RU2356668C1 - Manufacturing method of variable cross-section products from light alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metal deformation process and can be used during production of variable cross-section strips. Method includes compressing of variable cross-section strips and setting of longitudinal and transversal geometry. Compressed strips are implemented with preliminary dimensions, structure and allowance for clamping. Finished size, structure, mechanical properties and setting of longitudinal and transversal geometry are provided by allowance clamping, subject the strip to rolling with tension, including hot rolling and cold rolling with peening.

EFFECT: invention provides improvement of structure, stable properties, increasing of mechanical properties, productivity and setting quality.

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Description

The proposed solution relates to the processing of metals by pressure and can be applied in mechanical engineering and metallurgical industry.

The main method of manufacturing profiles from light alloys is pressing, which provides high accuracy in the size of the profiles.

The technology for manufacturing profiles of light alloys includes extruding the profile and then editing it by stretching on stretching machines using clamping jaws.

Editing provides longitudinal and transverse geometry, as well as improving the mechanical properties of the profile.

When editing profiles of constant cross-section, the ends of the profile are clamped with jaws installed in the heads of the stretching machine, and then the profile is stretched by a predetermined amount.

There is a known technology for manufacturing extruded profiles of variable cross section from light alloys, which also includes pressing the profile using special tools and subsequent editing of the profile on special stretching machines (see Matveev B.I., Zhuravlev F.V. Technology for pressing profiles of variable and periodic section from light alloys. M.: Oborongiz, 1959).

Using this technology, 50 years ago small profiles of a simple cross-section were made - corners, Tauris smoothly varying in length.

Editing of such profiles was carried out on a stretching machine, which had a movable head. Editing the profile was carried out in sections 500 mm long and began with the maximum section. After straightening the plot, the movable head was moved 500 mm, the second plot was fixed and corrected. So the subsequent sections of the profile ruled. About 30 types of profiles were mastered using this technology (see MZ Yermanok. Extrusion of profiles from aluminum alloys. M: Metallurgy, 1977, p. 8, 20, 21). However, the nomenclature of mastered profiles did not give a significant reduction in metal consumption, and editing sections in sections was low productivity and did not ensure the quality of products, and therefore, profiles of smoothly variable sections are not currently produced by the industry (see indicated, p. 9).

Nowadays, technical solutions have appeared that make it possible to obtain large-sized products by pressing - Tauri, I-beams, channels, angles, press strips and others with a section smoothly and stepwise varying in length (see, for example, AS USSR No. 1433516, class B21C 23/08, No. 1519811, class B21C 23/20).

The development of such products allows to reduce the metal consumption in comparison with profiles of constant cross-section by 30-40%.

However, product development is constrained by the lack of reliable and high-performance dressing methods.

In addition, a distinctive feature of extruding profiles of variable cross-sectional lengths from extruded profiles of constant cross-section is that such profiles have stretching coefficients of varying length. The maximum cross section has a minimum hood, which is limited by the minimum allowable mechanical properties and heterogeneity of the structure.

The minimum cross section has a maximum exhaust, which is limited by the permissible stresses arising in the pressing tool.

With small hoods, the unevenness of the mechanical properties, especially between the central and peripheral layers, can be quite large. With high hoods, this unevenness decreases and almost disappears. Studies have shown that with hoods of 10 or more along almost the entire length of the press product, except for a small area at the front end, the difference in mechanical properties between the central and peripheral layers is small. Therefore, in press products that are not further subjected to deformation, the minimum drawing should be at least 10, and for products undergoing further deformation, at least 5. For example, pressed rods subsequently serve as blanks for stamping products.

The greatest reduction in metal consumption can give press products of variable cross-section, having large differences in the sizes of the maximum and minimum sections. At the same time, products may have hoods less than 5.

In such cases, according to the specified standards, the maximum cross section or the entire product must be subjected to additional pressure treatment.

It is also known to manufacture semi-finished products from aluminum alloys by rolling (see the reference manual "Production of semi-finished products from aluminum alloys." M: Metallurgy, 1971, pp. 30-143).

Rolling is carried out in a rolling stand, which is a closed frame in which rolls are installed with a given gap against each other, compressing the workpiece fed into the gap.

Rolling is a high-performance metal forming process, as it is carried out at high speeds and continuously during the rolling operation. Large reductions during hot rolling reduce the unevenness of the deformation, contribute to the production of hot-rolled strips with a uniform structure and stable properties (see page 60). By cold rolling, a material is obtained with desired mechanical properties and structure, which cannot be achieved with hot rolling.

Cold rolling is also used for the production of sheets for special purposes: sheets with a variable cross-section; with a regulated structure, special mechanical properties (p. 75 specified).

The mechanical properties of sheets made of thermally unstrengthened alloys are ensured by harting - cold rolling.

