FRP Composite Material Forming Process:  Winding Forming Process

 

Composite Material Forming Technology is the foundation and condition for the development of composite material industry. With the expansion of composite material application fields, composite material industry has developed rapidly, some forming processes have been improved, and new forming methods have emerged. At present, there are more than 20 forming methods for polymer-based composite materials, which have been successfully used in industrial production, such as:

 

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

 

(2) Injection molding process;

 

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

 

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

 

(5) Vacuum bag pressing molding;

 

(6) Autoclave molding technology;

 

(7) Hydraulic kettle molding technology;

 

(8) Thermal expansion molding technology;

 

(9) Sandwich structure molding technology;

 

(10) Molding =Material production process;

 

(11) ZMC molding material injection technology;

 

(12) Compression molding process;

 

(13) Laminated board production technology;

 

(14) Rolled tube molding technology;

 

(15) Fiber winding product molding technology;

 

(16) Continuous board production process;

(17) Casting molding technology;

 

(18) Pultrusion molding process;

 

(19) Continuous winding tube making process;

 

(20) Braided composite material manufacturing technology;

 

(21) Thermoplastic sheet molding material manufacturing technology and cold die stamping molding process;

 

(22) Injection molding process;

 

(23) Extrusion molding process;

 

(24) Centrifugal casting tube making process;

 

(25) Other molding technologies.

 

Depending on the different resin matrix materials selected, the above methods are suitable for the production of thermosetting and thermoplastic composite materials respectively, and some processes are suitable for both.

 

Composite material product molding process characteristics: Compared with other material processing processes, composite material molding process has the following characteristics:

 

 

Material Manufacturing and Product Molding are Completed at the Same Time.

Generally speaking, the production process of composite materials is also the molding process of products. The performance of the material must be designed according to the use requirements of the product. Therefore, when selecting materials, designing proportions, determining fiber laying and molding methods, the physical and chemical properties, structural shape and appearance quality requirements of the product must be met.

 

Product Molding is Relatively Simple.

The resin matrix of general thermosetting composite materials is a flowing liquid before molding, and the reinforcing material is a soft fiber or fabric. Therefore, the process and equipment required to produce composite products with these materials are much simpler than other materials. For some products, only one set of molds is required for production.

 

Winding Molding Process

 

The winding molding process is to wind the continuous fiber (or cloth tape, pre-impregnated yarn) soaked in resin glue onto the core mold according to a certain rule, and then obtain the product after curing and demolding. According to the different physical and chemical states of the resin matrix during fiber winding molding, it is divided into dry winding, wet winding and semi-dry winding.

 

Duration 14:29

 

Dry Winding Dry Winding is to use pre-impregnated yarn or tape, which is heated and softened to a viscous state on a winding machine and then wound onto a core mold. Since the pre-impregnated yarn (or tape) is professionally produced, the resin content (accurate to within 2%) and the quality of the pre-impregnated yarn can be strictly controlled.

 

Therefore, dry winding can accurately control product quality. The biggest feature of the dry winding process is high production efficiency, winding speed can reach 100-200m/min, winding machine is clean, labor hygiene conditions are good, and product quality is high. Its disadvantage is that the winding equipment is expensive and it is necessary to add pre-impregnated yarn manufacturing equipment, so the investment is relatively large. In addition, the interlayer shear strength of dry wound products is low.

 

 

Wet Winding Wet Winding is to dip the fiber bundle (yarn-like tape) into glue and then directly wind it onto the core mold under tension control. The advantages of wet winding are:

 

① The cost is 40% lower than that of dry winding;

② The product has good air tightness because the winding tension causes the excess resin glue to squeeze out the bubbles and fill the gaps;

③ The fiber arrangement has good parallelism;

④ During wet winding, the resin glue on the fiber can reduce fiber wear;

⑤ High production efficiency (up to 200m/min).

 

The Disadvantages of Wet Winding Are:

① Large resin waste and poor operating environment;

② The glue content and the quality of the finished product are difficult to control;

③ There are fewer types of resins available for wet winding.

 

Semi-Dry Winding Semi-Dry Winding is to add a set of drying equipment after the fiber is dipped in glue and on the way to the core mold to remove the solvent in the dipped yarn. Compared with the dry method, it saves the pre-impregnation process and equipment; compared with the wet method, it can reduce the bubble content in the product.

 

Among the three winding methods, wet winding is the most commonly used; dry winding is only used in high-performance, high-precision cutting-edge technology fields.

