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42FEATURES OF CHIP FORMATION DURING PROCESSING OF POLYMER
COMPOSITE MATERIALS
Rustam Jaxongir o'g'li Karimov, Rustambek Davronbek o'g'li To'xtasinov
Ferghana polytechnic institute
ABSTRACT
A diagram of the equilibrium state of the components of the cutting force during orthogonal cutting is given and the role of each component of the force in the cutting process is determined. The analysis of the features of chip formation during blade processing of polymer composite materials is presented. The results obtained will help to assess the capabilities of physical models when cutting blanks from polymer composite materials.
Keywords: polymer composite materials; carbon fiber reinforced plastics; blade processing; cutting modes; shavings.
Polymer composite materials (PCM) are one of the most demanded material resources of modern industrial production. They are used especially widely and effectively in high-tech industries. PCMs provide high reliability and durability in load-bearing structures, which, in addition to traditional applications (aviation, astronautics, shipbuilding), is very important in the construction industry, energy, and transport engineering. However, the technology of PCM processing by cutting is still little studied and requires considerable attention. As you know, the concept of "machinability" includes a complex of technological properties of a material that characterize its effect on various aspects of the cutting process: cutting force and power, cutting tool durability, chip type and chip formation process, processing productivity and surface quality.
The properties of composite materials depend on the composition of the components (artificial resin and fillers), their combination, quantitative ratio and bond strength between them. Reinforcing materials can be in the form of fibers, ropes, threads, tapes and multilayer fabrics.
UGET and FUT carbon-fiber reinforced plastics were taken as the material of the blanks for the research. The selected antifriction carbon fiber is reinforced with carbon fabric based on ED-2 epoxy binder. Blanks of friction parts are intended for the manufacture of radial (support) and axial (thrust) plain bearings, guides, mechanical seals of various machines and mechanisms. Physicomechanical characteristics of UGTE samples are given in Table 1.
1. Physical and mechanical characteristics of samples made from UGTE press material.
Indicator name Norm for brands
UGTE FUT
Breaking stress in compression, MPa (not less) 220 250
Bending stress at failure, MPa (not less) 200 200
PCM processing is characterized by not always controlled internal destruction. The components of the cutting forces and the type of chips are not always typical, due to the difference in the mechanisms of internal destruction (pulling out) of the fibers. Thus, the processability of PCM is determined by the physical and mechanical properties of fibers and matrix, content (type of fiber) and its direction. Although the polymer matrix in the reinforced composite creates less resistance to processing due to lower strength and stiffness compared to reinforcing fibers, it has a significant impact on the type of chip formation.
The mechanical behavior of thermosetting and thermoplastic materials under stress varies greatly. Thermosets are brittle with very low elongation. Thermoplastic matrices, due to their plastic structure, can have elongation coefficients several times higher.
Depending on the viscosity, the ultimate strength and elongation coefficient of polymers also depend on the degree of deformation. The strength of the material increases and the ultimate elongation decreases as the degree of deformation increases. In other words, the material "shows" a transition from a soft to a brittle state with an increase in the degree of deformation. The type of chips produced by different polymers will vary significantly under different processing conditions.
Increasing the entering angle and decreasing the depth of cut will reduce the amount of deformation that occurs during chip formation. An increase in cutting speed affects the machining process: on the one hand, the material shows a high degree of deformation and, as a result, breaks down at a lower stress or becomes brittle; on the other hand, the generated heat raises the temperature in the cutting zone, increases the intensity of diffusion processes in the material and increases its fluidity. PCMs have little or no plastic deformation, and chip formation is mainly controlled by the degree of fracture of the reinforcing material (fraction).
Thermosetting plastics create some plastic deformation before fracture, but not to the extent required to create directional chips. Therefore, they are classified as fragile. On the contrary, thermoplastics show significant elastic plastic deformation before fracture, which greatly affects the processing of composites. Figure 1 shows the types of chips obtained by processing thermoplastics (Fig. 1, a) and thermosetting plastics (Fig. 1, b).
Fig. 1. Formation of matrix chips: A - thermoplastics; B - thermosetting plastics To simplify the analysis of chip formation, consider the process of two-dimensional or orthogonal cutting. Such a model can introduce some errors in the mechanics of the chip formation process, but it can significantly simplify the consideration and understanding of this process. At the same time, as calculations show, the errors that may arise due to such a simplification do not exceed 10% [4].
For orthogonal cutting, the cutting edge of the tool is perpendicular to the cutting speed vector v. A schematic representation of orthogonal cutting is shown in Fig. 2. Cutting forces acting on the chips: R = R '- resultant force; Fc - cutting force acting along the direction of cutting speed (main force); Ft is the axial force perpendicular to the direction of the cutting speed; Ff is the friction force on the front surface of the cutting wedge; Fn is the force acting perpendicular to the front surface.
Fig. 2. Schematic representation of orthogonal cutting A plane shift in area is generated in the material from the point of the cutting edge
and moves upward towards the chip root. Uncut material 60 thick passes through the
shear zone and undergoes shear deformation. The result is 6 chips, which are generally greater than the theoretical chip thickness. The chips are kept in equilibrium by the resultant force R 'acting on the rake face of the cutting tool. In orthogonal cutting, all forces of motion and deformation are in the plane formed by the cutting speed vector and in the direction perpendicular to it (see Fig. 2).
In fig. 3 shows the influence of the direction of action of the force R depending on the angle of orientation of the fibers of the PCM. In these cases, the cutting force Ft
and the axial force Fc can be projected by the shearing force Fs acting along the shear plane and the force Fn acting perpendicular to the shear plane. When cutting PCM with a fiber directional angle 0 = 0, delamination chips are formed.
Fig. 3. Influence of the direction of action of the force R depending on the orientation
angle of the PCM fibers.
Fig. 4. Types of shavings when processing PCM Studies have shown that the process of chip formation is mainly influenced by the following factors: cutting tool rake angle, fiber material and matrix material (Fig. 4). Elemental shavings are formed during the processing of brittle materials, for example,
thermosetting plastics (Fig. 4, a, b) and some thermoplastics with a large rake angle and a large depth of cut (Fig. 4, c, d). When processing these materials, a crack is formed in front of the inclined shear plane; Chips are generated by a bending moment that influences chip formation from the moment a crack reaches a certain length. This results in poor surface quality after processing. In fig. 4, e, f shows the type of chips obtained during the processing of thermoplastics.
Conclusions
1. When processing PCM, several types of chips can be formed, depending on the type of polymer, tool geometry and cutting conditions.
2. For materials that have high ductility, overflow chips are formed under the condition of low cutting speed and a large positive rake angle of the tool. In this case, the surface roughness decreases.
3. If polymers do not have high plasticity, especially with a thermosetting matrix, then elementary shavings are formed. In this case, the thickness of the chips is equal to the depth of cut (t = 1.0).
4. Elementary chips are generated when machining brittle materials such as thermosetting plastics and some thermoplastics with large rake angles and deep cutting depths. In this case, there is a deterioration in the quality of the surface after processing.
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