RU2638473C2 - Method of reverse screw pressing (rsp) and comprehensive screw pressing (csp) - Google Patents

Abstract

FIELD: machine engineering.

SUBSTANCE: method includes production of a blank and its subsequent reverse screw pressing. Prior to pressing, the blank is subjected to twisting by definite angle due to edges on its surface, then the twisted blank is placed in a die supporting blank faces onto its inner contour and reverse screw pressing is performed by a punch along the axis of twisting to preset size of the blank. At that, twisting and reverse screw pressing are carried out multiple times until specified size of the crystal structure of the blank is reached, and the number of twisting revolutions and degree of single deformation at reverse screw pressing are set depending on metal plastic properties.

EFFECT: production of article with improved mechanical properties due to increased rate of blank deformation.

3 cl, 1 dwg

Description

The invention relates to the field of metal deformation and can be used for pressing any metals, including refractory and chemically active ones. The closest analogue is the method of screw extrusion (CE) of a metal [1], where in specialized pressing plants deform metal by forcing it through a screw die, which allows to obtain a very fine-grained structure and, as a result, high mechanical properties in the processed workpieces.

As the first prototype of the invention, the method of high pressure torsion (HPC) in Bridgman anvils [2], where the plastic deformation of the sample is a result of shear of the material under the action of torque and pressing force, is adopted. When torsion under pressure, the moment and force are active. This prototype allows you to process any metals, including refractory and chemically active, grinding the structure to nanocrystalline dimension in a short time.

As a second prototype, the method of comprehensive forging (VK) of metals [2] is adopted, where a constant change in the axes of deformation is performed. In this case, from the transition to the transition, the direction of deformation of the workpiece and the direction of shear changes by 90 °. This allows bulk samples to be deformed to a nanostructured state, but with a relatively low rate of structure refinement. The disadvantage of this method is the small volume of the deformed sample.

As practice has shown, it is impossible to obtain billets of titanium more than 10 mm in diameter by equal-angle angular pressing of ECG and screw extrusion of HE. It is impossible to obtain a workpiece thicker than 1 mm and more than 10 mm in diameter by the high-pressure torsion method.

Comprehensive forging of VK allows producing a relatively large volume of the workpiece, weighing up to 10 kg, where it is possible to achieve the formation of a nanostructure. But for the manufacture of massive parts, workpieces of significantly larger dimensions are required.

The proposed ORP and GDP methods allow intensive plastic deformation of any metals, while solving the problem of obtaining a given structure in a large volume of the workpiece. The process makes it possible to produce both nanostructured and submicrocrystalline metals with the least time and cost.

The aim of the invention is to increase the efficiency of use and expand technical capabilities by obtaining products with special properties having enhanced mechanical properties.

This goal is achieved in that the method of screw reverse pressing of metal involves obtaining a workpiece and pressing it in a stamp with a punch, characterized in that the workpiece is twisted at a certain angle before pressing, due to the faces existing on its surface and then placed in a stamp beyond the counting is supported by the faces on its inner contour, it is pressed along the axis of twisting to the desired size, the number of turns of twisting and the degree of one-time deformation of pressing is determined based on plastic metal tv and achieving the desired size of the crystalline structure of the workpiece is achieved through repeated twisting and pressing. The billet for pressing in order to ensure the twisting operation can be made by casting or liquid stamping of a cut section, and in order to ensure high-speed heating, the billet can be produced of large length and small section. Between the operations of twisting and deformation, intermediate heating is possible, it is also possible to provide heating by selecting a certain speed of twisting and pressing, or it is possible to carry out stepwise deformation with decreasing temperature in the subsequent stages of deformation.