 

 

Advantages of fiber winding molding

 

The winding

rules can be designed according to the stress conditions of the product, so that the strength of the fiber can be fully utilized;

 

High Specific Strength:

Generally speaking, the weight of fiber-wound pressure vessels can be reduced by 40-60% compared with steel vessels of the same volume and pressure;

 

High Reliability:

Fiber-wound products are easy to realize mechanized and automated production. After the process conditions are determined, the quality of the wound products is stable and accurate;

 

High Production Efficiency:

Mechanized or automated production requires fewer operators and fast winding speed (240m/min), so the labor productivity is high;

 

Low Cost:

On the same product, several materials (including resin, fiber and lining) can be reasonably selected and compounded to achieve the best technical and economic effect.

 

 

Disadvantages of Winding Molding

Winding Molding has low adaptability and cannot be used to wind products of any structural form, especially products with concave surfaces, because when winding, the fibers cannot be close to the surface of the core mold and are suspended;

 

Winding Molding Requires Winding Machines, core molds, curing heating furnaces, demolding machines and skilled technical workers, which requires large investments and high technical requirements. Therefore, only mass production can reduce costs and obtain better technical and economic benefits.

 

Raw Materials

The raw materials for winding molding are mainly fiber reinforcement materials, resins and fillers.

 

Reinforcement Materials

The reinforcement materials used for winding molding are mainly various fiber yarns: such as alkali-free glass fiber yarn, medium-alkali glass fiber yarn, carbon fiber yarn, high-strength glass fiber yarn, aramid fiber yarn and surface felt, etc.

 

Resin Matrix

The resin matrix refers to the glue system composed of resin and curing agent. The heat resistance, chemical corrosion resistance and natural aging resistance of wound products mainly depend on the resin properties, and also have a great influence on the processability and mechanical properties. The commonly used resins for winding molding are mainly unsaturated polyester resins, and sometimes epoxy resins and bismaleimide resins are used. For general civilian products such as pipes and tanks, unsaturated polyester resins are mostly used. For winding products with high requirements for mechanical properties of compressive strength and interlaminar shear strength, epoxy resins can be used. Aerospace products mostly use bismaleimide resins with high fracture toughness and good moisture resistance.

 

Fillers

There are many types of fillers. After adding, they can improve certain functions of the resin matrix, such as improving wear resistance, increasing flame retardancy and reducing shrinkage. Adding hollow glass microspheres to the glue can increase the rigidity of the product, reduce density and reduce costs. When producing large-diameter buried pipes, 30% quartz sand is often added to improve the rigidity of the product and reduce costs. In order to improve the bonding strength between the filler and the resin, the filler must be kept clean and surface-active.

 

Core Mold

The inner mold of the hollow product is called the core mold. Generally, after the winding product is cured, the core mold should be removed from the product.

 

Basic requirements for core mold design

① It must have sufficient strength and rigidity to withstand various loads applied to the core mold during the product molding process, such as self-weight, product weight, winding tension, curing stress, cutting force during secondary processing, etc.;

 

② It must meet the requirements for product shape and size accuracy, such as shape size, concentricity, ellipticity, taper (demolding), surface finish and flatness, etc.;

 

③ Ensure that the product can be smoothly removed from the product after solidification;

④ Simple manufacturing, low cost, and convenient material acquisition.

 

 

Core Mold Materials

There are two types of core mold materials for winding molding: molten and soluble materials and assembled materials. Molten and soluble materials refer to paraffin, water-soluble polyvinyl alcohol molding sand, low melting point metals, etc. These materials can be made into hollow or solid core molds by casting. After the product is wound and formed, hot water or high-pressure steam is passed through the opening to make it melt and flow out of the product. The melt that flows out is cooled and reused. Commonly used assembled core mold materials are aluminum, steel, sandwich structure, wood and gypsum. In addition, there are lining materials. Lining materials are components of products. They are not removed from products after solidification. The main function of lining materials is corrosion protection and sealing. Of course, they can also act as core molds. Such materials include rubber, plastic, stainless steel and aluminum alloy.

 

Winding Machine

 

The winding machine is the main equipment for realizing winding molding process. The requirements for the winding machine are:

 

① It can realize the winding rules and accurate yarn arrangement of product design;

 

② Easy to operate;

 

③ High production efficiency;

 

④ Low equipment cost.

 

The winding machine is mainly composed of two parts: core mold drive and winding nozzle drive. In order to eliminate the loose fiber line when the winding nozzle moves in the reverse direction, maintain stable tension and accurately arrange the yarn tape of the end or conical winding product, and realize winding with a small winding angle (0°~15°), a lateral feeding (extending arm) mechanism perpendicular to the core axis is designed on the winding machine. In order to prevent the yarn tape from twisting when the winding nozzle moves in the reverse direction, a mechanism that can turn the winding nozzle is provided on the extending arm.

