Forming method of ordinary die forging for large arc-shaped 2618 aluminum alloy casing forging

Abstract

This invention belongs to the field of conventional hot forging technology, and relates to a method for conventional forging of large-arc 2618 aluminum alloy casing forgings. The method includes: upsetting a bar stock to a cuboid shape, then bending it to match the curvature of the forging; pre-reserving a boss in the width direction in the transition section between the upper and lower recesses of the bent bar stock to obtain a billet; pre-forging: performing a first forging on the billet to obtain a pre-formed forging; and final forging: performing a second forging on the pre-formed forging to obtain the final forging.

Description

Technical Field

[0001] This invention belongs to the field of hot working ordinary die forging technology, and relates to the forming method of ordinary die forging of large arc-shaped 2618 aluminum alloy casing forgings. Background Technology

[0002] The rapid development of the defense and aerospace industries has placed higher demands on heat-resistant aluminum alloys. 2618 aluminum alloy is currently the aluminum alloy with the best heat resistance, possessing good thermoplasticity and pressure processing properties, and is widely used in aero-engines and other components operating under high-temperature conditions. Traditional casting methods, due to their low production efficiency, can no longer meet actual production needs. By changing the forming method from casting to die forging, large aluminum alloy structural parts for aircraft are typically manufactured using isothermal die forging; however, this is limited by the high cost of isothermal forging dies. Summary of the Invention

[0003] Objective of the invention: To solve the problem of conventional die forging of double-shaped, thin-walled, high-ribbed 2618 aluminum alloy casing forgings. Due to their complex shape and asymmetrical recesses on both sides, these casing forgings exhibit an S-shaped metal flow path during die forging, making them prone to folding and resulting in significant forming difficulties.

[0004] Technical solution

[0005] A method for forming a large arc-shaped 2618 aluminum alloy casing forging using ordinary die forging. The casing forging is arc-shaped, with asymmetrical recesses on the upper and lower sides in the thickness direction. The recesses follow the shape and do not overlap in the thickness direction. The method includes:

[0006] The bar stock is upturned into a cuboid shape, then bent to match the curvature of the forging. A boss in the width direction is reserved in the transition section between the upper and lower recesses of the bent bar stock to obtain the billet.

[0007] Pre-forging: The billet is forged for the first time to obtain a pre-formed forging. During the first forging process, the billet in front of the boss is flattened and a shallow pit is pressed downward. The billet below the shallow pit is pushed out of the mold cavity, so that the lower surface of the front section forms a downward protruding arc surface. At the same time, a small boss is formed at the front end. The billet in the rear section of the boss is flattened and a shallow pit is pushed upward. The billet above the shallow pit is pushed out of the mold cavity, so that the upper surface of the rear section forms an upward protruding arc surface. At the same time, a small boss is formed at the rear end. The boss forms a slope transition section between the shallow pit in the front section and the upper arc surface of the rear section and between the shallow pit in the rear section and the lower arc surface of the front section.

[0008] Final forging: The preformed forging is subjected to a second die forging to obtain the forging. During the second die forging process, the preformed forging is pressed down by the upper die, two shallow pits are formed to form asymmetrical pits, the small bosses on both sides are formed to form irregular bosses, and the inclined transition section is formed to form the middle step of the forging.

[0009] The above forging process is ordinary forging.

[0010] The initial forging temperature is 450℃~470℃, and the heating coefficient is increased to 2.2~2.3min / mm.

[0011] The bar stock is made of large-diameter 2618 aluminum alloy bars with a diameter of 300mm or more.

[0012] Prior to pre-forging, the method further includes:

[0013] The mold was preheated using a precast steel model before both forging processes.

[0014] The pressing speed for both pre-forging and final forging is set to 4 mm / s.

[0015] The deformation amount per forging and final forging is controlled between 30% and 50% per forging.

[0016] Before die forging, the billet or pre-formed forging needs to be coated with a special lubricant for aluminum alloys.

