Aluminum alloy extrusion forming process for high-rigidity lightweight industrial robot arm

Abstract

The application relates to the technical field of aluminum alloy precision forming, and discloses an aluminum alloy extrusion forming process for a high-rigidity lightweight industrial robot arm, which adopts Al-Mg-Si-Cu-Zr-Sc-Er multi-element micro-alloyed aluminum alloy as raw material, realizes near-net forming of the complex-section industrial robot arm through a whole-process cooperative process of ingot surface gradient turning-gradient preheating composite pretreatment, segmented variable-temperature and variable-pressure extrusion, partition controllable water mist-air mixed online quenching and gradient heating two-stage aging strengthening, and cooperates with a special extrusion die with an integrated structure of bionic honeycomb flow guide-gradient working zone-predeformation compensation, solves the technical problems that rigidity and lightweight of the aluminum alloy robot arm cannot be considered simultaneously, internal organization is uneven, size precision is low, and fatigue life is short in the traditional process, and significantly improves the motion precision, load capacity and service life of the industrial robot, and is suitable for large-scale production of high-precision, high-load and long-life industrial robots.

Description

Technical Field

[0001] This invention belongs to the field of precision aluminum alloy forming technology, specifically an aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm. Background Technology

[0002] Industrial robots are core equipment in intelligent manufacturing, and their performance directly determines the level of automation and production efficiency in the manufacturing industry. As the core motion execution component of an industrial robot, the robot arm has extremely stringent performance requirements, needing to possess high rigidity, lightweight, high strength, high dimensional accuracy, and long fatigue life simultaneously. High rigidity ensures the robot's positioning accuracy and repeatability under high-speed motion and heavy-load conditions, avoiding processing errors caused by arm deformation. Lightweight design reduces motion inertia, improves the robot's response speed and acceleration, and reduces the power consumption of the drive motor. Long fatigue life ensures reliable operation of the robot under long-term alternating loads, reducing maintenance costs and downtime.

[0003] Currently, industrial robot arms are mainly manufactured using traditional Al-Mg-Si aluminum alloys such as 6061 and 6063 through extrusion molding. However, as industrial robots develop towards higher precision, higher load capacity, and higher speed, traditional processes and materials are no longer sufficient to meet increasingly stringent performance requirements, mainly due to the following technical bottlenecks:

[0004] 1. Insufficient alloy system performance, highlighting the contradiction between rigidity and lightweight: The elastic modulus of traditional 6061 aluminum alloy is only about 69 GPa, the tensile strength is generally below 310 MPa, and the specific strength is low; in order to improve the rigidity of the robot arm, it is necessary to increase the wall thickness of the arm body, which leads to increased weight and increased moment of inertia, which in turn reduces the robot's motion performance and load capacity; although some studies have improved the alloy strength by adding elements such as Mn and Cr, these elements are prone to forming coarse intermetallic compounds, which reduces the toughness and fatigue performance of the alloy, and the effect on improving the elastic modulus is very limited.

[0005] 2. The ingot pretreatment process is simple, but the internal structure is uneven: Traditional processes usually use a single temperature constant temperature preheating method, which can easily generate a large temperature gradient inside the ingot. This leads to uneven metal flow during extrusion, and the difference in structure and properties between the front and rear ends of the profile is large, generally exceeding 15%. At the same time, the segregation layer and oxide scale on the surface of the ingot are not completely removed, and they are easily drawn into the interior of the profile during extrusion, forming inclusions, bubbles and other defects, which seriously affect the mechanical properties and reliability of the product.

[0006] 3. Unreasonable extrusion process parameters and numerous internal defects: Traditional constant temperature and constant speed extrusion processes do not consider the deformation law and temperature changes of metal during extrusion. In the early stage of extrusion, the metal temperature is low, the deformation resistance is high, and cracks are easily generated. In the later stage of extrusion, due to the accumulation of deformation heat, the metal temperature rises, and the grains are prone to grow, resulting in a decrease in mechanical properties. In addition, traditional extrusion dies mostly adopt simple straight flow guiding structures, and the metal flows turbulently in the die cavity, which easily generates eddies and dead zones, resulting in large profile wall thickness tolerances (generally above ±0.2mm), requiring a lot of subsequent machining, which not only increases production costs but also destroys the continuous fibrous structure of the metal, further reducing the mechanical properties of the product.

[0007] 4. Outdated heat treatment process and poor strength-toughness matching: Traditional single-stage aging treatment process is difficult to obtain high strength and high toughness at the same time; if the aging temperature is too high or the time is too long, although high strength can be obtained, the toughness will decrease significantly; if the aging temperature is too low or the time is too short, although the toughness is good, the strength is insufficient; in addition, the traditional offline quenching process requires reheating and quenching the extruded profile, which not only has a long production cycle and high energy consumption, but also easily leads to profile deformation and affects dimensional accuracy.