 

my country successfully developed a chain winding machine in the 1960s, and introduced the German WE-250 CNC winding machine in the 1970s. After improvement, it realized domestic production. After the 1980s, my country introduced more than 40 winding machines of various types. After improvement, it successfully designed and manufactured a microcomputer-controlled winding machine and entered the international market.

 

Types of Mechanical Winding Machines

 

Arm-wrap type plane winding machine Its characteristics are that the arm (equipped with a winding nozzle) rotates uniformly around the core mold, and the core mold rotates uniformly and slowly around its own axis. For every rotation of the arm (i.e. the winding nozzle), the core mold rotates a small angle. This small angle corresponds to the width of a yarn sheet on the winding container, ensuring that the yarn sheets on the core mold are closely distributed on the container surface. When the core mold rotates rapidly, the winding nozzle moves slowly up and down in the direction perpendicular to the ground, and circumferential winding can be achieved. The advantages of using this winding machine are that the core mold is evenly stressed, the mechanism runs smoothly, and the wire arrangement is uniform. It is suitable for dry winding of small and medium-sized short and thick cylindrical containers.

 

Tumbling Winding Machine

The core mold of this winding machine is supported by two rocking supports. During winding, the core mold rotates on its own axis, and the two arms rotate synchronously to make the core mold roll over. The core mold rotates at an angle that is suitable for the width of the yarn sheet, and the fiber yarn is supplied by a fixed extension arm to achieve planar winding. The hoop winding is achieved by an additional device. Since the tumbling action mechanism should not be too large, this type of winding machine is only suitable for small products and is not widely used.

 

Horizontal Winding Machine

This winding machine is driven by a chain to drive the trolley (winding nozzle) to reciprocate and stop momentarily at the end of the head. The core mold rotates at a constant speed around its own axis. Adjusting the speed of the two can achieve planar winding, hoop winding and spiral winding. This winding machine has a simple structure and a wide range of uses. It is suitable for winding slender tubes and containers.

 

Track Winding Machine

Track winding machines are divided into two types: vertical and horizontal. The yarn ball, glue groove and winding nozzle are all installed on the trolley. When the trolley goes around the core mold along the circular track, the core mold itself rotates a yarn sheet width, and the angle between the core mold axis and the horizontal plane is the plane winding angle α. Thus, a plane winding type is formed. By adjusting the speed of the core mold and the trolley, annular winding and spiral winding can be achieved. The orbital winding machine is suitable for the production of large products.

 

Planetary Winding Machine

The core shaft and the horizontal plane are inclined at an angle α (i.e., the winding angle). During winding, the core mold rotates and revolves, and the winding nozzle is fixed. Adjusting the rotation and revolution speed of the core mold can complete plane winding, annular winding and spiral winding. The revolution of the core mold is the main motion, and the rotation is the feed motion. This winding machine is suitable for the production of small products.

 

Spherical Winding Machine

The spherical winding machine has four moving axes. The winding nozzle of the spherical winding machine rotates, the core mold rotates and the core mold deflects, which are basically the same as the rocker arm winding machine. The fourth axis movement is to use the winding nozzle stepping to realize the yarn winding, reduce the fiber accumulation outside the pole hole, and improve the uniformity of the container arm thickness. The core mold and the winding nozzle rotate so that the fibers are spread all over the surface of the sphere. The deflection movement of the core mold axis can change the size of the winding pole hole and adjust the winding angle to meet the stress requirements of the product.

 

Cable-Type Longitudinal Hoop Winding Machine

The longitudinal hoop cable-type winding machine is suitable for the production of cylindrical containers without heads and various pipelines. The rotating ring with the longitudinal yarn ball rotates synchronously with the core mold and can reciprocate along the axis of the core mold to complete the longitudinal yarn laying. The hoop yarn is installed on the trolleys on both sides of the rotating ring. When the core mold rotates and the trolley reciprocates along the axis of the core mold, the hoop yarn winding is completed. According to the stress conditions of the pipeline, the proportion of the number of longitudinal and hoop yarns can be adjusted arbitrarily.

 

New Tube Winding Machine

The difference between the new tube winding machine and the existing winding machine is that it relies on the self-rotation of the tube core and can simultaneously make reciprocating motion along the tube length to complete the winding process. The advantages of this new winding machine are that the winding nozzle is fixed, which brings great convenience to workers in dealing with broken ends, loose yarns and tube care; multi-channel yarn feeding can realize large-capacity yarn feeding and winding, fast winding speed, uniform yarn distribution, which is conducive to increasing product weight and output.