RU2325966C2 - Method of manufacturing parts from plate stocks with bulges in form of solids of revolution - Google Patents

Abstract

FIELD: technological processes; plastic working.

SUBSTANCE: invention is related to the sphere of metal plastic working and may be used for parts manufacturing with local deformation with application of local heating. On lower electrode of device for resistance spot welding, matrix of molding instrument is installed, and on upper electrode puncheon is installed. Plate stock is placed between matrix and puncheon. Electric heating of stock is done. For that purpose puncheon is lowered until it touches the stock, and heating current impulse is passed through the stock. Impulse duration is selected with the condition of its exceeding 1.5 - 2.5 times duration of impulse, which is necessary to weld package out of two plate stocks. After period of time, which amounts to 0.7 - 0.8 from the duration of heating impulse, forging force is applied on electrodes. At that puncheon is displaced, and the stock is deformed. As a result, quality of manufactured parts is improved, and method efficiency is increased.

EFFECT: improvement of the manufactured parts quality with increase in method efficiency.

2 cl, 6 dwg

Description

The invention relates to the field of manufacturing parts from sheets with local deformation using zonal heating.

A known method of stamping parts from sheet blanks is that the blank is placed in the maximum possible gap between the die and the punch, after which the blank is heated by electric influence and stamped (Modern aircraft building technology / Team of authors; Edited by A.G. Bratukhin, Yu. L. Ivanova. - M.: Mechanical Engineering, 1999, p. 58, Fig. 5.3). The total heat capacity of the die tooling must exceed the heat capacity of the workpiece not less than 100 times, which ensures a sufficiently high cooling rate of the workpiece after stamping. The die and punch are kept closed under pressure from the press until the workpiece in the die is completely cooled.

The use of this method of stamping parts from sheet blanks is advisable in the manufacture of large parts in combination with a large product release program. Otherwise, significant costs are the cost of manufacturing a stamp and a specialized transformer for heating the workpiece in the process of forming. In the manufacture of small parts in small batches, the application of this method is economically impractical due to the high cost of products.

The closest in technical essence to the claimed method is the method (patent RU 2021053 C1, 10/15/1994, B21D 37/16. "Stamp for forming parts with electrical contact heating of blanks"), in which a sheet blank is placed between the die and the punch of the molding tool, electric heating of the workpiece to the plastic state of its material and deformation of the workpiece in the molding tool by applying an axial force to the punch to ensure its movement in the axial direction until the workpiece contacts the mold razuyuschimi surfaces matrix.

This method provides for the general heating of the workpiece to the plastic state of its material, which in the manufacture of parts from titanium alloys entails a decrease in the mechanical properties of the material and enlargement of the grain. In addition, the use of general heating in the molding tool is accompanied by oxidation of the workpiece material.

The proposed method allows to form a protrusion in the form of a body of revolution from a sheet stock without changing the structure and properties of the initial semi-finished product (sheet) and perform the operation without general heating of the workpiece.

The technical result to which this invention is directed is provided by the fact that the manufacture of parts with protrusions in the form of bodies of revolution from sheet blanks is carried out by placing the sheet blank between the die and the punch of the molding tool, electrically heating the workpiece to the plastic state of its material, deforming it in the molding tool by applying an axial force to the punch to ensure its axial movement until the workpiece contacts the forming parts the surfaces of the matrix, in this case, a contact spot welding machine is used, on the lower electrode of which a molding tool matrix is installed, and a punch is installed on the upper electrode, the workpiece is electrically heated by lowering the punch until it comes into contact with the workpiece surface and then passing a heating current pulse through the workpiece, the energy value E _and which is determined from the following expression:

_And E = (0.45-0.65) E _b

where E _St - the magnitude of the energy of the current pulse required to weld a package of two sheet blanks,

the duration of the heating current pulse is selected from the condition of exceeding 1.5-2.5 of the pulse duration necessary for welding a package of two sheet blanks, and the axial force is applied to the punch by applying forging force to the electrodes of the resistance welding machine over a period of time, component 0.7-0.8 of the duration of the heating current pulse.