[0008] Meanwhile, some existing technologies have improved the strength of alloys by adding elements such as Mn and Cr, but the improvement effect is not obvious, and the wall thickness tolerance after extrusion molding is still above ±0.15mm; while other existing technologies have improved production efficiency by optimizing extrusion parameters, but have not solved the problem of uneven metal flow, and the difference in mechanical properties between the front and rear ends of the profile is still above 10%; and some technologies have improved the strength and toughness of alloys, but have not involved specific extrusion molding processes, and cannot guide actual production.

[0009] Therefore, developing a new extrusion molding process that can simultaneously improve the rigidity, strength, dimensional accuracy, and fatigue life of aluminum alloy robot arms is of great strategic significance for enhancing the overall performance and international competitiveness of my country's industrial robots. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide an aluminum alloy extrusion molding process for a high-rigidity and lightweight industrial robot arm, which solves the technical problems of difficulty in balancing rigidity and lightweight, uneven internal structure, low dimensional accuracy and short fatigue life in traditional aluminum alloy robot arms.

[0011] To achieve the above objectives, the present invention provides the following technical solution: an aluminum alloy extrusion forming process for a high-rigidity lightweight industrial robot arm, comprising five core steps: multi-element micro-alloyed aluminum alloy melting and homogenized ingot preparation, ingot surface gradient turning and gradient preheating composite pretreatment, segmented temperature and pressure extrusion forming, zoned controllable water mist-air mixing online quenching, and gradient heating dual-stage aging strengthening treatment, as well as a special extrusion die with an integrated structure of biomimetic honeycomb flow guide, gradient working zone, and pre-deformation compensation.

[0012] The core technical principle of this invention lies in:

[0013] 1. Synergistic Strengthening Mechanism of Multi-component Microalloying: This invention employs an Al-Mg-Si-Cu-Zr-Sc-Er multi-component microalloying system, by adding trace amounts of Zr, Sc, and Er elements to form a dispersed distribution... Zr、 Sc and Er nanophases; these nanophases possess extremely high thermal stability, effectively pinning grain boundaries and inhibiting grain growth during melting, casting, extrusion, and heat treatment, while significantly improving the alloy's elastic modulus and strength. Among them, Zr mainly forms a dispersed phase within the grains, improving the alloy's high-temperature stability; Sc mainly forms a dispersed phase at grain boundaries, refining the grains; Er can purify grain boundaries, reduce the segregation of impurity elements, and improve the alloy's toughness and fatigue performance. The synergistic effect of these three elements increases the alloy's elastic modulus from 69 GPa in traditional 6061 aluminum alloy to over 74 GPa, and its tensile strength to over 400 MPa, while maintaining good toughness.

[0014] 2. Composite Pretreatment Technology for Ingots: This invention employs a composite pretreatment process combining surface gradient turning and three-stage gradient preheating. Surface gradient turning can selectively remove surface defects and segregation layers according to the degree of segregation in different parts of the ingot, while ensuring the dimensional accuracy of the ingot. Three-stage gradient preheating can ensure uniform temperature distribution inside the ingot, avoiding internal stress concentration and uneven microstructure caused by traditional rapid preheating. In particular, the heat preservation in the two temperature ranges of 280-300℃ and 380-400℃ can fully dissolve and uniformly distribute the second phase in the alloy, laying a good microstructure foundation for subsequent extrusion deformation and age hardening.

[0015] 3. Segmented Temperature and Pressure Variable Extrusion Technology: Based on the deformation law and temperature changes of metal during the extrusion process, this invention adopts a segmented temperature and pressure variable extrusion process with low speed and low pressure in the initial stage and high speed and high pressure in the later stage. In the initial stage of extrusion, the ingot temperature is relatively low and the deformation resistance is high, so a lower extrusion speed and pressure can be used to avoid defects such as cracks. In the later stage of extrusion, due to the accumulation of deformation heat, the metal temperature rises and the deformation resistance decreases, so a higher extrusion speed and pressure can be used to improve production efficiency. At the same time, dynamic recrystallization refines the grains. In addition, this invention also precisely controls the extrusion ratio and the gap between each component, further reducing the generation of internal defects.

[0016] 4. Specialized Extrusion Die Design: This invention designs a specialized extrusion die with an integrated structure of biomimetic honeycomb flow guide, gradient working zone, and pre-deformation compensation. The biomimetic honeycomb flow guide structure enables the metal to be evenly distributed before entering the die cavity, reducing the generation of eddies and dead zones. The gradient working zone structure can adjust the flow speed of the metal according to the wall thickness difference in different parts of the profile, so that all parts of the profile flow out of the die cavity synchronously. The pre-deformation compensation structure can pre-counteract the springback deformation of the profile after extrusion, significantly improving the dimensional accuracy of the profile.

[0017] 5. Zoned Controllable Online Quenching Technology: This invention employs a zoned controllable water-mist-air hybrid cooling system for online quenching. Based on the wall thickness differences in different parts of the profile, the cooling rate is controlled zone by zone, ensuring that all parts of the profile are simultaneously cooled to below 80°C. This not only yields a uniform supersaturated solid solution, laying the foundation for subsequent aging strengthening, but also avoids profile deformation caused by uneven cooling. Furthermore, the online quenching process is carried out simultaneously with the extrusion process, eliminating the need for traditional offline quenching, significantly shortening the production cycle and reducing energy consumption.

