Method for weakening extrusion surface black lines and welding lines to improve surface yield of aluminum profile

Abstract

The invention discloses a method for weakening extrusion surface black lines and welding lines to improve the surface yield of an aluminum profile. The method comprises the following steps of aluminum ingot pretreatment, temperature control extrusion, die cavity welding strengthening and finished product aftertreatment. According to the method, through the synergistic effect of the whole process of aluminum ingot pretreatment, temperature control extrusion, die cavity welding strengthening and finished product aftertreatment, double weakening of the black line and the welding line is achieved, and the problems that the defects of the black line and the welding line on the extrusion surface of the aluminum profile are difficult to radically treat, the surface yield is low, and the production cost is high are solved; and high quality, high stability and low cost of aluminum profile extrusion production are realized.

Description

Technical Field

[0001] This invention relates to the field of aluminum profile processing, specifically to a method for reducing black lines and weld lines on the extruded surface of aluminum profiles to improve the surface yield of aluminum profiles. It is applicable to the extrusion production of architectural aluminum profiles, industrial aluminum profiles, rail transit aluminum profiles, and high-precision aluminum profiles for aerospace applications. Especially for aluminum profile products with high surface quality requirements, it can significantly reduce the occurrence rate of surface black lines and weld lines defects and improve the surface yield of products. Background Technology

[0002] In the aluminum profile extrusion process, black lines and weld lines on the surface are two common and difficult-to-eradicate defects that seriously affect the appearance quality and market competitiveness of products, resulting in a large number of defective products and increasing production costs.

[0003] Black lines typically appear as dark stripes distributed along the extrusion direction on the surface of aluminum profiles. The main causes include: first, impurities (such as iron and silicon compounds) present in the aluminum ingot raw material precipitate along the grain boundaries during extrusion and accumulate on the profile surface to form black lines; second, uneven temperature in the working zone of the extrusion die, with local high temperature causing oxidation or overheating of the metal on the aluminum profile surface, resulting in black lines; and third, poor lubrication during extrusion, causing severe friction between the die and the profile surface, resulting in deformation of the surface metal structure and the formation of black lines.

[0004] Existing solutions mainly focus on raw material purification and mold polishing. While raw material purification can reduce impurity content, it significantly increases raw material costs and cannot completely eliminate the impact of impurities. Mold polishing can only improve surface roughness in the short term. In long-term production, black line defects are prone to recurrence after mold wear, making it difficult to continuously guarantee surface quality.

[0005] Weld lines are interface marks formed when metal is divided into multiple streams in the die's flow channel during the extrusion of aluminum profiles (especially hollow profiles). These streams rejoin after entering the die cavity. If the welding is insufficient, obvious lines will form on the surface or inside of the profile, affecting not only its appearance but also potentially reducing its mechanical properties.

[0006] Existing technologies improve welding results by increasing extrusion temperature, increasing extrusion pressure, or optimizing die flow structure. However, increasing temperature can easily lead to oxidation of the profile surface, increasing extrusion pressure can exacerbate die wear, and optimizing die flow structure is limited by profile cross-section design and has poor adaptability to profiles with complex cross-sections. As a result, 30% to 50% of hollow profiles still have obvious weld line defects, and it is difficult to improve surface yield.

[0007] In addition, existing aluminum profile extrusion production processes lack integrated control solutions for black lines and weld lines. They mostly address single defects, failing to solve both types of problems simultaneously. Furthermore, they rely on operators' experience to adjust process parameters, resulting in poor stability and significant fluctuations in product surface quality. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for weakening black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles, thereby solving the problems of difficult-to-eradicate defects of black lines and weld lines on the extruded surface of aluminum profiles, low surface yield, and high production cost, and achieving high quality, high stability and low cost in aluminum profile extrusion production.

