Carbon Fiber Composite Material Molding Process and Application

 

Introduction to Carbon Fiber Composite Material Forming Process

1. Hand Lay-up Process

Hand lay-up process refers to a molding method in which reinforcing materials and thermosetting resins are laid on a mold manually or with the assistance of machinery, and a composite material is formed after the resin is cured.

 

Manual laying mainly uses two raw materials: unidirectional prepreg and fabric prepreg. Unidirectional prepreg can lay complex shapes, but the cutting waste rate is high. Fabric prepreg is less labor-intensive than unidirectional prepreg, but its performance is lower than that of unidirectional prepreg. At the same time, the common disadvantage of hand lay-up is that it is difficult to lay large-sized components.

 

 

2. Automatic Paving Process

It is suitable for flat plates with uniform thickness or simple-shaped components. It has high production efficiency and low laying cost. It also has automatic cutting, reduces ply cutting waste, and does not require vacuum compaction. Automatic paving can also lay shaped surfaces. Its ply thickness is precisely controlled, the void content is low, less than 1%, and the fiber angle is not restricted. However, the cost is too high, and it is mainly used in the production of large-scale industrial composite parts (such as wings).

 

 

3. Winding Molding

The prepreg wire or prepreg tape is wound on the core mold in a predetermined manner, and then cured and demolded to form a composite material product.

 

 

Winding Molding is Divided Into:

1. Dry winding: the pre-impregnated yarn tape (or pre-impregnated cloth) is heated to a viscous flow state on a winding machine and wound onto a core mold. The quality of dry winding products is stable (glue content, size); the winding speed is fast, the labor and hygiene conditions are good, but the equipment investment is large.

 

2. Wet winding: the untwisted roving is directly wound onto the core mold after being impregnated with glue. This method does not require pre-impregnation equipment, the equipment investment is small, and it is easy to select materials. However, the quality and tension of the yarn sheet need to be strictly controlled, and bubbles are easily generated during curing.
3. Semi-dry winding: After the untwisted roving is impregnated with glue, it is randomly pre-dried and then wound onto the core mold.

 

Winding molding has the following characteristics:

1. Applicable to rotating bodies (cylindrical shells and closed containers);
2. Production automation, high efficiency and low cost;
3. High fiber volume content;
4. High material utilization rate and no waste;
5. The resin content of large diameter parts is difficult to control;
6. The shape is limited, and it is difficult to maintain the fiber winding angle for curved parts.

 

1. Injection Molding

 

 

Advantages:

1. Less finishing after forming, improving the utilization rate of raw materials;
2. Low cost (no need for autoclave, no need to prepare prepreg).

 

Disadvantages:

1. The resin content of the product is high;
2. The thickness deviation is large;
3. The performance of chopped fiber is poor.

 

 

5. Pultrusion Molding

 

Advantages:

 

1. Continuous and large-scale production is possible;
2. High dimensional control accuracy;
3. High raw material utilization rate;
4. Automated production and low cost.

 

Disadvantages:

1. Currently only profiles with equal cross-sections can be produced;
2. A mold for pultrusion prepreg is required;
3. It is difficult to orient the layers in non-0° directions.

 

6. Autoclave Molding

 

 

Advantages:

1. Stable size of parts with good repeatability;
2. Parts with high fiber volume content (60%-65%) can be formed;
3. Reliable mechanical properties;
4. All materials can be formed;
5. Laminates of different thicknesses can be solidified;
6. Parts with complex curved surfaces can be manufactured.

 

Disadvantages:

1. The size of the parts is limited by the size of the autoclave;
2. Long cycle and low production efficiency;
3. High energy consumption and high operating costs.

 

VII. RTM Molding

 

 

Under the conditions of pressure injection or external vacuum assistance, the reactive low-viscosity liquid resin flows in the closed mold and removes gas, infiltrates and impregnates the dry fiber body, and the resin initiates a cross-linking reaction in the mold through heat to complete the curing.

 

Advantages:

1. The closed mold forming has stable dimensions, high precision, and smooth surface;
2. The amount of finishing after forming is small, and the utilization rate of raw materials is high;
3. The fiber volume content can reach 55%-60%;
4. The use of preforms improves the damage tolerance performance;
5. No prepreg is required, no autoclave is required, and the cost is low.

 

Disadvantages:

1. The closed mold has high sealing requirements and high initial cost;
2. The void content is high and needs to be heated before resin injection;
3. The preform is difficult to accurately place in the mold and keep it in the right position.

 

8. RFI Molding

 

The solid or semi-solid resin film is placed under the dry fiber body, and the resin penetrates from the bottom to the top, infiltrating the fiber and exhausting the air, and the solidification is completed in the infiltrated state.

 

Advantages:

1. The mold is simpler than the RTM mold;
2. The resin flows along the thickness direction, making it easier to infiltrate the fiber;
3. No prepreg is required, and the cost is low.

 

9. VARI Molding

On a single-sided mold, the resin is impregnated with the dry fiber and then molded under vacuum conditions.

 

Advantages:

1. There is no size limit for the part;
2. The amount of finishing processing is small, and the utilization rate of raw materials is high;
3. No prepreg is required, and the cost is low.

 

RFI Molding and VARI Molding Share the Following Disadvantages:

1. The dimensional accuracy and surface quality are not as good as RTM;
2. It is only suitable for parts with large planes or simple curved surfaces;
3. The production efficiency is lower than RTM;
4. The void content of the part is higher.