[0018] 6. Gradient Heating Two-Stage Aging Technology: This invention employs a gradient heating method for two-stage aging treatment. The low-temperature pre-aging stage forms numerous fine GP regions, serving as nucleation sites for subsequent precipitates; the high-temperature final aging stage transforms these GP regions into fine, dispersed... Harmony These precipitated phases are the main strengthening phases of the alloy; the gradient heating method can make the nucleation and growth process of the precipitated phases more uniform, avoiding the problems of coarse precipitates and uneven distribution caused by traditional rapid heating; in addition, the slow cooling process after aging can further adjust the size and distribution of the precipitates, and improve the strength and toughness matching of the alloy.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) Significantly improved rigidity and specific strength, achieving true lightweighting: The Al-Mg-Si-Cu-Zr-Sc-Er multi-element micro-alloying system adopted in this invention, through the synergistic strengthening effect of the three rare earth elements, increases the elastic modulus of the alloy from 69 GPa of traditional 6061 aluminum alloy to over 74 GPa, an increase of 7.2%; the tensile strength from 310 MPa to over 400 MPa, an increase of 29%; and the specific strength from 114.8 MPa・cm³ / g to over 163 MPa・cm³ / g, an increase of over 42%. Under the same rigidity requirements, the wall thickness of the robot arm can be reduced by 26%, the overall weight is reduced by 26%, significantly reducing the moment of inertia and improving the robot's response speed and load capacity;

[0021] (2) Significantly improved dimensional accuracy, achieving near-net-shape forming: The biomimetic honeycomb flow guide-gradient working belt-pre-deformation compensation integrated mold and segmented temperature and pressure extrusion process adopted in this invention make the metal flow more uniform, and the profile wall thickness tolerance is controlled from the traditional ±0.2mm to within ±0.03mm, which is more than 85% improved; the straightness tolerance is controlled from the traditional ±0.5mm / m to within ±0.1mm / m, which is more than 80% improved; almost no subsequent machining is required, which not only reduces the production cost, but also retains the continuous fiber structure of the metal, further improving the mechanical properties of the product;

[0022] (3) Significantly improved uniformity of structure and properties: The three-stage gradient preheating and segmented temperature and pressure extrusion process of the present invention enables the ingot to maintain a uniform temperature and deformation rate throughout the extrusion process. The difference in mechanical properties between the front and rear ends of the profile is reduced from more than 15% in the traditional method to less than 2%, which improves the consistency and reliability of the product. At the same time, the zoned controllable online quenching and gradient heating dual-stage aging process makes the structure and properties of each part of the profile more uniform, avoiding early failure caused by insufficient local properties.

[0023] (4) Significantly improved fatigue life: The multi-element micro-alloying system of the present invention can purify grain boundaries and reduce the segregation of impurity elements; the gradient heating two-stage aging process can make the precipitated phases finer and more dispersed, and the distribution more uniform; the near-net-shape forming process can retain the continuous fibrous structure of the metal; these factors work together to effectively inhibit the initiation and propagation of fatigue cracks, making the fatigue life of the product more than 2.8 times that of the traditional process, greatly extending the service life of the robot and reducing maintenance costs;

[0024] (5) Improved production efficiency and reduced energy consumption: The online quenching process of the present invention is carried out simultaneously with the extrusion process, eliminating the traditional offline quenching process and shortening the production cycle by more than 40%; the average extrusion speed of the segmented temperature and pressure extrusion process is more than 30% higher than that of the traditional process; at the same time, the energy consumption of the gradient preheating and online quenching processes is reduced by more than 25% compared with the traditional process, which has significant economic and environmental benefits. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0026] In the attached diagram:

[0027] Figure 1 This is a general flowchart of the overall process flow of the present invention;

[0028] Figure 2 This is a detailed block diagram of step 1, smelting and ingot preparation, of the present invention;

[0029] Figure 3 This is a detailed block diagram of step 2 of the present invention, the composite pretreatment of ingots.

[0030] Figure 4 This is a block diagram of step 3 of the present invention: segmented extrusion molding + special mold.

[0031] Figure 5 This is a block diagram of step 4, controllable online quenching, of the present invention.

[0032] Figure 6 This is a block diagram of step 5 of the present invention, which shows the gradient heating two-stage aging process.

[0033] Figure 7 This is a general execution flowchart of Embodiment 1 and Embodiment 2 of the present invention. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0035] Example 1

[0036] This embodiment produces the boom profile for a six-axis industrial robot. The cross-section is a complex hollow box structure with a maximum external dimension of 150mm × 100mm. The wall thickness of the main load-bearing area is 5.5mm, the wall thickness of the secondary load-bearing area is 4mm, the wall thickness of the non-load-bearing area is 2.5mm, and the length is 1200mm.

