Carbon Fiber Vacuum Pumping Experience

 

Since the vacuum method can effectively reduce the resin content and internal bubbles in the product, we use the vacuum bag molding method this year.

 

01 When cutting, you can cut the demoulding cloth a little larger to facilitate demoulding.

When cutting the vacuum bag film, cut it a circle larger than the area to facilitate pleating and sealing. The vacuum bag can leave more margin. If there is a small margin, the vacuum bag is difficult to pleat and easy to leak. Before applying the demoulding wax, use masking tape to determine the position of the four corners, and apply it evenly within the position. Do not apply it outside the specified area. If you apply too much, the sealant will not stick to the glass.

 

 

2. If the carbon plate and parts require high strength, a core will be sandwiched in the middle of the carbon plate, such as paper honeycomb and strong core felt. We have conducted experiments on paper honeycomb and strong core felt. The experiment found that strong core felt has some disadvantages, such as wasting resin and the carbon plate is too heavy to achieve the lightweight effect. Finally, we chose paper honeycomb.

 

At the same time, paper honeycomb also compared the two methods of hand-brush glass pressing and hand-brush vacuuming. The hand-brush glass pressing has a good surface effect, but the finished product is heavy, and a lot of polishing is required in the later stage to achieve the expected lightweight effect. The hand-brush vacuuming method has high requirements for sealing. If the sealing is good, the surface effect is very good and the quality is light, but once the air leaks, it will have a great impact on the surface effect.

 

For the car body, it is not necessary to apply three layers of carbon cloth. You can choose two layers of carbon cloth and add a layer of carbon cloth in key parts such as local areas. As for the aerodynamic kit, the rules stipulate that “all aerodynamic devices must be able to withstand a force of 200N applied on a minimum area of ​​225cm and the deformation in the loading direction must not exceed 10mm.

 

All aerodynamic devices must be able to withstand a force of 50N applied in any direction at any point and the deformation must not exceed 25mm”, which means that the aerodynamic kit must have a certain load-bearing capacity, so we finally used four layers of 3k carbon cloth and a layer of paper honeycomb for the end plate of the front wing.

 

Our rear wing is supported by carbon tubes, which are connected to the top of the end plate, so the rear wing end plate must have greater strength, so a layer of carbon cloth is added on the basis of the front wing end plate.

 

 

03 For infusion, pay attention to the direction of the guide net when applying it.

If the direction is not considered, the resin will flow too slowly when the resin is extracted. The guide tube layout should be arranged in a reasonable direction according to different shapes. If the layout is unreasonable, the resin will not flow sufficiently and some places will not be soaked by the resin.

 

The layout of the guide tube of the seat this year makes the resin flow faster, but the unreasonable position of the guide tube causes the two sides of the seat to be squeezed by the guide tube, resulting in potholes and unevenness at different levels on the two surfaces, which causes great trouble for subsequent finishing. Therefore, the layout of the guide tube must be carefully considered.

 

04 Be very careful when laying the vacuum bag to prevent some sharp objects from puncturing the vacuum bag.

Stick the vacuum bag along the shape, and be sure to determine the shape and fold position in advance, especially the folds, pleat moderately, not too tight, and press multiple times to ensure no leakage.

 

The most prone to air leakage during the entire bonding process is the seal of the injection tube and the vacuum tube. We adopted two methods. One is to directly wrap two circles of sealant on the tube and bond it to the sealant on the edge of the vacuum bag; the other method is to use a tee and bond it in the middle of the vacuum bag. Experimental comparison found that the method using the tee is better.

 

Because the tube is naturally curved and cannot be well attached to the plane, the first method is prone to warping and leaking. The key to the entire vacuuming is to prevent air leakage

 

 

05 Different resins have different proportions, and different shapes and sizes have different amounts.

Before using the resin, you need to experiment to estimate the curing time of the resin, and determine the amount of each mix according to the size and shape of the carbon cloth. Every time you start pouring, pay attention to the amount of resin and replenish it in time. Before officially doing it, you need to do an experiment to know the curing time of the resin so as to plan the time reasonably. If the resin cures quickly and there is no time planning, it will cure before the pouring is completed.

 

06 When brushing the resin by hand, pay attention to ensuring that each layer is fully and evenly infiltrated with resin.

Pay attention to the dripping of the resin when brushing. If it drips on the side, it will cause the sealant to be not firmly bonded and easy to leak.

 

When making irregular carbon fiber objects, first apply a layer of resin on the mold, and then apply the carbon cloth one by one. If you don’t apply it, it is easy to produce bubbles on the surface, resulting in pits of different sizes on the finished product.

 

Because there is no layer of resin on the surface of the mold, there are many potholes on the front of the car, which increases the workload of later repairs. For the surface repair of the car body, small pits can be filled with oily putty, and large pits can be filled with gel coat.

 

 

07 Finally, summarize the advantages and disadvantages of different processes

Analyze the advantages and disadvantages of infusion and hand brushing

 

Advantages of Infusion:

fast suction, resin is evenly distributed through the guide net, saving manpower.

Disadvantages: the location of the guide tube should be considered. Once there is a problem with the layout, the surface of the carbon fiber material will be affected.

Advantages of Hand brushing: ensure that the resin is fully impregnated, and the irregular shape is easy to fit the mold.

Disadvantages: labor-intensive, each layer of material needs to be manually brushed, which takes a long time.

 

Analyze the advantages and disadvantages of vacuum bag forming and glass pressing

Advantages Of Vacuum Bag Forming: low porosity, higher mechanical properties, lighter weight, suitable for designing large and complex shapes.

Disadvantages: waste of materials, complex process, and once leaking, it will have a great impact.

Advantages Of Glass Pressing: easy to operate, small carbon plates have the same effect as vacuum bags, and the surface quality is better.

Disadvantages: not suitable for large parts, and only suitable for flat plates, too much resin residue, and a lot of grinding is required in the later stage to achieve the expected lightweight effect.