A method for mitigating friction in conical shell components

Abstract

This invention discloses a method for mitigating friction in conical shell components. A main lubrication channel and branch channels with gradient density distribution are set within the hot extrusion die. A ball-type dynamic mitigation assembly, consisting of high-temperature resistant balls, a plug base, and high-temperature resistant springs, is installed. Based on finite element simulation, a critical force balance model, and Hooke's law, the spring stiffness is derived in reverse, and a partitioned dimensionality reduction strategy is used to select springs with gradient stiffness. During extrusion, the balls convert sliding friction into rolling friction. When the normal force of the billet overcomes the spring preload, the balls slightly retract, forming an annular liquid outlet gap. Lubricant dynamically overflows under the pressure difference and the ball entrainment effect, achieving on-demand mitigation lubrication where the greater the pressure, the more lubricant is released. This invention effectively solves problems such as lubrication disconnection, die sticking, and microstructure deterioration in the hot extrusion of large-size conical shells, improving the forming quality and wall thickness uniformity of the components, and significantly extending the die life. It is applicable to aerospace, weaponry, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of metal extrusion forming technology, specifically relating to a method for mitigating friction in conical shell components, applicable to the long-drawing and extrusion forming of large-size conical shell components. Background Technology

[0002] Conical shell components are key structural parts in aerospace, weaponry, and marine engineering (such as conical sections of rocket fuel tanks, conical shells of missile bodies, and pressure-resistant conical compartments of deep-sea exploration equipment). Their core characteristics are uniform or gradually changing wall thickness, a conical generatrix, and overall rotational symmetry. Extrusion forming technology, with its advantages of high precision, high material utilization, and excellent mechanical properties, has become the core manufacturing method for these components. The main principles involved in the forming process include: the principle of plastic forming, the principle of constant volume, and the law of least resistance.

[0003] According to the law of least resistance, metal billets preferentially flow in the direction of least resistance, and the die design must adapt to the cavity structure to guide the direction of metal flow. However, in the actual production of large, lightweight, conical shell components through hot extrusion, the following technical challenges remain insurmountable: 1. The "Lubrication Disconnection" Effect Caused by Large Dimensions and Long Strokes: Large components have long extrusion strokes. Traditional lubrication methods typically involve applying a lubricant statically to the die surface once before extrusion. Under high temperature (usually above the recrystallization temperature) and high pressure, as the extrusion shaft descends, the metal billet, which undergoes intense plastic flow in the early stages, acts like a bulldozer, pushing, peeling off, or even burning off the surface lubricant coating. By the middle and later stages of extrusion (i.e., when the metal reaches the lower part of the die), the lubricant film has already been exhausted, resulting in the areas that most require lubrication being in a state of complete "dry friction."

[0004] 2. Stress Surge and Severe "Metal Adhesion" Caused by the Variable Cross-Sectional Characteristics of Long Taper: The forming characteristic of tapered components is that "the lower the compression, the smaller the cross-sectional area." This means that in the lower part of the mold and the transition area of ​​the tapered angle, the deformation resistance increases sharply, and the normal pressure of the billet on the mold sidewall is amplified exponentially. Under the coupled effect of local high normal pressure and dry friction, "adhesive wear (cold welding effect)" is very likely to occur. Metal will stick to the mold surface, not only scratching the surface of the formed part, causing scratches and cracks, but also forcing frequent production stops for mold polishing, significantly shortening the service life of expensive molds.

[0005] 3. Microstructure deterioration caused by thermo-mechanical coupling imbalance: Localized intense dry friction generates huge frictional heat. Due to the limited heat dissipation space inside the mold, the heat accumulation will cause the local temperature in the friction concentration area to rise abnormally, which will lead to grain coarsening, local overheating, or even "thermal cracking". This results in extremely uneven distribution of the mechanical properties of the component, which cannot meet the stringent service standards of aerospace.

[0006] 4. Static lubrication cannot match the deformation requirements of dynamic gradients: The normal stress and metal flow velocity during the extrusion of a conical shell change dynamically along the axial direction in a gradient manner. However, the lubrication provided by existing lubrication methods such as smearing and spraying is uniform and fixed, and cannot achieve adaptive adjustment of "more oil where the resistance is high".