A method of comprehensive screw pressing involves obtaining a square billet and pressing it in a stamp with punches, characterized in that before pressing a square billet, it is twisted around a long axis and pressed, placed in a stamp with the edges resting on the inner contour of the stamp to a washer with a thickness equal to the side of the original square , then the puck is pressed in a constricted state due to the punches again to the square of the initial dimensions, changing the direction of deformation by 90 ° from the axis of twisting, while closed process that can be repeated many times. The all-round screw pressing process can immediately follow the reverse screw pressing process, where the billet for pressing can be produced by casting or normal deformation, where the direction of twisting during pressing can be reversed in relation to the previous pressing and where intermediate heating of the workpiece is possible.

In order to carry out the screw pressing process at the lowest cost, a blank with the smallest grain size is needed, where there is no accumulated deformation. It is possible to produce such a billet by casting or liquid stamping, filling small-section crystallizers with melt with intensive mixing of the melt until it is completely crystallized. To reduce costs, it is advisable to start the production of nanostructured metal from cast billets having the smallest possible grain size.

The formation of the smallest grain size is facilitated by intensive heat removal from the crystallizing melt, as well as intensive mixing of the melt until complete crystallization. Reducing the cross-section of the mold, where the melt enters, increases the rate of crystallization. But the reduction in the cross-sectional area of the mold can only be carried out to a certain limit, since the workpiece will not be produced in a sufficiently large volume.

The cooling area and the mass of the workpiece can be increased due to its length, but the increase in length must also be carried out to a certain limit. The most optimal dimensions of a workpiece for screw pressing must be selected based on the mass of parts that are produced by industry, for example, if the mass of finished parts is in the range of 150–300 kg, then the mass of the workpiece for intense plastic deformation should be in the range of 350–500 kg. For such a billet, if we take a cross-sectional area of 1 dm ² , for a mass gain of 450 kg, the length of the billet will be 10 m. When casting a billet of these dimensions, the heat transfer from the melt to the mold can be enhanced due to the internal geometry of the mold.

With an internal cross-sectional area of the mold equal to 1 dm ² , the round mold will have a perimeter length of 3.54 dm, the square mold is 4 dm, and the triangular mold is 4.56 dm. This means that heat from a melt weighing 450 kg in a circular mold with a length of 10 m will be removed through an area of 354 dm ² , in a square through 400 dm ² , and in a triangular 456 dm ² . As calculations show, with different geometry of the mold section, there will be different heat sink speeds, the lowest heat sink speeds will be for round molds, and the highest for triangular molds. All other equilateral polyhedra in the cooling area occupy intermediate positions. The more faces of the figure describing the internal circuit of the mold, the less cooling the ingot. Therefore, the triangular shape of the mold is most suitable for the production of cast billets. The presence of faces on the workpiece is of a technological nature, this is necessary for the operation of twisting the workpiece. For twisting, faces are required to hold part of the workpiece in a special mandrel, and turn the other part due to another mandrel.

As experience has shown, in the implementation of various types of intense plastic deformation, the torsion of the workpiece allows for the smallest time to grind the structure in comparison with other deformation schemes. For example, due to torsion under high pressure for 3 ÷ 5 revolutions, such a grain size is achieved that using conventional uniaxial deformation schemes can be obtained if the workpiece is compressed or stretched more than a million times. The restriction on the mass and volume of the workpiece when using the VE and HPC methods is associated with very large friction forces generated during deformation between the metal and the tool. An increase in the mass of the workpiece leads to an increase in friction and a limitation of the strength of the tool, which begins to break upon deformation.

To increase the volume of the deformable metal, the method of comprehensive forging of the VK is used, but this method allows you to deform a limited volume of metal with a low rate of structure grinding. Comprehensive forging does not allow deformation in the enclosed volume of the tool, as a result, this reduces the degree of deformation and the rate of grinding of the metal structure.

In order to solve the problem of increasing the strain rate and increasing the mass of the workpiece, a screw pressing process is proposed. For this process, it is most efficient to use a cast billet with a fine-grained structure of small cross section and long length, which can be heated at high speed.

On figa, as an example of screw pressing, shows a blank 1 of a length of 10 meters, triangular section with a side equal to 152 mm, an area of 1 dm ² , which after high-speed electrical contact heating, preventing grain growth, passes (Fig.1b) through the mandrel 2 and falls into the sleeve 3, the inner part of the mandrel and the sleeve corresponds to the geometry of the workpiece.