Sheets of heat-strengthened alloys are first subjected to hardening and straightened in a freshly hardened state by stretching. If required, these sheets are wound in several passes (p. 106).

The technical result of the proposed technical solution consists in eliminating the noted drawbacks in the known technology for the production of extruded profiles of variable cross section from light alloys, increasing productivity and quality of dressing, ensuring the possibility of manufacturing extruded products of variable cross section with improved structure and stable properties, the possibility of increasing mechanical properties due to additional strengthening factor - fretting.

The technical result is achieved by the fact that in the method of manufacturing products of variable cross section from light alloys, including the operation of pressing the product of variable cross section and providing the specified structure, mechanical properties, editing its longitudinal and transverse geometry, the pressed product of variable cross section is performed with preliminary dimensions, structure and allowances for compression, and the final dimensions, structure, mechanical properties, editing the longitudinal and transverse geometry, increasing productivity and its quality about provide compression of allowances, rolling the product.

Distinctive features of the proposed technical solution from the prototype is that the pressed product of variable cross-section is performed with preliminary dimensions, structure and allowances for compression, and the final dimensions, structure, mechanical properties, editing longitudinal and transverse geometry, increase productivity provide compression of allowances, rolling the product .

The technical solution is illustrated by figures, which show:

Figure 1. - dressing by rolling with tension, for example, an extruded strip of constant thickness and a smooth change in width dimensions.

Figure 2. - the same plan view.

Figure 3 - editing rolling with tension, for example, extruded strip with a smooth change in the size of the thickness.

Figure 4 - editing by rolling with tension and anti-tension of the pressed strip with a smoothly variable section length.

5 is a plan view of a pressed strip of variable width. In _pr - the size of the wide end, b _pr - the size of the narrow end, L _pr - the size of the length.

6 is a plan view of the strip after rolling. In _ok - the final size of the wide end, b _ok - the final size of the narrow end, L _ok - the final length.

Fig. 7 is a diagram of a rolling deformation zone and tensile rolling forces, where:

1 - rolled strip with dimensions H - before rolling and h - after rolling;

Δh = H-h - compression;

l - capture arc (segment AC);

α is the angle of capture;

ν is the neutral angle;

r is the radius of the rolls;

P is the pressure force of the rolls (reaction of the pressure force of the metal on the rolls);

R is the tension force;

T is the force that impedes the movement of the strip;

Fig - Examples of manufactured strips.

The capture angle is related to the angle of friction by the ratio α≤β. Those. metal capture by rolls is possible when the angle of capture is less than the angle of friction. In the case of equal angles, the process is unstable.

In the steady rolling process β≤α / 2. By the capture arc I is meant the segment AC. For rolls of equal diameter, the calculations taken

(одна из формул). Скорость продвижения металла на протяжении очага деформации не постоянна. В начале захвата скорость продвижения металла меньше горизонтальной составляющей окружной скорости валков V_пр<V_в. В зоне отставания силы трения направлены по ходу прокатки, а в зоне опережения - в противоположную сторону.

(one of the formulas). The speed of advancement of the metal throughout the deformation zone is not constant. At the beginning of capture, the speed of advancement of the metal is less than the horizontal component of the peripheral speed of the rolls V _CR <V _in . In the lagging zone, friction forces are directed along the rolling direction, and in the leading zone, in the opposite direction.

.The neutral angle ν determines the position of the section in the deformation zone, in which the friction forces change sign

.

The determination of the pressure force of the metal on the rolls practically comes down to determining the average value of normal stresses, depending on the deformation resistance and stress state, determined by the influence of contact friction forces, tension and the parameters of the deformation zone.

Thus, P = F · p _cp , p _cp = n _σ · 2kβ, where F is the contact area of the roll and strip, F = b · l, where b is the width of the strip, l is the capture arc.

n _σ is the stress coefficient.

k is the maximum shear stress.

β is the Lode coefficient.

The force T arises when the force P is present and in general can be represented as a friction force. Then T = f · P, where f is the coefficient of friction.

The size of the compression Δh during hot rolling is generally limited by the limiting angle of capture α, the pressure of the metal on the rolls β and the magnitude of the rolling moment.

In cold rolling, the criterion for setting the compression mode is the amount of deformation at which cracking occurs along the edges.

When rolling aluminum alloys, depending on the plastic properties of the metal and the condition of the edges, the specific tension can be (0.2 ÷ 0.6) σ _{0.2 of the} rolled material (see page 79 of this).

The rolling moment in general can be represented as the position at which the rolls turn, provided that the forces moving the strip become greater than the forces that impede the movement of the strip.

With the steady rolling process, the advancement of the strip can be ensured:

1. Drive rolls without tension.

2. Drive rolls with tension.

3. Tension force with the drive off the rolls.

The profiles of aluminum alloys supplied in the hot-pressed and annealed states are subjected to editing after pressing; profiles supplied in hardened aged state - after hardening.