[0037] An aluminum alloy extrusion molding process for a high-rigidity, lightweight industrial robot arm, comprising the following specific steps:

[0038] (1) Multi-element microalloyed aluminum alloy smelting and homogenization ingot preparation: each raw material is weighed precisely according to the mass percentage: Mg: 1.0%, Si: 0.8%, Cu: 0.6%, Zr: 0.2%, Sc: 0.12%, Er: 0.07%, Fe: 0.06%, Mn: 0.02%, Zn: 0.02%, Ti: 0.01%, the remainder being pure aluminum with a purity ≥ 99.95% and unavoidable impurities.

[0039] Pure aluminum ingots were placed in a 5-ton medium-frequency induction melting furnace and heated to 730℃ for melting. After the pure aluminum was completely melted, Al-20%Mg master alloy, Al-20%Si master alloy, and Al-50%Cu master alloy were added in sequence. After each master alloy was added, the mixture was stirred in the same direction for 4 minutes with a graphite stirrer to ensure uniform distribution of alloying elements. After all the master alloys were melted and stirred evenly, the melt temperature was raised to 770℃, and then Al-5%Zr master alloy, Al-2%Sc master alloy, and Al-10%Er master alloy were added in sequence. The mixture was stirred for 6 minutes and held at that temperature for 18 minutes.

[0040] After smelting, the argon rotary jet method is used for refining, degassing, and slag removal. The refining agent is a mixture of hexachloroethane and potassium chloride at a mass ratio of 1:2, and the amount used is 0.3% of the melt mass. The refining temperature is controlled at 740℃, the refining time is 15min, the argon flow rate is 2.0m³ / h, and the rotary nozzle speed is 350r / min. During the refining process, the rotary nozzle moves up and down slowly to ensure that all parts of the melt are fully refined.

[0041] After refining, the melt is allowed to stand for 25 minutes to allow impurities to float to the surface. Then, semi-continuous casting is carried out at 720℃ with a casting speed of 90 mm / min and a cooling water pressure of 0.2 MPa to obtain an ingot with a diameter of φ220 mm × 600 mm. After casting, the ingot is immediately transferred to a homogenization furnace for homogenization treatment and held at 470℃ for 14 hours. Then, it is cooled to room temperature with the furnace.

[0042] (2) The gradient turning and gradient preheating composite pretreatment of the ingot surface were carried out by gradient turning on the outer cylindrical surface of the ingot using a CK61125 CNC lathe. According to the segregation law in the casting process, the segregation at both ends of the ingot is more serious, so the turning depth is set to 5mm. The segregation in the middle of the ingot is less serious, so the turning depth is set to 3mm. Carbide tools were used during the turning process, the cutting speed was 120m / min, and the feed rate was 0.2mm / r. After turning, the surface roughness Ra of the ingot was ≤1.6μm, and the roundness tolerance was ≤0.1mm.

[0043] The machined ingot is placed in a bogie-type preheating furnace for three-stage gradient preheating. The entire preheating process is carried out under a nitrogen protective atmosphere with a nitrogen purity ≥99.99% and the oxygen content in the furnace controlled below 50 ppm. The preheating process parameters are as follows:

[0044] First stage: Increase the temperature from room temperature to 290℃ at a rate of 5℃ / min and hold for 2 hours;

[0045] Second stage: Increase the temperature to 390℃ at a rate of 3℃ / min and hold for 1.5h;

[0046] Third stage: Increase the temperature to 465℃ at a rate of 2℃ / min and hold for 1 hour.

[0047] After preheating, the ingot is immediately fed into the extrusion press for extrusion. The transfer time is controlled within 30 seconds to avoid the ingot temperature from dropping.

[0048] (3) The segmented temperature and pressure extrusion molding is carried out using a 1250-ton horizontal extruder and a special extrusion die designed in this invention. The die consists of an upper die, a lower die and a die pad. The upper die cavity entrance is provided with a biomimetic honeycomb flow guide structure, which consists of 42 regular hexagonal flow guide holes. The side length of the flow guide hole is 10mm and the wall thickness is 2mm. The axis of the flow guide hole is at an angle of 18° with the extrusion direction. Adjacent flow guide holes are transitioned by a rounded corner with a radius of 2.5mm. The lower die is provided with a gradient working belt structure and a pre-deformation compensation structure. The length of the working belt is continuously gradient distributed along the perimeter of the profile section: the length of the working belt in the main load area (wall thickness 5.5mm) is 7mm, the length of the working belt in the secondary load area (wall thickness 4mm) is 5mm, and the length of the working belt in the non-load area (wall thickness 2.5mm) is 3mm. The pre-deformation compensation structure is pre-set with a reverse deformation amount of 0.2mm at the die exit to offset the springback deformation after the profile is extruded.

[0049] The extrusion process parameters are as follows:

[0050] Extrusion cylinder temperature: 450℃;

[0051] Mold temperature: 480℃;

[0052] Extrusion ratio: 30:1;

[0053] The gap between the extrusion cylinder and the ingot is 0.3 mm.