[0009] To solve the above problems, the technical solution adopted in this invention is: a method for weakening the black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles, the method being as follows: (1) Aluminum ingot pretreatment: The aluminum ingots are sent to the impurity sorting module and qualified aluminum ingots with impurity content ≤0.3% are screened by X-ray fluorescence spectroscopy. The qualified aluminum ingots enter the homogenization heating module and are heated from room temperature to 480-520℃ at a rate of 5-8℃ / min using a stepped heating furnace. The temperature is held for 2-3 hours to make the internal structure of the aluminum ingot uniform and reduce component segregation. After the aluminum ingots are cooled, they enter the surface cleaning module and are cleaned with high-pressure hot air at 80-100℃ and 0.6-0.8MPa in conjunction with a wire brush to remove the oxide scale and oil stains on the surface of the aluminum ingots. (2) Temperature-controlled extrusion: The pre-treated aluminum ingot is fed into the intelligent temperature-controlled extrusion unit. The intelligent temperature-controlled extrusion unit includes: an extruder, a die temperature control module and an extrusion parameter monitoring module. The die temperature control module is started. The die temperature control module consists of an electromagnetic induction heating coil surrounding the die working zone and a cooling water circuit. The temperature of the die working zone is monitored by an infrared temperature sensor. The output power of the electromagnetic induction heating coil and the flow rate of the cooling water circuit are controlled to stabilize the temperature of the die working zone at 460-480℃ to avoid local high or low temperatures. The extruder is started. The extrusion parameter monitoring module is equipped with a pressure sensor and a displacement sensor to collect the extrusion pressure and the displacement speed of the extrusion rod in real time to ensure the stability of the extrusion process. The aluminum ingot is formed into aluminum profiles through the die under the action of extrusion pressure. (3) Mold cavity welding strengthening: The mold flow divider hole is modified from the original circular hole to a gradually tapered hole with a taper of 5° to 8°. The gradually tapered hole gradually expands with the flow direction. When the metal flow passes through the mold flow divider hole, the gradually tapered hole can make the metal flow flow evenly and reduce the flow resistance of the metal flow in the flow divider hole. An annular pressure boosting boss is set in the mold cavity welding area. After the metal flow enters the mold cavity welding area, the annular pressure boosting boss can increase the local pressure and promote the full welding of the metal. At the same time, heating plates are set on the outside of the mold cavity welding area to maintain the temperature of the welding area at 490 to 510°C, promote the full welding of the metal, prolong the high temperature plasticity time of the metal, enhance the welding effect, and thus reduce the formation of weld lines. (4) Finished product post-treatment: The extruded aluminum profile is heated to 120-150℃ in a hot air circulating aging furnace and held for 4-6 hours. Without affecting the mechanical properties of the profile, the surface metal stress is reduced and the black line marks are weakened. A flexible grinding wheel is used in conjunction with polishing liquid to lightly polish the surface of the aluminum profile. The polishing pressure is 0.1-0.3MPa and the polishing speed is 1-2m / min to further eliminate slight black lines and weld lines and improve the surface smoothness.

[0010] Furthermore, the aforementioned method for reducing black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles further includes: online surface inspection: using a high-resolution industrial camera, a light source system, and an image analysis module; three sets of industrial cameras are set along the aluminum profile conveying direction to capture images of the profile surface from the front, left, and right sides, respectively, with the shooting frequency linked to the profile conveying speed; the light source system uses a ring-shaped LED supplementary light to ensure uniform brightness in the shooting area; the image analysis module processes the acquired images, automatically identifies black lines and weld lines, and feeds back data such as defect location and size to the central control system; if the defect exceeds a preset threshold, the system automatically issues an alarm signal.

[0011] Furthermore, in the aforementioned method of weakening the black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles, the extrusion parameters of the extrusion press are: extrusion speed 1-10 mm / s, extrusion pressure 50-120 MPa.

[0012] Furthermore, in the aforementioned method of weakening the black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles, the annular pressure boss has a height of 1-2 mm and a width of 3-5 mm.

[0013] Furthermore, the aforementioned method for weakening the black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles includes: a grinding wheel with a grit size of 800-1200 mesh, and a polishing slurry whose main components are alumina micro powder and lubricant.

