MTI® How it works
Making a Carbon Fiber Car Hood with MTI® hose
MTI® (Membrane Tube Infusion) is a registered trademark and describes a cutting-edge composite production method, developed by German engineers to optimize and streamline the Vacuum Resin Infusion Process. The MTI® hose is based on a semipermeable membrane sleeve which supports air and gases to be drawn out of the bagged system while ensuring that the infused matrix material stays inside the laminate. This technology offers a decisive impact on:
- The fast and simple vacuum system setup reduces labor and material costs and provides the possibility to cut cycle time particularly with the serial production of larger products such as wind turbine blades or hulls.
- The membrane technology reliably prevents that resin is drawn out of the laminate so that the calculated fiber to volume ratio can be realized precisely.
- The closed hydraulic system makes it easy to adjust the compaction of the laminate from the resin inlet side only.
- The membrane system is self-regulating in terms of resin flow which leaves less room for failure. There is no complex timing of clamping and opening different vacuum ports.
- A resin catch container is no longer necessary which enhances the process safety, reduces resin consumption as well as it saves time and money for the preparation of the container and disposal of wasted resin.
- The MTI® hose is extremely easy to work with. It is flexible and pliable so it can be routed along the profile of very complex parts.
The Vacuum Infusion Process is often abbreviated as VIP for short. VIP is a process that is used in the composite industry to manufacture fiber reinforced plastic parts ()FRP). The manufacturing process consists of disposable films being applied over the laminate.
During the process setup, the dry materials are taken and stacked onto the female or male mould surface and then a vacuum bag or partially-stiff counter mould is then used around the part’s edge for a complete seal. Next, a vacuum is introduced to remove the air and apply pressure (atmospheric) to compact the dry materials and create a necessary vacuum cavity where strategically placed resin feeding lines will drive the resin into the part. In order to completely saturate the part in resin, there is a pressure differential that exists between the outside atmospheric pressure and the cavity which allows for resin to be pushed through the porous materials in a vacuum infusion process. To guarantee consolidation, the vacuum remains until the part has cured.
Elements that Determine VIP Filling Time for a Part
Viscosity – Resin viscosity will determine the time it takes to saturate a part. Ideal resin viscosity is between 100 – 300cps, with larger viscosities resulting in longer saturation times.
Permeability – The permeability or porous characteristics of the reinforcement materials affect the flow of resin. The use of flow media is an integral part for proper and timely infusion. A grooved or scored core may also be used.
Pressure Differential – The greater the pressure difference, the quicker the resin will flow during VIP. Optimal pressure is below 0.15psi absolute pressure (full vacuum).
Distance – The flow distance is also an area that will affect the filling time. If the flow distance is larger than 1.5 yards, more feeding points should be introduced.
The vacuum infusion process is the leading industry technique for the production of composite parts. This method creates stronger and lighter parts and even reduces costs. Part quality and reproducibility becomes easier to maintain versus conventional methods. Quality inspections are easily accomplished with the ability for inspection before resin is driven into the part. The process also reduces skin contact and odors of volatile organic compounds and air pollutants to the air around you. Setup time is also significantly enhanced during vacuum infusion offering unlimited time for readjustments. Resin is not catalyzed in the part until all the necessary materials are in place, leading to fewer errors under time constraints.
VIP is also known for its low transition or startup costs and ease of learning the method. With VIP, you also have the ability to easily conform to simple, larger and complex shapes because of evenly applied pressure via the vacuum bag. Finally, the use of a vacuum produces a stronger laminate because of the removal of air and volatiles during the process.
Developments During the Last Decade
Over the last decade the vacuum infusion process has received advancements in the ability to introduce resin into the vacuum bag. Using well-made resin distribution manifold systems and essential flow media in the vacuum bag has offered better management of the influx of resin into the vacuum bag; improving the process and its results. Saturation has been optimized to be faster and is more efficient because of the use of flow media on the laminate surface and the use of inflow media into the laminate. The latest technology from Germany uses the semi-permeable MTI® hose to evacuation the mould which offers a competitive advantage compared to the traditional method.
In order to implement VIP, you’ll need a few pieces of equipment. This equipment includes: the vacuum pump, leak detector, thermometer, clamps, hoses, several resin collectors, vacuum gauges, and vacuum bagging supplies. The biggest cost in introducing VIP into a larger shop is the need for a superior fail-safe vacuum system which consists of two pumps, a filter, reservoir and vacuum lines which are permanent and run throughout the shop for easy hookup.
If you’re familiar with traditional open molds, VIP tooling is almost identical in many ways. The use of an ample perimeter flange is needed to mount the vacuum bag. Building tooling will require no unique expertise except for open mold fabrication. The largest cost that you will run into in converting to VIP is the mold modification, and changes to the shops layout in order to support VIP. The use of standard open molding tooling is also sufficient to use and VIP shops often use polyester gel coat and polyester laminate molds. Another alternative would be epoxy tooling. A vacuum source will be required in VIP and a large system may be required for higher outputs and processes.
The good news is that the learning curve for VIP is manageable with limited downtime during a conversion. Vacuum infusion process courses are typically one week in length however it may take up to four weeks for the average employee to achieve quality production skills attainment.
If you are still working with a wet lay-up process, our expertise makes it simple to upgrade your production to a much higher performance level using MTI® hose technology. We are experienced in supporting clients throughout their transition to the MTI® infusion process.
