Vacuum Infusion: Part One
The Vacuum Infusion Process (VIP) is a technique that uses vacuum pressure to drive resin into a laminate. Dry materials are laid into the mold and the vacuum is applied before resin is introduced. Once a complete vacuum is achieved, resin is literally sucked into the laminate via carefully placed tubing. This process is aided by an assortment of supplies and materials.
In a typical hand lay-up, reinforcements are laid into a mold and manually wet out using brushes, rollers, or through other means. An improvement on that method is to use a vacuum bag to suck excess resin out of the laminate. Vacuum bagging greatly improves the fiber-to-resin ratio, and results in a stronger and lighter product. If you are unfamiliar with vacuum bagging, we recommend reading our guide, Vacuum Bagging Equipment and Techniques for Room-Temperature Applications, as VIP requires experience in this area and uses many of the same principles. Vacuum infusion builds upon these principles, providing further improvements to the lamination process.
Benefits of Vacuum Infusion
Better fiber-to-resin ratio
Less wasted resin
Very consistent resin usage
Unlimited set-up time
Vacuum infusion provides a number of improvements over traditionally vacuum bagged parts. These benefits include:
VIP offers a better fiber-to-resin ratio than vacuum bagging. A typical hand lay-up usually results in excess of 100% fabric weight by resin. Resin alone is very brittle, so any excess will actually weaken the part. Vacuum bagging can reduce this number significantly; however, it is still not ideal and can lead to additional problems.
While vacuum bagging certainly improves on the hand lay-up, there is still a hand lay-up involved. Because of this, the laminate will always begin in an oversaturated state. Vacuum pressure will remove much of the excess resin, but the amount removed still depends on the variety of variables. This includes reinforcement material, resin, time factors, as well as others.
Vacuum infusion takes a different approach, in that a vacuum is drawn while the materials are still dry. From that point, resin is infused using vacuum pressure. Rather than starting with excess and drawing resin out, VIP starts with none and pushes resin in. Ideally, any excess resin that is introduced will eventually be sucked out into the vacuum line. As a result, only the minimum amount of resin is introduced. This lowers weight, increases strength, and maximizes the properties of fiber and resin. Parts constructed using VIP can approach prepreg levels of resin content.
Due to the nature of VIP, resin usage becomes very predictable. While a standard lay-up varies in resin content due to the human variable, VIP is remarkably consistent. Even when creating a large product, resin usage will be predictably similar upon repeated attempts. This results in less wasted resin, and more importantly, less wasted money.
Vacuum infusion provides another valuable benefit: time. A frequent problem that can arise in vacuum bagging is the time factor. Many resins have a pot-life of about 30 minutes, though there are certainly some (such as our System 2000 Epoxy) that offer work times of up to 2 hours. Even so, that time limit is extremely critical in vacuum bagging applications. Large projects can easily approach the 2 hour mark, and even small, seemingly simple projects can quickly turn frantic when a pesky leak in the vacuum seal cannot be found. Also, depending on when the bag is applied, the amount of resin removed can vary from part to part.
Vacuum infusion, however, offers unlimited set-up time. Because the vacuum is applied while reinforcements are still dry, there is no resin clock to work against. After the bag is applied, leaks can be patiently sought out. If something is not sitting properly, simply release vacuum and readjust. No time constraints are introduced until it is decided that it is time to infuse the resin. Until that moment, changes can be made again and again.
Finally, vacuum infusion is a much cleaner process. There are no brushes or rollers, and therefore no splashing or spattering. No one will be required to hover over an open mold, saturating a laminate by hand, trying not to drip on themselves. In addition, there are less resin fumes to contend with. Because the only fumes radiate from the resin reservoir, they are somewhat containable. VIP provides a cleaner, safer, and friendlier work environment, though it is still important to work in a well ventilated area and wear a respirator and other appropriate safety equipment.
Easy to ruin a part
Trial and error
Like any laminating process, VIP is not without its drawbacks. When attempting infusion for the first time, it is important to keep the following ideas in mind.
Though set-up is time-limit free, it is somewhat more complicated. Vacuum bagging requires the placement of only the vacuum tubing. Vacuum infusion requires not only vacuum tubes but resin inlets as well, not to mention in-bag extensions of these tubes. Placement of these vacuum and resin lines varies from part to part, and there is no one way to set them up. These considerations must be evaluated prior to lay-up, or else the part could be ruined.
This leads into the next pitfall; it is very easy to destroy a part. Typically, once infusion begins, there is little that can be done to correct any errors. For example, if a leak were to occur, even the smallest amount of air introduced could be potentially fatal to a part. It would probably result in resin pooling, undersaturation, or even a complete stoppage of resin flow. Though there are certainly some cases where problems can be corrected, it should not be expected. The best protection from disaster is careful planning.
Due to the complexity and ease of error, VIP should be viewed as a trial-and-error process. The best mindset to have when attempting vacuum infusion for the first time is that a few parts (or more than a few) will be ruined before getting it right. The trick is to carefully document each attempt in order to learn from each trial. Keep track of the resin flow rates. Determine where the resin is reluctant to go and find a way to get it there. Even the smallest modifications can yield drastically different results. Practice with small quantities and inexpensive materials before undertaking full-scale projects. The key is learning from mistakes. This is especially the case when working with larger projects requiring multiple vacuum and resin lines. In a manufacturing environment, it is recommended that at least 6 months are set aside for testing and preparation.
VIP Set-up and Equipment
When preparing to experiment with infusion, it is important to understand some general concepts about how materials are used and arranged. Keep in mind that every project is unique and this guide is not intended to provide the only available options. We will discuss some variations later.
First, the general sequence of events that comprises vacuum infusion is illustrated in the following diagram.
For the purpose of this guide, we will be focusing on one general set-up idea with the notion that resin will be infused into a center point in the laminate. From there, resin will be pulled outward via vacuum pressure. The final arrangement of materials should look something like this.
Note: For the purposes of this diagram, the vacuum bag itself is not shown. With this final goal in mind, let's take a closer, step-by-step look at what materials are used and how to go about using them.
Vacuum Infusion Product Examples
Upcoming Steps in this Guide
Step One: The Mold
Prepare Your Mold
Select your reinforcement
Select your Flow Media and/or Core Material
Step Two: Resin and Vacuum Lines
Select your Resin Feed Lines
Select your Vacuum Lines
Step Three: Vacuum Bag
Build your Vacuum Bag
Allow for Prohibiting Resin From Entering the Vacuum
Step Four: Vacuum Pump
Attach the Pump
Ensure Proper Vacuum
Step Five: Prepare for Infusion
Select your Resin
Resin Bucket Set-up
Step Six: Resin infusion
Catalyze your Resin and Allow It to Start Infusing
Step Seven: Experiment and Test for Improvement
Helpful Supplies for Vacuum Infusion
Typical Variations in Set-up