[0017] Beneficial effects: In ordinary die forging, to ensure the operating temperature of the die, a pre-made model of heated steel is used to preheat the die, and the holding time is extended by increasing the forging temperature; the combined use of pre-forging die and final forging die not only saves raw materials but also simplifies billet preparation and reduces the operational difficulty for on-site workers; the selection of die forging equipment and the control of deformation ensure the microstructure and performance requirements of the produced forgings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the billet.

[0019] Figure 2 This is a schematic diagram of a preformed forging.

[0020] Figure 3 A schematic diagram of a forging. Figure 1 .

[0021] Figure 4 A schematic diagram of a forging. Figure 2 . Detailed Implementation

[0022] This invention provides a method for conventional die forging of large-arc-shaped 2618 aluminum alloy casing forgings. It solves the problem of conventional die forging of double-shaped, thin-walled, high-ribbed 2618 aluminum alloy casing forgings. Due to their complex shape and asymmetrical recesses on both sides, these casing forgings exhibit an S-shaped metal flow path during die forging, making them prone to folding and difficult to form. This invention combines pre-forging and final forging, along with the following steps, to complete the forging process and obtain a forging that meets the requirements.

[0023] Pre-forging: The billet is forged for the first time to obtain a pre-formed forging. During the first forging process, the billet in front of the boss is flattened and a shallow pit is pressed downward. The billet below the shallow pit is pushed out of the mold cavity, so that the lower surface of the front section forms a downward protruding arc surface. At the same time, a small boss is formed at the front end. The billet in the rear section of the boss is flattened and a shallow pit is pushed upward. The billet above the shallow pit is pushed out of the mold cavity, so that the upper surface of the rear section forms an upward protruding arc surface. At the same time, a small boss is formed at the rear end. The boss forms a slope transition section between the shallow pit in the front section and the upper arc surface of the rear section and between the shallow pit in the rear section and the lower arc surface of the front section.

[0024] Final forging: The preformed forging is subjected to a second die forging to obtain the forging. During the second die forging process, the preformed forging is pressed down by the upper die, two shallow pits are formed to form asymmetrical pits, the small bosses on both sides are formed to form irregular bosses, and the inclined transition section is formed to form the middle step of the forging.

[0025] Step 1: Increase the forging temperature and extend the billet holding time. For large-diameter 2618 aluminum alloy bars (∅300mm and above), insufficient heating temperature and holding time during heating will cause uneven deformation of the forging due to excessive internal and external temperature differences, resulting in uneven internal microstructure and properties. The phase composition of 2618 aluminum alloy is complex; insufficient heating and holding time will prevent the strengthening phases from fully dissolving. Therefore, the initial forging temperature is increased to 470℃, and the heating coefficient is increased to 2.3 min / mm.

[0026] Step 2: Save raw materials and simplify billet design

[0027] By combining different cross-sectional areas of forgings, the weight of the billet is strictly controlled during the design of the pre-forging die, which facilitates the forming of forgings and reduces material usage. The billet making process is simplified. The raw material for billet making is machined bar stock. After calculating the cross-sectional area of ​​the forging, the bar stock is upturned and squared into a cuboid, and then bent to match the curvature of the forging. A boss in the width direction is reserved in the transition section between the upper and lower recesses of the bent bar stock to obtain the billet.

[0028] Step 3: Preheating the steel precast mold

[0029] Given the properties of aluminum alloys, isothermal forging is the optimal solution. However, considering the cost of isothermal forging dies and the long processing cycle, conventional dies will be used in this production. Before forging, a pre-made steel mold will be used to preheat the die, increasing the die temperature and addressing the issue of rapid surface cooling of the forging due to the relatively low preheating temperature of the die.

[0030] Step 4: Selection of forging equipment and control of deformation

[0031] Aluminum alloys are sensitive to strain rate during hot deformation, especially in the machining of large aluminum alloy forgings. During intense deformation, the heat energy from the property transformation can cause a rapid temperature rise in localized areas of the forging, sometimes exceeding the upper limit of the forging temperature, leading to cracks or uneven grain structure. Therefore, forging equipment with relatively stable and low operating speeds is required. Large aluminum alloy forgings are typically produced using hydraulic die forging. The pressing speed is set to 4 mm / s.