The mandrel holds the workpiece, and the sleeve, along with part of the workpiece, rotates a certain angle around the axis. The rotation angle is calculated depending on the plastic properties of the material. Or twisting the workpiece using feedback, due to the sensors, which determine the maximum possible angle of twisting. Upon exceeding the degree of twisting, the metal will signal the sensors about the accumulated deformation, which can develop into a crack. Upon reaching this state of twisting stops. The workpiece, leaving the mandrel, is twisted by a sleeve with a periodic stop or with a constant feed. Figure 1c shows a twisted blank 1.

On Figg shows a diagram of the pressing (set of metal) twisted billet 1 in the stamp 4, the punch 5. The inner section of the stamp can be of different geometries - round, square, hexagonal, triangular, etc. A twisted blank, if viewed from the end, will describe the circumferences with the vertices of the faces, which, in turn, will fit into the inner contour of the second stamp.

For draft blanks in a stamp, a triangular shape is most suitable (Fig. 1d), where this circle fits. The area of the twisted triangular billet 1 and the area of the triangular section of the stamp 4 have a ratio of 1 ÷ 4. After pressing a twisted workpiece with a length of 10 m in a stamp, the length of the pressed workpiece will be 2.5 m, and the degree of deformation will be:

;

;

where H _o - the length of the workpiece before deformation,

H _to - the length of the workpiece after deformation.

A long workpiece is most efficiently pressed (Fig. 1d, d, e) by pressing with two punches 5, this allows to achieve a higher speed and a higher pressure of deformation.

Figure 1g shows the moment of extraction of the obtained workpiece 1, 2.5 meters long, 4 dm ^{2 in area,} with a side of 304 mm from the die 4, under the action of one of the punches 5. The workpiece enters the sleeve 6, which immediately begins to twist the workpiece at the exit from the die at a certain angle. The amount of twisting will depend on the plastic properties of the metal and the heating temperature. The twisting direction may coincide with the previous direction or may be directed in the opposite direction. Changing the direction of twisting allows more intensive grinding of the metal structure. After the second twisting of the workpiece, it can be sent for deformation or for heating under deformation.

After twisting, it is possible to produce additional deformation by pressing the workpiece into a circle, octahedron, hexagon or square. On figs, and, to, l shows the pressing of the workpiece 1 in the stamp 7 with an internal square section of the punch 8, where the workpiece rests on the stop 9. In this case, to simplify the design, you can use one punch. If pressed into a square, the twisted blank should be inscribed in its inner contour, where the diameter of the circle will be equal to the side of the square with a length of 351 mm. In this case, the area of the workpiece will be related to the area of the square as 1: 3.08. After pressing the blank, a square of 812 mm in length with a side of 351 mm will be obtained.

In Fig. 1m, when pressing the workpiece 1 from the die 7 with a punch 8, the workpiece enters the sleeve 10, which twists the workpiece along the entire length at the exit of the stamp.

On fig.1n, o, p, p shows the pressing of a twisted square billet 1 in a round stamp 11 with punches 12 and 13. The final thickness of the billet 1 in the form of a round washer will be equal to 351 mm, that is, equal to the side of the future square 812 mm long, which is further it will be pressed from this washer, with a rotation of the pressing direction by 90 °, as with all-round forging. Pressing (Figs. 1c, t, y) of the workpiece 1 is done by the punches 14 vertically and by the punches 15 horizontally with stops 16. Fig. 1f shows the moment when the workpiece 1 exits the die under the action of the punch 15 and is twisted by the sleeve 17. Next, the twisted workpiece 1 can again go to deformation in the stamp (Fig.1n).

At the first stage of deformation of a long workpiece, according to the twisting scheme and then pressing, where pressing is performed along the axis of twisting, the method is called reverse screw pressing (ORP). The term reverse denotes an increase in the cross section of the workpiece from small to large. With ordinary deformation, the cross section decreases.

