5 Axis Filament Winder
Filament winding is a process that can be used to create round fiberglass shapes with exceptional strength characteristics. Used for piping, tubing, and tanks, filament winding is normally an automated process that has computer-controlled equipment to place glass and resin around a mandrel- the piece that functions as the mold.
There are many variables that can be modified for filament winding, and these will affect the strength characteristics of the finished piece. The angle of the glass, number of passes (thickness), use of glass mat, and type of resin will affect the finished product strength characteristics.
I found a short video that demonstrates the equipment and the process.
As you can see, the glass is applied in a consistent manner across the part, allowing for uniform strength characteristics. As you can see, this is yet another process that the composites industry uses to create useful products with advantages over those of competitors.
Vacuum Bagging Video
Vacuum bagging is a process that requires unique materials and processes, but can be simple to operation in an ongoing basis.
There are many advantages to vacuum bag molding, a few of which include:
- Improved resin/glass ratio
- More consistency across the laminate and part -to -part as compared to open layup
- Containment of air emissions from the resins
As compared to hand layup and chop layup, there are a few disadvantages, including
- Higher consumable material cost
- Higher capital equipment cost
- Difficulty with superior surface finish
Some parts are more suitable for vacuum bag molding than others. It also depends upon which process it is being compared with.
Vacuum bag molding requires an extremely tight seal between the mold and the bag. Molds with multiple pieces or holes for inserts can be difficult to complete a seal.
Parts that are overly large and complex can present challenges with placing resin and reinforcement before the cure cycle starts. The bag must be completely sealed and under full vacuum before the curing cycle of the resin begins.
The basic premise of vacuum bag molding is that the air is removed from the bag, allowing the atmosphere (air on the outside of the bag) to push the bag onto the part on the mold, compressing the layers of resin and reinforcement. Many misinterpret the process as “sucking the extra resin out.” We are merely allowing the laminate to be compressed by the weight of the air above us in the atmosphere to consolidate it before cure. The excess resin is usually absorbed by extra layers of sacrificial material inside the bag.
Moldless Car Body
Building a custom car body with fiberglass can be achieved without using a mold! This will be a truly custom, unique vehicle. It will take lots of planning and hands-on work, but is very possible as shown in these YouTube videos.
There of course are several ways to go about building a basic structure to use for the basic shape. This video gave lots of good ideas and examples of materials that are relatively inexpensive.
The second part of the video shows some of the actual fiberglass work. This video of less than eight minutes does not nearly do justice to the amount of work and effort that went into finishing this project! It was great that the author documented his work and shared with all. This was a major project that is not for the faint of heart.
He does a very good job explaining the process and materials used in this construction. Every project is unique, however. When discussing the thickness of the fiberglass skin, there are many variables that determine the finished strength. The number of layers to use is dependent on the amount of underlying support structures, part geometry, and required load bearing capacity of the structure. Some areas may need to be stronger for impact resistance and structural loads.
The video author discusses only using epoxy resin with Styrofoam as opposed to polyester resin which will react with the Styrofoam. Polyester resin can be used if separated from the Styrofoam with an additional layer. While I have only seen it advertised, there are new spray on primer materials available to cover the Styrofoam and allow polyester resins to be utilized afterward.
Effects of Clear Gelcoat
One of the really cool effects that fiberglass parts can use clear gelcoat. The basic process starts with a properly prepared mold that is waxed and ready for production. The part build begins with a layer of clear gelcoat. Several manufacturers have this product available, and it is sprayed on the same as pigmented gelcoat.
Once the clear gelcoat is tacky, the visible effect is placed down. This can be a wide range of materials and patterns, depending upon the desired outcome. I have a table that has ground granite rock specks.
Granite Table Top
These granite specks are placed down uniformly and consistently to give an acceptable finish. Then some opaque gelcoat is used to finish off the look and help bind it together. After this is cured, the fiberglass buildup is added to the desired strength and structure to give the desired finished part.
This clearcoat can be sanded and buffed much the same way as the opaque gelcoat, though sanding though to the underlying effects would be disastrous.
One of the drawbacks to this style of part comes when an unknown mistake occurs with the detail layer. If contamination or uneven materials have visual problems, the whole part is built before the part is removed from the mold to find these problems. The shape and structure are complete, but surface defects that cannot be repaired relegate these parts to the trash heap. Extreme care must be taken in the detail application stage to prevent this action. Practice and experience with test panels can help minimize these sorts of problems.
Clear gelcoat can provide a very unique and interesting surface medium. A whole new look can be accomplished using existing fiberglass molds, gelcoat spraying equipment, and lamination schedules.
Gelcoat Application
Making a traditional fiberglass part is accomplished by working from the outside surface into the part. A clean and waxed mold is placed in a clean room where contamination will not interfere. Then gelcoat is sprayed on as the first layer, and followed by the rest of the laminate. The gelcoat application process is much more art than science.
The objective of gelcoat is to create a uniform thickness across the part, and have it be 18 to 25 mils thick when wet. As it cures, this thickness is reduced when some of the chemicals evaporate off. Spraying gelcoat onto a mold returns the best quality finish, but it may also be brushed in areas that are difficult to spray. Achieving a uniform thickness is difficult at intersecting corners, deep narrow areas, and difficult-to-reach sections of the mold.
The gelcoat is typically applied in three passes and allowed to “gas off” in between coats. This allows for some of the chemical evaporation to start, and can lead to problems if not done correctly. These passes are also usually bi-directional, where the first and third pass are in one direction and the second is in another, again to help achieve uniformity.
Areas of excessive gelcoat thickness can lead to cracking and surface finish problems. Areas of insufficient gelcoat thickness can “alligator” which is a surface flaw requiring extensive repair.
Gelcoat Application is a tricky part of the process and the manufacturer of the application equipment and the raw material is the best resource for best practices. Experience is the best formula for great results.
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