RU2499663C1 - Method of cutting ductile metals by high-strength thread - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to process of machine building, particularly, to cutting of ductile metal billets. Proposed method comprises cutting the article by applying cutting tool thereto. Cutting is effected by thread at heating temperature-to-metal melting point T₀=0.7-0.8. Thread is made of stainless steel or tungsten.

EFFECT: higher surface quality, ruled out metal losses.

2 dwg, 1 tbl

Description

The invention relates to mechanical engineering technology, in particular, to methods for plastic cutting of metal billets having high ductility and low yield stress.

From the prior art, various methods are known for cutting metal billets in the form of long products on press scissors and dies, band and circular saws, electrochemically and abrasive mechanical string cutting (Engineering. Encyclopedia. Volume III-2. Procurement production technology. - M .: Engineering, 1996. - 736 p., SU 1689089, 11.11.1991; machine for cutting semiconductor materials ALTEK-1300 SM, www // ite.inst.cv.ua)

The disadvantages of cutting methods for long products on shears are shear surface defects and section shape distortion as a result of separation of the workpiece by separation and plastic bending, and limitation of the ratio of the length of the cut workpiece to the size of the cross section. When cutting in stamps, these drawbacks are reduced. However, the complexity of the design of the dies, the high demands on the accuracy of the axial section size and the surface quality of the workpieces make the practical application of this method difficult. Mechanical cutting with circular and band saws and abrasive cutting with a string is laborious and leads to metal losses during the formation of a cut or cut.

The closest technical solution to the proposed method is a plastic method of cutting high-quality rolled metal on press scissors (Engineering. Encyclopedia. Volume III-2. Procurement production technology. - M.: Engineering, 1996, pp. 262, 263). When cutting in a known manner, plastic deformation occurs at the beginning of the introduction of knives in the form of a crescent-shaped “shiny belt” with subsequent tearing of the workpiece with a rough separation surface. The asymmetry of the forces acting on the knives leads to plastic bending in the cutting zone and distortion of the cross-sectional shape. Defects in the shape of the end surface require the use of additional calibration operations during pressure processing, or laborious mechanical processing of the ends by cutting. The ratio of the length of the workpiece to the size of the cross section is limited to a minimum value of 1.5.

The technical result of the claimed invention is to provide the effect of plastic flow around the metal being cut by the cutting tool in the form of a loop of a high-strength thread during the cutting process, which ultimately ensures a high quality of the cut surface and the elimination of metal loss in waste at high productivity.

The technical result is solved by a method of cutting products from aluminum alloys and carbon steels, including cutting the product by exposure to a cutting tool according to the invention, cutting is carried out by a thread made of stainless steel or tungsten, with the ratio of the heating temperature to the melting temperature of the metal of the workpiece T ₀ = 0.7-0.8.

Heating structural steels and alloys provides a decrease in yield stress and increase ductility, necessary to implement the proposed method of cutting. The relative temperature T ₀ at which this effect is achieved is defined as the ratio of the absolute heating temperature to the absolute melting temperature (W. Johnson, P. Mellor, Theory of Plasticity for Engineers, M. Mechanical Engineering, 1979, p. 31). For technically pure lead, low yield stress and high ductility, characteristic of carbon steels at T ₀ in the range of 0.7-0.8, are achieved at room temperature.

The invention is illustrated by graphic materials, where:

- figure 1 shows a device for cutting blanks of circular cross section,

- figure 2 shows a device for cutting workpieces of rectangular cross section.

The method of cutting ductile metals with high strength thread is as follows.

When cutting a round billet (Fig. 1), a workpiece 1 with a radius r is mounted on prismatic supports 2 on a base 3. A loop 4 of a flexible high-strength thread fixed on a movable block 5 with a radius R is put on the workpiece 1. The initial position of the loop 4 and the block 5 is shown by dashed lines. The base 3 and supports 2 have a gap for free movement of the loop 4. When moving the S axis of the block 5 under the action of the force P applied to the slider 6 through the cable 7, the loop 4 is inserted into the workpiece 1. The uncut part of the cross section of the workpiece is shown in figure 1 by hatching .