[0054] The gap between the extrusion pad and the extrusion cylinder is 0.15mm.

[0055] Front-end extrusion: extrusion speed 2.5 mm / s, extrusion pressure 20 MPa, extrusion to 65% of the ingot length;

[0056] Post-extrusion: extrusion speed 4.5 mm / s, extrusion pressure 27 MPa, extrusion until the remaining ingot length is 50 mm.

[0057] After extrusion, the profile is cut using hydraulic shears at a distance of 550mm from the mold exit at a cutting speed of 120mm / s; the cut profile is immediately sent to an online quenching system for cooling.

[0058] (4) Zoned controllable water mist-air mixing online quenching adopts a zoned controllable water mist-air mixing cooling system for online quenching; the system is divided into three cooling zones along the profile extrusion direction, with a total length of 5m; each cooling zone is equipped with 12 sets of independent water mist nozzles and air nozzles, the distance between the nozzles and the profile surface is 180mm, and the nozzle angle is 50° with the profile surface; the temperature of the four sides and the upper and lower surfaces of the profile is monitored in real time by an infrared thermometer, and when the temperature of a certain part is higher than the set value, the flow rate of the corresponding nozzle at that part is automatically increased.

[0059] The cooling process parameters are as follows:

[0060] First cooling zone (length 1.5m): water mist pressure 0.4MPa, air pressure 0.3MPa, water mist to air volume ratio 1:5, cooling rate controlled at 175℃ / s;

[0061] Second cooling zone (length 2m): water mist pressure 0.3MPa, air pressure 0.25MPa, water mist to air volume ratio 1:6, cooling rate controlled at 115℃ / s;

[0062] Third cooling zone (1.5m in length): Only air nozzles are open, air pressure is 0.2MPa, and cooling rate is controlled at 40℃ / s.

[0063] After online quenching, the temperature of all parts of the profile drops below 70℃, and the temperature difference is controlled within 10℃.

[0064] (5) Gradient heating and two-stage aging strengthening treatment: The quenched profiles are sent into a bogie-type aging furnace for gradient heating and two-stage aging treatment; the aging furnace adopts hot air circulation heating method, and the temperature uniformity inside the furnace is controlled within ±2℃.

[0065] The aging process parameters are as follows:

[0066] First stage: Heat to 125℃ at a rate of 2.5℃ / min and hold for 7 hours;

[0067] Second stage: Increase the temperature to 175℃ at a rate of 2℃ / min and hold for 5 hours;

[0068] The third stage: the temperature is reduced to 90°C at a rate of 1.5°C / min, and then the furnace is removed and air-cooled to room temperature.

[0069] After aging is completed, the profiles are inspected for appearance and dimensions, and then sawn, straightened and surface treated to obtain the final industrial robot arm product.

[0070] A comprehensive performance test was conducted on the industrial robot arm profile prepared in this embodiment. The test results are as follows:

[0071] Tensile strength: 402 MPa;

[0072] Yield strength: 348 MPa;

[0073] Elastic modulus: 74.3 GPa;

[0074] Elongation: 12.5%;

[0075] Density: 2.71 g / cm³;

[0076] Specific strength: 148.3 MPa・cm³ / g;

[0077] Wall thickness tolerance: ±0.02mm;

[0078] Straightness tolerance: ±0.08mm / m;

[0079] Difference in tensile strength between the front and rear ends of the profile: 1.8%;

[0080] Fatigue life (10 7 (next cycle): 236 MPa.

[0081] Example 2

[0082] This embodiment prepares a forearm profile for a six-axis industrial robot. The cross-section is a hollow rectangular structure with a maximum external dimension of 100mm × 70mm. The wall thickness of the main load-bearing area is 4.5mm, the wall thickness of the secondary load-bearing area is 3.5mm, the wall thickness of the non-load-bearing area is 2mm, and the length is 800mm.

[0083] An aluminum alloy extrusion molding process for a high-rigidity, lightweight industrial robot arm, comprising the following specific steps:

[0084] (1) Multi-element microalloyed aluminum alloy smelting and homogenization ingot preparation: each raw material is weighed precisely according to the mass percentage: Mg: 0.95%, Si: 0.75%, Cu: 0.55%, Zr: 0.19%, Sc: 0.11%, Er: 0.06%, Fe: 0.05%, Mn: 0.02%, Zn: 0.02%, Ti: 0.01%, the remainder being pure aluminum with a purity ≥ 99.95% and unavoidable impurities.

[0085] Pure aluminum ingots were placed in a 3-ton medium-frequency induction melting furnace and heated to 728℃ for melting. After the pure aluminum was completely melted, Al-20%Mg master alloy, Al-20%Si master alloy, and Al-50%Cu master alloy were added in sequence. After each master alloy was added, the mixture was stirred in the same direction for 3.5 minutes with a graphite stirrer to ensure uniform distribution of alloying elements. After all the master alloys were melted and stirred evenly, the melt temperature was raised to 768℃, and then Al-5%Zr master alloy, Al-2%Sc master alloy, and Al-10%Er master alloy were added in sequence. The mixture was stirred for 5.5 minutes and held at that temperature for 16 minutes.

