Fluid Injection Technologies

Lower Part Costs – Greater Design Flexibility
The production of thick-walled parts or parts of varying wall thickness often require very long cooling times and generally result in a high scrap rate due to defects. With conventional injection molding this is rarely cost-effective but the fluid injection process can provide the solution. The idea is to force excess melt out of the interior of the molding by means of a fluid and - and with that same fluid - create the necessary holding pressure from within the part. The practical advantages are obvious: part costs are reduced because less material is required. Faster cycle times mean higher output which, together with a lower scrap rate, can mean significant reductions in manufacturing costs.

In addition, the process offers increased design flexibility: irregular part geometries can now be produced economically. Typically parts suited to this process include the furniture, appliances and automotive industries. The fluid injection process can be used to ensure even shrinkage. It is also used in the production of parts with functional hollow geometries such as pipes.


The Process
After the mold cavity has been filled and holding pressure briefly applied to ensure a high quality surface finish, the fluid is injected directly into the liquid melt of the central core through special injection valves. This fluid displaces melt into secondary cavities which can be closed off (secondary cavity processing) or back into the barrel chamber (reverse pressure melt process). This patented process produces parts with remarkable surface quality (e.g. no surface blemishes) and can even seal off the core area. Another advantage of this process is that the displaced melt is ready to be used for the next molding cycle.  This reduces costs even more. The fluids used in the process are gases — usually nitrogen (Airpress) — or liquid — usually water (Aquapress). When water is used as the fluid an additional step is added to the process: a vent opening allows air pressure to displace the water resulting in an almost dry part.

Gas or Water?
While the gas injection process (Airpress) is well-established, the water injection process (Aquapress) is still quite new. Currently our development efforts are focused on injectors, molding materials, pressurizing units and optimizing the process in general.  The advantages and risks involved in using various fluids are outlined below:

Advantages of water over gas:
• Significantly shorter cooling time
• Smooth interior part surfaces
• Larger cross sections are feasible
• Thinner wall sections
• Less distortion thanks to more even cooling
• Evenly distributed wall thicknesses – even with thick parts
• Cost reduction and easy availability of water as a pressure medium

Risks associated with water over gas:
• Greater effort required to ensure safety
• Measures to avoid water-spray in cases of installation errors.
• Water has to be removed from the component parts.
• The involved process of removing of contaminated water may be required
• Larger injector openings are necessary.
• Not suitable for all parts

Thanks to our extensive experience with these technologies we can advise you which are the right fluids, parts, mold configurations, and processes for your application. We work together with manufacturers in the development of numerous applications, including customized mono-sandwiching solutions.

More for Everyone
Ferromatik Milacron offers an integrated Airpress control unit as an option for all of our machines (MAXIMA, ELEKTRA and K-TEC).  All the functions of this unit can be accessed via the IQT.  In addition, an external pressure unit for the fluid injection process can also be used with the standardized interface.