JEC COMPOSITES MAGAZINE - Issue #50 - July/August 2009 - 33

Process challenge, JHM Technologies released the ZIP LRTM technology in 2002, which provides a means to sense the actual resin injection pressure in the cavity in real-time during the injection process and then to maintain that internal pressure below the external atmospheric pressure, thus preventing the opening of the mould cavity. JHM Technologies pioneered the development of the ZIP LRTM technology, including the precise measurement of the injection pressure within the mould cavity, which has contributed to the growing success of the LRTM process. Accurate mould cavity calibration JHM Technologies has identified the precise control factors in mould building methods which can prevent the usual inaccuracies that come with composite tool building. By using a proprietary combination of mould lamination materials and methods, JHM Technologies has developed and now teaches moulders how to build tooling offering cross-section thickness accuracy well within + 0.15mm in all areas of the moulding. This level of mould accuracy is critical to the repeatable control of the moulding process and the quality of the mouldings produced. Having an accurate mould is crucial, yet there are two additional pillars of success in the process, i.e. fibre loading and controlling the injection pressure/flow rate. Most moulders operate without control After reviewing the LRTM moulding practices used today, it was found that the majority of moulders are not making the most out of the LRTM process. Many are wasting in excess of 17% of the resin injected into the mould as compared with the prescribed bill of materials for the LRTM mouldings produced. Documented experience of resin use shows that 17% is a conservative value, with many far in excess of that value. This excessive use of resin is often due to insufficient process control on the moulding floor, which is caused by the lack of automated injection equipment, combined with inaccurate mould cavity calibration and poor fibre loading techniques. Fig. 2: Example of radii precisely fit with fibre, then the nominal layer over the radii completing the mould fibre loading. Fibre loading The waste elimination issue Today more than ever before, the success of any business is built on eliminating waste in their overall operation. If the LRTM process is commonly associated with a waste factor of 17% for the resin alone, it will be labelled as a costly process. A solution to eliminating waste was found through a combination of process education, low-cost automation, and accurate low-cost tooling. The root cause of waste is due to excessive resin being pumped into the mould, some of which passes through the mould and exits to be captured in the catchpot connected to the mould exit vent, or remains in the mould cavity as excessive part thickness. Loading the fibre in the mould is an aspect of the LRTM process that relies on the operator. It is not practical to add automation to the fibre loading process, and we must rely on the operator to manage the critical fibre placement step. While some preform technologies are available in the market, preforms are not practical for the vast majority of moulders due to capital cost or part geometry. It is worth pointing out that fibre loading is an area that is often neglected by those offering technical support for the LRTM process. In fact, the most ingrained false idea circulating in the industry is that mould closure will “push the fibres into the details of the part cavity”. This is totally wrong and works against many moulding applications. The truth is that mould closure at best can only pull the fibre tightly into the inner radii of the geometry, thus leaving fibre voids in the outer radii and providing a path for the resin to race track, which defeats all efforts to achieve uniform or accurate mould cavity calibration. The solution is to teach the operators techniques to fill the tight radii with fibre before loading the nominal fibre and to “overstretch” the nominal fibre in the Z plane or vertical walls to make certain that the fibre properly fits the mould cavity before the mould is closed. When the mould is uniformly filled with fibre in all areas and has consistent cavity calibration, it is possible to achieve uniform resistance to the leading edge of the resin flow front towards the exit vents. Providing resistance to the leading edge of the resin flow creates a “plow” effect that compresses the remaining atmosphere in the mould, causing it to naturally flee Fig. 1: JHM Technologies LRTM mould building and process training classes. No50 July-August 2009 / jec composites magazine 33

JEC COMPOSITES MAGAZINE - Issue #50 - July/August 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #50 - July/August 2009