[0014] The advantages of this invention are: the method described achieves dual weakening of black lines and weld lines through the synergistic effect of the entire process of "aluminum ingot pretreatment - temperature-controlled extrusion - mold cavity welding reinforcement - finished product post-treatment".

[0015] The principle of black line weakening: In the aluminum ingot pretreatment stage, high impurity raw materials are removed by impurity sorting, and homogenization heating reduces component segregation, thereby reducing black lines caused by impurity enrichment from the source; In the extrusion stage, intelligent temperature control avoids local high temperature in the mold and prevents surface metal oxidation and overheating, while stable extrusion parameters reduce the structural deformation caused by friction; In the post-treatment stage, low-temperature aging releases surface stress, and light polishing eliminates slight black line traces. Multiple steps work together to inhibit the formation and manifestation of black lines.

[0016] Weld line weakening principle: The mold cavity welding strengthening unit optimizes the metal flow state through a gradual flow divider to avoid insufficient welding caused by differences in metal flow velocity; the annular pressure boosting boss increases the pressure in the welding zone and promotes the diffusion and fusion of metal atoms; the welding zone heat preservation extends the high-temperature plasticity time and enhances the bonding force of the welding interface, improving the welding quality from three aspects: flow state, pressure, and temperature, and reducing the visibility of weld lines; at the same time, post-processing polishing further weakens residual weld line traces.

[0017] Significantly improved surface yield: Through the weakening control of black lines and welding lines throughout the entire process, the occurrence rate of black line defects on the surface of aluminum profiles has been reduced from 25% to 35% in the existing technology to below 5%, and the occurrence rate of welding line defects has been reduced from 30% to 50% to below 8%. The surface yield has been increased from less than 80% to more than 95%, greatly reducing defective products and lowering production costs.

[0018] Cost controllable: No need to rely on high-purity aluminum ingots (only conventional aluminum ingots with impurity content ≤0.3% are required), reducing raw material costs by 10% to 15%; mold temperature control and mold cavity optimization design extend mold life (from the current 30,000 to 50,000 pieces / set to 80,000 to 100,000 pieces / set), reducing equipment maintenance costs by more than 20%.

[0019] Balancing mechanical properties: Low-temperature aging treatment weakens the black lines while avoiding the impact of high temperatures on the mechanical properties of the profile. Tests show that 6063 aluminum alloy profiles produced using this method have a tensile strength ≥205MPa, a yield strength ≥170MPa, and an elongation ≥12%, fully complying with the requirements of GB / T 5237.1-2023 "Aluminum Alloy Building Profiles Part 1: Substrate" standard.

[0020] Environmentally friendly: The surface cleaning module uses high-pressure hot air instead of traditional chemical cleaning, avoiding the discharge of chemical waste liquid; the polishing liquid can be recycled (recycled ≥ 5 times), reducing waste generation and meeting the requirements of green manufacturing. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments. Example 1

