COMPOSITES LAB MANUAL

Transcription

1 COMPOSITES LAB MANUAL Version 1 Lab 6: Post-cure Processing The original version of this manual was a one student senior design project written by Katherine White, the Composite lab assistant, during Spring 2016 semester under supervision of who captured almost all pictures in this manual. This current version (version 1) has been modified and amended by during Fall 2016 semester in order to be used by students enrolled in ME436/L course: Mechanics and Design with Composite Materials, as well as Senior Design students. 1

2 Post-cure Processing A. Cutting and drilling The part you made will most likely have excess material left around the edges. To remove this you can use a variety of tools. Common tools include using a Dremel, a multi-tool, belt sander, band saw, or just plain sandpaper. Be mindful and realize that common drills, end mills, and other tools will wear away quickly when used on composite materials. Carbide, carbide Kevlar, or diamond tools are recommended. Water jetting and laser cutting is another way composites can be cut. Water jetting can be useful because it creates sharp edges and will not cause delamination or burred edges like drilling can. The fibers you are cutting or drilling are very strong and thus can get pulled by the tool which causes burring. In addition, be careful about the temperature of the tools as they cut. If they increase in temperature too much the resin could reach its glassing temperature and the composite could delaminate (the laminae separate). Lastly, do not forget about PPE. Wear gloves, protective glasses, a particle mask, and use a proper vacuum that is designated for composites use. Do NOT cut, sand, or grind composites near other people without letting them know what you are doing and that they should be wearing the proper PPE gear as well. B. Post-cure Bonding Once your part is fully cured and post-cure operations like sanding down of jagged edges are done, you may want to bond this to another part or to a core piece of material. A core is a material that adds rigidity without adding too much weight. A core can be placed in during a layup or after depending on what will be easier or produce less weight. For example, the plates of carbon fiber like the ones made in the previous lab can be bonded to a honeycomb Nomex with adhesive film. Adhesive film is like a pre-preg without the fibers. It s a sheet of resin perfect for bonding, as seen in the figure below. 2

3 Figure 1: Adhesive film The Nomex honeycomb is made from a paper of aramid fibers (Kevlar). It forms a very strong honeycomb structure as seen in the figure below. Figure 2: Examples of core structures By bonding two already cured plates of carbon fiber to a core, it makes a very strong rigid component that would have otherwise been much heavier if only extra layers of carbon fiber were added to achieve the same strength. The adhesive film is cured in the oven or autoclave like the pre-preg. Currently at CSUN, the pre-preg and adhesive film use the same cure cycle (3 hour cure). Note that new materials may be acquired and you will need to reference their material data sheets for the proper cure cycles. It is best to use a caul plate when curing a core like honeycomb so that the sides do not get crushed. A caul plate provides a normal pressure and produces a smooth surface. Aluminum sheet metals, or similar items can be used as caul plates. The plate goes in with the bagging, and vacuum is applied. Be sure that it is on top of the breather cloth and that 3

4 some extra breather cloth is put around the corners of the plate so that the bagging does not rip around the sharp edges when vacuum is applied. Post-Cure Bonding Steps (using honeycomb core): (1) Take out the adhesive film (green) and let it thaw for at least an hour. Remember not to open the bag while it is thawing because you do not want condensation to form on the film. Please note that it is best practice to let materials like adhesive films and pre-pregs thaw for at least 12 hours when working in industry. (2) Use a flat piece of glass or sheet metal as your surface (tool). You will not be laying up on the surface but it will be used as the environment that you bag the piece on and used to put the piece in the oven. If the surface has never been prepped before: go through all of the surface preparation steps. Otherwise, since we are not bonding to the surface, but using an adhesive film between two carbon fiber plates, you will just need to put 2-3 layers of liquid release (TR-930) in case some of the adhesive film melts onto the glass around the edges of the carbon fiber plates. Figure 3: This is what the end result will look like in the oven (3) Two pieces of carbon fiber plates will be bonded together. They are the same exact size and layup sequence. A hydraulic press was used to cut them to size. 4

5 Figure 4: Two carbon fiber plates with the same layup sequence (4) Cut a piece of honeycomb core that is of the same size by using a Stanley cutting blade Figure 5: Core material being cut to size (5) Once the adhesive film is finished thawing, roll it out and cut two pieces for each side of the honeycomb. You want to cut it the same size as the carbon fiber plates. Figure 6: Cutting adhesive film using composites scissors 5

6 (6) Take one of the pieces and peel off the film. Apply the sticky side to the carbon fiber plate as evenly as possible Figure 7: Peel white paper off the film and carefully lay the film onto the plate sticky side down (7) Lay the honeycomb on top of the adhesive film and then apply the second piece of film on top of the honeycomb Figure 8: Lay the piece of core on top of the adhesive film and place the next piece of adhesive film on top of the core (8) Apply the second carbon fiber plate onto the adhesive film layer and lay over a piece of release film. Even though not much of the adhesive film is sticking out, it will still stick to the breather cloth when it melts in the oven so you still need the release film. 6

7 Figure 9: Place second carbon fiber plate and apply release film (9) Apply the breather cloth and bag as usual. Make sure to not forget the vacuum connection. Figure 10: Place breather film, vacuum connector, and then bag as usual 7