JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012 - 54

injection

the proprietary “algorithms and fuzzy logic” found in the Infuser PRG controls, making it possible to program the most elegant level of process control available for the low-pressure moulding processes of RTM and LRTM and as well, vacuum infusion. Capturing control of what is critical Filling the mould precisely in a timely, repeatable fashion with simple operator inputs requires the injection system to be in control of the entire injection process. To meet this challenge, the Infuser PRG is pre-programmed for each of the following variables: - Shot size – The exact amount of resin needed to fill the mould is programmed and repeated with each fill to accuracy within just a few grams from part to part regardless of the size of the part being injected, thus eliminating the common overfilling of the moulds and related cost. - Mould cavity vacuum level – The LRTM and VIP processes rely on a prescribed vacuum level in the cavity prior to the commencement of the injection process. The Infuser PRG uses an absolute pressure sensor in the nose of the mixhead to “sniff ” into the mould and confirms the correct vacuum level before the resin is injected. If the vacuum is not within set tolerance, it gives the operator a visual error message on the controls and will not begin the injection. - Maximum injection pressure limit – While flow rate is the focused controlling factor, the resin injection pressure is then limited to a pre-set limit, this setting acting as a “governor” to the injection flow rate. In the event the pressure exceeds the limit set, the Infuser PRG will automatically stop and re-set the flow 10% lower to prevent over-pressurizing the mould. If the Infuser PRG

Analysis and data

the mixhead. This helped preventing over-pressurizing the mould set and causing permanent damage to the mould. It did, as well, offer a level of process control which prior to then was non-existent. In the late 1990’s, the closed moulding process of RTM changed to the lighter tooling structure of LRTM methods. These new moulds were much lighter and generally not in any sort of press. At the time, the conventional RTM injection systems offered, at best, only a means to control the pressure and number of pump strokes to automatically stop the resin fill. In 2003, the control methods advanced to measuring the resin hydraulic pressure in the cavity as compared to the outside atmospheric pressure. The difference was initially the vacuum level within the cavity at the start of the injection as compared to the outer atmospheric pressure

clamping down on the cavity. Then the pumping system was given a signal to slow down if ever the resin pressure were to exceed the clamping pressure of the atmosphere. This then prevented the mould from opening and losing the flow front control. Over time, it was found that it is impractical to “react” to pressure as the means to control the feeding of resin into the mould, since at the point it has exceeded the differential between the cavity and outer atmosphere it is too late to hold the mould in the calibrated cross-section thickness.

Intelligent advancement
Reflecting on mature similar moulding processes such as Reaction Injection Moulding (RIM) and thermoplastic injection moulding, it is clear that the controls are focused more on rate than on pressure alone. Working from that foundation, the design team at JHM Technologies spent nearly 3 years perfecting

54 jec composites magazine / No76 October - November 2012

JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #76 - October/November 2012