Heat transfer from inside a thick molding will be far more limiting compared to heat removal from the tool. That is why conformal cooling or chilled air or more common systems that use nitrogen (very common in Germany) will not produce any substantial reduction in cycle time. Tool side cooling technologies work only when heat is delivered to tool fast enough and that is only in small thickness parts. Having rapid chilling can produce stress.

One thing that may really benefit with cooling time reduction will be to use as low as possible melt temperature. If melt is reduced by 20-30 deg. C you will get amazing cycle time reduction (combined with as high a practical ejection temperature). Look at frozen skin criterion for ejection, not text book % and adjust core cavity temperatures (differential) so that highest temperature is in geometric mid plane of part.

Spend the money on mold filling simulation analysis and allow the mold flow analyst to do the same things that create the variation, analyzing potential variables and review the results with your part designers, this will allow one the “wiggle” room needed for the best outcome. For example:

After running basic mold filling simulations - based on best practices or using molding parameters based on previous similar designs – start making simulation changes that allow one to understand the limits of the design tolerances based on varying the process – change materials, change the pressure, change the mold/process temperatures, change the filling parameters and gate freeze options to understand desired effects and those molding parameters that result in unwanted solutions. Each part geometry has its own optimized solution.

Without doubt having own fully equipped tool room in plastic injection molding company has huge benefits over the years in terms of winning new customers and not just for injection mold tooling. We often describe the tool room as the "heart" of the business as although it's only a small part of our companies turnover it's what is produced in there that goes onto to contribute to that turnover. We need to make injection molds that run at a predicted cycle times and that don't cause a problem in the mold shop so we cannot compromise on the quality.

It is always best combination to have tool room and plastic part producing facility under one management. We are a company in China having only injection mold making facility at one location and component manufacturing facility at other location, though just five minutes away from each other. Here the advantage is that some customers come to us only to buy molds while some customers are interested in buying molds and plastic parts. Also tool room engineers have a different way of thinking while a production engineer thinks differently. So it is better that these two facilities are kept separate.

China has a wide variety of skill sets available from high end to the lowest low. The culture is open to interpretation when the injection mold shop decides how to design the cavitation structures. I suggest having your own injection mold tooling expert and engineering determine the way the cavities function. I also suggest having certifications on hand for all the steel used in the plastic injection molds. This would include all receipts and traceability documentation. There are different levels of quality in China for steel and you made have a variety of heat transfer issues associated with it.

In short, the USA and others are leveraging the moment and getting some quality plastic injection molds out of China. Check the references and make sure you call non-competing companies to mitigate your risks. Also hire people that project managed these types of injection mold suppliers to deliver exactly what you ordered.

We had a clear nylon vessel that exhibited a "splay like" condition that emanated from the gate region. In our case, the mold had valve gates and what was happening is that some of the melt was being left on the face a sides of the valve pin. The next shot these now solidified pieces of nylon would break loose as the incoming melt stream re-melted the prior shot but because of the viscosity differences would result in a splay like appearance to the naked eye. Only under 30X microscopic exam could you actually see the residual debris and the flaring trails behind them like comets.

Because inserts are manually placed by an operator before the injection cycle you blow the tool surface with cold air, increase the residence time (furthermore not the same amount from one shot to another!) and bring potential pollution through the inserts and manual operation (even though operators usually wear gloves in this case). This makes a good number of possible root causes. I'd see the "over-shearing" as an interesting one to investigate (after moisture content of course) for 2 reasons: the PA12 you use has a high viscosity / low fluidity (it is hard to inject) + it first flows around an insert, that is made of metal. Trying to pre-heat these inserts (at least on 30 consecutive shots), this should ease the material flow near the sprue.