[0007] In view of this, the industry urgently needs a new technology that can achieve "on-demand lubrication" based on the changes in normal stress during the dynamic process of extrusion forming and can effectively convert sliding friction into rolling friction, so as to fundamentally solve the process bottleneck of hot extrusion forming of large-size conical shells. Summary of the Invention

[0008] The purpose of this invention is to provide a method for mitigating friction in conical shell components, overcoming the above-mentioned defects, achieving precise and dynamic mitigation of friction in the extrusion forming process of conical shell components, ensuring the quality of the formed parts, and improving the service life of the mold. It is also highly applicable to the extrusion forming of other large and complex shaped components.

[0009] To achieve the above objectives, the solution of the present invention is as follows: A method for mitigating friction in a conical shell component includes the following steps: S1: A main lubrication channel and multiple branch channels are machined inside the punch used for hot extrusion of the conical shell component. The branch channels are arranged in a gradient density along the conical generatrix of the punch. The branch channel distribution density is the highest in the difficult-to-deform area at the bottom of the punch, and the density of the branch channels gradually decreases upward along the generatrix of the punch. A ball-type dynamic slow-release component is installed in each branch channel. The ball-type dynamic slow-release component includes high-temperature resistant balls, a plug base, and a high-temperature resistant spring. The high-temperature resistant spring is matched with a corresponding stiffness according to the normal positive pressure gradient of different taper areas of the punch. S2: Inject high-temperature lubricant into the main lubrication channel and the branch channel. A high-temperature resistant ball is installed at one end of the branch channel near the surface of the punch, and a plug base is installed at the other end near the main lubrication channel. A high-temperature resistant spring is installed between the high-temperature resistant ball and the plug base. Under the elastic preload of the high-temperature resistant spring, the high-temperature resistant ball protrudes from the surface of the punch, and the plug base seals the branch channel and the main lubrication channel. S3: The heated conical shell component blank is placed in the conical cavity between the punch and the die and the extrusion is started. The blank contacts the protruding high-temperature resistant balls and drives the balls to rotate, converting the sliding friction between the blank and the punch into local rolling friction. S4: During the extrusion process, the normal positive pressure of the blank flowing under the punch increases. When the normal positive pressure overcomes the elastic preload of the high-temperature resistant spring at the corresponding position, the high-temperature resistant ball moves back slightly into the branch channel, forming an annular liquid outlet gap. S5: Under the pressure difference of the fluid and the entrainment effect of the ball's rotation, the high-temperature lubricant overflows from the annular liquid outlet gap to the contact interface between the blank and the punch; the greater the normal positive pressure, the greater the ball retraction and the more lubricant is released, thus achieving dynamic on-demand slow-release lubrication.

[0010] Furthermore, the method for selecting the stiffness of the high-temperature resistant spring in step S1 is as follows: S11: Import the three-dimensional models of the conical shell component and the punch into the finite element simulation software, set the extrusion process parameters, divide multiple discretized monitoring height nodes along the conical generatrix of the punch, and extract the peak value of the normal pressure of each node through simulation. S12: Establish a critical force balance model for the fretting return of high-temperature resistant ball bearings, and derive the theoretical stiffness of the high-temperature resistant springs at each node using Hooke's Law. S13: Divide the punch along the generatrix into an upper low-resistance zone, a middle transition zone, and a lower high-resistance zone. Take the average value of the theoretical stiffness of each zone and select high-temperature resistant springs with corresponding gradient stiffness. The stiffness of the upper spring < the stiffness of the middle spring < the stiffness of the lower spring.

[0011] Furthermore, the extrusion process parameters mentioned in step S11 include the initial forging temperature, extrusion speed, die preheating temperature, and constitutive equation of the billet material.

[0012] Furthermore, the equations of the critical force equilibrium model are as follows: , In the formula: P(h i ) represents the i-th monitoring height node h i Normal force (MPa); S ext The effective force-bearing projected area (mm²) of the contact between the high-temperature resistant ball bearing and the conical shell component blank. 2 ); F spring_i Let N be the initial preload of the high-temperature resistant spring at the i-th monitoring height node. P back A constant fluid back pressure (MPa) is set in the main lubrication channel for the lubricant supply system. S int The effective force-bearing projected area (mm²) of the inner side of the high-temperature resistant ball bearing to withstand back pressure. 2 ).

[0013] Furthermore, according to Hooke's Law F spring_i = K i Substituting ×Δx0 into the critical force equilibrium equation, we obtain the theoretical calculation formula for the high-temperature spring stiffness at the i-th monitoring height node: , Where K i Let be the stiffness of the spring at the i-th monitoring height node (N / mm); Δx0 is the uniform initial compression preload of the spring (mm).