For small ratios of the diameter of the thread d to the diameter of the workpiece D = 2r, the thread is completely immersed in the workpiece 1 and its stationary plastic flow around the metal: Nepershin R.I. Embedding a flat die in a rigid plastic half-space. “Applied Mathematics and Mechanics”, T.65, issue 1, 2002, pp. 140-146; Nepershin R.I. The introduction of the final wedge into a perfectly plastic half-space. “Proceedings of the RAS. Solid Mechanics ”, 2003, No. 4, pp. 176-182. In the absence of lubrication at the contact of the thread with the workpiece 1, a rigid zone is formed - a "build-up" of metal moving together with the thread. When the thread is introduced, relative sliding along the tangent to the contact arc with the workpiece 1 occurs, causing tangential stresses T, reducing the normal pressure q on the thread: Ivlev D.D., Maksimova L.A., Nepershin R.I. On the indentation of a flat die into an ideal rigid plastic half-space under the action of contact shear stresses. "Applied Mathematics and Mechanics", T.65, issue 1, 2002, pp. 134-139. At maximum friction, τ / σ _s → 0.5, where σ _s is the yield stress, and the thread is completely immersed in the workpiece 1 q≈2.64σ _s . Due to friction, the tension of the thread N increases along the arc of contact with the workpiece 1 from the point of symmetry A to the exit of the thread from the workpiece 1 and is determined by the equilibrium condition

$$N=(q_0\rho +\tau l)d,\text{(one)}$$

where q ₀ = 2.64σ _s is the normal pressure on the thread and ρ is the radius of curvature of the thread at point A; l is the length of the contact arc, measured from point A. At contact arc angles less than π / 2, the shape of the contact boundary with the workpiece 1 is close to a circle. The tension of the thread at the exit from the workpiece 1 is found from formula (1) at τ / σ _s = 0.5 and l / ρ = π / 2: N = 3.42 σ _s ρd. The maximum tension occurs at the beginning of cutting at ρ = r. When moving the axis of the block 5, the radius of curvature ρ decreases to zero and the thread tension decreases. The maximum diameter of the workpiece 1, limited by the strength of the thread, is determined by the allowable stress [σ] for tensile threads and the yield stress Gs of the material of the workpiece 1

$$D<0.46d[\sigma ]/{\sigma }_s.\text{(2)}$$

When cutting a workpiece 1 with σ _s = 20 MPa, a boron fiber thread d = 0.2 mm at [σ] = 3.5 GPa, we find D <16.1 mm. When the radius of the block R> r, the initial length of the contact arc l decreases, the thread tension decreases and the limiting diameter of the cut workpiece 1 increases. The force P of the tension of the cable 6 is determined by the condition of equilibrium of the thread with the block 5 without taking into account the gravity of the block and the cable

$$P=2N\cos \alpha .\text{(3)}$$

The initial angle of inclination α ₀ and the length of the closed loop L of the thread are determined by the radii of the workpiece 1, block 5 and the center distance a ₀ (figure 1)

$$\sin {\alpha }_0=(R-r)/a_0,\text{L}=\pi \text{(R}+\text{r)}+\text{2 [}{\alpha }_{\text{0}}\text{(Rr)}+{\text{a}}_{\text{0}}\text{cos}{\alpha }_{\text{0}}\text{]}\text{. (four)}$$

When setting the radius of curvature ρ of the cut section in the interval r> ρ> 0, the angle α is determined from the geometric relation

$$(R-\rho )\cos \alpha =[L/2-\pi /2(R+\rho )-\alpha (R-\rho )]\sin \alpha .\text{(5)}$$

The distance a between the center of curvature of the cut section and the center of block 5, the displacement h of the center of curvature and the displacement s of the center of block 5 are determined by the formulas

Figure 2 shows the cutting of a billet 1 of rectangular section b × H, fixed by clamps 2 on the base 3, by a loop of thread 4 when moving s of the axis of block 5 under the action of a force P applied to the slider 6 through the cable 7. The hatch shows the uncut part of the cross section of the billet 1 with the radius of curvature ρ of the arc of contact with the thread. Since the tension of the thread is proportional to ρ, then cutting a rectangular section should be carried out along the thickness of the workpiece b. The initial position of the loop 4 and block 5 is shown by a dashed line. The diameter of the block 5 is advisable to set more than the workpiece thickness 1 2R> b to reduce the contact length l and the thread tension N. The initial tilt angle of the thread α ₀ and the loop length L are determined by the cross-sectional dimensions of the workpiece 1 and block 5 and the initial distance a _{0 of the} axis of the block 5 from the reference base plane 3 according to the formulas

$$\sin {\alpha }_0(H+a_0)=R-b/2\text{L}=\text{b}+\text{R (}\pi +\text{2}{\alpha }_{\text{0}}\text{)}+\text{2 (H}+{\text{a}}_{\text{0}}\text{) cos}{\alpha }_{\text{0}}.\text{(7)}$$