In more detail the essence of the proposed method is illustrated by drawings:

- figure 1 shows the initial stage of the process of forming the protrusion from the sheet stock;

- figure 2 presents the sequence diagram of changes in current and compression forces of the electrodes in the process of forming a protrusion from the sheet blank;

- figure 3 shows the final stage of the process when closing the punch and the matrix;

- figure 4 presents a photograph of the appearance of a conical protrusion on a sheet part formed in accordance with the claimed method;

- figure 5 shows the initial microstructure of a sheet blank of alloy VT6S;

- figure 6 shows the microstructure of the workpiece material in the area of the protrusion after its molding.

When implementing the proposed method, the punch 1 is installed on the upper electrode of the resistance spot welding machine, and the matrix 2 is installed on the lower electrode. The punch 1 and matrix 2 have a profile according to the profile of the formed protrusion. On the matrix 2 set the workpiece 3 in the form of a disk from a sheet of semi-finished product (figure 1). The workpiece 3 is fixed with a clamp 4. After fixing the workpiece 3, the punch 1 is lowered until it contacts the surface of the workpiece 3. The punch 1 is pressed against the workpiece 3 by a force P ₁ equal to the weight of the punch 1.

After that, between the electrodes and, respectively, the punch 1 and the matrix 2 through the workpiece 3 pass a current pulse with a power of E _and (figure 2). After a period of time, comprising 0.7-0.8 of the pulse duration, the workpiece 3 is deformed by applying forging force P ₂ to the punch. Under the action of the forging force P ₂ , the heated material of the workpiece 3 is deformed and the protrusion is shaped in accordance with the shape of the punch 1 and matrix 2 (Fig. 3).

The surface quality and structure of the protrusion material are significantly affected by the magnitude of the pulse energy E _and , determined by the pulse current and its duration. If the value of the pulse energy will be less than 0.45E _sv , where E _sv is the energy of the current pulse required to weld the package of two sheet blanks 3, then in the contact zone of the punch 1 and the workpiece 3, the workpiece material will not be heated to a plastic state and during deformation, cracking will be observed in the area of the formed protrusion. Increased energy current pulse in a _{communication} 0,65E leads to heating of the metal in the deformation zone, grain coarsening and partial melting of the metal. Therefore, the optimal energy range in the current pulse should be considered (0.45-0.65) E _St.

In addition to the magnitude of the pulse energy, the duration of the heating pulse, i.e. the time during which thermal energy is introduced into the workpiece material. When forming a protrusion from the sheet blank, softer modes are selected in comparison with the spot welding modes - modes with a large current pulse. The duration of the current pulse, less than 1.5 times the pulse duration when welding a package of two sheet blanks, does not allow to heat up the plastic blank region of the sheet blank beyond the diameter of the punch in the zone of its contact with the surface of the workpiece. Therefore, when a forging force is applied to the electrodes of the contact machine for forming the protrusion, an annular crack is observed at the base of the protrusion.

The use of pulses with a duration of 1.5-2.5 times the pulse duration required for welding a package of sheets of material of the workpiece, there is a uniform heating of the material in the contact zone with the punch and high-quality formation of the protrusion during molding. In addition, in this range of powers and durations of the heating current pulse, the effect of electroplasticity of the material is manifested, which consists in the fact that the molding of the protrusion proceeds without the occurrence of stresses in the workpiece material. An increase in the pulse duration by more than 2.5 times in comparison with the pulse duration required for welding a packet of two sheet blanks creates conditions for grain growth in the heating region (contact between the punch and the surface of the workpiece) and the formation of micro-discontinuities in the metal of the formed protrusion.