In figure 1. and figure 2 shows:

1 - extruded strip of constant thickness with variable widths,

N is the size made by pressing,

h is the final size after rolling,

Δh - allowance for compression Δh = N-h,

- припуск на сторону,

- allowance on the side

2 - clamping jaw associated with the drive, creating a tensile force R,

3 - rolling rolls of radius r,

P is the pressure force of the rolls (reaction of the pressure force of the metal on the rolls),

T is the force that impedes the movement of the strip,

b _CR - the size of the width of the narrow end of the strip, made by pressing,

In _ok - the final size of the wide end of the strip after rolling.

To create the possibility of a larger reduction in Δh without the formation of cracks and concavity at the lateral edges, it is convex by pressing (see section).

Editing is performed in the following sequence:

1. Install the rolls with a gap h.

2. Set the strip in the rolls, squeezing the allowance Δh with the force P, create the force T.

3. On the exit from the rolls, the wide end of the strip is installed clamping jaw 2 associated with the drive force R.

Thus, two clamps are installed on the strip: fixed - clamping jaw 2 and rotating - rolls 3, clamped by force R.

Since P = F · p _cp , F = b · l and the dimensions of the strip width “b” are variable, decreasing towards the narrow end, the force P and the force T = f · P, as well as the force R will be proportionally reduced during rolling .

Rolling can be carried out according to the second or third above options.

In the second embodiment, the rotation of the rolls is created by two simultaneously acting forces - the force created by the rolls and the tension force, which overcome the force T, which prevents the movement of the strip, i.e. tension force is only part of the general forces promoting the strip. Therefore, it is not maximum and does not create maximum tension of the strip.

In the third option, the rotation of the rolls creates one force - the tension force, because roll drive disabled. In this embodiment, you can create maximum tensile strength and stretch the product of a larger area.

.4. Having established a clamping jaw 2 and having clamped a strip 3 by rolls, begin rolling, squeezing an allowance

.

When the rolls are turned, they create a tension of the force R leaving the deformation zone and the rolling is carried out continuously. In this case, sections of the strip passing the advance zone are stretched. In addition, when rolling the product is subjected to hardening by hardening.

After rolling, the extruded strip (Fig. 5), which had preliminary dimensions B _pr , b _pr , L _pr , acquires the final dimensions B _ok , b _ok , L _ok (Fig.6), as well as the final structure, mechanical properties, longitudinal and transverse geometry.

Figure 3 shows the editing of the product having a smooth change in the size of the thickness.

In contrast to dressing of a product of constant thickness, shown in Fig. 1, dressing of a product with a variable thickness is carried out on special mills, which differ from ordinary ones in that the pressure mechanism during the rolling process changes the gap between the rolls.

Such mills are used for rolling sheets of variable cross-section with a smooth change in size of the thickness. The manufacture of sheets is made from a blank of constant cross section for several transitions. The mills are equipped with a tensioning device that grabs the sheet at the exit of the rolls and helps to produce more even sheets (p. 88 of the specified).

Figure 4 shows the editing of the product with a smooth change in cross-section along the length using anti-tension.

To carry out dressing when installed on the maximum cross-section of the clamping jaw 2, an additional clamping jaw 4 is connected to the minimum cross-section, connected to the drive, which creates an anti-tension force Q. The force Q does not exceed the force required to stretch the minimum cross-section. When rolling, the sponge 4 moves with the product. To rotate the rolls, it is necessary to apply a force R of a larger value R> T + Q.

This creates the opportunity to increase the tension force, which allows you to edit products with a larger cross-sectional area or reduce the pressure force R.

Improving the structure and increasing the uniformity of the mechanical properties of the product provide compression allowances, using hot rolling.

For this, the size of the allowance for compression is increased, based on the fact that the allowance will be compressed in two operations - one part during hot rolling, and the second during dressing.

Hot rolling provides the penetration of high-altitude deformation over the entire thickness of the product, improving the structure and aligning the mechanical properties along the section and length.

The proposed method can be implemented using tools for pressing products of variable cross-section on existing presses and rolling equipment.

Compared with the base object, the proposed technical solution allows to increase productivity and dressing quality of products of variable cross-section, to obtain products of lower metal consumption, a better-developed structure, uniform mechanical properties.

Claims (1)

A method of manufacturing variable strip strips from light alloys, including pressing variable strip strips and editing longitudinal and transverse geometry, characterized in that the pressed strips are made with preliminary dimensions, structure and allowances for compression, and the final dimensions, structure, mechanical properties and editing of longitudinal and lateral geometry provide compression allowances, subjecting the strip rolling with tension, including hot rolling and cold rolling with hardening.

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