- Prepare the mold with release agent
- Stack dry fabric layer onto the mold. If necessary fix with adhesive spray
- Stack peel ply, perforated film, flow media on top
- Lay the MTI® hose around the mold lip onto the peel ply and fix it where necessary. Seal one end of the hose into with the vacuum line and seal the other open end. Make sure the connecting points are sealed accurately. We recommend sealant tape to do this
- Use a suitable vacuum film and sealant tape to create an airtight closed mold system. Install the resin line
- Evacuate the set-up with a proper vacuum pump. You should reach a vacuum below 0.15 psi absolute pressure for best results. The vacuum system must be 100% airtight. An airtight system keeps the vacuum easily without using the vacuum pump. We recommend a digital vacuum gauge for control
- Use resin which is suitable for infusion and degas the resin at least 20 min. Make sure you have prepared enough resin
- Feed the system with the degassed resin
- The pressure differential between the cavity and the outside atmospheric pressure is the driving force which pushes the resin through the porous materials. The resin fills the evacuated space between the reinforcement fibers. Resin cannot escape the mold cavity because of the barrier effect of the MTI® hose
- When the resin hits the membrane it stops there and flows through the rest of the fabric until the whole part is saturated
- End the process and clamp the feeding line in accordance of the fiber volume content you would like to achieve. There are different possibilities to adjust the FVC
- After curing, the bag is removed and the part demolded
Advantages and benefits in comparison with wet lay-up:
- The adhesive spray fixes the inserted fabric layer very reliable even in sharp edges where the traditional wet lay-up procedure fails. Inserting a fillet is no longer necessary. Enclosed air bubbles, particularly at edges and sharp corners are reliably avoided. You achieve a perfect finish in one shot. Crucial for carbon fiber cosmetic parts
- Particularly with bigger parts the laminating process becomes much more easier to handle since you can interrupt the lay-up process whenever you want. We have not discovered any restriction so far in the size of the mould to be infused. Our energy clients have been reliably producing windpower blades of 60 yards length with MTI®
- The closed mold process leads to enormously reduced work place load (emission of volatiles) and costs for protecting clothing and equipment
- Pinhole free surfaces and significantly reduced enclosed air bubbles offers a competitive advantage through reduced post treatment, less material consumption and much better component quality
If you would like to get supported alongside the transformation process towards MTI®, we are experienced to do that.
If your production process currently utilizes a Vacuum Infusion Process, our expertise makes it simple to achieve better results by assisting with your transition to the MTI® infusion process. Improving your existing vacuum infusion process is extremely easy. Simply replace the spiral hose with the MTI® hose. Seal one end into the vacuum line and close the other end with sealant tape.
A tiny change that opens up a wide range of advantages and benefits through:
One Shot Technology
- Pinhole-free finish in one shot.
- Reduce overall cost by avoiding post treatment (sanding, primer, paint, etc)
- The ability to perform one-step infusion processes at production quantities is a significant competitive advantage.
Maximized process reliability
- The reproducibility of vacuum assisted resin infusion processes is enhanced significantly through the use of the self-regulating MTI® hose.
- Risks traditionally associated with such processes, such as dry spots, are minimized when using the hose.
- When parts are manufactured correctly the first time, costs from the post-treatment associated with fixing parts are avoided.
Minimized impacts from air bubbles
- The low-pressure MTI® offers a decisive advantage in terms of minimization of air bubbles.
- Consistent high quality of the structural components results in higher resistance to dynamic loading.
Homogeneous component structure
- Due to the semi-permeable membrane, the infusion process is self-regulating. This supports a homogenous resin content across the entire component cross-section.
- The blocking effect of the hose ensures that resin flows through entire part.
- A resin trap is no longer necessary, so exact resin consumption can be calculated.
- Adjust the amount of introduced resin to achieve optimum fiber volume fraction.
- Infuse exactly the amount of resin that will be absorbed by the part.
- Since resin is not required to reach vacuum source uniformly, there is no need for complex calculations of resin flow.
Flexibilty with feed and vacuum lines
- MTI® offers flexible positioning of the resin feed lines- place them wherever they are needed.
- The integrated spiral hose allows for flexible handling and provides for an effective airflow channel for maximum evacuation performance even under difficult conditions such as extremely large or complex designed moulds.
- Even molds such as hulls or wind turbine blades are simple with MTI® hose.
- The MTI® hose is extremely easy to work with.
- Very low initial investment: no autoclave or resin trap required.
- It is flexible and pliable so it can be routed along the profile of very complex parts.
- Once you have used it you will love it.
We are experienced in supporting clients throughout their transition to the MTI® infusion process.
If you are thinking about upgrading your production process by investing in autoclave technology, first consider that the required component quality is possible using MTI® technology at a fraction of the cost of an autoclave.
MTI® is a process which is, in comparison with the autoclave process, characterized through:
- Easier handling of the dry fabric layers with much less workplace emission load
- Production and completion with perfect, pinhole-free surfaces in one shot
- No need to drive an autoclave pressure cycle on your vacuum set-up since you do not run the risk of producing air pockets like you do with laying wet prepregs
- Tremendously reduced processing time since you infuse the complete fabric layer set-up in one shot independantly from its cross-sectional dimension
- Investment and operational costs with a fraction of the autoclave expenses
If you need more information to make the right decision, a test-run with the MTI® hose will win you over! We are experienced in supporting clients throughout their transition to the MTI® infusion process.