Hollow article hot forging method

FIELD: metal working, possibly manufacture of flanged articles and articles without flanges of different alloys.

SUBSTANCE: method comprises steps of heating blank and deforming it in die set; sustaining relation of blank temperature to that of die set in range 0.7 - 7.4. Blank is heated in predetermined temperature range depending upon blank material. Said temperature range may be found from ductility diagram and(or) yield curves and(or) from blank material recrystallization diagrams.

EFFECT: enhanced factor of using metal, improved quality of articles, lowered labor consumption of forging and subsequent working of blank.

6 cl, 2 dwg, 2 ex

 

The invention relates to the field of metal forming and can be used in the manufacture of products as flanges and without them, of various alloys, such as aluminum, titanium, copper, magnesium, etc.

A method of obtaining details isothermal forging, which consists in heating the workpiece, stamping and removing stamped parts using puller (patent RF №2019356, IPC 5: 21 J 5/00, publication 15.09.94 g) is similar.

In the known method first carry out separation from parts of the shaping surface of the ejector, the resulting gap between the part and the ejector is placed on the separator strip, followed by removing details from the stamp when working stroke of the ejector up with the subsequent removal of parts together with a gasket or separately from it.

The main disadvantage of this solution is the increased complexity of the method associated with the removal of stamped products from matrix.

A known method of manufacturing hollow parts products from heat-resistant alloys, providing the deformation of the heated billet, followed by reverse extrusion of hollow cylindrical Cup (patent RF №1216879, IPC 5: 21 To 21/00, 21 J 5/06, BI No. 17 of 1994) prototype.

The disadvantages of this solution are:

- great complexity;

- disabled the ity of obtaining products with a deep internal cavity;

large machining tolerances and Smith inlets, and accordingly reduced the utilization of metal;

- low surface quality products, due to the possibility of occurrence of defects such as folds and crosses on the inner surface of the Cup;

- application of a known method for forming hollow articles does not allow to significantly improve their mechanical properties.

The problem to which the invention is directed, is to increase the utilization of the metal, the improvement of the mechanical properties of the products obtained (tensile strength, yield strength, elongation), reducing the complexity of the process as by forging and subsequent machining.

This task is solved in that the stamping is carried out in a heated die, and in the process forming the ratio of the blank temperature TZGthe temperature of the stamp TPCssupport in the range of 0.7 to 7.4, and heating of the blanks for stamping is carried out in a certain temperature range.

Temperature range depends on the workpiece material and can be determined from charts plasticity, and/or of flow curves or charts recrystallization of the material, for example metal or alloy.

When stamping products with a flange to receive the articles is s, characterized by the ratio of Df/Tf≤85, where Tf- flange thickness, Df- diameter flange of the product. In the method of hot stamping offset axis of the material from the vertical axis of the stamp does not exceed ±5°. The method of hot stamping may be made for one transition. The method of hot stamping can be carried out in a closed die.

When implementing the proposed method the workpiece is heated, for example, in an electric furnace, and then transferred to the stamp, and the ratio of the temperature of the workpiece to the temperature stamped in the stamping process support in the range of 0.7 to 7.4.

If the ratio of the temperature of the workpiece to the temperature of the stamp is less than 0.7, it leads to overheating and burnout of deformable material. Overheating leads to the formation of coarse-grained structure, and burnout is to increase the fragility of the material. In both cases there is a decrease in mechanical properties (tensile strength, yield strength, elongation) of a deformable metal.

If the specified value is greater 7,4, may appear on the product surface cracks, which are the result of intensive work hardening of the metal in these conditions; failure to complete a relatively high edges, for which the ratio of rib height to wall thickness > 2; failure to complete the protruding elements.

For stamping blanks of the above alloys temperature range punching is selected based on the analysis of charts plasticity of flow curves and charts recrystallization of the metal and/or alloy, in addition, to obtain the claimed technical result is necessary to maintain the ratio between the temperatures of the die and the workpiece in the present interval.

In General, the temperature interval stamping blanks of aluminum alloys can be selected based on the ratio (0,7-0,85)TPLwhere TPL- melting point alloy. Specified temperature range due to the temperature at which structural changes, leading to intense hardening of the alloy during its deformation. So, for example, by an applicant on the basis of the performed calculations and experimental studies have established that for alloys of the system Al-Mg optimal for stamping is the temperature range 430-390°C.