[0014] Furthermore, the high-temperature lubricant mentioned in step S2 is graphite high-temperature grease.

[0015] Furthermore, in step S2, the portion of the high-temperature resistant ball protruding from the forming surface of the punch is 1 / 3 of the ball's spherical surface.

[0016] Furthermore, the high-temperature resistant spring is a high-temperature resistant alloy spring made of Inconel X-750 or Nimonic 90 material.

[0017] This invention, through its innovative design of "converting vertical pressure into horizontal reciprocating thrust," achieves the integration of geometric forming and external gradient microstructure construction of aluminum-magnesium alloy tubing. Compared to existing technologies, it offers the following significant advantages: This invention employs a high-temperature resistant spring + ball bearing pure physical-mechanical feedback structure, using the normal positive pressure of metal flow as a natural driving source. It achieves dynamic adaptive supply where the greater the pressure, the more the ball bearings retract and the more lubrication is released. This fundamentally prevents the lubrication film from being pushed, peeled, or burned, ensuring continuous and effective lubrication throughout the entire extrusion stroke and eliminating dry friction in the middle and later stages. To address the problem of increased normal pressure caused by the variable cross-section at the bottom of the tapered component, this invention can accurately release sufficient lubricating medium in the high-resistance zone, significantly reducing adhesive wear between the blank and the mold, avoiding metal sticking to the mold, surface scratches and cracks, reducing the frequency of mold polishing, and greatly extending the service life of expensive molds. Dynamic uniform lubrication can effectively reduce local frictional heat accumulation, avoid abnormal temperature rise in friction concentration areas, suppress grain coarsening, local overheating and thermal cracking, and make the mechanical properties of components uniformly distributed to meet the stringent service standards of aerospace, deep-sea equipment and other fields. The lubrication supply of this invention responds to the gradient along the conical generatrix, providing more oil where the resistance is greater, perfectly adapting to the axial gradient changes of normal stress and metal flow velocity, overcoming the shortcomings of traditional static lubrication which provides uniform supply and cannot be adaptively adjusted. In the early stages of extrusion, sliding friction is converted into rolling friction, which significantly reduces the initial deformation resistance. In the middle and later stages, fluid lubrication is combined to form a double drag reduction of rolling and fluid, which improves the filling rate of the formed parts and makes the wall thickness tolerance more controllable. This effectively avoids insufficient filling, uneven wall thickness and cracking, and ensures high-precision forming of large-size conical shell components. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall mold cross-sectional structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of multiple ball-type dynamic sustained-release components arranged in a gradient density according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a ball-type dynamic slow-release component before releasing high-temperature lubricant, according to one embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of a ball-type dynamic slow-release component in one embodiment of the present invention when releasing high-temperature lubricant.

[0019] Labeling explanation: 1. Punch; 2. Main lubrication channel; 3. Branch channel; 4. High temperature resistant ball; 5. Plug base; 6. High temperature resistant spring; 7. Conical cavity; 8. Conical shell component; 9. Die. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] This embodiment provides a method for mitigating friction in a conical shell component, including the following steps: S1: A main lubrication channel 2 and multiple branch channels 3 are machined inside the hot extrusion punch 1 of the AZ80 magnesium alloy conical shell component 8. The branch channels 3 are arranged in a gradient density along the conical generatrix of the punch 1. The branch channels 3 in the bottom extrusion zone of the punch 1 have the highest distribution density, and the density of the branch channels 3 gradually decreases upward along the generatrix of the punch 1. A ball-type dynamic slow-release component is installed in each branch channel 3. The ball-type dynamic slow-release component includes high-temperature resistant balls 4, a plug base 5, and a high-temperature resistant spring 6. S11: Import the three-dimensional models of the conical shell component 8 and the punch 1 into finite element simulation software (such as DEFORM or Abaqus), set the initial forging temperature (such as 400℃), set the extrusion speed, the die preheating temperature and the constitutive equation of AZ80 magnesium alloy (such as the Arrhenius rheological stress model), divide multiple discretized monitoring height nodes along the conical generatrix of the punch 1, and extract the peak value of the normal pressure of each node through simulation; S12: Establish a critical force balance model for the fretting return of a high-temperature resistant ball bearing 4. The equations of the critical force balance model are as follows: , In the formula: P(h i ) represents the i-th monitoring height node h i Normal force (MPa); S ext The effective force-bearing projected area (mm²) of the contact between the high-temperature resistant ball bearing 4 and the conical shell component 8 blank. 2 ); F spring_i The initial preload (N) of the high-temperature resistant spring 6 at the i-th monitoring height node; P back A constant fluid back pressure (MPa) is set in the main lubrication channel 2 for the lubricant supply system. S int The effective force-bearing projected area (mm²) of the inner side of the high-temperature resistant ball bearing 4 to withstand back pressure. 2 ).

