Fabric production can be made possible by means of different methods in textile.
- Weaving
- Knitting
- Nonwoven surface creation methods
It is possible to produce traditional, two-dimensional fabrics.
Two-dimensional fabrics with anisotropic structure have a very low thickness value compared to the surface area, so they show low mechanical performance in the direction of their thickness.
Textile fibers and fabrics are widely used in the production of composite materials. Textile composite materials find application in many industries such as defense, medical, aviation industry.
Textile composite materials show higher mechanical behavior than metal and ceramic materials with their high strength values compared to their low weight.
- Composite materials produced with two-dimensional fabrics exhibit low mechanical behavior in the direction of their thickness, since they have low thickness values.
- Delamination problem, which is expressed as separation between layers, occurs in two-dimensional textile composite materials.
- The problems observed in two-dimensional composite materials constituted an important reason for the production of three-dimensional fabrics.
- Three-dimensional fabrics can be obtained by textile production methods such as weaving, knitting, nonwoven surface forming and diagonal knitting methods.
- Three-dimensional fabrics completely eliminate the delamination problem that occurs in composite materials.
In addition, it makes it possible to produce close to the shape of the final product desired to be obtained. Thus, a significant reduction in production costs and material waste amounts is achieved.
Production Methods of Three-Dimensional Fabrics
Three-dimensional fabrics can be obtained by textile production methods such as weaving, knitting, diagonal knitting, forming nonwovens and sewing.
Three Dimensional Knitting Method
The production of three-dimensional knitted fabrics can be achieved by weft and warp knitting methods, as in the production of traditional, two-dimensional knitted fabrics.
With the weft knitting method, it is possible to produce three-dimensional knitted fabrics with a shape very close to the desired end product.
Production of three-dimensional knitted fabrics on weft knitting machines;
The machines can be provided with modified beds and electronic equipment.
Another important advantage of three-dimensional weft knitted fabrics is that filling yarns can be included in the structure in the longitudinal direction if desired.
The most important problem experienced in these fabric types obtained by weft knitting method;
The structure is too bulky and void. The high number of voids per unit volume causes the fiber/volume ratio of the structure to decrease. This situation causes the structure to have a low strength value.
Three-dimensional knitted fabrics obtained with warp knitting machines have been in high demand in recent years compared to structures produced by weft knitting machines.
Three-dimensional knitted fabrics obtained with warp knitting machines;
Compared to two-dimensional woven fabrics, it has high elasticity modulus and strength values.
The reason for this difference;
- carbon fibre
- Cam
- Basalt vs.
The reason is that high modulus fibers such as warp knitted structures have less curls. Decreased crimp in the yarn structure causes an increase in strength. In addition, the preference of these structures instead of two-dimensional woven fabrics in the production of composite materials; It provides a significant reduction in the amount of fabric waste and production costs. The three-dimensional knitted fabric produced by the warp knitting method is shown below.
Three-dimensional warp knitted fabrics began to be produced in the early 1980s and used in the composite industry in the 1990s.
In these fabric types, due to their superior features such as low production costs and their ability to be designed in line with the desired properties;
- geotextiles
- Pneumatic systems
- Production of some parts for cars and airplanes
- Production of various body parts and artificial veins
They can be used in many different fields.
Production of these fabric types in warp knitting machines;
- It is achieved by laying the fiber layers in the desired direction and connecting these layers by means of a warp knitting loop.
Mayer and Liba companies make it possible to produce these structures with different production techniques. In the system developed by the Mayer company, four different fiber layers are deposited in the 0˚, +45˚, -45˚, 90˚ directions and produced by binding with a loop. In the method developed by the Liba company, the number of fiber layers included in the fabric can increase to seven. Below is the production technique of Liba company. Liba production technique also makes it possible to include nonwoven fabrics in the system.
The fiber layers in the structure;
While adding strength to the structure in the desired directions
Warp knitting loop;
It increases the strength of the structure in terms of thickness.
Loop in three-dimensional warp knitting machines:
- The use of such equipment as chain
- trikot
It can be obtained in two different ways. While providing the integrity of the structure, the loop creates a significant increase in strength and damage tolerance. Damage tolerance is a structural property of the material. It can be expressed as the ability of the material to keep the reliability of the material within certain limits until the repair process occurs.
Three Dimensional Nonwoven Surface Creation Method
In three-dimensional nonwoven surfaces, there is no connection between the yarns that make up the structure. These structures can be produced by needling and stitching methods.
