i will consult my engineer to offer a solution for you. 

Thanks Jois for your answer. But I don't have problem. I just interested what to do for future.

Hello Alexey: You are asking a good question. Base on my experience, plastics parts dimensions mostly decided by mold steel and resin material shrinkage rate, and adjust molding parameters will "affect" dimensions a bit via injection & packing pressure. Cooling time is to cool down the parts enough for easy ejecting and reduce warpage a little, and setting cooling time depend on which kind of resin material for the parts and how big the parts; one more thing, good cooling design in mold is very important anytime. Hope these will help you a bit. 

If cooling time is too long the molded part will be bigger. If you have parts too big you need to increase melt/mold temperature and decrease holding pressure and time also decrease cooling time. If parts are too small do the opposite..

Regards....F.Gallegos

Thanks everyone for your advises ana recomendations.

You could also try a Nucleating agent so that the parts set up quicker and have less time to shrink because it cools off quicker. It will also have the benefit of quicker cycle times. I hope this helps. We can help with other processing issues as well.

Brenda Garcia 

As per my experience Pls. check the material property
i have also this Problem

If you want a small part, inject fast with a hot mold and short cure time.
If you want a big part, inject slower with a colder tool and long cure time.
small part, lower hold pressure, big part higher hold pressure.
It all depends, but this are the basic rule of thumb parameters.

Sounds like the molding process is not fully defined. Cooling is a component of the entire molding cycle and, in itself, is not definitive of the dimensional issues you may be seeing. I would advise you to define your molding process per decoupled i.e. scientific molding practices. Doing so is the best way to get you the results you want.

The suggestions given so far are good but do not address the root cause. Go back to the basics and get your process understood.

If the molder you have is not conversant in this practice then find a consultant who can guide you.

OK, the reason to apply decoupled molding is that the result is an understanding as to what variables in the process affect the part. Defining the process will provide you a "window" showing you how varying the process will move the dimensions around, such as how higher pressure, heat vs. lower pressure, heat, etc. this will also provide you a cosmetic window.
Again, be pragmatic and map out your requirements. If this is not your area of knowledge then, again, I would advise you to obtain a consultant to guide you.

Actually I have found that there is very much a lack of good molding practice being done. So, no only a minority of molders practice scientific molding and of those that do a good percentage do not perform the process correctly. Scientific molding requires time and skills that are often outside those of the molder. In particular, the time to run a proper study and then to develop a robust QA program are prohibitive and just don't get done. Sad, but true.

look at the comments given here and at other posts... the content does not follow that a robust DOE was done, it's all piece meal... little bit here...little bit there. I apologize if that sounds harsh but engineering is pragmatic, process and data driven. If we are to be helpful then we should provide as complete an answer as possible. Often the question posted, as given here, cannot be answered simply and needs to be addressed in depth, face to face, with a competent resource.
OK, sorry for the rant and the high-jacking of the post... :(