[0086] After smelting, the argon rotary jet method is used for refining, degassing, and slag removal. The refining agent is a mixture of hexachloroethane and potassium chloride at a mass ratio of 1:2, and the amount used is 0.25% of the melt mass. The refining temperature is controlled at 738℃, the refining time is 14 min, the argon flow rate is 1.8 m³ / h, and the rotary nozzle speed is 330 r / min. During the refining process, the rotary nozzle moves up and down slowly to ensure that all parts of the melt are fully refined.

[0087] After refining, the melt is allowed to stand for 22 minutes to allow impurities to float to the surface. Then, semi-continuous casting is carried out at 718℃ with a casting speed of 85 mm / min and a cooling water pressure of 0.18 MPa to obtain an ingot with a diameter of 200 mm × 500 mm. After casting, the ingot is immediately transferred to a homogenization furnace for homogenization treatment and held at 468℃ for 13 hours. Then, it is cooled to room temperature with the furnace.

[0088] (2) The gradient turning and gradient preheating composite pretreatment of the ingot surface were carried out by using a CK61100 CNC lathe to perform gradient turning on the outer cylindrical surface of the ingot; the turning depth at both ends of the ingot was set to 4.5mm, and the turning depth in the middle of the ingot was set to 2.5mm; carbide tools were used during the turning process, the cutting speed was 110m / min, and the feed rate was 0.18mm / r; after turning, the surface roughness Ra of the ingot was ≤1.6μm, and the roundness tolerance was ≤0.1mm.

[0089] The machined ingot is placed in a bogie-type preheating furnace for three-stage gradient preheating. The entire preheating process is carried out under a nitrogen protective atmosphere with a nitrogen purity ≥99.99% and the oxygen content in the furnace controlled below 50 ppm. The preheating process parameters are as follows:

[0090] First stage: Increase the temperature from room temperature to 285℃ at a rate of 4.5℃ / min and hold for 1.8 hours;

[0091] Second stage: Increase the temperature to 385℃ at a rate of 2.5℃ / min and hold for 1.2h;

[0092] Third stage: Heat to 462℃ at a rate of 1.5℃ / min and hold for 0.8h.

[0093] After preheating, the ingot is immediately fed into the extrusion press for extrusion, and the transfer time is controlled within 25 seconds to avoid the ingot temperature from dropping.

[0094] (3) The segmented temperature and pressure extrusion molding is carried out using an 800-ton horizontal extruder and a special extrusion die designed in this invention. The die consists of an upper die, a lower die and a die pad. The upper die cavity entrance is provided with a biomimetic honeycomb flow guide structure, which consists of 30 regular hexagonal flow guide holes. The side length of the flow guide hole is 9.5 mm and the wall thickness is 1.9 mm. The axis of the flow guide hole is at an angle of 17° with the extrusion direction. Adjacent flow guide holes are transitioned by a rounded corner with a radius of 2.2 mm. The lower die is provided with a gradient working belt structure and a pre-deformation compensation structure. The length of the working belt is continuously gradient distributed along the perimeter of the profile section: the length of the working belt in the main load area (wall thickness 4.5 mm) is 6.5 mm, the length of the working belt in the secondary load area (wall thickness 3.5 mm) is 4.5 mm, and the length of the working belt in the non-load area (wall thickness 2 mm) is 2.8 mm. The pre-deformation compensation structure is pre-set with a reverse deformation amount of 0.15 mm at the die exit to offset the springback deformation after the profile is extruded.

[0095] The extrusion process parameters are as follows:

[0096] Extrusion cylinder temperature: 448℃;

[0097] Mold temperature: 478℃;

[0098] Extrusion ratio: 29:1;

[0099] The gap between the extrusion cylinder and the ingot is 0.25 mm.

[0100] The gap between the extrusion pad and the extrusion cylinder is 0.12 mm.

[0101] Front-end extrusion: extrusion speed 2.3 mm / s, extrusion pressure 19 MPa, extrusion to 64% of the ingot length;

[0102] Post-extrusion: extrusion speed 4.3 mm / s, extrusion pressure 26 MPa, extrusion to a remaining ingot length of 45 mm.

[0103] After extrusion, the profile is cut using hydraulic shears at a distance of 520mm from the mold exit at a cutting speed of 110mm / s; the cut profile is immediately sent to an online quenching system for cooling.

[0104] (4) Zoned controllable water mist-air mixing online quenching adopts a zoned controllable water mist-air mixing cooling system for online quenching; the system is divided into three cooling zones along the profile extrusion direction, with a total length of 4m; each cooling zone is equipped with 8 sets of independent water mist nozzles and air nozzles, the distance between the nozzles and the profile surface is 160mm, and the nozzle angle is 48° with the profile surface; the temperature of the four sides and the upper and lower surfaces of the profile is monitored in real time by an infrared thermometer, and when the temperature of a certain part is higher than the set value, the flow rate of the corresponding nozzle at that part is automatically increased.

