Know something about the molding process of composite materials （Ⅰ）

Composite material forming technology is the basis and condition of the development of composite material industry. With the widening of the application field of composite materials, composite industry has been developing rapidly, some molding process is improving, new molding methods continue to emerge, currently there are more than 20 polymer matrix composite molding methods, and successfully used in industrial production, such as:

(1) Hand paste forming process -- wet lay-up forming method;

(2) Jet forming process;

(3) Resin transfer molding technology (RTM technology);

(4) Bag pressure method (pressure bag method) molding;

(5) Vacuum bag pressing molding;

(6) Autoclave forming technology;

(7) Hydraulic kettle forming technology;

(8) Thermal expansion molding technology;

(9) Sandwich structure forming technology;

(10) Molding material production process;

(11) ZMC molding material injection technology;

(12) Molding process;

(13) Laminate production technology;

(14) Rolling tube forming technology;

(15) Fiber winding products forming technology;

(16) Continuous plate production process;

(17) Casting technology;

(18) Pultrusion molding process;

(19) Continuous winding pipe making process;

(20) Manufacturing technology of braided composite materials;

(21) Manufacturing technology of thermoplastic sheet moulds and cold stamping molding process;

(22) Injection molding process;

(23) Extrusion molding process;

(24) Centrifugal casting tube forming process;

(25) Other forming technology.

Depending on the resin matrix material chosen, the above methods are suitable for the production of thermosetting and thermoplastic composites respectively, and some processes are suitable for both.

Composite products forming process characteristics: compared with other materials processing technology, composite materials forming process has the following characteristics:

(1) Material manufacturing and product molding at the same time to complete the general situation, the production process of composite materials, that is, the molding process of products. The performance of materials must be designed according to the requirements of the use of products, so in the selection of materials, design ratio, determine the fiber layering and molding method, must meet the physical and chemical properties of products, structural shape and appearance quality requirements.

(2) products molding is relatively simple general thermosetting composite resin matrix, molding is a flowing liquid, reinforcement material is soft fiber or fabric, therefore, with these materials to produce composite products, the required process and equipment is much simpler than other materials, for some products only a set of molds can be produced.

First, contact low pressure molding process

The contact low pressure molding process is characterized by manual placement of reinforcement, resin leaching, or simple tool-assisted placement of reinforcement and resin. Another characteristic of the contact low-pressure molding process is that the molding process does not need to apply molding pressure (contact molding), or only apply low molding pressure (0.01 ~ 0.7mpa pressure after contact molding, the maximum pressure does not exceed 2.0mpa).

Contact low-pressure molding process, is the first material in the male mold, male mold or mold design shape, and then through heating or room temperature curing, demoulding and then through auxiliary processing and products. Belong to this kind of molding process are hand paste molding, jet molding, bag pressing molding, resin transfer molding, autoclave molding and thermal expansion molding (low pressure molding). The first two are contact forming.

In the contact low pressure molding process, the hand paste molding process is the first invention in the production of polymer matrix composite material, the most widely applicable range, other methods are the development and improvement of hand paste molding process. The biggest advantage of contact forming process is simple equipment, wide adaptability, less investment and quick effect. According to statistics in recent years, contact low-pressure molding process in the world composite material industrial production, still occupy a large proportion, such as the United States accounted for 35%, Western Europe accounted for 25%, Japan accounted for 42%, China accounted for 75%. This shows the importance and irreplaceable of contact low pressure molding technology in composite material industry production, it is a process method that will never decline. But its biggest shortcoming is the production efficiency is low, the labor intensity is big, the product repeatability is poor and so on.

1. Raw materials

Contact low pressure molding of raw materials are reinforced materials, resins and auxiliary materials.

(1) Enhanced materials

Contact forming requirements for enhanced materials: (1) enhanced materials are easy to be impregnated by resin; (2) There is enough shape variability to meet the molding requirements of complex shapes of products; (3) bubbles are easy to deduct; (4) can meet the physical and chemical performance requirements of the use conditions of products; ⑤ Reasonable price (as cheap as possible), abundant sources.

Reinforced materials for contact forming include glass fiber and its fabric, carbon fiber and its fabric, Arlene fiber and its fabric, etc.

(2) Matrix materials

Contact low pressure molding process for the matrix material requirements: (1) under the condition of hand paste, easy to soak the fiber reinforced material, easy to exclude bubbles, strong adhesion with the fiber; (2) At room temperature can gel, solidify, and require shrinkage, less volatiles; (3) Suitable viscosity: generally 0.2 ~ 0.5Pa·s, can not produce glue flow phenomenon; (4) non-toxic or low toxicity; The price is reasonable and the source is guaranteed.

The commonly used resins in production are: unsaturated polyester resin, epoxy resin, phenolic resin, bismaleimide resin, polyimide resin and so on.

Performance requirements of several contact forming processes for resin:

Molding method requirements for resin properties

Gel production

1, molding does not flow, easy to defoaming

2, uniform tone, no floating color

3, fast curing, no wrinkles, good adhesion with the layer of resin

Hand lay-up molding

1, good impregnation, easy to soak the fiber, easy to eliminate bubbles

2, spread after curing fast, less heat release, shrinkage

3, volatile less, the surface of the product is not sticky

4. Good adhesion between layers

Injection molding

1. Ensure the requirements of hand paste forming

2. Thixotropic recovery is earlier

3, temperature has little effect on resin viscosity

4. The resin should be suitable for a long time, and the viscosity should not increase after the addition of the accelerator

Bag moulding

1, good wettability, easy to soak the fiber, easy to discharge bubbles

2, curing fast, curing heat to small

3, not easy to flow glue, strong adhesion between layers

(3) Auxiliary materials

Contact forming process of auxiliary materials, mainly refers to the filler and color two categories, and curing agent, diluent, toughening agent, belonging to the resin matrix system.

2, mold and release agent

(1) Molds

Mold is the main equipment in all kinds of contact forming process. The quality of the mold directly affects the quality and cost of the product, so it must be carefully designed and manufactured.

When designing the mold, the following requirements must be considered comprehensively: (1) Meet the precision requirements of product design, the mold size is accurate and the surface is smooth; (2) to have enough strength and stiffness; (3) convenient demoulding; (4) have enough thermal stability; Light weight, adequate material source and low cost.

Mold structure contact molding mold is divided into: male mold, male mold and three kinds of mold, no matter which kind of mold, can be based on the size, molding requirements, design as a whole or assembled mold.

When the mold material is manufactured, the following requirements should be met:

① Can meet the requirements of dimensional accuracy, appearance quality and service life of products;

(2) The mold material should have enough strength and stiffness to ensure that the mold is not easy to be deformed and damaged in the process of use;

(3) it is not corroded by resin and does not affect resin curing;

(4) Good heat resistance, product curing and heating curing, the mold is not deformed;

(5) Easy to manufacture, easy to demoulding;

(6) day to reduce mold weight, convenient production;

⑦ The price is cheap and the materials are easy to obtain. The materials that can be used as hand paste moulds are: wood, metal, gypsum, cement, low melting point metal, rigid foamed plastics and glass fiber reinforced plastics.

Release agent basic requirements:

1. Does not corrode the mold, does not affect the resin curing, the resin adhesion is less than 0.01mpa;

(2) Short film forming time, uniform thickness, smooth surface;

The use of safety, no toxic effect;

(4) heat resistance, can be heated by the temperature of curing;

⑤ It is easy to operate and cheap.

The release agent of contact forming process mainly includes film release agent, liquid release agent and ointment, wax release agent.