For example, during hot stamping products with complex structures (deep-cavity, thin-walled, high edges and so on) to achieve optimal results forming, the temperature of the workpiece at the beginning of the stamping process must comply with the upper limit of the temperature is Val stamping, that is, for alloys of the system Al-Mg - 430°C. Reduction in temperature at the beginning of the stroke in the direction of lower bounds leads to the fact that the product is not filling a complicated configuration items (such as ribs, basting holes with high walls and so on), and, consequently, the quality of products. Therefore, in case of deformation of the alloy system Al-Mg it is advisable to heat the billet 20-30°With higher temperatures corresponding to the upper limit of the temperature range, and the stamp must be heated to a temperature lying in the claimed temperature range.

By forging titanium alloys for optimal results, forming the source of the workpiece depending on the type of alloy is heated, for example, in the temperature range 1100°-650°and also, as in the case of forming aluminum alloy system Al-Mg, transferred to the stamp heated to a temperature selected from the claimed ratio.

The proposed method it is possible to obtain preparations of various grades of titanium alloys, for example AT-1, W 3-1, etc. the temperature interval stamping may vary depending on the type of alloy, however, the ratio of the temperature of the workpiece and the stamp must be within the claimed range. Here are the temperature values stamping for some, the most common is United in industry alloys:

The choice of temperature range of stamping for titanium alloys are more stringent than for aluminum alloys. Thermomechanical mode forging of titanium alloys is set on the basis of their mechanical properties with respect to temperature full polymorphic transformation. When heated above the temperature of the beginning of the polymorphic transformation or during long-term exposure at this temperature, the observed grain growth and the formation of coarse-grained structure, the decrease in ductility and increases gasanalysis the billet surface. The latter leads to the formation on the surface alteromonas layer (scale), with increased fragility.

Accordingly, for optimal results, forming the upper boundary of the temperature range should not exceed the temperature of polymorphic transformation, or it is necessary to strictly control the duration of the workpieces at high temperatures to prevent formation of coarse-grained structure and alteromonas layer.

The lower limit of the interval is limited by the temperature at which there is a significant increase in the deformation resistance and the lowering of technological plasticity of titanium alloy. The underestimation of the lower bounds in some cases can lead to p is the phenomenon of surface cracks. As established practice, this is most likely when the deformation of titanium αand pseudo-α-alloys. It α-alloys include, for example, the alloy VT1-, WT and other pseudo-α-alloys include alloys, as OT-1, W 18, etc.

The choice of temperature range of stamping for copper and magnesium alloys is carried out by analogy with choice of temperature forming of aluminum alloys. However, there are a number of distinctive features. When selecting the temperature of the beginning and end forming copper alloys (copper, brass, bronze), consider the intensive cooling of the alloy during deformation. Here is the recommended temperature ranges stamping for some copper alloys:

Magnesium alloys have greater compared to aluminum and copper alloys are sensitive to the speed of deformation. The increase in the rate of deformation during forging of magnesium alloys leads to a significant narrowing of the allowable temperature range. In this regard, the forging of magnesium alloys, it is recommended to deform in hydraulic or crank presses at low speeds deformation. The recommended temperature intervals punching some brands of magnesium alloys:

For optimum results the Tobit hot stamping, for example, if TZG/TPCs≅1, it is recommended for hydraulic presses or low-speed mechanical presses. These conditions corresponds to the range of strain rate from 10-4up to 100with-1. The strain-rate may be as low. The lower limit speed is limited by the efficiency of the process and the design features of the forging equipment. The upper limit of the velocity due to the beginning of intensive hardening of a deformable material and reducing its plastic characteristics.

The inventive method can be used to obtain products with flange and without it.

The proposed method is illustrated in figures 1 and 2, where figure 1 presents the product with flange fabricated using this method, and figure 2 - the product without flange, fabricated using this method.

Optimum results when implementing the proposed method in the case of stamping products with flange achieved by forging products with the ratio of the diameter of flange Dfto its thickness Tfless than 85.

Increasing this value may result in the loss of resistance in the wall of the workpiece in a reverse extrusion, which precedes the displacement of metal in the flange part of the product, i.e. in the gap between the upper and lower tool is nami, and as a result of loss of stability with respect to the diameter DPLat the level of the flange appears stamping defect - fold, where DPL- inner diameter of the hollow product.