[0032] To avoid the formation of coarse grains during recrystallization, the deformation amount per firing should be 12% to 15% greater than the critical deformation. The deformation amount per firing should be controlled between 30% and 50%.

[0033] Step 5: Application of Lubricants in Die Forging

[0034] Special lubricants for aluminum alloys can effectively improve metal flow, reduce the adhesion between the metal and the mold surface, facilitate forging, and extend mold life. Lubricant spraying must be done before die forging.

[0035] The forging has an arc shape, as shown. Figure 3 and Figure 4 As shown, the die forging process of double-shaped thin-walled high-rib arc forgings presents the following technical challenges: the forging operation of the blanks is difficult, resulting in high blank consumption, numerous steps, and multiple heat treatments (4-5 heats), leading to a long production cycle. Manual operation errors cause poor dimensional consistency in the blanks and significant variations in the cross-section of the forgings. Machining and grinding the rough, fleshy areas on machine tools results in unstable quality, causing difficulties in subsequent die forging positioning, large clamping damage to the forgings, and a high scrap rate. In this context, optimizing the forging process design aims to reduce the weight of the blanks, simplify blank manufacturing, and solve the die forging challenges.

[0036] Positioning the forging billet is difficult. Therefore, a lower press speed and a suitable amount of deformation should be selected to ensure the final forming of the forging.

[0037] Example 1, Forged casing for a certain type of engine:

[0038] The forging is arc-shaped, such as Figure 1 , Figure 2As shown. The arc length reaches 1450mm; it is a double-shaped, thin-walled, high-ribbed forging with a projected area of ​​approximately 0.41m². 2 The forging is an aluminum alloy forging weighing approximately 154.3 kg. It is produced through free upsetting, squaring, bending forging, and die forging of a ∅300 mm bar. The forging temperature is 470℃, held for 690 min, with two passes for billet preparation and two passes for die forging. The deformation per pass is 30%-50%. This yields a well-formed forging with satisfactory microstructure and properties.

Claims

1. A method for forming a large arc-shaped 2618 aluminum alloy casing forging using ordinary die forging, characterized in that, The casing forging is arc-shaped, with asymmetrical recesses at the top and bottom along the thickness direction. The recesses follow the shape of the forging, and the upper and lower recesses do not overlap in the thickness direction. The method includes: The bar stock is upturned into a cuboid shape, then bent to match the curvature of the forging. A boss in the width direction is reserved in the transition section between the upper and lower recesses of the bent bar stock to obtain the billet. Pre-forging: The billet is forged for the first time to obtain a pre-formed forging. During the first forging process, the billet in front of the boss is flattened and a shallow pit is pressed downward. The billet below the shallow pit is pushed out of the mold cavity, so that the lower surface of the front section forms a downward protruding arc surface. At the same time, a small boss is formed at the front end. The billet in the rear section of the boss is flattened and a shallow pit is pushed upward. The billet above the shallow pit is pushed out of the mold cavity, so that the upper surface of the rear section forms an upward protruding arc surface. At the same time, a small boss is formed at the rear end. The boss forms a slope transition section between the shallow pit in the front section and the upper arc surface of the rear section and between the shallow pit in the rear section and the lower arc surface of the front section. Final forging: The preformed forging is subjected to a second die forging to obtain the forging. During the second die forging process, the preformed forging is pressed down by the upper die, two shallow pits are formed to form an asymmetrical pit, the small bosses on both sides are formed to form irregular bosses, and the inclined transition section is formed to form the middle step of the forging. The above forging process is ordinary forging; the initial forging temperature is 450℃~470℃, and the heating coefficient is increased to 2.2~2.3min / mm; the preheated die is preheated with a pre-made steel mold before each forging.

2. The method according to claim 1, characterized in that, The bar stock is made of large-diameter 2618 aluminum alloy bars with a diameter of 300mm or more.

3. The method according to claim 1, characterized in that, The pressing speed for both pre-forging and final forging is set to 4 mm / s.

4. The method according to claim 1, characterized in that, The deformation amount per forging and final forging is controlled between 30% and 50%.

5. The method according to claim 1, characterized in that, Before die forging, the billet or preformed forging needs to be coated with a special lubricant for aluminum alloys.

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