[0022] For 6063 aluminum alloy rectangular profiles used in construction (section dimensions: 100mm×50mm, hollow structure); The method for reducing black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles is as follows: (1) Pretreatment of aluminum ingots: 6063 aluminum alloy ingots (Fe content 0.25%, Si content 0.4%) are selected. The aluminum ingots are sent to the impurity sorting module and qualified aluminum ingots with impurity content ≤0.3% are screened by X-ray fluorescence spectroscopy. Qualified aluminum ingots enter the homogenization heating module and a stepped heating furnace is used to heat the aluminum ingots from room temperature to 500℃ at a rate of 5~8℃ / min and hold for 2.5h to make the internal structure of the aluminum ingots uniform and reduce component segregation. After the aluminum ingots are cooled, they enter the surface cleaning module and high-pressure hot air at 80~100℃ and 0.6~0.8MPa is used in conjunction with a wire brush to remove the oxide scale and oil stains on the surface of the aluminum ingots. (2) Temperature-controlled extrusion: The pre-treated aluminum ingot is fed into the intelligent temperature-controlled extrusion unit. The intelligent temperature-controlled extrusion unit includes: an extruder, a die temperature control module and an extrusion parameter monitoring module. The die temperature control module is started. The die temperature control module consists of an electromagnetic induction heating coil surrounding the die working belt and a cooling water circuit. The temperature of the die working belt is monitored by an infrared temperature sensor. The output power of the electromagnetic induction heating coil and the flow rate of the cooling water circuit are controlled to stabilize the temperature of the die working belt at 470℃ to avoid local high or low temperatures. The extruder is started. The extrusion parameter monitoring module is equipped with a pressure sensor and a displacement sensor to collect the extrusion pressure and the displacement speed of the extrusion rod in real time to ensure the stability of the extrusion process. The aluminum ingot is formed into an aluminum profile through the die under the action of extrusion pressure. The extrusion parameters are: extrusion speed 5mm / s, extrusion pressure 80MPa. (3) Mold cavity welding strengthening: The original circular hole of the mold is modified into a tapered hole with a taper of 5° to 8°. When the metal flow passes through the mold's flow hole, the tapered hole can make the metal flow flow evenly and reduce the flow resistance of the metal flow in the flow hole. An annular pressure boosting boss is set in the mold cavity welding area. The annular pressure boosting boss has a height of 1.5 mm and a width of 3 to 5 mm. After the metal flow enters the mold cavity welding area, the annular pressure boosting boss can increase the local pressure and promote the full welding of the metal. At the same time, heating plates are set on the outside of the mold cavity welding area to maintain the temperature of the welding area at 495°C, promote the full welding of the metal, prolong the high temperature plasticity time of the metal, enhance the welding effect, and thus reduce the formation of weld lines. (4) Online surface inspection: A high-resolution industrial camera, a light source system and an image analysis module are used. Three sets of industrial cameras are set along the aluminum profile conveying direction to take pictures of the profile surface from the front, left side and right side respectively. The shooting frequency is linked to the profile conveying speed. The light source system uses ring LED supplementary lights to ensure uniform brightness in the shooting area. The image analysis module processes the collected images, automatically identifies black lines and weld lines, and feeds back the defect location, size and other data to the central control system. If the defect exceeds the preset threshold, the system will automatically issue an alarm signal. (5) Finished product post-treatment: The extruded aluminum profile is heated to 130°C in a hot air circulating aging furnace and kept at that temperature for 5 hours. Without affecting the mechanical properties of the profile, the surface metal stress is reduced and the black line marks are weakened. A flexible grinding wheel with a grit size of 1000 mesh is used in conjunction with a polishing liquid. The main components of the polishing liquid are alumina micro powder and lubricant. The surface of the aluminum profile is lightly polished with a polishing pressure of 0.2 MPa and a polishing speed of 1 to 2 m / min to further eliminate slight black lines and weld lines and improve the surface smoothness.

[0023] The finished aluminum profiles were tested and found to have a surface yield of 97.2%; mechanical properties were tested and found to have a tensile strength of 210 MPa, a yield strength of 175 MPa, and an elongation of 13.5%; and a surface roughness Ra ≤ 0.8 μm, which meets the high surface quality requirements for architectural aluminum profiles. Example 2