To prevent the formation of microcracks in the metal of the protrusion during molding, it is necessary to observe a certain ratio between the duration of the current pulse and the moment of application of the forging force. The best formation of the protrusion from the sheet blank is observed when forging efforts are applied after 0.7-0.8 of the duration of the heating pulse. In the case of applying the forging force earlier than 0.7 after the duration of the heating pulse, delamination in the metal of the formed protrusion is observed. When a forging force is applied in time later than 0.8 times the duration of the heating pulse, the formation of surface cracks on the formed protrusion is observed.

Experiments were carried out to form a conical protrusion from a sheet of a VT6S titanium alloy with a thickness of 2 mm and a diameter of 52 mm. For forming the protrusion, an MT-2023 resistance spot welding machine was used, with a punch installed on the upper electrode and a BrBNT brand beryllium bronze matrix on the lower electrode.

A protrusion in the form of a truncated cone with a diameter of 20 mm at the larger base, 8 mm at the smaller base and 15 mm high was squeezed out of the sheet blank. The influence of the parameters of the heating pulse on the quality of the molding of the conical protrusion is illustrated in the table. For the basic mode, the mode of contact spot welding of a package of two plates of VT6S alloy with a thickness of 2 mm each was selected: current 8.5 kA, pulse time 0.26 s.

No. p / p Impulse current, kA Pulse duration, s Pulse Energy, J Features of the formation of a conical protrusion one 8.5 0.26 2818 Flashing material in the protrusion zone 2 6.85 0.26 1831 The formation of microcracks in texture in the protrusion material in the zone of a small base 3 5.70 0.26 1268 four 5.37 0.26 1127 A girdle crack forms along the contour of the larger base of the protrusion 5 6.30 0.26 1550 The formation of microcracks in texture in the protrusion material in the zone of a small base 6 5.36 0.36 1550 Separate microcracks in the protrusion metal 7 5.15 0.39 1550 The formation of a conical protrusion proceeds in the mode of electroplasticity without stress in the workpiece material (figure 4) 8 4.46 0.52 1550 9 3.98 0.65 1550 10 3.71 0.75 1550 The beginning of grain growth in the workpiece material in the protrusion zone, the appearance of microcracks and an alpha layer

A microanalysis of the structure of the metal of the protrusion after molding (Fig. 5) and the initial structure of the workpiece (Fig. 6) showed that when molding with heating by a current pulse on a contact machine, there are no changes in the structure of the material and, therefore, its properties. In this case, there is no need to conduct heat treatment of products after forming the protrusions in order to renovate the original properties of the material.

Using the proposed method for the manufacture of fastening tapes of composite materials in the aircraft industry eliminates the use of expensive technological equipment for stamping with electric heating, as well as the use of precision casting methods to obtain these parts of special fasteners.

Claims (2)

1. A method of manufacturing parts with protrusions in the form of bodies of revolution from sheet blanks, including positioning the sheet blank between the die and the punch of the molding tool, electrically heating the workpiece to the plastic state of its material and deforming the blank in the molding device by applying axial force to the punch to allow it to move into axial direction before contact of the workpiece with the forming surfaces of the matrix, characterized in that use a machine for contact spot welding, n a lower electrode which is preset matrix forming tool, and the upper electrode - punch, electrically heated preform is effected by lowering the punch until it contacts the workpiece surface and then passing through a billet heating current pulse, which energy value E _and is determined from the following expression: E _and = (0.45-0.65) E _sv , where E _St - the magnitude of the energy of the current pulse necessary for welding a package of two sheet blanks, the duration of the heating current pulse is selected from a condition of exceeding 1.5-2.5 times the pulse duration required to weld a package of two sheet blanks, and the axial force is applied to the punch by applying forging force to the electrodes of the resistance welding machine over a period of time constituting 0.7-0.8 of the duration of the heating current pulse. 2. The method according to claim 1, characterized in that the use of sheet blanks of steel or titanium alloys.

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