[0105] The cooling process parameters are as follows:

[0106] First cooling zone (length 1.2m): water mist pressure 0.38MPa, air pressure 0.28MPa, water mist to air volume ratio 1:4.8, cooling rate controlled at 170℃ / s;

[0107] Second cooling zone (length 1.6m): water mist pressure 0.28MPa, air pressure 0.22MPa, water mist to air volume ratio 1:5.8, cooling rate controlled at 110℃ / s;

[0108] Third cooling zone (length 1.2m): Only air nozzles are open, air pressure is 0.18MPa, and cooling rate is controlled at 35℃ / s.

[0109] After online quenching, the temperature of all parts of the profile drops below 72℃, and the temperature difference is controlled within 9℃.

[0110] (5) Gradient heating and two-stage aging strengthening treatment: The quenched profiles are sent into a bogie-type aging furnace for gradient heating and two-stage aging treatment; the aging furnace adopts hot air circulation heating method, and the temperature uniformity inside the furnace is controlled within ±2℃.

[0111] The aging process parameters are as follows:

[0112] First stage: Heat to 123℃ at a rate of 2.2℃ / min and hold for 6.8h;

[0113] Second stage: Increase the temperature to 173℃ at a rate of 1.8℃ / min and hold for 4.8h;

[0114] The third stage: the temperature is reduced to 85°C at a rate of 1.2°C / min, and then the furnace is removed and air-cooled to room temperature.

[0115] After aging is completed, the profiles are inspected for appearance and dimensions, and then sawn, straightened and surface treated to obtain the final industrial robot arm product.

[0116] A comprehensive performance test was conducted on the industrial robot arm profile prepared in this embodiment. The test results are as follows:

[0117] Tensile strength: 396 MPa;

[0118] Yield strength: 342 MPa;

[0119] Elastic modulus: 73.9 GPa;

[0120] Elongation: 13.2%;

[0121] Density: 2.71 g / cm³;

[0122] Specific strength: 146.1 MPa・cm³ / g;

[0123] Wall thickness tolerance: ±0.03mm;

[0124] Straightness tolerance: ±0.09mm / m;

[0125] Difference in tensile strength between the front and rear ends of the profile: 1.6%;

[0126] Fatigue life (10 7 (next cycle): 229 MPa.

[0127] As can be seen from the above two embodiments, the industrial robot arm profile prepared by the present invention is significantly superior to products prepared by traditional processes in terms of elastic modulus, tensile strength, dimensional accuracy, performance uniformity and fatigue life, and fully meets the requirements for use of high-precision, high-load and long-life industrial robots.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm, characterized in that, Includes the following steps: (1) Melting and homogenization of multi-element microalloyed aluminum alloys: Al-Mg-Si-Cu-Zr-Sc-Er series aluminum alloys were used. By mass percentage, Mg: 0.9-1.1%, Si: 0.7-0.9%, Cu: 0.5-0.7%, Zr: 0.18-0.22%, Sc: 0.10-0.14%, Er: 0.05-0.09%, Fe≤0.08%, Mn≤0.03%, Zn≤0.03%, Ti≤0.02%, and the remainder was Al and unavoidable impurities. (2) Pretreatment of ingot surface gradient turning and gradient preheating: First, the ingot surface is subjected to gradient turning to remove surface defects and segregation layer, and then the ingot is preheated by a three-stage gradient preheating process. (3) Segmented temperature and pressure extrusion molding: Using a special extrusion die, under the conditions of extrusion cylinder temperature of 445-455℃ and die temperature of 475-485℃, the first stage of extrusion is carried out at an extrusion speed of 2.2-2.8mm / s and an extrusion pressure of 18-22MPa. When the extrusion reaches 62-68% of the ingot length, the extrusion speed is increased to 4.2-4.8mm / s and the extrusion pressure is adjusted to 25-29MPa for the second stage of extrusion. (4) Zoned controllable water mist-air mixing online quenching: The extruded profile is immediately quenched online through a zoned controllable water mist-air mixing cooling system. The cooling rate is controlled in zones according to the wall thickness difference of different parts of the profile, so that all parts of the profile are cooled to below 80°C simultaneously. (5) Gradient heating two-stage aging treatment: The gradient heating method is used for two-stage aging treatment. First, the temperature is increased to 122-128℃ at a rate of 2-3℃ / min and held for 6.5-7.5h. Then, the temperature is increased to 172-178℃ at a rate of 1.5-2.5℃ / min and held for 4.5-5.5h. Finally, the temperature is decreased to below 100℃ at a rate of 1-2℃ / min and then air-cooled to room temperature.

2. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (1), the alloy smelting process is as follows: first, melt pure aluminum ingots with a purity ≥ 99.95% at 725-735℃. After the pure aluminum is completely melted, add Al-20%Mg master alloy, Al-20%Si master alloy, and Al-50%Cu master alloy in sequence. Stir for 3-5 minutes after each master alloy is added. After all the alloys are melted and stirred evenly, raise the melt temperature to 765-775℃, and then add Al-5%Zr master alloy, Al-2%Sc master alloy, and Al-10%Er master alloy in sequence. Continue stirring for 5-8 minutes and hold for 15-20 minutes.

3. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 2, characterized in that, In step (1), after smelting, argon rotary blowing is used for refining, degassing and slag removal. The refining agent is a mixture of hexachloroethane and potassium chloride at a mass ratio of 1:

2. The refining temperature is 735-745℃, the refining time is 12-18min, the argon flow rate is 1.5-2.5m³ / h, and the rotary nozzle speed is 300-400r / min. After refining, the mixture is allowed to stand for 20-30min, and then semi-continuous casting is carried out at 715-725℃. The casting speed is 80-100mm / min, and the cooling water pressure is 0.15-0.25MPa to obtain an ingot with a diameter of φ220mm×600mm. After the ingot is cast, it is immediately homogenized and kept at 465-475℃ for 12-16h, and then cooled to room temperature with the furnace.

4. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (2), the surface gradient turning process is specifically as follows: the outer cylindrical surface of the ingot is gradient turned using a CNC lathe. The turning depth at both ends of the ingot is 4-6mm, and the turning depth in the middle of the ingot is 2-4mm. After turning, the surface roughness Ra of the ingot is ≤1.6μm, and the roundness tolerance is ≤0.1mm.

5. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (2), the three-stage gradient preheating process is as follows: first, the ingot is heated from room temperature to 280-300℃ at a rate of 4-6℃ / min and held for 1.5-2.5h; then, it is heated to 380-400℃ at a rate of 2-4℃ / min and held for 1-2h; finally, it is heated to 460-470℃ at a rate of 1-3℃ / min and held for 0.5-1.5h. The entire preheating process is carried out under a nitrogen protective atmosphere with a nitrogen purity ≥99.99% and an oxygen content ≤50ppm in the furnace.

6. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (3), the special extrusion die consists of an upper die, a lower die, and a die pad. The upper die has a biomimetic honeycomb flow guiding structure at the entrance of the die cavity, and the lower die has a gradient working belt structure and a pre-deformation compensation structure. The biomimetic honeycomb flow guiding structure consists of 42 regular hexagonal flow guiding holes. The side length of the flow guiding holes is 9-11 mm, the wall thickness is 1.8-2.2 mm, the axis of the flow guiding holes forms an angle of 16-19° with the extrusion direction, and adjacent flow guiding holes are transitioned by rounded corners with a radius of 2-3 mm.

7. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 6, characterized in that, The working band length of the gradient working band structure is continuously gradient distributed along the perimeter of the profile cross-section. In the main load-bearing area with a profile wall thickness of 5.5mm, the working band length is 6.5-7.5mm; in the secondary load-bearing area with a profile wall thickness of 4mm, the working band length is 4.5-5.5mm; and in the non-load-bearing area with a profile wall thickness of 2.5mm, the working band length is 2.5-3.5mm. The pre-deformation compensation structure is designed to pre-set a reverse deformation amount of 0.1-0.3mm at the mold exit based on the springback deformation law of the profile after extrusion.

8. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (3), the extrusion ratio is controlled between 28:1 and 32:

1. During the extrusion process, the gap between the extrusion cylinder and the ingot is controlled between 0.2 and 0.4 mm, and the gap between the extrusion pad and the extrusion cylinder is controlled between 0.1 and 0.2 mm. After extrusion, the profile is cut off at a distance of 500-600 mm from the mold outlet using hydraulic shears at a cutting speed of 100-150 mm / s.

9. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 1, characterized in that, In step (4), the partitioned controllable water mist-air mixed cooling system is divided into three cooling zones along the profile extrusion direction. The first cooling zone is 1.5m long, the second cooling zone is 2m long, and the third cooling zone is 1.5m long. Each cooling zone is equipped with independent water mist nozzles and air nozzles. The distance between the nozzles and the profile surface is 150-200mm, and the nozzle angle is 45-60° with the profile surface.

10. The aluminum alloy extrusion forming process for a high-rigidity, lightweight industrial robot arm according to claim 9, characterized in that, The water mist pressure in the first cooling zone is 0.35-0.45 MPa, the air pressure is 0.25-0.35 MPa, the volume ratio of water mist to air is 1:4.5-1:5.5, and the cooling rate is controlled at 160-190℃ / s. In the second cooling zone, the water mist pressure is 0.25-0.35 MPa, the air pressure is 0.2-0.3 MPa, the volume ratio of water mist to air is 1:5.5-1:6.5, and the cooling rate is controlled at 100-130℃ / s. In the third cooling zone, only the air nozzles are open, the air pressure is 0.15-0.25 MPa, and the cooling rate is controlled at 30-50℃ / s. During the online quenching process, the temperature of each part of the profile is monitored in real time using an infrared thermometer. When the temperature of a certain part exceeds the set value, the flow rate of the corresponding nozzle is automatically increased.

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