Threads in the needling method; It is deposited into the system in the desired directions, but there is no connection between these yarns. Then, by means of needles, the fibers in the yarns pass through each other and merge and form a surface. Below, a surface created by the needling method and its production method are visually expressed.
In the stitching method, the layers formed by the fibers or threads are combined with the sewing process. In this process, the type of sewing, the type and number of sewing thread, and the density of the seam per unit area are of great importance.
The sewing thread density on three-dimensional nonwovens is between 0,4 – 25 stitches/cm². Usually as sewing thread kevlar is preferred. Because Kevlar has high strength and flexibility values compared to other fibers.
In machines where nonwoven surfaces are obtained by sewing, the sewing head can be one or more. The main problems for these machines are that the number of sewing heads in the machine is limited, sewing can be done up to a certain surface thickness value, and the surface can be obtained at a limited width.
Today, industrial machines can work with a maximum width of 1 m and a surface thickness of 5 mm. The machine used by NASA to obtain these structures is 28 m long, can sew at 15 m, and can sew on surfaces with a width of 3 m and a thickness of 40 mm.
The production of three-dimensional nonwovens is easier and cheaper than two-dimensional woven fabrics. At the same time, the fatigue and impact resistance of composite materials obtained with these structures are higher than traditional woven fabrics.
It is an important problem of these structures that curved areas in complex shapes are difficult to sew with today's industrial machines.
Not enough studies have been done on issues such as stitch density, thread type and number. The fact that these issues are not clarified is another important reason why their use has not increased. R&D studies are required in this regard. However, it is an inevitable fact that a solid contract that protects the rights of both parties in these R&D studies, as in other fields, is made.
Three Dimensional Diagonal Braiding Method
The three-dimensional diagonal knitting method is the first method used in history for three-dimensional fabric production.
In the late 1960's;
- It is produced with the aim of reducing the weight between 30-50% in the rocket engine compared to metal alloys.
Three-dimensional fabrics obtained by the diagonal knitting method;
- Medical
- Space
- Transportation
It can be used in many different fields.
With the diagonal knitting method, it is possible to produce structures that are very close to the final shape. This situation significantly reduces production costs and the amount of waste yarn and fabric. Three-dimensional composite materials produced by the diagonal knitting method are shown below.
In the three-dimensional structures obtained by the diagonal knitting method, there are two different yarn groups as axial and knitting yarns;
- axial threads; While the strength is included in the structure in the desired direction, the yarn connections are provided with knitting yarns. Knitting yarns are fed to the system from the shuttles.
- knitting system knitting yarn provided by the displacement movement of the coils.
Diagonal knitted fabric, knitting yarn bobbins and bobbin mechanisms are shown below.
- Three-dimensional diagonal knitted fabrics can be produced angular or circular.
- The production of these structures is done in circular or angular machines, depending on the purpose.
- Three-dimensional diagonal knitted fabrics are classified according to the number of steps.
Knitting process occurring in one revolution of the machine; represents my name. Three-dimensional diagonal knitted fabrics can be two, four or multi-stepped. Two-step diagonal knitting method It was developed by Popper and McConnell in 1987.
Below are the unit knitting patterns of two- and four-step diagonal knitted fabrics.
The production of small-sized structures with three-dimensional diagonal fabrics is a very cheap and easy process. Various problems arise in the production of fabrics with a width over 100 mm by diagonal knitting method. Because the increase in the size of the product to be produced reveals the necessity of increasing the size of the machine.
The most important reason why these structures are not widely used in aircraft production;
- It arises from the fact that the cost is quite high and the process is difficult due to the size of the machine that can produce the structure.
Modulus of elasticity in composite materials formed with three-dimensional diagonal knitted fabrics;
- The diagonal angle formed by the knitting yarns varies depending on the variables such as yarn counts and knitting patterns.
The other cons of the structure are that the strength values of the composite materials created with three-dimensional diagonal knitted fabrics are lower than those of two-dimensional composite materials, and that the machine is ready for production in a long time in the production of large-sized fabrics and that it works slowly.
Today, three-dimensional diagonal knitted fabrics in the automotive industry; It is being studied on its use in the manufacture of chassis and shaft. If the targeted success can be achieved, up to 50% weight loss can be achieved in cars.
Three Dimensional Weaving Method
Three-dimensional weaving method represents one of the important methods used for the production of three-dimensional fabrics. Since three-dimensional fabrics are used in the production of composite materials, their strength values are important.
Weaving method among three-dimensional fabric production methods;
It provides the production of fabrics with high strength value compared to other methods. For this reason, it is a more common and known method compared to other production methods.