[0022] Based on Hooke's Law, the theoretical stiffness of the high-temperature resistant spring 6 at each node is derived. According to Hooke's Law F... spring_i = K i Substituting ×Δx0 into the critical force equilibrium equation, we obtain the theoretical calculation formula for the stiffness of the high-temperature resistant spring 6 at the i-th monitoring height node: , Where K i Let be the stiffness of the spring at the i-th monitoring height node (N / mm); Δx0 is the uniform initial compression preload of the spring (mm); S13: Divide punch 1 along the generatrix into an upper low-resistance region, a middle transition region, and a lower high-resistance region, and determine the theoretical stiffness K for each region. i Taking the average value, high-temperature resistant springs 6 with corresponding gradient stiffness are selected, with the upper spring stiffness < middle spring stiffness < lower spring stiffness. The high-temperature resistant springs 6 are high-temperature alloy springs made of Inconel X-750 or Nimonic 90 material. This ensures that during the overall extrusion process, the lower high-pressure zone can accurately overcome the large spring preload when reaching the critical high resistance, releasing sufficient lubricating medium; while the upper low-pressure zone uses a softer spring to match its smaller normal positive pressure, achieving dynamic flow adaptive balance across the entire range.

[0023] S2: Inject high-temperature lubricant (graphite high-temperature grease can be used) into the main lubrication channel 2 and the branch channel 3. A high-temperature resistant ball 4 is set at one end of the branch channel 3 near the surface of the punch 1, and a plug base 5 is set at the other end near the main lubrication channel 2. A high-temperature resistant spring 6 is set between the high-temperature resistant ball 4 and the plug base 5. Under the elastic preload of the high-temperature resistant spring 6, part of the high-temperature resistant ball 4 protrudes from the surface of the punch 1. Under the preload of the high-temperature resistant spring 6, the high-temperature resistant ball 4 protrudes from about 1 / 3 of the spherical surface of the punch 1. The plug base 5 seals the branch channel 3 and the main lubrication channel 2 to achieve a normally closed state. S3: The conical shell component 8 blank heated to 400℃ is placed in the conical cavity 7 between the punch 1 and the die, and the extruder is started to extrude downwards. The conical shell component 8 blank contacts the protruding high-temperature resistant balls 4 and drives the balls to rotate, converting the sliding friction between the blank and the punch 1 into local rolling friction. S4: During the extrusion process, the lower part of the conical cavity 7 narrows, the metal flow is obstructed, and the normal positive pressure of the blank flow at the lower part of the punch 1 increases. When the normal positive pressure overcomes the elastic preload of the high temperature spring 6 at the corresponding position, the high temperature ball 4 moves back slightly into the branch channel 3, forming an annular liquid outlet gap. S5: Under the pressure difference of the fluid and the self-rotation and entrainment of the ball bearings, the high-temperature lubricant overflows from the annular liquid outlet gap to the contact interface between the blank and the punch. The greater the normal positive pressure, the greater the ball bearing retraction and the more lubricant is released, thus achieving dynamic on-demand slow-release lubrication and finally obtaining a conical shell component with a smooth surface, uniform wall thickness and no cracks.

[0024] This invention can adjust the flow rate of lubricating graphite according to the generatrix gradient characteristics of the conical shell component 8, thereby achieving lubrication supply to areas prone to friction concentration. It solves the defect that traditional fixed lubrication methods cannot adapt to conical structures, significantly improves the uniformity and effectiveness of friction mitigation, further increases the filling rate of the formed parts, and effectively avoids defects such as incomplete filling, uneven wall thickness, and cracking. The component forming filling rate is improved, the wall thickness tolerance is significantly reduced, the mold service life is longer, the manual operation intensity is reduced, and there are no defects such as sticking, tearing, or overheating, which fully meet the requirements of aerospace applications.