The tension N at the outlet of the thread from the workpiece 1 and the force P are determined by formulas (1) and (3) when the angle α changes depending on the displacement s of the axis of the block 5. At the beginning of the process, the plastic threading of the thread into the workpiece 1 takes place from the corners with an increase in the radius of curvature of the boundary contact to ρ = b / 2. Then comes the stationary stage of the cutting process with a constant radius ρ = b / 2 with the angle of inclination of the thread α, determined from equation (5). At the stationary stage, the distance h of the center of curvature of the contact arc to the base 3 decreases from the value of H-b / 2 to zero. The displacement s of the axis of block 5 is calculated by the formula

$$s=(R-\rho )/\sin \alpha -(h+a_0),\text{Hb / 2}>\text{h}>\text{0}\text{. (8)}$$

At the final stage of cutting, the radius of curvature ρ decreases to zero. The angle α and the displacement s are determined from equations (5) and (8) with h = 0 and a decrease in ρ from b / 2 to zero. The limiting thickness of the cut workpiece is determined from inequality (2) with the replacement of D by b on the left side of the inequality.

As a cutting tool in the form of a flexible thread, steel wire, boron or tungsten fibers with a diameter of 0.1-0.2 mm can be used. The tensile strength of these threads reaches values of 3.5-5 GPa: Rabnov Yu.N. Mechanics of a deformable solid. - M .: Nauka, 1979, pp. 709-713. The yield stress in the range of 10-20 MPa for aluminum alloys and carbon steels is achieved at a relative heating temperature T ₀ = 0.7-0.8. Stainless steel and tungsten filaments retain high strength at temperatures of 470-510 ° C and 1130 ° C, respectively: Composite materials. Directory. Ed. V.V. Vasiliev, Yu.M. Tarnopolsky. - M.: Mechanical Engineering, 1990, p. 23, 24.

To verify the described method for cutting workpieces, a laboratory setup was made according to the schemes shown in Fig. 1 and Fig. 2. The cable 7 was wound on a drum with a manual rotation drive by a handle with a shoulder length relative to the axis of rotation of the drum, reducing the force P by two to three times. Samples were cut from technically pure lead at room temperature, at which the workpiece had a flow stress of 10–20 MPa and high ductility, and from an aluminum alloy AD1 at a temperature of 430–450 ° C (T ₀ = 0.7–0.8) with a steel string for musical instruments, d = 0.2 mm, with tensile strength [σ] = 2 GPa. The maximum thickness (diameter) of the cut samples is 8-10 mm, which is consistent with the estimate (2). The cut surfaces were smooth with a slight burr of ~ 0.1 mm at the exit of the thread from the cutting zone in the lower part of the samples. For thermal insulation of a heated sample of alloy AD1 used asbestos gaskets on the clamps (figure 2).

Experiments on cutting specimens with heating have shown the importance of accurate control of the temperature range. At low temperatures, the strand breaks occurred due to the high value σ _{s of the} workpiece. At high temperatures close to the melting temperature, coarse fracture of the samples occurred due to the brittleness of the material with coarse grains with pronounced fusion along their boundaries.

The limitations of the proposed method for cutting heated billets with a low yield stress with a high-strength thread, depending on the relative heating temperature of the billet T ₀ are shown in the table.

Table T ₀ Clean cut surface of the workpiece Note 0.6 yarn break due to high σ _s 0.7 good 0.75 high 0.8 good 0.85 low 0.9 brittle fracture

Claims (1)

A method of cutting products from aluminum alloys or carbon steels, including cutting the product by exposure to a cutting tool, characterized in that the cutting is carried out by a thread made of stainless steel or tungsten, with the ratio of the heating temperature of the workpiece to the melting temperature of the aluminum alloy or carbon steel T ₀ = 0.7-0.8.

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