Nanotechnology and Resin Transfer Molding (RTM)
Resin Transfer Molding is a technological process useful to manufacture composite structures with different 3D complex shape, dimension and mechanical characteristics. The proposing company, with strong experience in the aerospace field, offers significant improvements to the characteristic of the materials with nanofiller dispersion into the resin in order to tailor the specific characteristics of the material and fit them to specific needs.
In Resin Transfer Molding process two chemical components (resin and curing agent) are mixed and injected in a closed mould containing a fiber dry preform. The mixing of the resin and curing agent is a critical phase of the process; it is possible to perform this operation with static or dynamic methods. The static method is characterized by a mixing chamber in which resin and curing agent are mixed in stoichiometric proportion. The mixture is then injected into the mould using suitable injection pipes. After the injection, a cleaning step (defined as a refreshing phase) is needed to avoid process degradation. Instead, the dynamic mixing method is characterized by a continuous circulation of the base materials (resin and curing agent) in a circuit; the final mixing is the last phase just before the injection into the mold. In this case, the cleaning procedure does not represent a critical step for the RTM system safety. RTM is an ideal solution for the manufacturing of composite products in many industries and categories as automotive and trucking industry, aircraft and aeronautics industry, marine and watercraft industry, public transportation, medical, building industry. In fact, by this method it is possible to produce high quality items with a significant cost and time reduction. Using dedicated software (ex. PAM RTM, Mould flow) it is possible, by numerical/FEM simulation, to determine and optimize the RTM process parameters: injection pressure and temperature, gate and vent position in the mould, resin flows, curing cycle, internal voids/cavity and porosity, resin over packing and/or poor region in the perform, welds and meld line, final curing degree. In summarizing the value of RTM composites for aerospace applications, there are several key physical attributes that continue to drive the development of new generations of these materials. Improved fuel economy, payload capacity, higher transport performance and pollution reduction that is driving the push to lighter weight innovative materials. The demand for higher performance composite materials opens the door for these materials to replace metal for weight savings as well as facilitating part consolidations. Furthermore the advancements of nanocomposite systems also open the door to replace other engineering thermoplastics (ETP’s) for improved processing as well as the overall recyclability. Furthermore, increasing design requirements continue to push for materials with dimensional stability. In particular, for space transportation needs, mass budget is definitely the most important issue. In this regard the implementation in launchers and payloads of novel materials allowing a significant mass saving and is considered highly eligible for upper stages and payloads (i.e. space exploration vehicles). Some of the innovative aspects of the proposed technology are:
- Filler Additives. Given the relatively low viscosity of injection quality resins, very high filler loadings can be realized. The addition of fillers to resin produces properties such as enhanced fire resistance, lower exothermal, less shrinkage and, above all, lower materials cost considerably
- Higher Volume Fractions (percentage of a mold cavity taken up by the reinforcement). While most industrial moldings typically have a volume fraction in the range of 15-20%, RTM will allow the molder to achieve volume fractions as high as 65%. The higher the volume fraction, the greater the strength of the finished part &
- Environmental Compliance. Because the process involves the use of closed molds, styrene monomer emissions are kept to an absolute minimum. Without ventilation of any kind, the RTM process produces less than 10% of the emissions of hand lay-up and spray-up. RTM will fall well within any minimum standards for emission currently in place or under consideration by regulatory authorities
Innovations & Advantages
The main innovation aspects of RTM respect to other technologies are listed in the following:
-Design Flexibility: the material selection is made complex by the multiplicity of possible resin / fiber combinations. With RTM, however, the designer has the flexibility of tailoring the materials more closely to the applied loading system (specific strength) and fabricate shapes which are difficult, if not impossible, to form using more conventional methods.
-Incorporation of materials. RTM allows the molder to easily incorporate core materials for strength and weight savings, complicated inserts, bosses, ribs, undercuts, etc.
-Improvement of surface finish. Both sides of RTM-made components will have high quality finished surfaces. This aspect gives high added value to the final product because it reduces the necessity of finishing operations.
-Faster Production. Depending on such factors as resin reactivity, heated vs. unheated tools, part size, etc., RTM-made parts can be produced at the rate of 5-20 times faster than conventional techniques.
-Labor Savings. Labor/part cost with RTM is significantly lower than other FRP manufacturing processes. The exception is compression molding but much lower capital cost (up to 90% lower) make RTM more attractive unless volumes of 50,000+ parts are required. Furthermore, RTM does not require skilled operators such as with hand lay-up or spray-up.
-Dimensional Tolerances. RTM parts can be designed around very tight tolerances (i.e. +0.005") in the X, Y and Z product planes.
-Part Reproducibility. Controlled tolerances provide for excellent reproducibility on a part to part basis. This permits very accurate cost estimating and tight cost control.
-Low Material Wastage. As little as 2-3% wastage rates are readily achievable. Proper mold design, tight product pinch-offs less preforms and accurate, controllable injection equipment assist greatly in keeping waste to a minimum.
The versatility of RTM technology is due to the possibility of tailoring the specific characteristic of the material. This can be done in two principal ways:
1 Selecting the resin (epoxy, polyester, ecc)/fiber (carbon, glass, kevlar) combination and the optimum number of fiber layers of the initial lay-up. It is also possible to manufacture sandwich material and this can be advantageous because it is possible to obtain the combination of composite face sheets and a foam core yields to a lightweight structure with high strength and flexural stiffness that is resistant to corrosion and moisture. For example syntactic and PIM foams have gained considerable importance as core materials in sandwich composites for a variety of application due to their high compressive strength, damage tolerance and low moisture absorption. Using RTM, sandwich structures can be fabricated in a one step process that is not limited in shape or size. Furthermore removing the complicated process of bonding the face sheets to the core enhances the viability of sandwich structures.
2 Improve the characteristic of the material with nanofiller dispersion into the resin in order to tailor the specific characteristics of the material and fit them to specific needs. In this way it’s possible to improve mechanical properties such as stiffness (for what concern structural components), or for example improve electrical conductivity (antenna reflector production). In addition, various other additives can be used to modify the performance in terms of impact resistance, magnetic properties, reflectivity, etc. of a polymer.
Depending on the selected nanoparticle, nanomaterials can improve the following functions of the material structures:
• Mechanical: strength, tenacity, crack propagation, hardness
• Electrical conductivity: ESD or EMI properties
• Thermal: thermal protection and improvement of thermal conductivity.
Current and Potential Domains of Application
RTM is an ideal solution for the manufacturing of composite products in many industries and categories such as:
• Automotive and trucking industry.
• Marine and watercraft industry
• Public transportation
• Medical and building industry
In terms of specific product different equipment can be easily produced with this technology:
• Auto body panels
• Truck air deflectors
• Wind blades
• Chemical storage tanks
• Solar collectors
• RV components
• Bathtub/shower units
• Antenna dishes
• Swim pool panels
• Boat hulls
• Aircraft radar