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.
Gas Assisted Injection Molding chairs have been produced successfully for the last 20 years. My company (Aco Mold) has recently supplied gas assisted molding equipment for a customer in Brazil who is making Stadium Seating for the 2014 World Cup. We also supplied all of the gas assisted molding equipment for the London 2012 Olympic Stadium Seating and the Kiev Stadium seating for the last Euro championships. We have one customer in UK who is making all polymer (PP) chairs for schools and offices using our equipment. The MOST IMPORTANT thing is to get the chair properly designed for the gas assisted injection molding process.
However, it is very unlikely that it will be cost effective to modify an existing chair mold to a Gas Assist part. To get the best out of the process you would need to re-design the chair using a new mold tool. The use of "box beam sections" with gas assisted molding does enable you to reduce the General Wall Section of the part in many cases (stadium seating is a good example) which would offer a potential overall weight reduction.
Any injection mold manufacturer can quote a low price mold, but it takes a committed partner who is familiar with your company and processes to engineer the lowest cost solution. That means an up-front investment in time and expertise which only comes out of strong working relationship.
The best practice is to avoid preparing the Excel sheet containing 3 to 4 different mold makers quote and make a rating based on the price. Visit the mold maker plant and check the facility available with him, his existing customers, past customers. Check the molds which are under manufacturing in the shop, see the procedures followed, look at the sample components made from the molds supplied by the mold maker. All this will give you an idea on the capability and the quality levels of the mold maker.
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.
As a injection mold manufacturer, we received a lot of inquiries from our website and B2B, an interesting phenomenon is the professional/ potential customers usually very clear about what they need, the information provided by them are very specific, we take serious for this kind of inquiries. On the other hand, inquiries with very little information could be a signal of no intention to purchase; we do not put it in priority. This explains why you get very few replies when you send inquiries to many injection mold manufacturers, you did not inquiry like a professional.
All the mold and injection molding project are custom manufacturing project, so it's not like other common product, the demands are always diverse, injection mold factories need to know the detailed demands of the customer before they can provide the most suitable solution, it's much more than pricing, it's a custom made 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.
A typical injection mold RFQ that we see includes CAD files, quantities to quote, EAU quantities, on occasion program life expectancy and resin specifications. The RFQ information is quite limited considering the capital expenditure that will be based on the quotations received, not just the initial capital requirement, but production ramifications as well. The determinations as to press size, mold quality, sample size, length of sample size, run time, mold qualification requirements even basics such as tolerance requirements are left to the quoting facility to determine in the initial RFQ/quote package.
I've never relied on a mold company salesman or rep to try to explain what is the best choices for my company or my customer. I find that 95% of the time the mold salesman is just that, a salesman with little or no practical knowledge of the molding process or industry and certainly not the best source of information that works best for my plant or my customers' plant. There are a lot of companies that rely on the mold maker to decide what to quote and how to quote it. Including what materials, components to use and design criteria. If one goes this route and allows each supplier to quote the job as they see it, you'll end with a wide range of prices, and probably quire different molds from each. Now you need to compare apples and oranges and sense out of it.
Buyer and supplier always hunting each other, there is always a good mold supplier with reasonable price somewhere, that's why we need to do more sourcing and survey, nothing is VERY cheap and VERY good, only reasonable price, a number accepted by the mold buyer and supplier both party. Take it, leave it or go somewhere else.
You need to watch what you get and follow up with what you ask for. That is what we do at Aco Mold, we have such a large group of experienced staff here stateside to manage your tooling and molding projects so that you are getting what you expect. It can be difficult at times but we travel there and build relationships to better the outcome for your companies.
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.