[0024] For 6082 aluminum alloy profiles for rail transit (cross-section dimensions: 300mm×80mm, complex hollow structure); The method for reducing black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles is as follows: (1) Pretreatment of aluminum ingots: 6082 aluminum alloy ingots (Fe content 0.28%, Si content 0.9%) are selected. The aluminum ingots are sent to the impurity sorting module and qualified aluminum ingots with impurity content ≤0.3% are screened by X-ray fluorescence spectroscopy. Qualified aluminum ingots enter the homogenization heating module and a stepped heating furnace is used to heat the aluminum ingots from room temperature to 500℃ at a rate of 5~8℃ / min and hold for 2.5h to make the internal structure of the aluminum ingots uniform and reduce component segregation. After the aluminum ingots are cooled, they enter the surface cleaning module and high-pressure hot air at 80~100℃ and 0.6~0.8MPa is used in conjunction with a wire brush to remove the oxide scale and oil stains on the surface of the aluminum ingots. (2) Temperature-controlled extrusion: The pre-treated aluminum ingot is fed into the intelligent temperature-controlled extrusion unit. The intelligent temperature-controlled extrusion unit includes: an extruder, a die temperature control module and an extrusion parameter monitoring module. The die temperature control module is started. The die temperature control module consists of an electromagnetic induction heating coil and a cooling water circuit surrounding the die working belt. The temperature of the die working belt is monitored by an infrared temperature sensor. The output power of the electromagnetic induction heating coil and the flow rate of the cooling water circuit are controlled to stabilize the temperature of the die working belt at 480℃ to avoid local high or low temperatures. The extruder is started. The extrusion parameter monitoring module is equipped with a pressure sensor and a displacement sensor to collect the extrusion pressure and the displacement speed of the extrusion rod in real time to ensure the stability of the extrusion process. The aluminum ingot is formed into an aluminum profile through the die under the action of extrusion pressure. The extrusion parameters are: extrusion speed 2mm / s, extrusion pressure 110MPa. (3) Mold cavity welding strengthening: The mold flow divider hole is modified from the original circular hole to a gradually tapered hole with a taper of 5° to 8°. When the metal flow passes through the mold flow divider hole, the gradually tapered hole can make the metal flow flow evenly and reduce the flow resistance of the metal flow in the flow divider hole. An annular pressure boosting boss is set in the mold cavity welding area. The annular pressure boosting boss has a height of 2mm and a width of 3 to 5mm. After the metal flow enters the mold cavity welding area, the annular pressure boosting boss can increase the local pressure and promote the full welding of the metal. At the same time, heating plates are set on the outside of the mold cavity welding area to maintain the temperature of the welding area at 505℃, promote the full welding of the metal, prolong the high temperature plasticity time of the metal, enhance the welding effect, and thus reduce the formation of weld lines. (4) Online surface inspection: A high-resolution industrial camera, a light source system and an image analysis module are used. Three sets of industrial cameras are set along the aluminum profile conveying direction to take pictures of the profile surface from the front, left side and right side respectively. The shooting frequency is linked to the profile conveying speed. The light source system uses ring LED supplementary lights to ensure uniform brightness in the shooting area. The image analysis module processes the collected images, automatically identifies black lines and weld lines, and feeds back the defect location, size and other data to the central control system. If the defect exceeds the preset threshold, the system will automatically issue an alarm signal. (5) Finished product post-treatment: The extruded aluminum profile is heated to 150°C in a hot air circulating aging furnace and kept at that temperature for 4 hours. Without affecting the mechanical properties of the profile, the surface metal stress is reduced and the black line marks are weakened. A flexible grinding wheel with a grit size of 1200 mesh is used in conjunction with a polishing liquid. The main components of the polishing liquid are alumina micro powder and lubricant. The surface of the aluminum profile is lightly polished with a polishing pressure of 0.3MPa and a polishing speed of 1-2m / min to further eliminate slight black lines and weld lines and improve the surface smoothness.

[0025] Aluminum profile finished product inspection results: surface yield rate reached 95.8%; mechanical property test: tensile strength 310MPa, yield strength 270MPa, elongation 12.8%; passed the special test for surface quality of aluminum profiles for rail transit (EN 12020-2 standard), and the defects of black lines and weld lines met the requirements of Grade 1 products.