The same defect can be obtained in the case of stamping products (as with flange and without it) of the cylindrical workpiece, the displacement of the axis of the workpiece and the vertical axis of the stamp more than ±5° (figure 1). In this case, on the inner surface of the glass diameter DPLmay be formed in the stamping process of stamping defect - fold. To prevent the formation of folds is offered on the source procurement to form a chamfer, which can be obtained either by machining or stamping draught in the profile tool. The presence of the bevel on the workpiece provides for positioning the latter accurately along the axis of the stamp.

Examples of implementation of the proposed method.

Example 1: stamping products with flange (figure 1).

To obtain the products presented on figure 1, the original cylindrical billet of aluminium alloy AMg6 (according to GOST 21488-97, OST 1.90073-85) is heated in an electric furnace to a temperature of 450°C. After heating, the workpiece is transferred to the stamp heated to a temperature of 430°C. When transferring the workpiece to stamp the temperature decreases on average by 20°C. Thus, the temperature of the workpiece at the beginning of the stamping is 430° C.

The design of the stamp corresponds to the closed circuit forming, i.e. without overflow. The excess metal is extruded into the gap between the movable and stationary tools. As a result, the product of the diameter Dfformed end of the Burr, which is removed by subsequent machining.

Stamping is carried out in one move the working tool on a hydraulic press with a nominal force of 2.5 MN and strain rate on the working stroke of 0.002 m/s When the forging temperature of the instrument is maintained constant and equal to 430°C. Thus, the hot forging products with flange carried out under conditions that are close to isothermal, and the ratio of the temperature of the workpiece to the temperature of the stamp is 1.

After receiving the products were metallographic and mechanical studies to determine the quality of the internal structure and mechanical properties of the material. As shown by the results of metallographic tests, the product structure is dense, without cracks and discontinuities, fine. The results of the mechanical tests show that the tensile strength and the yield strength of the material increases by 10-15%, elongation and hardness by 40% compared with compared with products obtained by the method described is WMD in the prototype.

Example 2: stamping products without flange (figure 2).

To obtain the products presented on figure 2, the original cylindrical billet magnesium alloy MA (according to GOST 14957-97) is heated in an electric furnace to a temperature of 470°C. After heating, the workpiece is transferred to the stamp heated to a temperature of 450°C. When transferring the workpiece to stamp the temperature decreases on average by 20°C. Thus, the temperature of the workpiece at the beginning of the stamping is 450°C.

The design of the stamp, as in example 1, corresponds to the closed circuit forming. The excess metal is extruded into the gap between the movable and stationary tools. As a result, the product of upper end formed end of the Burr, which is removed by machining.

Stamping is carried out in one move the working tool on a hydraulic press with a nominal force of 2.5 MN and strain rate on the working stroke of 0.002 m/S.

When the forging temperature of the instrument is maintained constant and equal to 200°C. Thus, the hot forging products with flange carried out under conditions that are close to isothermal, and the ratio of the temperature of the workpiece to the temperature of the stamp 2.25.

After receiving the products were metallographic and mechanical research goal is to determine the quality of the internal structure and mechanical properties of the material. As shown by the results of metallographic tests of the product structure is dense, without cracks and discontinuities. The results of the mechanical tests show that the tensile strength and the yield strength of the material increases by 5%, elongation and hardness by 20% compared with the products obtained according to the method described in the prototype.

1. The method of hot forming hollow articles comprising heating and deformation of the workpiece, characterized in that in the process of forming the ratio of the temperature of the workpiece to the temperature of the stamp support in the range of 0.7 to 7.4, and heating of the blanks for stamping is carried out in a certain temperature range, depending on the workpiece material.

2. The method according to claim 1, characterized in that the temperature range is determined from charts plasticity and/or of flow curves, and/or charts recrystallization of the material of the workpiece.

3. The method according to claim 1, characterized in that the stamping receive the product, characterized by the ratio

Df/Tf≤85,

where df- diameter flange of the product;

Tfthe thickness of the flange of the product.

4. The method according to claim 1, characterized in that the displacement of the axis of the workpiece from the vertical axis of the stamp does not exceed ±5°.

5. The method according to claim 1, characterized in that piece is novko produce for one transition.

6. The method according to claim 1, characterized in that the stamping is carried out in a closed die.



 

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