This article shows how the Vacuum Infusion Process works, what the benefits are and how the possible pitfalls can be eliminated.

“The Vacuum Infusion Process, or VIP for short is a composite process that offers the ability to create superior products out of fiber-reinforced plastics which are light in weight yet extremely strong.”

The Vacuum Resin Infusion Process starts with the dry reinforcement materials being placed on the mold’s surface. Specific types of flow media are then used to facilitate the resin flow. Tubing is inserted and a vacuum bag on top of the laminate is sealed on the molds perimeter – creating a closed mold system (CMS). Then a vacuum pump is used to evacuate the bagged system. The differential pressure between the low in-bag pressure and the higher atmospheric pressure is the driving force used to push the resin into the dry fabric until it is completely saturated. The lamination stack is compacted during this process. Hence the ratio between fiber to resin is significantly enhanced resulting in additional competitive advantages that aren’t available in the traditional hand lay-up or vacuum bagging technique for example.

In an industry and consumer market where lighter and stronger is better, the Vacuum Infusion Process is a proven and effective advantage in composite production leading to many enhancements over traditional methods. The closed mold process is also very clean. This results in less wasted resources and since epoxy allergy is still one of the evident dangers, minimal exposure to this material is desirable.

Benefits of the Vacuum Infusion Process (VIP)

There are several benefits to the Vacuum Infusion Process over other traditional methods. Some of which have already been mentioned above. Below is a tentative list of benefits as to why you should be using Vacuum Resin Infusion rather than open mold techniques.

  • Stronger products because of better consolidation ratios and better bonding
  • Optimized Fiber to Volume Ratio
  • Thickness control possible
  • Lighter products
  • Reduced production costs (less wasted resin and errors)
  • Consistency (product quality can be controlled with greater certainty of perfection)
  • Low initial investment to get started
  • Environmentally friendly (reduced VOCs and HAPs, and better worker conditions as well)
  • Large projects (VIP aids the easy production of large structures – boat hulls and more)
  • No rushing for time constraints

In making the decision to switch to VIP there will be some slight downtime in order to allow for the transition to Vacuum Resin Infusion. But that is quickly recouped with the benefits of the process over other techniques in the long-run. Most individuals are able to quickly learn the process. This makes the conversion an even more attractive option for composite production.

The ability to reduce skin contact and odors increases the safety of the   production processes” 

Resin is cured inside a bagged system. This reduces fumes of volatile organic compounds and air pollutants. This can also result in greater employee morale and better overall company recognition and image for supporting environmental preservation efforts.

Dry Spots in Vacuum Resin Infusion – How to Avoid

We clearly realize the great advantages of the Vacuum Infusion Process in comparison to wet lay-up or wet lay-up and vacuum bagging. But there are still some wasteful areas caused by the standard VIP process consumables. By using a spiral wrap as evacuation line, you run the risk of getting dry spots. When resin reaches the spiral wrap (the standard VIP evacuation line) it can easily been drawn out of the mold cavity if there is no effective barrier preventing that. The calculation of the resin flow path varies depending on certain parameters. E.g. the lamination stack is not homogeneous in terms of permeability. But resin runs faster through areas with less resistance compared to those with higher resistance. That increases the risk of producing dry areas which are not saturated by resin especially with more complex designed molds. Further down in this article we explain how this can be avoided by using membrane technology.

Pinholes in Vacuum Resin Infusion – How to Avoid

With the standard vacuum resin infusion process the permanent existing vacuum drives the resin out of the laminate into the bleeder fabric and/or resin trap. That leads to voids in the surface caused by pinholes. Pinholes are tiny holes on the surface which are hard to fix and require post treatment, resulting in additional labor costs. This is particularly evident with visible carbon fiber parts. These parts are only clear coated and pinholes affect their post treatment costs tremendously.

Also, to protect the vacuum pump from resin being sucked out of the mold system, the standard VIP has to apply a resin catch container or resin trap.

“Above all, the permanent existing vacuum in the system is the driving force for potential embedded air bubbles. They are able to grow to maximum size in the vacuum atmosphere which causes voids in the laminate”

Vacuum Resin Infusion and Fiber to Resin Ratio

In order to understand the physics behind VIP, net compaction, fiber volume, resin content and the effects it has on the quality of the finished composites product, we need to take a closer look into what happens prior to and during the infusion process.

Sealing the MTI hose with Butyl tape_1

First step to seal the open end of the MTI hose

 

Sealed open end of the MTI hose

Sealed open end of the MTI hose

2. To ensure a proper airflow to the vacuum pump the MTI® hose should have a connection to the laminate through any kind of porous material. The hose can be placed either on the peel ply fabric or even directly on the fiber material. A wide flange and break zone to brake resin flow is not necessary.
The MTI hose placed on permeable material

The MTI hose placed on permeable material to ensure a proper air flow

3. To connect the MTI® hose with the vacuum pump we recommend a 3/8” OD solid hose which is plugged into the spiral tube that is inside the MTI® hose. Pull the membrane sleeve over the joint and seal with sealant tape.

Connecting the spiral wrap with the vacuum hose
Step 1 to connect the membrane hose with the vacuum pump. Connecting the internal spiral wrap with the vacuum hose that leads to the vacuum pump
Sealing the connection between internal spiral wrap and the hose that leads to the vacuum pump
Step 2 to connect the membrane hose with the vacuum pump. Sealing the connection between internal spiral wrap and the hose that leads to the vacuum pump
Sealed connection between membrane hose and vacuum hose
Sealed connection between membrane hose and solid hose that leads to the vacuum pump

4. Connect the vacuum hose to the vacuum pump. You can incorporate a resin catch container as backup system in between but you will no longer need it.

Sealing the MTI hose with Butyl tape_1

First step to seal the open end of the MTI hose

 

Sealed open end of the MTI hose

Sealed open end of the MTI hose

2. To ensure a proper airflow to the vacuum pump the MTI® hose should have a connection to the laminate through any kind of porous material. The hose can be placed either on the peel ply fabric or even directly on the fiber material. A wide flange and break zone to brake resin flow is not necessary.
The MTI hose placed on permeable material

The MTI hose placed on permeable material to ensure a proper air flow

3. To connect the MTI® hose with the vacuum pump we recommend a 3/8” OD solid hose which is plugged into the spiral tube that is inside the MTI® hose. Pull the membrane sleeve over the joint and seal with sealant tape.

Connecting the spiral wrap with the vacuum hose
Step 1 to connect the membrane hose with the vacuum pump. Connecting the internal spiral wrap with the vacuum hose that leads to the vacuum pump
Sealing the connection between internal spiral wrap and the hose that leads to the vacuum pump
Step 2 to connect the membrane hose with the vacuum pump. Sealing the connection between internal spiral wrap and the hose that leads to the vacuum pump
Sealed connection between membrane hose and vacuum hose
Sealed connection between membrane hose and solid hose that leads to the vacuum pump

4. Connect the vacuum hose to the vacuum pump. You can incorporate a resin catch container as backup system in between but you will no longer need it.

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After evacuation and prior to resin flow, vacuum has been applied so that absolute pressure Pabs in the system is uniformly low (vacuum is uniformly high)and the mold, preform, flow media and vacuum bag are in a compacted state. With 10 mbar inside the bagged system and 1000 mbar outside the bagged system the pressure differential is 990 mbar, which is the net compaction pressure upon the dry preform and the force that drives the resin through the lamination stack.
“The pressure differetial between atmospheric pressure outside the bag and the low absolute pressure inside the bag is the driving force that pushes the resin through the lamination stack”