[0025] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A method for mitigating friction in a conical shell component, characterized in that, Includes the following steps: S1: A main lubrication channel and multiple branch channels are machined inside the punch used for hot extrusion of the conical shell component. The branch channels are arranged in a gradient density along the conical generatrix of the punch. The branch channel distribution density is the highest in the difficult-to-deform area at the bottom of the punch, and the density of the branch channels gradually decreases upward along the generatrix of the punch. A ball-type dynamic slow-release component is installed in each branch channel. The ball-type dynamic slow-release component includes high-temperature resistant balls, a plug base, and a high-temperature resistant spring. The high-temperature resistant spring is matched with a corresponding stiffness according to the normal positive pressure gradient of different taper areas of the punch. S2: Inject high-temperature lubricant into the main lubrication channel and the branch channel. A high-temperature resistant ball is installed at one end of the branch channel near the surface of the punch, and a plug base is installed at the other end near the main lubrication channel. A high-temperature resistant spring is installed between the high-temperature resistant ball and the plug base. Under the elastic preload of the high-temperature resistant spring, the high-temperature resistant ball protrudes from the surface of the punch, and the plug base seals the branch channel and the main lubrication channel. S3: The heated conical shell component blank is placed in the conical cavity between the punch and the die and the extrusion is started. The blank contacts the protruding high-temperature resistant balls and drives the balls to rotate, converting the sliding friction between the blank and the punch into local rolling friction. S4: During the extrusion process, the normal positive pressure of the blank flowing under the punch increases. When the normal positive pressure overcomes the elastic preload of the high-temperature resistant spring at the corresponding position, the high-temperature resistant ball moves back slightly into the branch channel, forming an annular liquid outlet gap. S5: Under the pressure difference of the fluid and the entrainment effect of the ball's rotation, the high-temperature lubricant overflows from the annular liquid outlet gap to the contact interface between the blank and the punch; the greater the normal positive pressure, the greater the ball retraction and the more lubricant is released, thus achieving dynamic on-demand slow-release lubrication.

2. The method for mitigating friction in a conical shell component according to claim 1, characterized in that, The specific method for selecting the stiffness of the high-temperature resistant spring in step S1 is as follows: S11: Import the three-dimensional models of the conical shell component and the punch into the finite element simulation software, set the extrusion process parameters, divide multiple discretized monitoring height nodes along the conical generatrix of the punch, and extract the peak value of the normal pressure of each node through simulation. S12: Establish a critical force balance model for the fretting return of high-temperature resistant ball bearings, and derive the theoretical stiffness of the high-temperature resistant springs at each node using Hooke's Law. S13: Divide the punch along the generatrix into an upper low-resistance zone, a middle transition zone, and a lower high-resistance zone. Take the average value of the theoretical stiffness of each zone and select high-temperature resistant springs with corresponding gradient stiffness. The stiffness of the upper spring < the stiffness of the middle spring < the stiffness of the lower spring.

3. The method for mitigating friction in a conical shell component according to claim 2, characterized in that, The extrusion process parameters mentioned in step S11 include the initial forging temperature, extrusion speed, die preheating temperature, and constitutive equation of the billet material.

4. The method for mitigating friction in a conical shell component according to claim 2, characterized in that, The equations of the critical force equilibrium model are as follows: ， In the formula: P(h i ) represents the i-th monitoring height node h i Normal force; S ext The effective force-bearing projected area of ​​the high-temperature resistant ball bearing in contact with the conical shell component blank; F spring_i Let be the initial preload of the high-temperature resistant spring at the i-th monitoring height node; P back A constant fluid back pressure set within the main lubrication channel for the lubricant supply system; S int The effective force projection area of ​​the inner side of the high-temperature resistant ball bearing the back pressure.

5. A method for mitigating friction in a conical shell component according to claim 4, characterized in that, According to Hooke's Law F spring_i = K i Substituting ×Δx0 into the critical force equilibrium equation, we obtain the theoretical calculation formula for the high-temperature spring stiffness at the i-th monitoring height node: ， Where K i Let be the stiffness of the spring at the i-th monitoring height node; Δx0 is the uniform initial compression preload of the spring.

6. The method for slow-release friction of a conical shell component according to claim 1, characterized in that, The high-temperature lubricant mentioned in step S2 is graphite high-temperature grease.

7. The method for mitigating friction in a conical shell component according to claim 1, characterized in that, In step S2, the portion of the high-temperature resistant ball protruding from the forming surface of the punch is 1 / 3 of the ball's spherical surface.

8. The method for mitigating friction in a conical shell component according to claim 1, characterized in that, The high-temperature resistant spring is a high-temperature alloy spring made of Inconel X-750 or Nimonic 90 material.

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