Claims

1. A method for reducing black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles, characterized in that: The method is as follows: (1) Aluminum ingot pretreatment: The aluminum ingots are sent to the impurity sorting module and qualified aluminum ingots with impurity content ≤0.3% are screened by X-ray fluorescence spectroscopy. The qualified aluminum ingots enter the homogenization heating module and are heated from room temperature to 480-520℃ at a rate of 5-8℃ / min using a stepped heating furnace. The temperature is held for 2-3 hours to make the internal structure of the aluminum ingot uniform and reduce component segregation. After the aluminum ingots are cooled, they enter the surface cleaning module and are cleaned with high-pressure hot air at 80-100℃ and 0.6-0.8MPa in conjunction with a wire brush to remove the oxide scale and oil stains on the surface of the aluminum ingots. (2) Temperature-controlled extrusion: The pre-treated aluminum ingot is fed into the intelligent temperature-controlled extrusion unit. The intelligent temperature-controlled extrusion unit includes: an extruder, a die temperature control module and an extrusion parameter monitoring module. The die temperature control module is started. The die temperature control module consists of an electromagnetic induction heating coil surrounding the die working zone and a cooling water circuit. The temperature of the die working zone is monitored by an infrared temperature sensor. The output power of the electromagnetic induction heating coil and the flow rate of the cooling water circuit are controlled to stabilize the temperature of the die working zone at 460-480℃ to avoid local high or low temperatures. The extruder is started. The extrusion parameter monitoring module is equipped with a pressure sensor and a displacement sensor to collect the extrusion pressure and the displacement speed of the extrusion rod in real time to ensure the stability of the extrusion process. The aluminum ingot is formed into aluminum profiles through the die under the action of extrusion pressure. (3) Mold cavity welding strengthening: The mold flow divider hole is modified from the original circular hole to a gradually tapered hole with a taper of 5° to 8°. The gradually tapered hole gradually expands with the flow direction. When the metal flow passes through the mold flow divider hole, the gradually tapered hole can make the metal flow flow evenly and reduce the flow resistance of the metal flow in the flow divider hole. An annular pressure boosting boss is set in the mold cavity welding area. After the metal flow enters the mold cavity welding area, the annular pressure boosting boss can increase the local pressure and promote the full welding of the metal. At the same time, heating plates are set on the outside of the mold cavity welding area to maintain the temperature of the welding area at 490 to 510°C, promote the full welding of the metal, prolong the high temperature plasticity time of the metal, enhance the welding effect, and thus reduce the formation of weld lines. (4) Finished product post-treatment: The extruded aluminum profile is heated to 120-150℃ in a hot air circulating aging furnace and held for 4-6 hours. Without affecting the mechanical properties of the profile, the surface metal stress is reduced and the black line marks are weakened. A flexible grinding wheel is used in conjunction with polishing liquid to lightly polish the surface of the aluminum profile. The polishing pressure is 0.1-0.3MPa and the polishing speed is 1-2m / min to further eliminate slight black lines and weld lines and improve the surface smoothness.

2. The method for weakening black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles according to claim 1, characterized in that: The method also includes: online surface inspection: using a high-resolution industrial camera, a light source system, and an image analysis module, three sets of industrial cameras are set along the aluminum profile conveying direction to capture images of the profile surface from the front, left, and right sides, respectively, with the shooting frequency linked to the profile conveying speed; the light source system uses a ring-shaped LED supplementary light to ensure uniform brightness in the shooting area; the image analysis module processes the acquired images, automatically identifies black lines and weld lines, and feeds back data such as defect location and size to the central control system; if the defect exceeds the preset threshold, the system automatically issues an alarm signal.

3. The method for weakening black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles according to claim 1 or 2, characterized in that: The extrusion parameters of the extruder are: extrusion speed 1~10mm / s, extrusion pressure 50~120MPa.

4. The method for weakening black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles according to claim 1 or 2, characterized in that: The annular booster boss has a height of 1-2 mm and a width of 3-5 mm.

5. The method for weakening black lines and weld lines on the extruded surface to improve the surface yield of aluminum profiles according to claim 1 or 2, characterized in that: The grinding wheel has a grit size of 800-1200 mesh, and the polishing slurry mainly consists of alumina micro powder and lubricant.