When changing the direction of pressing relative to the axis of twisting by 90 °, the method is called the comprehensive screw pressing of GDP.

Deformation by the method of redox potential can be performed many times by converting the final workpiece by conventional deformation into a long initial workpiece. As well as deformation by the GDP method, where the initial procurement can be done by conventional casting or liquid stamping. These methods can be considered independent, since after ORP or GDP, the workpiece can go to normal deformation. In this case, the method of GDP or ORP can be implemented immediately bypassing each other using a cast billet or a billet obtained by ordinary deformation. Deformation by the GDP method, where it is necessary to convert the obtained round washer into a square due to lateral pressing, then twist it and compress it into a washer, performed in a closed circuit, therefore, the pressing operation into a square - twisting-pressing into a washer can be performed many times, similarly to the comprehensive method forging. The fundamental difference between the VK method and the ORP and GDP is that in the first case, the metal is subjected to free forging, and in the second case it is cramped pressing, which passes into comprehensive pressing. As is known, pressing differs from free upsetting and forging, since during pressing the metal undergoes comprehensive compression and therefore has the greatest ductility. Therefore, using the methods of redox potential and GDP, it is possible to deform with a high degree of metal reduction.

Equal-drop angular pressing, screw extrusion and torsion under high pressure perform comprehensive compression of the metal over the entire temporary deformation section. Reverse screw pressing and comprehensive screw pressing occurs in time with a gradual increase in pressure in the volume of the wrought metal, which reaches a maximum at the end of the deformation. This allows the process of deformation with minimal friction between the workpiece and the tool. This feature allows for the processing of large volume and mass blanks using the AFP and GDP methods.

On fig.1n-f shows a recurring pattern of comprehensive screw pressing. On figa-p shows a diagram of the reverse screw pressing.

For difficult-to-deform alloys, it is possible to provide additional heating of the workpiece over the surface with an inductor. When pressing, it is possible to select such a strain rate when the heat generated is compensated by the heat transfer tool. To implement the processes of redox potential and GDP, it is possible to create a pressing machine that allows the metal to be deformed with a high degree and with a high deformation rate. The process can be fully automated.

With the practical implementation of this method at enterprises, it is possible to supply metal blanks with a nanostructure to the market. The price of these blanks will be significantly higher than ordinary metal bullion. This will allow enterprises to master new market sectors where the strength of the metal can increase 2-4 times while maintaining ductility. This is especially true when creating new aviation alloys.

LITERATURE

[one]. A.E. Beigelsger, V.N. Varyukhin et al. - Screw extrusion - the process of accumulation of deformation, - Donetsk, Donetsk company of high technology of the National Academy of Sciences of Ukraine (TEAN Firm), 2003

[2]. O.A. Kaybyshev, F.Z. Utyashev - Superplasticity, refinement of the structure and processing of hard-to-deform alloys, - M .: Izd-vo Nauka, 2002 (pp. 129-142, 229-232).

Claims (3)

1. The method of reverse screw extrusion of a faceted metal billet, including obtaining a billet and its subsequent reverse screw pressing, characterized in that before pressing the billet is subjected to twisting at a certain angle due to the faces on its surface, then the twisted billet is placed in a stamp with the support of the faces of the billet on its inner contour and carry out reverse screw pressing by a punch along the axis of twisting to a predetermined size of the workpiece, with twisting and reverse screw presses performed of repeatedly to achieve a desired crystal structure workpiece size and the number of revolutions of the twisting and deformation degree of the reverse single screw extrusion set depending on the plastic properties of the metal. 2. The method according to p. 1, characterized in that the preform is produced by casting or liquid stamping of large length and with a small cross section. 3. The method according to p. 1, characterized in that between twisting and reverse screw pressing carry out intermediate heating, while twisting and reverse screw pressing is carried out to ensure stepwise deformation and lowering the temperature in subsequent stages of deformation due to the selection of heating rates in subsequent stages deformation.

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